Hello all.

When i charge my 12v sealed lead acid battery with a 12v weston wall charger my battery only shows 12.25 on the multimeter regardless of how long i leave it on to charge. Is there anyway i could test my 12v charger with a multimeter?

Thanks,

 

Take the charger off the battery and see what the output is. Also, look at the voltage across the battery terminals with the charger running. If the charger shows something over 13 volts unloaded (13.2 - 13.6 volts is ideal), it is probably good.

If the voltage across the battery with the charger running is significantly higher than the 12.25 volts, then the battery is suspect.

The bad news is that if the charger is not putting out a voltage sufficient to charge the battery, then the battery may have gone down too far to recover. If you have jumper cables, you can always put the battery (I imagine this is something like a 7 amp hour gel battery) on the jumpers and charge it off the car. Just remember to connect positive to positive and then negative to negative. The small one will explode if you get the connections backwards - be careful.

 

Thank-you for your reply.

I would like to mention that i use the 12v acid battery to charge lipo batteries that i use to power a model plane.

Could you please explain how i check the output on the charger (i assume you were referring to the chargers output).

When i check the battery with a multimeter whilst conected to the charger the reading is the same 12.25.

Would a reading of 12.25 suggest the battery is damaged? I understood that a reading of 12.25 would suggest the battery is 60% full.

Kind regards,

 

It should be able to apply a charging current to the battery. That means being able to hold a voltage high enough to drive current into the battery while also supplying that amount of current. Since you state that the voltage with the charger running is still 12.25, it sounds like the charger may not be functioning.

To check the charger output voltage, just attach your meter leads to the charger while it's running, but not connected to the battery. You should read something over 13 volts. If that is the case, connect one charger lead to the battery, place the meter in the ammeter mode (use the highest range) - move the leads to the ammeter sockets if necessary - and check the current the charger can supply to the battery. With the charge down to 12.25 volts, the charger should be trying to supply several hundred milliamps charging current.

If the charger does not have an output, then you will need to replace it. Unless you're lucky and can get into the charger and find a blown fuse.

 

Thank-you for your help.

I have plugged the wall charger into the wall and put the multimeter onto DCV with range 20 being selected, i have attached the red and black multimeter leads onto the red and black charger leads and the reading is 0.11.

Should the black lead which is currently in the com socket on my multimeter be moved to the socket labled 10ADC in order to test ammeter, or do i move the red lead which is currently pluged into the VMA over to the socket labled 10ADC.

I do apologise for my ignorance.

 

Not at all. The voltage test pretty well tells us that the charger is not working. Your challenge is to either get into it and find a failed component, or to obtain a replacement.

You are correct about moving the meter leads in order to measure current. But the charger lacks a voltage output, so there is no need to look for current.

 

Thank-you very much for all your time and effort. I will take the charger back and get a replacement.

Kind regards,

Chris.

 

Some battery chargers don't turn on unless connected to battery. This eliminates sparking if the charger is on when connecting, also prevents problems of reverse polarity connections. I would check voltage with charger connected and turned on, then shut off charger and see there are any changes.