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#389523 - 05/21/17 08:21 PM Ammeter Accuracy
Rusty 37 Master Offline
Backyard Mechanic

Registered: 12/30/07
Posts: 426
Loc: Iowa
Having lots of fun driving around town in our' 37 Master Coupe. I have put about 120 miles on it with only a few minor issues.

What are your observations with respect to in-dash ammeter accuracy? Here is the situation I have.

Based on information in some prior posts and the '37 Engineering Specs I wanted to confirm that the generator was providing the right output. When I rebuilt the generator I set the 3rd brush at 2 commutator bars from the main brush.

I was concerned because the dash ammeter was showing 15-16 amps with no lights and over 20 amps with the head light switch in the second position (no resistor). With the lights on it does show a slight plus charge. This car does have a sealed beam 6v headlights and I have put the higher candle power bulbs in the brake and tail lights.

I connected an ammeter directly to the battery side of the cutout on the generator. I was getting about 14 amps with the lights off and about 19 with them on. Remember that the ammeter has already subtracted the ignition and fuel gauge load (about 2-3 amps).

Based on that difference I connected a different ammeter and got readings within 1 amp of the first one. I am also getting about 7.9 volts which I feel is very acceptable.

Should I be concerned with the what seem to be high reading from the in-dash ammeter? Am i getting too much from the generator and running the risk of overheating it?

Thanks for the help.

VCCA #44680

Vintage Auto Garage - 6 Volt
#389530 - 05/21/17 10:46 PM Re: Ammeter Accuracy [Re: Rusty 37 Master]
Chev Nut Offline

Registered: 01/08/02
Posts: 24989
Loc: West Allis,Wi.
I would say you have it adjusted as perfect as possible with out better equipment. The generator is designed to put out up to 21 amps or so . Being that the generator is air cooled it can safely put out 21 amps. That how I set the generator on my 1934 using the later air cooled generator with the pulley fan. Never had a problem. While I did not have sealed beams had higher C.P. head and tail light bulbs (dual) and would just be a bit on the + side unless you went over 50 MPH. The 3 brush generator peaks arounr 50 MPH and the charging rate drops after that.

#389563 - 05/22/17 08:39 AM Re: Ammeter Accuracy [Re: Rusty 37 Master]
tonyw Offline

Registered: 05/23/02
Posts: 4174
Loc: Goulburn Australia
I dont think you have a problem, most automotive instruments are not always spot on accurate. Your readings are very close and within specifications.
1938 1/2 ton Hope to drive it before I retire

#389578 - 05/22/17 03:32 PM Re: Ammeter Accuracy [Re: tonyw]
Rusty 37 Master Offline
Backyard Mechanic

Registered: 12/30/07
Posts: 426
Loc: Iowa
Hi Gene and Tony,

Thanks for the confirmation that my readings are in range.

One interesting point and the reason I had to question the ammeter + readings is that the discharger readings seem much more accurate. Those readings all match the calculated loads within about 1 amp.

Gene: Just got my confirmation for the Middle West Meet. It is a shorter time there than I would like but I will be there mid-Wednesday afternoon. See you there!

VCCA #44680


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