• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

F350 7.3 charging issue. Twin batteries, one alternator.


Dirtman

Former Middleweight Moss Fighting Champion
Joined
May 28, 2018
Messages
19,304
Reaction score
13,326
Points
113
Location
41N 75W
Vehicle Year
2009
Engine Type
2.3 (4 Cylinder)
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
It's up there.
Total Drop
It's down there.
Tire Size
Round.
My credo
I poop in the furnace.
Asking for a buddy. He bought a 2001 f350 with a blown up 7.3. We swapped in a new "used" motor and got it running great (had to replace the IDM) but now it's got a charging issue.

It started and drove fine, checked voltage at the batteries at startup and got 14.2 which is ok. But this is a twin battery single alternator truck. Out of my league. After a while the alternator apparently fried and now is only putting out 8 volts.

Swapped alternators, problem solved... for another 50 miles or so. Fried another alternator.

Now here's my understanding, with twin batteries it obviously must have a isolator so the alternator doesn't charge both batteries at once or let the batteries back feed each other correct? With 2 known good batteries and a known good alternator is it possible the isolator is bad and allowing the alternator to dump into both batteries at once and overloading it?

Thoughts? I'm not familiar with twin battery setups.
 


adsm08

Senior Master Grease Monkey
Supporting Member
Article Contributor
Ford Technician
TRS 20th Anniversary
Joined
Sep 20, 2009
Messages
34,623
Reaction score
3,613
Points
113
Location
Dillsburg PA
Vehicle Year
1987
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Tire Size
31X10.50X15
I don't see an isolator, The batteries share a positive cable, and ground independently.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,700
Reaction score
13,159
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
It's been awhile since I worked on one of those but I maintained 4 of those in a snow plow fleet. I don't remember an isolator. Batteries in parallel full time. I seem to recall a strange issue when the owner only replaced one battery of a set. But I can't remember exactly what it was now.
 

ericbphoto

Overlander in development
TRS Event Staff
TRS Forum Moderator
Supporting Member
U.S. Military - Veteran
TRS 20th Anniversary
VAGABOND
TRS Event Participant
GMRS Radio License
Joined
Feb 7, 2016
Messages
15,209
Reaction score
16,346
Points
113
Age
59
Location
Wellford, SC
Vehicle Year
1993
Make / Model
Ford Ranger
Engine Type
3.0 V6
Engine Size
3.0L
Transmission
Manual
2WD / 4WD
4WD
Total Lift
6"
Tire Size
35"
My credo
In theory, theory and practice are the same. In practice, they are different.
Shouldn't need an isolator. 2 batteries in parallel just act like one larger battery. No problem. Both batteries should be same size age and condition. If you replace one, you replace both. If using the stock size alternator, or larger, it should handle everything fine.
 

adsm08

Senior Master Grease Monkey
Supporting Member
Article Contributor
Ford Technician
TRS 20th Anniversary
Joined
Sep 20, 2009
Messages
34,623
Reaction score
3,613
Points
113
Location
Dillsburg PA
Vehicle Year
1987
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Tire Size
31X10.50X15
It's been awhile since I worked on one of those but I maintained 4 of those in a snow plow fleet. I don't remember an isolator. Batteries in parallel full time. I seem to recall a strange issue when the owner only replaced one battery of a set. But I can't remember exactly what it was now.
If you replace only one battery it tries to charge based on the average of the two, which leaves the older battery under charged and ruins the new one by over-charging it.
 

Uncle Gump

Token Old Guy
TRS Event Staff
TRS Forum Moderator
Supporting Member
VAGABOND
TRS Event Participant
Joined
Sep 17, 2018
Messages
13,700
Reaction score
13,159
Points
113
Location
Ottawa IL
Vehicle Year
2006/1986
Make / Model
Ranger/BroncoII
Engine Size
4.0L SOHC/2.9L
2WD / 4WD
4WD
My credo
Lead follow or get out of my way
If you replace only one battery it tries to charge based on the average of the two, which leaves the older battery under charged and ruins the new one by over-charging it.
Ultimately that was the cause... and why I mentioned it. I think it would turn on the battery light at times. What I do remember was putting another new battery in it cured whatever it was.
 

Dirtman

Former Middleweight Moss Fighting Champion
Joined
May 28, 2018
Messages
19,304
Reaction score
13,326
Points
113
Location
41N 75W
Vehicle Year
2009
Engine Type
2.3 (4 Cylinder)
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
It's up there.
Total Drop
It's down there.
Tire Size
Round.
My credo
I poop in the furnace.
Guess im more use to boat setups.....

The batteries hes using are 2 random ones from the shop but both tested good. He doesn't want to buy new batts untill he's sure of the issue so he doesn't fry them.
 

Biggfoot44

Active Member
Joined
Jul 6, 2019
Messages
110
Reaction score
42
Points
28
Location
USA
Vehicle Year
1994
Make / Model
Ranger 2wd
Transmission
Automatic
Never say never or always , but :

On Diesel powered ( consumer sized) trucks , dual batteries are wired together to give serious cranking power . The alternative used on early diesel pickup trucks like my early Dodge Cummins was a really huge ( & expensive) single battery , that was kinda marginal .

On gas powered RV, tow vehicles, etc typically one battery runs vehicular needs as if it were the only battery , and the second battery is dedicated to the RV , or whatever specialized equipment powered while parked . With an isolator between the batteries .
 

ericbphoto

Overlander in development
TRS Event Staff
TRS Forum Moderator
Supporting Member
U.S. Military - Veteran
TRS 20th Anniversary
VAGABOND
TRS Event Participant
GMRS Radio License
Joined
Feb 7, 2016
Messages
15,209
Reaction score
16,346
Points
113
Age
59
Location
Wellford, SC
Vehicle Year
1993
Make / Model
Ford Ranger
Engine Type
3.0 V6
Engine Size
3.0L
Transmission
Manual
2WD / 4WD
4WD
Total Lift
6"
Tire Size
35"
My credo
In theory, theory and practice are the same. In practice, they are different.
Never say never or always , but :

On Diesel powered ( consumer sized) trucks , dual batteries are wired together to give serious cranking power . The alternative used on early diesel pickup trucks like my early Dodge Cummins was a really huge ( & expensive) single battery , that was kinda marginal .

On gas powered RV, tow vehicles, etc typically one battery runs vehicular needs as if it were the only battery , and the second battery is dedicated to the RV , or whatever specialized equipment powered while parked . With an isolator between the batteries .
That makes perfect sense. On a boat or RV the need to keep one isolated and available for starting is important. I wonder if a diesel RV would be the same. Or would it have 2 starting batteries plus a third, isolated battery for auxiliaries.
 

adsm08

Senior Master Grease Monkey
Supporting Member
Article Contributor
Ford Technician
TRS 20th Anniversary
Joined
Sep 20, 2009
Messages
34,623
Reaction score
3,613
Points
113
Location
Dillsburg PA
Vehicle Year
1987
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Tire Size
31X10.50X15
Guess im more use to boat setups.....

The batteries hes using are 2 random ones from the shop but both tested good. He doesn't want to buy new batts untill he's sure of the issue so he doesn't fry them.
This may well be the issue. When you are using a single generator to charge a pair of parallel batteries having the batteries be unbalanced can place an incredible and unusual load on the generator.
 

Dirtman

Former Middleweight Moss Fighting Champion
Joined
May 28, 2018
Messages
19,304
Reaction score
13,326
Points
113
Location
41N 75W
Vehicle Year
2009
Engine Type
2.3 (4 Cylinder)
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
It's up there.
Total Drop
It's down there.
Tire Size
Round.
My credo
I poop in the furnace.
Thanks Adsm, I sent him off to get a new matching pair.
 

Dirtman

Former Middleweight Moss Fighting Champion
Joined
May 28, 2018
Messages
19,304
Reaction score
13,326
Points
113
Location
41N 75W
Vehicle Year
2009
Engine Type
2.3 (4 Cylinder)
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
It's up there.
Total Drop
It's down there.
Tire Size
Round.
My credo
I poop in the furnace.
That did it. Got 2 new matching batteries and its charging normally now. Thanks everyone. Now just gotta setup a third "house" battery since this is a camper rig. I'm afraid to mess with actually trying it into the trucks electrical even with an isolator switch so I think I'm just gonna do solar panels on the roof of the camper to keep it charged.
 

Dsetz

Member
Joined
Aug 16, 2019
Messages
94
Reaction score
27
Points
18
Age
38
Location
Montana
Vehicle Year
1984
Make / Model
Ford Ranger
Engine Type
2.8 V6
Transmission
Manual
2WD / 4WD
4WD
My 06 gas F250 has an(I assume aftermarket) isolator to separate the winch battery from the engine side battery. I'd never used the winch until the other day. It blew the isolator fuse and discharged my new Interstate, died as I limped up to the shop.
I'm hard pressed to believe that a diesel doesn't still have an isolator to avoid batrey issues, its still possible to charge both batteries and crank in paralell depending on how its setup.
Mine is essentially an aluminum heatsink mounted on the passenger sidewall behind the engine battery. My fuse was easy to find as the wiring was seperate.
On a diesel an isolator should be stock. Check the fuse map for it.
 

ericbphoto

Overlander in development
TRS Event Staff
TRS Forum Moderator
Supporting Member
U.S. Military - Veteran
TRS 20th Anniversary
VAGABOND
TRS Event Participant
GMRS Radio License
Joined
Feb 7, 2016
Messages
15,209
Reaction score
16,346
Points
113
Age
59
Location
Wellford, SC
Vehicle Year
1993
Make / Model
Ford Ranger
Engine Type
3.0 V6
Engine Size
3.0L
Transmission
Manual
2WD / 4WD
4WD
Total Lift
6"
Tire Size
35"
My credo
In theory, theory and practice are the same. In practice, they are different.
My 06 gas F250 has an(I assume aftermarket) isolator to separate the winch battery from the engine side battery. I'd never used the winch until the other day. It blew the isolator fuse and discharged my new Interstate, died as I limped up to the shop.
I'm hard pressed to believe that a diesel doesn't still have an isolator to avoid batrey issues, its still possible to charge both batteries and crank in paralell depending on how its setup.
Mine is essentially an aluminum heatsink mounted on the passenger sidewall behind the engine battery. My fuse was easy to find as the wiring was seperate.
On a diesel an isolator should be stock. Check the fuse map for it.
There's no need for it. No reason to separate the batteries. RV's, boats, vehicles with a winch or stupid huge stereo have a reason to separate the batteries.
 

Sponsored Ad


Sponsored Ad

Staff online

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Truck of The Month


Kirby N.
March Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top