Mixing lithium with AGM's - bashing around some ideas.

[@Michael]

I'm bashing around some ideas for adding battery capacity to my CrossFit & would like feedback.

I've read many thread on the topic, and would like to start turning the threads into rough diagrams.

Starting point is the two factory 105ah SLA's. They don't keep my Novakool fridge alive overnight. The low voltage cutoff is at 12.2v, likely to protect the fridge. They hit 12.2v just before sunrise. I'll likely dump the SLA's and put in AGM's no matter what.

For charging sources, I have a 55amp WFCO converter and GoPower solar charger with 2 @100w panels. The chassis batteries are connected via a battery combiner with a one-hour time-based cutoff.

The Transit chassis has the heavy duty alternator and battery options. If I am careful, I can draw up to 180a from the Transit chassis batteries when the alternator is charging - Ford has a kit that puts three 60a customer connection points alongside the drivers seat that can be combined into one.

Here's the existing wiring (as best as I can figure...):



I think an additional 100ah of lithium will go a long way. We don't have induction, don't have an inverter, and will not run the air conditioning from the batteries.

I can keep the lithium warm if I really want - the campervan is in my driveway all winter - but instead I'll likely pull the lithium out in between trips, so I want them to be easy to disconnect.

Background threads:

Lithium AGM Combo system like Hymer
Parallel lead acid and lithium circa 2018

My first idea is to charge both batteries and just switch the charge side and load side between them as appropriate. I'd either have the solar & converter matched to the AGM's and use a B2B to charge the lithium, or use two B2B's and not worry about the charge profile on the solar, alternator and converter.



I'm leaving out the details (ground, shunts, fuses, breakers, etc).

The above options would be nicer if I could find relays, an isolator or combiner that triggered at the right voltages so that I could eliminate the load side A/B.

Another idea is similar to this lithium/agm post by booster and hbn7hj where lithium is used to charge the AGM's via the B2B.



I'd have to have solar/converter chargers that match up with lithium. I'd flip the charge side A/B to lithium until they are charged, then flip that A/B to either AGM or off, and let the lithium's top off the AGM's. The load would always be on the AGM's. If the B2B has a voltage cutoff, I'd skip the low-volt disconnect on the lithium side.

A third option would be to use Sterling battery chemistry modules (BCM-1260) to match up the charger(s) to the batteries. It would look like the first option, but without aa charge side A/B. It would depend on the existing WFCO being compatible with the BCM's.

Any other idea's?

I'm open.

[hbn7hj]

None of your schematics match ours (I don't think). I have the output of the A/B both switch going to the panel. I use a Trik-L-Start for the chassis battery which takes it out of the system. I have separate AC chargers for the lithium and AGM. Solar goes to the panel and charges whichever battery is connected. The alternator goes to the AGM battery. A DC to DC charger is used to charge the AGM from the lithium. I usually leave the converter off when running the generator. I will switch to AGM with converter on if on shore power.

I did not have the ability for the alternator to charge the lithium unless I put the switch on both which I never did but it is an option.

Later I did add a DC to DC charger between the alternator and lithium battery. It may not be necessary but with a $1000 battery on the line I wanted to control the charging.

We did determine that connecting the lithium battery to the AGM battery didn't hurt anything but wasn't beneficial.

You don't need any automation. Run your evening on AGM, at lights out turn to lithium and your refrigerator will still be running in the morning.

[markopolo]

Originally Posted by @Michael

...................... The low voltage cutoff is at 12.2v, likely to protect the fridge. They hit 12.2v just before sunrise..............

A very low cost, quick and easy solution would be to adjust that cutoff voltage. If it is a Danfoss compressor then you probably can find a chart of the battery protection resistor value needed so that you get that extra hour or so of fridge runtime before solar kicks in.

[booster]

Originally Posted by markopolo

A very low cost, quick and easy solution would be to adjust that cutoff voltage. If it is a Danfoss compressor then you probably can find a chart of the battery protection resistor value needed so that you get that extra hour or so of fridge runtime before solar kicks in.

I would certainly agree with this and also add that if you really have SLA batteries it would benefit a lot to swap them out for some good true deep cycle batteries if you can find some that fit. SLA batteries will not survive going near dead every day for very long.

[Phoebe3]

Originally Posted by booster

I would certainly agree with this and also add that if you really have SLA batteries it would benefit a lot to swap them out for some good true deep cycle batteries if you can find some that fit. SLA batteries will not survive going near dead every day for very long.

The existing batteries are deep cycle. I haven't been paying attention to whether the refrigerator kicks off before daybreak since it cycles on and off anyway. I'll pay more attention next time we go out.

[@Michael]

Originally Posted by hbn7hj

We did determine that connecting the lithium battery to the AGM battery didn't hurt anything but wasn't beneficial.

Are you saying that the lithium didn't work well in keeping the AGM's charged? If so, then the idea of a B2B between the lithium & AGM's isn't going to fly.

Originally Posted by hbn7hj

You don't need any automation. Run your evening on AGM, at lights out turn to lithium and your refrigerator will still be running in the morning.

That would work for me.

Originally Posted by markopolo

A very low cost, quick and easy solution would be to adjust that cutoff voltage. If it is a Danfoss compressor then you probably can find a chart of the battery protection resistor value needed so that you get that extra hour or so of fridge runtime before solar kicks in.

I'll have to look at the Novakool docs. I thought that Forest River set the low voltage disconnect at 12.2 to match the fridge. The Novakool docs are ambiguous. They have 12.2v in the troubleshooting section, but imply elsewhere that it'll run at a much lower voltage. It's a Danforth compressor.

Here's the battery disconnect Forest River installed:

http://precisioncircuitsinc.com/product/battery-guard/

If none of the other components require a 12.2v cutoff, perhaps swapping that out with something with a configurable cutoff would help. I'll check into that.

Originally Posted by booster

I would certainly agree with this and also add that if you really have SLA batteries it would benefit a lot to swap them out for some good true deep cycle batteries if you can find some that fit. SLA batteries will not survive going near dead every day for very long.

I'm hitting the low voltage disconnect on the Precision Circuits battery protect device. The entire coach load gets disconnected. In the morning, if I hit the battery disconnect switch the coach comes back alive, the volt meter shows 12.3v, and if I leave it it'll drop back to 12.2 and hit the disconnect again in a few minutes.

The batteries are up under the rear fenders and up high enough that I have to jack them down to look at them. Coachmen says they are a Duracell 105ah Lead Acid deep cycle. Presumably these:

https://www.batteriesplus.com/Batter...p-31M/SLI31MDC

But unlike Phoebe3's, mine don't have a visible label. I'd pull them down, but it looks like a PITA and we're in a cold snap right now.

I'm assuming that simply putting AGM's under there will help, right? They have a more favorable discharge curve & will stay above 12.2 volts longer?

This is helping. Thanks

@Michael

[booster]

I just looked at the spec sheet for that low voltage disconnect and the 12.2v disconnect is intended to be for the STARTING battery and needs to be seen for two minutes. The coach battery should be connected to disconnect at 10.5v for two minutes which is a lot more normal.


It may just be that the disconnect is wired incorrectly.


http://www.precisioncircuitsinc.com/...ard-Rev1-1.pdf

[Bud]

If I understand correctly, the 12.2 is with 'battery sag' and thus 13.3 a little later.

Doesn't that mean that there is plenty of amps left? Plenty?

Bud

[booster]

Originally Posted by Phoebe3

The existing batteries are deep cycle. I haven't been paying attention to whether the refrigerator kicks off before daybreak since it cycles on and off anyway. I'll pay more attention next time we go out.

The pic that Phoebe shows is wet cell, not AGM, and is rated as a "starting, lighting, ignition" category, so most likely is what is normally called a "marine starting" battery. They have better deep cycle capacity than pure starting batteries, but are usually low water use chemistry now so not quite a good as in the past for capacity, but less hassle. I think the deep cycle life on them is about 1/2 or less of true deep cycle design batteries.


If the OP's van sat on a lot for a while with repeated dead batteries they could easily be bad. On our Roadtrek that had similar Exide marine starting batteries that is exactly what happened. They too, would go dead overnight running just the furnace.


https://www.batteriesplus.com/batter...p-31m/sli31mdc

[booster]

One thing this discussion points out is a bit of change in terminology, I think. For a long time it seemed that AGM and Gel batteries were the ones called SLA batteries, as all wet cells had removable caps. With the low water chemistry getting very common now and the manufacturers removing the caps so no water access, a lot of places are calling those sealed up wet cells SLA batteries also, which can get very confusing sometimes.


What we seem to have now for acronyms.


SLI or Starting, Lighting, Ignition batteries which are plain starting batteries and usually low water use wet cells and sometimes AGM.


SLA or Sealed Lead Acid and now covers AGM, GEL, and low water use wet cells without removable caps


AGM or Absorbed Glass Mat non wet cell sealed batteries we all know well


Gel batteries with are sealed non wet cell batteries not used much anymore


I have heard of a few people that got SLA that they thought were AGM but were really wet cells, so the great price they got wasn't so great.


IFAIK, you will never find a true deep cycle that you can't add water to, as the chemistry dictates it. If you can't add water, it is at most a starting/deep cycle battery.

[hbn7hj]

Just put a voltage stabilizer on the refrigerator power line and be done with it.

It is a lot of work and money to install a hybrid battery system.

If that isn't good enough add a lithium battery and charger to run the refrigerator only.

[markopolo]

Originally Posted by @Michael

......................... Here's the battery disconnect Forest River installed:

http://precisioncircuitsinc.com/product/battery-guard/

If none of the other components require a 12.2v cutoff, perhaps swapping that out with something with a configurable cutoff would help. I'll check into that.....................

Good idea. I wouldn't even want a cutoff in that position in the schematic on my rigs. A 12.2V cutoff would be problematic in a lot of usage scenarios. Earlier this winter my 400Ah bank was showing 12.2V when it was 14F outside and after lots of overnight furnace use. It was a temporary anomaly influence greatly by the temperature of the battery. A cutoff would have effectively disabled the RV and made some unhappy campers!

[booster]

Originally Posted by markopolo

Good idea. I wouldn't even want a cutoff in that position in the schematic on my rigs. A 12.2V cutoff would be problematic in a lot of usage scenarios. Earlier this winter my 400Ah bank was showing 12.2V when it was 14F outside and after lots of overnight furnace use. It was a temporary anomaly influence greatly by the temperature of the battery. A cutoff would have effectively disabled the RV and made some unhappy campers!

According to the specs, it should be able to be set to 10.5v, though, so maybe something else is going on if it is indeed set at 10.5v or it may be faulty.

http://www.precisioncircuitsinc.com/...ard-Rev1-1.pdf


Perhaps best to just jump it our for a while and see how it goes to confirm it is a problem with cutout. Very few of us have cutouts and there normally aren't big issues once a little history in use is seen.

[@Michael]

Originally Posted by booster

According to the specs, it should be able to be set to 10.5v, though, so maybe something else is going on if it is indeed set at 10.5v or it may be faulty.

http://www.precisioncircuitsinc.com/...ard-Rev1-1.pdf

Perhaps best to just jump it our for a while and see how it goes to confirm it is a problem with cutout. Very few of us have cutouts and there normally aren't big issues once a little history in use is seen.

It's wired for a 12.2v cutoff, and is reliably cutting off power to the coach at 12.2v. From what I see in the linked doc, I can simply disconnect the blue 'ignition' wire and it'll switch to a 10.5v cutoff. The question is why Coachmen set it at 12.2 instead of lower. There is a battery isolator between this and the Transit batteries, so they are protected from coach low voltage.

I've read through the docs for the Novacool and Truma. The Truma is OK down to 10v, and the Novakool docs are ambiguous as to whether or not it needs external low voltage protection @12.2v, or if it can rely on the built-in Danforth compressor low voltage protection at 10.6v.

I think that's plan A. Switch it to 10.5v and see what breaks.

Originally Posted by markopolo

Good idea. I wouldn't even want a cutoff in that position in the schematic on my rigs. A 12.2V cutoff would be problematic in a lot of usage scenarios. Earlier this winter my 400Ah bank was showing 12.2V when it was 14F outside and after lots of overnight furnace use. It was a temporary anomaly influence greatly by the temperature of the battery. A cutoff would have effectively disabled the RV and made some unhappy campers!

Yep - that's me.

Originally Posted by hbn7hj

If that isn't good enough add a lithium battery and charger to run the refrigerator only.

I'll think about that approach.

Also - Getting good AGM deep cycles underneath is probably a good ting no matter what.

Originally Posted by Phoebe3

The existing batteries are deep cycle. I haven't been paying attention to whether the refrigerator kicks off before daybreak since it cycles on and off anyway. I'll pay more attention next time we go out.

I'm hitting the coach battery disconnect, so the whole coach goes dark. Resetting the battery disconnect via the panel switch above the door lights up the whole coach, but only until it drops back under 12.2 volts a few minutes later. Charging the batteries is the only way to keep it from disconnecting.

Thanks all - this has been a great help.

[booster]

Originally Posted by @Michael

It's wired for a 12.2v cutoff, and is reliably cutting off power to the coach at 12.2v. From what I see in the linked doc, I can simply disconnect the blue 'ignition' wire and it'll switch to a 10.5v cutoff. The question is why Coachmen set it at 12.2 instead of lower. There is a battery isolator between this and the Transit batteries, so they are protected from coach low voltage.

I've read through the docs for the Novacool and Truma. The Truma is OK down to 10v, and the Novakool docs are ambiguous as to whether or not it needs external low voltage protection @12.2v, or if it can rely on the built-in Danforth compressor low voltage protection at 10.6v.

I think that's plan A. Switch it to 10.5v and see what breaks.

ep - that's me.
I'll think about that approach.

Also - Getting good AGM deep cycles underneath is probably a good ting no matter what.

I'm hitting the coach battery disconnect, so the whole coach goes dark. Resetting the battery disconnect via the panel switch above the door lights up the whole coach, but only until it drops back under 12.2 volts a few minutes later. Charging the batteries is the only way to keep it from disconnecting.

Thanks all - this has been a great help.

If the low voltage cutoff has an isolator or separator between it and the starting battery, there is about zero reason to have it set at 12.2 instead of 10.5. They use 12.2 so there is still enough power left in a starting battery to get the motor started, and the chassis side doesn't see as much voltage sag as the coach because the loads are small unless the van is running.


You can call Coachman and ask, but I don't see any reason to have it set at 12.2v unless it was on the starting battery side of the wiring.

[kite_rider]

Sounds like you've got a lot of options to keep your fridge up and running. You may want to test your existing batteries to see what sort of capacity you still have in them. I had an AGM battery that was spec'd at 105Ah (at the 20H rate - 5A load) and was only getting around 20Ah of capacity out it. It was replaced under warranty.

A couple of comments on your diagrams;

1. You may want to consider a 'smart' device to (dis)connect your lithium battery rather than a manual A/B/Both switch. I'm using the Thornwave PowerMon and have been pretty happy with it. It will disconnect my battery when the voltage gets too high or if it gets too low. You can set it to connect or disconnect based the total charge in as well. This way you don't have to manually monitor the battery. Of course, you can also use this to manually turn (dis)connect the battery as well. It costs about $110, but does a lot.

2. I think the DC-DC charger may be optional. I'm not using one and it seems to be fine. My primary concern was with charging the battery with too much current from the alternator. So far I've not seen this, and it's nice that the lithium batteries charge up fast!

If you have the hardware, it's a good idea to bench test the batteries. I was delighted to see that the used Lithium battery cells I bought off E*bay actually exceeded the specs I expected. The seller listed them as '60Ah cells' based on what he had observed with some bench testing. I believe they were manufactured as '80Ah' cells. I'm able to consistently get 60Ah out of each cell when just by taking it from 90% SOC to 20% SOC which is impressive. So the "180Ah" Lithium battery that I thought I was building, is probably more like a "240Ah" battery per the original specs.


I'm a fan of Lithium!

[@Michael]

I have an update to this post on my Coachmen Crossfit & would like feedback.

My goal is to have both more capacity and much faster charging than the SLA's.

Here's the plan:

Starting point is the two factory 105ah SLA's. I'm adding one 100ah Battleborn battery and a 40A Redarc B2B charger to keep the Lithium charged and separated from the SLA's.

For charging sources, I have a 55amp WFCO converter and GoPower solar charger with 2 @100w panels. The chassis batteries are connected via a battery combiner with a one-hour time-based cutoff and a 40A breaker in line to limit alternator current. I'll leave all that intact.

A manual On/Off switch will enable/disable the Redarc charger. This will allow me to decide when to charge the Lithium, and also allow for a manual disconnect in case of low temp or some other reason.

The coach loads will be on the far side of a manual A/B switch that allows me to run the coach loads from either the lithium or the SLA's, or disconnect the loads entirely. A low voltage disconnect is in line to drop the loads automatically.

I'll use a Thornwave to monitor the lithium battery and will have the option of using Thornwave to drive a solid state relay to automate the On/Of switch or some other voltage or time based function somewhere in the coach.

It's set up so that if I cannot keep the battery above -4F with a warmer of some sort, I can physically remove the lithium and still have a functional RV. (-30f is possible here).

The Redarc B2B should allow charging of the lithium from any/all of the converter, the existing solar, or the alternator at a max rate of 40A. My alternator can do much more than that, but I only have 8 AWG from the coach battery back to the compartment where all the stuff is and I only have one lithium, so I figure 40A is a good rate.

Here's a simplified diagram:

[hbn7hj]

Should work as drawn.

[hbn7hj]

Don't forget a circuit breaker coming out of the lithium. If the low voltage cutout doesn't work as expected you can remove it.

[hbn7hj]

You don't allow for the lithium battery to charge the SLA. For those of us that have a system like this that is a key feature.