M931A1 w/ Cummins NHC-250 won't start

The short story: It has sat for 13 months after a trip from Georgia to Texas. Batteries were dead. I disconnected them and connected them up into a 12v parallel string and put a regular car charger on them. I charged them for 14 hr., but it was like they were half dead and won't turn the engine over.

Question1: Is there something you can think that I might be missing like not charged lomg enough?

Question2: How do you guys charge 4 12v batteries in 24v array if you don't have a 24 volt source?

Question3: Any sources on 24v chargers?

Arlyn (by the way, Merry Christmas)

You can charge them one by one with your 12v charger !! Or if your batteries don not come back you can get some group 31 batteries !! You will need all 4 batteries to turn over the big NHC 250 in the cold it is a cold blood beast !!! Check all of the connections are clean and tight !! Good Luck !! Merry Christmas

yes that is not enought to charge all of the batteries if they were down that far. disconect and charge them one at a time

charge them up to at least 12.6 and then load test them. If you are close to a O'reillys, they will charge and test them for you for free.

Do not try to start truck with dead or weak batteries as there is a good chance you will blow the voltage regulator in the Alternator. Ask me how I know

Also 4 batts are better than two in cold weather but will crank with either system.Started at 19 this morning. no problem she fired right up.So post # 2 is not entirely correct they will start.

What kind of batteries? If they are hawkers they need a long deep 20 amp charge each. If they are 6tmf batteries you need to check the fluid levels and then trickle charge them over 2 days. How old are the batteries?

Charge one at a time with your 12v charger. No need to disconnect anything.

Does that work? Charging 1 at a time at 12v while wired to make 24v?

If it didn't, would I have posted it?

Individual charging the batteries is the best choice.

There is no need to disconnect anything while charging them(individually).

I just never thought of that, I've always disconnected everything thinking I'd short out the cells. I just learned something new.

Suprman said:

What kind of batteries? If they are hawkers they need a long deep 20 amp charge each. If they are 6tmf batteries you need to check the fluid levels and then trickle charge them over 2 days. How old are the batteries?

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They are 6TMF and they look like they were new when I picked up the truck in Nov., 2012.

juanprado said:

... If you are close to a O'reillys, they will charge and test them for you for free. …

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Yeah, uh huh, I’m in Backwater, TX.

The truck was a “Vehicle does not run”. The GL guy jumped it with an M923A2 and it not only cranked, it started right off (weather was 70). Batteries started it fine over a 3 day trip, including one breakdown (water pump belt). We parked it at my daughter’s place because we were out of time and had a blown tire on the outside duel. We planned to return within 3 months, but like the last time I won a truck at GL, I got laid off. Thirteen months later I’m trying to figure out how to deal with dead batteries and no GL guy or M923A2.

I went to Walmart to get an additional charger but it is Christmas. I am charging all of them in parallel. I did that by disconnecting one end of each of the middle plus-to-minus connectors and connecting them up with wires w/alligator clips. Tomorrow! I think I will not try to start it tomorrow, but let it charge more. I’ve already charged it for 14 hr. and drained them trying once.

I'm supposed to be rolling on Sunday.

dezert ratt said:

I just never thought of that, I've always disconnected everything thinking I'd short out the cells. I just learned something new.

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At least you cleaned up your connectors on a regular basis.

Anybody near Dublin, TX that could role by with a 24v system and a jumper cable?

Arlyn

Divide the battery pairs and independently charge them on 20 amp charge for 24 hours each. They may or may not come back. There are a bunch of guys who bought 2 really big replacement batteries at their local auto parts store at a reasonable price, each one was almost the size of 2 mil batteries.

Suprman said:

Divide the battery pairs and independently charge them on 20 amp charge for 24 hours each. They may or may not come back. There are a bunch of guys who bought 2 really big replacement batteries at their local auto parts store at a reasonable price, each one was almost the size of 2 mil batteries.

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Yeah 8d size.

dezert ratt said:

I just never thought of that, I've always disconnected everything thinking I'd short out the cells. I just learned something new.

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Me too. Thanks...that's good to know.

Suprman said:

Divide the battery pairs and independently charge them on 20 amp charge for 24 hours each. They may or may not come back...

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I took off one end of each of the short straps that connects them into 24v pairs. That leaves the neg on 2 bats connected to the neg rail and the pos on the other two connected to the pos rail. Then I took some short cables I built w/alligator clips and connected the open neg posts (or cable) to the neg rail and the pos posts (or cable) to the positive rail. NOW, everything is in a 12v parallel mode.

The old battery charger I have used for years on cars was charging at 4 amps and 13.8 volts. A brand new Stanley BC4009 40 amp charger runs the same setup at 7 amps and 15.0 volts. It has been on the old system for 26 hr. I will leave the new system on for 16 more hours and try it again. If it doesn’t work that truck is going to show up on the classified ads.

It occurs to me that if this happens way off-road I’m in it deep. I am trying to figure out how difficult it would be to convert EVERYTHING over to 12v. Anybody have a thought?

I apologize for not searching for voltage conversions. When I’m not pooped out, I’ll look. I’ll also look through the TMs for diagrams. Since the Cummins NHC-250 was used in the civilian world, there must be parts, except for the electronic logic and maybe the transmission controls.

Arlyn

The last thing you want to do is convert everything to 12V.

You can put 4 new NAPA commercial batteries in it or two of the big 8D batteries but leave it 24V.

If you can't get the current batteries to hold a charge then replace. When the batteries or charged or replaced start the truck and check the voltage across the battery bank. It should be around 25.2V fully charged and just over 28V with the truck running. If you only have 25 with the truck running the alternator is bad. If it is a little low you may just need to adjust the alternator.

I think 13 months is way too long to leave one of these trucks unattended to and expect it to fire right up. If you put 4 brand new batteries in it today and let it sit till next February in the cold it will be as dead as your is.

Try some either, It will save you from draining your batteries

IT LIVES !!

The thing I like about this web site is the good advice. I believe ALL of you are right, at least in context.

doghead said:

Charge one at a time with your 12v charger. No need to disconnect anything.

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Speaking as an engineer, doghead is absolutely right, as long as everything is turned off. If you have the time, a day per battery, do it, but on some schedule clean all your battery connections. This is good advice for your Volks Wagen, too.

My reason for thinking about switching to 12v is because I had several opportunities to jump to a 12v including a Kenworth. I also was offered a boost starter, 12v of course. In civilization, that is well and good; I bought a 40 amp Stanley charger, 12v of course, and I can deal with it by taking only 2 battery connectors off. But what am I going to do if I’m clear up at Holy Terror Reservoir, which is a 10 mile walk to a tow-truck-passable road? I’m 66 with bad hips and that would kill me.

I think if I’m really worried about that, I will come up with extra batteries. Has anyone out there had a back-woods incident with dead batteries?

I am trying to put together a rule-of-thumb about batteries and charging times. It looks like on these big military batteries it takes somewhere between 75 and 100 amp-hours to charge one from dead to topped off. That means 6 amps per battery for 12 to 15 hours or 10 amps per battery for 8 to 10 hours. With my 40 amp charger, that is 8 to 10 hours with the whole bunch wired in parallel. The charger I used hadn’t finished after 8 hours when I unhooked it and started the truck this morning. It cranked for a good 30 seconds before it caught and started and it was still going strong.

Leaving a truck with good batteries unattended for 13 months is bad. I didn’t intend to leave it more than 2 months, but my project got canceled and I was the last contractor in. There was nobody here in Texas I trusted to mess with the truck and we kept saying “this month we’ll go down there.”

Last word and I will go away; my truck came from GL with Michelin 11.00 R20 XL tires on the ground, radials, and an NDT, biased ply, in the spare rack. I am guessing that the truck was upgraded from NDTs all around but they didn’t change out the spare. I will be traveling with one tire and wheel missing on the right side of the intermediate axle because you can’t mix a radial with a biased ply; both tires will be damaged, according to a tire guy I trust. We will starting out as Sunday from Dublin, TX to Denver, CO, pulling an M101A2 trailer and expect to take 3 days. I’m happy with the way the truck runs and I don’t expect problems. It did well 13 months ago from Ft. Benning, GA and this is just the last leg.

Happy New Year !!!!

Arlyn

You can use a pair of 12v jump packs to jump start the truck. It works really well with the 8.3 and with the 250 it works sometimes depending on the size of the jump packs and how dead your batteries are. It's not really advisable to do with stone dead batteries though you have a good chance of killing your alternator. Bosch makes a nice charger/maintainer that does 24 volts. I put a slave plug on a cable to the charger it does the agm batteries too.