battery charge

[stranger12]

good morning all,

If i was to use a lower amp battery charger which is rated to charge batteries between 10-40 amp(ah), can it be used to charge a 100amp battery ? I thought the answer is yes but it just takes longer or am i incorrect ?

thanks
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[Islander]

Yep, it'll just take longer and if the battery is too discharged, it might not be able to do much at all.

[stranger12]

thanks shall get a alightly stronger one then
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[dolly3900]

Long Answer

Batteries are rated in Ah (Amper Hours) for use and a maximum current to be drawn without damage

So I am assuming your 100A battery is a standard bike battery which is probably about a 6Ah with a 100A max load.

This means it will provide 1A of load current for 6 hours, 6A of load current for 1 hour, or any other combination of multiples up to a 100A load current for about 3.6 minutes (obviuosly taking into account losses etc.)

Most batteries have a typical/maximum charging rate (usually a couple of amps), but when totally dead, can draw much more in order to kick off the chemical reactions inside the little beasties before settling down to charge normally.

If your charger is rated at 10-40A, this will mean that it is designed to give out a constant load up to 10A, with a peak/spike load of 40A (such as on initial charge from flat)

If your battery is designed for a 1-2A charge current, that is all it will take under standard charging, no matter what you plug onto it, so the 10-40 charger will be operating at about 20% of its standard trickle charge load, no matter what.

It is like your TV at home, it is designed to draw about 3A from the mains, but the mains to your house is able to provide enough for the cooker, the shower and the rest of the house to (several hundrend amps in total), but the telly only draws what it needs.

Short Answer
Plug it in, it'll be fine


Hope that explains and helps

Mike
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2002 Rieju RS2-50 (Sold, spares or repair), 2010 Suzuki DR-125SM (Traded for ->), 2007 Honda CBF 600 (Sold), 2010 Suzuki V-Strom 1000 (Briefly, now returned), 2007 Suzuki Intruder 1800m (Even More Briefly, traded in for ->), 2014 Suzuki V-Strom 650

[stranger12]

thansk great explanation.
I didn't quite get the A vs AH .
if mine is 6Ah that means you can draw 6 amp per hour?
what happens if you draw 50amp per hour ?

I am asking because you said my battery is most likely 100Amp

So if my small battery is 100Amp that means car battery which are 50-60 Ah are around 600-700 Amp? is the max load the cranking amp which for most cars it is around 400-600?
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R6 Red

[Islander]

Amps (or amperes) are a unit of current - that's the flow of electricity (Volts are a unit of pressure - the ability to pass current into a given load). Ah is a unit of charge that's used to rate the battery's discharge capability. A 100Ah battery can theoretically provide a flow of 1A for 100 hours, 100A for 1 hour, 4A for 25 hours, 25A for 4 hours etc etc.

In reality, that'll pretty much work for low current discharges but high current discharges will be less than the rating.

Batteries also have a rating called the CCA or cold cranking ampere rating which is the maximum instantaneous current they can provide for short cycle use - i.e. starting a cold engine. This is higher than the Ah rating.

[stranger12]

thanks for this but what confused me is the sentence which reads out as 100A is 6Ah which according to your description the 6Ah is 6 am for an hour before it drains thus where does the 100A comes from ?
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R6 Red

[Islander]

6Ah is the continuous discharge rating - i.e. 1A for 6 hours etc. 100A is the CCA or maximum instantaneous discharge rating.

This is why you should never wear jewellery when working on vehicle electrical systems.

[stranger12]

got you.

thanks both and oh yes I never has any metal parts on me when working on car/bike
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