Starter cranking amps

Farmall H, HV & Super H, 300 & 350, 1939-1958

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pokitisme
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Starter cranking amps

Postby pokitisme » Tue Oct 23, 2018 7:14 pm

I'm pretty sure I got a weak battery with dead cells. I'm almost 100% sure of it. What I'm curious about is with a voltmeter how do I determine the cranking amps for a starter on a 1948 Farmall h. Or does somebody have the actual listing for the amperage for the starter. I've charge this battery over and over and it reads 12 volts. But I suspect it's a pretty damn damage battery. I have not yet hooked up the voltmeter to it while I tried starting it I plan on doing that tomorrow. I checked all the connections and everything is pretty tight and I've cleaned everything when I hit the starter button it does attempt to turn just a little bit. but like I suspect I don't think it has enough volts to kick in. I know it's a screwed-up battery but the Curiosity part got the best of me so what is the starting and running amps for a 48 Farmall h
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John *.?-!.* cub owner
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Re: Starter cranking amps

Postby John *.?-!.* cub owner » Tue Oct 23, 2018 8:23 pm

I have never measured the cranking current on my old H, but typically on a 12 volt conversion you could expect 50 to 75 amps. The current drain will vary, rising as a piston comes up to TDC compressing the fuel air mix and drops off as it passes TDC, to repeat the cycle as the next piston comes up on TDC. Running current will be about .5 amp for the ignition, but I do not know what size alternator you installed when you converted to 12 volts. You cannot measure cranking current with a typical multimeter, you will either need an inline ammeter capable of handling that type current, or a clamp on DC meter.

Read voltage directly across battery, and then with lights on if you have them. See if it holds 12 volts. Then with lights off, read battery voltage while cranking. with a 12 volt system it should stay above 8 volts. Having a 12 volt system powering a 6 volt starter can make readings unusual though.
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Re: Starter cranking amps

Postby tst » Tue Oct 23, 2018 8:48 pm

a fully charged 12v battery should rear 13 to 13-5 volts so your battery is not fully charged or could have a bad cell, on a volt meter while cranking the engine it shout not drop down to less than 9 volts, a battery with low voltage will kill a starter if you continue to use it long enough

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pokitisme
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Re: Starter cranking amps

Postby pokitisme » Wed Nov 28, 2018 7:01 am

Too much guys. Yeah the point about the alternator is a good point because not everybody switches over to 12 volt with the same alternator. Which I had not considered. You know what really sucks about this is I had videos up on YouTube showing me starting the tractor with the voltmeter attached reading the actual voltage and stupid YouTube deleted my page I do have a second page but it only has like 4 videos up I think it does have a complete carburetor tear down and rebuild on it. Anyway guys thanks much for your info
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Re: Starter cranking amps

Postby ShawnAgne » Fri Dec 07, 2018 9:26 pm

When I converted the 300 and the Cub over to 12V with electronic ignition about a year ago I just got the biggest battery that would fit in the Cub box and used that in the 300 also. It doesn't take much as the 12V battery will spin the 6V starter pretty fast. Prior to conversion I had a cell go bad on a new battery I bought for the Cub, they won't start. However if I remember correctly it never read 6V, it only read around 4.5V.
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Re: Starter cranking amps

Postby NavyBM » Mon Jan 14, 2019 7:29 pm

I converted my 1946 H over to 12 volts. I did a compression test, have 120 psi +/- on all four cylinders. Have new 30W oil in the crankcase. Tractor is inside the shop. Have the biggest 12 volt battery that I could fit in the factory battery box, 525 CCA's. Had local starter shop go thru it. I made up new battery cables, new starter switch. Left the ign off, put my snap on amp gauge on. Cranked the engine over, it hit 400 amps for a brief moment then went down to 250 amps. Pulled ign switch out, it started so fast I couldn't even watch how many amps the starter took.
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Re: Starter cranking amps

Postby John *.?-!.* cub owner » Tue Jan 15, 2019 11:29 am

What kind of ammeter were you using, one of the clamp on digital meters, that 400 amps is awfully high, even the 250 amps for a 12 volt is high. If a digital clamp on, being close to the starter will cause them to give a false reading.
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Re: Starter cranking amps

Postby outdoors4evr » Tue Jan 15, 2019 1:18 pm

If you want an accurate reading of amperage, the only "good" way to do it is put a resistor in series and then measure the voltage across the resistor.
If you use a 1 ohm resistor, then measuring 1 volt across the resistor would equal 1 amp of current flowing through the resistor.
Since you are moving 50+ amps, it takes a high wattage resistor.
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You can spend less on this by reducing everything by a factor of 10 or 100.
Example factor of 10: use a 0.1 ohm resistor and a 1 volt measurement across the resistor would equal 10 amps.
Example factor of 100: use a 0.01 ohm resistor and a 1 volt measurement across the resistor would equal 100 amps.

You still need the ability for the same number of amps to go through the resistor so the terminals need to be hefty, but it won't get as hot and the lower resistance will impact the circuit less.
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pokitisme
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Re: Starter cranking amps

Postby pokitisme » Mon Jan 28, 2019 12:29 pm

I actually found what the starting voltage was. It's about 8.6 volts. I recently RI added some videos to my YouTube page that will help some people out with the international harvester Farmall h tractor.... My YouTube is
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I have a carburetor tear down and rebuild on there. And also a few random videos about the tractor itself. I plan on doing more when my sciatica is cleared up and I have a job LOL and I have free time
Favorite quotes by me. If you want to you can but if you don't you wont... most possibly yes but maybe no.... and as always buy guns keep America free


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