[Fred_fred2004]

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

 

[mugdecoffee]

Is the regulator overheating? Maybe its the thermal protection kicking in?

 

[cfcubed]

Quote:

Originally Posted by Fred_fred2004 /img/forum/go_quote.gif 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.