2nd Battery to Charge off Alternator, Question List.

[Eldritch Penumbra]

I would eventually like to add solar to my roof top, but in the mean time I would like to set up a 2nd battery to charge off my alternator.

I have seen kits like this Auxiliary Battery Isolator kit on Ebay:

http://www.ebay.com/sch/i.html?_fro...TRS0&_nkw=AUXILIARY+BATTERY+ISOLATOR&_sacat=0


...but know nothing of the brand or of user reviews. Also I do not know that this would be over spending and that perhaps I should put together the kit myself. I've also heard that you can use a solenoid and can accomplish the same thing, but again I do not know what type of solenoid to purchase, nor do I know for sure that it will do what I need it to do.

In short, I want to be able to charge the 2nd battery off of the alternator, though I only want it to do this when the primary battery is fully charged. Also I want to be able to use the 2nd battery, to be able to jump start the primary batter if needed. Lastly, when the van is off, I still want to be able to run my power inverter off of the 2nd battery. On a side note, the 2nd battery will be in the rear of the van, negative attached to the van's shell, and the positive, running under the floor and up to the hood on the driver's side.

As for the battery, I intend to use this with a 200 to 300 Watt Solar set up eventually. Also I live in Ohio where the weather changes constantly and is not always particularly hot or warm out, but the sun does emerge.
I am not sure if I should purchase a single 12v that is massive, or if I should go for 2 to 4 6v go cart batteries and put them together as one huge 12v. If I went with the battery cluster, would they still be able to charge off my alternator until I can get solar panels, or can a single 12v battery compete with the cluster of 6v? Lastly will this wear on the life of the alternator, and also, does it need to be upgraded?

Thanks in advance!

 

[Weight]

Two six volt Golf Cart batteries connected in series to be 12 volts are the same as one 12 volt battery. Except the GC batteries are sooo much better as deep cycle house batteries. Moving two GC batteries is better than moving one 12 volt battery of equivalent amp hour rating. I use 6 Golf Cart batteries in series/parallel, to be 12 volts and 690 amp hour rating. Setting up my system, and later replacing batteries, I get to move 60 pounds at a time, instead of hundreds, needing a crane. Charging large banks of deeply discharged batteries can be very hard on a alternator. But your stock engine management system will not allow the alternator to charge enough to be that problem. You will be faced with not enough charging to replenish the battery. Solar will help with that. I would make up my own "isolater kit".

 

[highdesertranger]

it takes hours of driving to fully recharge a depleted house battery. a depleted battery should be recharged asap at least daily. are you going to drive that much? using your alternator as one of your charging sources is always a good idea. using it as your only charging source is seldom a good idea. highdesertranger

 

[Trebor English]

Generally the alternator connection in a van or RV is not effective to provide large quantities of electricity.  It is quite useful dealing with solar when there are too many rainy days in a row.  Most people don't drive at speed for 3 or 4 hours every day.  220 or 440 amp hours, 2 to 4 golf cart batteries, is big.  Are you considering 4 batteries because 2 wouldn't be enough?  Restoring 110 amp hours won't happen by starting the engine and letting it idle for 20 minutes.  When I first started using a van I was using 2 to 4 amp hours per day.  Alternator charging is good for that.

The usual solar way is to start with figuring out what you need and what you want.  A CPAP to breathe would be need, a fridge to keep milk for your corn flakes would have a different priority.  For the need stuff you want multiple sources.  For the want stuff maybe not arranging 3 levels of backup.

Back to the original post  If you mount the battery in the back you have longer wire  If you mount the battery behind the driver's seat you get a shorter wire.  The resistance of the wire controlls the amount of charge.  Bigger wire helps but won't fix a loooong wire.

The switch to connect the run down battery to the van alternator comes in 4 flavors.
1) A manual switch.  You put your hand on it and turn it on and off.  These can be inexpensive and long lasting.
2)A diode isolator.  These have fins on the outside surface.  Inside there are diodes that let current flow one way but not the other.  The problem with these is that when passing substantial current they drop .5 to 1 volts.  If your van battery is charged and the regulator is keeping that at 14 volts your house battery will not charge much.  If you are getting 3 or 4 amps the diode drop will be .7 volts.  14 - .7 = 13.3.  That isn't even the recommended float voltage for most batteries.  Driving 24 hours would take days to recharge 4 golf cart batteries.
3) Voltage dependent relay.  This product has 2 parts.  There is a circuit that measures the voltage.  When there is enough voltage the circuit turns on the relay connecting the two batteries.  It waits until the van battery has enough voltage to be able to share.  When the van shuts off, the voltage goes down, the circuit turns off the relay.  
4) A plain solenoid.  Solenoid is a fancy word for relay.  An elecromagnet coil turns on a switch.  To use this you have to poke around in your van wiring to find a circuit that is on when the engine is running.  You tap into that to have it turn on the solenoid.  Some people add a manual switch to let you override and manually control the solenoid.  These can be had with high current ratings and they are not very expensive.  This is the same as the relay part of the voltage dependent relay.

Before buying a solenoid find a relay control circuit in your van.  The owner's manual tells which fuse powers the air conditioner fan.  If you don't find something you like go for the voltage dependent relay.

Whatever you have keep in mind that all of these eventually fail.  They stay stuck on when they shouldn't and they go off when they should be on.  

 

[SternWake]

The alternator has tremendous potential to get a well depleted battery to 80% charged fairly quickly, but it is severly limited by its voltage regulator, and the  circuit between the battery and the alternator.


The voltage regulator on vehicles is not designed to charge batteries, it is designed to not overcharge a slightly discharged battery.  They usually only allow voltages in the mid to high 14's for a few minutes after starting the engine, then drop to a 13.6v ish range which will generally not overcharge the battery.

The problem is this premature reversion to 13.6, will cause charging amps to drop by 2/3's, compared to 14.7v.

Adding this premature reversion to 13.6ish volts, to the voltage drop on the circuit to the distant depleted battery and it is possible that VERY LITTLE charging actually occurs, but the driver without an Ammeter measuring amps into the depleted battery, will largely remain completely clueless to this fact, and often have a very false confidence that the battery is being recharged as fast as possible, when it is far far from that goal.

So assuming one minimizes losses on the copper circuit.  this means thick copper cable from alternator (+) stud to isolation device to fuse to house battery, and the ground path, well it would be best if thick copper cable went from battery (-) to an alternator mounting bolt.  If the vehicle chassis is used as ground path, run an additional ground from frame to alternator mounting bolt.  Pay special attention to the quality of the cable terminations as chassis grounds become problematic quickly if not. 

 Hooking house battery to engine battery  instead of alternator, makes the original wiring from alternator to engine battery into an electrical bottleneck as it was never intended to handle the extra amperage a depleted house battery will ask for.  While this is commonly done and prescribed, the direct feed from alternator is a shorter circuit and much more effective, and requires one less fuse as the original engine battery to alternator circuit is already fused from the factory.

If the circuit is nice and thick one is still limited by the voltage regulator, and its premature proclivities to drop to a mid 13 volt range.

One can get a DC to DC voltage  booster inline to raise the voltage the depleted battery sees, raising its charging voltage, increaseng charging speed.  Sterling and some other companies makes such devices, they are 3 to 400$

One can get a better voltage regulator. How difficult this is to employ, depends on the vehicle platform.  My VR was in my engine computer, I tricked the ECM into thinking it was still attached to alternator and use an adjustable external VR, whose adjustment knob I put on my dashboard next to voltmeters and ammeters.  I can almost always charge my battery as fast as it is possible to recharge it. The time It cannot, is when it is super depleted and engine rpms are low and it cannot make the 65+ amps required to achieve and maintain 14.7v.  Larger battery bank capacity requires higher amperage to achieve absorption voltage quickly.  My alternator is rated at 120 amps, my battery is a 90Ah  Northstar AGM.

But no matter what, getting a battery that was down at 50% originally,  then recharged to 80% quickly at higher amperage, the 80% to 100% charge takes no less than 3.5 hours, and that is at the ideal voltages in the mid 14's, which we have established is NOT going to occur in 99.99999% of vehicles.

A deeply cycled lead acid battery whose only charging source is an alternator, even if the voltage it receives are ideal,  is not going to achieve many cycles before its capacity is so compromised simply because a battery requires regularly being 100% charged to keep its capacity mostly avaialable, from declining too quickly.

Solar, hopefully has the time to complete the charge silently.  Alternator amps applied early morning and then adequate solar wattage to maintain absorption voltage the rest of the day can keep a battery happy for quite a while and yield a reliable system.

Also nice is to be able to plug the battery into a charger every so often and simply get it to absorption voltage hold it for hours, and then float it for many many hours afterwards.

So one might save money initially by going for alternator only recharging, but they will likely pay more in replacing batteries prematurely, and in stress, in not knowing if they have enough battery capacity to power their needs, and stress in when the battery does require replacement, acquiring a battery in a specific location that can actually handle deep cycles, and not cost more than it should had the owner known replacement was coming and had time to plan and shop, not merely pulling old sulfated overpriced stock off the shelf and then being unimpressed with the voltages held under normal overnight loads.

 

[John61CT]

The voltage regulator on vehicles is not designed to charge batteries, it is designed to not overcharge a slightly discharged battery.  They usually only allow voltages in the mid to high 14's for a few minutes after starting the engine, then drop to a 13.6v ish range which will generally not overcharge the battery.

This is true for (many) stock alts.

If you convert or replace to one that allows an external regulator, Balmar's MC-614 gives pretty much complete control, just like an expensive bank charger.

Including custom setpoint programming, separate volt sense wire, temp sensors on both batt and alt.

Or the Sterling "BB" series of DC-DC chargers.

With either of these, even a small (<100A) alt can deliver great charge cycles, but with most lead banks, you still need a very long tail at low amps to get to 100%.

 

[MrNoodly]

Bob did a video on installing a solenoid to control charging a house battery via the alternator.

 

[John61CT]

Note the solenoid approach is good only for "combining" while the engine is running.

A more expensive ACR/VSR will combine based on any charge source raising the voltage. Like shore charger or solar.

Both assume same charge algorithm, usually NBD unless expensive batteries involved.

For unlike banks or long cable runs, DC-DC charger near the target bank is the way to go.

 

[Eldritch Penumbra]

Going by what you guys are saying, and the money I would be putting into all of this, I believe maybe I should skip messing with the alternator all together and install Solar Panels instead.

I will be powering the portable AC through a generator, I presume that is the best method? A compact, quiet, generator to keep the pets happy and alive while I am gone?
Likewise if I happen to be traveling during the Winter, which I probably will during break, I'll assume a generator is also the best go for a portable heater as well?

Those two appliances aside, I will need to charge my laptop, Nintendo 3DS, 10" Tablet, Battery Charger, Raspberry Pi 3, External Self Power Hard Drive, a Tell-Lie-Vision, and possible a tiny fridge the size of a large ice cooler if that.

Would a 200 Watt Solar Panel with 2 Golf Cart batteries suit my needs, or should I go 300 Watt Solar with 4 Golf Cart batteries. I'll assume that I'll watch movie or play video games off the Pi for an average of 2 to 4 hours a night.

 

[John61CT]

Yes, only worth beefing up the alt/VR if you do many hours of driving per week.

If you size the generator to power the A/C load you need, plus say a 60+A charger running concurrently, you should be able to get/keep the batteries pretty close to full most of the time at will.

Do that in the morning, and then the solar will help get the lower-amp long tail done, so the bank gets to 100% full each day, or at least most of them.

Always put in as much solar as will fit; that will help reduce gennie runtimes.

At that point, putting in more storage won't, you have to put in what you take out, but a bigger bank gives you more choice about going a while between charge cycles, like not disturbing neighbors.

But if you decide to try running the A/C off the batteries for part of the day, then you will need a **very** big bank, basically at least as much weight and space as you're willing to sacrifice.

 

[DannyB1954]

I am not a full timer. Last year I spent 3 weeks in the van camping. In my van I do not yet have solar, so I use a relay to charge a second battery from the vehicle alternator. I want this second battery to charge as quickly as possible so I don't use deep cycle batteries. I use what would be considered a combination marine start and deep cycle like the Walmart Everstart maxx 29dc. My electrical loads are light so I get by just fine. My main use is for the roof vent. I live where it gets hot in the summer. During the day I have a dog to keep cool while I shop or run erands in town. . At night I run it for a couple of hours till I fall asleep,( it has a thermostat that shuts it down). I do seem to drive everyday, I also carry a small generator and a battery charger if necessary. If the battery dies in the first 2 years, it is warrantied. After that, oh well time for another $100 battery.

 

[Eldritch Penumbra]

That's where I HAVE to have the generator because I have a dog and a cat that will be with me. I do not drive but maybe 40 miles a day if that.

I am grateful for all of the advice and I believe that I can fit 3 Panels on my roof with ease. As for the components I should get (battery size, type, etc) that will suit the needs I mentioned above, that is something I am still not clear about.

 

[SternWake]

If you have a generator you can get a high amp battery charger/ RV converter.

Some AGM batteries, like Lifeline, Northstar and Odyssey have much less internal resistance, and can accept huge charging amperages, but are $$$. The last 20% of charge still takes a long time, on ANY lead acid battery whether starting or marine/dual purpose, deep cycle, AGM or Gel. The difference between the best and worst of these in that last 20% of charge would not be much. The last 20% the more the battery ages, takes longer and longer anyway. Slow the aging by recharging to full as often as possible/practical/desirable.

Really, All possible charging sources should be utilized. Alternator, plug in charger on generator or grid, and solar. Since you require the generator for the AC, I'd start with that and a high amp charger, then get around to hooking up alternator and solar when you can. The solar is good for the last few% as it takes a long time, but the other charging sources are usually needed to get the really depleted batteries to where the solar can produce enough amperage to hold absorption voltage.

I am not sure how big of a generator you need to power this 70 amp charger:
http://www.bestconverter.com/PD-9270C-148-70-Amp-RV-ConverterCharger_p_619.html#.WR1FH5LyuQM

These chargers are automatic, but can be overridded manually to force any of 3 voltages/ charging rates. If you have to run the generator for the AirConditioner in the hottest part of the day, well then the solar would just reduce the load on the generator while it is running.

The linked product is a 14.8v version, Acceptable for Odyssey and Northstar below 75F, but Lifeline Says 14.4. The regular versions sold are 14.4v.

In your current vehicle, you can get some idea of the voltages it allows when driving, by installing one of these in a 12v port.
https://www.amazon.com/INNOVA-3721-...rd_wg=8AOr6&psc=1&refRID=A8GNXBCWMDXMQZSA3BMG

If voltages allowed by voltage regulator are still in the 14's after 45 minutes of driving with headlamps on and Hvac blower motor on high, then it is likely your alternator will contribute more to a depleted house battery than the average vehicle.

I would not recommend avoiding using the alternator just because it is not allowed to seek Ideal voltages. The first ~15 minutes when it seeks mid to high 14's, well if highway driving, it can send 70+ amps. Idling to recharge is usually produces much less amperage, and it will heat up much faster and wear out faster. Faster driving speeds means more underhood airflow and more rpms means alternator fan sucks air through it faster.

A cool alternator is a happy alternator.

 

[John61CT]

That 70A would use most of the HP output of a little ~1000 kW gennie.

Need to run the A/C unit full bore on a killawatt see what it says over an hour.

Put the two together, probably 1800-2400 kW would be enough, but best to be sure before you buy.

I would say buy these three, first along with the DMM and clamp ammeter, maybe a battery monitor?

Plan to buy the batteries last, only after you know some numbers so we can guesstimate AH. That will also require answers to some other questions, most vital is: are you sure you want to run the A/C only off the genny, never from the bank with the genny off? Are you ever going for days with no A/C?

12V is fine as long as it's a known-good deep-cycle. The Sam's Club GC2 is just such great value AH per $.

If you know you're running the genny they may be good enough, let you afford to buy a bigger set.

Also note running the genny all the time might wear it out in a year or two, make sure to get an hours meter and follow specs on oil changes.

The big ones rated for many thousands of hours would require a separate trailer.

 

[Spaceman Spiff]

Put the two together, probably 1800-2400 kW would be enough, but best to be sure before you buy.

 . . .maybe a battery monitor?
 
 . . .The Sam's Club GC2 is just such great value AH per $.

John61CT: I think you mean 1800-2400 Watts.  I have 24 kW coming into my house.

IMO a good battery monitor (like a Trimetric that shows amps in and out) is a good investment.  You will learn a lot by watching it.

+2 (3,4?) on GC2s.

If you are going to run a generator a lot investing in a good one is cost effective (Honda, Yamaha).  They will last longer.

Unattended generators have a tendency to disappear, so having them well secured is a must.  Also the quieter the generator the less problems you will have with neighbors.

 -- Spiff

 

[highdesertranger]

what I meant to say is, for sure do the alternator charging but don't rely on it as your only charging source. highdesertranger

 

[DannyB1954]

A 70 amp charger requires around 1,250 watts. https://www.progressivedyn.com/pdfs/109821F english.pdf
I tried to run a 40 amp charger off of a 800 watt generator. Unfortunately the charger needed 725 watts at full charge and the generator was rated at 700 continuous. The inverter style generator sensed the high output and would shut down to prevent overload. Generators are often advertised at their peak wattage, but this is usually only for a few seconds.

I deduced that a 1,000 watt Generator, (800 watts continuous) would run it. I didn't want to make the gamble so I bought another 1,200 watt generator. I now wonder if that generator could supply a 60 amp charger. Progressive Dynamics list that as 1,000 watt input max. The 1,200 watt generator is rated for 1,000 watts continuous, so it might be borderline.

My best guess for a 70 amp charger is you would need a 1,500 watt peak generator. If you went with a 1800 watt continuous generator, like the Ryobe which is rated at 2200 peak 1800 continuous), you should be able to run a small ac unit from it as well, 120 volts x 15 amps is 1800 watts.

 

[John61CT]

A charger that allows you to derate the output amps would give good flexibility.

 

[Eldritch Penumbra]

The idea is as such: I will be parking in the Ford parking lot (as close to shade as possible) while I work. My cat and dog will be in the van, so I will be running a quiet Yamaha generator to power the AC during these hours. I have read that the generator will only power the AC for 5 hours, but considering that I work in the evening, the AC will not be needed during the last couple of hours of the work shift anyhow.

I would like to install Solar for my laptop and gaming needs as I don't want to be running the generator when I am in the van my self as the noise will be annoying. At most I'll want to run a fan in addition during this time, but that is all as it tends to keep relatively cool at night, at least enough to not need to run the AC, and if it should get that muggy, then I'll just drive around with the van's AC cranked on until I've filled up the van with cool air.
This aside I might ad a tiny fridge to the equation later on, but again, it won't be used every day of the week or every week for that matter.

I'm going to have to wrap my mind around a lot of what you guys are telling me as some of it is French to me atm, but I believe you have set me on the right track. As for the alternator, I still believe I am going to leave it be for now as I don't want to risk wearing out the one I have until I have.

 

[SternWake]

Some chargers are power factor corrected. Which basically means more efficient. 

 My Meanwell power supply claims efficiency upto 93%, while no PFC charging sources can be as low as 65%.

So in theory a PFC charger can generate higher amps from less AC input.

Powermax converters, in their higher Amp versions claim to be PFC
A 100 amp powermax can be run on a normal 15 amp outlet, but a 80 amp PD9280 or Iota DLS-80 requires a 20 amp plug.  Powrmax makes adjustable voltage versions which are good for those seeking maximum charging contribution whenever the generator is running. 3 or 4 stage chargers might revert to a lower electrical pressure sooner and one wastes fuel charging slower on a generator

Any and all charging sources.  Use em, get the batteries to as high as possible a state of charge whenver possible is the best one can realistically do, with lead acid.  Make due, adapt and improve when one can.  Systems evolve, and so do the consumption numbers.  Many who come here are wanting excellent systems and to skip the evolution, and this is the wisest approach, but not always realistic to accomplish as there is a learnig curve and many unknowns until one is actually living on battery power

If one can never ever get to 100% then one should not expect even poor to fair longevity from lead acid batteries.

From about march through about october, if it is sunny, I basically know my battery is getting fully charged with few exceptions, and those exceptions are not going to put the battery into the grave instantly.   Winter time I need to either cut back on usage or employ more alternator or grid powered charging sources.