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  1. #1
    Shortman's Avatar
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    NIMH fast charge rate???

    Whats a a good fast charge rate for my Radical RC 1650 Mah 4.8V Nickel Medal Hydrate pack?

    I am not to familiar with the C rate charge. I Have the Dymond Super Turbo Charger which goes from C 0.1-C 5.0
    Steven Carroll
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  2. #2
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    NIMH fast charge rate???

    A C/10 charge rate is 10% of the rated capacity during an hour. For your 1650 pack, that would be the 165mah charge rate, for 12 to 14 hours.

    Its usually safe to fast charge NiMh packs at 1C rates, which would be the actual rated capacity in one hour. For your 1650mah packs, that would be the 1.65amp rate. However, this should only be done on chargers that are designed to charge NiMh packs at that rate. You can't use a NiCd charger. If you are using a NiMh charger, you can also treat your batteries a bit gentler by using a 3 or 5 hour charge rate. That would be approximately 650mah for 3 hours, or 390mah for 5 hours.
    Stephen

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    NIMH fast charge rate???

    The Dymond Super Turbo is a NIMH charger and nicad. I just don't fully understand what actual rate to charge it at. C what? I understand what your saying but to make sure....

    so if i wanted to charge it in 1 hour that would be C = 1.0 correct? or would that be C = 1.6 ? See what I am getting at, this doesnt make sense for me
    Steven Carroll
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    NIMH fast charge rate???

    Your battery is a 1650 mah battery. Capacity rate charging,"C", is 1650 milliamps. This would pump 1650 milliamp-hours of charge into it in one hour. This is referred to as charging at "C". C/5 is one fifth as much charging current, 2C is twice as much, or 3200 milliamps (3.2 amps).

  5. #5
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    NIMH fast charge rate???

    C/5? on my Dymond thats 5 AMPS

    i thought C/10 is = C 0.1?
    Steven Carroll
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    \"The more you know, the more you know you don\'t know.\"

  6. #6

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    NIMH fast charge rate???

    I think I might see why you are confused. I found a picture of your charger on the internet and it displays a 'setting' for a charge followed by a discharge. Hopefully you have an instruction manual that will clarify how it operates. I do not have a unit of this type so I do not have an instruction book. I can only go by what I see in the internet picture.

    You state your battery pack is composed of 1650 mah NiMH cells.

    To use formulas that allow discussions about charging and discharging the industry has decided to use an abbreviation of 'C' which means 'the capacity of your battery pack, whatever that might be.' The important thing is this 'C' abbreviation does not stand for CHARGE RATE in this case. This is completely different. It means 'Substitute YOUR battery pack capacity HERE.' So if a manufacturer makes two NiCAD battery packs, one being a 500 mah battery pack and the other being a 700 mah battery pack they can tell everyone to perform a 'slow charge' at C/10 which is 'your battery pack capacity' divided by ten. This is done for convenience. So for the first pack the slow charge rate would be 500/10 which is equal to 50 ma. For the second battery pack the slow charge rate would be 700/10 which is equal to 70 ma. See how the value 'C' becomes convenient to use no matter what capacity battery pack you own?

    Now on your charger I see a DIFFERENT 'C' being used. This appears to me to mean 'CHARGE CURRENT IN AMPS'. So that if you dial in 'C = 1.6' then the charger will charge at 1.6 amps until the battery if full, then it will trickle charge from that point on. So this is a completely different use for the letter 'C' than what was discussed above pertaining to the formula for determining the appropriate charge rate.

    I think that is where the confusion is coming from.

    Now for your battery pack the initial full charge should be performed at a rate of C/10 (that is the formula) which is 1650/10 or 165 ma (and this is the same as .165 amps) for about 16 hours. This means you should set your charger up to display 'C = .165' meaning 'Perform the charge at .165 amperes' (which is also equal to 165 milliamps).

    After you have performed the initial (very first) charge and then used the battery pack for a while or you decide to perform a discharge to deplete the cells you will at some point then consider charging it again. This second charge and all following charges from then on can be done at a factory recommended safe 'fast rate' of 1C which in your case is 1650 ma (and this is equal to 1.650 amps). To do this you would set your charger up to display 'C = 1.650' Note that 1C is also equal to C/1 so these two are just different ways of looking at the same value. The manufacturer generally states the formula for a safe recommended charge as 1C rather than C/1 .

    So the 'C' in the formula used to CALCULATE the suggested charge rate is NOT the same 'C' that you display on your charger when you dial in the charge rate. The 'C' in the formula stands for 'substitute your battery pack capacity here' and the 'C' on your charger stands for the 'charge rate in amperes' that you set with the controls.

    The 'D' on your charger appears to stand for 'discharge rate in amperes'. So to discharge at a rate of 250 ma (which is the same as .250 amps) you would dial in 'D = .250'.

    I also see that you can dial in the capacity value of your battery pack and assign this setup to memory. It seems like a pretty nice charger. You even have an option of using a temperature sensor to help prevent overcharging and some type of automatic battery detection mode.

    Also I see an article on the radicalrc.com website about fast charging and the author states he has used 'fast charges' greater than 1C but again, most manufacturers seem to recommend fast charges for NiMH cells to be 1C .

    Let me know if all of this clarifies things for you. I am afraid that without seeing the charger and having the instruction manual it was not clear you were trying to deal with two completely different uses for the letter 'C' without realizing it. If you indeed do follow what I talked about then you have 'seen the light' and all the confusion has been eliminated.

    Just a few calculations for you and your battery pack:

    Charge formula: 1C:
    means a charge of
    1650 x 1 = 1650 ma
    1650 ma = 1.650 amps

    Charge formula: 1.5C:
    means a charge of
    1650 x 1.5 = 2475 ma
    2475 ma = 2.475 amps

    Charge formula: 2C:
    means a charge of
    1650 x 2 = 3300 ma
    3300 ma = 3.3 amps

    Charge formula: C/10:
    means a charge of
    1650 / 10 = 165 ma
    165 ma = .165 amps

    Charge formula: C/3:
    means a charge of
    1650 / 3 = 550 ma
    550 ma = .550 amps

  7. #7

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    NIMH fast charge rate???

    These smaller capacity NiMH can handle 2C OK, in the case of your 1650mAh pack that would be a 3.2A charge rate, but between 1-1.5C would be safer. I've got some 1000 and 720mAh packs that I peak charge at 1C without issue.

  8. #8
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    NIMH fast charge rate???

    thanks all for your help and especially you Keith, i FULLY understand it now hehehe
    Steven Carroll
    AMA# 738035
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    \"The more you know, the more you know you don\'t know.\"


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