I searched the old posts and found this link. It shows a battery isolator between the 2 batteries. Is this the factory schematic?. If not, does anyone have the factory schematic for the dual batteries?. Did all 73 - 79 trucks have a provision for dual batteries?. My 74 has a 2nd battery tray on the drivers side, thought it might be an advantage to hook it back up!


http://www.clubfte.com/users/mil1ion...trations3.html

 

That's a basic isolator diagram

There was the Camper Special & Trailer special wiring and also wiring for winches.
Ford used the solenoid style battery set-up.

I'll see if I can find the original Ford setup for you.

 

Unless there is some special reason you want to install a basic design error, or the cheap factory style dual battery system, you should install the isolator type system. The Factory system really did not work well.

 

I've had the factory dual battery setup in my 76 F350, supercab, 460/C6 camper special for 31 years and I've not experienced any problems. What were the problems/weaknesses I've been able to avoid?

 

No problems with the ol solenoid setup, Just old technology.

Go to any 4X4 shop they'll help you set it up. Really easy to do. Especially since you have the extra battery tray setup already.

 

The batteries kill each other due to chemistry imbalance if they are not identical. Unfortunately chemistry imbalance develops during use because usage is not identical. It did not work in 95% of installations. Some people have just been extremely lucky with a few installations. Not the type of odds I would want to bet on. The isolator systems work well. If I had a working factory system I would remove it to avoid future problems.

 

I would have expected to see these "future" problems before the truck was 31 years old. I will wait a few more years to see if they show up.

 

When dual batteries were present, the standard battery was an R-27F (70 cranking amps) the optional battery was an R-27FA (80 cranking amps).

Using a combo of an R-27F/R-24F is what causes problems. The R-24F was the standard battery for the 302's, and earlier 352/360's w/o air.

Problem is...parts houses parts books may not list an R-27F, and will only sell the R-24F, which is inadequate for a 302/352/360/390/460 with a/c and/or Camper Specials.

 

Come on now. I gotta call BS on your stats.

The isolator system is a newer and a better technology from decades ago. However IMHO the old system did work for more than 5% of installations. Not sure where you got your stat from but I don't agree with it. To bad a mod can't post a poll here to get a better feel of how how the old system worked and/or works from fellow forum members with these systems installed.

 

I had lots of experience with them in the old days and I understand the chemistry problems well. They were problematic from the start and the statistics are my own based on my experience and that of other mechanics and engineers. Feel free to present better statistics. A "poll" is worthless. The relay system was as good as they could do with available technology back in the 60's but as soon as the solid state isolators came out the relay system should have been abandoned. Unfortunately cost was an issue back then. Ford never seems to abandon a design until forced to by competition or some "other" reason tho. It takes a lot of $$ paperwork to change a design and back then with only a 12,000 mile or 1yr warranty the warranty costs were not high enuf to justify the cost of the paperwork etc. The relay system design is junk and always has been. It was cheaper than an isolator but with price differentials nowadays I am not sure which is cheaper for an OEM. The RV industry with a very high percentage of dual battery systems in their vehicles abandoned the relay system many years ago.

 

Well, to begin with, the 'different batteries in parallel argument' is flawed, as 99% of the time they are tied together is when the engine is running, and the alternator is holding the batteries at 14.0 V., and they absorb current depending on their individual states of charge. When the truck is off and the system is at rest, the solenoid is open, and they are NOT tied together.
I added the solenoid system to my '84 and it worked fine. Main advantage is you are always cranking on two batteries. I wanted something that was foolproof for my wife who also drove my truck then, and not have to have her remember to do anything special in cold weather. Most of the dual battery systems have a 'tie' solenoid between the two batteries to allow you to jump start yourself, and the original Ford system does it automatically.
The only disadvatage is, one battery can go bad, and you don't know it since you're always cranking on two. I did make it a point to put a load tester on them once a year or so, usually in the fall, and make sure they were both still good.
If I was going to install a dual battery system today, I would use the solenoid system for these reasons, as well as not having to cut up the alternator wiring harness and worry about what side of the isolator the sense line to the regulator is on, etc.

 

I agree with n9lhm. I have used the solonoid setup in multiple vehicles, and with multiple combinations of batteries, and never a problem. On the other hand the isolators have a huge amount of voltage drop across them, and when they fail (which is usually at the most inconvenient time) they seem to like to let the smoke out of the wiring. When the solonoid system fails (if ever) then either the soloniod is closed or won't close.usually the last

Bushman

 

When people understand battery cell chemistry then they will discover that the 'different batteries in parallel argument' is NOT flawed. It has nothing to do with connection time. Even with the vehicle running the batteries are discharging into each other trying to equalize charge. While a shorted cell in one battery is usually worst case individual cell chemistry also comes into play. As I said, I have had a lot of experience over the years with these systems on vehicles, chemistry, and with industrial battery systems both in troubleshooting, maintenance, and engineering design. I have seen batteries literally fry each other. The isolators do fail if not sized correctly, everyone wants to go cheap. The voltage drop across the isolator diodes is current dependent just like the relays. Nominally it is 0.7V on older isolators and as little as 0.4V on some of the newer isolators. The voltage drop is less as the charge current tapers off. There is a voltage drop on the relays also but nobody ever measures it. Mainly due to advertising so that people are "aware" of the solid state device voltage drop. The solid state devices are less forgiving of abuse than the old relay technology, they both let the smoke out of things, but the solid state systems have advantages.

 

I gotta agree with Bushman and n9hlm on this one. I've mis-matched battery capacities and brands, and have never had a battery-related problem in my factory, dual battery setup. I might also add that I've not had any pre-mature battery failures. This on a truck that "sits" alot, as it's a 76 with only 72K miles. As I said above, I will start to worry about this one, when I have my first problem--31 years and counting.

 

It is a well known fact though that a Lead-acid automotive battery that doesn't regularily get energy drawn from it will sulfate and fail eventually becoming worthess.

Batteries need to discharge and recharge to remain healthy.