Hi all it's been a while since I've been here. I'm looking to hook up twin 6volt batteries on my 47 Buick. The car is still 6 volt but I want to start it with 12 volts to the starter. I'll put them is series and use 1 battery to operate the cars electric syst. My only question is will the charging system still work ok with both batteries hooked up?
You'd only be charging one of the batteries. Why don't you fix whatever issues you have with the starter instead? I'm pretty sure it worked fine on 6V 75 years ago, and batteries have got better since then.
It can easily be done. Cranking on 12v and running/ charging both batteries 6v I did this with 24v start and 12v running on a Lotus Cortina race car. You connect 2 batteries parallel via 2 x 70a spdt relays AND the 2 batteries in-series using a Ford starter relay/ solenoid. I'll attach a schematic to this reply within a couple of hours once I get my computer back from repairs.
You would need a series/parallel switch. They were used on trucks many years ago for much the same reason. https://www.roadtrains.com.au/tech-tips/how-a-series-parallel-switch-works/
I pulled a series/parallel switch from a Pete that had a Detroit engine was in it, 24 volt starter, 12 volt charging system. Kerry will show you what it needs. Edit: I just noticed jaracer’s link.
Band aid. Fix it right. Also, most 6 volt batteries these days are undersized. What you need is an Optima with 800 CCA; making it fit in the Buick battery location may present a problem, though. I'll bet an Optima has more oomph than any 8 volt "tractor" unit out there.
Just convert the car to 12 volts and be done with all the work arounds. Simpler and cheaper in the long run. Keep the stock gauges with Runtz voltage drops and change all the light bulbs. Change coil replace generator with either a 12 volt generator or an alternator.
Search here on the HAMB "RUNNING A SBC ON 6 VOLTS IN A 6 VOLT CAR" Scroll down to post # 14 and there is 2 schematics explaining how to do this. (2 scenarios) It automatically cranks in-series and defaults to parallel when the starter switch is released. And it has some failsafes featured so it cannot switch over to "in series" unless the parallel circuit is disconnected. This is the advantage of spdt relays.
Recommended reading: https://www.jalopyjournal.com/forum/threads/running-a-sbc-on-6-volts-in-a-6-volt-car.1326992/
If you can stay with 6 volt. Just get a 6volt optima and get new battery cable and grounds that are the heavier OO. I did this on my wife's Plymouth over 6 years ago. Still cranks hard. if you have to go to 12. Just update the bulbs and gauges call it a day.
You ever run a 6v starter on 12 or a 12v starter on 24? They run real good. Even if the whole thing is in great shape there's plenty of reason to want to start it on 12.
CHARGING vs. IGNITING: I saw your post and schematic on the other thread. It's a neat solution. Just to be clear, the ignition is wired 100% normal to the single bat and there is no need to doctor it to get fire while cranking the starter with 24v? ( I know the series/parallel solenoid does one, then the other and wont charge while cranking, which is fine for a diesel rig, but the ignition will still fire while cranking, yes? Or are there other steps to take for that function?) -thanks, -rick
That is correct. On my Lotus everything was 12v as normal. So the 2nd battery was connected parallel just for charging. When cranking the 2nd battery was diverted to "in-series" and only fed the starter motor. While cranking the ignition was still 12v from the 1st battery
Well I just hooked up 2- 6v optima's in parallel and it cranks fine . Made up #2 cable and kept them short as possible. I have 12v wiper motor but will used a step-up box for that. thanks All ,RJ
Good to have a lot of batteries around, but I'm surprised you need 2 of those Optimas to crank that thing good.
The one little Optima looks lost in there. But really, I was after the extra reserve 2 provide. Pict is a test
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