Battery Isolator (Diode)
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Mountain Pass
Joined: Aug 2002
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From: White Lake
Battery Isolator (Diode)
OK, My '05 w/ Dual Alternators will not turn on the alternators
when connected through the Isolator.
I see in the ford truck wiring diagram there is a "sense" circuit tied to
the PCM.
Has anybody solved this problem?
when connected through the Isolator.
I see in the ford truck wiring diagram there is a "sense" circuit tied to
the PCM.
Has anybody solved this problem?
Last edited by glafond; May 4, 2005 at 12:25 PM. Reason: pic
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From: Virginia
If all the 2awg wiring is new and what you installed, then you might be missing something that was included in the original wiring. Is the original wiring too small? I was wondering if it was big enough for the original set-up, and then just add the 2awg wire for the isolator and the rear batteries. Which brings me to my other question.
Why do you have to run the two front batteries through the isolator? One diode on the rear bank would do the job wouldn't it?
Why do you have to run the two front batteries through the isolator? One diode on the rear bank would do the job wouldn't it?
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Mountain Pass
Joined: Aug 2002
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From: White Lake
Played with this idea. Also, tried to use one alternator for the front & the other for the rear. NoGo - the PCM only uses one Alternator until the draw requires both.
Both Alternators are factory wired to the passenger side front battery.
The isolator is mounted in the lid of the tool box in the back with the batteries & inverters. I Just pulled the alternator wires off the battery and attached both of them to a 2awg wire that runs back to the isolator center post, then ran a 2awg wire back to the front and attached to the same post i removed the alternator wires from. The only thing that changed in this setup was the diode between the alternators and the original battery connection. I need the alternator isolated between battery sets. The rear batteries are deep cycle, and I can't have them drawing down the front set. For some reason the PCM will not turn the alternators (either one) on when the connection is through a diode. There must be some feedback current that is being blocked. I was hoping there was someone who knew what this current value was, and i could install a bypass resistor through a contact - closed with the engine running - to fool the PCM.
Both Alternators are factory wired to the passenger side front battery.
The isolator is mounted in the lid of the tool box in the back with the batteries & inverters. I Just pulled the alternator wires off the battery and attached both of them to a 2awg wire that runs back to the isolator center post, then ran a 2awg wire back to the front and attached to the same post i removed the alternator wires from. The only thing that changed in this setup was the diode between the alternators and the original battery connection. I need the alternator isolated between battery sets. The rear batteries are deep cycle, and I can't have them drawing down the front set. For some reason the PCM will not turn the alternators (either one) on when the connection is through a diode. There must be some feedback current that is being blocked. I was hoping there was someone who knew what this current value was, and i could install a bypass resistor through a contact - closed with the engine running - to fool the PCM.
Last edited by glafond; May 5, 2005 at 05:18 AM. Reason: Wiring
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From: Virginia
I would move the isolator up front.
The first thing I would do is hook the the front batteries up like you have them in the diagram with the isolator up front, and see if the alternators charge ok. The wiring path will be shorter, and it may work.
Then hook the wire going to the rear to the isolator and hook the other end of this wire to the rear batteries, and see if that works ok.
When you start messing around with very high current loads, having the load too remote can cause problems, especially since we are only talking about 12 volts.
If you plug in some theoretical numbers, a .1 ohm resistance in your wiring and connections, with a 120 amp draw will equal a 12 volt voltage drop in the wiring.
Voltage=current x resistance
Lets say your wiring only had a 3 volt drop under full load, which may be enough to fool the regulation circuit for the alternators.
3volts=120amps x ? resistance
resistance to create a 3 volt drop is only .025 ohms in the wiring and connections.
The regulation circuit monitors the system voltage. That is how it decides how much current the alternators should put out.
The first thing I would do is hook the the front batteries up like you have them in the diagram with the isolator up front, and see if the alternators charge ok. The wiring path will be shorter, and it may work.
Then hook the wire going to the rear to the isolator and hook the other end of this wire to the rear batteries, and see if that works ok.
When you start messing around with very high current loads, having the load too remote can cause problems, especially since we are only talking about 12 volts.
If you plug in some theoretical numbers, a .1 ohm resistance in your wiring and connections, with a 120 amp draw will equal a 12 volt voltage drop in the wiring.
Voltage=current x resistance
Lets say your wiring only had a 3 volt drop under full load, which may be enough to fool the regulation circuit for the alternators.
3volts=120amps x ? resistance
resistance to create a 3 volt drop is only .025 ohms in the wiring and connections.
There must be some feedback current that is being blocked.
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Mountain Pass
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From: White Lake
Nope, Moving the isolator did not help. I have found that a 1 sec bypass of the
diode after the engine was started would cause the alternator to turn on.
Looking at the wiring diagram, I'm thinking that the voltage sense for the PCM is pulled from the alternator itself.
With the alternator connected to the batteries through the diode the voltage cannot
be measured. tried with my fluke.
diode after the engine was started would cause the alternator to turn on.
Looking at the wiring diagram, I'm thinking that the voltage sense for the PCM is pulled from the alternator itself.
With the alternator connected to the batteries through the diode the voltage cannot
be measured. tried with my fluke.
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From: Virginia
So, if you hook another starter relay across the diode, and paralleled it's coil with the regular starting relay coil, it would click in when you where cranking the truck. Do you think that would be enough to turn the alternators on?
Someone had an interesting link on here a few weeks ago, that explained how one wire alternators worked. In the article, it said to bring the alternator offline was easy, the regulator just monitored the voltage from the stator. No voltage from the stator meant the alternator was not turning, so the regulator brought the alternator offline, so it would not run the battery down.
But they said bringing the one wire alternator online was much more tricky. It said what the circuit did was monitor the voltage level of the system at all times. When it detected a voltage drop(from starting the engine) it then brought the alternator online so it could start charging.
Do you think the alternators in your system work this way? The diode would definitely block the voltage, not letting it monitor the dip or sag when starting.
Someone had an interesting link on here a few weeks ago, that explained how one wire alternators worked. In the article, it said to bring the alternator offline was easy, the regulator just monitored the voltage from the stator. No voltage from the stator meant the alternator was not turning, so the regulator brought the alternator offline, so it would not run the battery down.
But they said bringing the one wire alternator online was much more tricky. It said what the circuit did was monitor the voltage level of the system at all times. When it detected a voltage drop(from starting the engine) it then brought the alternator online so it could start charging.
Do you think the alternators in your system work this way? The diode would definitely block the voltage, not letting it monitor the dip or sag when starting.
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Mountain Pass
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From: White Lake
Yep, What i have done, is leave the lower alternator wired to the original batteries.
wired the second alternator through the isolator to charge the rear bank, and also
aid in charging the front original set. Wired upfitter #4 to the provided wire through the firewall (used the red wire) and then ran it to the output wire of the second alternator. So, I'm just applying a momentary battery voltage level to it.
This works well, because i really do not want to continuously charge the deep cycle batteries in the back. When i want to charge them, i just toggle Sw.#4.
Also bought the A-Pillar guage set, with 2 voltmeters, to monitor both banks.
These alternators were tricky. But thanks for your input, it helped jog my aging brain.
wired the second alternator through the isolator to charge the rear bank, and also
aid in charging the front original set. Wired upfitter #4 to the provided wire through the firewall (used the red wire) and then ran it to the output wire of the second alternator. So, I'm just applying a momentary battery voltage level to it.
This works well, because i really do not want to continuously charge the deep cycle batteries in the back. When i want to charge them, i just toggle Sw.#4.
Also bought the A-Pillar guage set, with 2 voltmeters, to monitor both banks.
These alternators were tricky. But thanks for your input, it helped jog my aging brain.
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Postmaster
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Out of curiousity, what are you using your AUX batteries for? how many, from your drawing it looks like 4. Also, my neighbor has the dual setup, top alt as normal, lower added to charge two batteries for his inverter. He has a switch setup just like yours to control the second alt for charging the Aux batteries
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Mountain Pass
Joined: Aug 2002
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From: White Lake
Originally Posted by cangim
Out of curiousity, what are you using your AUX batteries for? how many, from your drawing it looks like 4. Also, my neighbor has the dual setup, top alt as normal, lower added to charge two batteries for his inverter. He has a switch setup just like yours to control the second alt for charging the Aux batteries
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Mountain Pass
Joined: Aug 2002
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From: White Lake
OK Franklin2, check this out.
Truck failed to start this morning. Tried a dozen times, waited a few minutes
then half a dozen more and it started, ran rough then smoothed out.
So I drove to work (see how dedicated i am?). Pull out my trusty Diablo and check for codes. "Glow plug circuit failure #1, #2,...,#8".
Checked the harness of the glow plug module - no voltage, and notice that the supply wires disappear into a huge knot in the harness, covered in electrical tape.
It seems, that in order to save a foot of wire, that instead of wiring the glow plug module directly to the battery, they spliced it into the output wire of the lower alternator inside the harness.
You guessed it, this is the alternator i ran through the isolator to the rear set of batteries. Luckily I was able to just swap alternator cables, took 2 minutes.
Man, these guys are tricky.
Truck failed to start this morning. Tried a dozen times, waited a few minutes
then half a dozen more and it started, ran rough then smoothed out.
So I drove to work (see how dedicated i am?). Pull out my trusty Diablo and check for codes. "Glow plug circuit failure #1, #2,...,#8".
Checked the harness of the glow plug module - no voltage, and notice that the supply wires disappear into a huge knot in the harness, covered in electrical tape.
It seems, that in order to save a foot of wire, that instead of wiring the glow plug module directly to the battery, they spliced it into the output wire of the lower alternator inside the harness.
You guessed it, this is the alternator i ran through the isolator to the rear set of batteries. Luckily I was able to just swap alternator cables, took 2 minutes.
Man, these guys are tricky.