Model A Starter amps ?

it could be in the hundred of amps. It depends on how tight or loose the engine is and how well charged the battery is charged.

Tom Endy
 
I did some tests a couple years ago with a stock engine, 6 volt starter, and using a 6 volt battery, then using a 12 volt battery. I posted the amps and volts measured at the starter while cranking, as well as the engine RPM. I think I still have all the figures written down somewhere. I'll see if I can find them.

I do recall the amp meter needle bouncing back and forth as the starter speeds up and slows down for each compression stroke, so I had to average the sweep of the needle. I seem to recall something like 125 amps on 6 volts, but if I find the numbers, I'll confirm that. This is cranking my well worn engine with 50 lbs. compression on each cylinder.
 
OK, I found my notes and I was a bit low on the amps. I did this test with the battery I bought at the recycling yard 6 years ago. It's a Startrite rated 86.8 Amps/6 hrs. 100/20 hr. rate. The temperature was 70* F.,the battery specific gravity measured 1.270 and voltage measured 6.5.

The engine was totally stock and cranking speed was 114 RPM. The cranking draw was 160 amps. The starter switch measured 5.35 volts and at the battery measured 5.6 volts while cranking.

I used a 12 volt battery and repeated the same tests. The battery was an Autolite group size 24F with 525 CCA @ 0* and CA 630@ 32*. The battery measured 13.4 volts.


The engine cranked at 269 RPM and used 190 amps. The battery measured 11.2 volts and the starter switch terminal measured 10.9 volts while cranking.
 
114 to 269 is a huge difference on thumping in of the pinion.

Thanks for info Tom.
 
pooch said:
114 to 269 is a huge difference on thumping in of the pinion.

Thanks for info Tom.
Click to expand...
Yes, it is and I wasn't too excited about doing the test on my car with 12 volts. 12 volts certainly isn't needed, as hand cranking fires the engine right up, and that's real slow cranking.
 
I did a test similar to Tom's a few years back when in a discussion of amp draw, 6v. vs. 12v. in a magazine. I didn't write down the figures but as I recall it drew fewer amps on 12v., but not as much less as I had expected. I had thought there would be 1/2 the draw with 12v. but hadn't figured in the fact that the starter was now producing more torque. I was testing on my A with a 6;1 head.
 
Would be interesting to now do your test with a 12v. battery and 12v. coils in the starter. We're presently running 12v. battery with original 6v. starter and I always thought it was pretty cool how fast it cranked and started. Sounded like it cranked about the same speed as a slow warm idle. Had been thinking some about converting the starter to 12v. someday to lighten the load on the bendix but after seeing the results of your test now am seriously thinking about it. Had always thought that 12v. going to starter would be about half the current but hadn't thought it through about how much more power starter is now producing. We recently had a battery totally give up when we were about 45 miles from home and tried to jump it with a medium size set of jumper cables. With our battery doing nothing to help we couldn't get enough juice to turn engine over. The cables sure warmed up though. Am thinking changing the starter to 12v. coils is a real plus to not only lighten the load on the bendix, but also would make it easier to jump start in case of battery failure, not that that would ever happen again....
 
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