Can both battery's go dead if one Alt. is bad?

[w5ood]

I have an 1985 CUCV and one of my GEN lights was not going out when driving. I pulled the dash and cleaned all the lights and put a new connector on the back of one of the ALT. because the wires looked frayed. Soon as I started it the same light, I believe GEN1 was on but when I got out on the road the light went out and my battery meter showed in the top of the green for charging.

Then the after a short time the light came back on and the meter was registering on the low green almost yellow area. I had a major flood in my area and had to get a family out of their home before they were trapped. I went through about 2 feet of water and on the way back water must have gotten into the alt. and the lights both came on. The green machine got me home like it always does, but it would not start anymore.

I pulled both batteries and they are both really low but the store charged them tested them and they are good. One is brand new so I had an idea it was ok.

Apparently something was not charging. So being new to the 24v system I didnt know if one alt being bad can kill both batteries. I had read tons on the CUCV issues here on this site but still am unsure about this issue.

It appears that each alt. is charging a separate battery, but I still dont know how that relates to my question.

Any and all help will be appreciated.

 

[cucvrus]

You will not damage the CUCV with driving thru water. You need to get out a book or open up the manuals and start reading. It could be something minor or major. Very hard to say this is what is wrong. It is not a difficult charging system. But you need to be able to read and use a multi-meter to resolve these issues. Start reading and testing. Do both lights light with the key on and the engine NOT running? That is where I would start.No charging problems here. It must be something else. I repeatedly expose my M1009 to extreme mud and water with no issues. Charging like designed. Check everything and clean and double check. Good Luck.

 

[cpf240]

I would start with checking the various voltage readings relating to the charging system. There is, I believe, a thread in the helpful stickies thread that lists what to expect at the alternator plugs, etc. Other than that, you could pull them and have a rebuild shop test them for you.

As to your original question, since GEN 2 gets its ground reference from GEN 1. Also, once the front battery discharged enough, there may not be enough combined voltage between the two batteries to provide the 'excite' voltage needed to 'turn on' GEN 2. I would think that it would be possible for GEN 2 to not be able to function properly if GEN 1 was not working. I have not tested this, so cannot say for certain.

 

[porkysplace]

here is a good place to start;
[h=1]CUCV Helpful Threads[/h]

 

[gimpyrobb]

It is only a 24v system for starting.

You should look at it as two 12v systems in the same truck. One alt charges one battery.

 

[w5ood]

Ok so I have read and read and read and I think I have a decent grasp on the charging system of my CUCV. I have the GEN1 light on and from what I can tell that is my drivers side alt. that runs the front battery. So I ordered the rebuild kit from this sight and rebuilt my drivers side alt. and reinstalled it. But before I did that I checked all the wiring as recommended. So I was getting 12v at the back of the alt. as I should based on when the key is on or off. Since that led me to believe the wiring is correct I pulled the alt. and took it to be tested. When they tested it they got nothing. So I rebuilt it.

Now I reinstalled it and it started up but that dang gen1 light still wont go off. I tested the back battery and was getting 14.4v running, and only 12.4v on the front battery. So I tested the back of the alt. that I rebuilt and I was only getting 12.5v but it would bounce all over from 12v down to 5v and back up to 10v. It was all over the place.

Any idea what would cause this? Can the alt. be bad in another way? Any advice would help. The site has really helped me learn a lot about the truck and it's a simple system with the right direction and manuals. But Im not an alt guy, so if this is a symptom someone has seen and knows the cause, I am all ears.

Thanks in advance!!

J

 

[cucvrus]

I will ask again. With the key in on and engine not running. Do both the Gen 1 and Gen 2 light illuminate? Has this been converted to 12 volts? If so I am out of ideas. But if it is still 24 volt. Both cluster lamps must lifght when the key is on and the engine not running. Do you have a volt meter in the dash. Does it stay in the green. I may have ask these questions before but I am trying to assist.

 

[w5ood]

Yes both of the Gen1 and Gen2 lights come on when I turn on the key plus the GP light and the alt lights stay on for a second when I start the truck. But Gen1 will not go off after it is running. I give the gas a tap but it still stays on. Yes it is 24v system, and I do have a meter on the dash. It used to work perfectly, then one day gen1 light stayed on and the meter went from high in the green zone on the dash volt meter to just at the top of the yellow, bottom of the green. I am headed to the parts shop and going to have them run a test on this rebuilt Alt. and see what it shows them. Who knows maybe I got a bad diode or something in the new parts. It wouldnt be the first time I installed new parts, that were already bad, on a vehicle. I was just curios if the bouncing voltage was indicative of a common problem or something i missed.

Ill let you know what the shop says about the alt. I really feel like something is still wrong with it.

Thanks,

J

 

[cpf240]

Perhaps one of the new components is bad? Or maybe an issue with the armature?

 

[w5ood]

Well the rebuild failed at the parts store, it shows that its putting out less that 12v. I brought it home and pulled it apart again and it looks like maybe some bearing grease got on the brushes. I am not sure what effect that would have on it but I don't think it could be good. I cleaned them off with a cloth and just a dab of electronics cleaner on my finger.

I checked continuity in the stator and it was good, I also checked continuity on the rotor and slip rings per the TM, and it all passed. I am going to reinstall it tomorrow after cleaning the brushes and see if it fixed the problem. If it did not then I have the guts to rebuild one more time, except the rectifier, and ill try all new parts again, maybe one of the new parts I used was bad. Everything else seems to be ok, I was almost hoping the stator was bad so I would at least have an answer.

Oh well back to the bench for more work. Thanks again for all the help and tips.

 

[tequilaiam]

Sounds like you got it narrowed down. If you see voltage bouncing, especially up toward the high end, it could be a bad battery connection or ground. I found a rusty battery tray by observing occasional voltage spikes that were blowing fuses even though everything seemed fine when in the garage. That brief loss of good contact caused regulator to spike the alt. output or something.

It doesn't sound like that's what's happening to you but it's something else to consider once you get your re-rebuild put in.

 

[w5ood]

Well I am done with this things. I have tested everything I can except the new components and it all seems fine, at least with continuity test. I rebuilt it a second time with all new parts except the rectifier bridge, I have two new ones but a screw broke off in one so I only had one to test. All other parts are new, and the shop is getting about 11.6v output on their test and I get about 12.5v with my multi-meter on the truck. I guess I am going to purchase a new one from Napa and throw it in there and not worry about the isolated ground, since its the driver side. I might try and convert it later if I am feeling the need. I just hate things not being how they are supposed to be.

 

[w5ood]

I just wanted to post a follow up. Rebuilding the old Alt. just didnt work. My guess is I either got a bad new rectifier bridge or something is wrong with the stator or rotor. I broke down and bought a new one and it works perfectly. One thing I noticed is the Gen 1 light was always dim. Even when it was running it was dim, with the new Alt. both Gen lights are super bright just turning on the key and both lights go off as they should once its running.

Maybe that dim light means something to you guys, I dont know. But if you are a newb like me and are just learning, the dimly lit gen lights are not a good sign. I have not taken the leap into modifying this new alt so it has an isolated ground. If I go down that road I will let yall know how it worked out. Thanks for all the advice.