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Thread: NiMh batteries maximum charge voltage?

  1. #1
    Flashaholic* LEDcandle's Avatar
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    Default NiMh batteries maximum charge voltage?

    Just received 4 x Powerizer 5000mah C-cells and a Powerizer charger from Batteryspace.

    The batteries came at 1.25v which is good and well, since the batts are supposed to be 1.2v resting voltage. I thought 1.25 was 'fresh out of the charger' kind of voltage.

    I used the batts for a little while in my flashlight then decided to charge them up full again to see how high it could go. The Powerizer charger has 4 slots to charge the batteries but it can only charge in pairs. So meaning 2 or 4 batteries can be charged together.

    The first pair stopped at 1.37v (green light came on) and the other pair kept going on for another 1 hour +! Afraid something was wrong, I stopped the charging then. The batts measured 1.4v.

    I'm wondering why the 'inconsistency' and also is there something wrong with NiMh's charging so far past 1.2v? Can they actually reach 1.5v?

    Hope nothing is wrong with one bank of the powerizer charger.

  2. #2

    Default Re: NiMh batteries maximum charge voltage?

    I'm one of very few people (that i know of, anyways) that use C cell on duty every night in several lights. Most cops like D cells mags or magchargers or streamlight rechargeables. All 3 of my primary duty lights are C cell lights.
    Anyways, I have to say that my Powerizer C-5000mah cells worked well "right out of the box" & didn't need any "conditioning" before i experienced good results. On the other hand i also use CTA C-5500mah cells & had to really condition then through several charge/use cycles before they started to perform well. Soon i'm going to upgrade to Accupower C-6000mah cells unless someone produces a C cell higher than 6000mah.

    Regards,

    John
    Primary duty lights: (metal) Elektrolumens Pentalux 4C; (polymer) Pelican M8 LED; (hybrid) StreamLight 3C-XP
    Searchlight: AE PowerLight PL14
    Back-up mini lights: Nuwai TM301X-5, X-3, X-1
    Special LED signaling lights: Torfino ICE light, Inova 24/7, Adventurelights VIP

    NYPD flag, adopted in 1919

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    Flashaholic* LEDcandle's Avatar
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    Default Re: NiMh batteries maximum charge voltage?

    D-cell powered lights are usually more powerful and last longer, but big capacity C-cells tend to suffice and give a nice balance to size and weight.

    If only battery mah ratings really came close to their value; I don't see a 3 x C-cell (15ah) 1-amp driven lux light running for anywhere near 15 hours.....

    Another question : Can I recharge unmatched voltage NiMh's in the Powerizer charger? It's supposed to be 'smart'. Since I'm using 3 cells for my light, I'll always have odd one out and to charge my 3 cells I will definitely have to pair one of the cells with the unused cell.

    I should have got the BC1-HU; didn't really know much about NiMh's when I ordered The 2 or 4 batt requirement is rather inconvenient.
    Last edited by LEDcandle; 01-08-2006 at 05:26 AM.

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    Default Re: NiMh batteries maximum charge voltage?

    Hello LEDcandle,

    NiMh cells will come off the charger at around 1.45 volts when they are "broken in" and fully charged.

    It sounds like you may need to leave your cells in trickle charge mode for a while to get to where they are fully charged.

    It is not a good idea to charge cells in parallel that are not at roughly the same state of discharge. When charging two cells at a time, one cell will terminate the charge before the other is fully charged. You then have to trickle charge for an extended period of time to bring both cells up into a balanced condition.

    With your current set up, you may want to go with 6 cells. This would give you two batches of 3 cells for use, and still allow you to charge in pairs.

    Of course, a charger with independent channels would be more ideal, in my opinion.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Flashaholic* LEDcandle's Avatar
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    Default Re: NiMh batteries maximum charge voltage?

    Hi Tom!

    Yeah, I kinda ordered the wrong charger Didn't read the specs carefully enough and was also trying to get a cheaper option. I prob was also thinking a "Powerizer" charger should be good enough for "Powerizer" batts. Same brand after all!

    But I guess an individual charger would be better.

    I needed to recharge that 1 cell (1.09v) anyway and I dumped it in with the unused NiMh (1.39v). After a few hours when the green light came on, the used cell came out at 1.39v and the unused one came out at 1.4v. Looks good to me??

    Probably the charger was smart enough to discharge the unused cell to the same level and then start charging up together? (But that shortens its life right?) Or somehow it 'bypassed' charging the unused one and just charged the used one ? (Though I can't see how as they should be in series)

    The 6 batt idea is great... However ordering 2 more batts ($6.90) costs $15.24 in shipping haha.. Thanks for the info about the max voltage! 1.45 is impressive, close to an alkaline. Do they discharge fast at that voltage and settle at 1.2 or it goes down gradually?


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    Default Re: NiMh batteries maximum charge voltage?

    Hello LEDcandle,

    The 1.2 volts is supposed to be the mid point voltage during discharge. If you look at the graphs in the NiMh Shoot Out thread, you will see that the voltage drop is dependent on current draw.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  7. #7

    Default Re: NiMh batteries maximum charge voltage?

    You can easily get mislead by putting too much stock in terminal voltage, especially when you're dealing with new cells.

    First off, an important detail; we're talking about *series* connection of the two cells, one after the other. Each has to get an equal charge current. The charger cannot treat them differently (in terms of selectively discharging or charging), no matter how smart.

    The key is in the trickle charging as has been stated. While generally questionable, it's the only way to get the weak one in the pair 'up to specs' in this sort of charger. Although I guess you could carefully discharge them.....

    Doug Owen

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    Flashaholic* LEDcandle's Avatar
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    Default Re: NiMh batteries maximum charge voltage?

    I measured the battery current (hope this isn't a big no-no) directly with my 10A channel on my multimeter and all my batts got around 5.1-5.2 amps.

    If I put a 1.09v batt paired with a 1.39v batt, technically the charger will terminate the charge soon because it detects one of the batteries as fully charged? But in my case it seemed to have continued charging the 1.09v batt, bringing it up to speed with the full one.

    I guess I will have to drain my unused batt off somewhere to bring it closer to its partner batt before charging, but I'm just wondering how come the above seems to work (as in charging unmatched batts).

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