Piston Slap: An 8-volt conundrum in a 6-volt world
John writes:
When a 6-volt battery is replaced with an 8-volt battery, will the 8-volt receive a full charge from the 6-volt system?
If not, what items need to be replaced or adjusted?
Sajeev answers:
Unfortunately not, because you need a voltage regulator that will charge an 8-volt battery. The generator/alternator is always (usually?) robust enough to feed that voltage regulator, at least in any automotive application my mind can consider: Even old tractors have generators and alternators, right?
I see potential problems, because parasitic losses inside any battery mandate charging levels over that battery’s stated voltage rating. In this case it will be over 9 volts of charging for an 8-volt battery. That could be too much for frayed/corroded/oxidized 6-volt wiring (on either the power or ground sides). It could also overpower 6-volt lights and other marginally durable accessories that run on the same system. This is application specific but always worth considering.
However, let’s assume the rest of the system is OK with the 9.5-ish volts needed to top up the battery on an ongoing basis. Finding an adjustable regulator that meets your needs is a concern, unless a 6-volt regulator can be tweaked up to charge an 8-volt battery?
Well, look at that handy little adjusting screw! This video from Moss Motors may not necessarily apply to every voltage regulator out there, so perhaps this article is better to print off and add to your collection of repair manuals. Sometimes there’s nothing better than instructions on a sheet of paper, especially when working under the hood of a car. Or tractor, especially out in the field where harsh sunlight washes out any electronic display.
Bottom Line? Get familiar with the internals of your voltage regulator, check the quality of all your wiring, and give it a shot. If something fails, go back to a 6-volt battery. Let’s hope that isn’t necessary!
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I have never performed the mod myself, but this is a pretty common trick to get a little more starting oompf out of old 6V systems
My 1951 Buick Super had a bad starting problem and by the time the engine started the battery was nearly flat. An auto electrical friend of mine installed an 8 volt battery, set the, non original alternator, to charge at 10 volts and I never had another problem. The headlights were wonderfully bright, the dash lights were much brighter and nothing ever blew it’s fuse.
Way back in the day, when batteries had exposed Buss bars, you could run a 12 volt battery, regulator, and generator, and then tap off 6 volts for lights, fan, horns, etc. Want a 12 volt radio – just hook up to the Pos terminal direct (with a fuse, of course).
He didn’t get into the real issue with 6 volt systems. The battery and starter cables themselves are using internally corroded and that itself you causevyou problems. Change them all out for AWG # 2/0 cables along with grounding your battery ground cable right to one of the starter bolts or the engine block itself. From there run a jumper to ground your frame and a jumper to ground the firewall sheet metal. You will be amazed how well a 6 volt system will start with a new set of thick 2/0 cables, good grounding, and a good battery.
I had a 1946 Bedford 5 ton truck that had been converted into a breakdown truck which I used to tow classic cars that had broken down during a rally. It had a 6v battery and was a bit(h to start. I bought a new battery and still the same. I thought the battery was a dud so they gave me another. Same story, so the dealer sent one of his technicians to check out my ground connections. He spent about 20 minutes removing all the connections and cleaning them but the cable to the chassis was badly corroded so he fitted a new one. Problem solved! I could leave that truck for 6 weeks and it would start immediately every time.
Good point, I should have made a bigger deal about the problems of decades old wiring at the battery and starter…as that’s usually the biggest problem!
Good stuff about better battery cables and grounding. Possibly a solution to the problems that a lot of mid 50’s Fords had but at the time an 8 V battery and matching regulator was the common fix. Blew me away as an early teenager when I noticed that the battery in my friends Ford had 4 cells instead of 3 or 6.
Hi Joe!
Yes, many have described the 6 to 8 volt battery switch nothing more than a hack. Because the real problem is the cables are bad, not the battery. It will work or help initially, but what then happens is most people fail to get their volt regulator re adjusted. So the battery charge goes down over time and the battery still has to flow current through the same, probably internally corroded battery cables. So they end up wondering why their newish 8 volt battery is no longer working properly.
If you ever run into this problem. Change the cables before going to the 8 volt battery. Most folks I have talked to found out they didn’t need thec8 volt battery. Just good, properly sized cables, and good ground connections right to the engine block. The motor mounts have rubber isolators in them and so do some body mounts. So it helps if the frame is grounded to the motor, as well the body.
Such a charged issue! Better to get a positive answer than a negative outcome! Thanks for grounding us with good information. I’m outta here…
:^)
Good thing you left, Gary. I was getting ready to zap you!
Ooo-Ooo, just had some coffee and this hit me: “Gary, you are discharged, sir” – better, huh?
The coffee helped. It clearly “revolted” your regulator to the correct specifications!
We should probably stop now. Don’t want 80 percent of your readers to revolt…
Let ’em get amp’d up. All good.
Well, they could try meditation. Repeat after me: ohm …ohm….ohm…
I’m shocked that you all got that much out of that gag
It takes a lot out of you, that’s for sure. Luckily I remain grounded.
I think this is currently the longest thread running
Just you wait until DUB6 gets recharged…
I don’t know… we might have closed the loop on this one, of course I could just be a little negative
Maybe you’re right. Im sitting here trying to think of something, but my brain cells seem to be low – or maybe I’ve just short-circuited them. Or possibly, as a child, I got into too much lead – or even acid. But I don’t wanna talk about that now. I just wanna wish everyone a Merry Christmas (or whatever YOU celebrate, maybe a Festivus for the Rest of Us)…