Hot hot batteries after 20A discharge

[bholio]

I've decided to 'step up' mine and my son's racing efforts a bit this year. I'm kinda tired of having my batteries fail at the 4:30 mark in a 5 minute race and I'm tired of having my car duck-taped together etc.

First step was to purchase some good chargers. I ebay'd an Indi 16x3 v2.5 pro and a Reedy Quasar pro (Need to send it in for recall still). Also ended up with an indi Octane 2 discharger. I'm out of money now, and to make do with my current batteries. With these chargers, I can now make the move the NiMH when funds allow.

I hooked up one of my old matched Sanyo 2000 NiCD and ran it thru the 20A discharge on the Reedy. I've never had a battery get this hot. I couldn't hold it.

Next time, I'll drop the discharge rate down to 10A, but I thought that 20A was the recommended discharge rate and that the hardcore guys go up to 30A. Is this heat just an indication that my battery is very old (which it is?). Or am I wrong in using 20A?

Thanks

[fury_dice(2)]

quote:Originally posted by bholio

I hooked up one of my old matched Sanyo 2000 NiCD and ran it thru the 20A discharge on the Reedy. I've never had a battery get this hot. I couldn't hold it.

Next time, I'll drop the discharge rate down to 10A, but I thought that 20A was the recommended discharge rate and that the hardcore guys go up to 30A. Is this heat just an indication that my battery is very old (which it is?). Or am I wrong in using 20A?

Thanks

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id="quote">id="quote">

Was the Sanyo NiCd a stick pack? If so, won't the heat-shrink and tight packing of the cells reduce the heat dissipation? I'm guessing that a) discharging cells does get them very hot and 'race' packs will dissipate the resulting heat better as they aren't so tightly packed or covered in heat-shrink. Of course I could be wildly wrong!

[bholio]

Nope, side by side pack with no shrinkwrap.

[GPZ1000RX]

A 20A discharge will get batteries hot and the older the batts the hotter they tend to get.

If they are getting much hotter than when you are racing use a more gentle discharge rate (as you suggest!)

Might it be time to pension off your 2000s anyway? You can always use them for practise and general mucking about.

I've always found that "budget" matched packs are good value, the matching seems to improve performance and battery life quite a lot.

I once had 6 budget 1700SCRC stick packs, all used for a season, I took them all apart and got my local friendly battery man to run them once through his turbo matchers and label them up.

Got them home and matched them up as best I could and reasembled them into "race" packs.

The results were impressive, the worst "new" pack was as good as the "old" worst pack, all the others were improved by about 10%+

I've always bought matched packs since, they are well worth the extra cash.

[tamiya-phile]

holy ****, thanks for mentioning the recall on the reedy pro. my batteries get too hot to the touch while charging with the pro and I was not sure why. generally, i unplug it before it finishes charging. but for a 180USD charger, that's kinda lame.

darwin

[WillyChang]

When trying stunts like that, my batteries sit on a bank of fans.

Your cells would get some moving air when they are whizzing around in your RC, so its not logical to discharge them merely sitting on your bench. No surprise they get hot, a lot hotter than if they're being run.

If your car really draws ("on average") 2000mA within 4.5 mins, perhaps you should upgrade to 3000/3300.

Modern motors are less efficient than those designed even 5 yrs, as today we've got ample run-time to waste. Back when 2000 was the king, dumping was always an issue.

[Jimmy_GT-R]

A very good point from Willy there. older motors are far more efficient than the new breed of motors we now have. Battery capcity is just getting insane and unusable, for racing. Nosram now has 3500 packs for sale at £30, and soon Sanyo will relese 4000nimh packs and cells. Why I really don't know, as even with a 12 turn motor i can easilly make the 5 minutes of the race before the pack starts to drop off too much and i run Powers Matched 3000GT-R cells, can you imagine 4000nimh batteries[:0][?]. But I have to say batteries are very important to the speed of the car. I though my 2000 and 2400nicads were punchy, until I got the new breed of 3000nimh cells and there just great, more punch and speed than the nicads and the huge heat problems seems to have gone a way a little bit, although they still get warm when charging with a fan. I must say I am very impressed with my nimh batteries over the old nicads.

Thanks

James

[WillyChang]

Not hard to tell when a motor was designed... just check the windings.

Old style "efficient" motors have very full windings. There is a lot of copper on those poles!

New style are all sparse... much less copper wire wound on. Makes for better spin-up but is bad for efficiency.

With 4000mAh, we'll soon be going to see 6-singles with hair-thin wires. They'll rev to 80,000 and have no torque so you'll have to gear 10:1 for your tourer. 20% efficiency and it'll take off like a scalded-AND-skinned cat, but don't forget the cooling fan! []

[bholio]

I'll definitely try using a fan next time. I know I need new batteries. I needed the chargers first, as my old chargers were NiCD only. I'll probably get a few GP3300s next month.

2 of my Sanyo 2000s can get me thru 5 minutes in my XXCR buggy with an 11t speed gems. The other 2000 can't (which is the first one I tried on the new Quasar & got hot) and my other battery is a 1400scr which also can't. So, I'll try to pick up at least 1 GP3300 in the near future.

If I run the new GP3300 first and last on race day (and the 2000s 2nd and 3rd), it will have enough time to run, tray discharge, cool, recharge and run again on race day. I've read that NiMH are fine to run 2 or 3 time in a day, as long as they get to cool off before recharge.

I guess I'll find out.