37 generator cut-out

rich b

rich b

Well-known member
Father-in-law is having trouble with
his taillight bulbs burning out.
He hasn't checked the actual voltage
yet; but is the cut-out adjustable?
The wiring is new. Generator and cut-out are
Original to the car and the bulbs are old stock US.
He has had the 37 for years; but is just getting
It going now.
 
No, the cut-out is not adjustable, but the 3rd brush on the generator is. If not set correctly, and the voltage is too high, it will cause bulbs to burn out. The 3rd brush should be set to put out 7.2 volts. If you dont have a voltmeter, I used to set the 3rd brush so the ampmeter showed zero with the lights on high beam with the engine running about 1500 rpm.
 
The purpose of the cutout is to disconnect the battery from the charging circuit when the generator output falls below the battery level. The voltage in the system must be adjusted by moving the "third brush" in the generator up and down. Connect a voltmeter across the battery terminals and with the engine running, and rear band off the generator, move the brush up or down to get a reading of about 7 1/2 volts at fast idle. If the car is driven at night, turn on the headlights and readjust the generator out put to the level set out above. C&G (800/266-0470) sells a voltage regulator to replace the cutout. The part number is 1050R-V8 for your '37, $82. It should eliminate the adjustment in the future.
 
Rich, If the cut out is the original ford round one mounted on top of the generator then it has no adjustment to alter the charging rate amps, it is only an automatic switch to connect and disconnect the generator to the battery. All charging adjustments are done by moving the third brush back and forth which alters the charge rate amps output of the generator. It is NOT A VOLTAGE ADJUSTMENT. If the charging system has been modified to accept a separate voltage, current and cut out box then it has adjustments inside which control the voltage and current output. This unit requires some expertise to fault find and adjust it to the correct settings. An auto electrician would have this knowledge, Preferably and older person. Regards, Kevin.
 
In addition to the super advice and assuming your car is stock, Standing on the driver's side, locate the band on he generator and remove it. To adjust the 3rd brush to decrease output, gently move the brush up in small 1/8" increments. (Down to increace) then start the car and either test the output or look at the gauge on the dash. Keep adjusting until the desired output is made.
 
fordscript said:
No, the cut-out is not adjustable, but the 3rd brush on the generator is. If not set correctly, and the voltage is too high, it will cause bulbs to burn out. The 3rd brush should be set to put out 7.2 volts. If you dont have a voltmeter, I used to set the 3rd brush so the ampmeter showed zero with the lights on high beam with the engine running about 1500 rpm.
Click to expand...

In my opinion this is the correct answer, plus get 8 volt rated bulbs. G.M.
 
Thanks for all the info.
I learned he has not hooked up the headlights yet, so will wait until they are in the circuit; before checking/setting the voltage.
 
fordscript said:
No, the cut-out is not adjustable, but the 3rd brush on the generator is. If not set correctly, and the voltage is too high, it will cause bulbs to burn out. The 3rd brush should be set to put out 7.2 volts. If you dont have a voltmeter, I used to set the 3rd brush so the ampmeter showed zero with the lights on high beam with the engine running about 1500 rpm.
Click to expand...

The cut out IS ADJUSTABLE but not to set the maximum voltage output of the generator. You can carefully grind the small tack welds along the bottom edge holding it together. You need a good volt meter and a DC variable power supply. Connect POS lead of DC to body of the cutout and the NEG to the gen side terminal of the cutout. You should put a meter or light bulb from battery terminal to POS cutout body. Increase the DC voltage VERY slowly and watch what the voltage is when the light lights.
It wants to be set at between 7.0 and 7.2 volts when the light comes on.
If it comes on at a lower voltage move the tab anchoring the spring to put more spring pressure on the spring. If it don't pull in until higher than 7.2 relax the spring pressure. Once the cutout is pulled in and you slowly lower the voltage the cutout will remain pulled in until the gets down below about 6.5. This is due to the fact it takes more power to move the spring when the contacts are open and the cutout will hold in with less power once it is engaged. Clean the contacts before making this adjustment and using an acid flux solder to the spots that were ground off to open it. G.M.
 
Rich,,,, check out Tom Wesenberg's Electronic Voltage Regulator you can buy them direct from him, takes the place of the third brush AND is a life saver for your electrical system plus helps keep the battery and genny from getting overcooked from voltage spikes.

Tom is over on the Model A side of this forum, lives near Minneapolis may be close to you!

You don't want to keep wasting those original bulbs the new ones today are not as good as the old ones.
 
Fun Products makes a Cut Out that is a voltage regulator inside the regular round cut out . Have run them on my 32 and also on my 35. About $80.oo. Problems solved and no need to adjust the 3rd brush once installed. JMHO Kerk
 
this thread seemed somewhat relevant on my search so i thought i would continue it a bit further.

yesterday went to start the engine, and not enough juice in battery to do it. put it on a 10A charger for about 15 minutes and it was running. i put a voltmeter on the battery much later on and noticed that at idle i was reading around 11.8V, when you increase the RPM voltage would go up to 12.4 or so (higher at faster RPMs) headlights brightness would increase, and amp meter would jump back up over 0.

so i started doing some research and thought i would go out today and fiddle around with the 3rd brush, maybe it wasn't set right.

i noticed that with the engine running at idle and reading 11.7-11.8 on volt meter, that when i lifted a brush i would hear a click from what felt like the cutout, and the voltage would jump up to around 12.4 or so. it would remain there until you turned on the headlights or ran the RPMs up and then back down to idle, at which point it would drop back down to around 11.7.

i am of the current thinking that the genny is ok, 3rd brush adjustments are ok and that the cut out is not working as it should. before i went out and spent money on a new cutout wanted to get opinions from this group.

thoughts?

also for the life of me i don't see how to adjust that brush. i am obviously missing something basic here, and would appreciate a clue for the clueless??

https://drive.google.com/open?id=0B98HkOcty2iVdVFmdHJBVUloVTg
 
FoMoCo moved on to the 2-brush generators in 1939 or so. The 3-brush are generally 6-volt systems where the field winding design will only put out a little over 7-volts. The third brush is to adjust the amperage output for a balance between running in the daytime with no lights and running at night with the lights on. If you set the amperage to high , it will boil the water out of the battery if it's run a lot in daytime hours. When amperage changes, the voltage changes a bit too but I haven't seen too many 12-volt 3-brush generators. Most 12-volt systems have a 2-brush generator with a 3-pole regulator. 6-volt systems continued in use up thru 1955 or so.

When you adjust the 3-brush, you need to have a good amp meter and do the connections and adjusting per the manufacturer's specs. They only have a single pole cut out to keep the battery from motoring the generator after you shut the engine down. It's not a voltage regulator unless someone converted it to one. There is a solid state voltage regulator available that all fits inside of a cut out body.
http://www.funprojects.com/products/5055r.aspx
 
Last edited:
DD931 said:
Are there people actually using 12 volts with a three brush generator?
Click to expand...

yes, i have such a set up. i did not put this engine together, and the person that did is not available to get information from.

there is not near as much information on the pre '39 generators as there is on the later ones, and there is seems to be good reason that ford went to the 2 brush generator along with the 3 terminal 'regulator' that you can adjust easily. Even the FMC 1933-1947 repair manual for Generating and Starting Systems doesn't go into a lot of detail on the pre '39s.

let me pose my questions another way, which 6 or 12 volt really shouldn't make a difference.

when you hook up a voltmeter to the generator side of the cutout (and assuming it is correctly working), what would you expect to see at initial startup? running up the RMPs? and allowing the engine to go back to idle??


as rotorwrench pointed out there are a couple of products out there for this:

http://www.funprojects.com/products/10505v.aspx

http://cgfordparts.com/ufolder/showproducts.php?c=1&s=17&g=149&t=6314

http://www.macsautoparts.com/early_...rd-script-12-volt-negative-ground-ford-1.html
 
The fun products regulator solves problems but also opens up new ones. Finding an original looking 12-volt battery is difficult and they don't tell you that the output for the 12-volt conversion is pretty low. It compares with original for the early pre-39 Fords but it isn't a 35 amp set up like the later 6-volt 2-brush generators are.
 
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