Charging mystery

[haggis6145]

My 86 M1028 front battery is not charging. This model has the Duvac 'blue box'. So far, both batteries, belts and Duvac box have been replaced. The auto electric 'expert' tells me it is charging properly at 14.4 volts and maybe the belts should be tightened (then why is it charging properly?). I boost the truck, it runs properly and the volt gauge shows that the system is charging properly. During the day when I'm not using any accesories such as headlights, it starts several times before going dead. At night with the headlights on, the gauge shows lmore draw and when I use the turn signals, they don't flash but if I turn the headlights off temporarily, the signals flash. As soon as it is turned off, battery dead. It seems that the accesories drain the battery. Strangely, the system was working fine until I left the headlights on once and drained the original battery. All of the problems started after that. I have replaced all of the parts since then. Also, the 'fasten seatbelt' idiot light has remained on since then(only when running). Any ideas?

 

[Blood_of_Tyrants]

Did you replace the battery?

 

[Ken_86gt]

If you have 14.4 V across the battery it sounds like it is charging properly. Maybe you have something draining the battery when it is off. Try removing the battery wire when not in use to verify.

 

[haggis6145]

This is the new battery. It has been drained and boosted several times.

 

[haggis6145]

OK, I'll try that. But, what explains why the battery is dead after driving while the system is supposedly charging. I literally turn the truck off, then immediately attempt to turn it over and it's dead. It seems that the battery is not charging, despite all the indications that it is.

 

[tshermankb]

huh so if you disconnect the cables to the batteries then check the voltage its below 12? could be the ignition system has a slight short...

 

[papakb]

It's never a good idea to disconnect an alternator from the battery with the engine running unless you have a spare on the shelf.


Most modern military vehicles use a voltmeter to indicate if a system is charging or not. If the system is healthy this works fine. The internal resistance of a battery will cause the battery to charge if the alternators output voltage is above 12.6 volts and discharge if it falls below that. Most vehicle alternators output 13.4 volts or more and the type of battery can raise this. Maintenance free batterys tend to be over 14 volts.


Batterys are energy storage devices and their internal chemistry causes them to store energy flowing into them. However, if their internal resistance is high because of an internal failure, a voltmeter can show proper voltage but without current flowing into them they won't charge. Older systems used to use an ammeter to measure the flow of current into and out of a battery and is a more accurate way to indicate charging. This is why corroded terminals cause charging problems.


There are a couple of things you can do to check this. Install an ammeter inline with the battery. You can leave the voltmeter in the system. If you have a DC clamp on ammeter handy you can clip it around the lead to the batterys positive terminal and see if there is true current flowing into the battery. Remember, no current flow, no charging.


Don't put the ammeter directly in the alternators output line because all the current being drawn by the vehicle to run will also be measured. It needs to be at the battery.


Good luck

 

[Ken_86gt]

It does sound like a bad battery- I know you said that it was replaced. but the symptoms do indicate a possible bad one. Take it to your local store to get it load tested. Also bad, loose, or corroded connections can cause these types of issues.

 

[Milbikes]

I had a similar problem, but on a later model Chevy....my 1999 diesel Suburban. It turned out to be the smaller red wire on the positive battery cable that went to a junction box near the firewall. At the box, the connecting nut was loose. As soon as I tightened it, all my electrical troubles, starting troubles etc went away. I know the M1008 is a different system, but wire connections and grounds are always suspect when electrical gremlins pop up. H.

 

[haggis6145]

Thanks alot guys. First, I'm going to try a different battery. Then the connections and DC ammeter.

 

[lavarok]

You mentioned replacing the DUVAC?

If you have the 24v Leece alternators and the duvac setup in your truck, I would bet the issues lie in the charging system and not the battery. Search on "duvac" and you will find a few threads discussing this topic. Good luck! Maybe add a photo or two so we can see what your dealing with.

 

[haggis6145]

Ian,

In a previous thread relating to M1010 (which is the same set up as my M102 charging issues, you mentioned an alternative to installing a battery equalizer would be changing the top 24v alternator to a 12 volt. That seems like a simple fix. I don't need a lot of power. Why wouldn't I just do that?
Thx

 

[combatmech]

I am having the SAME problem with my 1009. It runs fine....but after a while ( this is with the lights and what not turned on ).....the seat belt light comes on. I have changed several items. Guess I'll try yet another battery.....Good luck as well Haggis

 

[lavarok]

Ian,

In a previous thread relating to M1010 (which is the same set up as my M102 charging issues, you mentioned an alternative to installing a battery equalizer would be changing the top 24v alternator to a 12 volt. That seems like a simple fix. I don't need a lot of power. Why wouldn't I just do that?
Thx

You most certainly could! Being a M1028 ( without a shelter ), you don't need the additional power the setup was supposed to provide. Go for it! For that matter, some might recommend you abandon 24v completely.

 

[hfmt93]

Its an old truck. I searched and chased my tail on similar problems. Check and double check the wires and terminals. Ricky the Redneck PO replaced a bunch of wires in mine and the terminal crimp jobs looked like a chimp did them. I fixed those and it is good.