2009 Lmtv M1078A1 Charging System

[Ronmar]

Just saw your post. I have a 2007 A1 that the no charge light just came on. I’m wondering how you resolved your problem and if so share that with me. Checking the voltage on the two leads going to the regulator I have 24 V on the AC terminal and 0 V on the exciter terminal the one closest to the pulley. I jumper 24 V to the exciter terminal and disconnected the wire to the AC terminal alternator putting out correct voltage. Reconnected the wire to the AC terminal Alternator Stop pudding out power. Changed out the polarity protection box no help. Appreciate any pointers she could give. Thanks

On the A1, the polarity protection box is called a LBCD or load and battery connection device if I recall correctly. The “AC “ wire on the regulator connects to the LBCD. The AC lead is actually a field sense wire which is a way to measure alternator load. The LBCD monitors alternator load with this wire and uses this information to disconnect a failed or badly depleted battery so you can complete the mission without burning up a really expensive Neihoff alt.

A little history: In the A0, Some knucklehead specced a monster battery bank 2-1/2 times larger than the alternator can adequately charge, to meet some perceived military need. So what did they do in the A1, larger alt? Smaller Battery? Nope, they added the LBCD to disconnect the batt and feed it a trickle charge. They finally started in the right direction in the A1R with an alt(you guessed it) 2-1/2 times larger But they kept the LBCD system… You would think this would fix all the alt/batt issues, but it didn’t really as The larger alt was absolutely needed to deal with the introduction of AGM batteries as they require nearly double the acceptance charge current of the wet lead acids the A0 was designed with, so same basic problem was maintained.

Enough History So reconnect the AC wire as it is necessary. The Excite wire on the alt is what tells the alt it is OK to begin charging/providing power after the engine starts. it keeps the alt from trying to charge at low RPM while the starter is drawing hundreds of amps of current. That excite power comes from the de-energized contacts of relay K11 up in the power dist panel(PDP). When you turn on the main sw, K11 should energize, along with the oil loght in the dash annunciator panel. When you start the engine and oil pressure goes above 15PSI, the dash light goes out. That same signal de-energizes K11 and allows it to send 24V to the excite terminal on the regulator to bring the alt online… The first thing I would check is the K11 operation. It should also de-energize when the truck is shifted out of neutral as the neutral relay(K26) is where K11’s power comes from.

 

[Dave21]

On the A1, the polarity protection box is called a LBCD or load and battery connection device if I recall correctly. The “AC “ wire on the regulator connects to the LBCD. The AC lead is actually a field sense wire which is a way to measure alternator load. The LBCD monitors alternator load with this wire and uses this information to disconnect a failed or badly depleted battery so you can complete the mission without burning up a really expensive Neihoff alt.

A little history: In the A0, Some knucklehead specced a monster battery bank 2-1/2 times larger than the alternator can adequately charge, to meet some perceived military need. So what did they do in the A1, larger alt? Smaller Battery? Nope, they added the LBCD to disconnect the batt and feed it a trickle charge. They finally started in the right direction in the A1R with an alt(you guessed it) 2-1/2 times larger But they kept the LBCD system… You would think this would fix all the alt/batt issues, but it didn’t really as The larger alt was absolutely needed to deal with the introduction of AGM batteries as they require nearly double the acceptance charge current of the wet lead acids the A0 was designed with, so same basic problem was maintained.

Enough History So reconnect the AC wire as it is necessary. The Excite wire on the alt is what tells the alt it is OK to begin charging/providing power after the engine starts. it keeps the alt from trying to charge at low RPM while the starter is drawing hundreds of amps of current. That excite power comes from the de-energized contacts of relay K11 up in the power dist panel(PDP). When you turn on the main sw, K11 should energize, along with the oil loght in the dash annunciator panel. When you start the engine and oil pressure goes above 15PSI, the dash light goes out. That same signal de-energizes K11 and allows it to send 24V to the excite terminal on the regulator to bring the alt online… The first thing I would check is the K11 operation. It should also de-energize when the truck is shifted out of neutral as the neutral relay(K26) is where K11’s power comes from.

 

[Dave21]

Thanks I’ll check those two Relays.

 

[Dave21]

Just a thought does it make any sense that I have zero voltage on the exciter wire and 24 V on the AC Wire?

 

[Dave21]

Another question there is a Waterproof circuit breaker in the battery disconnect box do you know what that It’s powering?

 

[Ronmar]

Just a thought does it make any sense that I have zero voltage on the exciter wire and 24 V on the AC Wire?

Under what conditions, engine running?

I have never seen schematics for the LBCD or regulator so it is difficult to determine how exactly it does it’s job or exactly what the signal carried on that line between LBCD and AC term on the regulator Are.

That AC terminal is labeled F- on other regulators. And mine has an AC waveform there when the alt is online, the duty cycle of that waveform being equivelent to the alternator output. I am messing with my truck today anyway, if I get a chance I will measure mine with the alt offline to see what it measures there. I suspect I will probably see 24v

Alternator 101: The field current determines the strength of the magnetic field in the rotor and how much power the alternator outputs(more current, more field, more power) In many regulators, field current is Controlled by regulating the path to ground based on what it measures at the alternator output. so output goes low/gets loaded, the regulator increases the field current flow to boost alt output to it’s regulated/set level. By seeing 24v on that AC terminal, you are probably seeing raw field voltage as without the excite terminal powered, the regulator is not switching any of that field voltage to ground to creat field current and alternator output…

I have heard of people measuring DC voltage on the AC terminal before, I wouldn’t worry about it for now. The lack of 24 on the excite terminal after the engine starts is a prime problem and will cause no output until it is resolved.

 

[Ronmar]

Another question there is a Waterproof circuit breaker in the battery disconnect box do you know what that It’s powering?

Not sure, have not seen one in the circuit diagrams. can you get wire numbers off of the attached wires? What amperage? Is it set or tripped?

 

[Dave21]

Under what conditions, engine running?

I have never seen schematics for the LBCD or regulator so it is difficult to determine how exactly it does it’s job or exactly what the signal carried on that line between LBCD and AC term on the regulator Are.

That AC terminal is labeled F- on other regulators. And mine has an AC waveform there when the alt is online, the duty cycle of that waveform being equivelent to the alternator output. I am messing with my truck today anyway, if I get a chance I will measure mine with the alt offline to see what it measures there. I suspect I will probably see 24v

Alternator 101: The field current determines the strength of the magnetic field in the rotor and how much power the alternator outputs(more current, more field, more power) In many regulators, field current is Controlled by regulating the path to ground based on what it measures at the alternator output. so output goes low/gets loaded, the regulator increases the field current flow to boost alt output to it’s regulated/set level. By seeing 24v on that AC terminal, you are probably seeing raw field voltage as without the excite terminal powered, the regulator is not switching any of that field voltage to ground to creat field current and alternator output…

I have heard of people measuring DC voltage on the AC terminal before, I wouldn’t worry about it for now. The lack of 24 on the excite terminal after the engine starts is a prime problem and will cause no output until it is resolved.

With the engine running. I jump heard 24 V to the exciter terminal if I leave the wire connected to the AC terminal which has 24 V on it hooked up there is no output voltage from the alternator. When I remove the wire from the AC terminal the alternator charges As it should but has no regulation. Seems to be if the batteries are charged the voltage will creep up toward 15 V. If I let the batteries discharge down to 12.1 V And then apply power to the exciter terminal it will charge at 13.4! Took this on a 300 mile road trip by turning on and off the power to the exciter had no problems keeping the batteries in range.

 

[Dave21]

With the engine running. I jump heard 24 V to the exciter terminal if I leave the wire connected to the AC terminal which has 24 V on it hooked up there is no output voltage from the alternator. When I remove the wire from the AC terminal the alternator charges As it should but has no regulation. Seems to be if the batteries are charged the voltage will creep up toward 15 V. If I let the batteries discharge down to 12.1 V And then apply power to the exciter terminal it will charge at 13.4! Took this on a 300 mile road trip by turning on and off the power to the exciter had no problems keeping the batteries in range.

With the AC wire hooked up there is no output to the alternator but the two green lights are flashing back-and-forth.

 

[Ronmar]

Ok, lets get some clarification here. Where are you getting 24v from to apply to the excite terminal. Do not get it from the AC terminal, because as soon as the alt tries to come online, that 24v goes away as the reg starts sending it to ground to pull the field current and develop output. The best way to drive that excite input on an A1 is to jumper it from the alt 24 output terminal provided the batteries are connected(relays and cutoff sw closed).

where are you measuring voltage at? If I recall two flashing green means the regulator thinks the alt is doing it’s thing, so you should have 14.1 and 28.2V at the alt terminals. Now if for some reason your batteries are putting a large load on the alt, or the regulator thinks they are(weak alt output driving the field to full) when connected, when you connect that AC wire, the LBCD will sense this overload condition and disconnect the batteries…

I got a chance to measure mine, and on the AC/F- terminal I see 24v when the alt is offline, so I suspect it is raw field voltage before the regulator starts switching it to ground to make field current/alt output, so is perfectly normal…

 

[Dave21]

Ok, lets get some clarification here. Where are you getting 24v from to apply to the excite terminal. Do not get it from the AC terminal, because as soon as the alt tries to come online, that 24v goes away as the reg starts sending it to ground to pull the field current and develop output. The best way to drive that excite input on an A1 is to jumper it from the alt 24 output terminal provided the batteries are connected(relays and cutoff sw closed).

where are you measuring voltage at? If I recall two flashing green means the regulator thinks the alt is doing it’s thing, so you should have 14.1 and 28.2V at the alt terminals. Now if for some reason your batteries are putting a large load on the alt, or the regulator thinks they are(weak alt output driving the field to full) when connected, when you connect that AC wire, the LBCD will sense this overload condition and disconnect the batteries…

I got a chance to measure mine, and on the AC/F- terminal I see 24v when the alt is offline, so I suspect it is raw field voltage before the regulator starts switching it to ground to make field current/alt output, so is perfectly normal…

I’m getting the 24 V from the connector that provides power to the air conditioning unit I’ve installed a switch on the dashboard. I have a 12 V digital voltmeter across the batteries. So when ISupply 24 V to the exciter I see no change in the volt meter. When I disconnect the lead to the AC terminal when I say 14.2 V
I’ll get a chance to check those relays tomorrow. I really appreciate all of your help.
Thanks

 

[Ronmar]

I’m getting the 24 V from the connector that provides power to the air conditioning unit I’ve installed a switch on the dashboard. I have a 12 V digital voltmeter across the batteries. So when ISupply 24 V to the exciter I see no change in the volt meter. When I disconnect the lead to the AC terminal when I say 14.2 V
I’ll get a chance to check those relays tomorrow. I really appreciate all of your help.
Thanks

Ok, well that sounds like the LBCD is trying to do exactly what it is supposed to be doing, and disconnecting the alt because it is sensing an overload.

Do you have a voltmeter measuring the 24V? The 12-24 v batts should be reading the same 14.2 individually or 28.4 across the two in series.

For troubleshooting I would recommend you pick your best two batteries and install one in an inner(closest to the frame 12-24V) and one in an outer position(furthest from frame 0-12v) in the bay and leave the other 2 disconnected… Batteries can do some weird things, sometimes they break down under load and sometimes they break down under charging voltage. Batteries in parallel can mask the issue with a good battery covering for a bad one IE, one floating to a good voltage while the other absorbs a buttload of current when charge voltage is applied. Getting rid of the parallel batts eliminates this, and if you pick a bad one for the pair you choose to keep online, you will probably know it pretty quick

 

[Dave21]

Ok, well that sounds like the LBCD is trying to do exactly what it is supposed to be doing, and disconnecting the alt because it is sensing an overload.

Do you have a voltmeter measuring the 24V? The 12-24 v batts should be reading the same 14.2 individually or 28.4 across the two in series.

For troubleshooting I would recommend you pick your best two batteries and install one in an inner(closest to the frame 12-24V) and one in an outer position(furthest from frame 0-12v) in the bay and leave the other 2 disconnected… Batteries can do some weird things, sometimes they break down under load and sometimes they break down under charging voltage. Batteries in parallel can mask the issue with a good battery covering for a bad one IE, one floating to a good voltage while the other absorbs a buttload of current when charge voltage is applied. Getting rid of the parallel batts eliminates this, and if you pick a bad one for the pair you choose to keep online, you will probably know it pretty quick

I’ll check the individual batteries for voltage this morning replaced all four batteries less than two years ago. It sounds like the LBCD Is working properly it must be assuming that the batteries are fully charged correct? But still do not understand why I’m not getting 24 V on the lead going to the exciter Terminal?
Let me check a few things this morning and I’ll get back to you. I really really appreciate your help.

 

[Ronmar]

I’ll check the individual batteries for voltage this morning replaced all four batteries less than two years ago. It sounds like the LBCD Is working properly it must be assuming that the batteries are fully charged correct? But still do not understand why I’m not getting 24 V on the lead going to the exciter Terminal?
Let me check a few things this morning and I’ll get back to you. I really really appreciate your help.

Simple voltage tests can sometimes be deceiving. You really need to check them while under load. this is true of any DC troubleshooting. Voltage isn’t good untill it is measured good under load. Batteries have the added twist of state of charge, which can effect how they perform under load. And as I mentioned above an internal short might not pass any real current at normak static voltage(12.6V) but when the alt voltage of 14.1 rolls in it starts to conduct heavily…

The LBCD’s sole purpose is to disconnect the batteries if they are overloading the alternator. If the alt is not overloaded, the LBCD should keep the batteries connected. It could be that the alt is having trouble making rated output and is driving the field hard even at what would be a normal load. The LBCD sees this field drive and is thinking the alt is overloaded.

again look to the operation of K11. It should energize at ign switchon and de-energize once 15 PSI of oil pressure is reached After start. Once it is running you can pull K11 you should have 24V at the top pin 30. Then y0u can put a jumper between it’s pins 30 and 87A(top pin and the first pin below it) which should feed the alt excite terminal…

You do have a 5 pin relay in the K11 position right? This is a place where a 4 pin in a 5 pin position will cause you issues…

 

[Dave21]

Simple voltage tests can sometimes be deceiving. You really need to check them while under load. this is true of any DC troubleshooting. Voltage isn’t good untill it is measured good under load. Batteries have the added twist of state of charge, which can effect how they perform under load. And as I mentioned above an internal short might not pass any real current at normak static voltage(12.6V) but when the alt voltage of 14.1 rolls in it starts to conduct heavily…

The LBCD’s sole purpose is to disconnect the batteries if they are overloading the alternator. If the alt is not overloaded, the LBCD should keep the batteries connected. It could be that the alt is having trouble making rated output and is driving the field hard even at what would be a normal load. The LBCD sees this field drive and is thinking the alt is overloaded.

again look to the operation of K11. It should energize at ign switchon and de-energize once 15 PSI of oil pressure is reached After start. Once it is running you can pull K11 you should have 24V at the top pin 30. Then y0u can put a jumper between it’s pins 30 and 87A(top pin and the first pin below it) which should feed the alt excite terminal…

You do have a 5 pin relay in the K11 position right? This is a place where a 4 pin in a 5 pin position will cause you issues…

OK checked all the batteries two of them are 12.5 and two of them are at 12.7 installed a new five Pin relay And it is clicking when turning on and off the main power switch. If you would be so kind to give me a call area code 702-622-1909 I’d really appreciate it hard to do this by text. Thanks

 

[Mxpert]

It ended up being the voltage regulator. Also removed the fusible links located under the alternator wire studs, just put a larger washer there to take up the slack so it does not bottom out. Hope that helps.

 

[Dave21]

It ended up being the voltage regulator. Also removed the fusible links located under the alternator wire studs, just put a larger washer there to take up the slack so it does not bottom out. Hope that helps.

Thanks I did replace the voltage regulator. And relay K 11 but I’m still not getting 24 V on the exciter terminal. If I jump 24 V to the exciter terminal the alternator works both lights are flashing green but the battery voltage does not change. Removing the wire from the AC terminal which has 24 V on it Disallowed the alternator to put out 14.1 V and seems to be charging the batteries normally but this did not turn off the no charge light on the dash. Nor did it provide 24 V on the exciter wire. Will do some more checking today. I’m glad you resolve your problem. Mine looks to be a little more involved.
Cheers

 

[Dave21]

Thanks I did replace the voltage regulator. And relay K 11 but I’m still not getting 24 V on the exciter terminal. If I jump 24 V to the exciter terminal the alternator works both lights are flashing green but the battery voltage does not change. Removing the wire from the AC terminal which has 24 V on it Disallowed the alternator to put out 14.1 V and seems to be charging the batteries normally but this did not turn off the no charge light on the dash. Nor did it provide 24 V on the exciter wire. Will do some more checking today. I’m glad you resolve your problem. Mine looks to be a little more involved.
Cheers

You wouldn’t happen to have a wiring diagram of the system?

 

[coachgeo]

You wouldn’t happen to have a wiring diagram of the system?

A1 wiring diagram is in here somewhere; if Im not mistaken

 

[coachgeo]

A1 wiring diagram is in here somewhere; if Im not mistaken

here you go.... it is linked to in below thread. Quick search via google found it.

m1088... FMTV Wiring Diagram

Does any one know were I can get a Wiring Diagram for my M1088's A0 and A1 not having much luck looking in the TM Section. Thanks Chip

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