Jump starting M923A2

[Gunzy]

opcorn:

 

[helomech]

On the electrical system on the 939 series trucks trying to charge bad batteries will most certainly cause generator failure.....

I don't buy that. I have a extensive background in things like this. Been a aviation A&P for over 20 years now. A battery (unless it is shorted will not cause a alternator to fail). A bad battery will just refuse to take a charge and will not be any load on a electrical system. Since he knows the cause of the weak batteries (the switch was left on) then they are just low and charging them enough to start the truck will be all that is needed. Even for our aircraft if the battery is weak because of being left on, we are allowed to jump start the aircraft and allow the aircraft's electrical system charge them up. Now if the battery is down because of unknown reasons then we are required to change the batteries. Please explain to me how a bad battery (not a dead shorted on) will hurt an electrical system. If you can then we can continue this discussion.

 

[98G]

..... Since he knows the cause of the weak batteries (the switch was left on) then they are just low and charging them enough to start the truck will be all that is needed....

I agree with what's quoted.

I won't pretend to know more than I do about the electrical systems. I can't tell you *why* or *how* trying to charge bad batteries with our 5 ton trucks will result in failure. HOWEVER, there are simply too many examples of people that have fried a generator doing it for it to be coincidence: mechanism of failure not understood, but result fully understood.

 

[helomech]

I agree with what's quoted.

I won't pretend to know more than I do about the electrical systems. I can't tell you *why* or *how* trying to charge bad batteries with our 5 ton trucks will result in failure. HOWEVER, there are simply too many examples of people that have fried a generator doing it for it to be coincidence: mechanism of failure not understood, but result fully understood.

Not saying things don't happen, but they are almost always the result of a messed up system. If a weak battery hurts your alternator than you have other issues with the truck. Like I said something like a internally shorted battery could cause issues. A bad regulator could hurt things, but this guy knows his batter is dead because the switch was left on. Millions of people jump start trucks with dead batteries and then take off driving with no issues. Heck I had a 2005 nissan titan that would sit so long it needed a jump start every time I used it. Never did it hurt the truck, the battery would charge up and start the next time just fine ( as long as I didn't wait too long).

 

[98G]

Not saying things don't happen, but they are almost always the result of a messed up system. If a weak battery hurts your alternator than you have other issues with the truck. Like I said something like a internally shorted battery could cause issues. A bad regulator could hurt things, but this guy knows his batter is dead because the switch was left on. Millions of people jump start trucks with dead batteries and then take off driving with no issues. Heck I had a 2005 nissan titan that would sit so long it needed a jump start every time I used it. Never did it hurt the truck, the battery would charge up and start the next time just fine ( as long as I didn't wait too long).

I've done it a bunch on other vehicles also. It would never have occurred to me that it was a bad idea until I read about people having problems with it on these trucks.

I recently recovered an m925, with utterly dead batteries. Before reading here I would have simply slave started it and driven it a few hundred miles before shutting it off. Instead I changed out the batteries. You'll read multiple accounts where people have done what I would have done and as a result they added generator replacement to the battery replacement bill.

I dismissed the first couple of accounts as coincidence, but there's simply too many cases of it happening. I still can't tell you the mechanism, but empirical evidence always precedes full understanding.

Back on topic regarding the OP, his batteries weren't utterly dead or bad, just mildly discharged. Slave and go.

But let them sit with the lights on for four years or so and then try it and you'll buy a new generator.... too many cases for it to be coincidence.

 

[helomech]

I've done it a bunch on other vehicles also. It would never have occurred to me that it was a bad idea until I read about people having problems with it on these trucks.

I recently recovered an m925, with utterly dead batteries. Before reading here I would have simply slave started it and driven it a few hundred miles before shutting it off. Instead I changed out the batteries. You'll read multiple accounts where people have done what I would have done and as a result they added generator replacement to the battery replacement bill.

I dismissed the first couple of accounts as coincidence, but there's simply too many cases of it happening. I still can't tell you the mechanism, but empirical evidence always precedes full understanding.

Back on topic regarding the OP, his batteries weren't utterly dead or bad, just mildly discharged. Slave and go.

But let them sit with the lights on for four years or so and then try it and you'll buy a new generator.... too many cases for it to be coincidence.

I would be willing to bet those cases the generator was probably part of the reason why the batteries where dead in the first place. The big pull on the weak/bad generator just was too much for it to handle. Weak batteries won't take lots of amps no matter how much you put on them. The only way to get a battery to pull lots of amps is to put a load on it. That is why if you have a really dead battery and you are trying to jump it and it won't take a charge, you put a huge load on it, then it will start taking the charge. Ever seen when you put a battery charger on a battery that is dead and the amp meter only goes up a few amps. Then if you hit the starter while it is charging then amp meter will shoot up to 10 maybe 20 amps.

 

[doghead]

The alternators go to full output and burn out. This has been seen many many times, with dead batteries.

Same thing can happen with a bad(loose) battery connection.

Read the years of experiences posted and you too will believe this.

 

[helomech]

I don't believe this is the cause. I believe many people have burned up generators, but I believe that was because the where bad to begin with. A generator is not a complex device, what exactly are you burning up inside it?

 

[doghead]

The alternators were not bad to begin with.

The regulators fail.

 

[juanprado]

Not just in military vehicles, but standard troubleshooting electrical system repair.
Step one is always check battery voltage in each battery, If below 12.6 -12.5, charge battery and bring up. If battery is charged at that range 90%+, perform load test. See chart for quickly diminishing capacity as just a slight voltage decrease is huge.

Starters can burn up solenoids and windings because of the high amp draw when low voltage at battery because they typically need 100% for a short period.

Most alternators and military ones have solid state electronics and are not tolerant of trying to charge over 100% because the voltage regular is over excited making the system work hard over 100% capacity to bring a system up. If the battery is shorted or toast the Alt/reg will still try to compensate and bring a system up. Something will give and the regulator's electronics are usually the first to go.

From my limited knowledge, The "standard" military alternators are pretty simple affairs but the regulators are solid state and prone to overheating and melting components when outside of their parameters.

I am not an engineer but I am ASE certified and sold parts for 20+ years. I have literally sold 1000's of batteries and electrical components to diy all the way to shops and fleets. Don't take my word, look at Industry troubleshooting flow charts and those who crank voltage meters and wrenches for a living in the automotive / hd market.

Aviation can be different and I have zero knowledge base.

I do know I left my battery switch "on" in my m923. First natural action was I attempted to start truck. No go. Charged batteries. One dead that would not come up. Got new battery and 3 charged ones. Started truck. Truck ran fine. Voltage gauge low. Charging system not putting out 28V. Pulled Alt. Bad regulator. Replaced assembly as I am fortunate to have many scrappers and sources close to me. On I go.

Sure, a jump start / slave can work to start a vehicle that is down but many will experience more broken electrical components down the road costing more $. Yes, I know time is $ and it is all an equation at the end.

Not trying to argue but give you my perspective from running retail stores, distribution center, and Wholesale Sales management for a few years. YMMV

 

[Scott88M]

Well a small update. Bought a battery charger pulled 2 of the batteries out so far and hooked them to the charger (one at a time). Looks like 1 of the batteries is dead dead. The one showing 3.8v it charges up t to about 6ish then charger shows a fault in the battery. Other one is showing 12.2 and seems OK. I haven't given up completely on the dead one yet but today I'm pulling the last 2 out to charge if at least 1 looks good I'm switching to just using 2 batteries. The batteries are from 04/08 with unknown maintenance so I'm not too surprised.

Quick new question. My truck has 2 small solargizers when going to 2 batteries do I hook 1 to each or only use 1 for the pair? If 1 for the pair where do they connect?

 

[helomech]

Quick new question. My truck has 2 small solargizers when going to 2 batteries do I hook 1 to each or only use 1 for the pair? If 1 for the pair where do they connect?

What is the voltage of the solarizer? If 24 volt the hook to both batteries. If 12 volt, then hook one to each.

 

[helomech]

. YMMV

They put a lot of stuff in manuals to CYA..I see it all the time.

Have you ever seen the current draw on a 18k lb winch. If what you are saying is correct then every 5 ton with an electric winch would fry its electrical system when they used it. They pull 278amps at full load. Please don't say that the battery carries that kind of load for 10 minutes. Climb in the cab and let me know what the amp meter reads. All generators are basically the same, the regulators vary a bit. Aircraft generators are the basically the same as these, at least in design and principle.

 

[Scott88M]

What is the voltage of the solarizer? If 24 volt the hook to both batteries. If 12 volt, then hook one to each.

Haha I guess that should've been obvious. I'll have to check them when I get home. I guess I figured they were all the same.

 

[VPed]

Helomech - I understand what you have been saying and agree that generally, you would be correct. I also have extensive experience in electricity, both stationary and vehicular and would have been prone to stating just about what you have. However, it has become apparent to me since being bit by the green bug that the regulators on these alternators do in fact, have a high incidence of failure due to dead batteries. When the regulator fails, it does so in a manner that drives the alternator output to maximum.

My theory: So, when you first start the truck by slaving, all is cool. After a while, the regulator overheats and alt goes to full voltage. The batteries take what they can for as long as they can, then the system voltage starts to climb. Soon after that, the smoke is let out from all manner of places. Wires burn, gauges burn, sending units burn, protective control boxes burn, alternators burn.

My deuce had all of the gauge coils burnt, the oil pressure, temp, fuel sender, and regulator burnt. Both batteries were completely dead but were recoverable with many days of slow charge. They continue to serve some 2 years plus later.

Respectfully, my 2 cents.

EDIT: Tech schooled in auto mechanics specializing in electrical systems, F-4 Phantom electronics technician, industrial electrician, instrumentation technician, stationary generator technician, etc. The F-4 part is a clue to how long I have been working with electricity.

 

[doghead]

5 ton trucks do not have electric winches.

 

[helomech]

5 ton trucks do not have electric winches.

Many on this site do, and mine will soon.

 

[helomech]

Helomech - I understand what you have been saying and agree that generally, you would be correct. I also have extensive experience in electricity, both stationary and vehicular and would have been prone to stating just about what you have. However, it has become apparent to me since being bit by the green bug that the regulators on these alternators do in fact, have a high incidence of failure due to dead batteries. When the regulator fails, it does so in a manner that drives the alternator output to maximum.

My theory: So, when you first start the truck by slaving, all is cool. After a while, the regulator overheats and alt goes to full voltage. The batteries take what they can for as long as they can, then the system voltage starts to climb. Soon after that, the smoke is let out from all manner of places. Wires burn, gauges burn, sending units burn, protective control boxes burn, alternators burn.

My deuce had all of the gauge coils burnt, the oil pressure, temp, fuel sender, and regulator burnt. Both batteries were completely dead but were recoverable with many days of slow charge. They continue to serve some 2 years plus later.

Respectfully, my 2 cents.

EDIT: Tech schooled in auto mechanics specializing in electrical systems, F-4 Phantom electronics technician, industrial electrician, instrumentation technician, stationary generator technician, etc. The F-4 part is a clue to how long I have been working with electricity.

Good post.

Come on you mean the phantom is not still active duty.

I still don't see how a dead battery can pull that many amps. A battery with no load on it just won't accept lots of amps. You can put a charger on a dead battery and set the charger to 60 amps and the battery just won't accept that many amps unless there is something wrong with the battery, or there is another load on the battery.

Now my theory is that the generator was already weak/bad and that is what caused the low battery situation in the first place. Now we have a weak battery and the vehicle is jump started, the generator is then pulled past it's abilities and starts to cause the issues you described. I just can't buy that a properly functioning electrical system would cause these problems just because of a weak battery.

I appreciate your post. Thanks.

 

[doghead]

Pull a cable off your battery and watch the alternator burn out. That would be no load, and it will fail. I've seen this more than once(after rebuilding the alternator with a new regulator), not my truck. The same issue occurs when an old dead battery has an open cell, and the truck gets jumped.

It is more expensive to learn by your own experience, rather than learn from a group of other people trying to help you.

You can spend your money wisely, or not.

There is a good reason why the 5 tons do not have electric winches, they do not have the charging system to support them.

 

[VPed]

Detour but I think they still fly Phantoms as target drones out here on McGregor and/or White Sands missile range. I saw one get blown out of the sky some 12 - 15 years ago out at McGregor. O.K. I have to stop as I seem to be overcome with allergies all of a sudden.

Back to topic...please note how many years of experience and/or vehicles some of these guys have that are telling you it does happen. There is a very good reason they use the terms like "letting the smoke out" often.