Reversing polarity?

Lowly · Post by **Lowly** » Tue Jan 13, 2009 6:09 pm

My starter/alternator guy told me he thinks my 420 isn't charging because I reversed the polarity of the regulator while installing a reman genny. He gave me a sketch of how to reverse it back but it didn't work. Any tips on how to do it, specific to a 420? Any way to check if it is reversed? Any ideas or suggestions at all?

Thanks,

Lowly

Howard Weeks · Post by **Howard Weeks** » Tue Jan 13, 2009 7:28 pm

A good way to check whether or not it is charging is to use a digital voltmeter and check the battery voltage when the motor is not running. Then start the motor, idle it up, and check the battery voltage again. If the voltage is higher when running, the system is charging. If it is the same or lower, it is not charging. Most analog meters do not have enough resolution for small voltage changes of less than a volt - so I use a digital meter.

Assuming that the system is wired correctly with a good regulator and generator, you can polarize the generator by momentarily connecting a piece of wire between the GEN and BAT terminals on the regulator. Touch the wire to the terminals, get the spark, and remove it. Do this with the motor shut off. Then start the engine and, if everything is in operating condition, it will be generating. Be sure to have the battery connected properly with respect to the ground connection. Assume the 420 has a positive ground.

Lowly · Post by **Lowly** » Wed Jan 14, 2009 7:12 am

Thanks, your tip on the charging question is, like most good ideas, really obvious once someone points it out!

Thanks again.

Lowly

roadbuilder · Post by **roadbuilder** » Sun Mar 15, 2009 12:51 pm

After gen rebuild, I was getting -19 to 0 wild fluctuations at Bat. Tried shorting across, grounding etc but no noticable spark. Nothing showing on ammeter. Unhooked white wire, and grounded gen pole "F" to frame. With a different tester,now getting 7.2-7.3V at bat posts. Ammeter spiking 0 to -10 at approx. 1 second intervals. Also get wild fluctuations of both testers when approaching gen. with leads. I believe gen is charging bat okay, now what should I do to get ammeter working right? My Dad has had this MC for at least 36 years and the serial# appears to be 18626.

snoopy · Post by **snoopy** » Sun Mar 15, 2009 3:31 pm

Since the MC does not use a voltage regulator, it has a cutout relay that has to close to connect the generator to the battery when running. If it does not close then the ampmeter will not show a charge or discharge. Also sthe ignition switch has two positions in the run mode, one for high charge and one for low charge. the connections in the switches have been know to not work sometimes on my MC. You may just have abad ampmeter also.

Just some ideas for ou.

Lowly · Post by **Lowly** » Mon Mar 16, 2009 1:57 pm

My problem turned out to be a bad voltage regulator. Got a new one(my Deere parts guy steered me towards a much cheaper alternative to the one from Deere). Put it on, hooked it up and now my ammeter shows charge when it's running and the battery stays charged. My only question now is, it seems to me that my father's old Ford Jubilee would show a discharge on the ammeter when the starter was cranking, then when the motor started the ammeter would swing way over to charge, then after a little while it would settle back to show a slight charge. The ammeter on my 420C is not nearly that active, just goes from 0 to less than 10 amps when the motor is running and that's pretty much where it stays. It works so I am not complaining but I do wonder why it is not more active.

roadbuilder · Post by **roadbuilder** » Mon Mar 16, 2009 5:44 pm

Thanks for the responses. I'll start testing my way around the circut. JD parts said cut-out is no longer available but gave some numbers to try a cross-reference. Might have it figured out by this time next week. Don't have much time to spend on it just yet. I'll let you know what we come up with, or have more questions later.

roadbuilder · Post by **roadbuilder** » Mon Mar 16, 2009 8:20 pm

I was inspired by your responses, and since I still had some daylight left, I went to the barn and started testing. Started with bat. and seeing what was hot with eng. off. Traced out according to wiring diagram and found which poles were hot with switch off so I knew which should energize after startup. Started eng: Ammeter still neg spikes at 1 second intervals so started with bat. then cut-out. Tester was going wild again, so I made a good ground with pos. lead, and tried bat again. Inbetween wild readings, I got a readable 7.4V which increased to about 8.2. Happened to glance at ammeter, and it was reading approx. 8V on the pos. side. Idled down and guage dropped accordingly. Moved the dozer into a lighter section of barn, shut it off and started it again with the same results. Everything seems to work right. Dumb luck! Didn't have to replace anything. Tempted to try reconnecting white wire from F on gen to low charge on switch(low volt resistor?) Did I just clean up a connection or ground something with my test lead? Should I reduce the charge rate or just leave well enough alone?

roadbuilder · Post by **roadbuilder** » Mon Mar 16, 2009 8:23 pm

I was inspired by your responses, and since I still had some daylight left, I went to the barn and started testing. Started with bat. and seeing what was hot with eng. off. Traced out according to wiring diagram and found which poles were hot with switch off so I knew which should energize after startup. Started eng: Ammeter still neg spikes at 1 second intervals so started with bat. then cut-out. Tester was going wild again, so I made a good ground with pos. lead, and tried bat again. Inbetween wild readings, I got a readable 7.4V which increased to about 8.2. Happened to glance at ammeter, and it was reading approx. 8V on the pos. side. Idled down and guage dropped accordingly. Moved the dozer into a lighter section of barn, shut it off and started it again with the same results. Everything seems to work right. Dumb luck! Didn't have to replace anything. Tempted to try reconnecting white wire at F on gen to low charge on switch(low volt resistor?) Did I just clean up a connection or ground something with my test lead? Should I reduce the charge rate or just leave well enough alone?

snoopy · Post by **snoopy** » Mon Mar 16, 2009 9:15 pm

I would get it working right, meaning so you can select either the high charge or low charge setting. You may have disturbed a bad connection. there is not a lot of wirng so I would go thru and clean all the connections. There are some other cutout relays out there (ford) I use a switch instead, at least for now. Just have to remember to turn it off.

Good luck

JDcrawlers Messageboard

Reversing polarity?

Reversing polarity?

Had same type of problem with a twist

reversing polarity

reversing polarity

reversing polarity

Who is online