question for DC experts

[foxfire42]

Here's a picture of how I currently have 2 Optima batteries wired in my 53 Mercury (1st drawing). It's still wired Neg Gnd. I want to run an A/C system but they are all 12V. I read in another thread that 6V's can be tapped from the older style 12V batteries to run 6V's where necessary. Rather than changing the car over to 12V is there a way I can tap into 6V if I rewire the 2 Optima's as in the second drawing? Can I run 6V to power the car and use the 12V just for the AC? My thoughts were to install a 12V generator also.

I was told there could be a charging issue and the batteries would not charge equally. Any thoughts or suggestions?

[Fordestes]

There is a series parallel switch to work for a 12v run 6volt start while using two batteries. I worked those 24volt start ,12 volt run systems on the big rigs, there is also a 12 volt setup.

[4t8v8]

I am not a fan of jerry rigging so I converted my F1 to 12V negative ground. Changed the bulbs, put a reducer on my gauges and a 12V motor in my heater years ago. Since then I've added a few 12V accessories easily. The 6V starter works just fine.
Just a thought.

[rotorwrench]

I would highly recommend a 12-volt conversion. Some AC systems can easily max out the electrical system load limits leaving you nothing left for lights or other systems. The old standard systems were only 35 amp in the 8BA era and a person would still have to keep both 6-volt batteries independently charged. The dual battery riggs can have problems keeping both batteries charged.

[blucar]

I am not an expert on electrical systems, however, I have had a lot of experience with same. I was a fire control tech in the Army, we dealt with 28 V DC to operate many anti-aircraft systems and self propelled weapon systems.
Rather than trying to re-invent the wheel I would suggest that if you want 12v convert the entire electrical system to 12v, you then have the power, volts/amps to run the systems that need 12v, however, you can use a voltage reducer to run the few accessories that need 6v.
Many Class A RV's use 6v batteries hooked in a paired series of at least six batteries to run the 12v systems in the RV to power fans, lights, etc., the 12v is then ran through an inverter to power 110. v 15 amp appliances. However the AC units have to run on 110v therefore the on board generator plant or shore power has to be used because there is not enough amps in the 12v system to run the AC unit (s).
Golf carts use 6v batteries, generally at least 8 of them hooked in series to supply power to the electric 36 hp motor. These batteries have to be charged with a 110v 30amp charger.
The 6v batteries in RV's and golf carts are huge deep cycle batteries that cost over $125. each, that equates to over $1,000. for a set of batteries and a weight factor of almost 800 lb's..

[Fordestes]

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I mis- read what you were asking, as for me , I try to keep it simple, I switched over to 12 generator 40 years ago. The next move will be a one wire alt, I am going with a 471 blown 8BA. ,and a 59a 6-53 Detroit blower, I know of very few who went with the series parallel on a light duty vehicle, I believe the constant duty Regulator for the gauges was inexpensive and simple to maintain, been doin it wrong since about 1967, the only problem I had was with the generator, back when I pieced the old girl together that was all we had to work with, now the one wire is the system for me. the slingshot alt mount don't look too bad if I keep my hood closed.

[38bill]

I rig boats and we do a lot of 24V trolling motors that also require 12V for a stowing motor. In our installation using two 12V batteries in series the + lead at the battery that is grounded will have the voltage of a single battery. It would work similar with two 6V. Just check the voltage across the posts to make sure. Dont know about charging as our chargers all have separate banks for each battery.

[foxfire42]

Thanks all. I have a lot to digest. It's looking like 12V NG is where I need to head.
I converted my Model A to 12V NG decades ago. It doesn't get simpler then that. But, my Merc is a conv with power top, seats, and power windows. The thought of replacing those 6V relays etc makes my wallet shiver. Should I just install the appropriate voltage drop resister or get complicated with a step down transformer?

[drolston]

When I converted my '41 to 12v I used GREE step down voltage converters for the wiper motor and heater motor. Rated at 3 amp output and they work fine. Might not be enough current capacity for top motor and power windows, but other higher capacity converters are available.

[rotorwrench]

Some 6-volt relays and motors work OK on 12-volt but they do work faster. Smaller electric motors with finer armature windings might take a beating but I couldn't say for sure if it would damage them or not. Going the AC route can get expensive on the old cars.

[Cecil/WV]

My '52 F-7 was converted to 12 v before I got it and it has no voltage reducers on the gauges at all and they work fine. When I restored it I put it back the same way and even the gas gauge is accurate. I've had the truck since 1991 and have driven it many miles.

[JSeery]

Are you sure it doesn't have a later Ford OEM voltage reducer installed? Ford used the reducer when they switched to 12v and kept the 6v gauges (up into the 80s). Only one installed for the entire gauge system. If Ford was going to the effort and expense to install them one would assume they were required!