M35A2 Charging system questions

[DavidWymore]

Just put a used alt off a 900 series truck on my deuce. I've searched for keywords and skim read through the Alternator TM 9-2920-225-34 twice, as well as searched the forum I can't find the exact procedure for on-the-truck voltage adjustment. Closest I could find was on the testing machine, they adjusted the load to 60a and volts should read "about" 28.

I tested at idle at the alternator with no lights or accessories on exc fuel pump. I was getting 28.5v and read on Erik's that it should be 27.6v (13.8x2), so I turned it down to 27.1 to be on the safe side.

My pot is backwards...I turned it counterclockwise or out initially and got 30+v.

Should I test with load...? Test at batts too...? Anything else?

Thanks

 

[DavidWymore]

Aha! It figures that as soon as I give up searching and post a question, I find the answer.

http://www.steelsoldiers.com/showthread.php?20172-Alternator-Problems-on-5-Ton

 

[gimpyrobb]

Just so it has been stated, typical charging in a 12v system is 14.4, so you should adjust a 24v system to 28.8. Your alt needs to put out a higher voltage then nominal for the batterys to charge.

 

[DavidWymore]

I *think* 12v alts usually charge up to 14.4, and batts take up to 13.8...so yeah makes sense. Here's the pic from the 5 ton link I posted above. I'm going to bump mine up and do some more tests. (At batts, etc.) I wonder if putting out more voltage makes the alternator produce more heat and might slightly shorten it's life.

 

[daytonatrbo]

Just so it has been stated, typical charging in a 12v system is 14.4, so you should adjust a 24v system to 28.8. Your alt needs to put out a higher voltage then nominal for the batterys to charge.

28.8 is as high as you would want to go. Even that is slightly over charging per prestolite.

 

[DavidWymore]

Read that 12v batts get unhappy and hot and start gassing and losing live at about 14.6

 

[patracy]

I keep things at 28V on the dot. I had set mine to 29v at one time. Ended up flubbing it a hair putting it back together and actually went to 30v. Boiled out a set of batteries....

 

[74M35A2]

All correct. A 100% fully charged healthy 12v flooded lead acid battery will display 12.8v OCV (open circuit voltage). This is after any surface charge has been removed. Surface charge is an superficial voltage above 12.8 that is really not of use, turn headlamps on for 60 seconds to remove this before measuring if you just recharged the batteries. Any voltage above 12.8v is charging, and, the higher it is the more forceful the recharge. Battery recharge voltage is typically between 13.5v and 14.4v, depending upon ambient temperature. In colder weather, the battery will not out-gas as easily due to colder electrolyte temp vs the summer. Most automotive vehicles accommodate for this with a battery temp sensor in the bottom of the tray, or just internally with a temp sensor in the alternator, or ambient air temp sensor input to the ECU, and adjust the target system voltage via a simple look up table of temp vs voltage. Considering most under hood temps of automobiles can reach 200F at a summer stop light with the A/C on, and considering our batteries run much cooler than this because they are not under hood, I set mine at 14.4V x 2 = 28.8v. Just double all of above as GR said. Each battery cell generates 2v, so linking two batteries in series is just like having one in a single case anyway since all the plate cells are in series regardless, just more of them.

 

[rustystud]

All correct. A 100% fully charged healthy 12v flooded lead acid battery will display 12.8v OCV (open circuit voltage). This is after any surface charge has been removed. Surface charge is an superficial voltage above 12.8 that is really not of use, turn headlamps on for 60 seconds to remove this before measuring if you just recharged the batteries. Any voltage above 12.8v is charging, and, the higher it is the more forceful the recharge. Battery recharge voltage is typically between 13.5v and 14.4v, depending upon ambient temperature. In colder weather, the battery will not out-gas as easily due to colder electrolyte temp vs the summer. Most automotive vehicles accommodate for this with a battery temp sensor in the bottom of the tray, or just internally with a temp sensor in the alternator, or ambient air temp sensor input to the ECU, and adjust the target system voltage via a simple look up table of temp vs voltage. Considering most under hood temps of automobiles can reach 200F at a summer stop light with the A/C on, and considering our batteries run much cooler than this because they are not under hood, I set mine at 14.4V x 2 = 28.8v. Just double all of above as GR said. Each battery cell generates 2v, so linking two batteries in series is just like having one in a single case anyway since all the plate cells are in series regardless, just more of them.

I've found and so did the transit agency that normal batteries (not Odyssey's) don't like being charged higher then 28 volts. They loose too much water due to outgassing . In a perfect world I'm sure the 28.8 volts works fine but as we all know this is not a perfect world. Better to run on the side of caution and save your batteries.

 

[DavidWymore]

I got tired of fooling with it and left it at 28.4

 

[rustystud]

I got tired of fooling with it and left it at 28.4

Just keep an eye on your fluid level in those batteries, and remember to only use "distilled" water to fill them with.

 

[18operator]

I had the problem not too long ago with the alternator overcharging. I would start the engine and set it at just under 1000 rpms, then a minute or two later I get a terrible squeal from the alternator belts. Did a voltmeter check with the squeal at the battery and had 35 volts.
I did some thread searching and found that first I should check the connections from the alternator all the way to the batteries.
That included all the grounds running from the engine to the frame. I cleaned all the connections I could get to and found one ground wire had come loose from the frame. Reattached to the frame.
With all connections tight, I started it up. No squealing belts and putting out 28.2 volts at the batteries.

 

[18operator]

Now if that doesn't fix the problem, then I'm probably looking at a bad voltage regulator. Hopefully It'll be easy to change?

The other thing is, I couldn't get the plug out to adjust the regulator pot. Not that it needs adjusting. But I would like to have the ability to do so. Steel plug in an aluminum alternator case. I think it's seized. Any suggestions on how to remove the pot plug without damaging the alternator?

 

[DavidWymore]

Patience.

Heat slightly.

Soak it with Kroil, or acetone and trans fluid 50/50 mix for a few days.

Put an allen insert in it and tap it lightly for a good long while.

If you can get a 3/8" air or electric impact, turn the power way down and just let it tap away at it.

A few cycles of this for a couple days might get it loose.




Mine is dropping .1v from alt to batts. Probably should go through all my connections thoroughly.

 

[74M35A2]

0.1V drop is normal through cable. You're good. We tested a 160A alternator on a 12V system with factory wiring to have a full 1V drop when pushing the full 160A. This is the exact reason some alternators offer remote voltage sensing.