72v Charging options, please help me decide!

[Kartman]

So, I'm building a high powered go kart. 12kw outrunner, 700w kelly. It's all coming together except I cant figure the best way to manage the pack.

I've got a single 72v pack made from 24 high quality Lifepo4 cells. I'm not going to run a BMS, too complex, plus finding one that can handle 24 cells with peak current round 250amps isnt easy or cheap. On the discharge side I'm going to run several metres and alarms on the weakest cells. No problems. The bit thats doing my head in is how to get charge into these things.

I was set on running three 8 cell balance chargers from hobbyking, but, thats still kind of complex and expensive. Now I'm back to the idea of running two 36v smart chargers into each half of the pack. I'll be bottom balancing the whole pack and using a single cell charger periodically to keep it balanced. I can pickup two 3A 36v Lifepo4 smart chargers for $50 each. Slow charging from what I read balances cells better. Charging time isnt a concern so low power chargers would seem to be the way to go.

So I guess my question is, if I go two 36v chargers, is it simply a matter of plugging them into half the pack each and letting them do their work? How well are they likely to get maximum balanced charge into these cells? I suggest two 36v chargers because I presume they'll balance the cells better if they only have 12 cells each to deal with?

Or should I get a 72v charger like http://www.batteryspace.com/Smart-Charger-3.0A-for-76.8V-24-cells-LiFePO4-Battery-Pack-100-240V.aspx, and just balance with a single cell charger occasionally?

Whats the pros and cons?

Yes, I'm a noob, that needs to be acknowledged Any thoughts on the above would be greatly appreciated!

 

[dogman dan]

Whether a 36v or 72v, a "smart" bulk charger cannot balance your pack. So get the 72v, no advantage to 36v I can see.

There is a simple solution, put a bms on the pack, but use it just for charging. That will simply and easily keep your pack top balanced. A separate set of wires bypassing the bms can be used to discharge.

You will of course, need a low voltage cutoff, warning, or something. You will be on your own for making sure you do not overdischarge.

 

[dnmun]

you could use two of the D131 in parallel and have 240A surge capacity and run at 160A continuous. i use a pair on my 44Ah lipo pack which gave me 95A through one and 90A through the other at max power. i also use a pair on my 87Ah lifepo4 pack but never measured max current in them.

or just run without one and replace the pack whenever you need to.

 

[knighty]

why not use a BMS

but wire the controller directly to the bike ?


then the BMS would only control charging. you could wire it's cut out into an LED, so you could have an LED warning if any cell voltage dropped too low ?

then pretty much any kind of charger or 88v psu will do ?