Electrical system design questions

[Anhedonic]

Over the next two weeks, before my maiden voyage, I will be constructing my electrical system and there are some questions I haven't been able to resolve through web searches and talking to people. I'm hoping you folks can provide a little insight. 

I'm going to get some of the Renogy AGM deep cycle batteries. Yes, I know wet cells will give me more bang for the buck, but my situation does not allow for them. At all. 

I've already got a 2000/4000w inverter. 

I'm going to connect a fused line to the batteries from the starter battery to the deep cycle batteries. What I don't know is if this is enough or if I need some kind of charger in between the two batteries. 

I also want to be able to charge the batteries from a generator, from shore power, and eventually from solar but I'm not sure how to integrate this. What happens for example if I have DC coming from a generator as well as DC from the starter battery/alternator? What about if I have the engine running and also have shore power hooked up? What happens when you have two or more power sources active? 

From the deep cycle batteries, there will be a line to a breaker box. 

From the breaker box, there will be lines to the inverter and to the Maxxair fan and lights and some spots left open for water pumps, a fridge and other such things. 

The inverter will power a CPAP, charge a power wheelchair, and even run the AC so the lines need to be pretty robust. I was thinking I might skip the breaker box and run a direct fused line from the batteries to the inverter instead of going through the breaker box. 

I also need to leave whatever opening I need to add solar at a later date, though I have little idea of what making accommodations future solar looks like. 

Before you ask, I know that the AC will eat the battery power pretty quickly. My current plan is to have an auto-starter on the van that will track the battery charge and, when the charge hits 50%, will turn on the van and start charging the batteries and running things off the alternator. I'd be interested to know if anyone has tried to get or create such a system. I may also be looking at a bigger or second alternator, but that's for later. 

I'm sure there are more questions I haven't put in here yet. Honestly, this is the scariest part of the build for me because it is both the most complex and the part that I know the least about. 

Thank you all for any help. I know I'm new and all my recent posts have been "help me" posts. I'm sorry for that and hope once I have more experience I shall be able to contribute in turn.

 

[highdesertranger]

first off that's a lot of questions. do you realize that if you take your battery bank down to 50% then try to charge it with the alternator it will take around 7 hours of driving at highway speed to fully recharge your bank and that is without running the AC. if you just let it idle it will take days to recharge. if you plan on a idling vehicle to run an AC you are going to be replace alternators quit often. not to mention the wear on the engine will be horrendous.

also you need some type of switch/solenoid between the vehicle battery and the house battery.

I say start breaking your questions down and ask one or two at a time.

highdesertranger

 

[Weight]

You have made up your mind for the batteries, so I will let others debate that. There a few ways to charge the house bank from the alternator. (one) Just a simple switch, on off, you have to remember to turn the switch. Or you risk having a dead starter battery. (two) A continuous duty relay. With a small switch to trigger it on. You have to remember to turn this switch. But we can automate, this relay can be triggered using a circuit that is only live when the ignition is on. You only have to remember to turn the ignition off. (three) There are some automatic devices that connect the batteries together whenever there is a charging voltage, either direction. Everyone has an opinion about which way is best. Everyone must agree that fuses are required at each battery positive post! Run away from anyone that tells you different.
Don't think about air conditioner using battery power. It can be done, but at great cost and much knowledge. At best you will have a microwave and a gas stove.

 

[Trebor English]

With a Prius you get a lot of that included in the car design.  The big lithium batteries that drive the car can run the air conditioner and the engine starts to recharge.  You could buy a car trailer and a Prius just for the battery and generator.

Lead acid means you have slow charging with partial state of charge issues.  You really don't want lead acid for running an air conditioner from the battery with a generator automatically starting to recharge every few hours.  Two or three hours at a time will not fully charge a lead acid battery.

You need to use an engine and generator that match.  100 amps at 14 volts, 1400 watts, is about 2 horsepower.  To get 2 horsepower electric will take 3 or 4 shaft turning horsepower.  A 200 horsepower van engine is not a good match.  There are many generators like Honda eu3000 that are electric start when you get up to the 3000 watt size.  

120 volt 60 Hz from a generator or shore power needs a battery charger to connect to a battery.  The max size charger depends on your battery size and generator size.  Multiple charge sources generally play well together at the beginning.  When the battery gets to the absorb voltage programmed into your charge sources they start to drop out.  For example, I have a converter / power supply that causes the solar controller to quit when it sees pulses even though the average voltage is lower than the solar charge controller setting.  

For the air conditioner and wheel chair charger you probably want a generator or campground shore power plug in.  For just the CPAP the battery makes sense unless you also need the air conditioner over night.  In that case, forget batteries and inverters.  The Harbor Freight 3500 inverter generator is reasonably quiet, efficient on fuel and only $700.  That is probably doable in two weeks.

 

[Anhedonic]

first off that's a lot of questions.  do you realize that if you take your battery bank down to 50% then try to charge it with the alternator it will take around 7 hours of driving at highway speed to fully recharge your bank and that is without running the AC.  if you just let it idle it will take days to recharge.  if you plan on a idling vehicle to run an AC you are going to be replace alternators quit often.  not to mention the wear on the engine will be horrendous.

also you need some type of switch/solenoid between the vehicle battery and the house battery.

I say start breaking your questions down and ask one or two at a time.

Yeah, I know it's a lot of questions. Honestly, my head is a whirl with them at the moment because of my time frame. 

The two big questions are about multiple power inputs to the deep cycle battery and charging from the starter battery.

With multiple potential power inputs, what happens if the battery has two incoming streams of current? 

As to the connection between the starter battery and the deep cycle battery, I'm planning to put a constant duty solenoid in there. The question was more about charging. Essentially, do I need some sort of hardware device to be an intermediary in the charging process or is it sufficient for these sorts of batteries to charge them with a direct connection. 

I'm hoping to have between 400 and 800ah of battery capacity eventually. I know it will take time to charge up once the engine turns on. What I mostly need is to be able to get through a night. I have a generator that I was going to incorporate, but that has its own host of problems. I'm OK with extra wear on the alternator and the engine, at least to a certain degree. 

I'm just trying to make this work in a way that will allow me to travel given my health limitations. I've got to be able to charge the chair and it's got 50ah 24v batteries in it. I've got to be able to run the AC in the heat and humidity. I've got to be able to run the CPAP. These are non-negotiable requirements and there are many situations where unloading and running a generator is either impractical, unsafe, or just plain impossible. This is the only system I can think of that will make this work in my van without one.  Don't think it hasn't been frustrating trying to come up with a good solution.

 

[Anhedonic]

With a Prius you get a lot of that included in the car design. The big lithium batteries that drive the car can run the air conditioner and the engine starts to recharge. You could buy a car trailer and a Prius just for the battery and generator.

First, thank you for this response. You've given me a lot of information that I really needed to hear. 

A Prius and trailer a good suggestion. I even looked at that fiberglass Prius mod that turns one into a camper. If I didn't have to tote around a 300 lb. power wheelchair, I would seriously think such a setup. As it stands, I've got the van and have already gotten parts of the build done.  

Lead acid means you have slow charging with partial state of charge issues.  You really don't want lead acid for running an air conditioner from the battery with a generator automatically starting to recharge every few hours.  Two or three hours at a time will not fully charge a lead acid battery.

This does sound significant. So basically, if the engine turned itself on when the battery hits 50% it would end up staying on all night because of how slow the batteries charge? Is that what you're getting at here? I honestly don't have a deep knowledge of the behavior of this type of battery; I'm much more familiar with lithium ion batteries from my years in tech. 

You need to use an engine and generator that match.  100 amps at 14 volts, 1400 watts, is about 2 horsepower. To get 2 horsepower electric will take 3 or 4 shaft turning horsepower.  A 200 horsepower van engine is not a good match. There are many generators like Honda eu3000 that are electric start when you get up to the 3000 watt size.  

I've currently got a Westinghouse iGen4500 which has both an electric start and a remote. I was going to integrate it into the van and had a pretty good plan for doing it, but this seemed on the surface to be better, safer, and more space (if not fuel) efficient. I'm not certain I understand what you're saying here except that pulling power from a vehicle engine is terribly inefficient. Is that the message? 

120 volt 60 Hz from a generator or shore power needs a battery charger to connect to a battery.  The max size charger depends on your battery size and generator size.  Multiple charge sources generally play well together at the beginning.  When the battery gets      to the absorb voltage programmed into your charge sources they start to drop out. For example, I have a converter / power supply that causes the solar controller to quit when it sees pulses even though the average voltage is lower than the solar charge controller setting.  

So I will need a charger for external sources? I mean of course I'd need a converter to get from AC to DC power and the proper voltage, but for managing the rate of charging as well? Should all input sources including the starter battery go through such a device? What is the practical limit to how fast I can charge a battery with one of those? Also, will I be able to pull enough power *through* such a device to run things or should I bypass it when running the line from the starter battery to the deep cycle? 

For the air conditioner and wheel chair charger you probably want a generator or campground shore power plug in.  For just the CPAP the battery makes sense unless you also need the air conditioner over night. In that case, forget batteries and inverters. The Harbor Freight 3500 inverter generator is reasonably quiet, efficient on fuel and only $700.  That is probably doable in two weeks.

Unfortunately, I do need the AC overnight. Also, the batteries in my power wheelchair are of a fairly considerable size. Also unfortunately, there are many places I will be where pulling out and running a generator won't be practical. I'm trying to come up with a solution that is at least viable, given that there isn't a solution I've found that is optimal.

 

[Anhedonic]

I did look at Nissan leaf and Tesla batteries but they were both too expensive and had charging and cooling challenges that are well beyond my abilities.

 

[highdesertranger]

multiple charge sources are fine. the regulators take care of the charge current.

many of us have no AC we just move with the temps, it much less complicated and a lot cheaper then trying to run AC off of batteries.

what type of vehicle are we talking? idling most vehicles to charge batteries or run stuff is a losing proposition. you are much better off just to drive where it's cooler. highdesertranger

 

[Anhedonic]

I'm not going to be full timing and where I will need to be will often be without regard to weather.

The van is a 2015 Ram Promaster 2500 136wb

My original, original plan when I started thinking about this a while ago was to just try to do without AC using fans and good ventilation. On a trip in a borrowed van, I found out just how bad an idea it was for me. The trip was very educational with regard to my limitations, I must say. It made me have to entirely re-evaluate the whole plan. It also made the whole thing a lot harder to do, especially on my budget.

 

[Anhedonic]

Could you explain what a regulator is in this context? Is it something I need to add?

 

[John61CT]

Many hours of aircon off batteries?

Possible but need LFP, but just that bit will need to cost almost as much as the van.

Look at Frigomar, Italian marine vendor, their inverter-based 16000 btu apparently pulls under 10A (1200W continuous) and has a great slow start built in so it runs off a Honda 2000.

Apparently nice and quiet. Maybe $4K delivered?

So 120AH LFP bank capacity at 12V is required for each hour you want to delay running the genny, at at least a grand each if doing DIY, say double if buying a Lithionics or Victron turnkey system.

So between $8-20 grand for overnight.

 

[John61CT]

As for TL;DR

all those other questions, break them down to 1-2 per post.

What makes you think Renogy is a good source for AGM anyway?

Not that any lead bank will be suitable for this use case anyway.

Really, for that much aircon, cheaper to stay in S&B housing.

 

[John61CT]

I'm not going to be full timing and where I will need to be will often be without regard to weather.

The van is a 2015 Ram Promaster 2500 136wb

My original, original plan when I started thinking about this a while ago was to just try to do without AC using fans and good ventilation. On a trip in a borrowed van, I found out just how bad an idea it was for me. The trip was very educational with regard to my limitations, I must say. It made me have to entirely re-evaluate the whole plan. It also made the whole thing a lot harder to do, especially on my budget.

If your funds are limited, I'm afraid so are your options.

Needing something doesn't make it possible I'm afraid.

Great you started asking before sinking a lot into it.

 

[Anhedonic]

So it sounds like you are saying that my design is not a good one. I don't doubt that. I know it is not optimal or even necessarily workable. The question is this: how bad is it? If I went ahead with it, what do you predict would be the result? Is it The-Van-Will-Explode-And-You-Will-Die bad? or is it "You'll-Ruin-Your-Batteries-And-Have-To-Replace-Them-Every-Year bad? Or Your-Van-Will-Be-Toast-In-6-Months bad?

Will it work?

I would love to have enough money for lithium batteries, but as you have observed, that's a little out of my price range.

As to why Renogy, they appear to be a trusted brand with good customer service, a history of standing by warranties, and ready availability via Home Depot or Amazon at a (relatively) reasonable price for an AGM deep cycle battery. There are so many options and so many conflicting opinions on the topic, I finally fell back from "I want to get the best ones" to "I want to get some serviceable ones that will do the job."

 

[John61CT]

So it sounds like you are saying that my design is not a good one. I don't doubt that. I know it is not optimal or even necessarily good. The question is this: how bad is it? If I went ahead with it, what do you predict would be the result? Is it The-Van-Will-Explode-And-You-Will-Die bad? or is it "You'll-Ruin-Your-Batteries-And-Have-To-Replace-Them-Every-Year bad? Or Your-Van-Will-Be-Toast-In-6-Months bad?

Will it work?

Define "work".

If you include the ability to run aircon for many hours without running your genny,

I outlined what is required to make that practical?

Does "your design" now include those elements?

Can to afford that sort of outlay?

Or are you modifying "your design"?

Go ahead and get a lead bank from whatever vendor, sized for overnight aircon will weigh lietally a ton, it will need replacing quickly since you can't get back to 100% Full and you'll be wearing out the genny and spending all your money on fuel trying.

In order to design, you need to learn enough to know what is realistic.

The brand of battery is like what color cardboard base to use when learning how to bake a cake.

I suggest you ask one Q at a time, and then ask more followup Qs until you really understand the fundamental reasons behind the answers you get.

Then as your design starts to take shape, you will be in a position to change your approach, or even modify your goals from a more solid foundation.

And one factor you need to realistically establish is, how many thousands do you have, and willing to invest in electrickery.

Maybe paying for powered campgrounds will actually be cheaper, if you find you still don't like the lifestyle even with aircon.

 

[Anhedonic]

I'm not looking for the best. I'm looking for adequate to get me through. I'm looking to know if running the van's engine for part or most of the night, leaning on the batteries some of the time will get me through the night.

 

[highdesertranger]

one more time, idling a gasoline vehicle engine overnight is going to seriously shorten your engine life. gasoline vehicle engines are not designed to idle for long periods of time. I hate to keep harping on this but relying on your vehicle engine to power an AC is a very bad option.

your alternator, solar charge controller, and better battery chargers all have built in regulators to regulate the charging current.

highdesertranger

 

[John61CT]

I'm not looking for the best. I'm looking for adequate to get me through. I'm looking to know if running the van's engine for part or most of the night, leaning on the batteries some of the time will get me through the night.

Very expensive in fuel bad for your engine - means super expensive long term - a genny will be much cheaper, and

very dangerous, CO can be fatal.

Spending more up front for lower running costs is a smart investment.

Also just following the 60's is cheap if possible.

 

[John61CT]

An hour idling is like 25-40 miles travel wear and tear.

 

[Trebor English]

Lead acid batteries are different from other chemisty batteries.  

One plate is lead oxide, other is lead.  Sulfuric acid is the electrolyte.  When they discharge both plates take up sulfur converting the sulfuric acid to water.  On both plates the sulfur forms lead sulfate.  The thickness of the lead sulfate increases as the discharge continues.  At 10.5 volts the battery is dead.  The electrolyte becomes less conductive and the amount of lead remaining vanishes.  

Recharging is not like putting gasoline in a tank.  With gasoline you can pump in 5 gallons per minute or 8 or 10 and it makes no difference to the tank.  With a lead acid battery ions move from one place to another.  The rate at which lead can be redeposited on a plate matters in a way that has no gas tank analogy.  A gas tank has no wear associated with refilling.  The gas goes to the bottom of the tank.  Lead ions don't go back to where the manufacturer originally put them.

The beginning charge, up to 75% to 80%, can go quickly.  Quickly for lead acid is 20% of C, the capacity.  A 220 amp hour battery, C=220, can charge at 22 amps for a 10% of C rate, or 44 amps for a 20% of C rate.  On discharge the Peukert effect causes less energy at a higher discharge rate.  When charging the charge efficiency varies similarly.  A higher rate of charging makes more heat that doesn't move sulfur back to the acid as effectively.  

After the beginning of a charge cycle the applied voltage required to maintain a 10% of C charge rate goes up.  The battery voltage should be limited to the range of 14.4 to 14.8 volts.  The battery manufacturer specifies the absorb or absorption voltage.  Sometimes other words are used.  When this voltage is maintained the charge current drops off.  This current will drop to 1/2% to 1% of C when the electrolyte specific gravity gets up to 1.275  and all of the sulfur is removed from the plates, the lead put back, and the acid back to full strength.  This will take 2 or 3 hours.  If the beginning charge rate is low it gets closer to finished before the voltage gets too high.  If your 220 amp hour battery is discharged 110 amp hours (the often recommended 50% limit) then you would think that 2.5 hours at 44 amps would put that back.  With the higher 20% of C charge rate you get to the 14.8 volt limit quicker making the slow tail longer.  If you charged at 22 amps it would take longer to get to 14.8 volts but the finishing the last part would take less time.  Total time would be longer, total energy would be lower.  It will take much more than 2.5 hours to complete the charge.  5 hours should be expected.  

The main problem with lead acid batteries is the need to avoid partial state of charge cycling.  If you recharge the battery to 80% then start discharging it again that 80% will become the new capacity after a few such cycles.  As the charging happens the outer layer of lead sulfate gets converted to lead.  The unconverted lead sulfate is buried under a layer of converted lead.  The voltage necessary to reach deeper into the plate goes up.  The last 20% of charge goes slower.  If you cycle the battery after a partial charge you have a PSOC, partial state of charge cycle.  The buried lead sulfate gets harder over time and that portion of the capacity is gone.  When the battery no longer has enough capacity to meet your need then the battery is "sulfated" and gets recycled.  Some recommend recycling the battery when the capacity is 80% of new.  There is no accurate, quick and easy battery capacity meter so determining that it is 80% of new could cost as much as new batteties.  

Bottom line:  you don't want lead acid.  To run the air conditioner the way a Prius does with the key in ready mode and the engine starting and stopping every hour or two requires a different battery chemistry.  

Lead acid is good for a slow overnight discharge to run some LED lights and a fan.  A low power low energy small efficient refrigerator works well too.  Then the next day the sun shines for 5 hours fully recharging the battery getting all that lead sulfate back to sulfuric acid and lead.  Lead acid is also great for a very short high rate discharge to start an engine followed immediately by a full recharge.  200 amps for 3 seconds (600 amp seconds, 10 amp minutes 0.166 amp hours) is only a .16% depth of discharge for a 100 amp hour starter battery.  Deep cycle batteries for one, starter batteries for the other.

The gasoline powered generator mounted in a box connected to a hitch receiver can do the generating to power the air conditioner and recharge the electric wheel chair.  A tiny fridge and a CPAP can be powered too.  If your generator is close to what your air conditioner needs it won't be horribly inefficient.  You might get as low as 1 gallon of gas per day.  Under two is quite likely.  If you get a kilobuck of batteries you still need to run the generator to charge them, actually 20% more.

I have seen a you tube video of an exhaust pipe that goes up to the van rooftop.  CO has a density very similar to air, hot exhaust CO will be lighter.  Since you have the generator getting it mounted may be within your 2 week limit.  A battery powered air conditioner is unlikely in 2 weels, unlikely ever using just two lead acid batteries, any brand.