Discharge appliance for LiFePo4 Battery

[Steve Hogan]

Hello. Need help. Not a DIY Guy. I have 2 brand new FPV 12 volt 50 AH batteries running in parallel for my kayak.. Kayak is not here yet. The batteries are at 100% full charge and showing 12.4 volts. For fun I want to be able to discharge this battery. I've read about not not doing a full discharge... The batteries do have over charge and discharge protection. I just want to have an appliance to discharge the battery. Please I'm asking for a pre made appliance and not a DIY project. I'm good on spending up to $200.00 if that's what it takes. Also interested in something for the kayak that displays amount of charge left on the batteries discharge rate etc...again... I am not a DIY guy. Looking for a solution I can buy. Thank you very much. Steve H.

 

[Supervstech]

What cell chemistry is your battery? 12.4 sounds low for most types.
Lead acid would be about 60% lifepo4 would be about 50%, LiNMC would be about 90%... I don't know of a chemistry where 12.4 is 100%

 

[John Frum]

What cell chemistry is your battery? 12.4 sounds low for most types.
Lead acid would be about 60% lifepo4 would be about 50%, LiNMC would be about 90%... I don't know of a chemistry where 12.4 is 100%

For a 3s explody flavour lithium ion battery 4.2 volts * 3 = 12.6 volts is full to the brim.

 

[Steve Hogan]

Cell chemistry is in the title. It's lifepo4. The 12.4 is what is showing on my $5.00 tester
So do you guys know of a good discharge device I can use for an lifepo4 12 volt 100 Ah battery Hope this pi. helps.

 

[John Frum]

Cell chemistry is in the title. It's lifepo4. The 12.4 is what is showing on my $5.00 tester
So do you guys know of a good discharge device I can use for an lifepo4 12 volt 100 Ah battery

Glad you know better.
Lots of people that we help don't, so we double check and/or infer.

 

[Supervstech]

Ok, just confirming.
Lifepo4 12.4 is nowhere close to 100% (14.4 would be 100%)
3.6v/cell is 100% 3.2v/cell is nominal
So, nominal would still be 12.8V...

 

[Supervstech]

There are several ways to manage the discharge.
I would get a hobby charger that can dump the watt/hours into another battery bank.
But resistance loads also are out there.

 

[John Frum]

Your battery should have a built in BMS to keep the cells in their safe envelope so you should be able to discharge your battery to the point where it disconnects with any load.

 

[Steve Hogan]

lol @ smoothJoey I have no idea. I am not even able to follow any of the "DIY" suggestions from Will. Each sentence contains words that i have no understanding of the meaning.

For example Supervstech is suggesting I get a Hobby charger... that can dump watt hours to another battery bank.. I am not concerned with saving what hours... I don't have another battery bank... And there are a blue zillion "chargers available... I have no idea which ones will discharge. Is it possible to suggest a specific make model that we know will discharge my batter without saving the charge or is there a specific device that will read real time charge level, Voltage,, Charge my battery and discharge my batter.
I think I'm unusual here in that I'm 73 and not into solar or "Free" energy. unless there is something that is complete, that I can buy, I'm pretty much stuck. I don't have hole saws, I don't have a power tools... Don't have a workshop.. I was not even able to walk 50 feet until very recently. I've bought a "powered" Kayak. Knowing I can't pedal or paddle more than about 200 yards. If I can get the kayak in the water that will be enough execrise and more than I've been able to do in a long time. Really appreciate you guys helping me here.

 

[Steve Hogan]

smoothJoey, It does have a BMS. "". The batteries do have over charge and discharge protection."" Know the name or make and model number of a good discharge device?

 

[John Frum]

smoothJoey, It does have a BMS. "". The batteries do have over charge and discharge protection."" Know the name or make and model number of a good discharge device?

I'm struggling to find one that is really dead simple and safe to use.

 

[Steve Hogan]

smoothJoey...I'm apparently more ignorant than either of us realized. I'm reading the instructions that came with my batteries. My brain has been saying Lithium ion polymer... After reading I started thinking Lithium Iron Polymer... I'm now reading the instructions and it states FPV POWER 12v 50 Ah Lithium Ion Polymer Battery instructions... so are you saying that two of the batteries, (I think in parallel so I have increased Ah) should higher than a 12.v or 12.5 or 12. 3 reading... so sorry for my ignorance here.

 

[Steve Hogan]

Ah just saw your reply. Yes, I did too. I have ordered a little heat sink with fan thing a mjig, similar to what Will shows in some vids but it's coming from china and last messae was.... should be here in 35 days... Anyway let me know if you find anything and again Thank you.

 

[John Frum]

smoothJoey...I'm apparently more ignorant than either of us realized. I'm reading the instructions that came with my batteries. My brain has been saying Lithium ion polymer... After reading I started thinking Lithium Iron Polymer... I'm now reading the instructions and it states FPV POWER 12v 50 Ah Lithium Ion Polymer Battery instructions... so are you saying that two of the batteries, (I think in parallel so I have increased Ah) should higher than a 12.v or 12.5 or 12. 3 reading... so sorry for my ignorance here.

Lithium ion polymer is one of the dangerous "vent with fire" lithium chemistries.
It is not anywhere near the same as lifepo4.
I'm glad you checked.

 

[SolarQueen]

So it sounds like they are LiPo, not LiFePO4. Those are often used on radio controller airplanes because of their dense energy and lightweight design. I'm betting there is no Battery Management System (BMS) on it. Be extremely careful with them, especially on the water where there is no escape route. Have a way to throw them overboard if needed.

The cell's full voltage is 4.2V, so 3 in series is 12.6V full. That lines up with what you are seeing.

As for the original question of a load to discharge, just get any 12VDC device that you may want to use on the boat later, like a 12V fan.

 

[John Frum]

@SolarQueen I don't think its safe to discharge them without a BMS.

 

[Steve Hogan]

Here is a shot of wat is on the batteries. I have 2 of them (12V 50 Ah) They weigh 7 lbs each. They should be charged to as high as the charger and the BMS will allow. I probably have the meter I'm using set for the wrong battery. Thanks

 

[SolarQueen]

@SolarQueen I don't think its safe to discharge them without a BMS.

Good point. I'm not thinking fully discharge, I was assuming he just wants to test it out before installing, but I should know better than to assume. Quite frankly, this whole thread is making me nervous.

If you do put a load on it, be sure to monitor it with a volt meter and turn off the load when it is in the low 12V range.

 

[Steve Hogan]

@SolarQueen. The batteries do have a BMS.

 

[Steve Hogan]

They are not wired in series, they are wired in parallel.