The Stovebolt Site Forums The Shop Area The Electrical Bay 8 Volt Conversion

I have read many of the pros and cons concerning this conversion and decided to try it on my '53 GMC. A local shop has done several conversions on older cars (20's and 30's) and has had no problems with the installation, put in the battery and had no issues with the voltage regulator. I am having starting problems. If the starter gear is in line with the flywheel gear there are no problems. When not, I have to manually nudge the crank to get them in alignment to get the starter to engage. With the 8v battery the starter engaged every time. I did notice that the ammeter needle was on the discharge side of the gauge and never changed. I expected that after several starts and stops the battery would start charging but never did and soon went dead, so the ammeter reading was correct. Re-charging the battery with my battery charger did not correct the problem even though the charger indicated the charge was at 100% and 8.1 colts. The local shop is charging it now so will see if theirs is a better charger.

My inquiry is whether anyone who has done the conversion had to adjust the voltage regulator. I have read Jerry's thread on his opinion that this conversion should not be done butt also provided the procedure for adjustment of the VR. I re-installed the 6v Optima battery and the ammeter showed it was charging as normal, once the engine started. Could be that the Optima battery is the problem.

If you convert to 8 volt you MUST adjust the voltage regulator. As Jerry stated it is not really the way to tackle a hard starting issue but it’s been done thousands of times. I did it about 55 years ago to one of mine.🛠

Image result for how many car battery manufacturers are there
As of May 1, 2013, there are three major automotive starting flooded battery manufacturers in the United States. There are four absorbed glass-mat (AGM) starting battery manufacturers and there are four flooded deep cycle battery/major deep cycle battery manufacturers in the United States.Jun 8, 2017Image result for how many car battery manufacturers are there
As of May 1, 2013, there are three major automotive starting flooded battery manufacturers in the United States. There are four absorbed glass-mat (AGM) starting battery manufacturers and there are four flooded deep cycle battery/major deep cycle battery manufacturers in the United States.Jun 8, 2017

I will post only a brief opinion regarding going to eight volts to "solve" a starting problems.

Farmers often used to do this in "the good old days", because they usually had an 8v tractor battery in the barn.
In general, this method is avoiding figuring out what was wrong with your 6v charging/starting system.

Did you install the 8v battery to work on a positive ground GMC electrical system?
What voltage regulator did you use?

Did you clean-until bright all sides of the various ground cable/straps connections?

Maybe someone knows how you should be wired from the 8v battery to other GMC 6v positive ground electrical devices?

Why to people go out of their way to create problems? Not every store on the road has an 8V except a golf cart shop. Adjusting regulator? Finding a battery charger for 8V?

12V conversion is so easy. Negative ground conversion is so easy.

The 8V is overcoming some kind of starter/wiring connection/ignition issue that will catch up to you.

I’m missing something here. Maybe my mind.

In order to charge an 8 volt battery, the charger needs to put out a little over 9 volts. An 8 volt battery showing 8.1 volts is not fully charged. Should show about 8.4-8.5V, like a 12V battery fully charged is at 12.7V.

Like bartamos said, why would you create a bastardized system instead of fixing the actual problem??

I've expressed my opinion on the subject several times. While the starter is capable of handling the overload of an 8V battery, if you do everything necessary to keep the battery charged properly, the rest of the system will be running on the ragged edge of over-voltage. The headlights in particular will be on the verge of failure all the time, and the generator and regulator will be running at the extreme upper limits of their operating range.

A much more effective approach would be to use two 6V batteries in a series/parallel system where the charging system and other circuits operate on 6 volts during normal running, and the batteries get connected in series during cranking to put 12V on the starter. Really, it's much less expensive to just fix the 6V system properly.
Jerry

Just to add to it, you do not want to run two batteries in series it will double the voltage, they must be in parallel to maintain 6V but you will have twice the starting amperage,IMHO.

A couple of Ford-type starter solenoids can be used to fabricate a series/parallel system where both batteries run and charge on 6V and are only run in series during starting. That system has been used as a 12/24 volt setup on big Diesel trucks in cold climates for over 60 years that I can remember, and probably long before that.
Jerry

Thanks to you all for your input, it is greatly appreciated.

A question for justhorsenround. When you converted to 8v did you experience problems mentioned in some of the responses above and others I have found on the internet?

To answer tciederman questions, the battery is connected positive to ground. Terminal connections have been cleaned and tightened recently. The voltage regulator from the original truck was toast, so I found another with the same number 1118303E. The generator number is 1107135 with another number 3E21. The Electrical Specs in the Maintenance Manual lists neither of these numbers so I can only assume both have been replaced at some point.

As I mentioned when posting this request I am looking for experience pro or con for this conversion. I am not committed to either but based on the experience from the local shop that converted several old vintage cars without any problems and not having to make VR adjustments seemed a solution. The experience with the dead battery certainly raises questions in my mind and if VR adjustments are needed upward of 40% of normal, it has to have some impact on the charging system and other components.

Reviewing the operation tests in the maintenance manual, they warn about burning relay contacts if the generator is not polarized after disconnecting any leads to the generator or VR, which I did do while trouble shooting a hi beam light problem. I did not polarize the generator so wonder if this may be part of the charging problem, whether 6 or 8 volt.

I've beaten this dead horse until my arms are tired. Over 50 years' experience working on, and teaching automotive electricity tells me it's impossible to make an 8 volt setup work. Maybe I'm just too dumb to see the light (even with too-bright headlights), but I'm out of this discussion! Bye!
Jerry

BillK, I personally experienced 0 problems with the set up. I was a 16 year old kid and even adjusted the VR myself. Maybe I was lucky. I only had the car a couple of months before sending it on down the road.

So BillK ended up with Martin's 8V Truck? How weird is that? Awesome!!

Now.........convert to 12V with an alternator and get rid of 8V, the generator, voltage regulator and all that wiring.

I did the 8 volt battery deal 30 years ago. Adjusted the voltage regulator up and didn't burn out any bulbs. I ran it until the 8 volt battery died of old age. I couldn't find another 8 volt battery for a decent price, so I went with a 12 volt conversion with an alternator.
The thing I liked about the 8 and the 12 volt battery was how it made the 6 volt starter turn the engine over so much faster which aided in dependable starting under less than desirable conditions. (Another topic worthy of further discussion since these "less than desirable conditions" are often the reason why some of us went with 8 volts to begin with.)
I am guessing that the reason why I did not burn out any bulbs was due to the natural loss of voltage inherent to these trucks (like the one which requires relays to make the headlights to be bright with 6 volt systems).
Carl

I'm going to turn this discussion off, as it seems that the question has been answered, and this is a discussion that could go south fairly quickly. Thanks for your understanding.