70D: Generator/VR problem

So, problem was no charge. I could not remember replacing the generator brushes, so I ordered a set and tore the generator down. Brushes look like new. Guess I had changed them.

VR is "new" from Kenneth and worked fine before ("new meaning it has been in there for 8-9 months, but not too mnay hours). No jumping of batteries. Checked all grounds and belt tension. Generator discharges with lights on. Battery voltage is 6.2. If I ground the field the ammeter goes to 20+ (basically full scale) and the voltage will climb to 7.5. Remove the field ground jumper and the ammeter goes to a nominal charge (3 or 5A) the system voltage to around 6.4, then it slowly works it's way down to 6.2 . Ammeter seems jumpy when it's trying to maintain a low rate of charge, then it falls out of charge. Battery water is up and the pony cranks and starts fine.

What do you think it might be ? Bad Voltage sensor side ? Output is 15+ with all lights on bright. All wires are secure and in good condition.

Where should I look ?

Frank-in-Tallahassee
70D // 855

1) Basically, if grounding the field makes her gen, but she dont hooked to the VR, the gen is good at least and theres either;

a) VR isnt grounded (Run a good ground to its frame and see if she gens then)

b) The wire form the gens field post to the FLD terminal on the VR is open or not well connected (try a good new junp wire there and be sure BOTH terminals are not corroded not making good wire contact) I have loosened and wire brushed and re attached wires and made them gen again. Check those connections!!!!! !!!!! !!

c) The field control relay inside the VR is bad like burned or carboned points or its stuck in the low charge (grounded through a resistor) position or theres an open in one of its ground circuits. Its grounded via a resistance for low charge and dead to ground for high charge.

Once the relay points are burned or carboned you might polish them BUT once that silver coatign is gone and they are carboned, it can happen again.

Gotta run, sorry so short, but this is a good start at least. Be sure and let me know what the prob was, if the VR ground and connections are good, its probably a bad field control relay inside the VR.

God Bless John T Nordhoff in Indiana

~Lets find the problem [I know you like troubleshooting?],,,Start it back up & run at fast idle, then ground the [Fld] terminal at the regulator [if it charges now suspect a poor regulator ground or failed regulator] if it doesn't charge when grounding the [Fld] terminal on the regulator suspect an open in the wire from the generator [F] post to the regulator [Fld] terminal, or ,,,next try just grounding the regulator case to a good CLEAN ground [if it charges then you know what you have.

~If grounding the regulator doesn't make it work & you don't have an open wire, your problem is in the regulator field points area. See if the points are oxidized, with the engine not running those points should have a good contact to ground. ON A GOOD FUNCTIONING REGULATOR you should be able to place a volt meter or test light between battery power [that's the [BAT] terminal on the regulator] & the field terminal & it should show battery voltage or the light should light. Those field points only open when the charging voltage has reached your set value [probably around 7 volts plus or minus a few tenths..... .

~With all the electrical troubleshooting you have done on that diesel this will be the easy one..... .All those regulator field point do is ground the field UNTIL the set charging voltage is reached then they oscillate open & closed to keep the voltage within the charging window [7 volts + or- a little]..... ....

I used to use that stuff on noisy potentiometers and TV tuners, but I never noticed much difference. Our electricians used to carry it around in our shop, but about all it was good for was degreasing oily contacts on broaches, mills and machining centers. Most of them are just dry cleaner fluid (Perchlorethylene) which you can get in a high end brake part spray cleaner. If you buy the non-flammable type that's the kind with Perc.

Frank

Ground of the VR is fine. FLD wire is fine to the VR. Next I'll take the lid off the VR and check the points. I know not to file them, maybe drag a new dollar bill through them. It charges like a big dog and like you say the cut out works fine. Maybe I have just the slightest bit of oxidation on those the VR side points.

70D: Clooney and JohnT can help you best on your charging problem. About all I've ever learned is to MOMENTARILY ground the field terminal and if she charges (probably off the scale), then you start to look for bad grounds, breaks in wires, shorts to housing, etc. If the full field check works, look next at the ground of the voltage regulator to the generator case. I like to fine a good bare ground and attach a long-ish jumper wire, then just touch it around as you work your way through. It helps to have someone watching the ammeter. I also like to use a voltmeter.

Frank

Thanks as always 70D