Voltage, wiring questions

[Oxyacetylene]

I have been looking over some of the electrical on my truck, at first to see why my headlights might be dim, and now I have a few questions. Here are my observations, followed by the questions that some of you might be able to help with.

Observations:

• Alternator appears to be working just fine. The 14v terminal shows 14.3v output, and the 28v terminal shows 28.6. Output voltages are steady here.
• On the alternator voltage regulator box on top, the 28v terminal shows steady voltage, a little over 28 v. The 14v terminal shows a fluctuating voltage less than 14v. It fluctuates by about 1v.
• Both lights on the alternator blink green
• When the truck has been parked and I crank it up, the voltage gauge comes right up into the green, over halfway of the green section, but after it runs for a while, presumably after the batteries are "charged" then the voltage drops to the left side of the green section.
• When I check the individual batteries, the voltages are different between the two batteries in the 12v circuit, and the other two that are in series to make 24v. The two batteries in the 24v circuit show about 1v more than the two batteries in the 12v section.
• On the reverse polarity protection relay, full alternator voltage is going in both on 14 and 28v but coming out there is a voltage drop. About a .3v drop for 28v and about .8v on the 14v side.
• I have about 13.5v at the headlight terminals when the truck is running. I think I just need the right bulb to use with my H4 conversion housings. Anyone have a suggestion for a known good LED H4 headlight bulb that fits? The headlight buckets do not have a lot of room behind the lamp housing so I don't know if I can even fit it one that has a heatsink or fan on the rear of the bulb.

Questions:

• On your alternator, has anyone checked the voltage on the top two regulator terminals? Is yours steady voltage on both? How much voltage difference between what you see on those terminals vs the large output terminals on the main body of the alternator?
• If you test each battery individually, do you also see a voltage difference between the 12v parallel batteries and the other two that are in series to make 24v?
• Have you checked the reverse polarity protection relay to see how much voltage drop it exhibits? It sounds more like a set of diodes than a relay, which I know diodes exhibit some small voltage drop, but .8v seems excessive on the 14v side.
• On the alternator, where does the voltage come from that is present on the two top regulator terminals? I started looking through the manuals but haven't found this yet. Are these voltages fed back to the alternator so it produces output based on what is present "downstream" of the reverse polarity protection relay and other components?

 

[Ronmar]

Those two terminals on the regulator Are not voltage test points… The forward terminal, closest to the pully is the energize input terminal. Applying 24v here enables the alternator to start outputting power. That power comes from the de-energized contacts of relay K11 which along with K24(starter lockout) are controlled by the oil pressure sw on the A0/A1 and by the gauge controller on the A1R Basically it keeps the alternator offline until the engine is running.

the rear terminal is the F- terminal. It is sampling the field winding where the regulator connects to it. The other end of the field is connected to 24V. The redulator switches the field to ground in pulses to control the field current which determines the field strength/alternator output. By measuring the duty cycle of this switching you can get an idea of how hard the alternator is being told to operate. On the A0 this signal goes to the STE connector for testing purposes, so is basically not used. On the A1/A1R that terminal goes to the LBDC which uses the signal to determine when the alt has reached an overloaded condition, so it can disconnect the batteries to save the alternator.

The alternator senses it’s output voltage at the alt output terminals(no remote sensing) and regulates it’s output voltage to it’s correct voltages at that point. it assumes good connections at the polarity box and the batteries, so that part is up to you

The individual voltages measured at each battery or between battery and alternator while running should be very close to one another. If they are not I would look for bad/dirty connections. Disconnected and measured individually the batteries should also be close if they are not, well bad connections can cause differences in charging.

You should see a voltage drop between where the batt and alt connect to the polarity box input terminals and it’s output terminals that feed up to the power panel. Diodes typically drop the voltage between 0.3-0.5V. if you are seeing any more than that at the power panel, again dirty connections could be a contributing factor. If it drops under load then definitely failing connections or the polarity box could have failing diodes. it is out in the weather, so dirty connections there are not unusual…

The alt should be putting out 14/28V all the time it is running. The gauge should reflect this, so perhaps it is breaking down as it operates or you have loose connections. It could also be polarity diodes in the polarity box breaking down as they get warm? I would connect a test meter to the power points in the power panel and compare readings there with the dash voltmeter to see which way to go from there…

And as always I recommend to everyone that they drop to 2 batteries. The alt/battery bank mismatch they created on these trucks is the root cause of many of their power system issues…

 

[Oxyacetylene]

You should see a voltage drop between where the batt and alt connect to the polarity box input terminals and it’s output terminals that feed up to the power panel. Diodes typically drop the voltage between 0.3-0.5V

Very good info in your reply thank you! I think my alternator is doing fine at least. The voltage drops that I have seen on the reverse polarity protection relay were measured right on the terminals themselves, so that may warrant some further checking. Maybe I can get my hands on another A0 for comparison. The voltage that I measured in the fuse panel 12v and 24v points were the same as what I measured at the posts coming out of the reverse polarity protection relay, or at least pretty darn close. I think when I have some more time that I will also disconnect all the batteries and charge them individually and see where they settle afterwards. Mine already had the 6T AGM batteries when I got it from auction so I am gonna try to make them last.

 

[Ronmar]

Well the AGM’s make the alternator overload situation even worse. Standard wet lead acids need about 25% of the AH capacity in amps to meet the charge demands of the batteries. Four 6T batts is a 240AH bank. That is 60A neededout of the alt. In the case of the 12v side, that is about all you have available from the alt, but the lights pull around 25A(over 30A for a M1079) so you are already exceeding the capacity(150%) of the alt to charge the 12v side with the lights on. That and the 12v vampire are why the 12v side is usually the issue on these trucks. Ihas trouble getting to a full state of charge with limited run hours, so it sets at a partial charge and sulfates to death.

Because of their lower internal resistance, lead acid AGM’s can deliver a lot more current for a given size of battery. But this also means they will draw more charge current. AGM’s need 45% of their AH capacity in amps out of the alternator during most of their charge cycle. In a 240AH bank thats a 108A. Thats more than the combined output of the alternator with no 12 or 24v loads applied…

Systems that work rarely get changed. They modified the charging system on these trucks twice. The first was to add the LBCD which, big surprise, disconnects the batteries and puts them on a trickle charge if it detects alternator overload... Then they went to a standard 260A alt on the A1R. The 260 was an absolute must-have to properly deal with 4 AGMs…

You want to get the most out of these batteries(and your alternator), put two of them on a shelf and throw a maintenance charger on them every now and then… personally I would sell two, as the two in the truck will probably then last longer than you want to store the other two

 

[Oxyacetylene]

Well...

Very interesting. That explains your recommendation to only run the two batteries. On mine I have switched all of the lights to LED bulbs, which should help the current draw a bit. I'm just using cheap LED bulbs in the factory lights. I used to always keep the batteries on a maintainer when I wasn't driving it, but right now that isn't practical due to where the truck parks. I have been thinking about a solar maintainer setup with a couple of panels and a charge controller. I am using one of the pulsetech units right now. Those have a bad reputation, but it hasn't drawn down the batteries on mine yet. Not sure that it has enough capacity to really help either, but it's on there.

Edit to add that this also reinforces my goal to put a separate battery in the enclosure to run whatever and not be drawing from the truck batteries. I have ordered a LiFePo4 battery and waiting for it to ship. Eventually I would like to have that in the enclosure, and a couple solar panels mounted to charge the enclosure battery, as well as to keep the truck batteries maintained.

 

[Ronmar]

Very interesting. That explains your recommendation to only run the two batteries. On mine I have switched all of the lights to LED bulbs, which should help the current draw a bit. I'm just using cheap LED bulbs in the factory lights. I used to always keep the batteries on a maintainer when I wasn't driving it, but right now that isn't practical due to where the truck parks. I have been thinking about a solar maintainer setup with a couple of panels and a charge controller. I am using one of the pulsetech units right now. Those have a bad reputation, but it hasn't drawn down the batteries on mine yet. Not sure that it has enough capacity to really help either, but it's on there.

Edit to add that this also reinforces my goal to put a separate battery in the enclosure to run whatever and not be drawing from the truck batteries. I have ordered a LiFePo4 battery and waiting for it to ship. Eventually I would like to have that in the enclosure, and a couple solar panels mounted to charge the enclosure battery, as well as to keep the truck batteries maintained.

Yea if you keep a maintainer on it you will be in a much better situation And will keep the alt from having to run at an overload for long durations Trying to top off the batteries. The vampire is only about 20MA on my truck. I have a 15w panel and a buck converter set to deliver a 13.2v float voltage to the 0-12 batt and a small equalizer to float the two batteries to within .2V of each other. Has been working well for about a year now. That reminds me I need to go clean the snow off the solar panel

 

[Oxyacetylene]

Yea if you keep a maintainer on it you will be in a much better situation And will keep the alt from having to run at an overload for long durations Trying to top off the batteries. The vampire is only about 20MA on my truck. I have a 15w panel and a buck converter set to deliver a 13.2v float voltage to the 0-12 batt and a small equalizer to float the two batteries to within .2V of each other. Has been working well for about a year now. That reminds me I need to go clean the snow off the solar panel

Remind me to bug you about your thoughts on putting together the electrical for my enclosure when I get further along! I may post over on the M1079 conversion thread to get some ideas. Thanks again for all of the info! I will also check and see how much parasitic drain I have on mine sometime soon.