warlord385

I have some promatch gp3300. Because they are NiMH do I have to discharge them at 30amps. Do i have to discharge them at all. According to the chemistry of NiMH batteries they do not suffer from memory effect therefore to discharge them at 30amps to create a memory is not necessary. I've read all over the internet about people discharging their NiMH, but i do not understand why. Because they are NiMH they never suffer from memory effect and maintain constant voltage. Please help if i am misunderstanding something

Trips

iTrader: (16)

Here's what I do with my Gp3300 packs, and as a bonus I'll tell you why I do it:

After a heat or main, I discharge the pack at 25 amps to .9 volts per cell. I don't do this because of memory, I do this because my 1/12 car averages around 25 amps throughout the run, and I want to see how much run time was left in the pack.

After the discharge I put the pack away until the next race day.

The next race day, I charge the pack (5 amps for mod, 6.5 amps for stock) and race it.

Approximately every fourth or fifth time I race, I'll tray the pack down just before I charge it on an equalizing tray. I do this just to get the cells working from an equal standpoint, I don't think it's necessary every time, however)

I've got almost a full season on my 3300 packs, racing every weekend, with no loss of voltage or runtime so far.

T

Telengard

Check out this link from Trinty:

http://www.teamtrinity.com/tips/batts.asp

I've pretty much used Trinity's recommend tips on my batteries and haven't had any problems.

I hope this helps...

coolrcdad

Trips,
I did a search on this topic and found your advice. I just got some Promatch 3300 packs. I have an Indi Reactor 20 discharge device that brings packs down to an auto cutt-off. What's the difference between 20- and 30-amp discharge as far as battery life and performance is concerned? Is one better than the other for certain applications? Should I buy a 30-amp discharge device for NiMH?

Thanks for your help.

Trips

iTrader: (16)

coolrcdad,

Back in the NiCad days, we liked to discharge at a high rate because NiCads seemed to perform better when discharged that way (less tendency to feel "flat" near the end of a run.)

NIMH cells apparently don't exhibit this memory effect, thus I don't think that it matters whether you go for a 20 or 30 amp discharge after a run. I try to choose a discharge rate that will be approximately the same as what the car sees on the track, so I can time the discharge after the run to get an estimate of how much runtime was left in the pack. For 1/12 scale, we run 8 minutes, which would average approximately 24 amps during the race if we dump jsut after the heat is over. By discharging at 24 amps right after the race I get an idea if I had enough runtime left to go to a hotter motor or gearing setup.

For 5 minute touring car racing, I'd discharge at 38 amps if I could, again just to get an approximation of true remaining runtime. My Victor won't go that high, so I settle for 35 amps.

If you don't care to get as compulsive as I do, I think either a 20 or 30 amp Reactor will do the job just fine. If I were racing touring cars, I'd go with the 30, but again, I'd go that route to get a better idea of remaining runtime, not because I feel that 30 amp discharges benefit NIMH cells more than 20 amp.

T

coolrcdad

Thanks for replying. Good info and it applies well to us because we do both 12th stock and 10th stock and 19t mod.

johnbull

Hi guys. Greetings from Malta.

INTERESTING!!!!!!!!

We don't run 3300s yet. We still have a top limit of 3000 so I can only speak about them.

In Mod we run Panasonic UMH on my son's TC3. In stock I run Sanyo HV on my MR4. We treat them all the same way.

I charge (mod at 4 amps, stock at 6 amps) so that the cells are ready about 15 minutes before our race. I then peak once at 8 amps just before the race.

After the race I leave the cells as they have finished the race, and put them away that way.

At the next meeting, before charging I discharge down to 5 volts.

After about 6 cycles I tray them, just to equalise. I have just done that with cells that are just 5 months old and they were pretty unequal, so it was a necessary exercise. Incidentally we run the top quality Corally Pro Team cells only.

What I have found is that with every cycle the cellsloose a bit of time. The first time I tested them, when they were new, I was getting 510 seconds on my Protrak. They are now down to 450, but still give good power.

Regards

Joe from sunny Malta.