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Old 01-22-2019, 03:33 AM   #1
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Default Mixing lithium with AGM's - bashing around some ideas.

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.
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Old 01-22-2019, 04:35 AM   #2
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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.
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Old 01-22-2019, 10:42 AM   #3
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...................... 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.
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Old 01-22-2019, 12:50 PM   #4
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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.
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Old 01-22-2019, 01:19 PM   #5
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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.
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Old 01-22-2019, 01:28 PM   #6
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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.

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Originally Posted by hbn7hj View Post
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.

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Originally Posted by markopolo View Post
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.

Quote:
Originally Posted by booster View Post
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

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Old 01-22-2019, 01:52 PM   #7
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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
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Old 01-22-2019, 02:25 PM   #8
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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?

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Old 01-22-2019, 02:26 PM   #9
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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
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Old 01-22-2019, 02:42 PM   #10
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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.
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