Chinese LiFePo4 battery concerns

[morphix]

I decided to unwrap one of my 36v 5Ah Chinese batteries earlier which I bought off eBay. Mainly to see the size of the cells and assess if the size of the battery could be changed to suit a housing enclosure as I had trouble finding a housing tall enough. My reason for wanting to put the battery into an enclosure was to better protect it in case it should ever accidentally got dropped.

It seems, looking at the fragility of the cells, my concerns are justified.. the cells appear to be made from a kind of soft foil material that is very easily marked and damaged (you can see this from the marks left by the scissors I used to remove the tap on the last picture below).

I wonder is it safe to continue using batteries wrapped in just tape if they are this fragile? Perhaps it would be a lot safer to pad them with foam inside a plastic ABS box...

 

[flecc]

Shouldn't be a problem as they are tough, even the highest priced li-polymers are like that, the high end Panasonic one shown below for example, not even taped together:

 

[morphix]

Oh that's surprising, but reassuring to know..I thought perhaps these particular batteries might be cutting some corners to reduce costs. Do you think the marks I made with the scissors could potentially alter the internal resistance of the cells making them risky to use? It's only surface marks, none of the foil has been pierced luckily. Bit foolish of me to open the battery with scissors!

 

[flecc]

I very much doubt it could have any effect. The big advantage of li-polymer is the way in which the cells can be any shape and be flexible, so they can withstand a lot of abuse.
.

 

[onmebike]

I think your choice of a 5ah pack may have been a wise move as its the only capacity using 5ah cells where each individual cell is monitored by the Bms.
In the larger capacity packs, cells are linked in parallel, 2 for 10ah 3 for 15ah and so on. The Bms cannot monitor individual cell's in these cases and see's each parallel block as a single cell possibly resulting in poor cell management.
One or more faulty cells in a parallel block may not be detected by the Bms because the remaining good cell/s may fool the Bms into thinking all is well.
Obviously a big drop in performance would be evident if this were the case.
A possible problem with the 5ah pack may be the C rating which would be half of that of a 10ah pack if I'm correct?
I'm no expert and may be wrong in which case I'd welcome some input from the experts.

 

[aseb]

The endless sphere forums are always worth a look for this kind of thing, as is U Tube.

 

[morphix]

I think your choice of a 5ah pack may have been a wise move as its the only capacity using 5ah cells where each individual cell is monitored by the Bms.
In the larger capacity packs, cells are linked in parallel, 2 for 10ah 3 for 15ah and so on. The Bms cannot monitor individual cell's in these cases and see's each parallel block as a single cell possibly resulting in poor cell management.
One or more faulty cells in a parallel block may not be detected by the Bms because the remaining good cell/s may fool the Bms into thinking all is well.
Obviously a big drop in performance would be evident if this were the case.
A possible problem with the 5ah pack may be the C rating which would be half of that of a 10ah pack if I'm correct?
I'm no expert and may be wrong in which case I'd welcome some input from the experts.

Interesting, learn something every day! I haven't really had chance to put either of the batteries through their paces yet but when I do I will report back on how well they perform and how long it lasts. On Friday when I did my first test ride (which granted was only 20 minutes) I used the throttle the whole time and a lot of stopping and starting plus a big steep hill, none of which seem to have any effect on the battery life. It was still showing full power when I returned. I have put the battery on charge today and it only needed a top-up charge of a few minutes to reach full charge.

 

[flecc]

I think your choice of a 5ah pack may have been a wise move as its the only capacity using 5ah cells where each individual cell is monitored by the Bms.

In practice this need not be a problem. The quality Panasonic unit 10 Ah battery that I illustrated above has paired 5 Ah cells in parallel and has a two year warranty. Some of those lighter used batteries have now been in use in Kalkhoffs since late 2007 and still ok at 3 years.
.

 

[onmebike]

In practice this need not be a problem. The quality Panasonic unit 10 Ah battery that I illustrated above has paired 5 Ah cells in parallel and has a two year warranty. Some of those lighter used batteries have now been in use in Kalkhoffs since late 2007 and still ok at 3 years.
.

I wonder if parallel cells could be linked by diode's so the Bms could monitor each cell individually, but then the Bms would be much more costly.

 

[flecc]

I wonder if parallel cells could be linked by diode's so the Bms could monitor each cell individually, but then the Bms would be much more costly.

That should be possible. I know the Panasonic battery has reverse polarity protection, but don't know how that is organised or if the cell pairs are included in that.
.

 

[Deleted member 4366]

Remember that 5ah Chinese lifepo4s are only rated to supply 5amps (10 amps max) - not enough for an e-bike. They may well be able to deliver more current than that, but probably at the expense of shortening the service life of the battery. If you want a small, light battery, other battery technologies would be better.

 

[morphix]

Remember that 5ah Chinese lifepo4s are only rated to supply 5amps (10 amps max) - not enough for an e-bike. They may well be able to deliver more current than that, but probably at the expense of shortening the service life of the battery. If you want a small, light battery, other battery technologies would be better.

Seems to be ok far, no problems to report on performance..but what would you suggest as alternative technology and can you recommend any suppliers?

 

[Deleted member 4366]

Seems to be ok far, no problems to report on performance..but what would you suggest as alternative technology and can you recommend any suppliers?

LiPOs. A 5AH pack can give 100amps or more. They're not as safe as LiFePOs, but you can't have everything. It seems that everything has advantages and disadvantages. You can get a 5AH LiPO pack for less than £60, but you need a LiPO charger/balancer and something to show the state of discharge.
18.5v 5200mAh 20C LiPo 5S 18.5 Volt RC Akku Battery WF on eBay (end time 28-Feb-11 13:39:01 GMT)
Mystery MY-650 Lipo Balance RC Battery Charger NiMH 6s on eBay (end time 25-Feb-11 13:44:08 GMT)
Lipo Battery Voltage Tester 1S-8S link Low Buzzer Alarm on eBay (end time 26-Mar-11 09:08:34 GMT)

 

[NRG]

I wouldn't advise anybody to use Lipo's for every day use unless they fully understood the issues. Charging is a problem, to get 36v 5Ah you will need two packs in series meaning you will need to split the pack each time you want to charge using an RC charger and balancer, so you will need two chargers one for each half to keep charge time down. Then there's the HVC and LVC which you need to be very careful about not only to extend the life but also to stop them exploding. There's no ready made BMS than can be bought and added, although the tppacks one is viable but very DIY.....All this makes it quite a faff and certainly not plug 'n' play that the average person is probably looking for.

Having said that I use them on my Peugeot and think they are fantastic but I've had my share of scares with them...

 

[jbond]

Mentioned this on a couple of threads. Cellman on the ES for sale threads is selling custom packs of A123 cells with a 30A BMS. For small packs of 12s-1p (36v2.3Ahr) or 12s-2p (36v4.6AHr) this looks like a very good option. High C rating, LiFePo safe. Built in BMS. There's a couple of threads about using RC LiFePo A123 batteries on Bromptons. It shouldn't be hard to buy a BMS from Cellman for these with a 2A 36v LiFePo charger as an alternative route. Even 1P of A123 cells should be able to cope with a typical 250w controller.

This is all getting a bit costly, but there's a holy grail here. That's building up a lightweight bike with a pair of batteries. One 12s-1p for running down to Tescos or getting from Waterloo to the City and back. And a 12s-4p (or bigger) for weekend jaunts in the country. Mount one in a detachable frame bag and the other in a rack mount. Use cheap 2A LiFePo bulk chargers. Nothing else on the bike needs to change.

 

[Trout]

It seems, looking at the fragility of the cells, my concerns are justified.. the cells appear to be made from a kind of soft foil material that is very easily marked and damaged (you can see this from the marks left by the scissors I used to remove the tap on the last picture below).

I wonder is it safe to continue using batteries wrapped in just tape if they are this fragile? Perhaps it would be a lot safer to pad them with foam inside a plastic ABS box...

You should be really careful with lipos. If you poke a hole in the foil, the battery will burn/explode. Search for "Lipo fire" on youtube and you'll see what i'm talking about. I cant even imagine what would happen to that big pack of lipos you got, if you would to damage it.

Also, never ever charge a lipo unattended!!
Second also, if a battery pack get "fat" (bloated,inflated), dont use it. It can selfignite.

 

[jbond]

You should be really careful with lipos. If you poke a hole in the foil, the battery will burn/explode. Search for "Lipo fire" on youtube and you'll see what i'm talking about. I cant even imagine what would happen to that big pack of lipos you got, if you would to damage it.

Also, never ever charge a lipo unattended!!
Second also, if a battery pack get "fat" (bloated,inflated), dont use it. It can selfignite.

There's LiPo and then there's LiFePo both packaged in soft envelope pouches. What you're saying is all true about RC Lipo from suppliers like Turnigy[1]. I'm not sure it's true or true to the same extent for soft cased LiFePo as seen above and in typical Ping batteries.

One question I had. What chemistry are RC LiPo typically? It's surely not LiCo but maybe it is? LiMnO4 (as used in typical Phylion e-bike ally cased batteries) is considerably safer than LiCo and shouldn't have the same fire danger.

The safest and easiest to handle are probably A123 cells. They've got the high C rate of RC Lipo but are LiFePo and also have a fairly solid casing. You pay for that in quids, weight and volume.

 

[morphix]

You should be really careful with lipos. If you poke a hole in the foil, the battery will burn/explode. Search for "Lipo fire" on youtube and you'll see what i'm talking about. I cant even imagine what would happen to that big pack of lipos you got, if you would to damage it.

Also, never ever charge a lipo unattended!!
Second also, if a battery pack get "fat" (bloated,inflated), dont use it. It can selfignite.

Ok thanks for the advice..lesson has been learned, I just had no idea they would be so fragile.. I checked the battery over and appears to be no holes just some slight indents.. I haven't used this battery yet but I will take extra care and charge it supervised.. I'm currently looking for a suitable sturdy plastic housing for my batteries (proving difficult to find them large enough) and will use foam inside to protect them.

 

[jbond]

There's a thread on here about cheap lifepo where there was a lot of discussion about boxes. See if you can find a CD case where the CDs are stacked sideways CDs are a bit smaller but roughly the same as the battery pouches. Rip out all the guiderails and the battery might fit.

 

[morphix]

There's a thread on here about cheap lifepo where there was a lot of discussion about boxes. See if you can find a CD case where the CDs are stacked sideways CDs are a bit smaller but roughly the same as the battery pouches. Rip out all the guiderails and the battery might fit.

Excellent idea why didn't I think of that! I have a few of those lying around somewhere in storage.