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What setting for charging NiMH batteries

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Rocker15/07/2018 18:04:22
341 forum posts

Change all my receiver batteries over from 4 volts to 6 volts and have started using my lipo charger ( set on NiMH setting ) to charge them .Been told to charge them at 0.1 on the charger but it is taking for ever .What is the best setting to charge the NiMH receiver battery ,(can I charge them on a higher charge or should I stick to the 0.1 amps setting

ken anderson.15/07/2018 18:13:05
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8349 forum posts
768 photos

hello Rocker, you'll get different answers...I charge the 2000 m/a ones at 0.5 amp,after they have had an initial forming slow charge when first bought......I've done this for 20 years + without any problems whatsoever. Smaller capacity I charge at lower settings...

ken anderson...ne..1...battery dept.

Martin Harris15/07/2018 18:20:38
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8299 forum posts
210 photos

Beware of false peaks if charging at 0.25C - make sure you've put back a reasonable amount bearing in mind the mount used. Charging at 0.5 -1C is supposed to give the most reliable results.

However you charge, beware of any overheating - this is the real killer of NiMHs...anything more than warm to the touch will be damaging your cells.

cymaz15/07/2018 18:21:35
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8308 forum posts
1148 photos

I do my 2000mah at 900mah ( 0.9 A) . No worries

Ron Gray15/07/2018 18:27:58
1324 forum posts
346 photos

Initial charges will take ‘forever’ but stick with it and top up charges are then relatively quick.

Richard Wills 215/07/2018 19:45:55
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160 forum posts
7 photos

I Always use 1c, unless i'm really in a hurry and then it's 2c. No problems once you have set the cut off sensitivity, standard setting seems to let them overheat a bit too much.

Rocker15/07/2018 22:42:53
341 forum posts

Not having much luck charging up my nimh battery been on charge now for 6 hours at 0.5 ,still not fully charged ????????

Richard Wills 215/07/2018 23:24:17
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160 forum posts
7 photos

Rocker, is the pack getting warm/hot to touch?

ChrisB15/07/2018 23:25:09
1226 forum posts
34 photos

500-800mah for me.

Jon - Laser Engines16/07/2018 08:34:27
4441 forum posts
164 photos

500mah for 1200+mah packs. If i am in a massive rush i will use 1amp but thats not very common.

New batteries get cycled up/down at 10% of their capacity a few times to make sure i dont kill them straight off.

John Lee16/07/2018 09:44:03
598 forum posts
43 photos
Posted by Martin Harris on 15/07/2018 18:20:38:

However you charge, beware of any overheating - this is the real killer of NiMHs...anything more than warm to the touch will be damaging your cells.

What evidence do you have for that?

Panasonic, the maker of Enerloop, state that a temperature rise to 50 degrees (hot to touch) is normal & is not detrimental to the battery life of 2100 cycles, see the Q&A's on the link.

Rocker16/07/2018 20:52:08
341 forum posts

Problem solved .Not sure if it the correct procedure but gave up trying to charge the battery on 0.2 / 0.5 amps (forgot to mention it is a single cell 1.2 volt battery for a on board glow not a 4.3 receiver pack )Put the charger on 1 amp and bingo in under a hour it was fully charged

Geoff Sleath16/07/2018 20:58:24
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3201 forum posts
247 photos
Posted by John Lee on 16/07/2018 09:44:03:
Posted by Martin Harris on 15/07/2018 18:20:38:

However you charge, beware of any overheating - this is the real killer of NiMHs...anything more than warm to the touch will be damaging your cells.

What evidence do you have for that?

Panasonic, the maker of Enerloop, state that a temperature rise to 50 degrees (hot to touch) is normal & is not detrimental to the battery life of 2100 cycles, see the Q&A's on the link.

My calibrated finger can only just bear 50 c for a second or two.

Geoff

Martin Harris17/07/2018 01:25:56
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8299 forum posts
210 photos
Posted by John Lee on 16/07/2018 09:44:03:
Posted by Martin Harris on 15/07/2018 18:20:38:

However you charge, beware of any overheating - this is the real killer of NiMHs...anything more than warm to the touch will be damaging your cells.

What evidence do you have for that?

Panasonic, the maker of Enerloop, state that a temperature rise to 50 degrees (hot to touch) is normal & is not detrimental to the battery life of 2100 cycles, see the Q&A's on the link.

I didn't put that quite as I meant it. As I understand it, when a NiMH is fully charged, it converts the energy being put in to heat. Overcharging NiMH cells damages them and the fact that they are getting hot can be an indication of overcharge if the charging process hasn't terminated correctly.

It may well be the case that the different technology in Eneloop cells is more tolerant of overcharge or that heat generated during the charging process before the cell is full is allowable.

robert chamberlain29/10/2018 01:33:37
102 forum posts

While we are on the subject of NiMH charging, what MV cut off point should I set for the peak termination?

Cuban829/10/2018 08:35:56
2356 forum posts
8 photos

I have never fast charged RX or TX batteries, either Nicads in the old days, or Nimhs now. I have never suffered a battery failure while in use. Fast charge by all means, but it will put your pack under stress compared to a 0.1C charge (hence the temperature rise) and lead to premature loss of capacity in the long run. So, if you are happy to fast charge, it's even more vital to make a regular on-load discharge check on capacity, to warn of an impending failure.

One pays one's money etc...............

Philflyer29/10/2018 08:46:37
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109 forum posts
66 photos

I teach battery charging for aircraft batteries. These are either lead acid or NiCd, not NiMh but as a modeller in the past I used NiMh a lot (not at all now as I prefer LiFe). I have to keep up to speed with battery research and one of the web sites I have respect for is Battery University, sponsored by Cadex Electronics. The following is an extract from their opinions on charging NiMhs. Take note of the last paragraph.

The charge algorithm for NiMH is similar to NiCd with the exception that NiMH is more complex. Negative Delta V to detect full charge is faint, especially when charging at less than 0.5C. A mismatched or hot pack reduces the symptoms further.
NDV in a NiMH charger should respond to a voltage drop of 5mV per cell or less. This requires electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. Well-designed NiMH chargers include NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm. These “or-gates” utilize whatever comes first. Many chargers include a 30-minute topping charge of 0.1C to boost the capacity by a few percentage points.

It is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold.

Edited By Philflyer on 29/10/2018 08:48:04

Peter Christy29/10/2018 08:57:40
1261 forum posts

The small fall in voltage - and the difficulties in detecting it - are fairly well known in NiMhs. Nice to see a professional assessment of it!

I always charge NiMhs at between 0.5 and 1C, and never had a problem with that.

Interestingly, in the days of NiCads (the vented variety, not DEAC button cells), it was always the packs that were abused that seemed to last the longest! By abused, I mean high discharge rates, and fast charges rather than operated outside their spec!

Packs that were treated gently always seemed to be the first to fail....

Also, since most people now use "intelligent" chargers, rather than trickle charging, many of the problems that used to be associated with NiXX cells seem to have vanished!

--

Pete

Denis Watkins29/10/2018 10:19:51
3495 forum posts
165 photos
Posted by Peter Christy on 29/10/2018 08:57:40:

Interestingly, in the days of NiCads (the vented variety, not DEAC button cells), it was always the packs that were abused that seemed to last the longest! By abused, I mean high discharge rates, and fast charges rather than operated outside their spec!

Packs that were treated gently always seemed to be the first to fail....

Pete

There is some science related to this Pete

My work in the past involved electrolysis and the Japanese were the first to spot that AC charging worked admirably on cell longevity.

Applying a bias, the charge was some in, less out, some in less out

And this delayed the growth of dendrites from internally shorting the cell

Your " abuse " does pretty much the same thing

The High charge and Discharge rate would and seemingly did hinder the propagation of these damaging crystals

Peter Christy29/10/2018 10:40:59
1261 forum posts

Denis: Yes, I remember hearing that theory being put forward "back in the day", and it made a lot of sense!

Something else that helped NiCad longevity was using un-smoothed, half-wave rectified current in trickle chargers. Many chargers used full wave rectification and smoothing capacitors, but as with so many things, it appeared that the simplest was best.

The theory was that the pulses of current (and resulting vibration?) also reduced dendrite formation. Perhaps a variation on the Japanese conclusions?

Mind you, it did confuse a lot of people who tried to measure the output voltage of the chargers. They couldn't understand why a charger that read below the pack voltage on an analogue meter could charge the aforesaid pack.....!

--

Pete

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