12 Volt negative ground Alternator on a car that is all 6 volt positive ground

[Vintagecarguy]

My dad and I bought a 1930 Model A Ford. The head/tail lights, brake lights, and horn were not working. We started working when I noticed that the Alternator said '12V Neg' on the top and on the back I think I read Delco. But everything on the car is 6 volt, even the battery. Could someone have rewired the Alternator to be a six volt? My grandfather ran wire with a six volt bulb from the charging point on the alternator and then another wire to ground with engine running and the bulb lit up and got brighter when the idle was raised but the bulb didn't blow??? I'm confused but everyone else is either confused or says not to worry. What should I do? Thanks in advance. Vintagecarguy. 

[cahartley]

I wish I could help.

There's LOTS of stuff about going the other way but not from 12 to 6.

Ebay has loads of 6 volt generators.

My Model A never had a problem with the 6 volt system so........good question...... 

[GK1918]

Although you used a test light , I use a voltmeter to find if it is putting out a true 6 plus volts.  Markings of 12vt Delco don't mean it hasn't been tweeked

to put out 6vts  its done all the time in a 12 vt housing.  Maybe they forgot to grind off the 12vt marking...And then if it is truly 12vts?  damage will be done

unless there's a reducer 12 to 6 hidden somewhere.

[jpage]

If it is all 6 volt then ,in my opinion, it would be better for you to install an original Model A generator. My "A" ran fine for the 16 years I had it with an original system! I don't get this alternator craze with old cars. Fix cars correctly and the original equipment works fine!

[Vintagecarguy]

Thanks everyone for the information. I'm going to put a voltmeter on the alternator and see what its putting out. The car was restored 10 years ago, but I don't know how long the alternator has been on there. The car has quarts headlight bulbs and a CB radio so I guess the alternator has to be there but not a 12 volt alternator. I'm going to check and see what's going on.

Thanks again everyone. Vintagecarguy.

[Friartuck]

Some definitions are in order here:

 

Generator- produces Direct Current (DC) to the electrical system and charges the battery. Sometimes there is a regulator to throtle the charge rate. The generator produces at mid to higher engine speeds

Alternator - produces Alternating Current (AC) which is then converted to DC via a rectifier (an arrangement of diodes is common). All alternators require a regulator which can be internal or external to the unit. In some cases the rectifier is included (embedded) with the regulator. The advantage of using an alternator over the original generator is that the alternator will produce more power at the slower engine speed. 

 

The original poster (OP) mentions the bulb getting brighter when the engine speed is raised. Sounds like the bulb was being used as a crude regulator. Its a way to divide the 12 volt alternator voltage to approx 6 volts across the bulb, leaving 6 or so for the rest of the car. This is not a good practice.

 

Since the car is set up for 6 volts, I recommend using the original 6 volt generator configuration. Brattons model A Ford supplier offers both a 6 volt generator and a 6 volt alternator. Using the alternator would provide the best power output while sacrificing original appearance.  Nice if you plan to drive in a lot of parades when the engine speed is expected to be low or do a lot of touring and using lights at night. The answer will dictate do you want originality or are you going to drive a lot on tours and need the extra power.

 

The OP just provided some clues. The CB radio is a 12 volt item. There are 6 volt to 12 volt inverters if its necessary to operate a 12 volt accessory. Vendors such as Brattons offer brighter bulbs in 6 volt as opposed to the 12 volt quartz (OP doesn't say which). 

Edited June 24, 2015 by Friartuck (see edit history)

[Vintagecarguy]

Some definitions are in order here:

 

Generator- produces Direct Current (DC) to the electrical system and charges the battery. Sometimes there is a regulator to throtle the charge rate. The generator produces at mid to higher engine speeds

Alternator - produces Alternating Current (AC) which is then converted to DC via a rectifier (an arrangement of diodes is common). All alternators require a regulator which can be internal or external to the unit. In some cases the rectifier is included (embedded) with the regulator. The advantage of using an alternator over the original generator is that the alternator will produce more power at the slower engine speed. 

 

The original poster (OP) mentions the bulb getting brighter when the engine speed is raised. Sounds like the bulb was being used as a crude regulator. Its a way to divide the 12 volt alternator voltage to approx 6 volts across the bulb, leaving 6 or so for the rest of the car. This is not a good practice.

 

Since the car is set up for 6 volts, I recommend using the original 6 volt generator configuration. Brattons model A Ford supplier offers both a 6 volt generator and a 6 volt alternator. Using the alternator would provide the best power output while sacrificing original appearance.  Nice if you plan to drive in a lot of parades when the engine speed is expected to be low or do a lot of touring and using lights at night. The answer will dictate do you want originality or are you going to drive a lot on tours and need the extra power.

 

The OP just provided some clues. The CB radio is a 12 volt item. There are 6 volt to 12 volt inverters if its necessary to operate a 12 volt accessory. Vendors such as Brattons offer brighter bulbs in 6 volt as opposed to the 12 volt quartz (OP doesn't say which). 

Friartuck,

Thank you for the information. I am somewhat a purest, liking things to be as original as possible but I say that if I didn't change it I'm not going to worry about it. But when it comes to this alternator I am confused. If the alternator turns out to be a 12 volt I have to see about buying a new alternator or a good old generator.

Thanks again, Friartuck.

Vintagecarguy.

[MCHinson]

I would recommend switching back to an original 6 volt generator but I have seen alternators retrofitted on Model A Fords. There are several companies who convert 12 volt alternators to 6 volt positive ground for use on Model A Fords. Usually you will find that they either restamp the housing or a apply a sticker to the housing indicating 6 volt positive ground. I suspect yours had a sticker and the sticker has simply come off of it. 

[Vintagecarguy]

I would recommend switching back to an original 6 volt generator but I have seen alternators retrofitted on Model A Fords. There are several companies who convert 12 volt alternators to 6 volt positive ground for use on Model A Fords. Usually you will find that they either restamp the housing or a apply a sticker to the housing indicating 6 volt positive ground. I suspect yours had a sticker and the sticker has simply come off of it. 

MCHinson,

Thank you for this information. My grandfather had mention that the alternator could have been rewired to be a six volt alternator but I wanted to be sure. Thank you again.

Vintagecarguy.

[joe_padavano]

I have personally installed a Delco 12V alternator on an old farm tractor that was originally a six volt positive ground system. I also changed the battery.  All bulbs have to be changed, as does the ammeter.  Otherwise, the starter works fine (it actually spins faster now) and everything else on the tractor (admittedly what little there is) also works fine on 12V.

[benjamin j]

There are external voltage regulators that can be used on alternators with internal voltage regulators. Sounds like a crazy statement but yes and they are adjustable from 6volts all the way up to 20 volts. They are commonly used in racing and car audio competitions. It’s hard to tell what has been done with your cars electrical system without checking it all with a meter.  

[Guest BillP]

Cue the jokes:

 

The radio listens.

The lights cast shadows.

The horn... well, never mind.

[mrspeedyt]

fyi ampmeters are not voltage sensitive but they are polarity sensitive. just simply have to switch the leads between on the ammeter to change it to negative ground.