M1010 DUVAC Removal Plan "B"

[markx250]

It should go to the rear battery negative (as shown in the photo) or the front battery positive, which are connected. I think he went with the rear battery negative since it is closer and easier to route to.

My alternator should be here tomorrow and I will be doing the same thing on my 1028 this weekend.

 

[still standing still cyco]

Yes, run it to the front battery positive. I'm guessing that hooking to the rear would have bad results.

 

[azdiesel]

It should go to the rear battery negative (as shown in the photo) or the front battery positive, which are connected. I think he went with the rear battery negative since it is closer and easier to route to.

My alternator should be here tomorrow and I will be doing the same thing on my 1028 this weekend.

Thanks. That's what I was looking for. Makes perfect sense.

Yes, run it to the front battery positive. I'm guessing that hooking to the rear would have bad results.

Yes. I just realized I mistakenly said rear battery positive. That would be bad since there is 24V there. I need to go to the front positive, or the rear negative. Thanks, And Ill keep ya posted how it goes.

 

[still standing still cyco]

Mark, I originally tried the rear Neg terminal, and the wire heated up quite a bit. When I switched it to the front battery Pos it stayed cool. I'm not sure but it may have contributed to my battery frying (not sure, I've been through multiple batts on this, until fixing the system with this mod).

 

[azdiesel]

Got the new alternator mounted and the alternator wires removed and taped off. Then it got dark. After work I plan to finish it with the duvac removal. Seems pretty straightforward but I have one more question I am unclear on..... Where is the 12V Buss? And the orange wire...does it need removed or taped off?

There is also a wire(mine was orange) going to the 12v buss that needs to be removed and taped. Now I have a reliable, servicable 12v supply to the 12v system. The alternator is a standard over the road heavy truck unit and according to Prestolite is "A" or high availability making service or parts easy. I still have the 24v alternator in the bottom location so the electrical system has not changed making all the original items still operable, AC, slave port, rear heater, etc.
View attachment 403141View attachment 403142View attachment 403143View attachment 403144

 

[GRmilitia88]

I did this mod recently and it works great. Here is a pic before the mod, I circled the 12V Bus in red.
The Orange wire should be removed and taped

.

I'll take some pics tonight if I get back home with sunlight left

 

[markx250]

Just to the left of the glow plug relay on the firewall. If you got to the stickies for the GP Resistor Bypass there is a nice closeup on Thread #4.

Mine has a small red wire following along with the orange and also ending up at the 12V bolts. But instead of being connected to the Duvac, it terminates in a plug.

 

[azdiesel]

Just to the left of the glow plug relay on the firewall. If you got to the stickies for the GP Resistor Bypass there is a nice closeup on Thread #4.

Mine has a small red wire following along with the orange and also ending up at the 12V bolts. But instead of being connected to the Duvac, it terminates in a plug.

Ok. Got the "plan B" swap completed. Thanks for all the clarifications. So far it seems like its working properly. Running the rear battery is charging 25-26 volts. The front is charging at 13 volts . But I'm worried I may have damaged a battery because the rear battery is at 13.5volts when engine is off. I will keep you informed. I had to go out if town for a week and won't be able to play with it. I also have many detailed photos to post that should be helpful. Anyway, big thanks to everyone that helped me.

 

[TechnoWeenie]

Just an FYI, the alternator I got was not a direct fit. I did have to grind down the alternator bracket a fraction of an inch so it would go down far enough to allow the belt around the pulley.

The factory 24V are almost completely round, whereas the replacement had some square corners on it...

 

[jamesgrizzlyadams]

I'm new here and new to automotive electronics in general, so bear with me. I've recently acquired an M1010 and am having charging issues: after reading through this thread multiple times, I would like to implement the "PLAN B" solution as it seems to be the best option. I also like the idea of doing away with the DUVAC.

My main question/concern is, eventually I would like to have a separate 12V battery in the back for all of my auxiliary items in the camper (on-board air, fridge, water pump etc). Would it be wise to connect this aux battery with a 200A surepower separator solenoid to the front 12V battery under the hood? Or is this a case where a battery equalizer/converter would make more sense, to feed the aux battery or batteries in the back. (to prevent worsening the imbalance between the two batteries under the hood)

this was the first trip with the new alternator set up. everything worked great. charged both batteries and had good 12 volt supply for my camper items.

SandM1010: Are you powering your 12V camper items from the front battery under the hood?


m38inmaine: from a fellow retired combat engineer (Canadian), thanks for the simple solution.

 

[319]

Recently, I acquired an M1010 with intermittent charging issues. I went through and cleaned all of the charging system connections, then reading about all the issues with the stock DUCAV system (and wanting a reliable charging system), I decided to start with m38inmaine's "Plan B", removed the DUVAC and associated wiring, then replaced the top alternator with a 12 volt unit. Afterwards, I discovered the bottom 28 volt alternator wasn't charging at all, and neither was the 28 volt alternator I removed from the top. So rather than taking a chance on rebuilding the 28 volt alts, I went and did the ChevyC60 modification (post #11). Using identical 12 volt isolated ground alternators, I wired one (top alt) to the front battery, and the other (bottom alt) wired to the rear battery. So, now I get 14.21 at the front battery and 14.17 at the rear battery.
Voltmeter is back in the green and all is well.
Next step is to replace the battery terminals.
This Harbor Freight hydraulic crimper does a superb job as well!

 

[Recovry4x4]

Awesome news. Glad to see another system upnand running.

 

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I have a question about the plan B mod. Say you do something stupid like leave the headlights on and deplete the front battery. If you jump the truck and start it, you now have 2 alternators pumping out as much as 260 amps (160 from 12V plus 100 from 24V) trying to get the voltage up to 14.5 on that flat battery. That's a lot of amps. Most batteries don't like to receive more than 10% of their amperage capacity, which for a typical type 31 would be much closer to 12 amps than to 260.

I understand that if the battery stays charged, the voltage will stay high and the alternator will put out an appropriate number of amps. I further understand the advantage of having plenty of amps available for 12VDC items in the vehicle.

How do you keep this mod from cooking a flat front battery with too many amps?

 

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How do you keep this mod from cooking a flat front battery with too many amps?

I got the answer from an engineer at a major US battery manufacturer. Here is my not-brief-enough summary, for those who might have the same question I had. For the experts out there, if I misunderstood something and there is an error in this post, please let me know and I'll fix it.

Assuming it's calibrated for charging lead/acid batteries, when a 12v alternator is running, it wants its output voltage to be around 14.5v. If the voltage is lower, the alternator pumps out as many amps as necessary to raise the voltage to 14.5v. If the load exceed's the alternator's capacity, the voltage will drop.

Battery capacity is tricky to measure. It depends on temperature and the rate at which you draw current. Cold Cranking Amps is one common measure, but there are others. Within limits, the more slowly you draw from an automotive battery, the more total amps you can extract. The warmer the battery, the more amps you can extract. C/20 is the Current, in amps, that the battery can provide continuously for 20 hours before depletion, at 77 degrees F. C/100 will be a bigger number, and C/10 will be smaller.

When you charge a depleted battery, there is a limit to the amount of current (amps) it can absorb. That limit is often about 10-20% of the battery's C/20. If the alternator exceeds the battery's max absorption rate and sends more amps than the battery can absorb, the voltage rises. Once the voltage hits 14.5v, the alternator stops trying to send more current. As the battery recharges, its absorption rate falls, and the number of amps required to hit 14.5v also falls, so the alternator puts out fewer and fewer amps as the battery charges.

If the battery is depleted and the alternator is small, the alternator may not be able to put out enough amps to raise the voltage to 14.5v. Then the alternator will crank out as many amps as it can, until the battery becomes charged enough that the voltage rises to 14.5v. At that point, the alternator will reduce the current it produces in order to maintain 14.5v.

For my M1010, soon to have the plan B mod, the new top alternator will put out up to 200 amps at 12V. When fully depleted, the new battery can absorb 30 amps. This leaves 170 amps of alternator output available for other 12V loads, like headlights etc. The alternator can't tell where its amps are going. It just puts out enough amps to maintain 14.5v.

The only time a battery gets damaged by charging is if the voltage gets too high. As long as the voltage regulator keeps the max voltage at around 14.5v, the battery will be happy. (14.5 is the magic number for lead/acid batteries. Charging voltages are different for AGM and Gel batteries.)

When the DUVAC fried front batteries, it was trying to regulate a 24v alternator to produce 14.5v, but that alternator's designed minimum output is 18v. No wonder the front batteries got fried.

So a properly adjusted high-output alternator should not damage a battery by overcharging, as long as that alternator's voltage regulator keeps the voltage below that battery's max.

With this understanding, my M1010 is getting a new Bosch 200 amp 12v alternator. This was the least expensive quality alternator readily available that would fit. It's also getting new commercial grade batteries. The DUVAC is not connected anymore.

My thanks to those who pioneered and recommended this approach. It's much more economical than a battery equalizer, and uses readily available parts that any mechanic knows well.

Correction: The readily-available Bosch alternator does not fit, in spite of all the alternator guy's assurances. So it goes back and we ordered the not-so-readily-available Neece alternator recommended by the OP.

 

[Recovry4x4]

I didn't know the exact details as you had laid them out but I do know that my truck has never faltered after 2 years on the road with it.

 

[319]

Although it's only been a few months, mine is working just fine as well.

 

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I understand that this mod has been working for folks. I'm enough of an engineering geek that I wanted to understand *why*. I may be wrong, but I think I now understand why the DUVAC killed batteries and alternators, why the Plan B Mod works so well, and why it doesn't cause problems. I tried to express that understanding in my write-up above. The Plan B Mod solves my problems without causing any new ones that I can think of.

This is my happy dance. Like it?

 

[richingalveston]

You have one large misunderstanding of the alternator and electricity. The alternator is not pushing the electricity. It responds to what is demanded of it. It only puts out the load demanded on it.

As you put more load on the alternator it will load the engine more. When the demand on the alternator is less, there is less load on the engine that is turning the alternator.

The battery recharge rate is just additional load. The battery will only draw what it needs. The only way the alternator can fry the battery is to much voltage by a bad voltage regulator. You cannot push the amperage to the battery. The battery draws it from the alternator.

Electricity is similar to the plumbing of water with one exception. The device at the end is sucking the water to it and not a pump pushing the water to it.
The pipe size and pressure determine how much it can put out. Where electricity is concerned the wire size and length will determine how much electricity can get to the device, If the device requires more, the wire will be sacrificed.

Hope this make sense. If you like learning experiences take some time to study water wheels and power generation. You add additional electrical load via heater load banks to control the rpm of the wheel when the water flow has not changed but the electrical demand has. This is done to control Hertz.

 

[captw]

are two or three batteries being using in this application?...I assume that three are being used, one charged by the 12v alternator separately and two others connected in series being charged by the 24v alternator. Correct??

 

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are two or three batteries being using in this application?...I assume that three are being used, one charged by the 12v alternator separately and two others connected in series being charged by the 24v alternator. Correct??

No. The CUCV power system has 2 batteries wired in series for 24V, plus it draws 12V from between those 2 batteries. So it has both 12 and 24V. When you open the hood, the battery nearer the front is connected to ground and the other battery, so the battery further back has 24v between it's positive terminal and chassis ground. The front battery has 12v between its positive terminal and ground.

The stock M1010 has 2 100-amp 24v alternators. The bottom alternator charges the 24v battery bank and provides 24v power to the truck. The top alternator charges just the front 12v battery and provides 12v power to the truck. The DUVAC is a voltage regulator that tries to make the top alternator provide 12v, but this works poorly.

For me, the top alternator died. A replacement is $1800, rebuild parts are $650, or a new 12v Bosch alternator was $200. So I chose the Plan B Mod and the Bosch alternator. But before I could make an informed choice, I needed to understand whether this could potentially fry my front battery, as some warned could happen. Now I understand that they were wrong. Once I understood it, I wrote it up for the next newbie who tries to understand it.

This "Plan B Mod" simply replaces the top alternator and DUVAC with a 12v alternator. The rest of the system remains the same. 2 batteries wired in series, with 12v between the first battery's positive terminal and chassis ground, and 24v from the second.

The TM wiring diagrams document the stock system, and others on the forum understand this far better than I. Search the forum and you'll find lots of discussion on this topic. Reading the TMs is also important.

Some folks keep both 24v alternators and replace the DUVAC with a battery equalizer. This approach is more expensive, and those alternators provide 200 amps of 24v power, from which you can draw 100 amps of 12v from the equalizer, plus more from the battery. My 1010 alternators will provide 100 amps of 24v plus 200 amps of 12v. Depending on your power needs, one or the other of these approaches might be better for you. If either one will work, the Plan B Mod costs much less, and uses parts all mechanics work with every day.

Correction: The readily-available Bosch alternator does not fit, in spite of all the alternator guy's assurances. So it goes back and we ordered the not-so-readily-available Neece alternator recommended by the OP.