8 Volt Batteries ?

[Kilgore47]

I have a 1947 P15 with the original 6 volt positive ground.  There is a 6 volt lead acid battery in the car now.  At idle the volt meter reads 8 volts at the battery.  With the engine revved up it reads 9 volts at the battery.  After running for a while and then shutting the engine down the battery reads 6.9 volts.  Could this car be set up to use an 8 volt battery?  I am getting ready to switch to a sealed battery and wondering if I should go with an 8 volt.  Or does the charging system need to be fixed.

[chrysler1941]

Charging 9 volt on 6 volt is bad. You'll cook battery dry. 

Sealed battery will crack or  explode with this voltage, better adjust regulator or get a correct one. 

8  volt battery? Like a golf cart? 6 volts has worked for over 50 years, why shouldn't it now?

[Kilgore47]

There was no battery in the car when I got it.  Just wondering if the PO set it up for an 8 volt.  Are the above numbers correct for charging an 8 volt battery.  If yes then I'll try to track down an 8 volt.  I not then I'll have to fix the regulator or replace it.

[chrysler1941]

9.6v is max charge voltage for a flat 8v battery, so 9v would be low. But since it's trying to charge a 6v battery, it's not working optimal. Also your generator is working overload.

Only way to know if regulator is set correct, by charging an 8v battery.

[Marcel Backs]

Ditch old regulator and get a new one which provides correct voltage to properly charge the battery. Get yourself an Optima 6 volt and forget about 8 volt ones. Over voltage is the enemy of your 6 v positive ground system. Overheated cloth wire aged for decades will cause catastrophic results pretty fast. Keeping to original specs is what your electrical system was optimized for, no tweaking necessary. Ensuring proper integrity of electrical components and wiring is a must in order to protect your ride. M

[knuckleharley]

23 minutes ago, Marcel Backs said:

Ditch old regulator and get a new one which provides correct voltage to properly charge the battery. Get yourself an Optima 6 volt and forget about 8 volt ones. Over voltage is the enemy of your 6 v positive ground system. Overheated cloth wire aged for decades will cause catastrophic results pretty fast. Keeping to original specs is what your electrical system was optimized for, no tweaking necessary. Ensuring proper integrity of electrical components and wiring is  must in order to protect your ride. M

Bingo! If you have trouble starting your car with a 6 volt battery,tune it up!

[kencombs]

8v swaps were really common back in the 60s.  Just a quick cover-up for a weak starter, cables,  bad connections or poor state of tune. So I wouldn’t fix the symptom.  Find the reall issue and fix it.  
 

I disagree with replacing the reg without knowing more.  If the contact points look ok and no obvious heat damage it can be adjusted and likely be superior to most new ones. 

[Kilgore47]

Thanks for all the input.  I prefer to stay stock so a 6 volt Optima is on order.  I have re wired the car complete with 00 battery cables.  The tune is good.  I believe the starting problem is being caused by the 6 volt lead acid battery wearing down.  When I come back from a run the top of the battery is wet and the level is down.  That makes me think it has been boiling.  That's why I got the meter out and started checking everything.  I keep adding distilled water and that is slowly diluting the acid.  There is info on this site about adjusting the voltage regulator.  I'll track that down and get that done.  After cruise night tonight.  First get together in a long time.

 

Have jumper cables will travel

[Marcel Backs]

Hopefully accompanied by a good fire extinguisher. An attempt at adjusting the regulator if possible would be a move in your favour before getting out on the cruise.

[Kilgore47]

The word cruise may be a little deceiving.  It's about two miles to down town where we park along the street, walk around and talk to everyone.  Small town.  Then about two miles back.  The fire extinguisher is a good idea.  I'll take the one out of the old jeep.

[Kilgore47]

The Optima battery did the trick.  Reach through the window hit the starter button and it cranks right up.  Did a road kill tie down for the run downtown tonight.  I have some brass sheeting to make a hold down tomorrow.  After I fix the VR.  Looks funny with that little battery. 

[Marcel Backs]

Enjoy yourself Kilgore and be safe. I’m about to take my old sled out too! M

[desoto1939]

How old was the other battery?  I use a Pulse Trickle charge on my 6v battery and the unit has the meter on the unit to tell you the number of volts it is charged at and when charging. The same unit can work on 6 or 12 volt the unit determine which voltage battery you are hooking the unit to.  The unit is about the size of a pack of hardbox cigarette, has a 14 foot cable with the two alligator clips.

 

My 6v volts battery lasts approx 6-8 years. Only fill with distilled water when needed.

 

Rich Hartung

desoto1939@aol.com

[Kilgore47]

The old battery was a little over two years old.  It didn't have the cranking amps to do the job.  The new optima spins it like a 12 volt.

 

This is a picture from yesterday.  Not a good picture.  My car is the one in the middle with the stick holding the hood up.  It's missing one of the hood springs.  It really amazed me that so many people were interested in that old crusty car.  Most of the cars there were modified and mine is original.  Modified is OK.  As people looked under the hood I could almost heat them think "does that run".  There were many younger people looking and asking questions.  That surprised me.

[Marcel Backs]

I hope everything worked out with the regulator Kilgore. A word of caution on the Optima, being a deep cycle battery requires a slow and low current from your charging system. Since charging current is proportional to electrical pressure (voltage) it would be way better for battery life to keep the regulator voltage in spec at the earliest possible opportunity. Deep cycle batts can fail prematurely when exposed to over voltage conditions. M

[Sam Buchanan]

The Optima is AGM battery technology, very different from the flooded lead acid batteries. Is the old Mopar regulator compatible with this type of battery?

[chrysler1941]

5 hours ago, Sam Buchanan said:

The Optima is AGM battery technology, very different from the flooded lead acid batteries. Is the old Mopar regulator compatible with this type of battery?

All mechanical regulators are terrible for AGM charging due to on/off function of current regulating relay. Motors that take long to start will drain too much and voltage drop sensed by the primitive regulator will excite generator for max current output and this is where the AGM suffers.

But if engine is a fast starter, and AGM battery fully charged with a tender, then it's ok. Ideally you need an electronic regulator after the mechanical one

Long story short, keep you AGM fully charged at all time as Marcel Backs recommends.

Edited June 2, 2021 by chrysler1941

[Pete]

Hi all,

 

I've gone through two Optima 6v batteries.

 

One mechanic jumped it with a 12v charger, and another mechanic switched the + and - terminals. Neither would then take a charge. Had both batteries gone over by a local auto electric shop. Neither could be saved even using the detailed instructions on Optima's website. I've had both of these scenarios happen on lead acid batteries which apparently are more robust as they handled it well and continued in service for a decent lifetime. Both my old Mopars have alternators.

 

Lesson learned: take very good care of those Optima batteries even when they are out of your sight.

 

Second lesson learned: never but another Optima product. The cars work great with a lead acid battery.

 

I've read that Optima used to make very good batteries. Then they were bought by a conglomerate that move production to Mexico and quality has suffered.

 

Pete

 

[Kilgore47]

Finally got back to working on the 47.  Turns out the generator has problems also.  This was discussed under "Hidden Noises".  

 

I have a 6 volt positive ground alternator on order and this should solve the charging problems.

 

Thanks for all the information

[keithb7]

I bought a 6V flooded acid battery 5 years ago. "Crown" brand at a local tractor supply. I have no idea if it's a half decent battery or not. I do know that I keep it in the car, disconnected all winter. I put .75A 6V to it every month for about a week. No issues. 5 years so far. I have no complaints.

[Sam Buchanan]

19 hours ago, Kilgore47 said:

Finally got back to working on the 47.  Turns out the generator has problems also.  This was discussed under "Hidden Noises".  

 

I have a 6 volt positive ground alternator on order and this should solve the charging problems.

 

Thanks for all the information

 

Yep, the alternator will solve a bunch of problems....good move.  ?