Looking for good 7070260 pouch cell LiFePo4

[tongxinpete]

Hi, Looking for above cell in UK / Europe to repair pack. Only $14 from Bmsbatteries but shipping a killer.
open to other idea such as can I substitute another cell same chemistry & roughly same Ah on BMS common to both. Otherwise am thinking as last resort to get 8s BMS 24v nom, rescuing some of the pack & going series with 1 SLA brick. Even here the supply of small (15A) BMS for this dried up. Can only find this,
http://www.ebay.co.uk/itm/Battery-Protection-BMS-PCB-Board-for-8-Packs-24V-Lifepo4-ion-Cell-40A-w-Balance-/131574426689?hash=item1ea2726c41:g:UU8AAOSwqu9VKmOZ
Is 25 / 40A max, can I run it at a lower max amps on my pack or totally unsuitable?

 

[Deleted member 4366]

Surely, it would be more sensible to get the correct cell from BMSB. If you buy a SLA and a BMS, that'll cost about £50 and it'll be really crappy. How much does one cell cost from BMSB?

 

[tongxinpete]

The cell is £10.78, Shipping is £ 27.24 so £38.02 in total (without any UK customs charges). If I do get a Q128 as well for the other project then the cell adds no more shipping cost to the motor order.
On the other side of the coin the remaining cells are several years old but low cycles. The SLA brick I already have. These cells have a max C rate of 15A.
At the time the high C rate cells were not offered, I would not go with them now. So it is a question of life left in the other cells.

Interested anyway in the theory of can I use a higher amps BMS than the one I need, the cells would be limited by a 15A DC breaker backed up by an HRC fuse as now. Also how to charge this theoretical set up, could I charge the LiFePo4 & BMS in series with the SLA @ 36v, OR do I need to charge the Li cell group @ 24v nom, & the SLA separately on its own charger. I have various chargers lying round so not an issue here. I was told that the same charger will work with LiPo4 & SLA but not Li ion. My only cost is the BMS, was surprised at the difficulty of finding the ideal 15A nom 24v LiPo4 from the HK sellers. Will look further, motivation limited money for hobbies.

 

[Deleted member 4366]

One of the functions of the BMS is to limit the current to protect the cells. It doesn't make sense to fit a higher rated one. 15 amps from those LiFePO4 batteries is already quite high. 20 amps is about the limit. Charging in series is theoretically possible, but could be disastrous if either battery developed a problem because there's nothing to shut off the charging.

If you need some cheap bits for a project, I've got loads of stuff and if you want to have a go at building one of those Vruzend batteries, I've got loads of free cells.

 

[tongxinpete]

Thanks for the kind offer, but two things, I was completely unaware of Vruzend, only had time for a brief look yet, seems a great new idea, will study carefully. The 128H project - well I would be offering my time free but feel the end user must stand parts cost, if the thing should go ahead. He is far from poor.
Looking at Vruzend etc & the dominance of the 18650 cell in today's market, it seems there has been a shift from pouch cells & toward Li ion chemistry (despite the fewer cycles it offers). So am really looking at a stop gap way of using up the pouch cells, when the one puffed it slightly deformed another.
So I have my doubts, the 24v way would leave me a couple of spares.
I take on board the points about the 15A BMS - seems my gut feeling was correct here. There are a lot of SLA traction batts still around, mainly in disabled scooters where the batt weight is an integral part of stability in some designs. I seem to remember a period when some SLA was being used in series with LiPo4 on ES, not ideal I know, just wondered if viable. Work now but I have much to study later, Thanks