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lal cenIA

Posted 7/25/2016 21:50 (#5432515)
Subject: Change of polarity on 3020 gas

Haven't worked with to much JD, can the polarity (change from positive ground to negative ground) cause the starter and maybe something else, to run backwards? They were going to change the lights to LED and would a positive ground create and problems with the lights? Need some electrical advise. Also change the generator to alternator? Thanks for input.

ccjersey

Posted 7/25/2016 22:54 (#5432663 - in reply to #5432515)
Subject: RE: Change of polarity on 3020 gas

Faunsdale, AL

No, the original starter will still run the same direction on negative ground. If you had an aftermarket permanent magnet type gear reduction starter then a different brush rig would be required to keep the starter rotating correctly so it will engage the flywheel.

An alternator is a great swap. If you look at the harness to the old regulator you should find a wire that will turn on the GEN light when you ground it with the switch on. This can be used to feed the excite terminal on many internally regulated alternators like the Delco 10SI. This gives you some indication that the alternator has excited and should be generating (light goes out). A "1 wire" alternator does not require this wire to be connected but I like to use it if possible. A volt meter probably provides the best information as to the state of the battery and charging system if you want to install one.

You should also see the BAT wire in that regulator harness that runs around to the starter solenoid terminal where the battery cable connects. This will be very small to carry the potential amperage the alternator can dish out. Need to either replace with a much larger gauge wire or run another larger wire in parallel to it.

Gerald J.

Posted 7/25/2016 22:56 (#5432670 - in reply to #5432515)
Subject: RE: Change of polarity on 3020 gas

The starter will work fine. With the series fields its rotation is independent of polarity. A shop vac motor is often wound the same way and runs on AC just fine.

Incandescent lamps work fine either polarity or on AC with not changes of connections. Some LEDs are arranged that way, but probably most made for tractor lights are sensitive to polarity. I haven't tried any yet.

I changed my gas 4020 from generator and positive ground to alternator and negative ground. The gas gauge doesn't like the polarity change and is mostly useless. A dry wood stick works reliably. Making it work requires a gauge made for negative ground which good Deere parts guys can find, some can't find the right one I've heard. Then the sender needs to be new to match the gauge, there are many variations possible in that circuit. Gauge and sender must match for it to read right.

The ignition coil primary connections need to be swapped, for positive ground the + terminal goes to the points, for negative ground that terminal needs to go to the supply and the - terminal goes to the points.

An alternator is a really great improvement because it has a better voltage regulator and a lot greater power capability. That means the wire from the big terminal on the alternator needs to be larger going to the starter solenoid, like 6 or 8 gauge.

There are a couple alternator wiring options. A one wire alternator is simple to install but needs to be goosed to start charging. I bought the smallest diameter alternator pulley for the wide belt I could find and it takes about 1650 RPM to start the alternator charging. After it starts (I also added an ammeter before making these other changes) charging it will charge at engine idle just fine. Otherwise one of the wires on a classic 10-SI alternator needs a wire from the ignition circuit through a lamp, a resistor, or a diode to keep it from back feeding the ignition circuit so the engine wouldn't stop running with the ignition switch turned off. An other option is to run that triggering voltage from the battery to the alternator through an oil pressure switch that closes on pressure rise and isn't grounded.

Gerald J.

thorfarms

Posted 7/26/2016 00:12 (#5432746 - in reply to #5432670)
Subject: RE: Change of polarity on 3020 gas

Lincoln, North Dakota

Well said Gerald

twraska

Posted 7/26/2016 00:29 (#5432761 - in reply to #5432515)
Subject: RE: Change of polarity on 3020 gas

Wallis, TX

If you do the polarity swap, remember to swap the wires on the coil. Sometimes it doesn't matter, and some engines won't run right with it reversed.

tedbear

Posted 7/26/2016 06:15 (#5432840 - in reply to #5432515)
Subject: RE: Change of polarity on 3020 gas

Near Intersection of I-35 & I-90 Southern Mn.

I switched a 3020 over myself with minimal problems in that respect. Starter was fine, changed polarity on coil etc as mentioned above.

Best change was when my nephew finally got rid of the tractor. The 3020 Gas was really a dog. Never started well nor ran decent and took lots of gas. Hard to believe it came from the same folks who made the 4020 Diesel.

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