Lighted indicator display illuminates in chase pattern

[Wes11293]

Voltage drops on the lbcd in and out? Have you checked your batteries and their connection?

Superman .. need help. Have a m1088a1P2 and replaced Alt and regulator and all relays. My lights are rambler that batteries all tested good and I’m getting good charging on 12v side but the 24v side I’m sitting at 25-26 volts ? What would cause it to charge but not to 28v?

 

[Suprman]

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

 

[Ronmar]

Superman .. need help. Have a m1088a1P2 and replaced Alt and regulator and all relays. My lights are rambler that batteries all tested good and I’m getting good charging on 12v side but the 24v side I’m sitting at 25-26 volts ? What would cause it to charge but not to 28v?

Define good 12v charging(whats the voltage and where are you measuring it)?

 

[Wes11293]

I swapped out a LBCD known good one from one that was working fine on another truck. No change. The terminals on the regulator on top of the ALT are putting out 13.5-14v charging on the 12v side and 25-26v charging on the 24v side. On the 24v gage in the cab it shows it hover into the yellow range and then barely back into the green range. It’s reading correct from using a meter on the regulator and ALT big lugs. I’m just lost because the batteries are check and tested good, the ALT and regulator is new. The LBCD box was swapped and no change.. idk what else could cause a 24V not to charge to 28V like it should ? I understand the system from what I’ve read on it. The 24v excite wire signals and lets the ALT charge like it should. But if I’m seeing 25V on the ALT and regulator that should be enough for the regulator to see the 24V to command the ALT to charge I would think.

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

 

[Ronmar]

Ok, you should have 14.1 and 28.2 on the large bolted terminals on the alternator chassis.

The forward terminal on the regulator is the alt excite terminal. You need at least 21V applied to that terminal by K11 after the engine has oil pressure to bring the alt online.

The rear terminal on the regulator is an ac RpM signal to tell the LBCD that the alternator has exceeded 1500 RPM.

The LBCD looks for alt RPM and voltage output from the alternator to determine if the alternator is malfunctioning. It will turn on the charging system light in the dash and it also controls the disconnect relay in the power box behind the battery box to disconnect the batteries from a suspected overloaded alternator.

So what causes an alternator to not deliver rated output.
1. Something is wrong with the windings/diodes and it cannot meet rated voltage with the load applied to it.
2. Something is wrong with the regulator and it cannot meet rated voltage
3. The alternator is overloaded and it cannot meet rated voltage.

in the case of this regulator it monitors 28V and the regulator controls field current to control 28V output just like any other alternator. The regulator also controls SCRs attached to the middle of the stator windings and pulses them like a switching power supply to regulate the 14V output to 1/2 of the 28V output to keep the batteries in balance.

The voltages you listed look like it's trying to half the 28V output. So is it overloaded or incapable? I have noticed with my alt that if it does not have a good path to 12V/visibility of the 12v out of the middle of the 24V string, it will derate and deliver voltages similar to what you measured.

if this were me, I would insure the batteries are connected properly with the 12v lead connected to the cable that connects the batteries in series..

I would then insure I have a load testable link between batteries and alternator. Do you have a couple of 50W headlights? A 50W headlight pulls ~4A @12V. A pair in parallel would pull 8A, 3 would pull 12A ect. The wiring between batteries and alt should support 200A with only a 3% volt loss when loaded from batteries to alt, so 8-12A should have very little volt drop from battery to alt. Put a pair or 3 wired together in parallel and at the alternator connect to the ground and 12v bolts on the alt. The lights should light up bright and you should have virtually the same voltage measured there as you measure at the batteries while the lights/load is connected.

next connect the load test lead to the 12V alt terminal and the 24V alt terminal. Since that 12 comes from the middle of the 24V, the voltage should also be 12V across those terminals. You can check it with a meter. With load applied across the 12 and 24 terminals, again lights should be bright and the voltage at the alt 12-24 terminals should be virtually the same as the voltage measured from the 12-24 terminals(12v) at the batteries.

 

[Ronmar]

Now if this were a regular alt, you could briefly jump the field(bypass the regulator) and drive the field to full saturation. And see if the voltage increases. If the alt was overloaded, this test would not increase voltage because it was already giving all it can.

another option is to throw in an instrument shunt and see how much current it is actually delivering. But if the batteries are good, it shouldn’t be pulling that much current.

how many batteries are you running?

 

[Wes11293]

Now if this were a regular alt, you could briefly jump the field(bypass the regulator) and drive the field to full saturation. And see if the voltage increases. If the alt was overloaded, this test would not increase voltage because it was already giving all it can.

another option is to throw in an instrument shunt and see how much current it is actually delivering. But if the batteries are good, it shouldn’t be pulling that much current.

how many batteries are you running?

It’s military so 4 batteries brand new Agm hawkers. Can’t run two due to military QC. And ok I’ll try the jumper 24v from batt to excite wire and see if I get voltage out the big lugs.

 

[Third From Texas]

It’s military so 4 batteries brand new Agm hawkers. Can’t run two due to military QC. And ok I’ll try the jumper 24v from batt to excite wire and see if I get voltage out the big lugs.

Yeah, I did a double take when I saw P2

 

[Wes11293]

Yeah, I did a double take when I saw P2

 

[Wes11293]

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

So jump from 24 side on batteries to the 24v terminal lug on the regulator? Leaving all the wires hooked up or disconnected?

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

So jump from 24 side on batteries to the 24v terminal lug on the regulator? Leaving all the wires hooked up or disconnected?

 

[Suprman]

The lbcd is involved with voltage regulation. When you put battery voltage directly to the front regulator terminal you are bypassing all of that. If you have battery voltage at that terminal the alt should put out proper voltage. Did you make sure the alt had a good ground strap. Ive seen simple stuff like that cause all kinds of issues.

 

[Ronmar]

Engine off, If you have 24v at the alternator 28v bolt to ground, that is coming from the batteries. You can get 24v from that bolt to apply to the exc terminal on the reg with a small piece of wire. But since the alt is going over battery resting voltage I suspect it is probably getting what it needs at that exc terminal on the reg, thru the normal excitation circuit.

what amp rating is this alt?

The problem with 4 batts is that a good batt in parallel with a bad one can mask the bad one, so this could still be a batt issue. AGMs when depleted also want nearly twice as much charge current as a similar AH rated wet cell. You cannot leave it like that, but you can certainly disconnect two for troubleshooting.

this is as simple as loosening only the battery terminals on the forward(toward front of truck) pair or rear pair of batts, leave all other interconnected wiring tight and loosen and lift the terminals up off the posts and slide something under them to keep them isolated from the posts. This will drop you to a pair of batts in series(one inner, one outer).

do you have a batt load tester? I described one above with headlight bulbs, but a pile type loadtester is even better. Do a 100A load test on the batts, ground to 12(outermost pair of batteries) and 12 to 24(innermost pair of batteries) note the drop with 100A applied. Do the same test at the alt ground to 12v bolt and again across the 12v bolt to 24v bolt. The voltage drop should be the same As at the batteries

A voltage test alone is not a complete test. It is not valid untill tested UNDER LOAD… a bad connection will pass full voltage throughout a circuit untill you try to pull current thru it.

if one of the circuits between battery and alt is breaking down with current flow, the alt will be unable to sense the batteries properly. This is not just a regulated alternator it is a battery balancer. it MUSE SEE 12V from the middle of the 24V series battery under load/with current flowing. if it does not see this it will not regulate properly.

I have seen this on my own alt while experimenting and learning how these things operate, and it delivered voltages similar to the ones you described.

the only way to truly test that circuit is to do a low amperage 12 and 24v battery load test AT the alternator terminals...

 

[Wes11293]

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

So jump from 24 side on batteries to the 24v terminal lug on the regulator? Leaving all the wires hooked up or disconnected?

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

I jumped 24 v to the 24v lug on the regulator and no change. It’s very weird. I swapped LBCD with known good and no change. The green light on top the LBCD is green saying good and batteries and everything looks good. The regulator LEDS are green for a little then go amber here and there. When AC cuts on. I’m looking at now after changing batteries 26.5-27.5v in the alt big lug and the regulator 24v is at 25.5-26.5v? I’m lost here and why it’s doing this. That regulator lug voltage dips under and light goes amber sometimes. The gauge is matching. Why would the alt be putting out 28v on big lug like every other truck?

 

[Wes11293]

The lbcd is involved with voltage regulation. When you put battery voltage directly to the front regulator terminal you are bypassing all of that. If you have battery voltage at that terminal the alt should put out proper voltage. Did you make sure the alt had a good ground strap. Ive seen simple stuff like that cause all kinds of issues.

Should I be disconnecting the wire on the regulators harness when supplying this voltage test? Meaning no wire attached then supply the 24v power ? I’m getting the 25.5-26.5 Ish from the 24v side on regulator Yeah I’ll check the ground strap and clean up the mounting points and see.

 

[Wes11293]

Engine off, If you have 24v at the alternator 28v bolt to ground, that is coming from the batteries. You can get 24v from that bolt to apply to the exc terminal on the reg with a small piece of wire. But since the alt is going over battery resting voltage I suspect it is probably getting what it needs at that exc terminal on the reg, thru the normal excitation circuit.

what amp rating is this alt?

The problem with 4 batts is that a good batt in parallel with a bad one can mask the bad one, so this could still be a batt issue. AGMs when depleted also want nearly twice as much charge current as a similar AH rated wet cell. You cannot leave it like that, but you can certainly disconnect two for troubleshooting.

this is as simple as loosening only the battery terminals on the forward(toward front of truck) pair or rear pair of batts, leave all other interconnected wiring tight and loosen and lift the terminals up off the posts and slide something under them to keep them isolated from the posts. This will drop you to a pair of batts in series(one inner, one outer).

do you have a batt load tester? I described one above with headlight bulbs, but a pile type loadtester is even better. Do a 100A load test on the batts, ground to 12(outermost pair of batteries) and 12 to 24(innermost pair of batteries) note the drop with 100A applied. Do the same test at the alt ground to 12v bolt and again across the 12v bolt to 24v bolt. The voltage drop should be the same As at the batteries

A voltage test alone is not a complete test. It is not valid untill tested UNDER LOAD… a bad connection will pass full voltage throughout a circuit untill you try to pull current thru it.

if one of the circuits between battery and alt is breaking down with current flow, the alt will be unable to sense the batteries properly. This is not just a regulated alternator it is a battery balancer. it MUSE SEE 12V from the middle of the 24V series battery under load/with current flowing. if it does not see this it will not regulate properly.

I have seen this on my own alt while experimenting and learning how these things operate, and it delivered voltages similar to the ones you described.

the only way to truly test that circuit is to do a low amperage 12 and 24v battery load test AT the alternator terminals...

It’s a 260Amp dual voltage Alt with regulator and the lights on the regulator. What trips me out is I’ve changed the components out with brand new or known good ones. The batteries I put in today were brand new out the box and charged. I ran the truck and it was at 26-27 sometimes charge on the big lug on the alt then came back hour later and all the batts are at 5 volts? I’m totally confused on this and now the alt isn’t charging at all again. I understand it’s because the batts are low but what the heck? Why and how is my alt brand new not putting out 28v?

 

[Suprman]

Wire rubbing shorted somewhere. Bad lbcd under spare tire.

 

[Ronmar]

It’s a 260Amp dual voltage Alt with regulator and the lights on the regulator. What trips me out is I’ve changed the components out with brand new or known good ones. The batteries I put in today were brand new out the box and charged. I ran the truck and it was at 26-27 sometimes charge on the big lug on the alt then came back hour later and all the batts are at 5 volts? I’m totally confused on this and now the alt isn’t charging at all again. I understand it’s because the batts are low but what the heck? Why and how is my alt brand new not putting out 28v?

ok, I dont see fully charged batts dropping to 5v in one hour under normal properly connected operating conditions…

I will say it one last time, do a 100A battery load test AT the alternator terminals(truck off) on both the 12 and 24v circuits. you do have 12 and 24 AT the alt right? This alt does not behave like a normal alternator, it is a battery balancer... The regulator must sense a proper series connected 24v battery with 12 out of the middle. You could have a bad crimped cable connection a bad manual or remote disconnect relay contact that you cannot see, and which passes full voltage when only under no/light load… you could also have improperly connected wiring… voltage is only considered good when tested UNDER LOAD… those wires, crimps and the disconnect switch and relay were produced by the lowest bidder…

or mock it up outside the normal truck wiring. Take a pair of charged car batteries, connect them in series near the right front tire. Disconnect and insulate all the wires from the alt and reg. connect the test batteries to ground, 12 and 24v on the alt. Start the truck and using a small jumper wire connect 24v from the alt 24 terminal to the front/exc terminal on the regulator And then measure the alt voltages.

this will take all the truck wiring out of the equation and you can prove the alt and reg. If you have a load tester, put 100A or so of load on the test batteries while the alt is online and see if the alt maintains 14.1/28.2V output under the test load.

first rule of troubleshooting, always work from a known. If you don’t have any known facts, start establishing them. The external battery test will take a lot of unknown out of the equation, so you can then hunt down the unknown that is kicking your ass…

 

[Wes11293]

Maybe bad lbcd. Jump 24v from the battery terminal to the front terminal on the regulator see if it comes up

Is there a way to safely bypass the load box under the spare tire? Could I just connect to a boat load and battery together on the battery post and the same thing for 24?

 

[GeneralDisorder]

Is there a way to safely bypass the load box under the spare tire? Could I just connect to a boat load and battery together on the battery post and the same thing for 24?

Yes. And disconnect the cannon plug.

 

[Wes11293]

That won’t affect the safety of anything or cause shorts or burning up of anything?