The Voltage at my battery is only about 12.4 Volts at idle and it increases very little with engine RPM. This seems to me to be about a Volt low. What can I do to increase the Voltage? I have a discrete firewall mounted voltage regulator. I know I would do better with a alternator, but because I don't run any accesories (lights only), I don't care to make the switch.

 

Steve, it could be a bad generator but I think it's far more likely that your regulator needs to be adjusted or is bad. There is a whole section in the shop manual on adjusting the regulator. If you'd rather, you can still find a few places that will do it for you. You can also buy a new regulator for about $35 if you want to go that route. I think, though, that you'll still have to check the new regulator to make sure it's adjusted correctly.

 

Sounds like gen is not charging at all. for infrequently driven cars with gen, the brushes get stuck, make poor contact with copper..you can check thru end holes of most of em..push it around a little with small screwdriver..it should slide easily, in and out at least 1/4" ..never oil them..Or ,remotely, they be worn down and not touching at all.If homemeade setup, be sure gen goes with regulator..there are different ways of powering field..they do not interchange, but must be used as pair from same car

 

JGrady:

I think you are correct regarding not charging. I had a voltmeter on it last night and it was a steady 12.3 Volts and it stayed unchanged as I increased engine RPM. Last week, it was a steady 12.6 Volts (regardless of engine RPM) immediately after spending a night on the charger. Next week, it will probably be below 12.

I will check the brushes and all connections.

Thanks

 

SteV8e,

How did you measure the voltage? Disconnect the charging wire from the generator and measure at this post and ground with the truck running. It sounds to me that you are measuring the voltage of the battery, not the output of the generator.

Generators are easy to put new brushes in. The hard part is holding the brushes back while you put the armeter back in. There should be a small hole in the end of the brush holders. Push the brushes in and put a straightened paperclip in the hole to hold each brush back. When you have it back together, pull the paperclips out. The brushes should pop into place. Brighten up the armeter with emery cloth while you have it apart.


Danny

 

hi Danny..you can't measure the output voltage of a generator that way, as it will be very high..the regulator will think there is no output with arm ("A") disconnected, and will try to increase voltage, by turning field on full, with no regulating action, taking it to the max..which can be 30 v or more.It will rise with RPM, directly, without limit...even to 100V! The best way is to leave everything connected and look at dash,or use a clamp on DC ammeter on the armature lead..you should see 30 - 35 A with all the lights on and heater fan on high. If so, it is working. Or same thing, it does not show discharge with all the lights on, engine at 2 grand. Not sure he has an ammeter? You can also tell by brightness of headlights..they should brighten up some as you rev off idle..."the headlight ammeter" ----Or use your voltmeter method..It will show 12-12.6 V (battery only)at rest;once you start engine , and rev to say about 2 grand, it should read 13.6-15V depending on battery charge. As said earlier, all that really goes wrong with generators is bearings and brushes..in that sense better than alternators with diode hassles. But the old mechanical regulators do fail, maybe every 50 K or so, by burning the points, or much more commonly, some "expert" tries to "adjust "them by bending or turning critical adjusting screws and screws them up; Those screws never need adjusting, just like valve gear lash, once set right, and it is even more critical than valve gear lash. They do not turn by themselves to a wrong setting. Burned out resistors under regulatir can also happen by miswirng or "shorting" field terminal, "polarizing" field without disconnecting regulator connection, etc

 

Thanks for your inputs. I'm fairly certain that it is not charging. The Voltage at the battery should increase with RPM above what the battery Voltage reads (with the engine at rest). Also, the lights do not brighten with RPMs.

Recently, I killed the battery by leaving the blower motor running for about 4 hours while the truck was parked. I got a jump start and the truck drove fine for a short distance and then lost power and ran quite poorly. I checked the battery and it was showing between 7 and 8 Volts with the engine running (poorly).

I will start with checking the brushes on the genny.

 

You can put the generator in full charge to test it.(with the engine running) Hook your volt meter to the arm post on the regulator unhook the fld wire and touch it to the battery post. For a very short time. If the voltage goes up then I would think the regulator was bad.

 

You mean touch the field terminal on the generator to the battery,,after disconnecting the regulator F wire. The way you wrote it (touch field post to battery) it sounds like putting volts into regulator, which can pop it,. The reason I did not say that above is some generators have the field connected to the A terminal at the other end,you ground those to get output (reg disconnected) Others have the far end grounded , you do what you are sayng..put F to battery , with regulator disconnectd to turn on those types..not so easy to say waht ya got unless you go thru all that on any particular generator

 

I think that somewhere in the dark recesses of my toolbox I have a set of "Full Fielders" They are basically a set of connectors that attach to the wiring harness at the regulator to do what jgrady mentioned above. They were used in conjunction with the old Sun Equipmnet VAT 25 that I have (or maybe the older VAT-10). Haven't had a need or seen them in years......

I know that I have ruined a regulator or two by messign around with the adjustments...oops


Bobby

 

That is what I ment unhook the feld wire from the regulator and touch that wire to the battery post. All ford 12 v generators that I have seen the felds are grounded all the time, the feld is controled with positive voltage by the regulator. I know other brands use a ground to control the feld.
Thanks for clearing that up I don't want any one letting the smoke out of their regulator.