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Battery charging question...

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DewAddict

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This is way off topic, but I have several wall chargers hanging around that have an output of 12v and some 16v at 500ma to 1000mah rating. I want to use one of these to charge a sealed Lead Acid battery of mine that is 7 Amp Hours. I am thinking that I will just cut the end off of the power cord and add connectors that will fit onto the battery posts.

How long will I need to charge the battery and is this going to work? If so, which voltage should I use? I looked online at a "smart charger" that is used to charge the same type of battery I have but they want $20 plus shipping for what appears to be the same thing I have but it has an auto shut off. I can unplug it myself and save the money.

Rob
 

DaveH

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Jul 29, 2001
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3,072
Location
Ottawa, Ont.
DewAddict said:
This is way off topic, but I have several wall chargers hanging around that have an output of 12v and some 16v at 500ma to 1000mah rating. I want to use one of these to charge a sealed Lead Acid battery of mine that is 7 Amp Hours. I am thinking that I will just cut the end off of the power cord and add connectors that will fit onto the battery posts.

How long will I need to charge the battery and is this going to work? If so, which voltage should I use? I looked online at a "smart charger" that is used to charge the same type of battery I have but they want $20 plus shipping for what appears to be the same thing I have but it has an auto shut off. I can unplug it myself and save the money.

Rob
My suggestion is not to rely on any of these crude unregulated wallplug chargers
to do that job. They will likely damage the battery and possibly themselves (and
the surroundings if you are unlucky), especially the 16v one. Spend a little time
and money to do the job properly.

What is needed is something that can supply reasonable charge current and
taper off or cut off completely at a certain voltage. These wall plugs, unless
specifically designed for the job, will do none of this. If left on trickle charge
continuously, the circuit should adjust its voltage for temperature to minimize
long-term overcharging effects.

You could use the unregulated suppy as a source, with a follow-on regulator.
The 500mA one will take more than 14 hours to charge the battery assuming
it is completely dead, which is not a good place to start. To last, these type
of batteries should not be discharged much past the 50-60% level. From 50%
it would be 7 hours plus some allowance for "charging effeciency" so I'd say
roughly 10 hours.

A simple charger would be a regulated "stiff" (roughly) 14v supply with current
limiting, either inherent to the supply or with a series resistor. I'm not sure
what the upper limit of charge current is for these batteries.

Dave
 
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