12v to USB charger

[smith]

Hi all, I'm new to all this and my electronics knowledge is non existent. I'm trying to create a 12volt to usb charger to take on hols or fishing etc. currently i have a 12volt lamping battery which is connected to a switch which then in turn is connected to a 12v car adapter to usb connection which then is connected to a 4 port usb. All of this works fine and no problems, everything charges / powers through the usb ports fine. my issue is I'm having issues charging the 12v battery. It's connected directly to the charger. fopr some reason the battery isn't charging. Is this because its somehow bypassing the battery and going directly to the switch? Is there anything I have done that I shouldnt of or anything i'm missing?
regards

Smith

 

[urbantuckerman]

Hi, how are you charging the battery? from a car alternater or from a mains charger? have you tried charging battery with usb adapter disconnected?

 

[smith]

Hi, how are you charging the battery? from a car alternater or from a mains charger? have you tried charging battery with usb adapter disconnected?

I'm charging via mains adapter. (its the genuine charger) and yes I have tried charging the battery with the usb disconnected with success.

 

[urbantuckerman]

I'm really no expert, but i have lived off grid for the last six years and i'm definately no stranger to home brewed 12v stuff. Perhaps the 12v to usb adapter is drawing enough power to drop the charger voltage below that which the battery needs to charge. If you switch the adapter off i should have thought the battery would charge. However i'm guessing you probably already tried this. You could check with a cheapo digital multi-meter, mine cost €4 and has been invaluable. You'd need to set it to dcv20 to test for 12v (usually). 12v also tends to need fairly heavy guage wire, depending on the amps and distance travelled. I'd have thought the usb adapter would be pretty low amps and so this would be unlikely to be a problem, but like i said i'm no expert. Make sure the wires don't get hot under load though, i nearly set my van on fire once!

good luck!