The Ford Barn

azlkk · 09-18-2025, 08:54 PM

How well do Optima batteries handle third brush generators? I understand that they can be a bit sensitive to voltages which I understand third brushes vary quite a bit.

Lawrie · 09-18-2025, 09:06 PM

Have them in both my 33 and 34, the one in the 33 is 13 yrs old ,both have the 6v stock 3 brush generators on
Lawrie

koates · 09-19-2025, 02:01 AM

azlkk Your 35 original stock V8 Ford will operate very well with an Optima battery provided the third brush in the generator is set down low with about 3 amps charge showing on the dash ammeter whilst driving in daylight (no lights on). Remember the third brush system is not a regulator and does not compensate for any electrical loads switched on or the charged condition of the battery. The only thing special about an Optima battery is the type of assembly of the plates, it is still a lead acid battery. Bear in mind also that the ammeter shows about 3 amps current draw of the ignition coil which means with about 3 amps charge showing on the ammeter then the generator is outputting 6 amps. Dont fall for the trap of setting the third brush at 15 or more amps because you will cook the battery. The original drivers handbook that came with the car when new will give some information on setting the third brush. Just remember, keep it down low. Regards, Kevin.

Lawrie · 09-19-2025, 03:29 AM

Kevin, you are right, 34 has just done a 3013 mile trip, 6v 3 brush generator ,charging is about 2 amps on the meter, no trouble starting hot or cold(4c)
the stock stuff works ,the ford engineers were not dunces.
Lawrie

ndnchf · 09-19-2025, 04:21 AM

Koates advice is spot on.

I restore Ford generators and often see generators set to too high a charge rate. I run optimas in both my '31 and '35. The only difference is I've installed Mike Hill's Electronic Voltage Regulator (EVR) inside both generators. This converts them to 2-brush and provides full regulation. It is the ideal set up and completely hidden.

Steve

38 coupe · 09-19-2025, 05:49 AM

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If you are only driving in the day then setting the third brush so the generator outputs 2 amps on the ammeter should work well. If you drive at night then ndnchf's solution of installing an internal voltage regulator is the solution. I have used an internal voltage regulator on a third brush generator charging an optima 6V battery for over a decade with excellent results.

petehoovie · 09-19-2025, 10:32 AM

Quote:

Originally Posted by ndnchf

Koates advice is spot on.

I restore Ford generators and often see generators set to too high a charge rate. I run optimas in both my '31 and '35. The only difference is I've installed Mike Hill's Electronic Voltage Regulator (EVR) inside both generators. This converts them to 2-brush and provides full regulation. It is the ideal set up and completely hidden.

Steve

Kurt in NJ · 09-19-2025, 02:26 PM

I have long life with my optima batteries at 14 amp charging rate.
The first one went 16 years,the second one is 10 years so far I think.
I do drive a lot at night and have halogen headlight bulbs.
Never on maintainer.
If i take a100 mile drive the headlights get turned on for part of the drive.
The generator is original to the car (date code matches engine month)and it was the first generator I rebuilt over 50 years ago and just had a bearing failure— the cage of the original bearing came apart and that was the only part replaced.
I think many worry too much about burning up the generator and keep too low of a charge rate for their use.
I would reduce my charging rate for a long daylight trip say doing 3-5 hundred miles per day.

09-18-2025, 08:54 PM	#1
azlkk Member Join Date: Oct 2019 Location: Phoenix, AZ/Cayucos, CA Posts: 38	Optima 6v batteries and third brush generator How well do Optima batteries handle third brush generators? I understand that they can be a bit sensitive to voltages which I understand third brushes vary quite a bit. __________________ '35 5 Window Deluxe Coupe w/radio- wife's uncle purchased new

09-18-2025, 09:06 PM	#2
Lawrie Senior Member Join Date: May 2010 Location: Qld, Australia Posts: 4,728	Re: Optima 6v batteries and third brush generator Have them in both my 33 and 34, the one in the 33 is 13 yrs old ,both have the 6v stock 3 brush generators on Lawrie

09-19-2025, 02:01 AM	#3
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,218	Re: Optima 6v batteries and third brush generator azlkk Your 35 original stock V8 Ford will operate very well with an Optima battery provided the third brush in the generator is set down low with about 3 amps charge showing on the dash ammeter whilst driving in daylight (no lights on). Remember the third brush system is not a regulator and does not compensate for any electrical loads switched on or the charged condition of the battery. The only thing special about an Optima battery is the type of assembly of the plates, it is still a lead acid battery. Bear in mind also that the ammeter shows about 3 amps current draw of the ignition coil which means with about 3 amps charge showing on the ammeter then the generator is outputting 6 amps. Dont fall for the trap of setting the third brush at 15 or more amps because you will cook the battery. The original drivers handbook that came with the car when new will give some information on setting the third brush. Just remember, keep it down low. Regards, Kevin.

09-19-2025, 03:29 AM	#4
Lawrie Senior Member Join Date: May 2010 Location: Qld, Australia Posts: 4,728	Re: Optima 6v batteries and third brush generator Kevin, you are right, 34 has just done a 3013 mile trip, 6v 3 brush generator ,charging is about 2 amps on the meter, no trouble starting hot or cold(4c) the stock stuff works ,the ford engineers were not dunces. Lawrie

09-19-2025, 05:49 AM	#6
38 coupe Senior Member Join Date: May 2010 Location: South Texas Posts: 2,135	Re: Optima 6v batteries and third brush generator Sponsored Links (Register now to hide all advertisements) If you are only driving in the day then setting the third brush so the generator outputs 2 amps on the ammeter should work well. If you drive at night then ndnchf's solution of installing an internal voltage regulator is the solution. I have used an internal voltage regulator on a third brush generator charging an optima 6V battery for over a decade with excellent results.

09-19-2025, 02:26 PM	#8
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,672	Re: Optima 6v batteries and third brush generator I have long life with my optima batteries at 14 amp charging rate. The first one went 16 years,the second one is 10 years so far I think. I do drive a lot at night and have halogen headlight bulbs. Never on maintainer. If i take a100 mile drive the headlights get turned on for part of the drive. The generator is original to the car (date code matches engine month)and it was the first generator I rebuilt over 50 years ago and just had a bearing failure— the cage of the original bearing came apart and that was the only part replaced. I think many worry too much about burning up the generator and keep too low of a charge rate for their use. I would reduce my charging rate for a long daylight trip say doing 3-5 hundred miles per day.