Lithium on the Cheap

[wincrasher]

What do you all think about these two items? To retrofit an existing van could be done for around $2000.

First you'd get a replacement converter like this:

https://bestconverter.3dcartstores.c...100Lmanual.pdf
Not alot of amperage, but would fit the existing electrical loads in most vans. But simply changing out an old converter for the new one.

And then maybe a smallish LiFePO4 pack like this:
http://www.amsolar.com/home/amr/page...m_battery.html. Comes with their own BMS.

You'd re-use all your existing wiring. It's a fairly dumb system. You could always add some better monitoring down the road.

[eric1514]

Looks doable but what are the advantages over what you have now with your 2 group 31 AGM batteries?

[wincrasher]

You'd have more useable capacity (~50% more) and save about 80lbs of weight.

What I don't fully understand is if you replace your converter with one that puts out 14.6 volts, does that mean all your coach lights and DC systems are going to get hit with that kind of voltage? Will it fry them? You'd think, if you are charging with your alternator when running, you see the same thing, but you don't. The meter I put in the cab cigarette outlet sees 14.4 when the engine is running.

[markopolo]

You'd have to build an enclosure or put them inside the RV. No apparent heater.

If you use existing wire then performance would be limited to what you'd get from AGM's. You'd probably blow a lot of 50 amp fuses (assuming 6 gauge on the the alternator run) when charging via alternator with the lithium battery at 20% SOC (just a guess).

[wincrasher]

Yeah, you'd need to heat them if you were going to use in the winter. If you had no plans to do that, then you wouldn't. A tank heating pad may do the job though.

Why would the alternator charging be an issue? It's going to put out the same amperage as it does now wouldn't it? Wouldn't the wiring be sized for max output on the alternator anyways?

[markopolo]

I doubt that it's wired for max alternator output. It would probably have been spec'd for the 1 house AGM.

Note: I'm guessing here - I have no experience with lithium batteries in RV's and I don't know what gauge wire is in your rig.

My understanding is that lithium batterys can handle a lot of amps - charging or discharging. The battery might take 100 amps if low. 6 gauge would be rated and fused for probably 50 amps.

You should be able to see the gauge # on the wire from the isolator to the house batteries.

Isolator might have to be upgraded as well.

Maybe there's some sort of current limiting device you could use and keep the existing wiring if it's undersized.

[markopolo]

Originally Posted by wincrasher

Why would the alternator charging be an issue? It's going to put out the same amperage as it does now wouldn't it?

I should add that I'd expect the alternator to try to output maximum amps for a sustained period of time with lithium batteries if they are very low.

Lead acid batteries won't accept as much amps as lithium when charging and the amps taper off as they get more charged.

Great topic - lots of us are probably wonder how to switch to lithium even if just in theory.

[wincrasher]

Well that's the thing. Does the alternator "push" amperage down the line up to it's limits, or does the battery "pull" what it wants. That's what I'm trying to understand.

Another reason to keep the size of the pack down. 200ah I think is big enough.

The converter, operating up to 45 amps, is not going to charge very quickly, but that is OK for the use I'm envisioning.

[booster]

The alternator, in reality, does not create amps, as odd as that sounds. It creates voltage to a (mostly) fixed level.

The rest of the system wiring, batteries, motors, etc create a resistance to the flow of current.

The amps then show up based on the other two items, up to the capacity of the alternator.

The formula is volts = amps X resistance

So the alternator will only put out the amps that its voltage can push through the system resistance. It could be max of the alternator, or it could be very close to zero.

[markopolo]

It's the "pull" aka the current flow along the wire that I'd be concerned about.

If you have fully charged or 90% charged lead acid batteries and you use an ammeter to measure current (amps) you'll see it's low - just a few amps on the wire. If the battery is low it'll pull a lot more amps up to what it can accept limited by the output source.

Or use an inverter as an example. No load - no amps flowing on the wire. Start a microwave oven and you'll see 80 or more amps flowing.

(typing while Booster posted)

[wincrasher]

Well, I'll check tomorrow on the size of the wiring I'm dealing with. Should it all be the same size? Look at the disconnect switch, or at the batteries? At the alternator?

[markopolo]

Check everything you can get to.
Definitely check the wire from the alternator to the isolator and from the isolator to the house batteries.

The gauge size might be printed the wire's insulation or a Winnebago code might be used. If codes are used you should be able to find a chart on Winnebago's site.

Look at any breakers or fuses also.

[Jostalli]

Originally Posted by wincrasher

What do you all think about these two items? To retrofit an existing van could be done for around $2000.

First you'd get a replacement converter like this:

https://bestconverter.3dcartstores.c...100Lmanual.pdf
Not alot of amperage, but would fit the existing electrical loads in most vans. But simply changing out an old converter for the new one.

And then maybe a smallish LiFePO4 pack like this:
http://www.amsolar.com/home/amr/page...m_battery.html. Comes with their own BMS.

You'd re-use all your existing wiring. It's a fairly dumb system. You could always add some better monitoring down the road.

No reason to pay AM Solar the big bucks when they are using basic off the shelf parts. Buy your own LiFePO4 cells and buy the HousePower BMS and a high current contactor and you have what they are offering.

I've posted the best resource for DIY LiFePO4 batteries so read the info in that link and learn.

The charger you posted has too high of voltage for me but you could program your BMS high voltage cutoff to alert you when to cut charge.

Now you need to look at your other charging sources: alternator and solar.

You should ensure proper wire size from your alternator since these batteries have a lower internal resistance and will take all the charge current your alternator can produce.

Is your solar charge controller programmable for this new battery? You don't want to use any of the charge profiles that come standard.

Other than those things I don't see any issues.

[wincrasher]

What should I do with my portable solar panel? It only has 3 battery types on it's simple built in controller and really no other way to control the voltage.

[gerrym51]

Originally Posted by wincrasher

Yeah, you'd need to heat them if you were going to use in the winter. If you had no plans to do that, then you wouldn't. A tank heating pad may do the job though.

Why would the alternator charging be an issue? It's going to put out the same amperage as it does now wouldn't it? Wouldn't the wiring be sized for max output on the alternator anyways?

lithium batteries would keep an alternator going at max longer and might cause it to burn out.

[wincrasher]

Doesn't that depending on the size of the bank, Gerry?

The bigger the bank, the more time the alternator will be active.

The more I think about this, the more I think it would be wiser to just use a single 100 AH Smart Battery. The useable capacity is actually greater than my 2 Group 31 AGMs. Trying to significantly increase battery capacity may just be a fool's errand and alot of $$ wasted.

So what I'd get out of going with that is weight savings, quick recharge time and it would fit in my existing steel frame.

The Smart Battery has a 5 year warranty.

[eric1514]

Originally Posted by wincrasher

The more I think about this, the more I think it would be wiser to just use a single 100 AH Smart Battery. The useable capacity is actually greater than my 2 Group 31 AGMs. Trying to significantly increase battery capacity may just be a fool's errand and alot of $$ wasted.

So what I'd get out of going with that is weight savings, quick recharge time and it would fit in my existing steel frame.

The Smart Battery has a 5 year warranty.

Are these really a drop in replacement? Can you use your PD converter? Would you still need to keep these batteries warm in the winter? Total newb, here.

[wincrasher]

They claim it's a drop in. It uses the cylindrical cells and has BMS and a hard plastic casing. Dimensionally, it's a tiny bit smaller than an AGM Group 31.

It says you need 14.4 to 14.6 volts. So changing out your converter is necessary. Looks to be a simple project if you use the PD version of a lithium charger. They don't give alot of info - it says nominal voltage of 14.6. In their manual they describe that it tapers off current as the battery gets full. Whatever that means.

On the Smart Battery site, they don't address temps other than giving a charge showing battery output as the temperature drops. I see no thermal protection features built into the battery, other than it is a hard plastic case with some airspace around the cells.

Considering they offer this 5 year warranty, it may be worth the risk to just get one, use it and see what happens. I don't really adventure in the winter months, other than getting in the van and heading to Florida.

[markopolo]

You could run your AGM's down to 20% SOC like lithium batteries. The AGM's won't last long using them that way - maybe a year or two.

That would give you time to see how this all evolves. I think we all expect prices for these batteries to drop and the tech behind it all to improve.

It's sounds boring I know. The hardest thing sometimes is to do nothing with these types of decisions.

You've been having a ton of fun with your B vans. A battery is not going to change that.

If someone is in the market for a new van or new DIY build I can see going with lithium. And Gerry's rig could benefit from more battery also and his only choice appears to be lithium from Roadtrek. If he could figure out how to add a second TPPL battery to his Zion he'd probably save $5000 though and have great performance.

I don't see the value in ripping things out to get the same or less battery capacity than you already have.

[avanti]

+1 Marko. This whole "you can only drain your lead acid battery to 50%" needs to be kept in perspective. The energy is there, and there is no law against using it. The statement applies ONLY to maximizing the lifetime of your battery. (In Wincrasher's case, that might not even be a goal ). I for one would not spend a night in the cold just because running the heat a little more might shorten the lifetime of my old-technology batteries a bit. Indeed, if you do the math, it isn't clear that the relative cost/amp-hour is particularly bad even if you have to replace the batteries half-way through your system's lifetime.

I'm excited about Lithium because I'm that kind of guy. But my current plan is to add a couple of more AGMs, run them out without being paranoid about SOC, and then evaluate.