[Milsurplus] Li Ion batteries

[James Whartenby]

By code, do you mean National Electric Code?
As far as I understand the discussion, the charger is floating and is a trickle charger.  The FET switch in question only disconnects the charger from the battery it is charging to prevent a higher then normal battery terminal voltage.  It is not switching the battery load so should not see a voltage much higher then the battery terminal voltage.  
If it is a "smart" charger, when the terminal voltage is much lower then it would be when the battery is at it's lowest terminal voltage, the charger will not turn on.  If the terminal voltage is much higher then what would be expected, the charger again will not turn on.
The system  described is below 30 volts, so if the NEC code still applies, could you cite chapter and verse?  It would be interesting to know what issue is being addressed.Jim

      From: Peter Gottlieb <kb2vtl at gmail.com>
 To: Bill Cromwell <wrcromwell at gmail.com> 
Cc: milsurplus at mailman.qth.net
 Sent: Saturday, November 4, 2017 1:52 PM
 Subject: Re: [Milsurplus] Li Ion batteries
   
I disagree. Draw it out. Any series switching element must be rated for the string voltage. This is also a code requirement. 


Peter

> On Nov 4, 2017, at 2:47 PM, Bill Cromwell <wrcromwell at gmail.com> wrote:
> 
> An FET inside a 12 volt pack won't see or crae about and batteries in series above or below it.
> 
> 73,
> 
> Bill  KU8H
> 
>> On 11/04/2017 01:01 PM, Peter Gottlieb wrote:
>> Generally yes. During normal use everything is fine; it is during charge and at end of discharge where things can go wrong. You already mentioned separate charging so that’s off the table. At end of discharge packs have electronics which open up a FET to keep cells from getting too and being damaged or posing a hazard. The FETs may not be rated for the higher voltage of series packs and fail shorted, posing the hazard. See if you can find out what their max voltage is.
>> 
>> Also use iron phosphate cells, they are much safer.
>> 
>> 
>> Peter
>> 
>>> On Nov 4, 2017, at 12:43 PM, John Watkins via Milsurplus <milsurplus at mailman.qth.net> wrote:
>>> 
>>> Just wondering if you could series up 2 12 volt Li Ion batteries?  I need a 24 volt unit, but have seen 12 volt units complete with chargers and thought can I use those.  Would have to charge separately I think.  Any ideas?
>>> 
>>> Thanks,
   
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