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Question on switching to LiFePO4 batteries.

Sterling1
Explorer
Explorer
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?
35 REPLIES 35

Sterling1
Explorer
Explorer
3 tons wrote:
With LFP’s, Wishful thinking can also be fun 🙂

3 tons

I don't know if this is in reference to my post on what is connected downstream of my switch but I do know for sure what is connected directly to my batteries. When I replaced my off-on switch with an A/B switch there was nothing connected to the battery side of the switch other than the cable from the batteries. I ran another cable along the original cable to allow me to select which battery to use and there were no other junctions.

3_tons
Explorer
Explorer
With LFP’s, Wishful thinking can also be fun 🙂

3 tons

Sterling1
Explorer
Explorer
mbloof wrote:
Sterling1 wrote:
For now I plan to use a volt meter I have installed in my camper for SoC level which should be good enough for my use. I've "calibrated" the camper meter with a multimeter at the batteries when the isolation switch is switched off to eliminate parasitic draw. So far there no significant difference between the camper volt meter and the multimeter but I haven't taken measurements when the batteries are in a low SoC.


Good luck with that. As an example on my NL that switch only breaks the connection to the Converter/charger - the jacks+controller and fridge are directly connected to my battery(s) bypassing that switch.



- Mark0.

On my camper everything gets disconnected from the batteries by the switch other than the generator and inverter which are connected directly to my batteries.

StirCrazy
Traveler III
Traveler III
3 tons wrote:
Follow-up to WarrenS65:

When it comes to accurate SOC’s, I kinda see the Bluetooth feature mostly as marketing gimmickry, while their real utility is for checking individual cell status…Further, it remains to be seen how the Bluetooth will respond to two batteries in parallel or series connection…My view is there’s no substitute for the credibility of a Victron shunt based meter..

Of all possible features, the Bluetooth feature wouldn’t be high on my ‘must have’ list - JMO

3 tons


The biggest issue here is different companies use different BMS, and sometimes even the same company will change their BMS if they are not in stock and are running out. Hopefully if this happens the company will list a different model number and let you know if it is compatible with the other BMS they have used. Most are not. It goes the same for mixing different sized batteries or exceeding their limits in series or parallel.

Then you must throw in the fact that some BMS' are better than others. but all of them should be decent at SOC as that's what they base their protection on, so that would never be one of my concerns. a cell drifting out of spec because of partial charging and lack of top balancing would be more concerning to me.

I like my Bluetooth in my camper, do I used it for looking at the capacity remaining, not really, as my phone is pretty must put away when I am in the bush, but I do use the Bluetooth and my phone to look at it once and a while and when I need to change the charging profile. for that it has been a godsend as when I want to do a cell balance, I just switch user profiles in the BMS by Bluetooth, then when it is done balancing, I put it back to the 90% cap. same with the day before I leave for camping, I always take it from the storage voltage to 100% to make sure everything is balanced before I leave. I can do that from my chair in the morning while I am watching the news.

Steve
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

mbloof
Explorer
Explorer
Sterling1 wrote:
For now I plan to use a volt meter I have installed in my camper for SoC level which should be good enough for my use. I've "calibrated" the camper meter with a multimeter at the batteries when the isolation switch is switched off to eliminate parasitic draw. So far there no significant difference between the camper volt meter and the multimeter but I haven't taken measurements when the batteries are in a low SoC.


Good luck with that. As an example on my NL that switch only breaks the connection to the Converter/charger - the jacks+controller and fridge are directly connected to my battery(s) bypassing that switch.



- Mark0.

WarrenS65
Explorer II
Explorer II
3 tons: I agree with you about the accuracy of the BMS vs the SmartShunt and now that everyting is working, that's what I monitor. My shunt would read full for a long time then drop to 20% - 30% very quickly. At the same time, one BMS would show 96% or higher and the other would show around 70%.
Cycling the batteries let everything calibrate. Now the 2 BMSs and shunt all show within a percent or 2.
2022 F450
2023 Host Everest
2021 Yamaha YXZ1000R
1987 Honda TRX250R
2002 Honda 400EX
2023 Yamaha Raptor 700SE
2018 Look 24' enclosed trailer

Sterling1
Explorer
Explorer
For now I plan to use a volt meter I have installed in my camper for SoC level which should be good enough for my use. I've "calibrated" the camper meter with a multimeter at the batteries when the isolation switch is switched off to eliminate parasitic draw. So far there no significant difference between the camper volt meter and the multimeter but I haven't taken measurements when the batteries are in a low SoC.

3_tons
Explorer
Explorer
Mark0 said;

“ While the simple solution is to always have more AH then you need/use our truck campers have limited space to stuff more AH in…..”

Absolutely, I couldn’t agree more - two 200a/hr beneath the dinette seats!!


3 tons

mbloof
Explorer
Explorer
3 tons wrote:
3 tons wrote:
Follow-up to WarrenS65:

When it comes to accurate SOC’s, I kinda see the Bluetooth feature mostly as marketing gimmickry, while their real utility is for checking individual cell status…Further, it remains to be seen how the Bluetooth will respond to two batteries in parallel or series connection…My view is there’s no substitute for the credibility of a Victron shunt based meter..

Of all possible features, the Bluetooth feature wouldn’t be high on my ‘must have’ list - JMO

3 tons


Upon edit, the aforementioned Bluetooth SOC inaccuracy may be associated with personal charging practices, and the number of less than a FULL charge, charge cycles which overtime leads to cumulative meter drift, whereas the Victron could be FAR better at resolving cumulative drift…Just MO…

3 tons


IMHO: this is where inline current shunts (Bluetooth or not) come in handy.

Fairly simple - measure AH In/Out of battery(s).

Also IMHO: anything that relies on battery voltage to calculate an implied SOC can't possibly take into account the parasitic loads our campers have in their calculation and therefore will always be an 'approximation meter' at best.

While the simple solution is to always have more AH then you need/use our truck campers have limited space to stuff more AH in. 🙂



- Mark0.

3_tons
Explorer
Explorer
3 tons wrote:
Follow-up to WarrenS65:

When it comes to accurate SOC’s, I kinda see the Bluetooth feature mostly as marketing gimmickry, while their real utility is for checking individual cell status…Further, it remains to be seen how the Bluetooth will respond to two batteries in parallel or series connection…My view is there’s no substitute for the credibility of a Victron shunt based meter..

Of all possible features, the Bluetooth feature wouldn’t be high on my ‘must have’ list - JMO

3 tons


Upon edit, the aforementioned Bluetooth SOC inaccuracy may be associated with personal charging practices, and the number of less than a FULL charge, charge cycles which overtime leads to cumulative meter drift, whereas the Victron could be FAR better at resolving cumulative drift…Just MO…

3 tons

3_tons
Explorer
Explorer
Follow-up to WarrenS65:

When it comes to accurate SOC’s, I kinda see the Bluetooth feature mostly as marketing gimmickry, while their real utility is for checking individual cell status…Further, it remains to be seen how the Bluetooth will respond to two batteries in parallel or series connection…My view is there’s no substitute for the credibility of a Victron shunt based meter..

Of all possible features, the Bluetooth feature wouldn’t be high on my ‘must have’ list - JMO

3 tons

Sterling1
Explorer
Explorer
DWeikert wrote:
A little late to the thread but just throwing this out there. Instead of 2 100ah batteries is there a chance you would have the space for one 200ah battery? For example -
JITA 12V 200Ah Plus LiFePO4 Battery
Wiring is much easier and solves the problem of trying to balance the cells across 2 different batteries.

My $0.02
Dan

The battery would probably fit but I've already got the batteries. I could just put a jump wire across the positive terminals (like I have on the negative terminals) if I wanted to bypass the positions on the switch (there would be no difference between A/B/Both from an operational standpoint) to alleviate any balancing concerns. But I do like the ability to isolate the batteries from each other if I want.

Thanks

WarrenS65
Explorer II
Explorer II
I have 2 206Ah SOK batteries, a Victron SmartShunt, and a Victron Multiplus 3000 inverter/charger. The two batteries are connected in parallel with the negative going to the SmartShunt and the positive going to a battery disconnect switch.
The other side of the shunt and switch are connected to my bus bars with the MultiPlus, Victron Orion DC/DC converter (2 of these), Victron MPPT controller, and the 12V wiring going to the camper.
The SOK batteries have BMS with Bluetooth. I was having "trouble" with the SOC on the two batteries and the Victron all being different. I called CurrentConnected.com (where I bought the batteries and most of the other Victron components), and they had me disconnect one battery then discharge it and recharge it twice, then repeat with the other battery. After this, I reconnected both batteries and everything is working well.
My advice is to buy all your components from one source that will give you good support.
I also have the Victron Cerbo GX and it's connected to my router. I get e-mail alerts when the batteries cross thresholds I've set, but with the solar panels, I haven't had to plug it in since March.
2022 F450
2023 Host Everest
2021 Yamaha YXZ1000R
1987 Honda TRX250R
2002 Honda 400EX
2023 Yamaha Raptor 700SE
2018 Look 24' enclosed trailer

DWeikert
Explorer
Explorer
A little late to the thread but just throwing this out there. Instead of 2 100ah batteries is there a chance you would have the space for one 200ah battery? For example -
JITA 12V 200Ah Plus LiFePO4 Battery
Wiring is much easier and solves the problem of trying to balance the cells across 2 different batteries.

My $0.02
Dan
Dan
2008 Chevy D/A 2500HD ECSB
2010 Northstar 8.5 Adventurer

StirCrazy
Traveler III
Traveler III
Sterling1 wrote:
StirCrazy wrote:

so, the plot thickens everything I find says 50% or higher and if you're not using them for a long time recharge every 3 to 6 months. I think this is another area where older chemistry myths might be carrying over

Yea, different manufacturers have different recommendations. I just wonder how much difference it makes in the real world.

For someone that really cycles the batteries a lot and is concerned about maximizing the cycle life it may make sense to take extra effort to store them in optimum conditions.

For someone like me who doesn't put a lot of cycles on the batteries storage conditions may not make much of a difference (as long as they aren't stored in a discharged state). They are more likely to die from old age than anything else.

It would just be nice to see how much of an impact storage SoC has on LiFePO4 battery life.


I try not to go by the manufactures but rather from the makers of the cells. What people call manufacturers in this area are really just assemblers. they don't make anything themselves; they just assemble off the shelf components. They may have custom cases made for them, or they might make custom solutions to hold everything together so there is a small possibility they might make a tiny part...

So, I tend to look at CATL, BYD, ELB and EVE cell manufactures, of which, the first three are the biggest in the game, and while EVE isn't as big they are known to be one of the highest quality cells on the market.
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100