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Old 11-13-2005, 12:01 AM
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6 volt-12 volt battery question

I could be mistaken', but I'm sure that I have seen in a hotrod before... a battery that is sort of two 6 volt batteries in one. It is a single battery with two sets of terminal-posts.... the first set is for the stock 6 volt system, the second set of posts is for the 12 volt system. where can I get one of these? please. If I'm mistaken' about this battery.... then my second question is...... could i put two 6 volt batteries in line one after the other (just like two batteries in a flahlight), then for the newer stuff that requires 12 volts use both 6 volt batteries in tandom, and everything else just tap off of the first battery; or would the amperage be different with two 6 volt batteries than it is with one 12 volt battery?
Also, if I did either of these two things... putting a 12 volt pull on an alternator that was origanaly charging 6 volts, would I need to put a different alternator in the car? thank you for any information I might get in reguards to this. Sincerely; Rob

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Old 11-13-2005, 04:09 AM
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Doc here,

Welcome to the Forums!

I'm not sure exactly what your asking..

First I need to establish what type of vehicle were dealing with? and 6 volt or 12 volt?

Next , I did a brief search..I found nothing that exists in a duel voltage battery, You may be confusing it for those that were 2~ 12 volt battery's in one (had 4 terminals) and if one half went dead, you could jump from the other half..Or maybe one with duel terminals (side and top post)

The old "SOFT TOP" 12 volt non maintenance free battery's had two flat lead terminals on the top , where if you tapped between them, you could get 6 volts..But I haven't seen one of these in years..

You can put 2 Six volt battery's in series to get 12 volts, but on a 6 volt car it has to be hooked up : one battery hooked to power and ground on the Vehicle, Then a Cable run from the positive of the first battery, to the Negative of the second battery, then a Power cable off that to a 12 volt buss...The down shot is, the #2 battery would never get a charge.

I don't think even an isolator will work because #2 battery must be separated from the vehicle system or else it will (can) produce 12 volts..you'd have to come up with a pretty complicated automated cable switching system to make it work.

The Danger in running a duel voltage system is in future you can make a mistake and accidentally grab a 12 volt wire and hook it into a 6 volt system, and fry things..including the harness..or your whole rod (older vehicles didn't have fuse links ) Charging is usually a hassle, and replacement parts must be thought out..(Gee, was that 6 volts or 12 volts?)

You can't charge 12 volts on a 6 volt system..The generator won't reach enough speed to do so, and If it did, the regulator won't allow it to go that high.You can do it the other way around, and regulate it for 6 volts...but this is whistling past the graveyard..If the regulator fails, you will overcharge the battery and possibly explode it.

If you feel you need 12 volts, the BEST thing to do is plan a harness upgrade to 12 volts..Older wire is cotton clad, soaks up 50 + years of oil, gas and grease..and will support a flame..AND act like a FUSE or WICK if ignited!

To upgrade your system, you need to change :
All the lighting
Alternator/generator swap out
Horn relay
Heater motor and Speed controller
Wiper motor and speed controller
You can run the stock instrumentation on a dropping resistor as well as a stock radio (if retro theme)

You can run a 6 volt motor at 125% of rated value, but you drastically shorten It's lifespan..so starters , heater and wiper motors should be upgraded. The Solenoid WILL NOT run on 12 volts..(besides, 6 volt stuff is getting hard to find anymore as a "SHELF ITEM" where 12 volt stuff that will fit the block are standard.

If your wipers are vacuum, It's a good time to upgrade to electric..at best consider a vacuum canister for continued operation going uphill..

Install fuse links if your new harness does not already have them, and I'd put them on your 6 volt system now while planning the change to avoid tragic fires.

That's about it..

There are good cheap harness makers out there , if you do a search or go to the thread at the top of this forum (comparing harness makers) and plan around one.

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Electronic & Electrical
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Old 11-13-2005, 08:49 AM
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Try this http://www.antiqueautobattery.com/prod011.htm

I have used one of these in an old International Utility tractor for a couple of years. I use only the 12 volts to the starter and Delco alternator.. 6 volts power the rest of the system.
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Old 11-13-2005, 11:25 AM
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Hey Bob, Nice link to some great time saving batteries!
I think it can be done like this too {the generator ground diode could probably be eliminated}:

although I'd just take the simple and clean approach of the Optimas it is nice to know how the system works.
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Old 11-13-2005, 11:25 AM
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re: 6 volt-12 volt battery question

I used one of these 12 volt batteries with a 6 volt tap in about 1965. I had a 324 Olds in my 40 Ford. I used the 12 volt portion for the starter and electric fuel pump and the 6 volt tap for everything else. What I didn't know at the time was to make sure the 12 volts ran through a resistor so I kept on frying the points. The 12 volt generator seemed to keep everything charged fairly well even with the battery relocated to the trunk. One thing I did use was battery cables made for six volt (heavier wire guage) system. I wouldn't do it now but it worked when I was 19. I drove that car from Regina, Saskatchewan (north of North Dakota) to San Francisco and back in 1966. I just sold it last year.

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Old 11-14-2005, 01:49 AM
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thank you guys for all the info, and such. that all was a realy great help.
the link to the web site for replica batteries is great.

thanks again sincerely Rob L.
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