NiMh Help big time!

[the wildman]

Im new to this. I have a charger MRC Super Brain 989.......

What settings should i use to charge this?
9.6V 2300mAh NiMh Battery
Charge Amp:?
Cut off Peak mV:?
Cut off Temp:?
Trickle:?

What settings should i use to charge this?
6.0V 1500mAh NiMh battery:
Charge Amp:?
Cut off Peak mV:?
Cut off Temp:?
Trickle:?

How do you attach the temp probe? Just sit the battery on top of it????

Thanks:

[timie1]

I'm unfamiliar with that charger, but in general if you charge the 2300 nimh battery at 1C ie, 2.3amps, you should be fine. There really isn't a clear and cut way to pick the mV. Each charger is different. Start low, maybe 3mV per cell and see how it goes. When it shuts off charging, the batteries should be warm, and it should take about 66 minutes at 2.3amps. If it shuts off early and cells are still room temp, raise the mV setting and try again. It would be good to discharge whatever charge is in them before starting another charge, it'll give you a more accurate result while adjusting the mV. Use a discharge tray, or discharge to .9V per cell, so 7.2V for the whole pack for your 2300, and 4.5V per pack for the 1500.
I wouldn't worry too much about cutoff temp. Basically, if the cells start getting hot, stop the charge. Cells always heat up while charging. With my infrared thermometer I check the temps of mine occasionally. If they start getting in the 50°C range, I like to shut it off manually. Don't trickle charge them!!! When the charger is done a 1C charge, take them off the charger. ONLY "trickle charge" nimh occasionally from flat, it's a poor man's way of balancing the cells, but it works. When you do this, try to charge at 1/10C, or .2 - .3 amps. It'll take about 15 hours give or take.
Just don't do a fast charge and set it to go into trickle charge once fast charge is terminated

Use the same settings for your 1500 pack, but change the amps to 1.5amp (1C). It should also take about 66 minutes.

*******************

After you experiment with the settings and you decide the packs are only just warm after 66 minutes or so, you could try increasing the amp rate to make it charge quicker. If charge time isn't a major concern though, and your wallet isn't as big as your dreams, then stick to the 1C rate, it'll keep your batteries lasting better, longer.

[the wildman]

what is "1C"?

[the wildman]

what is "1C"?

[timie1]

Don't mention it; you're welcome!!

I gave the example in the first sentence, but I'll elaborate now.
Basically, if your battery is say, hypothetcially, 3000mah, 1C would be 3amps. If it were 2000mah, 1C would be 2amps. If it's 600mah, 1C would be 0.6amps.

1C rating for a 2000mah pack means it can supply 2000mah/2 amps for 1 hour before it goes flat. If you had an 8000mah LiPo pack, a 1C for that would mean it could be drained at 8 amps constant for 1 hour before it would go flat. With charging, one can control, quite easily, the charge rate and maintain a constant rate, but when discharging in your car, it's very hard to know exactly what rate it's discharging at because it's all over the place with accelerating, braking, cornering and so on. Typically when running the pack in your car, you can expect an average discharge rate at 20 amps, give or take. 20 amps on a 2000mah battery pack would equate to a C rating of 10C, ie, if 1C = 2amps on a 2000mah pack, then 2C = 4amps, 3C = 6amps, 4C = 8amps, and so on.

Regardless of capacity of any battery, a "1C" rating will mean it'll take 1 hour to either charge or discharge, because the value of "C" changes with the capacity.

Get it?? ;)

[timie1]

Oh yeah, when looking at LiPo packs, you'll quite often see something like,....."5000mah 25C". This means the battery is good for supplying 125 amps before it'll blow up, or start to overheat at the very least, and in theory it could supply 125 amps for 1 hour.

Think of the examples above and substitute the values:
5000mah pack: c/10 ***(1/10th of C)*** = 0.5 amps or 500mah
5000mah pack: 1C=5 amps
5000mah pack: 5C=25 amps
5000mah pack: 10C=50 amps
5000mah pack: 20C=100 amps
5000mah pack: 25C=125 amps

[the wildman]

Here the complete story about my car:
I used to race Motocross here in Minnesota and about a year I had a terrible crash the completely destroyed my left shoulder and I mean everything. Nerves, ligaments, tendon, bones, rotator cuff I mean everything. The only thing hold my arm on was the flash. I’ve in physical therapy for 10 months now and another 6 months to go.

Anyway I also own an awards company called Race Rewards Inc. (www.race-rewards.com) and I’ve been doing the Snowbird National awards for a while now. When Mike Boylan & Jeff Maturo heard what happen he was instrumental in getting me an X-ray XB808. It been sitting dormant on my diningroom table fully assembled and waiting for a transmitter and receiver batteries to bring it to life at the time I didn’t really know what I had but now I’m starting to realized and the huge learning curve I have to understand RC racing and all the tech info that goes with it.

I tried charging that battery at the specs you mentioned. It only took 15min and the charger read when finished that it only had 500mah in it.
The battery spec was:
8cell, 2300mah, 9.6v NiMh battery
2.3amp charge
5mV
Cut off temp was 120F (default)
No tickle

Does this sound correct or am I missing something?

Again sorry for not expressing my appreciation earlier.

[guver]

Both NiMh Batteries

Charge Amp:? .5 for AA cells and 2-5 for subC cells
Cut off Peak mV:? 3 for AA and 5 for subC
Cut off Temp:? 125
Trickle:? 0 for AA 200 ma for subC

Probe can be under the pack or rubber banded to pack.

[the wildman]

I understand the "AA" making = the size of a typical "AA" battery.
But the subC: does this mean larger than a "AA" but smaller than a typical "C" battery

Thanks you!

[timie1]

I don't know why they call them sub c, they could have just chosen a different letter for them. Maybe B size??? hehehe. But yeah, they are bigger than an AA, but smaller than a C size.

Ok, your charger shut off early, much too early. Raise the mV and try again. You'll find the mV eventually that assures a good full charge is in them. Golden Rule: if the charger shuts off charge and the packs are cold and it hasn't been about an hour, raise the mV. Only raise it 1mV per time, or maybe in your immediate case, 2mV seeing as it shut off after only 15min.

Do you know what "mV" is??
If you do, you can just ignore what I'm saying, otherwise read on..............
As a cell is charging, the voltage rises at a relatively steady rate. When the cell approaches full charge, the voltage will drop. It's to do with all the chemical reactions inside the cell. Anyway, adjusting a higher mV per cell will instruct the charger to "look" for that voltage drop and when it sees it, it'll stop charging. This is how it detects a fully charged battery pack.
Here lies the problem.....each cell in the pack never really charges at the same rate, so while some cells are 90% full, others may already be 100% charged. A low mV setting on the charger is very sensitive, so as soon as 1 cell starts to drop off a tiny amount, it stops. This leaves some cells as near perfectly charged as can be, while others aren't. To counteract this, you have to raise the mV setting. The higher the setting, the less sensitive it is, and the more likely you'll get a full charge. But be careful, too high a setting and you could severely overcharge some cells, and this will be seen to you as hot cells, as opposed to just warm.
The best way to keep each cell close in their capacity and ability to all peak at the same time is to use a cell balancer/discharge tray. I use a Tekin Battery Doctor 8.0. Other good ones are Novak Smart Discharger. In the case of mine, the cells are all brought down to 0.9V at 2amps, then 0.7V at 200mah, then they stay at that amount. What it means is, they all accept the same amount of charge without some peaking too early. It keeps them in tip top shape much longer.

If you don't have a discharge tray, then use the "trickle charge" method I posted earlier, but use it occasionally. This slow charge is slow, so when some cells reach their peak, the extra charge burns off, so to speak, as low temp heat. It gives the lesser charged cells time to reach their charged state without damaging the more charged cells. Using the slow charge technique the first time could be very beneficial to help balance the cells. Using a fast charge rate doesn't work because the charged cells heat up too quickly and can't shed the extra charge as heat properly. Also note, if you use this trickle charge method, raise the mV right up to about 10mV per cell. If you have the charger programmed to shut off once it reaches a certain mah, it will stop and not just continue charging until the end of time.

FYI - on my charger, I usually charge at 5 - 7 mV/cell. On a 6 cell pack, 5mV per cell would mean......per PACK (not cell) the charger is looking for a drop of 30mV (5mVx6cell), or a drop of 0.3V for the whole pack, or something like that ;)

[the wildman]

I understand why to balance and have looked at the balancer/dischargers you recommended. I’m assuming that to discharge each cell you need the leads to that individual cell within the pack.
What about a battery pack that has plastic wrapping around it like the Trinity TRI20508 for a receiver with a wire only coming out of it and not exposed leads on each cell? Maybe they do not need to be balanced? Thanks

[timie1]

Yes you do need access to each cell, and the battery you mentioned doesn't give you access unfortunately.

In that case, you're going to have to do a slow charge every once in a while. You could dis-assemble the pack and solder them up using battery bars, but, that's a hassle and may render it difficult to fit in your chassis if it's in a tight place, not to mention your disabled arm because you need both hands to hold the battery bars in place.

[the wildman]

I'm going to try these settings tonight and see what happens.
Thanks you very much for your help. :wave: :D :)

[rccardude04]

This means the battery is good for supplying 125 amps before it'll blow up, or start to overheat at the very least, and in theory it could supply 125 amps for 1 hour.



A 5000mAh pack will supply 5A for 1 hour. 125A is 2.4 minutes.

I wish they'd standardize the "C" rating procedures. I've seen some graphs but they never say how they actually rate the packs. It seems to be the maximum before bursting into flames for some companies, whereas other companies appear to rate them for the max discharge while still maintaining X% of capacity.

It's weird and seemingly random. Oh well. :)

As far as charger settings go, 1C is good for larger cells, but I'm very uncomfortable charging AA cells over about 1.0A. 1.5 if you're in a huge hurry but the slower the better to an extent.

I assume you have a transmitter and receiver pack? I'd do each of them at 1A and expect the mAh rating to be a timer basically. The 2300 is 2.3Ah, which will charge at 1A in 2.3 hours. The 1500 will take 1.5 hours.

-Eric

[timie1]

Yes you are right Eric, I was forgetting about constant and burst rates in my waffle:) Thanks for correcting me:)

[rccardude04]

Yes you are right Eric, I was forgetting about constant and burst rates in my waffle:) Thanks for correcting me:)


Haha, no problem. Just wanted to make sure we keep info as accurate as possible. :)

-Eric

[the wildman]

I charged the 1500mah 6.0v NiMh Trinity TRI20508 receiver pack at:
Charge Amp: 0.5
Cut off Peak mV: 8mV
Cut off Temp: 125F
Trickle: 0.0
It took about 1 hour.
The results from the charger said 1000mah capacity. Should it be reading 1500mah and or does this sound correct?

Then I charged to the 2300mah 9.6v NiMh transmitter pack at:
Charge Amp: 0.5
Cut off Peak mV: 8mV
Cut off Temp: 125F
Trickle: 0.0
It took about 1.5 hour.
The results from the charger said 1500mah capacity. Should it be reading 2300mah and or does this sound correct?


Thanks

[guver]

The capacity screen is showing only the "added capacity" and not the total.

Was the battery full? it should be. The capacity added is a nice even number for some reason.

[the wildman]

The capacity screen is showing only the "added capacity" and not the total.

Was the battery full? it should be. The capacity added is a nice even number for some reason.

The Charger said it was full. A least the little graphic showed it was full. Is there another way to double check?

Thanks

[rccardude04]

1 hour at .5A = 500mAh. Not 1000mAh. It takes 2 hours to put in 1000mAh. 3 hours to do 1500mAh.

-Eric

[timie1]

Had you depleted what charge was in it before you put them on at those settings?

Remember, you put 15 minutes of charge in before. If you didn't deplete the previous charge, then what you've done is add an extra 1000 and 1500 mah (going on what the charger said). Although, as Eric has just pointed out, 1 hour at .5A = 500mAh. Not 1000mAh.

Is there any way you can discharge it at a constant rate down to 0.9V per cell? Such as a bulb discharger? Time it to see exactly how long it takes to get it down to 4.5V for the 6V 5pack. Then you are able to calculate the amount of actual mah in it. Make sure you know exactly the amp rate you discharge at. 1amp would be the easiest to calculate, or 10A is also easier than other rates.

[the wildman]

Had you depleted what charge was in it before you put them on at those settings?

Remember, you put 15 minutes of charge in before. If you didn't deplete the previous charge, then what you've done is add an extra 1000 and 1500 mah (going on what the charger said). Although, as Eric has just pointed out, 1 hour at .5A = 500mAh. Not 1000mAh.

Is there any way you can discharge it at a constant rate down to 0.9V per cell? Such as a bulb discharger? Time it to see exactly how long it takes to get it down to 4.5V for the 6V 5pack. Then you are able to calculate the amount of actual mah in it. Make sure you know exactly the amp rate you discharge at. 1amp would be the easiest to calculate, or 10A is also easier than other rates.


Yes it does have a discharge option on it. I'll discharge it at 1amp and .9v per cell (4.5v for the 5 cell receiver pack) and recharge and take careful notes along the way and see what happens.
Thanks again! :D

[guver]

The other way to tell if it's full is to temp the pack. It should be quite warm when done. 110-125 deg F.

[timie1]

The problem with going on temp alone is, the temp varies depending on the charge rate. Charging at 0.5A will yield a much cooler pack when fully charged, then if you were to charge at 1 amp or more.

[the wildman]

Here is my results on:
9.6v 2300mah NiMh 8 cell pack .5amp 130F 10mV
Discharge:
took 60min 44 seconds

Charging took:
200 Min
MAH 1722

Does this sound correct?

[guver]

This is getting very complex. An hour at .5 as pointed out above is 500 mah (removed) and then 1722 was replaced. The pack was partial at start or has a bad/weak/unbalanced cell.

It really shouldn't be so hard, set the charger to match battery and push start. It stops and gives a message at end describing why the charge was ended. The manual is best source of instructions and the stop code for a normal peak detect is C 0.