Please help - Weak voltage

[Wakesurfection]

Hi All

I would be really grateful if anyone knows what is wrong with my voltage on my 2007 Tige RZ2. I've changed my alternator twice and they are both 70amp 12volt alternators. However, the voltage reading on my instruments says that it is only 12.3 volts coming out of the first alternator and 12.1 volts out of the 2nd alternator. Any suggestions on what is wrong?

The alternator wire ends up in this box. Anyone know what this box does and could this be the problem? IMG_9689.JPG

Really appreciate your help

[IDBoating]

Did you measure it without the alternator connected to anything? i.e. right at its output terminal with no cable(s) connected? If two alternators yield the same oddly low reading, it's likely something else in the electrical system. Could also be that you have a bad ground at the alternator. Where are you getting your ground reference?

[wired1236]

I had the same issue. I did check the voltage coming from my alternator and batteries, checked every connection I could find; both neg and pos. Never found the cause. Many of my connections are buried in other wires and the mess under the dash ad harness running through the boat. I finally broke down and ran a parallel pos wire from the battery fuse connection to the main connection under my dash then disconnected the old wire. My voltage now reads accurate. It had to be a connection somewhere in that main run. Never did find the fault.

[chpthril]

That box is a diode isolater thats part on the EIDB Dual Battery system. The alternator's charge goes to the center post. Each battery B+ is connected to the outer posts. It prevents the loads drawing on one battery, from drawing off the other. One battery is the main cranking and the other is house battery.

Ignore the reading on the gauge for now. Using a digital volt meter, measure the voltage at each battery B+ post, working your way to the alternator until you find the source of the low voltage. Do this with the engine speed above idle. Dont overlook a ground cable as a possible issue, is its just as important in the circuit as the B+.

Im pretty sure your original 5.7 MP alt was 90A.

More after I eat lunch

[IDBoating]

I interpreted "voltage reading on my instruments" to mean he is measuring with an actual meter (to me, "instruments" are actual tools and not just dash displays). If he's just looking at the dash gauge, then there may be nothing wrong at all. The isolater will have a voltage drop right off the bat, and transient protection components can add more drops along the way.

Follow ChpThril's advice, get a handheld digital meter (Harbor Freight has some for under $10), and see what THAT says. Report back!

[Wakesurfection]

Yup got the multimeter - good tip. I think it maybe because I used spacers to mount the alternator onto its bracket. The alternator was not the correct size so I used some spacers and washers to mount it properly.

I touched the positive probe to the stud which connects the red thick cable to the rear of the alternator and the negative probe to the screw that mounts the alternator via these spacers and it read 13.4V. I then kept the positive probe on the stud to red thick and then touched the negative probe to the alternator mounting bracket and the reading dropped into the millivolts.

I think the alternator is not grounding properly. I was thinking of screwing a black ground wire into the alternator. Which part of the alternator should I screw into? A, B or C or D?

Is it OK if I screw the other end of the black ground wire into the negative terminal of the battery or should I just screw it into the other side of the alternator mounting bracket? If I screw it into the negative terminal of the battery which battery should I screw into? Cranking battery or house battery? Is it 1 or 2 in the picture?

[chpthril]

I would get some steel spacers so you have the same metal to metal engine to alternator continuity that there was with the original. The alternator needs to ground through its housing, thats why the battery grounds go to the block. Anything short of a solid ground, and the alternator could short out. Make sure there is no paint between the spacers and brackets.

[IDBoating]

Hmm... I'm worried about electrolysis in a high current circuit with potentially dissimilar metals, if he doesn't match those washers carefully.

[chpthril]

Theres already an aluminum alternator housing bolted to steel brackets.

[Wakesurfection]

Hi chpthril - good advice but I'm having problems getting the steel spacers. Is it OK if I link a ground wire (black negative) wire from alternator to alternator mount block? If that is no good should I attach black negative ground wire to negative battery terminal? If that works, where should I connect the ground wire to on the back of the alternator - at A, B, C or D marked in the picture below

Alternator.jpg

If I attach ground wire to the negative battery terminal should it to be to the cranking battery or house battery? Which battery is it - 1 or 2 in the attached picture?

Battery.jpg

[chpthril]

Wake,

If those spacers are anything other than metal or a strong nylon, you likely going to have some unwanted vibration and movement. At a minimum, you could sling a belt or hew it up. At the worst, it could break a mounting ear off the alternator.

A, B and C are not usable for this application, they are holding internals in. Placing a cable behind one could allow it to work loose.

D looks like its a mounting bold. I think bolted a cable lug down under it, could also result in it working loose.

Unfortunately, I dont see a fix other than a proper metal spacer where needed, that does not alter the alternator's alignment. Or, finding the proper alternator.

[ericinmich]

Agree with the above, don't add an extra ground strap. If there is not a perfect 0 ohm connection (which there won't be after some corrosion), there can be some ground offset and a ground loop. This can do a lot of weird things, cause crank/cam sensors to shift and pick up noise extra pulses, knock sensors become flaky, etc. It can act like an antenna...

[IDBoating]

Absolute worst case, he could use a short woven braid (say, one inch width) with two lugs on one of the alternator mounting ears that would normally provide the ground. One lug goes right up against the block; the other right up against the alternator case; and whatever spacers are needed go between. Braid is a good grounding material because it has a high surface area to cross-sectional ratio which helps reduce RFI/EMI effects (we use it in ham radio for this reason). It also has low series resistance. This would allow the selection of spacer material to be based on mechanical issues rather than also worrying about electrical conductivity.

Best solution, I agree, is to find the proper alternator. But if this one must work, I would use braid.

[Wakesurfection]

Hi Guys

Thanks for the advice -really appreciated. I found a nut on the alternator casing which I could screw a thick black negative ground wire onto. It was the same thickness as the positive red wire from the alternator to the diode isolater box (part of the EIDB Dual Battery System). My voltage improved from 11.9 to 12.9 (its 12.8 when the blower is running) - these readings come from the instruments on my dashboard. I ran the black negative wire from the alternator to the negative terminal on the battery.

I did a check on my alternator by placing the red probe on the alternator bolt (from which the red thick wire runs to the diode isolater box) with the black probe on the mounting screw. Its reads 13.8V at the alternator bolt.

However, when I do a test of the diode isolater box I get 13.4 when I place the red probe on the stud connecting the red wire running from the alternator to the box. When I tested the stud connecting the cranking battery to the diode box, it reads only 12.9 (same as the readings from my instruments on the dashboard). I got the same 12.9 reading when I placed the red probe on the stud connecting the house battery to the diode box. The black probe was always on the negative terminal of the house battery during the testing. Is the diode isolator box meant to draw so much power? I think I might replace to red thick wire from the alternator to the diode box since this may be the cause in the reduction of power from 13.8 to 13.4. However, I am not sure why the voltage from the diode box to the batteries is only 12.9. Would replacing the red thick wires from the diode box to the cranking battery and house battery fix the problem?

Many thanks for your help guys

[chpthril]

Is the diode isolator box meant to draw so much power?

Yes. You can see up to a .7 of a volt loss through the diode isolator. Sounds like the alternator is charging again. Im sure the voltage output will increase with engine speed.