Two 6v=12v or 6volt

[31 LaSalle]

I am thinking of having two optima 6v battery's in parallel on my 1928 Chrysler 72 as there is room on battery tray.

would that still be 6v or 12v. would both battery's charge 

and more importantly is there any benefit in doing this ie cranking power.

[PONTIAC1953]

when batteries are connected in parallel, same voltage, twice the reserves, when batteries are connected in series, the voltage doubles or 6 + 6 = 12.

 

[Bloo]

13 minutes ago, 31 LaSalle said:

would both battery's charge

Yes. Since there is twice the capacity, it takes longer go dead, but also longer to charge. You're much less likely to run out of power. If for some reason you do run them down, just put the charger on when you get home. The car isn't going to take care of it on it's own in a reasonable amount of time.

 

19 minutes ago, 31 LaSalle said:

more importantly is there any benefit in doing this ie cranking power

It depends. It would give you a truly awesome amount of cranking reserve. One Optima is electrically larger than a typical group 1 6v battery of the 20s-50s. Some forum members have done it.

 

If by some chance the car is having trouble chugging down while cranking and not starting easily I would fix that first. It should have started fine on a battery available in the 20s. More battery capacity won't compensate for undersize cables, dragging starter, etc., at least not for very long.

 

[alsancle]

From my Reo.

 

 

[edinmass]

Your ground strap is inadequate……….

[Curti]

Personally I am not a fan of cut-off switches. A diode in the generator handles that problem.

 

Edited July 10, 2022 by Curti
update (see edit history)

[Larry Schramm]

Remember that parallel is ground to ground, and positive to positive like shown in the picture.  That way your car will remain a 6 volt system.  With good clean connections and proper cables 6 volt cars operate fine.

 

Series is negative on one battery, positive on that battery to negative on the next battery, and positive to the car.  = 12 volts. 

[JRA]

I have used two-6v-Optima’s in parallel for more than a decape in many cars, including my 1929 Chrysler 75. This is a very good setup to increase cranking power.

[BillinMd]

2 hours ago, edinmass said:

Your ground strap is inadequate……….

Agreed. Two straps will carry the extra current from the two batteries.  The set up in the photo employs a single strap and, while neat, will not do what is intended.

[31 LaSalle]

3 hours ago, edinmass said:

Your ground strap is inadequate……….

should it be two straps or larger straps

[Marty Roth]

3 hours ago, JRA said:

I have used two-6v-Optima’s in parallel for more than a decape in many cars, including my 1929 Chrysler 75. This is a very good setup to increase cranking power.

 

2 hours ago, BillinMd said:

Agreed. Two straps will carry the extra current from the two batteries.  The set up in the photo employs a single strap and, while neat, will not do what is intended.

 

1 hour ago, 31 LaSalle said:

should it be two straps or larger straps

I have a similar setup in our '41 Caddy, and it was that way when I first got it from the gentleman , a Mr Shipman, who owned the four NAPA stores in Casper, Wyoming in 2007.

 

Our 6-Volt cars use 000 or 0000 battery cable - maybe overdone, but it can't hurt

Edited July 10, 2022 by Marty Roth (see edit history)

[BillinMd]

Remember, the local auto store straps are usually sufficient for 12 volt systems and subsequent current demands. The 6 volt systems require twice the current carrying capacity, thus the need for two straps.  That having been said, it looks as though the set up in the photo is adequate provided it is maintained and the system demands stay relatively low.  Should any corrosion or loose terminals appear, the current will  increase dramatically. Just something to consider when designing a safe and effective electrical system.

[alsancle]

Ed already pointed out the issue with the ground strap a while ago. I’ll make sure we address it.  

[Matt Harwood]

One of the very first things I did on that '35 Lincoln was upgrade to dual Optimas. The thing ran crazy hot and refused to start unless it cooled off. Just couldn't crank at all. I put two Optimas in there with 1600 amps of cold cranking power and there was no way that thing wouldn't start. Hot, cold, overheated, whatever--those batteries kicked that giant V12 over like a moped. Of course, I later learned that there was a whole host of additional problems including a starter with bad bushings, but the fact that it started effortlessly with dual Optimas as a Band-Aid solution suggests that they will start almost anything under almost any circumstances.

 

 

Edited July 10, 2022 by Matt Harwood (see edit history)

[PONTIAC1953]

2 hours ago, 31 LaSalle said:

should it be two straps or larger straps

two straps, one for each battery.

[BillinMd]

Another practice that really gets to me is owners using the bolt on clamps to afix the cables to the battery lug. Many cats are quite valuable but still  use those cheap cable clamps. If there is any corrosion or loose fitting cables, that will present problems. Sorry for the rant.

[trimacar]

What I enjoy is an owner sandblasting frame, painting it with DP-90 or equivalent epoxy primer, then painting it with enamel.

 

Now, bolt a ground strap to the frame and expect the electrons to say "hi" to the paint and primer as they pass by....uh, the paint and primer is a dam to the energy...

 

[Bloo]

9 minutes ago, BillinMd said:

Another practice that really gets to me is owners using the bolt on clamps to afix the cables to the battery lug. Many cats are quite valuable but still  use those cheap cable clamps. If there is any corrosion or loose fitting cables, that will present problems. Sorry for the rant.

Do you mean this kind? They are a guarantee of constant trouble.

 

[BillinMd]

Yes. Spend a little time to find the correct cable. You more than likely spent hundreds if not thousands in the engine compartment, a correct cable will reward your efforts.

[maok]

Just a note, the current (amps) draw and hence the size of the cables are not related to the battery voltage (6v or 12v), its related to the size of the engine ie., larger capacity engines will draw more amps than smaller capacity. In fact, if you swap a 12 volt battery into a 6volt starter motor setup with the same engine, the 12 volts will have slightly more current draw due to the high turn speed of the starter which causes slightly more friction.

Edited July 11, 2022 by maok (see edit history)

[Bloo]

While that is technically true, it is a bit misleading.

 

If one compares a properly designed whole 6v system with a 6v battery to a properly designed whole 12v system with 12v battery, the 6v system will require twice the current (Amps) to do the same work. That is why the cables are always bigger on 6 volt cars, and why only a very few people get away with using cables that were intended for 12v systems on 6v cars without trouble. They are typically 4 gauge, and that is just too small for most 6 volt cars.

[1937hd45]

1 hour ago, Bloo said:

While that is technically true, it is a bit misleading.

 

If one compares a properly designed whole 6v system with a 6v battery to a properly designed whole 12v system with 12v battery, the 6v system will require twice the current (Amps) to do the same work. That is why the cables are always bigger on 6 volt cars, and why only a very few people get away with using cables that were intended for 12v systems on 6v cars without trouble. They are typically 4 gauge, and that is just too small for most 6 volt cars.

This is why I'll die never understand electricity. 6 Volt system is six less than 12 Volt but needs larger wire to move less material.

[Bloo]

Think of voltage as pressure in a water pipe and current (Amps) as flow. To get more flow at a lower pressure, you need a bigger pipe. If the water in that pipe were feeding a water wheel grinding grain or something like that, to do the same amount of work you would need move the same amount of water up to the water wheel.

 

 

[Bryan G]

4 hours ago, trimacar said:

What I enjoy is an owner sandblasting frame, painting it with DP-90 or equivalent epoxy primer, then painting it with enamel.

 

Now, bolt a ground strap to the frame and expect the electrons to say "hi" to the paint and primer as they pass by....uh, the paint and primer is a dam to the energy...

 

I once saw the entire wiring harness in a late model Toyota suffer a catastrophic meltdown. The ground mount on the inner fender is supposed to be bare metal but the body shop had painted it. As soon as they attached the battery cables, poof! They have a TSB on that issue, but of course you have to read it...

[1937hd45]

25 minutes ago, Bloo said:

Think of voltage as pressure in a water pipe and current (Amps) as flow. To get more flow at a lower pressure, you need a bigger pipe. If the water in that pipe were feeding a water wheel grinding grain or something like that, to do the same amount of work you would need move the same amount of water up to the water wheel.

 

 

If you have two 12x12x8 boxes of water attached to a wall the 12volt with a 1/2 pipe and the 6volt with an inch ID pipe as I see it the water wheel will be spinning for a longer time with more water hitting it, gravity being what it is. 

[Bloo]

Gravity would make the pressure the same in both boxes. The smaller pipe has more resistance to flow, and it will take longer to get the same amount of water through it. If you raised the pressure in the box with the smaller pipe, so there was more "push" than just gravity, you could make it flow like the other one.

 

These water pipe analogies fall apart pretty quick, but it is a start.

 

 

[maok]

2 hours ago, Bloo said:

While that is technically true, it is a bit misleading.

 

If one compares a properly designed whole 6v system with a 6v battery to a properly designed whole 12v system with 12v battery, the 6v system will require twice the current (Amps) to do the same work. That is why the cables are always bigger on 6 volt cars, and why only a very few people get away with using cables that were intended for 12v systems on 6v cars without trouble. They are typically 4 gauge, and that is just too small for most 6 volt cars.

The cable size still applies to a 12 volts system, a larger capacity engine will have a larger battery cable than a smaller capacity engine. Compare a modern v8 5litre engine battery cable to say a 3 cylinder 1litre engine of both 12 volt battery. Though, modern starter motors will have a reduction gear, hence more torque available to turn the engine over with the less amp draw.

 

But in our vintage cars, replacing the 6 volt battery with a 12 volt does NOT reduce amp draw, slightly increases it.

[Frank DuVal]

13 hours ago, Curti said:

Personally I am not a fan of cut-off switches. A diode in the generator handles that problem.

How does a diode in the generator circuit keep a short circuit somewhere else in the wiring from catching fire?

 

24 minutes ago, 1937hd45 said:

If you have two 12x12x8 boxes of water attached to a wall the

Then you have the same voltage, as long as the two boxes are the same height from the load (object using water). 

 

Power in electrical terms is volts times amps. If you have half the volts and want the same power, the amps have to be doubled. Simple math. 

 

If you have a shower head that needs 3 gallons a minute and it is only 20 feet from a well tank with 50 psi, then 1/2" pipe should be just fine. Keep that same 50 psi but run the pipe 200 feet, seems to me using ohm's law you will need a larger pipe! BTW, the length of the pipe is the resistance, R in ohm's law. Now if you only have 25 psi and 20 feet away, a bigger pipe would be good too, ohm's law!

[Frank DuVal]

6 minutes ago, maok said:

But in our vintage cars, replacing the 6 volt battery with a 12 volt does NOT reduce amp draw, slightly increases it.

Only because the starter (load) is the same. Get a proper 12 volt starter for the same displacement engine, the amps will be less.

[maok]

46 minutes ago, Frank DuVal said:

Only because the starter (load) is the same. Get a proper 12 volt starter for the same displacement engine, the amps will be less.

Yes, a 12 volt starter with a reduction gear will draw less current(amps), and a modern EFI engine will start almost instantly, hence less time required for the amp draw (amps is also about time) on the starter.

 

But that is not what we encounter here, we are replacing the 6 volt battery to a 12 voltage battery with a 6 volt designed starter.

Edited July 11, 2022 by maok (see edit history)

[Bloo]

This thread is about replacing a 6v battery with two 6volt batteries in parallel. Voltage does not add when the batteries are in parallel. The larger cables are still needed.

Edited July 11, 2022 by Bloo (see edit history)

[maok]

15 minutes ago, Bloo said:

This thread is about replacing a 6v battery with two 6volt batteries in parallel. Voltage does not add when the batteries are in parallel. The larger cables are still needed.

Sorry Bloo, my above comment wasn't about this particular thread, its more in general when this topic of 12volt battery replacing a 6 volt battery with our vintage cars and amp draw halving comments are made regarding cable size. I'm sure you know that I understand how voltage adds up or not with series or parallel connections.

[maok]

1 hour ago, Frank DuVal said:

Only because the starter (load) is the same. Get a proper 12 volt starter for the same displacement engine, the amps will be less.

Also Frank, yes, the load is the same, however the power has increased to double the amount. The starter with a 12v battery (powering a 6v starter) is turning the motor about twice as fast, hence twice the power.

Edited July 11, 2022 by maok (see edit history)

[JRA]

11 hours ago, Bloo said:

Do you mean this kind? They are a guarantee of constant trouble.

 

What would be a better option?

[Bloo]

A soldered on terminal preferably, or at least one crimped very well, better if insulated or sealed somehow. The battery shops have heatshrink tubing with goo inside that can seal up the connection.

 

The trouble with those ones in the picture is the clamp connection is subject to all the same corrosion that the terminal itself is, but the clamp to the wire typically never gets cleaned out when the terminal does. That's two points of failure instead of one. Worse, the corrosion develops around a bunch of little strands, and even if someone realizes it needs cleaning, it gets harder and harder to clean every time. After a while you just have to cut it off. The corrosion continues to wick up the wire, and it isn't too long before you can't cut off enough to fix it anymore. They are literally designed to fail.

 

EDIT: Something like this would be a good choice:

 

 

 

Edited July 11, 2022 by Bloo (see edit history)

[prewarnut]

19 minutes ago, Bloo said:

A soldered on terminal preferably, or at least one crimped very well, better if insulated or sealed somehow.

 

The trouble with those ones in the picture is the clamp connection is subject to all the same corrosion that the terminal itself is, but the clamp to the wire typically never gets cleaned out when the terminal does. Worse, the corrosion develops around a bunch of little strands, and even if someone realizes it needs cleaning, it gets harder and harder to clean every time. After a while you just have to cut it off. The corrosion continues to wick up the wire, and it isn't too long before you can't cut off enough to fix it anymore. They are literally designed to fail.

 

 

Probably we should consider woven grounds disposable at the time of battery replacement. In Amateur radio I have checked and replaced from time to time.

 

The pic of the Optima shows 800 CCA. I like Matt's comment that wiring in parallel will act as a band-aid. Do we really need 1600 CCA through not just the grounding wires but supply to the starter and including armature windings and brush terminals? Unintended consequences may arrive one day....

[alsancle]

5 minutes ago, prewarnut said:

 

Probably we should consider woven grounds disposable at the time of battery replacement. In Amateur radio I have checked and replaced from time to time.

 

The pic of the Optima shows 800 CCA. I like Matt's comment that wiring in parallel will act as a band-aid. Do we really need 1600 CCA through not just the grounding wires but supply to the starter and including armature windings and brush terminals? Unintended consequences may arrive one day....

I don't disagree with this.   That picture is 6 years old and those batteries have just sat.  Replacements with less cranking amps might be a good idea.

[intimeold]

Just be careful and double check everything.  

 

 The main difference in wiring batteries in series vs. parallel is the impact on the output voltage and the capacity of the battery system. Batteries wired in series will have their voltages added together. Batteries wired in parallel will have their capacities (measured in amp-hours) added together.

 

intimeold

[Ben Bruce aka First Born]

37 minutes ago, alsancle said:

I don't disagree with this.   That picture is 6 years old and those batteries have just sat.  Replacements with less cranking amps might be a good idea.

 

 Me? I would not bother replacing.  May not need the amps, but can not hurt. I believe the "power" will only be used if needed. Meanwhile, one has double the reserve.

 

  Ben

[alsancle]

For years dad‘s cord would barely turn over. When I looked at the battery cables, he was running 12 V cables that have been put on in the 60s. A cable to the starter is almost 6 feet long. This is the set up he replaced it with, which has worked great.

Edited July 11, 2022 by alsancle (see edit history)