38120 cells for a 12v application

[Peter Brigg]

I have a 7 amp hour lead acid gel cel battery which has a few uses:
First when I go camping and boating it provides lighting etc
Second-it provides the spark on a coil based ignition system for a rotary hoe(it was a magneto spark system which became irreparable)

I was thinking that 4 38130 lithium iron Phos cells could be linked up to do the same job with less weight and a longer life.
With the rotary hoe there is a fair bit of vibration and some knocks are inevitable with the camping use.

With only 4 cells could they be be balanced manually without the need for a BMS-would a conventional 12 lead acid charger be OK to use?
Any ideas on doing this? The cost of the 38120 cells is about $20 each so the costs either way are similar.
Thanks
Peter

 

[scoot]

Well first of all, I'm not feeling sufficiently informed (technically speaking) to comment regarding your scintillating relationship with your "hoe" , but you will probably need at least some means of electrical connection (wire & connector) for each cell end so you can either individually top off each cell one at a time on occasion with a single cell charger, (manual balancing so to speak) or with a 12v bulk charger using and LiFePO4 capable cell balancing device. As long as your cells/pack are sufficiently strong (C-rate) to motivate you devices, including starting your hoe, it shouldn't be too hard 8). But if you are talkin' about a great big HOE, then then you probably need some extra beefy electronics to protect your cells. I recall some devices for adapting Hi-C rated Headway LiFePO4 for auto ignition starting systems out here... givit a search :wink:

 

[999zip999]

My hoe runs on 2c cells for over a half and then it's an earthquark. Even at that time it's best just to watch. Hoe bott you.

 

[Jeremy Harris]

I have been running a 4P pack of Headway 38120 cells for a fair while now, as a "12V" battery substitute. I regret to say they do need some sort of balanced charging, as they will drift out of balance fairly quickly without. My experience is with the older Headway cells, those in cardboard tubes, but I would hazard a guess that this is really just a characteristic of pretty much all LiFePO4 cells. If balanced very well initially it takes a while longer for them to get out of balance, but it still happens.

PS: scoot - How the heck can you have a "relationship" with a garden implement? Inquiring minds need to know.

 

[Peter Brigg]

Thanks for those ideas-the rotary hoe is hand cranked so there is no need for lots of power for an electric start motor.
From your responses I think a BMS would be a good idea.
Where do you buy a BMS?
Any places on this forum to look up how to wire them?
Thanks
Peter

 

[Jeremy Harris]

Buying a 4 cell BMS is difficult, maybe impossible. I made mine, as there didn't seem to be another way to get one.

One way of keeping your 4 cell pack balanced would be to charge it with a balance charger, one that either charges each of the 4 cells individually, or one that charges by sensing the voltages across the cells, like an RC type charger. Some of these are pretty cheap (like this one: http://www.hobbyking.com/hobbyking/store/__14857__HobbyKing_50watt_5A_X_Charger_Balancer.html) and would run from a 12 V power supply (maybe your existing lead acid charger) and manage the charge and balance the cells.