[MRCA] Batteries; (Was On Patrol Cuttyhunk Island)

[Al Klase]

Pater,

Ah ha!  The secret word was "BMS."  I'd been kultzing around with 18650 
cells, but was uncomfortable with keeping them under control. Thanks for 
the info.

Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

On 9/24/2016 5:47 PM, Peter Gottlieb wrote:
> When I can get cells with straps welded on that's the best but in my 
> case I got the cells out of surplus packs so what I did was use a 
> Dremel cutting disk to carefully cut the nickel alloy weld straps 
> leaving short bits I could easily solder to. Then I just soldered 
> short pieces of teflon wire to make up the pack.  These aren't 
> protected cells, they are just standard A123 iron phosphate 
> nanoparticle cells, in this case the 26mm diameter ones.  For the 515 
> pack it is a rectangular block of 8 by 2, and wired as 8S2P. For the 
> 2000 I made a little jig to glue sets of 3 cells together then glued 
> four of those to make 4S3P blocks. These particular cells are rated 
> 2.3 AH although they all do better than that with most over 2.4 AH.
>
> I use BMS boards I but off of ebay which are all Chinese.  There are 
> no great ones out there that are small and do exactly what I want. But 
> many are close enough.  I want two things, cell balancing and under 
> and over voltage cutoff.
>
> These boards resistively load cells (or more precisely cell groups) 
> which go over a certain voltage.  This preferentially charges the 
> other groups.  It's a subtle loading but that's all that's needed 
> because it improves the pack balance at every charge.  If you don't 
> overcharge or overdischarge a pack it is amazing how long you can use 
> it without any balancing or protection, as in years of daily use.  But 
> you really should have a balancer especially with cheap Chinese cells 
> if you use them.
>
> These little boards have voltage monitoring for each cell group and 
> will trigger on any one going under or over voltage by opening some 
> power MOSFETs to interrupt charging or discharging as appropriate.
>
> Without protection, if you under voltage a pack, immediately recharge 
> it as leaving it over discharged can permanently damage it.
>
> If you overvoltage an iron phosphate pack enough, cells could vent. It 
> will be an odd but not overpowering kind of smell and the cells that 
> vented will soon dry out and be useless.  Sort of like what happens to 
> a vented electrolytic capacitor.  Any vented cells must be replaced, 
> ones that didn't vent should still be fine.  If you over charge a 
> cobalt oxide or similar lithium ion cell you can have a vicious fire 
> or explosion.  Charging any kind of pack of those type of cells is 
> inherently risky, more so with amateur equipment which hasn't gone 
> through a lot of safety qualification.  I have just a few of that type 
> of pack around and I charge on a metal sheet and never overnight.  In 
> contrast, I've always charged iron phosphate cells without worry 
> although I try not to ruin them with overvoltage as sometimes I've put 
> a lot of time and effort into building the packs.
>
> With the BMS board you just treat the pack like a lead acid battery.  
> A 12 volt pack?  I charge to 14.4 volts float.  28.8 volts for the 515 
> pack.  You can actually go higher but it hurts you on charge as the 
> BMS will cut out on overvoltage before the cells have fully absorbed 
> full charge and you then have this cycling of too much current then 
> none.  Yes it will work but not ideally.
>
> Maybe tomorrow I'll play some more with the solar panels.
>
> Peter
>
>
>
>
> On 9/24/2016 3:48 PM, Al Klase wrote:
>> Hey Peter,
>>
>> I'd like to hear more about your batteries.
>>
>>   * Are you using holders or welded straps?
>>   * Are they "protected cells"?
>>   * How do you control charge and prevent over discharge?
>>
>>
>> Inquiring mind want to know.
>>
>> Al
>> Al Klase – N3FRQ
>> Jersey City, NJ
>> http://www.skywaves.ar88.net/
>>
>> On 9/24/2016 12:03 AM, Peter Gottlieb wrote:
>>> Great fun to get out in the field for some portable operations with 
>>> mil radios.  I was out with a digital head PRC-515 as well as a 
>>> Racal Syncal 2000.  The 515 has a H-189 handset, the racal a 
>>> Clansman RA-250.  Both have lithium ion packs I built out of A123 
>>> 26650 M1B cells:  4.6 AH 26.4V for the 515 and 6.9 AH 13.2V for the 
>>> 2000.  They powered the radios flawlessly and were very light.
>>>
>>
>>
>>
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