I've tried to answer my own question but...

[gypsychic]

I'm trying to answer my own question but my electrical and automotive ignorance is really a handicap. Ultimately I'm trying to find out how much driving I need to do to keep a set of 6v GC batteries reasonably happy. I've read so much on batteries and their maintenance that I'm trying to decide if I should continue with my plan to be battery free until I can afford solar or if I can start my hands on learning, the best way I learn, sooner rather than later. That being said, I don't want to start off under circumstances that will knowingly shorten the life of my batteries. I'll make enough mistakes as it is, no doubt. Nor do I want to have to drive around just for the sake of charging my batteries. That seems a foolish waste of energy, both in terms of gasoline and my own.

This I know:

* I will be able to plug into the grid each week for up to 48hrs at a time.
* I currently drive less than 500 miles a month. That will likely change when I start fulltiming as I drive between day & night parking but I don't see it increasing substantially.

I thought I'd find out how many amps my alternator generates. I've found replacement quotes for my vehicle (1995 Dodge Ran Van 2500 3.9L V6) alternator with amperages between 75-120. I can't seem to find the rating on the OEM alternator. That info may not even help me to determine my answer but I didn't think it would be difficult to find out.

What information do I need to figure out the answer to my question, what variables should I be cognoscente of and how might I go about arriving at my answer? Any and all constructive comments would be greatly appreciated.

I'm not afraid of learning or getting my hands dirty. In fact I find both very satisfying. Its the chasing my tail thing that is getting old.

 

[gypsychic]

Yes the limited time to edit is really a bummer.

I'm getting a Kill a watt kit from the library to monitor my energy consumption. I've already thought of what I'll need to use and for how long most days. Just need the hard numbers now. No microwave, fridge or TV. Just phone and a Chromebook, some led lights, and if possible a therapeutic heating pad and a small dehumidifier. I've already purchased as many 12v power supplies for my electronics. The only thing I'd have to run on an inverter would be the heating pad and rechargeable toothbrush.

 

[SternWake]

Being able to plug in for upto 48 hours each week is your free pass. A pair of gc batteries plugged in the grid weekly can be ridden hard those 5 other days.

Of course utilize alternator with 4 awg cabling to get them as.close as possible to 80% every time you drive. And they will be better treated than most cycld lead acid batteries just with that 48 hours on the grid to be topped off properly.

Typing on phone. Plz excuse mistakes

 

[SoulRaven]

I have a single 12v deep cycle house battery that I charge while driving via a cigarette lighter to cigarette lighter jumper cable.

Unless I'm traveling, I rarely drive more than maybe 20-30 miles a week, which has successfully kept my house battery charged for over a year now. I never plug into shore power.

 

[[email protected]]

One end is 12v socket and the other end is alligator clips? That charges it at a safe rate? That could be useful if im understanding you

 

[SternWake]

One end is 12v socket and the other end is alligator clips? That charges it at a safe rate? That could be useful if im understanding you

12v Ciggy plugs and receptacles are very poor designs for passing currents over 4 to 5 amps.  The stock wiring to the plug from the battery in most vehicles is very long and very thin, and when passing larger currents this causes a lot of voltage drop.  If the stock engine battery is being brought to 14.5 volts it is quite likely at the far end of that ciggy plug, the depleted house battery is getting only 13.5v and well under 5 amps.  Once the house battery nears 13 volts( which will take forever via this method), the voltage difference will be even less causing even less amps to flow.

Voltage is electrical pressure so trying to do any meaningful charging via 2 sets of Ciggy plugs, over 18 awg wiring is like trying to breathe through a kinked cocktail straw.

Offgrid's remarks about things electrical basically require that the rules of Physics no longer apply. He once claimed to be able to fully charge a well depleted battery in 25 minutes despite this being an impossibility.  His words lead many people down a wrong path because he tells them what they want to hear about things they do not understand and seek the answers to.

Trying to get any meaningful charging of a depleted battery accomplished through Ciggy plugs, is folly.  It will be a small fraction of what would occur over a properly wired house battery.  Only those who have extremely small electrical demands can get away with this, and such people will never even realize the capacity loss from chronic undercharging, and chronic undercharging is the biggest lead acid battery killer out there. 

Idling the engine for 5 minutes with a set of  4 awg jumper cables attached between batteries will restore more amp hours into a depleted battery than 5 hours of driving with 18 awg and 2 ciggy plugs and receptacles between the batteries.

Batteries are just rented. The length of that rental contract is determined by how they are treated.  The effort required to keep the batteries in absolute top health for the maximum length of that contract, can be taken to extremes, and simply not be worth the effort compared to worrying less and replacing the battery sooner.

But so few people have any idea of what a battery can power and for how long, and the TIME it actually requires to fully charge it, that batterycide is all too common by those transferring their stick and brick lifestyle into a mobile lifestyle

 

[ccbreder]

second for Sternwake. Nothing larger than a pad, phone or flashlight battery should be charged from a cigarette lighter socket. The convenience is not worth the damage.

 

[towhee]

Disclaimer: I am quite new at battery management myself.

I think you will just need to start using power and adjust over time.

You can get a voltmeter that plugs into the cig lighter. I got one at a truck stop. It was around $10. The voltage will tell you generally the state of charge of your battery. I think that 13 volts is fully charged. 12.5 is pretty depleted. That's all I know. But it's a start.

My guess is that the dehumidifier and the heating pads will draw the most current of the items you mentioned.

 

[gypsychic]

Yes, today I've been playing with my kill-a-watt that I borrowed from the local library yesterday. The small dehumidifier and the heating pad is the reason I'm considering getting a house battery at all. Everything else I could easily charge on a power strip wherever I happen to be. That being said it's good to know what my power consumption would be.

Everyone's different and everyone has different needs and things that make their life comfortable. I'm often ill to the point that I don't leave my bed much during the day. This can be for several days in a row. It would make my life easier if on those days I could sit back and use my phone to surf the web or my kindle without having to leave my vehicle for an hour or two just to recharge the items battery. Getting up from bed to drive between spots will be the most I'd want to deal with.

On those days that I'm ill I find my heating pad helps to make me more comfortable, whatever the season. About 2.5 amps an hour, averaging the high amps to get up to temp, the amps to maintain and the 0 amps between maintaining cycles.

In addition to seasonal allergies I have an extreme reaction to mold in my living or working area. Several times I've had downturns in my health and later found out mold was near where I spent a significant amount of time while others didn't seem to have any issues. Because I live in the PNW where dampness and mold are a problem in regular living situations I've considered the advice of someone on this forum and a separate friend, both in a similar environments.

So I purchased an Eva-Dry 1100 dehumidifier to see if indeed it did work. I was skeptical but it works great. So well in fact that I can't run it 24/7 because it dries my room out to much, as the person on this forum who initially recommended it also said. I'll eventually do a product review and post it. 0.34 amps @ 120v so 3.4 amps @ 12v if I'm moving the decimals correctly.

Still looking at my list of things that require electricity. So easy to forget something used often when I don't have to think about it except flipping a switch. But I think my list is pretty comprehensive now. Not much is absolutely vital except the diy ventilation computer fan system I've purchased components for but haven't put into use yet.

As far as learning, I've read and reread threads on here in which Sternwake, Mike Ruth, Jimindenver and a few others have discussed batteries/12v/solar. Also Mainsail on another forum, HandyBob and some links jimindenver posted a while back. Recently the lightbulb went off and I started retaining much more information. Before I kept reading and it flowed from my brain like water through a sieve. Now I think I might know enough to ask a partway intelligent question. Hence my borrowing my killawatt now instead of earlier. Now I know what information I need and what to do with it.

Now the fun begins. Trying to figure out a battery charger that will allow the higher volts. Also trying to buy things that will allow me to expand into solar in the future without breaking the bank now. A relay or a solenoid? And looking around for places where I might get wires made or will it be less expensive in the long run to buy a crimper? Should I use heat shrink or crimps? Every little thing seems to have so many questions to analyze and research. It's a wonder people do 12v at all.

Sorry for the long post. I'll chalk it up to being semi-giddy that I understand what to do with the killawatt and what that info means to me. In other words, I'm bragging (just a teeny, tiny bit.) [emoji6]

 

[SoulRaven]

One end is 12v socket and the other end is alligator clips? That charges it at a safe rate? That could be useful if im understanding you

Both ends have a male cigarette lighter plug on them.

My house battery box has accessory outlets wired into it.  So the jumper cable simply plugs in on each end.

If you look at the cables on most battery chargers, they are about the same size as the cables on these jumpers.

Some will argue this isn't a good way of doing it, but I disagree.  I have been using this method for a little over a year now, and have never run out of power yet.  Both my house and starting batteries are over 5 years old now, so it obviously has no ill effects.

 

[SoulRaven]

Sternwake,


I don't like to argue but...

You're confusing technical mumbo jumbo with practical usage.

What's technically a perfect scenario doesn't mean nearly as much as having a reliable system that works in practical application.

You are making erroneous assumptions about such things as 18 gauge wires, and how low the batteries are being drawn.  Unlike you, my batteries have protectors on them which prevent them from being drawn below 11.8v, so my batteries are NEVER drawn down as low as some people claim is acceptable.

I don't care if my batteries are at 14.5v, what I care about is whether or not I have power when I want it.  This system provides that for me, and has done so flawlessly for a little over a year now.

While physics may or may not allow a perfect scenario as you describe it, it does not prevent our imperfect systems from providing everything we need.

We don't need perfect systems, we need systems that work for our needs.  Every house and every vehicle are full of imperfections, and far from optimal.  We don't live in a perfect world, yet all of these things with all of their imperfections, fill our needs and allow us to thrive.

By your description of the 12v gas generator I used for years, the charging system on every vehicle is flawed, since it basically worked the same way.  Maybe it is flawed, but that doesn't prevent millions of vehicles from using that flawed system to their advantage every single day. IT WORKS...

While perfection may be an admirable goal, learning to survive in our imperfect world is a better skill set.

 

[highdesertranger]

11.8 on a 12v battery is considered dead way over discharged. ciggy plugs can't deliver more than about 10 amps they will overheat and melt if held at 10 amps for any amount of time. off grid if you think it works for you, fine keep doing it. I myself will take sternwakes advice because it is what I have found to be true, though many years of doing this. highdesertranger

 

[SoulRaven]

11.8 on a 12v battery is considered dead way over discharged.  ciggy plugs can't deliver more than about 10 amps they will overheat and melt if held at 10 amps for any amount of time.  off grid if you think it works for you,  fine keep doing it.  I myself will take sternwakes advice because it is what I have found to be true,  though many years of doing this.  highdesertranger

I'm not so sure about this.  When I've had my protector cut out an 11.8v, I still had plenty of power to start my van with no noticeable loss of ooomph.

These jumper cables are capable of charging a flat dead battery in a second vehicle to being able to start that vehicle within 10-15 minutes.  Charging your own house battery is no different except that hopefully it isn't as dead to start with.

I can not detect any noticeable differences in usability between this system and one using an actual isolator.  Both types of systems provide more than enough power for my needs.

I know at least a dozen other people who are using this same method successfully.  I learned it from another fulltimer.

 

[brightbluejim]

Gypsychic:

It surprises me greatly to see so many expert answers to your question, since it is not possible to answer your question without some additional information!

If you want the short answer, go straight to the last paragraph.

There are three things that must be known in order to calculate how many hours (or what fraction of an hour) you must drive to keep your house battery charged:

1) The capacity of the house battery,
2) The average load on the house battery, and
3) The average current your alternator can deliver to the house battery.

One thing I can say definitively without any of this information, though, is that you are without question better off by using a separate battery to run your house electrical devices (lighting, appliances, charging of battery-powered devices), than you are trying to power these off your vehicle battery. The main reason for this is that while it may be inconvenient to run out of power for your living needs, this inconvenience gets radically worse when running down the battery also takes away your ability to start the vehicle engine. Having done this the wrong way before, I can state from personal experience that there are plenty of electrical devices (laptop computers, lighting, 120V inverters) that will happily continue operating and draining your battery after your battery's charge is down to a level where the engine won't start in the morning, and every time you do this reduces the life expectancy of your vehicle battery. And then you have to get it jump-started, which is both inconvenient and embarrassing. Using a separate battery and either a solid-state isolator (which I don't recommend because it reduces the voltage to BOTH batteries), a switch, a solenoid, a relay, or even an 18-gauge wire with cigar lighter plugs on both ends, means that no matter how badly you treat your house battery, this will never leave you stranded as long as you ensure that the two electric systems are disconnected from each other when you shut off your engine. And as an added bonus, if you should happen to leave your headlights on and run the vehicle battery down, you have the house battery to jump start it from!

Now on to the other things:
1) The capacity of the house battery is the easy one: all of the gel-cel batteries I've used have their capacities printed right on the label, which is in "Amp hours", or Ah. Note that this is NOT the same as Amps/hour or Amps per hour - there is no such thing as Amps/hour, and as a guy with a degree in electrical engineering and decades of engineering experience, I can back that up if you want to discuss it elsewhere. Saying "Amps per hour" makes no more sense than saying "Miles per hour per day", and I cringe every time I see the term. Most people who say "Amps per hour" really mean "Amp hours per hour", which intuitively just seems like it must be wrong, but is the same thing as "Amps", which is what they SHOULD be saying. I only bring this up because in my experience it causes a GREAT deal of confusion between Amp hours and Amps, when people say Amps/hour when they really mean Amps. Okay. The next part is a little more controversial: for most lead-acid batteries, the rule of thumb is not to use more than 50% of the Amp hour rating in any given charge/discharge cycle, but for "deep cycle" batteries you can safely use more than that. How much more depends on the manufacturer's specifications for the battery. But in any case, for maximum battery life, you should never let the voltage get below about 12.6V (or for 6V batteries, 6.3V each) when the battery is unloaded. That's controversial, because many devices are set to "protect" your battery by shutting off when they get down to somewhere in the range of 11.5V to 11.8V, at which point you may already be damaging your battery. The reason they set this threshold so low, is that when you plug things into a cigar lighter, there is enough voltage drop between the battery and the device, that 11.8V at the device MAY indicate 12.3V at the battery. So they set the cutoff at 11.8V when they really want the circuit to cut off when the battery gets down to 12.3V. Or more, or less, depending on what length and gauge of wire connects the cigar lighter to the battery. If they set the limit to 12.6V, it would cut off the current way before your actual battery voltage was that low, and people's satisfaction with 12V devices drops of pretty abruptly if they shut off too soon. (Off grid: this is probably why you were able to start your engine even though the measured voltage was 11.8V.) So to be on the safe side, let's just assume you want to keep your house battery more than half charged at all times. Since you said you're using 6V gel-cells, I'm assuming you're using two of them in series, in which case the total Amp hours is the same as the Amp hours for either battery. Batteries wired in series should have the same Amp hour capacity.

2) Average load (current consumption) from the house battery. It sounds like you've already done the work for most of your devices, but I want to make one correction: when you say that 0.34A @ 120V is 3.4A @ 12V, you are making an assumption that your inverter is 100% efficient. At best, inverters are about 90% efficient, and that's when they're running near their full rated continuous power. At lower power levels, typical efficiency is closer to 80%, so it takes more 12V amps than that, by a factor of about 25%, so really that's going to be about 4.25A @ 12V. It seems like a small thing, but these small things add up.

3) Average current from the alternator into the house battery. This one is tricky, because knowing the current rating of your alternator will not help at all. Why not? Because that's the maximum current that alternator will provide rather than the typical value, and because there are plenty of devices on the vehicle already that consume much of that, such as lights, ignition, fuel pump, heater fan, and charging of the vehicle battery. Also, if the alternator delivered its full current all the time, it would boil your vehicle's battery dry in a matter of days, so this current is reduced as the batteries charge, so the charging current depends more on the battery's charge level than it does on the alternator's rating. The only time you'll ever see the full current coming out of an alternator is right after starting the engine, when the vehicle battery is at its lowest charge level. The only way to know the charging current is to buy, borrow, or steal an ammeter (a device that measures DC Amps) and put it in the circuit between your alternator and your house battery. Do this with the house battery partially discharged, like at a starting voltage of around 13.0V. When you start your engine and rev it a bit, say to 1500 RPM or higher, the charging current will start out relatively high, and will taper off slowly and settle to an steady current, and that's your average charging current. Off grid is correct - you can charge through an 18-gauge wire between cigar lighter plugs and still get a full charge. BUT, SternWake is also correct - this will only work if the devices connected to the house battery aren't consuming much current at all, because if they are, it will take more time to charge the house battery than you will be willing to drive. Using small wire like that restricts the current that can go from your alternator to the house battery, and as SW says, this causes a voltage drop, BUT, as the house battery charges up, it accepts less and less current, and the voltage drop decreases, so as the battery (slowly) approaches a full charge, it rises to the full alternator voltage, and you still get a full charge. It just takes longer. This is according to the laws of physics, SW, and I got pretty good grades in physics. A good thing to remember about electrical sources and loads, is that the source primarily determines the voltage, and the load primarily determines the current.

Once you have all three of these figures, then it's a simple matter: you can calculate how many hours you can use your house battery with all of your devices by taking the total capacity of the battery (in Amp hours) divided by 2 (because remember, you only want to use half of that capacity) and dividing that by the total average consumption (in Amps). The answer will be in hours, so if you want to know how many days, just divide that by 24. If you want your house battery to live a long life, you should not use it longer than this between full recharges. To know how long it will take the vehicle's alternator to fully recharge the house battery from that half charge, divide the amount of charge you need, which again is half the house battery capacity, by the average current the alternator supplies to the house battery (again in Amps). Again that is in hours, so if you want minutes, multiply by 60. If you DO mess up and discharge the house battery more than that, you must extend the charging time by a corresponding amount to get back to full charge.

There's also a somewhat quicker way to do this that may be more practical at times, such as determining how long you need to drive to recharge on a particular day: if you divide the average current consumption from the house battery by the average charging current to the house battery, you will get a number that indicates the ratio of discharge time to charging time. For example, if your average current consumption is 5 Amps and the average charging current is 50 Amps, this ratio is 1:10, which means that for every 10 hours you discharge the battery, you need to charge it for 1 hour. But remember that this is just an example - your results will be different, based on YOUR average charging and consumption currents.

Just keep in mind that because all of these average currents can vary in actual operation, these calculations only give you an approximate answer, so you should treat the charging time as a minimum and the discharging time as a maximum. Also, most alternators produce very little current when the engine is idling (this is a design feature, to reduce the fuel consumption at idle), so driving time does not include time spent waiting for the engine to warm up, waiting at traffic lights, or any of the "stop" time in stop-and-go traffic.

So that's the correct answer - that you need to take some measurements and do the calculations before you will know the true answer. The rest of what I'm seeing in this thread is all guesswork. So in the spirit of the thread, I'll throw in a little guesswork of my own: if you're driving 500 miles/month, I'm guessing 25 miles/hr average (i.e., driving around town), that's 20 hours/month, or about .67 hours/day, which SHOULD be enough to fully charge your house batteries unless they're huge and you're using a wimpy little wire like Off grid's, but no promises from me until the charging current measurement is taken. And if you're plugged into the grid 48 hours/week, it matters whether that means two days in a row, like every weekend so it goes five days between charges, OR for example, home every Tuesday and Friday, so it never goes more than three full days without being on a charger. What's significant isn't the number of hours plugged in, but the maximum time between plug-ins. Here I'm guessing that your charger has enough output current to fully charge the house battery overnight, so there's no additional benefit to having it plugged in two days in a row. And just to be TOTALLY guessing, I would say that driving 500 miles/month AND plugging in two nights per week should be enough to keep your batteries happy. But since we're just guessing here, buy a cheap digital voltmeter and make sure your house batteries never go below 6.3V each when everything is turned off - that is, engine off, house battery disconnected from the vehicle battery, and inverter and other high-current loads shut off.

Thanks for getting all the way to the end of such a long, painfully detailed, and sometimes nit-picky reply.
Jim

 

[SternWake]

Off grid, anybody who is actually cycling their batteries deeply, nightly, and depending on them, and takes your Ciggy plug advice is going to find out quickly that your system will not work for them, and their batteries are now capacity compromised from taking your advice and they now have to do what they should have done in the first place, which is have a large copper conduit in between alternator and depleted battery.

The OP Needs a reliable electrical system for health reasons and will be cycling a pair of GC batteries deeply nightly, and there is simply no way, no how that a ciggy plug can return anywhere near the amount of amp hours used, and your continuous mentioning of this extremely poor method of recharging is detrimental to this forum, and to members trying to learn what they can realistically power from a set of batteries, for how long, and how long the batteries can be expected to last.

If you insist on interjecting your opinions and methods which supposedly work for you, then you should also mention that your electrical usage is extremely light. If you claim to be using anywhere near 50 amp hours nightly and that 30 to 40 minutes of driving and recharging via a ciggy plug is keeping your batteries happy, then you are delusional human with a disgusting unknown agenda.

I am going to recommend that no one place any heed whatsoever on your words regarding things electrical and battery charging. I will also not respond to you or your comments, and only steer people away from listening to your advice regarding your methods and claims on this subject.

 

[SternWake]

Some good points and words brought up by BBJ above, and I could nit pick some details but there is no real point as getting too technical tends to confuse and frustrate those trying to learn.

Dodges, from 1988 on, have the voltage regulator built into the engine computer, and this VR is programed to keep battery voltages from exceeding certain levels, and it assumes that the task is to power the normal vehicle loads and return the small portion removed during engine starting.

This VR was not programmed to properly or quickly recharge an additional set of deeply cycled batteries tacked onto the end of the circuit. When any battery is near full charge, like an engine starting battery should always be, it does not require much amperage to bring and hold the battery upto 14.5 volts, and after a short time it will lower the maximum allotted voltage to the 13.6 range, and the amperage required to hold the still depleted battery at 13.6v is much less than what was required to hold it at 14.5v.

So if a set of GC batteries are tacked onto the end of the charging circuit, over thin wiring, then the VR has little idea that those depleted batteries exist, and drops voltage to 13.6v, and amp flow into the depleted house batteries is a tiny fraction of what the alternator could deliver, If the cabling were larger, and If the alternator were spinning fast enough to give the batteries what they desire. The batteries are actually self limiting at the voltage allowed. As long as the voltage is regulated, there is no danger( to the batteries) in allowing the batteries to suck as much juice from the power source as they want.

So, when the alternator is to be required to replace as much as possible in a minimum amount of driving I recommend a minimum of 4 awg cabling, and instead of tacking the new charging circuit on the end of the original charging circuit, take the power right from the alternator(+), properly fused at both ends of the cable.

This yields shorter circuit with less voltage drop, and also allows the voltage regulator to see that the battery is depleted, and to allow 14.5 volts for longer, and more amps can flow into the battery. If instead, the cabling to house batteries comes from engine starting battery, the likely hood that the VR drops the maximum allotted voltage to 13.7 is greater, especially when the cabling used is thinner.

A pair of GC batteries can easily accept 80 amps when depleted, but even if the alternator is rated for 80 amps. this number was figured out in a laboratory, with a cool alternator spinning extremely fast with 80+ amps of load asking for that much current over cabling capable of passing it. In other words it is nearly impossible to achieve the alternator's rating when it is in the vehicle. And it is also possible that a higher rated alternator, actually produces less amperage at lower RPM's than its lower rated cousin.

While the serpentine belted dodges of your era do better at low rpm than the V belted dodges of earlier years regarding idle speed amperage, They are far from being powerhouses at idle speeds. My '130 amp' alternator cannot produce more than 32 amps when hot at idle speed, yet I have seen it produce 110 amps when cool at 3000+ rpm. So Idling to recharge is not very effective on this vehicle platform.

My 89 dodge also drops the maximum allowed voltage prematurely, sometimes, and other times allows 14.9V to occur for longer periods. I am not sure what factors trigger 13.7 when the batteries would still prefer 14.9v, but with the voltage regulator being internal to the engine computer, there is not much I can do. However, when I disconnect my parallel alternator charging circuit, forcing the current to take the original Dodge provided thinner longer circuit, it almost guarantees that the voltage reverts to 13.7v very prematurely.

Not knowing your mechanical aptitude or skills with tools, I'd recommend having the battery cables made professionally, as proper crimping requires the right tools and the skills to use them. While dwellers need not goto the extreme lengths of meeting ABYC standards regarding battery cabling, simply crushing cabling inside a Lug with a vice yields a poor connection, both electrically and mechanically. If a 4 awg cable slips out of an improperly crimper termination, very bad things can happen, even when fused, depending on fuse location.

Suddenly removing a heavy load on the alternator can destroy it too, so this house battery charging circuit must not be halfassed.

Now when maximizing the alternator's contribution to the depleted house battery(s) via thick copper, this places a much higher load on the alternator, shortening its lifespan to some degree.

While each platform will be different, My POS reman'd 130 amp alternator has been installed since 2006 or 7, and it gets maxed out nearly daily for shorter drives, and maxed out for extended periods fairly regularly.


http://www.genuinedealz.com/custom-cables

The above link makes very high quality cables with top quality cable and terminations, and the prices are also very good, and the shipping fast and free. Figuring out the lengths needed beforehand is the only negative. Please beware of good prices on cabling on Amazon or Ebay, even if they claim it is 100% copper, it is most likely not.

I am also reluctant to recommend any automatic grid powered charging source for your 48 hours of plug in time. If you plan on using 12v devices when recharging the batteries, you need an RV converter, as loading the batteries while charging via an automatic smart charger will confuse it and shut it down. RV converters are designed to both power loads and recharge batteries, but their charge algorithms are far from perfect for any battery, and often they are hard to get into 'Boost' mode where they try and bring the battery up into the mid 14s for a n hour or two. Sometimes they just decide to allow only 13.8v even with depleted batteries. Again shorter thicker cabling helps greatly in this regard where as long lengths of thinner cabling almost insure the converter will not go into boost mode and come close to delivering its maximum rating into the thirsty batteries.

Iota, Progressive Dynamics and Powermax are the big three converter makers yet all of them are a disappointing compromise to some degree or another. Which is why I went with an adjustable voltage switching power supply instead, but this is not an Automatic charger, and unattended can easily overcharge and damage batteries, but at least it can indeed fully charge batteries and not revert to premature float voltages as all automatic chargers do.

 

[gypsychic]

Thank you BBJ & SW for taking the time to write such detailed replies. I have read them slowly and will reread them again. For the most part I understood most of what you have stated. I'll go over it again & ask any questions that might pop up. I just wanted to let you know how deeply appreciative I am for you taking the time to help me, through the computer, understand a subject that is confusing to me. It will help make me much more comfortable. I'm sure others are benefitting from your thoughtful replies as well.

Gypsychic

 

[SoulRaven]

BrightBlueJm,

Thank you for a far more eloquent explanation than I am normally capable of supplying.

I would like to make one very important point here though. Sternwake inaccurately assumed that these jumper cables are 18 gauge wire, when in fact they are 10 gauge which makes a considerable difference in charging times.

I tend to get flustered when somebody calls me a troll and claims that physics won't allow something when neither are true, or that 2 x 6v batteries wired in series will double the amp hour capacity.

I have been living a primarily mobile lifestyle for over 40 years now, and some of my friends with even more experience than myself.

I learned early on that the technical specs of a system only confused the average person, and what they really wanted was simple, easy to understand directions, and that an easily expandable system usually was a better fit than trying to get them to figure out what they needed in advance. Over the years this approach has returned excellent results, and it is basically as simple as adding more batteries until your needs are met. That concept is easier for people to understand, and the end result of having a working, efficient system is the same.

 

[brightbluejim]

Hi Gypsychic,

I know there's a lot more to it than people expect - our life experience is that we plug things into 120V outlets and they just work.

SternWake and Off grid both made some good points, and yet it seems like they're worlds apart. It seems the major point of contention is how big the wire should be that connects your alternator with your house battery, and that SternWake made an incorrect assumption about what Off grid was using. I don't know how long a wire run it's going to be, and since nobody else asked, they can't possibly know what they're talking about. The resistance (the amount that a wire restricts current going through it) depends on both the wire gauge and the length. These are equally important, so saying what your wire gauge should be without stating your assumptions about the wire length is irresponsible. I'm going to guess that your wire will be about 20 feet long for a moment, just to illustrate a point. Your results WILL be different depending on the actual wire length, so please don't take my results as a recommendation.

I usually wouldn't go into wire resistance, but since that's what the argument comes down to, it's important to look at the numbers, and not just what one person has used as a rule-of-thumb with a high safety margin, versus what another person says has worked for him for 40 years.

4 gauge wire has a resistance of .00025 ohms per foot (source: Wikipedia article on American Wire Gauge), so a 20-foot length will be .005 ohms, which means that you will lose .005 Volts for each Amp of current flowing through it. If you have 50 Amps flowing through it, you will lose 0.25V, which seems like a reasonable amount if you really need 50 Amps of charging current. This is the basic physics of the situation, based on Ohm's law.

Likewise, 10 gauge wire has a resistance of .001 ohms/ft - about four times as much as 4 gauge, so a 20-foot length will be .02 ohms, and will drop .02 Volts for each Amp of current. The simple fact, as I'm sure SternWake would point out, is that you will never get 50 Amps through that 20 feet of 10 gauge wire, because that would drop one full Volt, and the battery just wouldn't draw that much current if it had that kind of voltage applied to it. In reality, with a 20 foot 10 gauge wire, you would probably get somewhere between 10 and 20 Amps of charging current. Which is perfectly fine if that's all the charging current you need.

But I would NOT go so far as to say that SternWake is right and Off grid is wrong. There is another factor SW seems to not be considering, and that is that you WANT your vehicle battery to have first priority when charging, which means that it's a good thing to have a little voltage drop (from wire resistance) in the charging path for the house battery, so that the vehicle battery will get the bulk of the charge during the first few minutes of driving. If you give your house battery just as good a path to your alternator as your vehicle battery has, you run the risk of under-charging your vehicle battery if you don't drive enough. But as I said, this is a hypothetical example based on my wild-ass guess that your charging wire length will be 20 feet. I prefer not to make wild-ass guesses, but in the absence of actual numbers (specifically, your battery Amp hour rating and the length of the charging wire) it's all I can do.

I hope this doesn't confuse things any further, but I don't like people accusing other people of giving bad advice and potentially damaging their electrical systems, without all the facts, and when all Off grid was saying was what has always worked for him. I don't recall Off grid EVER saying "you should use 10 gauge wire". The fact is that unless I missed a post somewhere, neither of these guys knows what the Amp hour capacity of your batteries is, so neither of them is in a position to say how much charging current you need. The way an electrical system should be designed, is to determine your average current consumption (day and night combined), and multiply that by the number of hours you need to be able to run without charging your batteries, i.e., how long you want the rig to be able to be parked without hooking up to shore power. Then you double that, and maybe you increase it again by some margin to allow for the unexpected and for future expansion, and this tells you how much battery capacity you need. Only THEN should you go on to determine the optimum charging current so that you're not needlessly overstressing your vehicle's electrical system. But nobody has done that - nobody else has even asked what your battery capacity is. All I'm hearing is a pissing match, which does nobody any good.

I will stress the one fact that I can give you without knowing any other numbers: there are only two ways to determine the charge state of lead-acid batteries: by measuring the specific gravity of the electrolyte, or by monitoring the voltage. And since gel-cells don't give you access to the electrolyte, that leaves only voltage. There are voltage monitors available on eBay and Amazon for under $10 that plug into a cigar lighter jack, and I would recommend buying one of these. They're like the fuel gauge on your vehicle - you don't absolutely HAVE to have one, but it's kind of silly not to.

Jim

 

[SternWake]

In this case GC batteries stand not for gel cell, but golf cart, and most golf cart batteries are 220 to 232 amp hours, and Trojan, pretty much the top dog of the Golf cart battery, recommends 14.8v absorption voltages and warns against voltages of less than this. US battery recommends finishing charges upto 15.3v. It is not easy to get recommended absorption voltages from Johnson control, who are currently making the sams club and Costco golf cart batteries, though in the past these were made by USbattery for these retailers.

 Golf cart batteries are however much more tolerant of non perfect charging methods, especially compared to 12v batteries with deep cycle or dual purpose/marine internals stuffed into them.

The pink wire with a red stripe from the fuse block to the stock ciggy plug on 80's era  Dodges is 18 awg, and even the best designed ciggy plugs and receptacles use spring loaded steel contacts and heat up greatly passing  just 7 amps.  It might be a convenient and ubiquitous connector, but it is a very poor electrical connection that wastes battery or alternator power as heat, to the detriment of the device and battery and the person depending on them.

The starting battery on a healthy fuel injected engine is depleted so very little during engine starting that time delaying prioritizing its recharge is not a factor, if the starting battery, which is not designed to ever be discharged lower than 80%, is indeed fully charged to begin with.   If there is a house battery system, then there is absolutely no reason to discharge the engine starting battery, and such a battery has an easy life indeed remaining at 95%+ state of charge.

Since there is no room for a pair of GC batteries under the hood of a mid 90's Dodge, the actual cable length, one way, to reach from alternator or engine battery to a pair of GC batteries secured close behind the driver/passenger seats is about 10 feet minimum when routed and secured properly against chafing.


Either way, minimizing voltage drop to the house batteries will more quickly recharge the batteries, upto 80% state of charge range, and it is hard to go too big on cable thickness, other than price of the copper, the weight, and the difficulty of bending cables thicker than 4awg.

So going too thick can only help charge the batteries faster, and the only detriment is the price of the copper, the weight and the difficulty of routing thicker cabling.  Going too thin will greatly extend the times required to get the batteries to 80%, and the greater voltage drop will not let the batteries reach their desired absorption voltage, so that even a 500 mile drive in 8 hours will not truly top charge the batteries where the specific gravity reads 1.275 or higher on every cell.

And if lead acid  batteries which are deeply cycled each and every day, do not get to a true 100% every 14 cycles or so, their available capacity diminishes and for the most part, is not recoverable without extended times on a plug in charger and voltages upto 16V in an attempt to dissolve all the sulfates back into solution. The longer the battery remains partially sulfated, the harder the sulfates become, never to dissolve again, and greatly affecting battery capacity.

Voltage is a piss poor method for determining battery state of charge.  It is only accurate on a well rested battery, one which has not seen charging nor discharging currents for a long period of time. It is far from being a battery fuel gauge on a battery under loads, though it is certainly battery than nothing, and with enough time, a person regularly discharging batteries will notice trends and tendencies of voltage under load and make estimates as to battery state of charge, but these observations need to be adjusted as the battery ages, and all batteries will vary slightly on what voltage corresponds to what state of charge though often one will see 12.2v=50% or 12.6v=100% stated as fact for all batteries.  

When recharging, the amps required to hold the battery at absorption voltages is a good indication of state of charge.  If the battery is requiring 10 amps to be held at 14.8 volts it is still  far from being fully charged. If only One amp is required to hold 14.8V then a single 12v battery is very close to that elusive and very desirable 100% mark.  Again this varies between batteries, and the numbers will change as the battery ages.

Clamp on DC ammeters or shunted ammeters are wonderful tools to understand how much electricity is flowing to or from batteries and to make educated guesses at their states of charge.  Voltage alone does not tell very much unless the battery is well rested, and there are previous observations to make comparisons to.  Cycled Batteries are rarely well rested in a full timers vehicle, so the voltage only gives a vague range, and the Hydrometer would likely call the voltmeter for the liar that it is.