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Old Dec 28, 2013, 01:52 AM
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Help!
B6AC not fully charging NiMH battery!

Can anyone help??

I am trying to charge my 6800mA 7.2v batteries using a B6AC iMax charger but it keeps finishing after a few minutes and the batteries aren't holding much charge. Tried it with 4 new batteries. Last attempt it beeped and said full after only 600mA.

Settings on the B6AC are...

Type: NiMH
Peak delta: default
Amps: tried both 3 and 3.5 with the same result
Capacity cutoff:6800mAh

Its a new B6AC and trying with 4 new 7.2v 6800mAh Ni-MH batteries.

Thanks in advance.
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Old Dec 28, 2013, 12:22 PM
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Unlike LiPo's ... NiMH are usually sold near full charged over counter ... are you sure they are not already nearly charged up.

Try them in model ... get them discharged and then charge up again.

Nigel
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Old Dec 28, 2013, 12:32 PM
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Thanks Nigel. Yes they are definitely not fully charged as the car I'm using them in only runs for a minute or two. If I use the charger that came with the car it runs for much longer. But they take a long while to charge.

Given they are 6800mAh and I'm running at 3A I'd expect them to charge over a couple of hours. Usually the machine buzzes and says full in a few mins and only a few hundred mAh showing on the display. It's the same with all 4 batteries. Do I need to adjust peak sensitivity from default?
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Last edited by Charsuifan; Dec 28, 2013 at 12:32 PM. Reason: Autocorrect error.
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Old Dec 28, 2013, 12:34 PM
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No idea as I always just use my B6 chargers at default and no problem.

Have you tried a lower amp setting ... just to see if it carries on ?

Nigel
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Old Dec 28, 2013, 12:35 PM
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Avoid the above advice as attempting to discharge an unbalanced NiMH pack can cause cell reversal and irreparable damage.

The reason why your charger is cutting out is that it is sensing a false peak due to cells in your new packs having different charge states.

Since your packs are new, they first need to be fully charged and balanced. This is accomplished by performing a very low current (1/10C or less) charge for an extended period of time (14+ hours) with a non-peak detecting charger.

If you don't have a non-peak detecting charger, you can perform several charge cycles with your B6 charger set at low current (.5-.7A) and stop repeating when all cells within the pack are warm (not hot) to the touch.

Welcome to RCGroups!

Mark
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Old Dec 28, 2013, 12:40 PM
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Thanks. Could I use the charger that came with the car? It has no settings - just a transformer that you plug in the socket. Guess it's basic.

Alternatively could I discharge using the B6AC? Would that work?
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Old Dec 28, 2013, 12:46 PM
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And thanks for the welcome. Not been the best day. Had some friends over to use the car and no cell worked for more than 5 mins. Also managed to destroy a Qrx350.

What does C refer to in 1/10C. I've seen this C referenced in a few postings. Is it 100 milliamps?
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Old Dec 28, 2013, 12:50 PM
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Do the sequence mrforsyth said. If you still have a problem? Post back.
You should be good to go.
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Old Dec 28, 2013, 01:02 PM
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Originally Posted by mrforsyth View Post
Avoid the above advice as attempting to discharge an unbalanced NiMH pack can cause cell reversal and irreparable damage.
OI !! - Who said DISCHARGE ?? If you read properly - I did advise to try a lower charge setting ... I was going to move onto suggesting a 1/10th rate if all else failed.



Nigel
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Old Dec 28, 2013, 01:05 PM
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Nigel

Read your post # 2 again. You do say to discharge them . Then recharge.
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Old Dec 28, 2013, 01:06 PM
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Quote:
Originally Posted by Charsuifan View Post
And thanks for the welcome. Not been the best day. Had some friends over to use the car and no cell worked for more than 5 mins. Also managed to destroy a Qrx350.

What does C refer to in 1/10C. I've seen this C referenced in a few postings. Is it 100 milliamps?
C is todays way of saying charge / discharge capability.

You have a 6800mAh pack ... which is 6.8A/hr capacity.

1/10C = 6.8 / 10 = 0.68A charge rate..... 680mA

The reason you see 1/10th quoted - is that is the age-old recc'd charge level that does not stress a pack and allows it to charge up over a 14 hour period from discharged ... hopefully equalising the cells in the pack.
It also means that you can safely connect up at that rate and charge overnight even if pack is partially discharged only.

Nigel

Nigel
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Old Dec 28, 2013, 01:10 PM
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Originally Posted by cyclops2 View Post
Do the sequence mrforsyth said. If you still have a problem? Post back.
You should be good to go.
Ok will do. Given I can't adjust the small charger that came with it I'll try changing a 0.7A. I assume once it beeps just run the program again?
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Old Dec 28, 2013, 01:12 PM
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Originally Posted by cyclops2 View Post
Nigel

Read your post # 2 again. You do say to discharge them . Then recharge.
Read it PROPERLY ... it was in terms of making sure they were not fully charged so that would explain the fault guy was experiencing. It is in conjunction with the comment that NiXX are often sold over counter near full charged. If near full charged then the 600mA would make sense.
He then went on to qualify that running in the model only gave him short run - but you guys jump in both big boots with this before I have chance to continue the path we were on ...

Lets make another profound statement - I have never had packs fail as his and need the so-called forming charges that people go on about ... I raced NiCD and used NiMH when NiCD was banned ... all packs bought were good to go and charged up fast or slow without trouble the MANY years I used them.

I still have some packs left over and chargers from those golden years ...

Nigel
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Old Dec 28, 2013, 01:15 PM
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Originally Posted by Charsuifan View Post
Ok will do. Given I can't adjust the small charger that came with it I'll try changing a 0.7A. I assume once it beeps just run the program again?
What the 'experts' have failed to advise you on ... the B6 will default out at 120 mins .. so you will find that at 0.7A - which needs at least 10 hours + losses ... will never happen ..

It means that you will have to restart the B6 each time it defaults out on 120 mins time. That is the maximum time a B6 can be set to - it's a safety regime set into the charger.

the only way you will get a continuous slow charge is to use the charger supplied with the car ...

Nigel
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Old Dec 28, 2013, 01:16 PM
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Quote:
Originally Posted by solentlife View Post
C is todays way of saying charge / discharge capability.

You have a 6800mAh pack ... which is 6.8A/hr capacity.

1/10C = 6.8 / 10 = 0.68A charge rate..... 680mA

The reason you see 1/10th quoted - is that is the age-old recc'd charge level that does not stress a pack and allows it to charge up over a 14 hour period from discharged ... hopefully equalising the cells in the pack.
It also means that you can safely connect up at that rate and charge overnight even if pack is partially discharged only.

Nigel

Nigel
Got it. Great, thanks. Makes complete sense.
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