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Some advice - Laptop power supply - Please

post #1 of 3
12/17/09 at 3:28am
Thread Starter 
I'm trying to charge 2 x 9volt Nimh batteries, I have the usuall trickle charge circuit (Lm317, 2 diodes, resistor ) I have the current set at about 19mA (1.125/68R) and it works fine with a normal 18volt unregulated plug pack.

I thought I'd use a 19volt laptop supply, hooked it up all good then I noticed the current dropping its now down to 8ma and falling, the voltage out of the supply is 19.96Volts its rated at 3 amps, but its acting like its bored with the job

any ideas

thanks
FRED
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post #2 of 3
12/17/09 at 4:56am
Is the regulator overheating? Maybe its the thermal protection kicking in?
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post #3 of 3
12/17/09 at 12:07pm
Quote:
Originally Posted by Fred_fred2004 View Post
but its acting like its bored with the job
Only a guess, but perhaps it is. Think some (all?) PS designs have something akin to a load hurdle that much be reached for them to supply juice. IOW, they are designed to feed certain loads & if not presented w/expected loads (cell/cell-charging PCB resistance/impedance) they do not supply associated current.
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