[aprssig] Appalachian Golden Packet Battery Report
bruninga at usna.edu
Sat Jul 15 23:18:50 EDT 2017
Ran the entire ATGP event with a D710G on high power from about 1100 to
maybe 1500 and used maybe under 6 AHrs of battery (estimate). First D-cell
3 AH NiCd pack died about half way through. But sun came out and second
one was still going strong to the end (with maybe 1A coming in from solar).
But I also had a TESLA Lithium battery pack in reserve. Here is the
background I posted a day ago on APRSSIG...
On Fri, Jul 14, 2017 at 5:06 PM, I wrote:
> Lesson re-learned on NiCd charging: Several years ago I made three 12v
> batteries from ten D cell NiCd’s each.
> They have been a huge disappointment. I have tried to use them at GD hill
> and occasionally once or twice a year on critical field work and they
> always fail far earlier than estimates. But I had always just charged them
> the night before with a fixed voltage charge of 14 volts since I most often
> forget about batteries I put on charge and end up ruining most of them.
> Charging at fixed voltage is safe…(but apparently useless for NiCd's! See
> For the AT Golden Packet event, I left them on my usual 14 volt overnight
> charge and they were “fully charged” by morning, only drawing a 50 mAh each
> in the morning at 14 volts..
> But to test them, I put them on a battery analyzer at work and their
> capacities came in at 10%, 8% and 3%! No wonder they have been so useless!
> Then the battery analyzer quick charged them at 1C rate for 1 hour with
> them getting up to 17 and 18 volts while pushing in the charge current,
> then a 4 hour equalization charge of 0.1C or 400 mA.
> Then he analyzer retested them and got 75%, 65% and 85% of rated
> capacity! Just in one charge, but that took most of the day and so I took
> them home and planned on using them for the event anyway.
> So, Apparently little-used NiCd’s are not going to get a good charge from
> a FIXED voltage charge! Duh....
> Wish I had time to cycle them two more times. On batteries at work we see
> huge recoveries from little used NiCd’s when “rejuvenated” which is the 3
> cycles of charge and discharge I started with above.
Then I did the same test with several 7 and 8 AH Sealed Lead Acids. They
were coming in at around 50, 60 and 68% rated capacity. SO they actually
had more capacity than the NiCd's. So, next I weighed them all and found
out quickly that the Leads were coming in at under 1 Ah per kg, the NiCd's
were coming in at over 2 Ah per kg even with their not-full capacity.
Next I found some TESLA Lithium cells like the ones used in the Tesla Model
S. (Actually, of course these are just cells from a laptop) and so I found
12 of them and spent more time than I had available cobbling together a 6
AH lithium pack. Was astonished to see it come in at nearly 10 AH per kg!
But the problem is, I have never used Lithium before and an initial test
showed their thermal cutouts would cut out immediately on 7A draw (D710 on
high power needs maybe 10A?) so I decided I could not use Lithiums directly
but could use them in parallel to keep the NiCd's up. Turns out, the
rejuvenated NiCd's worked fine and so I didn't have to use the lithums...
But, NEXT year, Ill change out the thermal cutouts and go lithium for me!
That will cut battery weight in the backpack to only 20% of what we have
used in the past.
Oh, 4 in series gives 16v, so I put three 10A diodes in series to bring
that down to 14v for the pack.
A nice spinoff of EV's!
Maybe by next year I will also have an EV trail bike to ride to the top of
the hill too...
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