overcharging batteries

[capercanuck]

I posted this question over in engines section but no one seemed to want to tackle it.<br />I just bought a used 1986 Sunray with a V8 motor. The batteries are overcharging. I changed the alternator which only changed the voltage by .9v. The voltage at the batteries was 16.9v before alternator change and 16v after. My buddy says he believes the problem is in the ignition circuit, but he can't look at it for a couple of weeks. He owns an auto electric shop. I'm an electrician but I haven't got a clue as to where to start looking. There is a rubber plug on the back of my alternator that has two wires in it, a purple one and a red/purple one. When I disconnect the plug and read the resistence across each, one appears to have the characteristics of a diode, the other one a dead short. I d'loaded a manual from the internet and the wiring diagram shows what appears to be a diode in each of these wires. It isn't very clear in the diagram, so I'm only assuming. Does anyone have any ideas? Oh yeah, it's a delco alternator, just out of the box.

 

[chiefmike58]

Re: overcharging batteries

capercanuck, it may be possible that you have a loose or bad electrical connection somewhere in line, such as a bad battery connector or dirty connection, forcing alternator to keep working.

 

[capercanuck]

Re: overcharging batteries

I cleaned the posts on both batteries. They appeared ok. One battery is practicaly new, the other is a couple years old. I have a battery switch and tried both batteries independantly charging. I still get 15v. Even if one battery is bad would I still get overcharging on the other? I can't see how, but I've been wrong before. I'm kind of focusing on the apparent burnt out diode in that female plug. If there is a diode there. I seem to remember something about zener diodes in charging systems but I can't remember their function. I wish I could remember some DC theory. Anyway, all the information I can get is appreciated!

 

[petryshyn]

Re: overcharging batteries

if you can post the diagram, or the address to it, I can tell you for sure, but I believe its the sense line that is not being satisfied.....

 

[capercanuck]

Re: overcharging batteries

I just had my overcharging problem fixed, I think. I had an auto/marine electrician down to the dock and he found the battery isolator was affecting the alternator and the voltage it was seeing. The alternator, with the isolator installed, was seeing 10.5v. This was on either battery. When the isolator was removed we got a charging voltage of 14.5v. There is an inline diode on the rubber plug on the back of my alternator which apparently keeps the alternator from back feeding which inturn eliminates the ability for the engine to be shut off. I'm posting this to let others know what we found. Also, I'm wondering if anyone sees problems with disconnecting the isolator? I have a "1-2-both-off" switch and I was assured I would have no problems without the isolator, anyone have any comments on this? Thanks again!

 

[martyscher]

Re: overcharging batteries

In the automotive world, overcharged batteries are usually by a faulty voltage regulator.<br /><br />Is there a voltage regulator or similar device utilized in outboards with alternators?<br /><br />I have been too lazy to trace wires in my 2001 Johnson.<br /><br />Good luck with your repair.

 

[petryshyn]

Re: overcharging batteries

A battery switch will do you better than an isolator. Its more versatile.........but its only as effective as the operator, as its needs some intervention.