Re: 4020 12v/24v system

Posted by jdemaris on October 19, 2006 at 05:13:22 from (66.218.17.231):

In Reply to: 4020 12v/24v system posted by nickg on October 18, 2006 at 20:14:36:

That starter needs at least a consistent 18 volts under load to crank properly. As Bob stated - other than the 24 volt cranking system - one side of the tractor is 12 volt negative ground, and the other side is 12 volt positive ground. But - as far as the system working "great" when it was in production - I'd argue that. I went to MANY Deere service schools when those systems were new or recent. Deere had several problems that could not be fixed sucessfully and was constantly coming up with new "band-aids.". #1 problem was the starter itself. For the entire electrical system to work properly - the starter needs to stay isolated or "groundless." But - over time it will develop internal grounds from brush-dust and create havoc. On some systems, a small fused ground wire is used on one battery -and it will blow constantly once the starter develops a slight ground. Also - the higher the voltage - the smaller the wire-diameters. The Delco 24 volt used by Deere had very fine wires in the starter-windings that burnt up much easier than a 12 volt or 6 volt starter. So, starters on such tractors in cold climates had short life-spans. I assume if directions were followed closely -this would not happen. But - how many people - when they need their diesel tractor running - let their starter cool for five minutes after every 30 seconds of cranking?
In regard to the two separate 12 volts systems used in the tractor for lights and accessories - it was dependent on a balanced load between both sides. It could not sense and accomodate separate 12 volt demands. Even with small-draw loads - e.g. a 3 amp load from a radio - the system would suffer unless a dummy-load was installed on the opposite side to compensate. We had some serious problems with a few farmers attemtping to use corn-planters with a 6 amp per row draw.
When the 24-12-12 system first came out - Deere engineers were bragging about it - saying it was the first of its kind - and custom tailored for Deere by Delco-Remy. I didn't get it then - and still don't. My old Allis Chalmers crawler - circa 1956 - has a non-complicated 24 volt system and has been much more reliable than the mess Deere used.

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