Just need confirmation that I'm making sense.

Okay I have a prestolite ALK6222 alternator with regulator. I kept noticing that my battery was dying after a day or so of sitting in the boat, and when I launched the boat the starter was sluggish to say the least, but would start sitting on the trailer. I metered the leads from the battery, found a slight short (boat is on trailer) I managed to track this short to the alternator, (on the 2000K ohm range I was getting 224-318, and was fluctuating all over the place), pulled the alternator, tested it again, no short no load at all on battery. Does that make sense that the alternator is fried? Should I get it rebuilt just to make sure?

Thanks
Jon

Re: Just need confirmation that I'm making sense.

To determine if you have a load on the battery while sitting, you need an milliamp meter. Yor ohm meter probably has this function. Disconnect a battery cable and connect the meter between the battery and the cable. Do not attempt to start the engine when connected like this or you will probably waste your meter. This will read any load present in the system. You cannot use a clamp-on amp meter for this as they are meant to measure larger loads such as starter motor draw while cranking engine.

Re: Just need confirmation that I'm making sense.

I would start on the 10A range, rather than miliamps to prevent potentially blowing a fuse in your multimeter (if it has one- many don't and just die a smoky death over 2 amps or so)- meters with a 10A range usually require the + lead to be plugged into a separate 10A receptacle.

Then disconnect either battery cable and put the meter in series between the cable and the post.

If there is a significant draw, start pulling fuses one at a time and see which circuit makes it drop off.

Re: Just need confirmation that I'm making sense.

Okay well I have tested the Alternator (see pic) and there is a short between the two. I should have done an amp test but unfortunately I've already pulled it from the boat. My theory thus far is that the s/c is what is slowly draining the battery while sitting, and then once I put the boat in the water, the boat is now grounded so it's darning the battery even more. Current is going from positive to alternator out negative to block to water. Now does that make sense? and if so do you guys think it's the regulator or the alternator itself?

Re: Just need confirmation that I'm making sense.

I don't really understand that resistance test - did a manual or something tell you to test it that way? The excitation with the small current of the meter could make all kinds of weird readings and different from meter to meter....
380 ohms through the regulator and rectifier circuitry might very well be normal- I dunno enough about Prestolites- but a shop that does auto electric should be able to bench test the alternator - it could very well have 1 bad diode that's causing the draw.
Bottom line I guess is that you can't really test an alternator externally with an ohmmeter and make any real conclusions.
And the "BAT" on the screen of your meter probably means the internal battery in the meter is weak, which is critical to accurate readings on ohms scale -when you short the 2 leads together it should show 0 ohms

Re: Just need confirmation that I'm making sense.

jontoronto27 said:

Current is going from positive to alternator out negative to block to water. Now does that make sense?

Click to expand...

not really, no- the electrons only want to go back to the battery - they have no desire to flow into the lake

Re: Just need confirmation that I'm making sense.

With your ohm meter setting at the highest sensitivity of 2000K or 2 million ohms your reading is not 318 ohms it is 2 million times 318ohms or 63 million ohms which is nearly infinity. That isn't much of a short.

Re: Just need confirmation that I'm making sense.

I have seen a bad alternator run a battery dead. The best way I know of to check a short is to use a standard volt meter. Unhook the + cable on the battery. Hook the neg lead off the volt meter to the + cable and the + lead off the volt meter to the + post on the battery. If you have a short it will read close to battery voltage. Then as someone else suggested pull fuses until the voltage drops. The fuse that make the voltage drop it the circuit with the short. If none do unhook the alternator and see if the short goes away.

Re: Just need confirmation that I'm making sense.

sker........fyi............that 318 meter reading would equate to 318K ohms or 318,000 ohms..............

Re: Just need confirmation that I'm making sense.

Oh okay thanks guys. What I'll do is I'll have someone bench test the alternator, if they see it as being good, then I'll re-install it and do amp test with the battery hooked up. and see what's going on. That reading I was getting in that picture was the exact same reading I got when I just went + to - from the leads to the battery, and just by process of elimination that's what I ended up with. The battery will only last a couple days MAX in the boat even just sitting on the trailer. Darnit thought It had it I'll check it out and update. Thanks again.

Update

Update

Okay I took it to an alternator rebuilder and he says that what I was doing made no sense because the negative is the engine itself, and what I was metering was for the ammeter in the dashboard. He tested it. It was charging at 17 volts and failed the diode test. So he's going to look at it some more and give me a quote, he's pretty sure it's the regulator itself.

Thanks for all your help.