mmm not really
if the internal resistance of the cells is high then when you try and pull current the output voltage of the battery will drop meaning less current is put through the circuit.
the batteries that cook themselfs generally have low internal resistance so they will put out bucketloads of current which allows that small resistance to become a dominant heat generating factor. _________________ Mechanical engineers build weapons, civil engineers build targets
Sat Sep 18, 2004 11:17 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Is the rated current limited only by the cells ability to disapate heat?
Meaning if i used one of these blowers in my robot so that it points at the open end of my nimh battery pack with heat rings in it so the cool air can blow threw the pack would the cells be able to give out more contin current without killing them selves?
Joined: 25 Aug 2004
Posts: 21
Location: New York City, USA
Based on our in-house experience and some testing, we've updated our storage recommendations for NiMH battery packs. See the
Storing your cells
section of our Tech Tips page for more information:
In summary:
- If storing NiMH packs for a month or less, leave them discharged down to 0.9V/cell. Do not partially charge them.
- If storing NiMH packs for over a month, discharge them to 0.9V/cell and partially charge them (20% or so) to prevent any self-discharge from possibly causing cell-reversal. Be aware that the packs might have to be cycled a couple of times to regain their original capacity and voltage under load.
We've always discharged our NiMH packs down to 0.9V/cell without problems, no matter how long we stored them, but feel this is the safest advice for NiMH battery pack users. _________________ John Muchow, CamLight Systems
http://www.camlight.com
Wed Sep 22, 2004 4:41 pm
kkeerroo Experienced Roboteer
Joined: 17 Jun 2004
Posts: 1459
Location: Brisbane
Secretary of the Queensland Robotics Sports Club inc.
Fri Sep 24, 2004 12:44 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Iv just made up some of my drill nicads into packs for running my bot at home untill they die to save my good cells for battles.
How long before the drill batts die?
BTW im running two drills and a ev. _________________ Tim Team Reaper.
Wed Sep 29, 2004 10:49 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Are heat saver rings realy worth worrying about? _________________ Tim Team Reaper.
Mon Oct 04, 2004 6:44 pm
ffej Experienced Roboteer
Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW
If you've ever felt how hot the sanyo's are after the end of a taxing heat, you'de definetly think so. They cool down faster with the gap between the cells too, allowing you to charge them sooner. _________________ Jeff Ferrara
fb@ffej.net
ffej.net
Mon Oct 04, 2004 8:41 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Dose anyone know locally where i can get some? _________________ Tim Team Reaper.
Mon Oct 04, 2004 8:55 pm
Spockie-Tech Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
Just head for your local bearing or auto parts shop and buy some rubber O-rings to go around the cells. they're cheap (around 10c each), add some shock protection and give you nice spacing, with a variety of sizes and thicknesses available. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
Tue Oct 05, 2004 2:05 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
The other thing you might try if you can't get O-rings is PVC water pipe. it doesn't come in the right size, but the 25mm stuff can be slotted and expanded to make a C shape around the cell. Its a bit more rigid if you wanted something to glue together and shrink-wrap like the battlepacks. This would probably give you a bit more space than the O-rings for ventilation, at the expense of the shock absorbtion. _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Tue Oct 05, 2004 7:14 am
Valen Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
we use 2 foam sheets with holes cut in them to space our cells
with a 60mm fan sucking air through the pack (2x 14.4 V strings) it cooled from 80C down to room temp in about 10-20 minutes _________________ Mechanical engineers build weapons, civil engineers build targets
Tue Oct 05, 2004 9:43 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
I like the "intercooled" design but what a pain to cut out! any tips on drilling all those holes (apart from laser cutting )? I was thinking this might be a good use for the cheap 5mm chopping boards from Woolies. _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Tue Oct 05, 2004 10:04 am
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
I was thinking of makeing an inter cooled pack with the chopping boards too.
BTW i have found some cardboard tube from spotlight to make some heat saver rings that will fit c and d cells and i think i can find some stuff to fit sub c's too its the stuff they us for there material rolls you can get it for free _________________ Tim Team Reaper.
Tue Oct 05, 2004 7:13 pm
Valen Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
we used foam so like it was pretty easy to cut out,
its only 24 holes per sheet (and if you stack them 24 holes in total)
for our complete pack. I believe we used a hole saw to cut them.
hard part was insulating under the connections so that the steel / copper links wouldnt wear through the heat shrink on the batteries and short them out.
one old floppy disk to the rescue. _________________ Mechanical engineers build weapons, civil engineers build targets
Wed Oct 06, 2004 9:38 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Cool idea with the material rolls! I will have to check that out. I thought it would be hard to get a tight fit between the bateries and the plate with a hole saw? Perhaps the 29mm battery and a 30mm hole saw is OK?
I was going to use an adjustable wing cutter and a chopping board cut-off for a no cost test - just as soon as Master Instruments has our batteries. _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
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