Dual batts/dual alts, but wheres the power?

[cabledawg]

I've installed dual batteries and dual alternators (one still needs the pulley replaced, but it works) but I have a question as to where the power for the truck is coming/going. The original lead from the original batt is on one alt(added #2 alt), and the 1ga cable is off that batt to the starter. The smaller red wire w/fusible link is on the other alt(original, so we'll call it #1), with a lead to the second batt. So I searched for wiring diagrams and found none, but I was able to get an idea that the my hot-all-the-time stuff is on #1 and switched power is on #2 as well as the cranking (no brainer cuz the 1ga cable is still attached to this batt). But where is the reading for the stock voltmeter taken? I'm adding a second meter, but dont know which alt/batt it needs to be hooked to.

 

[Fordum]

Ok, I have read and reread your post, and I'm still not sure what is what.
BUT, if I understand what you are saying, and I may very well not, you need to not drive that truck right now!

First, get a voltmeter, start the truck, and measure the voltage across each battery. You should have 13.5 to 14.5 volts. I am afraid that you are going to find you have 18 volts plus across one of them.

It sounds like you have the output of one alternator on one battery and the voltage sense line on the other. Which means that the alternator has no way to determine how much voltage it is putting out. Which will fry both the battery, any electronics hooked to it, and eventually pop the diodes in the alternator.

You need to figure out exactly what you want this system to do, and wire accordingly. It is VERY tricky running two alternators.
It is almost essential that they do not see each other's output. It is possible to run two in parallel, but its a real pain.
You are better off running one big one. If both circuits are completely separate, then you can get away with it, or if you isolate the two from each other with big honking diodes, that will work too.

Why the two alternators? Big electric winch, or underhood welder?
Usually one big one with one of the several types of isolators to let it charge both batteries without either one discharging into the other is the simpleist way to go.

 

[cabledawg]

I measured the voltage on each battery and each alt and found that one system has 14.2 volts and the other had 13.9 volts. The reason I have all this is due to the high amount of electronics and a somewhat large inverter, plus charging the batteries in the travel trailer when we on the road. I had all the parts, so why buy yet another alternater?

In order for both alternaters to work, I split the pigtail and ran two connectors, one to each alt. I know these need to be separated, which is why I'm trying to find out where the switched power comes from and where the constant power comes from. Right now it works, but one system is getting "mirrored" because of the other. Originally the one would have all the stock functions and one would have the inverter and trailer batteries. And I'll most likely move it back to that, but I still want to know where the split is in the power. My Haynes just shows what is hot and when, but not where the power is coming from.

 

[Dabba]

why not just copy a cucvs sytem? its a 24volt system though, with a 24v starter

 

[cabledawg]

I dont have one to copy from and I dont have a 24v starter. Would any diesel engine be setup with 24v starting? If so I might be able to find some around here.

I did isolate the two systems, but they are still using the same pigtail with two connectors. One is running as the stock setup, with all the normal vehicle wiring, the second has only the isolator running off of it. So as long as the main system is running right, the second should be fine.

I still want to completely seperate the two, so if anyone knows of an easy way (without buying a ton of stuff) to split these two, let me know. Otherwise I'll just keep it the way it is.

 

[cabledawg]

Ok I think I have this figured out. Hopefully my picture shows on here if not, I'll try to explain what I'm doing. The brown lead on the alt plug is the reference voltage through the voltmeter. So i will tap into the power on the second system and run it to a relay. That relay will be switched from the main system to prevent the voltmeter from being on all the time. From the relay to the voltmeter to the alternator. By doing this, both systems are 99.9% independant with the second system using the primary as the on switch for the charging cycle.

 

[BGKYK5]

I have nothing useful to add, but I'd like to see pics of how you mounted both alternators.

 

[cabledawg]

I still plan on getting pics, but I've been busy lately with other truck and work problems. I'll try to get some today if it doesnt rain

 

[cabledawg]

New wiring diagram, as I think I need a resistor inline for the alt to work properly.

 

[cabledawg]

I hate to necropost, but finally got pics of this setup for anyone interested. The setup has been working all year and works awesome as I've always got a battery to jump from and run all the additional electronics. Right now my 'lectric fans, the inverter and soon the headlights and windows will be running off the second battery. I'll be doing the same thing to the other Burb once I get moved and have some extra cash.

The first two are the primary alt in the smog pump location. The last is the second alt in the stock alt location.

 

[4X4HIGH]

I am very interested in what it took to place an alternator where a smog pump would have went. I'm wanting to do an onboard welder and that is the place i would like to mount the alternator. Did you have to fab anything or did you use factory parts to do the install?

 

[BGKYK5]

x2!

And what length belt did you use? The stock smog pump length?

 

[cabledawg]

I used the stock alternator for the 88 v-belt setup. CS130 with the mounting tabs about 180* instead of the 120* used in the serp setup. In the second pic, you can see the bracket that usually bolts to one side of the alt. This is the bracket on the pivot side of the alt. I flipped it around and made a small notch to clear the alt housing. The adjustment tab of the alt was bolted to the lower hole in the smog pump bracket. The modified alt bracket was then bolted to the pivot tab. A long bolt then runs through the top mounting hole, the other end of the modified bracket, then a spacer and into the block.

Doesnt look to sturdy but this had no wiggle before the belt was installed. I honestly expected the belt tension to twist the alt, but it didnt and has lasted several months and about 6-7k miles.

I cant remember what size belt was used, but I'll check tomorrow for the numbers. I went though a few before I found one that wasnt too tight or too loose. Not much grip on that primary alt, so once the belt starts to wear out, it'll start squealin.

The diagram in my last wiring post is what I ended up using, but with a 250 ohm resisitor on the brown wire to the alt. Dyeager gave me that info. I think a serp alt would work better, but I used what I had on hand.