Lithium and AGM combo system like Hymer

[hbn7hj]

OK, Booster, you bench check it and I'll field test it. Let me know if a Lithium charges a lead acid and I'll buy a 25ah or 50ah lithium Iron with BMS and a coulomb counter, probably another Trimetric, and see how it works.

I'm on the road from the middle of March till October and have given up on shore power costs (I can pay 'em but refuse) so should be able to make some smoke if possible. If it works I'll add it to the Roadtrek.

Harry 2006 Lazy Daze with two 6 volt Trojan flooded lead acid batteries.

[Bud]

"OK, Booster, you bench check it and I'll field test it. Let me know if a Lithium charges a lead acid and I'll buy a 25ah or 50ah lithium Iron with BMS and a coulomb counter, probably another Trimetric, and see how it works."

Well booster, please keep on boosting.

But there seem to be limited advantages other that curiosity and Fun.

Bud




Keep b

[booster]

Originally Posted by Bud

"OK, Booster, you bench check it and I'll field test it. Let me know if a Lithium charges a lead acid and I'll buy a 25ah or 50ah lithium Iron with BMS and a coulomb counter, probably another Trimetric, and see how it works."

Well booster, please keep on boosting.

But there seem to be limited advantages other that curiosity and Fun.

Bud
Keep b

I certainly agree that for a lot of people the benefits would be quite small. If you have shore power regularly or drive long days (8 hours) regularly, you will be getting your AGMs or wet cells full often enough. If it worked, it could be a big deal to those that off grid essentially all the time and don't have a way to charge for the long periods needed to take lead acid batteries to full, as in the examples like those that do short charges with the generator or alternator. Because the lithium battery is small compared to the main battery bank, the cost would get much more reasonable than a complete lithium bank and wouldn't require heaters. If the setup saved the AGMs from earlier failure once it would probably pay for itself, plus those with smaller AGM banks would gain some surge capacity for running high load stuff. It would also keep the ability to function and charge in below freezing conditions.

All that said, even if it works fine, it would very unlikely we would put it in our van, as the combination of our charging systems and the fact that we nearly always wind up in a shore power campground every week or ten days (easy to do laundry that way for us), we don't have the issue of short charging, at least not yet.

I think I would see a kind of sweet spot for those the have, the now fairly standard, two AGMs in the 200ah range, but stay offgrid a lot. They would gain the 20% capacity in the AGMs on nearly every charge cycle, so more capacity and also increase the lifespan of the batteries, and also be able to have get that with the same amount of generator or alternator charging as before. Boats also chronically short charge as they can't run their engines long enough to get full, so they might also benefit.

Of course, this is all predicated on the assumption that it works at all, which in my mind is still totally up for grabs.

[hbn7hj]

It should work. 14.4 volts should charge 12.9 volts. What happens if, at the same time, you are using some power remains to be seen. Maybe there would be no charging.
Harry

[booster]

Originally Posted by hbn7hj

It should work. 14.4 volts should charge 12.9 volts. What happens if, at the same time, you are using some power remains to be seen. Maybe there would be no charging.
Harry

Yep, it will likely depend on how well the lithium holds voltage.

[Mfturner]

Firstly, I feel compelled to say: y'all be careful out there.

My years of EE work has no battery chemistry so what follows are speculations, moderate temperatures are assumed:

1. If I were to take a fully charged LA battery and short its terminals to a fully charged LFP battery on my driveway, I would expect the LFP to slowly dischare through the LA, probably current limited by the series resistance or acceptance of the LA. My guess is this leakage would need a disconnect to be acceptable, and a BMS might help keep you from totally depleting the LFP. Hopefully this would not get dangerously hot, but who knows.

2. If a load were presented to the paralled batteries while the LFP still had some juice, my money is on the LFP providing most (90%?) of the current until 5-10% SOC (or BMS cutoff) when the LA helps or takes over. You might wind up with a mostly discharged LFP and a partially discharged LA. I think this is what you want to take advantage of the LPF for most of your discharges.

3. If a partially discharged LA battery is connected directly to a full LFP, I agree that the LFP would charge the LA, I buy that. However, I bet that once charged you would need to disconnect them or the slow discharge would eat up what was left in the LFP. I think this is also what some of you want to try, but I don't think it will model the general way paralled batteries will work since I think the LFP would be drained by loads first.

4. I agree that the easiest way to recharge is with independent charging systems while the batteries are disconnected. It may be possible to charge them in parallel, where the bulk charging phase charges both batteries and the absorption only really charges the LA. My no-power solar controller might actually work in this application. But I still bet that without the charger or a disconnect, the LA slowly eats the LFP. I wonder if the disconnect could be a blocking diode, but a diode's Vt would mean the LA wouldn't help until the LFP was very low SOC, maybe less than 5%. Complicating things significantly might be a pmos switch for the disconnect controlled with a microcontroller watching both battery systems to control things, I bet Roadtrek/Hymer is doing something like this, out of reach of most diy'ers.

[cruising7388]

Originally Posted by Mfturner

4. I agree that the easiest way to recharge is with independent charging systems while the batteries are disconnected. It may be possible to charge them in parallel, where the bulk charging phase charges both batteries and the absorption only really charges the LA.

From what I understand, this arrangement is already operational in the Galleria Li3. The engine and coach batteries normally utilize separate charging sources but if coach alternator regulator executes a bulk charging command, the normally independent alternators are paralleled. When the regulator reverts to absorption charging, the paralleled alternators separate.

[booster]

I would say yes to essentially all you say, and some of it is why I think it might work out, note "might".

The discharging of the lithium first would actually be preferred, and I think that is also what Hymer may be doing, also. The AGM is just there for added capacity if the lithium runs out in that case as you would want the quick charging to full that the lithium would be capable of. On the Hymer with the lithium larger than the AGM, the AGM would get used very little or none for some people. Depending on how big the AGM bank is, with the lithium at 25% of it, there are likely times when the system would be able to run on the lithium only if charging is happening often enough. In that case the lithium would just sit. For longer off grid times where charging isn't allowed or not available, the AGM would get used, the rest of the time it would just sit full, or shut off if it would kill the lithium. It will be interesting to see how low the lithium will go in voltage to see if that will happen or not before it gets to the AGM resting voltage of about 12.8v. If the AGMs are truly full, they will use very low amps, Lifeline rates at .5%C, but ours will actually go to about 1/2 of that currently.

The other scenario is that the lithium is not used to run the van off of and is either turned off or allowed to go to low voltage shutoff by the BMS. This would be in the case where you charge both together at an absorption setting of 14.4v and stop the charging when the AGMs get to 80% full. At that point the lithium should be nearly at 100% which more like 14.7v, but on a very steep part of the charge curve so could be 98 or 99%. When the charging is removed, the lithium would hopefully top off the last 20% of capacity at the very slow tapering rate and at that point be empty or close to. You would then run on the AGMs until the next charge cycle, which would be quite short to get to the 80% on the AGMs and then the process repeats. In this case, the lithium is used only as a top off charger and could be allowed to go to low voltage cutoff or shutoff manually if needed.

My original thought was along the lines of the second example and primarily to be able to charge the AGMs to full, to extend life compared to continual short charging, and gain 20% usable capacity out of them, using a lithium as a topping charger but not necessary to run the van.

The stars definitely need to align to make it work out in a way that makes it worth while, but if it could done so it really got the AGMs full regularly their life would greatly (some say 2-4 times over continuously short charging) and pay for itself quickly as it would be a small lithium and not terribly expensive unless you had a huge battery bank of AGMs. A 440ah bank like we have would only need 110ah of lithium to do it.

I would put the potential for success pretty low at no more than 50% chance, but for under $70 to bench test it will be worth it to see how they actually react to each other and the charger. That may give some insight into the Hymer system so we get an idea how that will work for them as a bonus.

As the first post said, hairbrained, for sure, and so far out of the box the box is already in the recycling. Of course, that is the kind of stuff I like to try, just to see what happens!

[hbn7hj]

So far the consensus is, for the field test, we need to be able to switch either battery out of the system, need a coulomb counter for each battery, need a temperature readout for each battery, and a generator charging system that tops out at 14.4 volts. I've got all of that figured out.

My 200 watts of solar will be switched off with the Lithium battery in the system.

All we need is a "Let's try it" from the bench test.

[booster]

Originally Posted by hbn7hj

All we need is a "Let's try it" from the bench test.

As they seem to say in Washington a lot lately, "stay tuned"

Batteries are looking to be a week or so out.

[hbn7hj]

Need some help here picking a battery. Need one with a BMS 50-100ah. First looking at Smart Battery but not all reviews are good. Lithionics doesn't have something that small. I can work with two separate systems if the bench test says they don't work well together.

Anyone have other suggestions to look at? Right now the Smart 50 is the choice.
Harry
P.S. Battleborn 100 looks pretty good and has a BMS

[booster]

I am afraid I am no help on that one. Ebay has a lot of LiFePo4 batteries but who knows about the quality of them.

I have been spending some time overlaying the discharge curves for lithium batteries with the charge curves for AGM, and it does look like it will be very close to not having enough voltage to get all the way finish on the AGM charge, depending on what the voltages actually turn out with real batteries. There is quite a variance in the curves between sources.

There is a real possibility that if this is to work, you would need to use a small 12v to 12v charger from the lithium to the AGM to boost the voltage. There would be enough energy to complete the charge but not enough voltage without.

As I said, it is going to be very close if the curves are correct.

[hbn7hj]

I haven't found a 12 volt to 12 volt charger that will boost voltage. If you look into the one at Smart Battery it doesn't do it. I guess it is just there to limit current and drop voltage from the alternator.

A 16 volt computer 12 volt source power supply would do it!

As you can tell, I'm gonna do this and if I have to run them separatly I will. The Trimetric is on it's way as is the switch. All I need is the battery. My smart charger uses 14.4 volts. Having both lead acid and lithium is a great idea. Lithium inside to solve temp problems and lead acid outside using the space provided.

I'll give the battery thing a day or two to settle out. Right now I like the Battleborn 100.

[booster]

I just ordered a cheapo DC to DC converter on ebay for $20. 150 watts and settable output voltage so should be fine for the testing, it it is needed.

It is fixed voltage which should not be an issue for this setup as I can set it to 14.4 volts or even a bit higher to get faster finishing of the AGM.

Need to look how it would wire in with common charging but separate or common discharges, though. Hopefully, won't be needed, but certainly could be.

[GeorgeRa]

How about this one, https://www.amazon.com/gp/product/B0...1J7877QL&psc=1

or https://www.amazon.com/KISAE-Technol.../dp/B01K44TJYE

or https://www.powerstream.com/DCC.htm

[hbn7hj]

I like the Power Stream one. And we could play with the cheap one.

Now that you got me going there are a lot available and various power levels. 10 amp oughta do it. A bit of switching to do. Probably wouldn't want to run the coach off the lead acid battery while finishing up the charge cycle
Thanks.

[booster]

The first one is interesting but might be a bit small depending on a lot of things. Likely would work though for testing and very cheap.

The other two are multistep so overkill as fixed voltage would work fine, I think.

Powerstream also makes fixed voltage converter in 15 and 20 amp versions which would certainly be higher quality and probably good for a real installation with full size batteries. They are about $150.

[booster]

I took a look at as many of the specs on DC to DC multistage chargers today to see what they used for charge profiles, and from what I found I don't think that they would work for what we want to do in topping off the AGM.

We need a long time period, 6+ hours likely, at full absorption voltage and all that I found with fixed timers were in the 4 hour range tops. Some "calculate" absorption time based on what they see earlier in the charging, but with no bulk stage because that is already done, they likely would choose very short absorption times.

There is the possibility of the lithium setting I found on one being better, as it was fixed at 14.6v, but it didn't give any profile information about times, etc.

Of course, we still don't know for certain that a DC to DC charger will be needed, but if we do I think fixed voltage (adjustable) with no or settable timer, would probably be the best.

[booster]

Originally Posted by hbn7hj

I'll give the battery thing a day or two to settle out. Right now I like the Battleborn 100.

Battleborn appear to be the Dragonfly that we have heard about in the past, same location, same two battery sizes.

The Dragonfly has a lot more, and more accurate, specs than the Battelborn site does (they have the horribly inaccurate cost caparison chart) including the BMS specs.

Batteries - Dragonfly Energy

[hbn7hj]

Originally Posted by booster

Of course, we still don't know for certain that a DC to DC charger will be needed, but if we do I think fixed voltage (adjustable) with no or settable timer, would probably be the best.

Agreed, I intend to run the charging, both lithium and AGM manually and will start with separate systems. I am interested in the B to B charger and have a $10 one coming but want something with a fan if it is out of sight,

All parts should be here by tomorrow except for the battery. Battleborn just called and said the 100AH battery was shipping today.

I'm outta here for some off grid camping at Borrego Springs for two weeks come Monday. Returning March 13 to put everything together for a smoke test before leaving for off grid at Moab for two months.

When it is all together I'll start a thread titled Field Test Lithium/AGM battery system. Open to suggestions, of course.

Parts inbound or here: 50 amp switch, Trimetric Battery Monitor, Aquarium thermometer, battery tray with hold down, and the gold plated battery. Xantrex smart charger set at 14.4 volts already installed and solar that can be set at any voltage.

B to B charger yet to be determined.

Two large Halon extinquishers already mounted.
Harry