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Cycling Battery packs

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Neil Wyatt07/05/2017 09:46:38
13849 forum posts
583 photos
68 articles

We have often discussed the merits of various brutal ways of 'refreshing' worn out NiCad and NiMH battery packs.

I have long been aware of a gentler way of refreshing the packs, but never tried it in a structured way.

I bought an inexpensive iMax B6 charger, I have no idea if it is 'genuine' or a 'clone'. This give you the option of putting a battery pack through multiple (up to five) charge/discharge or discharge/charge cycles. You set the minimum discharge voltage and a few things like charge current, discharge current, maximum charge time etc. to prevent overcharging.

I have various nicad packs of various ages and even more varied origins. I put a 3 sub-C pack through its paces yesterday and the five cycles went something like: 60, 125, 250, 600, 1000 mAh.

OK I have 'rounded off' the numbers but basically the capacity doubled with each cycle, and it now appears to be a usable pack again. If I had done a normal single charge I would probably have assumed it was U/S.

OK, 1000mAh isn't very much, but sub-C cells can deliver more current so there is probably a use I can find for it. I'm putting it through a further five cycles to see if the capacity increases further and where it tops out (they are probably 1.8 or 2 Ah cells originally).

I have a (rather less old) Tamiya 9.6V 4600 Ah pack that has suffered from neglect and is well down on capacity. A replacement costs three times as much as the charger, so if it can get it back up to around 4Ah I think it will have more than paid for itself, that's the next experiment. I have charged it once, and it took over an amp hour, but it was partially charged already.


Brian Oldford07/05/2017 10:28:02
395 forum posts
4 photos

A bit more info in the genuine/clone iMax B6 here

peak407/05/2017 10:58:23
544 forum posts
41 photos

According to the links, the Imax B6 does up to 15 cells.

I have a 19.2v pack I'd like to improve a bit as new ones are a small fortune, so does anyone have any recommendations for a reconditioning charges for 16+ cells please. (Sealey CP3004 1/2" impact driver)

Failing that I may try one of these B6 chargers and dive into the battery pack and split it into two halves.

I appreciate I could re-cell it for about £45



Edited By peak4 on 07/05/2017 11:00:21

Howard Lewis08/05/2017 16:34:16
1300 forum posts

Have two 18 volt drill battery packs , one is dead, the other is very capacity.

1) Any hope that the Imax B6 would rejuvenate them?

2)What PSU is required for the Imax B6?

3) What is it likely to cost?



peak410/02/2018 00:25:03
544 forum posts
41 photos

To rejuvenate an old topic, as well as a battery pack;

I did pick up an IMAX B6, though I suspect it's a clone looking at the "manual" supplied with it, but only just got round to investigating how to use it. I do have a copy of a genuine manual, which shows how to drive it, but not the best settings to use.

Does anyone, with any experience of these things, have a recommended group of settings for this particular job; the one listed a couple of posts above.

19.2v Nicad pack, which will take a charge from the Sealey charger OK, but won't hold it for long at all.

Apparently the internal, sub C, Nicad cells are 2AH, according to one of the web sites who sell the packs (@ £130-170+ per pack). the cells themselves aren't sign-written.

The cells are quite old, but it never had regular usage which might be part of the problem; i.e. charged up and part discharged on a job on the car, then left until the next major job. I'm guessing the memory effect can't have helped either.

I'm hoping that a few measured discharge/charge cycles will breath some more life into it, but unsure of the best settings to use in terms of charge / discharge currents, and minimum discharge voltage etc.

Unfortunately the Imax claims only to go up to 15 cells, and of course, this is 16, but I guess I could dive into the pack and treat it as a 12v + 7.2v packs in series, or maybe use a custom program.



Danny M2Z10/02/2018 03:19:37
637 forum posts
252 photos

Why not try it as 2 x 9.6V packs (if you can can gain access to the cell links)? This saves re-doing the settings plus you can store them in one of the B6 memories for future use.

2000mAh (2Ah) is typical capacity for a sub -C nicad so your reference is probably correct.

When I built some automatic NiCad battery cyclers many years ago the advised lower limit for discharge was 1.1V per cell (from a SAFT data sheet), so I would set the B6 to cycle your two 9.6V packs down to 8.8V at 1000 mA (1A) charge/discharge current (it's probably less load than they use in service).

If the packs get too warm then drop the current. The charger also has the ability for a cooling time delay to be inserted between cycles although I suspect that this is only used if one is hammering the pack with large currents.

I would not try to charge the 2 x 9.6V packs in parallel in case one has a bad cell, it will mess things up. Do them individually.

Also, when you have the pack open, check for white powdery deposits around the + connectors of each cell. A little you can get away with, a lot and the cell is probably stuffed.

My charger is the B6AC model, input 240VAC or 12-18V DC. I recently found some nice new Sanyo NiCads with solder tags in a local specialist battery shop so I am about to rebuild some packs myself.

* Danny M *

not done it yet10/02/2018 04:58:22
1961 forum posts
11 photos

My question is: When ‘refreshed’ in this way, how long do they stay ‘refreshed’. My experience is minimal for this type of ‘refreshment’, but past ‘kicking them back to take a charge’ has been a short-lived solution.

Clive Hartland10/02/2018 09:17:25
2304 forum posts
38 photos

Dendrites in Ni-Cads are your enemy, a normal ni-cad cell set will normally last 500 charge and discharge cycles and by then will have a memory effect that reduces capacity. Normal procedure is to replace the batteries. A basic failure is to discharge the pack completely and then recharge, many people think that doing a, 'Top up' at dinner time is enough to keep the cell up to scratch, but. 'No', it will degrade the battery pack quickly.

A dedicated discharge and then a re-charge is the way to go. They can be stored charged or discharged.Dendrites can be flashed over by a reverse voltage so I am told, maybe just touch the terminals momentalary. Never done it myself. I have seen them blow up though!

What i have done is to use them hard and then charge them on the 1/2 upon C time cycle and they do improve after about 3 or 4 cycles.


Peter G. Shaw10/02/2018 09:51:38
890 forum posts
36 photos

K.C. Johnson in Wireless World in the 1970's went into this. Apparently, NiCads last best when worked hard. If used lightly, they form these internal whiskers which eventually short circuit the cell. To recover a s/c cell, he advocates a car headlamp bulb in series with a 12 v car battery to melt the shortcircuiting whisker.

Peter G. Shaw

Danny M2Z10/02/2018 10:17:10
637 forum posts
252 photos

Clive is correct. Apart from overcharging and discharging electrolyte through the vents the growth of dendrites can cause degradation of a NiCad cell.

For the 'curious', dendrites are like stalagtites/stalagmites that grow in caves. They can grow between the electrodes of a NiCad cell thus compromising capacity.

'Flashing' with a momentary high reverse voltage is a practical way to vapourise dendrites and my current commercial NiCad Charger (Ace R/C it is over 20 years old.) uses this technique. It is a PCR (Periodic Current Reversal) charger.

Basically it tests a pack and then charges with a DC current that has the polarity momentarily reversed to cause a large negative spike in the charging current thus blasting away the dendrites. (This the same technique that was used to 'recharge' carbon -zinc cells in the 80's-90's, with limited success btw).

In practice, I have had one spare r/c Tx 9.6V 800mAh Sanyo NiCad pack hooked up to this charger for about 3 years in the workshop. Sometimes the power supply meter needle gives a flicker as a brief pulse tops up the battery pack. Might be interesting to hook up the oscilloscope and see what is going on.

I have some data to back this up btw but it's on a microfich card.

* Danny M *

peak410/02/2018 11:00:07
544 forum posts
41 photos

Thanks folks, I'm away at a wedding do for a couple of days, so I'll have a play when I get back.

I have successfully reverse flashed some D cells in the past, using similar methods to those described above.

I'm well behind the times, never come across a PCR charger.



Rob Rimmer10/02/2018 20:29:21
36 forum posts
1 photos

I am currently (no pun intended) cycling a 3.6V nicad battery pack using a B6 charger bought a couple of days ago after reading Neil's post - I shall report back on what happens.

To power it, I am using an old ATX PSU from a scrap computer to supply 12 volts. Instructions for doing this are easy to find with a quick Google search. I tried an old laptop PSU, but at 19.5V it was just a bit too high for the B6.

Regarding reverse flashing, I made a unit for doing this back in the 80s based on a design in the American magazine Popular Mechanics. It was very simple, and just discharged a capacitor through the cells at the press of a button. It seemed to do the trick on the couple of occasions I used it.

Rob Rimmer11/02/2018 13:25:58
36 forum posts
1 photos

Well, the cycling completed with the following results - not as good as I'd hoped, but worth a try:

50 (I guess this was because the cells were not charged at the start), 579, 599, 605, 582 - this is the odd bit, can't explain why it dropped at the end.

Anyway, with little to lose, I'm running it through another five cycles.

Regarding Popular Mechanics, I've found this **LINK**

But of course I can't recall which issue it was in, so am having fun reading through them. laugh

Rob Rimmer13/02/2018 16:35:16
36 forum posts
1 photos

If it's of any use to anyone, the article about a NiCad 'rejuvenator' can be found on page 62 of the Feb 1982 issue of Popular Mechanics here **LINK**

john fletcher 113/02/2018 17:19:06
415 forum posts

I used to read Electronics Today International and made several pieces of very useful test gear from their articles. I think Zapping your Ni Cads was one of them, unfortunately I am unable to find the article. I still use ETI Ni- cad battery charger. I zap my cordless drill batteries as and when they need it, burning off the whiskers, using a worn out car battery that seems to go on for ever.John

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