What happens to starter brush leads when you don't know when to stop cranking

[wwillson]

These leads used to have brushes attached to them. This is what happens when you don't know when to stop cranking. Someone, who shall remain nameless to protect his young pride, was trying to start a 1961 John Deere 4010, which had low batteries. The engine wasn't turning over fast enough for the engine to start, but that didn't stop him from having hope that if he just kept cranking it would start. He said it, "just stopped cranking", then he noticed one of the ground straps from the battery to the frame was on fire.

He took the starter off and I took it to the electric motor repair shop in the next town over. The internals had gotten so hot that the armature needed to be turned and the brush leads where melted and completely separated from the brushes. When we went to put the starter back on, I asked for the picture of the wiring he took before he removed the starter. He looked at me like I had three heads. The starter has two relays and several wires running to it. It took me an extra 30 minutes to figure out which wire went to which terminal.

While we were installing the starter I took the time, patiently, to explain that you always take a picture of something before you take it apart. Then I explained Ohm's law and why batteries with low voltage can still melt things.

I also explained to him that virtually everything I know I learned the hard way, so he shouldn't feel too bad.

 

[wpod]

Lots of heat is generated cranking .

 

[wwillson]

Lots of heat is generated cranking .

Yep

Heat = current² x time

 

[Texcl2]

Glad you took the time to teach him.

 

[RobbyDawg]

Counter Electromotive Force (emf)

www.flight-mechanic.com

This is a good explanation of why not to crank an engine with low battery voltage/low cranking speed.

 

[14Accent]

Love your outlook on this. When I was young and learning from my geezer of a mentor, I had plenty of moments like these. From installing tapered seat lug nuts backwards to hooking up a battery in reverse. The repair industry is a perfect example of learning while doing.

 

[Cruzer4326]

If that was a diesel it has a very unique electrical system. It is neither a negative ground nor a positive ground.
It's actually an insulated ground. Many have not researched this carefully and burned up radios learning this lesson. Not to mention other electrical problems encountered while jumping/being jumped.

 

[wwillson]

If that was a diesel it has a very unique electrical system. It is neither a negative ground nor a positive ground.
It's actually an insulated ground. Many have not researched this carefully and burned up radios learning this lesson. Not to mention other electrical problems encountered while jumping/being jumped.

This tractor is a diesel and it's a negative ground system.

 

[Cruzer4326]

This tractor is a diesel and it's a negative ground system.

Converted to 12v?

 

[BeerCan]

I thought these tractors were 24v floating ground? At least the ones I have seen are that.

 

[Cruzer4326]

Floating= insulated.
In the early '70's (I'm not certain of the exact year as I'm 30 years removed from the auto electric industry), John Deere changed the electrical system of the 40 series tractors to a 12v system and at that time changed from a generator to an alternator.

 

[wwillson]

Converted to 12v?

Yes

 

[wwillson]

I thought these tractors were 24v floating ground? At least the ones I have seen are that.

From the factory in 1961, yes, but it was converted to 12v.

 

[wwillson]

Floating= insulated.
In the early '70's (I'm not certain of the exact year as I'm 30 years removed from the auto electric industry), John Deere changed the electrical system of the 40 series tractors to a 12v system and at that time changed from a generator to an alternator.

I think they made the change in the late 60s on the 20 series. As far as I can remember all 30 series and up are 12v negative ground. All of them that we owned (late 20, 30, 40, 50, 55, and 60 series) certainly were.

 

[BeerCan]

From the factory in 1961, yes, but it was converted to 12v.

Makes sense. the old style was a mess.

 

[wwillson]

Makes sense. the old style was a mess.

No truer words have been spoken.

 

[Cruzer4326]

Makes sense. the old style was a mess.

I need to clarify,
With my first comment I was reviewing in my rusty memory and the construction of the generator and starter on the 40 series diesels. Their "ground" brush is insulated. So, in my calling it an insulated system, that is in reference to the starter/generator. They are insulated ground components. The actual chasis of the tractor is a connecting battery cable that caused some confusion. I suppose that might be where your term of floating ground comes from.

 

[Blackstack]

No truer words have been spoken.

I've looked at a wiring schematic of one before and got a headache. Don't know what the point of it all was? My Dad had a 4010 Diesel when I was a teenager. He had our family mechanic who is a pretty sharp guy come over to do something to it and he was pretty dumfounded by it. He was a mechanic in the Air Force with 20 years experience after that by the time I'm thinking he was over so it certainly wasn't his first rodeo with 24 volt systems either.

 

[Blackstack]

I think they made the change in the late 60s on the 20 series. As far as I can remember all 30 series and up are 12v negative ground. All of them that we owned (late 20, 30, 40, 50, 55, and 60 series) certainly were.

That sounds about right to me. I think the late side console JD 4020's were 12 volt.

 

[wwillson]

That sounds about right to me. I think the late side console JD 4020's were 12 volt.

We have one of those to this day. Yes, it's a 12 volt system.