Thursday 23 February 2017

Electrical Project - Battery Voltmeter/Ammeter

Having four bikes (3 runners, 1 donor) means that some don't get used for long periods and I like to keep their batteries charged. A lead acid battery will self-discharge and I've had a flat battery freeze. (although it's rarely that cold here)

I use an old battery charger or a cheap battery tender that can be permanently attached. These don't give much indication of what is going on charging-wise. I can check the voltage being applied across the battery and the current flowing into it using a multimeter. But it's awkward doing this and it's easy to blow up cheapo meters by shorting them out across the battery on the current setting.

I thought that it would be good to have a device to measure voltage & current between the charger and the battery. A quick look on eBay found that such a device was available at a low price.

Now I'll say right here I not good with electronics. They are a bit of a mystery to me so I might start talking a load of rubbish.

The digital voltmeters/ammeters come in different ranges but I got a 100V/10A model.

It didn't come with instructions but I found a diagram on the internet.

The meter arrived from China yesterday and I made a unit to hold the meter, battery etc.

I tested it out using a fan.....

.....and it worked!

I hesitated attaching it to a battery. I was worried that if the charger was switched off the battery would discharge back into the meter and blow it up. The charger is protected by diodes so I fitted one to the meter. (a 3A Schottky Barrier Recifier if that means anything to you - 50p from Maplins)

The final arrangement with a battery being charged and the meter working.

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