LiFePO4 - better life with shallow discharge?

[pschmatz]

Hello,

I'm running a 48V 10Ah LiFePO4 (a 16 cell "discounted" experimental one from ebikes.ca) on an e-bike for my commute (8 miles one way), and it looks like I can easily do the round trip on a single charge.

My question is if it is better for the battery to carry the charger along and recharge in the office, or to do the round trip and charge over night only?

Do I get better life out of the battery with a shallow discharge, or is it just the same?

Thanks
Peter

 

[dogman dan]

Better to charge at work. Shallow discharges are better for allmost every chemistry. The prius battery lasts forever since they allways undercharge and never discharge below 50% or so. You can use a cheapo sla scooter charger that is kept at work instead of carrying. You can still get a balanced charge at home each night. I screwed up and cooked my ping charger a month ago and my pack is still balanced. All the sla chargers do is slightly undercharge them. In my case, the lifepo4 charger would run for about 15 minuites after the sla charger had finished.

 

[ort5]

I would add that the Prius battery actually never fully charges though either. The key is keeping the NiMh batteries in the say 40% to 70% charged state.

I don't know the answer to the original poster's question, but I don't think you'll really have a problem either way.

 

[pschmatz]

Thanks.

SLA charger? Can I use one on a LiFePO4 battery?

The current charger I have is a "Li-Ion" 58.4V 4 amps. What SLA chargers would have this voltage? Would the BMS work with it?

Thanks
Peter

 

[flip_normal]

Thanks.

SLA charger? Can I use one on a LiFePO4 battery?

The current charger I have is a "Li-Ion" 58.4V 4 amps. What SLA chargers would have this voltage? Would the BMS work with it?

Thanks
Peter

If your current charger only has 2 wires (+/-) coming out of it then it isn't balancing the pack and you're at risk overcharging some of the cells. Also if you don't have cell level LVC then charging at work is best to avoid killing a cell through over-discharge. I highly recommend getting the New 16 cell BMS as soon as it is ready. Your current charger should work fine with it.

 

[leamcorp]

I'm so glad you guys are around with all these info.

I'd just got a duct tape LifePo and it only came with 2 wire charger. I didn't know it wasn't a Lifepo4 specific charger.

I have a 48v Lifepo4 - can someone point me so I can buy a charger for Lifepo4?

 

[Rassy]

flip_normal wrote:

If your current charger only has 2 wires (+/-) coming out of it then it isn't balancing the pack and you're at risk overcharging some of the cells.

I don't think this is true. It is the BMS that protects the battery from overcharging. True, the charger has been tweaked to work with the BMS properly for LiFePO4, but the standard duct tape charger still only has two wires.

 

[flip_normal]

Yeah, sorry, I wasn't sure if there was a BMS already or not. Pics of the whole setup would be good, if possible, and help to avoid any confusion. Totally agree that shallow discharge should help extend pack life.

 

[leamcorp]

flip_normal wrote:

If your current charger only has 2 wires (+/-) coming out of it then it isn't balancing the pack and you're at risk overcharging some of the cells.

I don't think this is true. It is the BMS that protects the battery from overcharging. True, the charger has been tweaked to work with the BMS properly for LiFePO4, but the standard duct tape charger still only has two wires.

I'm so confused. So how do we know if we have a Lifepo4 charger. My charger just says 48v 20ah and several lines of Chinese characters.

 

[Rassy]

leamcorp wrote:

I'm so confused. So how do we know if we have a Lifepo4 charger. My charger just says 48v 20ah and several lines of Chinese characters.

Don't feel alone. I purchased two LiFePO4 batteries several months ago, both 48V 20AH. The first was sent with a 36V charger which I exchanged with a fellow ES member that got a 48V charger with his 36V battery from the same vendor. This charger works great. The second battery came with a completely different shape/size/color/ etc. charger that is marked as 48V but seems to work more like my 48V SLA charger. I have thought of several ways to check it out, but have not done so yet. Now that I know how the LiFePO4 batteries react to a proper charger, I think I'll just try the other charger with close monitoring. If the batteries do not come hot off the charger at about 59V, I'll try the charger on one of my SLA packs, which should come hot off the charger at about 55 or 56V.

It is my understanding that an SLA charger being used through the BMS of the LiFePO4 will not harm the battery, it just will not fully charge and balance the battery. If this is not a true statement, I hope someone corrects me.

 

[dogman dan]

As I understand it, the duct tape lifepo4 chargers that come with the battery are unsophisticated sla chargers that go to slightly higher voltage than a normal sla charger. That is all lifepo4 needs if it has a bms. Some other batts come with the bms in the charger. I only found less than a volt difference between several sla chargers and the one that came with the ping battery I have. The only effect I am seeing from using the sla chargers is a very slight undercharge. If i fully charge with the sla, and then put the ping charger on it, the ping runs for about 15 more minuites. I haven't seen any balancing activity since I first got the pack. Mine is staying balanced fine, and I have checked to see. My sla chargers put out about 44 volts and the ping put out about 44.5 My ping is the 36v. With the sla chargers i usually get a battery charged to 43 volts. Since my pack is staying balanced, I have no problems with this. A lipo charger going to 58v should be ok too, on a 48 volt battery, since lifepo4 is supposed to be tolerant of overcharging. You still need to use a charger that does not exceed the charging rate in the specs, which for my ping is 5 amps. I think my 4 amp sla charger from monsterscooterparts is just the thing. 2 amps is too slow if I want to leave work early, which is like everyday.

I don't know if my sla chargers will balance the pack since it has never been out of balance since the first three charges. I did get an undercharge once and ran the pack till cutoff, but it still stayed balanced after the next full charge. They say lifepo4 likes to stay balanced and it is sure true for my pack, with about 600 miles on it.