Topic 'effect of high charging current on NiMHs' in forum 'Electronics' - dslreports.com

Re: effect of high charging current on NiMHs

Thu, 01 Nov 2012 01:24:15 EDT

aurgathor posted : Charging individual cells is easier than charging multi-cell batteries.

Re: effect of high charging current on NiMHs

Thu, 01 Nov 2012 01:07:46 EDT

neonturbo posted : I charge AA and AAA batteries at 1C all the time with my Maha C9000 charger, and they don't get remotely warm. I believe it PWM's (pulse width modulates) the current rather than doing a steady current which is supposed to be better for the batteries.

From what I understand, too slow of a charge makes it hard to detect when the battery is full. Too quick causes heat and you won't get the battery full. I gather 0.5-1C is optimal by the research I have read.

Re: effect of high charging current on NiMHs

Thu, 01 Nov 2012 00:00:20 EDT

lutful posted :

said by aurgathor:

... TN141-2-Bay-9V-Smart-Charger ... is rated 100 mA while the 9V batteries are rated 20 mA standard, and 38-40 mA rapid charge. WTH is going on? I'd expect that they would match their batteries and chargers, but given the over 2x difference in rapid charging currents, that doesn't appear to be the case.

The battery charge current specs are for generic chargers.

Tenergy's TN141 and any negative delta V (NDV) cut-off method fast chargers must set the charge current between 0.5C and 1C for that approach to work. Temperature and voltage checks prevent damage.

Re: effect of high charging current on NiMHs

Tue, 23 Oct 2012 10:10:15 EDT

shdesigns posted :

said by public:

said by shdesigns:

I have seen 3000mah A cells charged at 10 amps. Then again they are designed for it and are discharged at 25+ amps.

Typical nimh aa cell will run hot when loaded at 1A. Which AA cells can supply 25A?

I did not say AA, I said A cells (often 5/4 A). Yes, they get hot enough when discharged you cant hold them in your hands very long. I remember they were Sanyo. Used in R/C plane, flight time of 6 to 8 minutes.
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder

Re: effect of high charging current on NiMHs

Tue, 23 Oct 2012 10:06:22 EDT

public posted :

said by shdesigns:

I have seen 3000mah A cells charged at 10 amps. Then again they are designed for it and are discharged at 25+ amps.

Typical nimh aa cell will run hot when loaded at 1A. Which AA cells can supply 25A?

Re: effect of high charging current on NiMHs

Mon, 22 Oct 2012 16:57:55 EDT

shdesigns posted : Yes, i do AA's at 750ma regardless of capacity. That is enough to peak charge. If I'm in a hurry i use 1.25A, again the 0.5C level.

I have seen 3000mah A cells charged at 10 amps. Then again they are designed for it and are discharged at 25+ amps.

Re: effect of high charging current on NiMHs

Mon, 22 Oct 2012 15:42:36 EDT

public posted :

said by shdesigns:

said by public:

Fast charging nimh quickly degrades capacity, in spite of what product ads claim
For best results use 0.1C charge current.

The problem with that is NiMh do not like being overcharged. NiCads handle it much better. Preventing overchargeing is not easy on lower charge rates.

0.5C is not bad. Most smart charges charge at 1-5C (have seen 10C used). That will degrade them.

If you charge 2500mAh AA cell at 1C that is 2.5A. It will be sizzling hot and quickly ruined.

Re: effect of high charging current on NiMHs

Mon, 22 Oct 2012 02:10:55 EDT

aurgathor posted : Yeah, incorrect/outdated specs for the batteries were one possibility I was thinking of.

I did some more search on optimal charging rate for NiMH, and stumbled onto this:
»www.candlepowerforums.com/vb/sho···atteries
A very good thread, unfortunately, most of the cited material is now 404.

In any case, I concluded the following:
a) 0.5C - 1C is used partly because detecting completion is most reliable in that range (and also because the charging is reasonably fast)
b) if a charger is going much over 1C, the life and cycle time of the batteries may plummet
c) 0.1C may put in more charge with less stress, but it's much easier to miss completion at such a low rate, and overcharging is bad, even at such a low current

Looks to me NiMH charging is actually much more SW than HW, and so I may just try to roll my own charger when I get some spare time.
--
Wacky Races 2012!

Re: effect of high charging current on NiMHs

Sun, 21 Oct 2012 12:37:52 EDT

shdesigns posted :

said by public:

Fast charging nimh quickly degrades capacity, in spite of what product ads claim
For best results use 0.1C charge current.

Re: effect of high charging current on NiMHs

Sun, 21 Oct 2012 12:26:26 EDT

public posted :

said by shdesigns:

100ma is a 1/2C charge rate. Not that high.

Fast charging nimh quickly degrades capacity, in spite of what product ads claim
For best results use 0.1C charge current.

Re: effect of high charging current on NiMHs

Sun, 21 Oct 2012 01:23:03 EDT

shdesigns posted : 100ma is a 1/2C charge rate. Not that high.

For a peak charger, that would be a normal rate. Too low and you can't detect the peak.

I suspect the 20/40ma rates are for dumb chargers.

I have some 180mah 9V NiMh batts and they are near useless. Don't store much and self discharge.

Those batts are 200mah. Not much better.

Check out ebay item 230847565106
Tenergy site seems to have older version on their site:
»www.tenergy.com/30593

Rated for 500mah. That's 2.5x as much and they won't self discharge.

I will be getting some for my DMM as I'm tired of buying 9v batts (forget to turn off and batt dead in 24 hours.)
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder

effect of high charging current on NiMHs

Sun, 21 Oct 2012 00:21:57 EDT

aurgathor posted : I wanted to buy a 9V NiNH + charger combo such as this off eBay, looking like a nice, matched set.

Since I'm such a nitpicker, I decided to look up the official specs on tenergy's site:
»www.tenergy.com/01141 (charger)
»www.tenergy.com/10002 (LSD 9V)
»www.tenergy.com/10003 (LSD 9V)
»www.tenergy.com/10005 (regular 9V)

The charger is rated 100 mA while the 9V batteries are rated 20 mA standard, and 38-40 mA rapid charge. WTH is going on? I'd expect that they would match their batteries and chargers, but given the over 2x difference in rapid charging currents, that doesn't appear to be the case.

I looked up a some other 9V chargers, but the majority appear to be timer based, and I already have one such charger.

The reason I wanted to buy a microprocessor controlled charger because that should be able to charge the battery faster and able to detect when the battery is full, but something doesn't appear to be right here.

TIA
--
Wacky Races 2012!