1981 75HP Chrysler Electrical issue

Gentlemen,

My motor (756h1g) has a battery drain somewhere and is making its own power some how. If i connect the + lead to the battery i get voltage readings on the rectifier's two DC + - terminals, off the unhooked - battery cable and on the bus bar on the engine from the +. How can this be? I only have one battery and it isn't even hooked up except the +. You can watch it charge up slowly to 8 volts in a couple minutes. Is the rectifier making it's own power some how reversing polarities and causing a charge? Things get worse from there while i am playing with the multi-meter and trying to read the manual for it I dropped the unhooked - Battery cable on to the positive it shot out sparks, at this point i decided to give up before i do any more damage. What do you all think is causing this? Also the sparks resulting from my dropping the unhooked neg. battery cable onto the positive, what damage could that have caused. Any help would be appreciated as i am stumped on how my motor is deifying the laws of quantum mechanics.

Re: 1981 75HP Chrysler Electrical issue

Damage from dropping your neg cable on the connected pos cable: If it was for a very short time and if you didn't melt any insulation in the wires, none.

RE voltage build up: Your Volt meter has an input impedence of 10 meg Ohms or higher. So a current of as low as 1 micro amp will can build a charge of 10 volts across, say, a capacitor in your CDI unit with the 10 megs of the meter as the only load. The slow build up over time is the kicker here.

I haven't personally measured this, but I would expect that just the current from galvanic reactions due to moisture on metals would be enough to generate this phenomenon.

If you suspect a parasitic drain somewhere, set your meter to current (start at 10A or the highest setting) and put the meter leads in SERIES with the positive batt cable. So, connect the neg battery cable and disconnect the postive cable, put the black meter lead on the positive batt terminal, red on the positive battery cable lug. With all boat systems turned off, what current do you measure?

Comments, anyone?


Good Luck!

Re: 1981 75HP Chrysler Electrical issue

First, I am assuming that the engine is not running when you take these measurements. If the black ground wire in the cable is connected somehow to your instruments and the boat system, then even with the battery ground cable disconnected, you will have grounding through the boat system--not enough to start the engine but enough to give a good spark if shorted as you did.

It's not defying physics laws, You just have not found out how the previous owner wired it.

Re: 1981 75HP Chrysler Electrical issue

Maniac: Well shorting the cable was quick, i was down there the second it happened, so hopefully all is good. I have a drain somewhere used the test light method it lit up pretty good. I will measure the current when i get home. It must be from the engine as i have a main shut off switch on the console that kills power to everything but the motor but who knows with the way this thing is wired. Back to the multi-meter manual to find out how to measure current. That is one thing neat about boats you always got to learn something new just to use the thing.

Frank: The engine is off, I have read enough to know disconnecting the battery is a big no no when the motor is running. I am not sure what you mean by grounding from the boat system, but understand about the wiring. Who ever wired this boat had a big roll of red wire and just went to town so trying to sort out any electrical issue is a great puzzle of undoing rat nests and hand tracing the wire to where ever it goes. the real kicker is they didn't even remove most of the old wire just left it there hanging and bypassed the fuse box. If i can not get the drain figured out i am ripping everything out and starting fresh with at least different colored wires for certain things. I saw a marine wiring code post on Iboats a while back i think i will use it. At least i will know what wire does what. Oh and don't worry i put in a new fuse block even before it ran in the driveway.

soooo, I do not have to worry about the small build up of charge, I just need to find the drain and leave the motor's CDI or what ever to do its thing. Awesome one last thing to do on that puppy.

I will let you know what the current is or what the energy thieving culprit is if i find it tonight.

Thank you guys!!!

Re: 1981 75HP Chrysler Electrical issue

All right,

After cleaning up the cables and making sure everything was tight i still have a current draw of 1.5 ma. Is this a normal draw for something on the motor or is something stealing power. Could this be caused by a dirty connector somewhere on the motor, a bad wire going to the ignition or somewhere else or by a bad ignition switch. It seems to me that is a very small draw but I am no expert. (Example: I had to buy a new multi-meter because i fried the last one hooking it up wrong. Good thing Harbor Freight has those things for like 5 bucks.) So is this something caused by corrosion or is this something that is wrong or screwed up. The good thing is when I turn on the main battery switch to power the boats lights, bilge pump, and eight track (pause for laughter) there is no additional draw so it must be something with the motor but the ignition is off. Any Help would be appreciated.

Re: 1981 75HP Chrysler Electrical issue

1.5 mA will take approximately (assuming a 75Ah battery)... 50,000 hours to drain your battery. Or about 2,000 days, almost 6 years... I wouldn't worry myself to sleep over it.

It's likely something simple and expected, like the reverse current in the rectifier diodes.

BTW, Harbor Freight has those meters on sale RIGHT NOW for $2.89... I usually buy 10 at that price, so I can stuff one everywhere, boat, trailer, motorhome, truck, kitchen, etc. If I fry one, what the heck, I've got more. And if a neighbor needs to borrow one, I can just say "Keep it!"... you should see the looks on their faces. Good neighbor points!

Re: 1981 75HP Chrysler Electrical issue

Thanks Maniac for your help. I thought that sounded like a small draw seeing how i had to keep dropping the meter down. 2000 days wow, most likely the boat will be in the junk yard or in some one elses garage at that point. I might need to stock up on Multi-meters seeing how their life span in my garage is only about a week so far.

Thanks again for your help and happy boating.