How to build a LiFePo4 battery bank.

[StirCrazy]

A lot of people dont have any idea how easy it is to build a DIY LiFePo4 12V battery so I'll post a deicent video of how to do it so people can decide for themselves if it is in there capability.

this video is pretty decient on how to do it, what is missing is some sort of case. the Prismatic cells like to be clamped togeather slightly if you going to be running high currents. I have seen cases made out of wood with threaded rod providing the pressure, and several other ways also.

also I am not a fan of the BMS he uses, there are lot better ones, but he explains he needed the high capacity one to do a torture test on the cells.

so he builds a 280Ah 12V battery in this video, if you need more you could build 2 and then just tereat them like two 12V batterys and run them in parralell, or just build it all in series and do a 24V set up if you want to do the higher voltage systems.

280Ah LFP build

Steve

[time2roll]

Ivylog wrote:
I just paid $350 for 8-280AH cells and $370 for 8-310AH cells.

Almost too good of a price. Please update when you get them.

[Ivylog]

I just paid $350 for 8-280AH cells and $370 for 8-310AH cells. Will build 2 12V batteries out of each group of 8 cells. Bought 4 200A BMS for $240 plus probably $100 in cables and parts… works out to 90 cents/AH plus probably 20 hours of my time. Doubt the cells will be grade A so I may only have 1100 AH pushing my price to $1/AH…OH well, I can live with that as 9 months ago I thought I’d done well building 600AH for $1200.

Not worried about charge them below freezing as rarely am I in freezing weather. If needing to charge…turn off the chargers (solar included) and run the generator, putting an electric heater in the outside battery area until the cells are above freezing and then charge.

[StirCrazy]

time2roll wrote:

Itinerant1 wrote:
If the heating pads are wired directly to the batteries terminal and if needing them because the actual cells are below 32f and not the ambient temp how would a generator help unless you have a heater cube plugged into it throwing heat to the compartment.

Are you going to add extra insulation on the walls/ floor to help keep heat in and cold out during the colder months if using them during that period?

Heaters will be wired on the load side of the BMS. If the load side is powered by generator, solar or vehicle, the power will go to the battery heater.

Insulation will not be added unless it seems to be needed. Most camping is in fair weather. Not intended to be a north pole expedition vehicle. Just some minimal protection for a mild cold snap.

I think everyone is going on about a mute issue, unless the batteries are totaly dead then just the charging is going to be cut off at 32 degree ish, the discharge will still be available so the heating pads will work untill it gets down to a heck of a lot colder. if you insulate good around the batteries you may never come to this as the discharge from using/charging the batteries will create there own internal heat and with the right insulation it might be enough to keep them above zero down to a pretty cold temp, but that just theory...

Steve

[BFL13]

pianotuna wrote:

time2roll wrote:
I do wonder if these self heated batteries only allow external power for heating.

The ones I've found online draw from the battery, and have no provision for an external energy source.

PT, this a typical blurb for a "cold weather" drop-in LFP:

"In cold temperatures, the BMS ( battery management system) disconnects from the cells to protect your battery. Prior to charging, the built-in heating systems draw power from the charger in order to heat up the battery."

Time2roll would set his BMS to allow charging at X temp, and also set his heat pad Tstat relay temp to keep them above that BMS set charging temp.

No idea where his charging rate setting might be for cooler temps, if he even does that. Once set up and camping proven after any adjustments, it should be easy after that to just go camping no worries.

[pianotuna]

Thanks BFL13 for the information.

[pianotuna]

time2roll wrote:
I do wonder if these self heated batteries only allow external power for heating.

The ones I've found online draw from the battery, and have no provision for an external energy source.

[BFL13]

time2roll wrote:
I do wonder if these self heated batteries only allow external power for heating.

Should still be able to keep them warm with heat pads, etc. Only then use the charger heating method as an emergency back-up.

I see I forgot the actual Trillium charging specs. They do allow a little charging a little below freezing, but also only allow full charging at 73F. No clue how that may apply to other LFPs.

https://www.trojanbattery.com/pdf/Trillium_UsersGuide.pdf

[time2roll]

I do wonder if these self heated batteries only allow external power for heating.

[BFL13]

pianotuna wrote:
BFL,

Where did 5C come from?

Trojan Trillium charging specs. Also some(all?) drop-in self- heating LFPs have the battery charger (there is your generator requirement) power the internal battery heater and get the bank up to 5C before it switches the charger power over to battery charging. It takes about two hours to warm them up from -20C to 5C I saw somewhere, but not so long when it is just under freezing of course..

The better idea is obviously to not let the batts get that cold in the first place, and the DIY set-up like time2roll has built should be way better than the drop-in method.

If the bank is inside the RV you keep it warm with propane furnace or if in outside compartment, you can perhaps DIY a way to get hot air or hot water (also from propane) to it, or else you are stuck with having some kind of DC heater.

Some say you can charge the LFPs at full blast once they are above 0C freezing, but others say you should/must use a reduced charging rate between 0 and 5C, scaling up the rate, like the Trillium specs.

Not many RVs will have a converter or charger that can do higher rate charging on a bigger AH LFP bank anyway.

[time2roll]

pianotuna wrote:
BFL,

Where did 5C come from?

5C would be 6000 amps. The battery is fused at 0.2C

[time2roll]

Itinerant1 wrote:
If the heating pads are wired directly to the batteries terminal and if needing them because the actual cells are below 32f and not the ambient temp how would a generator help unless you have a heater cube plugged into it throwing heat to the compartment.

Are you going to add extra insulation on the walls/ floor to help keep heat in and cold out during the colder months if using them during that period?

Heaters will be wired on the load side of the BMS. If the load side is powered by generator, solar or vehicle, the power will go to the battery heater.

Insulation will not be added unless it seems to be needed. Most camping is in fair weather. Not intended to be a north pole expedition vehicle. Just some minimal protection for a mild cold snap.

[time2roll]

pianotuna wrote:

time2roll wrote:


solar would provide for heating even if the BMS had cut power. Not sure the solar will work with no battery connected. 😉

The solar might burn out the charge controller with no battery connected. I wonder if a capacitor would prevent that from happening?

I find it ironic that a generator may be needed to provide for heating the battery bank.

This would not be unexpected if a person is aware of the situation.

The solar panel disconnect switch would be turned off until the situation was stabilized.

Controller needs 8 volts to wake up and operate. Small 9v battery should be able to jump start. Power would go to the heaters until the BMS allows charging. Yes the generator could get it working. Same for rolling out and getting power from the vehicle.

If the furnace and battery heaters are running continuous it should still give two full days of run time to figure it out.

[Itinerant1]

If the heating pads are wired directly to the batteries terminal and if needing them because the actual cells are below 32f and not the ambient temp how would a generator help unless you have a heater cube plugged into it throwing heat to the compartment.

Are you going to add extra insulation on the walls/ floor to help keep heat in and cold out during the colder months if using them during that period?

[pianotuna]

BFL,

Where did 5C come from?

[pianotuna]

time2roll wrote:


solar would provide for heating even if the BMS had cut power. Not sure the solar will work with no battery connected. 😉

The solar might burn out the charge controller with no battery connected. I wonder if a capacitor would prevent that from happening?

I find it ironic that a generator may be needed to provide for heating the battery bank.