[Oeva-list] The ever misunderstood Volt

cje at hevanet.com cje at hevanet.com
Wed Dec 22 13:02:20 PST 2010

Okay, so I got bored and started going through a box of wall wart adapters 
I had. I found a 12v one and I grabbed a dead 12v motorcycle starter 
battery that was sitting on my workbench. I measured the battery voltage, 
and it was something like 8v (dead dead). So I did some quick cutting and 
soldering and put some alligator clips on my wall wart. I then hooked it 
up to my battery. I measured across the terminals and the voltage showed 
like 17volts. I left it plugged in overnight (outside, so if it blew up it 
wouldn't start my house on fire). Next day I measured across the 
terminals, with the charger still on it, and the voltage measured  
14v, so I took the charger off it and my battery seems to be charged. 

Did I do a stupid thing? It seems like wall warts would be a lot cheaper 
than expensive trickle chargers. Is it normal that as the battery got more 
charged, the wall wart would put out LESS voltage? Is there a resistance 
thing going on? Anyone got a clue? I tried googling "how does a battery 
tender work" but couldn't find anyone that knew, or would say, what's 
actually happening in the machine -- just how you hook one up. Do all 
chargers do that? 


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