Ameters
 

I have a bunch of Model A ammeters. How can I test them before I try to use them?

Re: Ameters
 

You could test them for response by just connecting a D cell battery across the terminals. Short term high current won't hurt the D battery much.

You could test them for accuracy by putting them in series with an ammeter of known accuracy, also in series with a variable resistor all fed by the D cell.

Twiddle the pot to limit current to something within the meter range. You can even do a little arithmetic to find out what range of pot you need. Volts equals current times resistance, V=IR. (Ohms Law and V would be 1.5v as the ammeters both have negligible resistance.)

Harbor Freight sells an el-cheapo digital meter which will measure up to 10 amps. Small money for these like $5 on sale.

http://www.harborfreight.com/media/c...mage_23327.jpg

What you read on one meter you should read on the other.

Hope this helps
Joe K

Re: Ameters
 

I use a sealed beam headlamp that draws about 8 to 10 amps, then connect it in series with the Model A ammeter and my known accurate ammeter and my 6 volt battery or a battery charger. Model A ammeters are very close as long as the needle isn't bent. I've had to straighten bent needles caused by careless handling.