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Author Topic: Charging problem  (Read 4737 times)

OneBladeMissing

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Charging problem
« on: May 14, 2007, 05:52:57 PM »

Hello peeps!  I've got a bit of a charging problem.
Two 4350 mAh / 7.2 volt / NiMh packs wired in series. Charging using Ripmax Mercury EX charger. Charge settings at 12 cell / NiMh / 4350 mAh. Charge current 2.1A. Charger bleeps and shows 'task finished' at 615 mAh.
New cells. Charger working ok, 8 cell packs charged ok earlier.
What am I doing wrong?
Any ideas / suggestions?
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Ian Robins

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Re: Charging problem
« Reply #1 on: May 14, 2007, 06:17:06 PM »

Hi,
If those cells were mine I would trickle charge the pack at approx 450ma for fourteen hours
 and then discharge (cycle them). Do this for Three times and then charge at a quicker rate.
hope this works
ro88o
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Faraday's Cage

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Re: Charging problem
« Reply #2 on: May 14, 2007, 08:10:27 PM »

One blade,

I suspect that you're asking too much of the charger by charging 12 cells at such a high rate of charge.

Each charger will have a maximum power output (in watts).  This is the voltage output (in your case around 20 volts) multiplied by the current (again, in your case - 2.1amps).  So we're looking in the region of 42 watts of power needed.

By reducing either the number of cells charged at once or the charging current you should be able to get a full charge.

Any other suggestions anyone ?

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cbr900

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Re: Charging problem
« Reply #3 on: May 15, 2007, 10:31:49 AM »

I charge twelve batteries in a pack at 4 amps for 20 minutes and they have always been filled up with maximum charge no problems, maybe your charger cannot handle what it says....



Roy
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OneBladeMissing

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Re: Charging problem
« Reply #4 on: May 15, 2007, 04:35:14 PM »

My charger should be able to handle the number of cells and charge current.
I discharged one set of cells fully and put them on trickle charge, 12 cells at 400mA. They stopped charging at 685mAh.
I might try charging the packs one at a time, but I can't see any reason why it's not possible to do 12.
I've e-mailed the bloke I bought them from, and he suggests fully discharging them then re-charging at 1.0A. But if they won't charge at 400mA I can't see them charging at 1.0A.
He sells batteries and chargers, etc. but doesn't seem to know much about actually using them.
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OMK

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Re: Charging problem
« Reply #5 on: May 15, 2007, 09:06:23 PM »

But if they won't charge at 400mA I can't see them charging at 1.0A.

Why?
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Ian Robins

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Re: Charging problem
« Reply #6 on: May 15, 2007, 10:04:43 PM »

Hi,
Are the two packs wired together?,
as a connector can give strange readings on a delta peak charger.
Do the packs charge individually?
Also you could discharge and charge each cell separately and then cycle them as a pack, It will take ages but it does work.
The single cells will then all be at the same rate of charge.

good luck
ro88o
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Ian Robins

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Re: Charging problem
« Reply #7 on: May 15, 2007, 10:08:06 PM »

Hi,
I ust checked the charger specks and it should charge all the cells, I have a supernova charger and nical hydrides need charging via manual programming (which is a pain). are you auto charging these packs (ie nicad settings) as the detection rate is different
ro88o
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OneBladeMissing

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Re: Charging problem
« Reply #8 on: May 16, 2007, 12:04:54 PM »

My charger should be able to charge up to 25 cells.
The cells are in sealed packs of six. I can't access individual cells.
Single 6-pack now on charge at 400mA. I'll see what happens!
I set the charger up manually. It only needs to be set up for the first pack, then subsequent packs just need putting on charge on the existing setting.
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OneBladeMissing

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Re: Charging problem
« Reply #9 on: May 17, 2007, 05:05:08 PM »

Single 6-pack trickle-charged ok yesterday. Another pack on charge today.
I still can't fathom why a pair of packs in series wouldn't charge.
Thanks for your responses and suggestions, folks.
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justboatonic

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Re: Charging problem
« Reply #10 on: May 17, 2007, 09:22:57 PM »

If they are Nimh cells, I wouldnt trickle charge them. If you intend racing, I'd buy a discharger \ equaliser tray. I've started using one for our car batteries and the performance of the cells has increased, especially for the older packs we have.

What connections do you have between cells and charger? Are you using tamiya types plugs? If so, throw these away and use some proper gold connectors. The tamiya type just cannot handle high current when charging or discharging. We had problems with the charger 'peaking' early when we had tamiya connectors. Since switching to gold pin and tube connectors, we havent had the same problem.

I'd seriously suspect the connectors are the cause of your problems.
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OneBladeMissing

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Re: Charging problem
« Reply #11 on: May 18, 2007, 04:49:18 PM »

I use 4mm banana plugs & sockets. They work fine on my 8-cell packs, and seem to be ok on the 6-cell packs I've just charged. I use the same type of connectors for plugging my charger into the PSU with no problems.
When I connected the two 6-cell packs in series I used a 'chocolate block' type connector. The grubscrews in it were nice and tight, so I reckon I had a good connection. Could it be that the two packs of cells were not 'matched' with each other?
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justboatonic

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Re: Charging problem
« Reply #12 on: May 18, 2007, 11:57:55 PM »

Could it be that the two packs of cells were not 'matched' with each other?
Im assuming both packs were of the same capacity? If so, that shouldnt be a problem since the variance between the packs wouldnt be that great ie its not like one pack was 4300's and the other was 3700. BTW this would be a complete no - no!

Have you tried charging one 6 cell pack at around 4amps ie 4000mah (this is what I charge our 7.2v 3700mah packs at) and what results did you get? If the cells still dont charge to capacity or near it, I'd suggest either your charger is not set up correctly for 6 cell packs or one or more cells in a pack are venting.

If you have a voltmeter, try measuring the voltage of individual cells. This may give a clue to any potentially dead cells in a pack. If all the cells seem ok but still dont quick charge to capacity, I'd suggest borrowing another charger from a friend and see if the same 6 cell pack charges ok on it. If it does, this would tend to suggest the problem is with your charger.
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OneBladeMissing

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Re: Charging problem
« Reply #13 on: May 19, 2007, 12:24:13 AM »

The individual 6-cell packs are charging ok, on their own. I don't understand why a pair of them in series won't charge.
When I tried to charge a pair the charger was set to : NiMh / 12 cells / 4350mAh / 400mA charge current.
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justboatonic

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Re: Charging problem
« Reply #14 on: May 19, 2007, 01:04:52 AM »

The individual 6-cell packs are charging ok, on their own. I don't understand why a pair of them in series won't charge.
When I tried to charge a pair the charger was set to : NiMh / 12 cells / 4350mAh / 400mA charge current.
Im puzzled by your very low charge rate. You are charging at less than half an amp. For a charger capable of charging multiple cells of more than 4300mah capacity, I'd expect a charge rate of about 4000mah or 4 amps. Does your charger have a variable charge rate?

Im beginning to think the fault may lie with your charger, either in the set up you have chosen or the processor inside it
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OneBladeMissing

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Re: Charging problem
« Reply #15 on: May 19, 2007, 06:52:35 PM »

I'm trickle-charging them, not fast charging. As a rule of thumb, when trickle-charging, I set the charge current to one tenth of the battery capacity. With the charge current set to 400mA, the actual current the cells charge at is always slightly higher than the setting. I have a pack of cells on charge at present, with the current set at 400mA the actual rate of charge reads at 450mA. When I fast charge them I'll do it at 2.2A, as recommended by the manufacturer.
There is nothing wrong with the charger, or the settings I'm using. I'm just wondering why it won't charge two packs in series.
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justboatonic

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Re: Charging problem
« Reply #16 on: May 19, 2007, 10:33:25 PM »

IMO you wont get the 'punch' from your cells trickle charging them or, charging at 2 amps. I know manufacturers recommend low charge regimes but if you want to use the cells for fast electric, everyone but everyone in the RC Car world recommends charge rates of around 4.0 - 4.5 amps. All RC Car people trickle charge niCads for the first couple of charges then fast charge them. (I've never experienced niCad memory effects either.) For NiMH cells, no one I know in RC Cars trickle charges these cells first. They all go fast charge then discharge, fast charge.

If the charger manufacturer says the charger should charge more than 6 cells in series but it peaks at 400mah if 12 cells are charged, something has to be wrong somewhere. The fact it trickle charges a 6 cell pack to capacity but wont with 12 suggest the problem is with the charger or settings.

I can only advise if you know someone who can charge 12 cells in series you ask them to charge these for you. If they can charge them this would confirm your charger as the area to investigate.
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Welsh_Druid

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Re: Charging problem
« Reply #17 on: May 20, 2007, 09:45:30 AM »

I wonder if your problem could be the INPUT to the charger.

My friend and I both use pro-peak chargers. I have not had any problems but he had similar problems to yourself (not such large packs though) - the charger would only charge his batteries to a fraction of their capacity.

When he changed the input to a source with a much higher amperage rating his problem was solved.

Don B.
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OneBladeMissing

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Re: Charging problem
« Reply #18 on: May 20, 2007, 02:37:55 PM »

I'm using a Great Power PSU. Up to 10A current supplied.
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cbr900

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Re: Charging problem
« Reply #19 on: May 21, 2007, 01:29:25 PM »

OBM,

Do yourself a favour and try giving them a charge at 4 amps, I have been charging racing packs four eight years at that rate and not yet had a battery faiure.......



Roy
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OneBladeMissing

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Re: Charging problem
« Reply #20 on: May 23, 2007, 12:43:35 PM »

I haven't had a battery failure either, whether fast-charging or trickle-charging.
Anyway, had the hydro on the water on monday afternoon, running on 12 cells. Highly enjoyable, despite two flips. Once when I tried to turn while on full speed, then when the lake chopped-up a bit. More work needed on watertightness as a bit of water got inside, but no harm done.
Water screws DO work as airscrews when the boat is inverted. I never managed to do that with an IC engine!
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