Author Topic: MAKING A TEST AMMETER  (Read 692 times)

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Offline Brooklands

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MAKING A TEST AMMETER
« on: November 27, 2011, 09:58:30 pm »
Most test meters typically cover volts, but are not able to measure amps. I made up this simple meter from the innerds of a car 12 volt ammeter that I'd originally bought at a boot sale for its bezel for a £1. The ammeter is mounted in an old aerosol paint cap, with the lid of some potion my wife puts on her face (£35 a little pot!!), and a couple of old crocodile clips, all insulated.
Originally I used it on my modern battery charger that has fancy lights, but gives no idea of the charging rate, but it is useful to check out any component, especially when you are looking at charging rates/power consumption. It doesn't especially matter about polarity, as it is the deflection that is important.
A 12 volt ammeter gives a 1:1 reading on 12 volt systems, and when used on 6 volt systems the reading is doubled.
A 6 volt ammeter reverses this when used on 12 volts, with only half the deflection.
To work out power consumption  use the formula Volts x Amps  = Watts, so a 30 watt bulb, on a 6 volt supply draws 5 amps., and a 30 watt bulb on a 12volt supply draws 2.5amps.
Joe
Norfolk 'n good!