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Tell me if I am crazy here.

My car is a 1948 packard with a Delco-Remy 6v Postive ground genny and regulator. My idea is this. Instead of converting the car to 12v. Instead i will run 2x 6v batteries in Parallel and then draw off of them in Series for my 2 loads "a 12v cig lighter and a 12v stereo system"

These 12 volt loads will have to be direct wired to the battery instead of using the frame for ground

How insane is this idea?
the stock genny is 35amp. so it has only a 210 ish watt output. even with that low power output i could still run a small stereo and amp with a small sub. I could also upgrade the 6v genny to one of the larger 60amp units so i can have a sexy 360watts of POWAH

Also i understand that the negative Hot comes from the regulator not the genny, but for simplicity sake on the drawing i show it coming directly from the genny.

This setup allows you to operate ALL of the cars stock electronics un-altered and at their native 6v positive grounded state. While also having a source to power 12v accessories up to a modest wattage. The 12v output could be used to charge 12v batteries in the trunk that directly supply high powered amps with juice while the genny just provides modest support with its meager 200ish watts of output. This seems like it would be able to play music at fairly high enjoyable wattages "500 watts of sound is usually enough to rock most peoples worlds without going into insane bass levels that rock neighbors out" Currently my experiment batteires are a pair of 200AH duracell 6v golf cart batteries that i plan on forcing my poor old genny to charge in parallel

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I don't know if they are still made but there used to be aftermarket solenoid add ons available for this very purpose.

If no luck finding one maybe you could reference their wiring diagram for your implementation. Instead of just limiting the 12v to the starting circuit as they do, make provisions for the extra needed to power other items you wish to include.

One thing you do need to watch out for when charging batteries in parallel is they need to be somewhat close in spec and condition. If one has a significantly higher internal resistance than the other, the charging current will not be split very evenly. In that situation one could be overcharged while the other is always low.

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WOW great information thank you! an actual product that does exactly the thing im thinking of this is amazing. this schematic is extremely helpful. it also shows me im not that crazy. Also you are right to point out how important charge balancing is. I plan on making a fancy cable for hooking the power up to teh batteries and they are both the same brand. spec and even production month. My idea was to make a T shaped pair of jumpers that have the power wire come in right in the center so it is balanced physically. the rest is up to physics! i call it my eyeball battery balancer. Ideally it would be cool to put the batteries right in the engine compartment. but they are large golf cart batteries so i may end up having to run some wires to the trunk and relocate the battery to there. This is gonna take some big chunky wire and careful planning but it doesnt seem too far off from working.on the other hand i could buy a couple of those small optima AGM 6v batteries and try to cram them both in the engine compartment.

After some more thought, that commercial unit may not do the job you want it for. I think I considered it for another project but after reading the info more closely the 12v is only available when starting and not when driving down the road.

A few years ago I decided to make a module to work a 12v AC in a 6v car. In theory it is good and does what I wanted but never actually finished the project to know if it would have been successful long term and in real time. Maybe you could take something along those lines and make it work. Of course the relays and other components would need to be substantially upsized as I only used small batteries and planned for a max 20 amps out. Also, not sure if the polarity protect circuit R1 provides is needed. I threw it in to avoid any explosions if the remote battery accidentally got reversed. It does always have a small drain on the battery so not suitable for a long period of inactivity without disconnecting the main battery.

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Ohh wow that is very fancy. I dig it Thankfully i live in an area where AC is not really needed so i get to have a nice simple engine compartment. The work you did though is very useful. And yeah i see the "Series-Parallel Switch" is for starting really but what it does more than anything is show me that its OK to run 2 different voltages at the same time. The thing i guess i was worried about was charging batteries at 6v in parralel while also having them wired in series so they can be drawn from in such a way to get 12v. i dont THINK ive cauzed any crazy short situation. it should just work.... and the batteries i would think, should ever so smoothly balance themselves if i keep a constant 12v load upon them with something like say a standby headless bluetooth enabled amp sitting in the trunk.

Aside from pulling too hard off of this setup and making sure muh batteries are being charged in a balanced way + making sure my charge wires from my regulator are nice n fat + having nice fat generator wires to my regulator and to my frame ground point. i think this sonofabitch will work....

How much stuff do you need to run off of 12V? Surely somewhere there is a boost PSU to go from 6V to 14V. Just depends on the expected current draw.

I don't believe there is a way to get 12V while charging at 6V purely from batteries as I can't think of a way to do it without shorting the charging circuit. In your schematic the brown wires are shorting both the charging circuit and the batteries themselves.

However you could make such a setup work if you only charge one battery at a time, and use some type of crossover switch to change which battery is charging.

I have a new relay made for the purpose at my shop. Years ago, though, I had a battery what was made specifically for the purpose and was basically two 6v batteries in one housing with the relay mounted to a pair of leads posts coming out the top. This relay on my site will do the same thing but will require two batteries.

What was called Antique Auto Battery (closed in 2018, though someone is using their website address) used to produce this 6/12 battery which was two 6V batteries connected via that solenoid above, which activated when you hit the starter button, and only sent the 12V through the starter. It was designed to make up for cars with worn starters, etc. Not exactly the application you are thinking of, but something to be aware of. Each of the batteries was normally charged as 6V batteries in parallel, and ran the accessories and everything that way when the solenoid was unactivated.

When I got my car it had one of these, and it worked o.k., really made the starter rip (maybe bad for that!) but the solenoid would sometimes stick and I'd have to get out of the car and hit it with something.

Eventually, those units becoming very expensive, I purchased a regular 6V battery and just re-did all my connections, and the thing started fine just on 6 volts, and eventually I rebuilt my starter and now it is even better.

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i want to run basically a 12v accessory socket and a stereo. and you do point out a problem that i am mulling over now. the crossover wire that turns the set of batteries into a series set, shorts the charging circuit. and thats no good. so then yes i think your idea of using basically a 6v to 12v power supply to create a seperate 12v circuit is a better idea. that way i do not have to hook the batteries up in series. hell i dont even need 2 batteries just 1 big good 6 volter. on amazon they sell 6v to 12v DC to DC converters and they are 120. on ali express i see 500 and 700 watt units.

how do i delete this topic, its now debunk'd