Re: (ET) Lithium batteris for EGT200

["David Roden" <etpost drmm net>]

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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