The Ford Barn

glenn in camino · 01-26-2014, 10:48 PM

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

Joe K · 01-26-2014, 11:52 PM

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.

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

Hope this helps
Joe K

Tom Wesenberg · 01-27-2014, 07:49 AM

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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.

01-26-2014, 10:48 PM	#1
glenn in camino Senior Member Join Date: May 2010 Location: Camino, CA. Posts: 3,086	Ameters I have a bunch of Model A ammeters. How can I test them before I try to use them?

01-26-2014, 11:52 PM	#2
Joe K Senior Member Join Date: Jul 2010 Location: Cow Hampshire Posts: 4,610	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. What you read on one meter you should read on the other. Hope this helps Joe K __________________ Shudda kept the horse.

01-27-2014, 07:49 AM	#3
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Ameters Sponsored Links (Register now to hide all advertisements) 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.