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Lithium battery setup for fridge?

nakman

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I am trying to talk myself into, or out of, doing a Lithium setup in the back of the 200 for powering a fridge. And I suspect someone else on the forum either has, or is considering, adding a lithium battery to the mix, so figured let's chat about it. The PO of my 200 was kind enough to include a DC to DC inverter in the package, along with a fuse block right where I need it, as well as put this idea into my head... so in theory I'm just a battery & a few cables away from Lithium bliss here.. few other details on my setup:

- My primary and secondary batteries are both Die Hard Silver- deep cycle flooded style. Like this: https://shop.advanceautoparts.com/p/diehard-silver-battery-group-size-27f-710-cca-27f-3/2040183-P
1647031598703.png

- My DC to DC converter is currently on the bench, but it's this one: https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/

- Looks like $400 gets you a 100 amp hour battery? https://www.amazon.com/WINGDA-Batteries-Rechargeable-Off-Grid-Applications/dp/B09DQ35JV7/ref=sr_1_3?crid=1LCCABQGZHTPN&keywords=100+amp+hour+lithium+battery+12v&qid=1647030760&sprefix=100+amp+hour+,aps,109&sr=8-3 the 50 amp hours are cheaper, but wonder what's really necessary here.

So first obvious question is what would be the benefit here- the fridge lives off the Lithium deal, and conceivably never really needs to dip into the 2nd battery on a typical outing? I am guessing worst case scenario Lake Powell in the summer a fridge sucks about 50 amp hours in a day (4 amp spike at startup, 3amps when running, and it's running about 80% of the time for 14 hours or so, slightly less when the sun goes down)... I know the math never really adds up to reality though. So battery 1 remains untouched other than a few door and dome lights, battery 2 powers all radios, scene lights, RC crawlers, etc., then battery 3 runs the fridge. Also guessing in threory that if battery 3 ran down it would start to suck off battery 2. And I know from experience that if battery 2 runs down the IBS controller will start beeping, and I'd need to manually combine 1 and 2 to charge it. Or start the truck.

Does the DC converter also act as a check valve? So current only flows one way? I know I could rtfm, but figured someone else was curious... and would battery 2 have any issues being middle man like that?

My experience with small/medium fridges is you get about 1 day per battery. So camp one night, drive tomorrow, you don't need a 2nd battery. Camp 2 nights and don't start the truck on the middle day, you need 2 batteries, by that 2nd morning you're likely getting beeped at. But all of this varies widely based on temperature, ventilation, fridge use, etc. these are kinda worst case experiences. but enough of me, what do you think?
 

DaveInDenver

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Downsides to lithium batteries is cost primarily and that you may need a special charger. You have the charger covered.

One thing important to watch is whether the battery has a BMS, battery management system. At this price I'm wondering if this one does not have BMS. This is a concern because another very important thing about lithium is that it's not stable and potentially dangerous. So a BMS allows you to use less well regulated power sources to charge and discharge a lithium battery. You may be familiar with 18650 batteries that are protected or unprotected, it's for this reason. A battery that is unprotected could be charged and discharged at rates that make them get too hot, which causes a thermal runaway and in a worst case situation catch fire. OTOH LiFePO4 is a fairly stable type, so it's a better option than lithium-ion or others.

The upside is weight, which is significant. Also you can take them to deeper discharge.

Regular lead-acid should only be taken to about 50% depth of discharge (e.g. use 50 A-hr from a 100 A-hr) to prevent excessive aging. Lithium is fine to use 80% of it's capacity on a routine basis and not seriously harm them.

Yes, DC-DC charges are one-way. They only flow current from the source to the battery you're charging. They can't work in reverse like a plain combining relay.
 
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nakman

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yeah that battery has a BMS, it says that right in the description. I do worry about fire, but keep getting assured it's not an issue and lots of other trucks are already running this without issue. but still... life affords you 2 eye injuries lifetime, but you really only get 1 vehicle fire. I dunno.

I'm pretty sure @Hants has this in his 200, maybe he'll stumble across this and talk me down.
 

DaveInDenver

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It's hard to think of a reason not to go this way since you have a way to charge it. LiFePO4 is pretty safe, more so than the lithium-ion they use in electric cars for sure. It's not any cheaper to get a 100 A-hr deep cycle anymore.
 

Hants

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I have a 75AH Renology battery with a 40A Redarc DCDC charger. Love it!

As Dave notes, 75AH Lithium is 75AH usable (not that I run it that low), whereas a 75AH AGM for instance, only has about 30AH usable on a regular basis.

Even with the extra usable capacity, I wouldn’t go smaller than 75AH for this use.

A DCDC charger that knows how to charge Lithium batteries is important. I’m told that an AGM profile can work, but is suboptimal (more time to charge).

All of the Lithium batteries I’m aware of have a built in charge controller. It will control both the charge and discharge rate. You can size your DCDC charger up to that charging limit.

With the charger in the rear, the voltage regulator and wire distance (voltage drop) are not a problem anymore for that battery. :). Mine is generally 100% charged within a couple hours after camping for a day or two.

I installed an inexpensive battery monitor ($200 or so), so I can track the battery state from my phone (no hard mounted display). Helps with peace of mind - I haven’t dropped below 50% SOC with the type of camping we do (not desert camping).
 

Hants

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Remember that due to voltage drop to the DCDC charger, it may draw more than its rated charge current. For instance, my 40A DCDC charger may draw 50A from the alternator (and wiring needs to be sized for 50A).
 

nakman

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good to see you Hants! :cheers: Hypothetically, if you parked at Cruise Moab with a back door window cracked, how many days would your 75AH battery keep your fridge running? without charging it (solar, engine, or otherwise)


edit: so with the 20amp DC to DC converter, am I right to assume it won't charge as fast? So maybe it takes 4 hours, instead of 2? On their site it states they recommend 16-18ga wire, which is kinda small... I think I can live with a 4 hour charge time though, geez.
 

gungriffin

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One item to be aware of is you cannot charge lithium below 32* without causing permanent damage to the battery. As a result, you really want a Lifepo4 battery that has low temp charging cutoff. There are some newer batteries that actually have a built in heater pad too. This preheats the battery to ~40* and then starts charging.

You can also pull most all Lifepo4 batteries down to 0% charge. They just won't last as many cycles, but before suffering loss of capacity. Many batteries can go 2000 cycles or more at 100% Depth of Discharge (DOD). It all comes down to the quality of the cells installed in the battery. Even the cheap batteries can usually go 500 cycles at 100% DOD. That is a lot of weekends of camping.

My CFX75 Dual zone fridge tends to pull an average of about 1.3 Amps per hour over a 24 hr cycle.
 

DaveInDenver

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Some chargers take care of the low temperature shut off for lithium but Renogy doesn't mention it specifically in their owner's manual. They do say the charger does temperature compensation but it appears that only affects lead-acid. The only setting for lithium appears to be voltage.

That would be an unknown I suppose.
 

jps8460

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I’m doing this setup on my 80 as well Tim. I’m putting 2 smaller 20ah’s in parallel (package fits better). But I have a tiny Engle to run. It’s crazy efficient. I think the wire size you mentioned seems too small. You might want to double check that.
 

Hants

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@nakman Hope to see you in Moab shortly!

Just like any battery, the acceptance/bulk rate is pretty high. Call it up to 80% SOC. So, if you’re down to 10 or 20%, at 20A, 2 hours of driving will give you about 40AH of charge.

When you’re out, no need to top off… it will top off on the drive home. :)

Rough estimations:

30-40AH per day for the fridge

100AH gets you 2-3 days with no recharging.

In practice, I almost never go 2-3 days without driving at least a little. I never even think about battery when we’re out.

No solar or other charge sources on the Lifepo and fridge (and I have some lights, aux ports, and all my radios running off of it, too).
 

Hants

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Regarding wire size, auto wiring typically rates for 10% voltage drop (round trip wire length). Marine uses 3%.

If you want conservative, check out one of the marine wire size tables.
 

Hants

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I have a charger hooked up to the rig (not my daily driver), when it is parked in the garage. Went with a 5A one. Keeps my main AGM battery happy, and the LiFePo fully charged.

Note that there is one scenario to be cautious of: If your LiFePo is significantly discharged, your DCDC charger will gladly draw 20A for a very long time if it senses charge voltage. In that case, plugging in a trickle charger (keeps the voltage up but can’t provide sufficient amperage), can cause your LiFePo (technically the DCDC charger) to fully discharge your main battery (very bad for lead acid, and bad for AGM).

Driving back from camping mitigates this.

Parking for a while is the real risk, then using a trickle charger to recharge. Do not do this. If you end up with low batteries from sitting, fully disconnect the LiFePo until the main is healthy. Better yet, charge the LiFePo first. Or use a charger that puts out sufficient amperage that it can drive the DCDC charger.

Edit: Note that if you have solar on your rig, it should be charging the LiFePo, and NOT your main battery.
 

Hants

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Product note: The redarc DCDC charger has a solar controller built in (and is perfect for the above post with solar). The LiFePo profile on their DCDC charger works a treat. Their solar controller isn’t the best out there, but does get the job done.
 

Hants

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@nakman Do you have a DCDC charger, or an ACR (automatic charging relay)? Both will “charge” when charging voltage is detected. The ACR relies on the Alternator voltage to charge the LiFePo. The DCDC charger draws from the alternator, and uses its own charging profile to charge the LiFePo. Using an ACR will make your LiFePo very unhappy (it will *never* get 100% SOC - more like it will stop charging at 50% or less SOC).
 

nakman

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This guy has a boatload of videos on different LiFePo4 batteries including tear downs and built in temperature shutoff and BMS testing.

wow that's a bunch of content... will bookmark that one for the next snow storm, thanks!
I’m doing this setup on my 80 as well Tim. I’m putting 2 smaller 20ah’s in parallel (package fits better). But I have a tiny Engle to run. It’s crazy efficient. I think the wire size you mentioned seems too small. You might want to double check that.
just reading what it says on their website, a couple different times under the description tab https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/ I agree it seems small though, would go bigger.

Protect Your Starter Battery
This Renogy DC-DC battery charger is compatible with traditional and smart alternators. The D+ Ignition cable is capable of identifying whether the generator is started, to prevent over-discharge of the starting battery and protect the generator. 18-16AWG copper cable recommended.
Please note the D+ Ignition Cable is not included.
@nakman Do you have a DCDC charger, or an ACR (automatic charging relay)? Both will “charge” when charging voltage is detected. The ACR relies on the Alternator voltage to charge the LiFePo. The DCDC charger draws from the alternator, and uses its own charging profile to charge the LiFePo. Using an ACR will make your LiFePo very unhappy (it will *never* get 100% SOC - more like it will stop charging at 50% or less SOC).
it's a DC to DC charger. I have an ACR between batteries 1 and 2.

But I don't see where you plug in a solar panel.. I don't have that model, looks like they make a dual input one though. like this one: https://www.renogy.com/dcc30s-12v-30a-dual-input-dc-dc-on-board-battery-charger-with-mppt/

@gungriffin Ryan that temperature thing has me pausing again on this deal... I will park in sub zero temps overnight at least a couple times per year, and heck my garage at home will get below 30 even, ever since I cut a hole in the back door to put an exhaust fan to make a paint booth it just doesn't insulate as well for some reason... :rolleyes:

So I can already go 2 days without any charging, and I've got a charge controller and foldable solar panel sitting on the shelf here... maybe I'll just go that route instead. Just not seeing how this is worth it at this point or why it would be that much better than what I have? If I didn't already have the 2nd battery it would be a little easier to make a case for it.
 

Hants

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The redarc ones have solar controller built in:

 

Hants

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The YouTube channel has a recent video stating that in most cases, a battery warming pad is not necessary.

My experience supports this - I’ve never had a problem even in sub-freezing temps for days. My battery is in the vehicle, under the drawer system. Temps just don’t get that low back there (I have looked - my battery monitor also has a temp sensor).

The content creator states that the charge controller will simply disable charge/discharge if it is too cold. Sounds like you’d have to work really hard to destroy a LiFePo due to cold.
 

jps8460

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If anyone is considering the renogy. I think the B+ Mentioned above is just the wire to turn it on with a key cycle. Actual input cable is 8awg +\- depending on length of run.
 

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