Caring for LifePo4 batteries?

[Bohh]

Hi,

I've decided to use a LifePo4 for my ebike. It will cost more but I think it will be better in the long run. I was wondering if there is anything important I need to know while using these. For my R/C planes I can not over discharge or over charge Lithium Poly batteries, or I will risk explosion. I must constantly balance the cells, and check voltage levels.

With the duck tape batteries, do I need to do any of these things?

I don't understand the BMS... is that something to be concerned with or just ignore it and let it do it's thing?

Thanks!

 

[swbluto]

Supposedly, a good BMS will do that and more for you!

It just so happens that not many BMS's are good(at least for the cheaper packs), to my chagrin. Some will prevent over-discharge and over-charge, but there's still the possibility that *eventually* a few cells will go out of balance and you'll need *gasp* check voltage levels to spot the culprit and take the necessary measures to bring that lagging cell up with the rest pack.

If you're unlucky, like me, you'll find the capacity of a cell severely diminished(for some reason) and the cell will need replacing or you'll forever be limited by that capacity of that runt(I'm currently at 7AH from my 10AH ping 1.0 pack: Ping's now at ping 2.0 so it may've been bettered.), or you can take more desperate measures like cutting the cell out. I'd definitely suggest the cylindrical type of cells(the nut and bolt version) over anything that relies on soldering(like duct-tape packs) for the current state of the market: The eventual problems that'll surface will be so much easier to repair.

I'm making my next purchase cylindrical. And... replacement cells are going to be easily obtainable. And, I'm going to design my BMS or buy a knowingly competent one. The few extra hundred dollars for better performance, longevity and increased reliability is well worth it down the road IMO. Plus, they can be re-used and re-configured with ease for any other future projects.

 

[dogman dan]

It can be luck of the draw too. My pack, from Ping, has stayed balanced all summer with no problems. Others have had issues with smaller batteries or larger motors being a poor fit when combined. With the duct tape batteries a few main rules of thumb have emerged in my opinion.

Protect em. The first time a bike falls over has damaged a few batteries. So you need to build or buy something to protect em.

Charge em all the way. This helps keep em balanced.

Don't connect two together unless you use diodes. Bms of one tripping can fry the others bms.

Dischage them less that 100% Like other batteries, the risk of ruining them is less if you don't run em completley dead routinely. Again helps to keep em balanced.

Don't exceed the c rate. Same as any battery, they hate it.

One think I'd like to see different on duct tape batteries is to have the thing broken up into cell units, with some type of easier to cut connection between the cell groups or whatever it's called. That way your could snip a wire to remove the runt cell group, and then either replace the whole group, or at least more easily work on one cell group at a time. The current connections work well, but are hell to work on later. 12v packs that each have thier own bms would be nice too if you could connect em any way you wanted.

 

[Bohh]

Do I have to do anything special to "break them in" when getting them?

Does it harm them to charge them up when they are not discharged a lot? Does it hurt to run them if they are not fully charged?

I plan on using a 12ah 36v LifePo4 pack on a Ampedbikes 500w motor. Danny from Ampedbikes says it will draw 19 amps up hill. Will this pack be ok for that?

Thanks!

 

[Link]

Do I have to do anything special to "break them in" when getting them?

Nope. They will increase a bit in capacity over the first dozen cycles or so, however.

Does it harm them to charge them up when they are not discharged a lot? Does it hurt to run them if they are not fully charged?

No, assuming a proper charger, and no, assuming a proper BMS.

I plan on using a 12ah 36v LifePo4 pack on a Ampedbikes 500w motor. Danny from Ampedbikes says it will draw 19 amps up hill. Will this pack be ok for that?

It should, spec wise, but check with Ping, anyway.

 

[swbluto]

It can be luck of the draw too.

If you're unlucky, like me,

That's what I think as well. There's variation in manufacture so it's not odd to see someone with a "dud", so to speak, eventually. Though, I have a feeling there's a significant percentage of ping 1.0 users who, after 200-300 cycles, have unusually diminished capacity if they're the type who don't periodically manually rebalance the cells: Not necessarily a 30 percent decrease, but something on the order of 10-20% due to one(or more) cell(s) "prematurely aging" which then limits the pack as a whole. But, it's not like that matters much when you nominally have 20AH.

I just did an analysis and... oh my god... you SHOULD NOT parallel Ping's batteries(Even with diodes!). I suspect that's may have accelerated one of my cell's death with the previous owner.

 

[Bohh]

How would you go about manually balancing the cells?

 

[swbluto]

How would you go about manually balancing the cells?

Assuming you're comfortable with electronics, after charging the battery and disconnecting the BMS from the cells with the ribbon cable, you'd basically hook up a 3.3 voltage source(if the cell is less than 3.3V) to the cell that has a lower voltage than the others. Once it reaches 3.3V, you'd hook it upto a 3.7V voltage source until the cell reaches 3.7 volts. Re-connect the BMS and you're good to go.

By the ways, removing all the duct-tape to get to the cells is a sticky pain in the rear.

If you're not comfortable with electronics, you have two main options: Let someone else do it or become comfortable with electronics. If you have a power supply that's hanging around that provides a voltage greater than 4 volts or so, you can use a potentiometer to divide the voltage(After hooking it up) to the necessary voltage and you'll need a multimeter to check the voltage just to make sure you have it correct.

Or, you can do what I did, and just buy an adjustable power supply. I'd heavily suggest avoiding that option, though, unless you know what you're doing and you have some future use for it. It's really easy to mess up and they're not cheap. You can ask ping if he's selling a single-cell charger or you might find one on eBay: That's an easier and financially cheaper option(Should be, anyways).

Here's a single cell charger: https://s.p10.hostingprod.com/@www....og/product_info.php?cPath=1_23&products_id=28

 

[dogman dan]

Hmm, maybe not so much luck after all? I haven't heard of too many problems with Li Pings batteries that didn't have something li does not approve of behind it. The only one I can think of had a broken bms wire. Maybe a couple of bad bms cases, but I don't recall any bad cell cases where the use was just a normal 500 watt bike.

As for riding the bike without charging, not a problem as long as you are not riding till the bms cuts out. The bms protects the cells from overdischarge, but I think It's unwise to rely on it every ride. What I do, I have 20 mile range, and my normal route home is 15. That leaves me rarely riding till cut out. In 1200 miles I have rode till cut out 4 times now. Mostly as a result of the flaky connection on a charger I was using. 25% reserve will go fast if I have to ride home into a 30mph wind for 15 miles.