[Shop-talk] dewalt battery charger testing

[Wayne]

On 12/22/2010 10:25 AM, john niolon wrote:
> I'm having trouble charging Dewalt batteries... some it may be old batteries
> but I'm wondering if my one hour charger is dying...   Dewalt 9107  one hour
> charger   when I put a meter across the contacts down in the charger I read NO
> d.c. voltage.  although the battery is getting warm and slowly taking a
> charge... I had a completely dead 12v battery and started charging it with a

I actually read the instructions (little embarrassed to say..) last week 
for a DeWalt drill I own.  Surprised to see the warning that the charger 
has "AC line voltage present at the terminals."  Hmmm...  So I ignored 
the warnings "not to probe the charger's terminals" and stuck the 
multimeter on it.  On AC it read 100V one way, and zero with the probes 
swapped.  On DC it read 50V.  Wish I owned a 'scope;  I do not.  I 
*think* that means it has 100V peak to peak AC with a 50VDC bias on 
it???  I really need to buy a 'scope.  If so, the DeWalt batteries must 
have internal rectifiers and regulation.  Guess this is why you can 
charge any of the batteries on the same charger?

-Wayne