Sparking when connecting battery charger

[Hial]

Does anyone know why the negative terminal on my battery charger (Sterling) is at the same voltage as the positive terminals, after connecting the positive terminals to the two boats batteries. When I then attempt to connect the charger negtive to the battery negative I get a fair sized spark. Both batteries were isolated from the boats circuits and the charger was unplugged from the mains. The charger seems to be working fine apart from the initial connection sparking.

 

[macnorton]

Is the charger designed to be left connected? it could have a capacitor across the dc which will draw current when first connected.
Sparks near a battery can be very dangerous as batteries give off explosive gas!!

 

[William_H]

The sparking you see is most likely caused by a capacitor in the charger being suddenly charged by current from the battery you are connecting to.
I would expect if you connected the negative first then the positive you would still get a spark.
The capcitor will be a large capacitance electrolytic type which is almost like a small battery except it can be instantly charged hence the initial high current into it.
The capcitor is used to smooth out the pulsed power from the rectifier and from the AC supplying the power.
Often also the smart chargers need to detect the correct battery connection before they start to charge hence the current flowing into the charger again most likely into a capcitor which is used to smooth out any variations or pulses at the battery from varying loads. So don't worry good luck olewill

 

[Hial]

Thanks very much guys for the quick replies! Yes the charger is meant to be permanently connected. I noticed a similar but smaller spark when I reconnected my wind turbine charge controller so it must have capacitors across the output too.

Alex

 

[Jim@sea]

Is the charger designed to be left connected? it could have a capacitor across the dc which will draw current when first connected.
Sparks near a battery can be very dangerous as batteries give off explosive gas!!

I had a truck where when you turned the key the starter did not work. I called an auto-electrician, while I was waiting I charged the battery, three hours later when he turned up the battery was fully charged. I told him that the battery was fully charged, but he had to test it himself, anyway he reached under the truck with a heavy discharge tester, there was a spark, and the battery exploded, OK this type of battery was the type where there were individual cells with top up caps but the principal is the same when testing batteries in an enclosed area, vent it first.

 

[Daydream believer]

When i was young I was disconnecting a battery charger when the battery exploded blowing the acid in my face
It was only the prompt action of my mother ramming my head in the washing up bowl then flushing my eyes under the tap ( causing a massive bruise on my forehead) that saved my sight. I spent 3 days with eyes bandaged & I began to understand the problems a blind person has
My mother was holding my arm when she took me to see the specialist in a hospital. She told me about the steps & that we were going through double doors but did not tell me that the half my side was shut
She walked me straight into the shut half while she went through the open half. So I needed a nose specialist as much as an eye specialist

 

[Hial]

They can be very dangerous things to work with. I let them "rest" for a while after charging before disconnecting or moving them.