On 11 Aug 2016 at 13:22, Barry Elkin wrote:
> I had one problem when I had a 36 volt to 12 volt DC-DC converter
> running all the time ... It ran down the [traction] cells .... I
> removed the DC-DC converter and install a separate charger for the 12
> volt batteries.
I would instead connect the DC:DC so that it's powered on only when the
tractor or EV is in use. I've done this with road EVs, where the DC:DC was
sized for around 30-50% above average load, and a smallish motorcycle
battery handled peaks.
Your method would work too, and might be cheaper, if you hadn't already
bought the DC:DC.
> I am not running a BMS.
Your choice, but I wouldn't want to use lithium batteries without a BMS. I
think it's just asking for trouble. Lithium cells are too easily damaged by
both overdischarging and ovvercharging.
IMO you absolutely need a BMS with Chinese cells because their manufacturing
tolerances tend to be somewhat loose. They'll drift apart in state of
charge unless they're kept on a short leash. Next thing you know you have a
cell that's overcharging or overdischarging. At best it's damaged, at worst
it causes a fire. Fire risk is lower with LiFePO4 cells such as the CALBS,
for sure, but it's not nonexistent.
I would use a BMS with higher quality cells too, if only because there's
more expense at stake.
I realize there's some controversy over the use of a BMS. However, not to
the sound like a preacher here, but the controversy is solely among
hobbyists. No serious manufacturer sells an EV without a BMS. In fact you
won't find a decent high-power consumer product with lithium battery that
doesn't have a cell level BMS.
The BMS is omitted only in cheap junk products, where it's likely that the
manufacturer will have folded his tents and slipped away (to start a new
business under a new name) by the time anything bad happens.
Not to be alarmist, but I would recommend against using (and especially
charging) a BMS-less lithium battery inside any structure. Keep it out in
the open and away from anything flammable.
David Roden - Akron, Ohio, USA
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