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spurrinit
07-06-2012, 01:00 PM
Using a mulitmeter I am getting 14.8 volts at the back of the alternator but when I measure at the battery I'm getting around 13.5 volts. I have traced the orange wire off the back of the alt and it appears to go all the way to the ammeter in the dash and then back to the solenoid. Can anyone confirm this or am I missing something? A lot of the harness is wrapped up so I might have missed it jumping off to the breaker or solenoid. I also checked for resistance from the alt to battery and my meter is showing nothing at least with in 2 decimal places. Any help is much appreciated.

Eli

This is on a 1986 prostar skier Power Slot with 351 pcm

mikeg205
07-06-2012, 02:55 PM
You mean voltmeter in dash? What does it show? was this measurement at idle or what RPM? Does voltage reading on gauge show 13.5?

DH9441
07-06-2012, 04:26 PM
His boat has an amp meter. Not volt.

mikeg205
07-06-2012, 06:58 PM
ok..cool on the amp meter... I would check all grounds... looking forward to reading your solution...

spurrinit
07-07-2012, 08:11 PM
I messed around with boat again today checking for resistance and trying to trace where the orange wire goes. I am pretty sure that the orange wire goes from the alt to to the dash and then back to the breaker and solenoid as a red wire. I also pulled apart the harness connectors to see what shape they were in. They could be cleaned up a little but not to bad considering their age.

One thing that puzzles me a little bit is that my multimeter still shows .00 ohms from the back of the alt to positive battery cable connector but there is a little over a volt lost. I'm pretty sure that in order for there to be a voltage drop there has to be resistance and I would assume that it would be more than .00 to cause more than a volt drop.

Does anyone have any pointers on what else to check?

Philscbx
07-07-2012, 08:19 PM
It could be just the length of cable getting back to the battery is the drop in voltage.
Combined with crimp on connectors not fully crimped.
Soldered & I bet you get the 14.

JDC
07-07-2012, 09:18 PM
Are you having a problem you're trying to diagnose or did you just stumble onto this reading and are curious as to the the 1.3v drop?
I agree it's high, and as a rule you should be no more than .5v, but wondering what problem you're trying to fix?

spurrinit
07-07-2012, 10:46 PM
It could be just the length of cable getting back to the battery is the drop in voltage.
Combined with crimp on connectors not fully crimped.
Soldered & I bet you get the 14.

Good point. Maybe I shouldn't be worried about the voltage drop. Has anyone else measured the voltage at the battery?

Are you having a problem you're trying to diagnose or did you just stumble onto this reading and are curious as to the the 1.3v drop?
I agree it's high, and as a rule you should be no more than .5v, but wondering what problem you're trying to fix?

I kind of stumbled onto it. I usually hook the battery up to a charger when I get home from the lake and notice that it usually has to run a while to charge it back up(depending on how low the batt is the charger adjusts how many amps it pushes and displays what its pushing). So just for the heck of it I measured the voltage at the battery and thought it was low.

You bring up a good point though. Should I be concerned about it charging the batt at 13.5? I guess I'm used to trucks getting upper 14's at the batteries and figured I had a problem.

JDC
07-08-2012, 08:36 AM
As the saying goes. "If it ain't broke, don't fix it". :)

I've not check my voltage at the battery while charging on my boat but I've never had a problem starting it. I always hook mine up to the Battery Tender when I get home. It max's out at only 1.5 amps, so naturally mine would take a while to come to full charge (no meter on it either).

I can check the voltage on it today just for grins.

So let me ask: You hook your charger to your battery. You measure voltage at the battery while charging and get 13.5v. Then, while charging, you checked voltage at the alternator and got 14.8v?
Or are you saying you measured voltage at the alternator with the engine running, and then at the battery with it running, and saw the difference.
I could maybe see the difference in scenario 2 (eng running), but with the charger... that would be weird.

Table Rocker
07-08-2012, 11:05 AM
Don't forget that there are two paths of current from the alternator, the positive and the negative. You can check the voltage at alt (+) and alt (-) by using the positive stud and the alternator case. You can then check alt (+) to bat (-) followed by bat (+) to alt (-) at the alternator case again. Finally you can check bat (+) to bat (-). That way you might get an idea where your drop is.

If you have a drop on the negative, you can move your negative test lead from the alt case to the ground cable bolt, to the ground cable and then to the battery post and check your readings.

spurrinit
07-09-2012, 08:21 AM
So let me ask: You hook your charger to your battery. You measure voltage at the battery while charging and get 13.5v. Then, while charging, you checked voltage at the alternator and got 14.8v?
Or are you saying you measured voltage at the alternator with the engine running, and then at the battery with it running, and saw the difference.
I could maybe see the difference in scenario 2 (eng running), but with the charger... that would be weird.

No I was measuring the voltage with the engine running and no charger hooked up.

Don't forget that there are two paths of current from the alternator, the positive and the negative. You can check the voltage at alt (+) and alt (-) by using the positive stud and the alternator case. You can then check alt (+) to bat (-) followed by bat (+) to alt (-) at the alternator case again. Finally you can check bat (+) to bat (-). That way you might get an idea where your drop is.

If you have a drop on the negative, you can move your negative test lead from the alt case to the ground cable bolt, to the ground cable and then to the battery post and check your readings.

Thanks for the info. I will try and measuring the ground and see what I get. This alt is a one wire unit so I'm guessing it grounds through the mounting bracket. I wonder if I should take the brackets off and clean them up and make sure its getting a good ground from the case to the engine. Is there a way to run a wire from the case of the alt to a known engine ground?

JimN
07-09-2012, 08:58 AM
Good point. Maybe I shouldn't be worried about the voltage drop. Has anyone else measured the voltage at the battery?



I kind of stumbled onto it. I usually hook the battery up to a charger when I get home from the lake and notice that it usually has to run a while to charge it back up(depending on how low the batt is the charger adjusts how many amps it pushes and displays what its pushing). So just for the heck of it I measured the voltage at the battery and thought it was low.

You bring up a good point though. Should I be concerned about it charging the batt at 13.5? I guess I'm used to trucks getting upper 14's at the batteries and figured I had a problem.

The voltage at the battery is ALWAYS supposed to be measured when there's an electrical problem.

BTW- if the crimped connections hadn't been made properly, it wouldn't have worked for this long so don't worry about those too much unless you have a demonstrable problem.

spurrinit
07-09-2012, 12:17 PM
The voltage at the battery is ALWAYS supposed to be measured when there's an electrical problem.

BTW- if the crimped connections hadn't been made properly, it wouldn't have worked for this long so don't worry about those too much unless you have a demonstrable problem.

Jim do you think I have a problem? If so do you think it might be in the grounding of the alt?

JDC
07-09-2012, 04:57 PM
No I was measuring the voltage with the engine running and no charger hooked up.OK, thanks. That makes more sense.

JimN
07-09-2012, 08:34 PM
Jim do you think I have a problem? If so do you think it might be in the grounding of the alt?

Does everything work properly? If so, then, I don't think you have a problem. Why did you check the voltage, originally?

spurrinit
07-10-2012, 08:13 AM
Does everything work properly? If so, then, I don't think you have a problem. Why did you check the voltage, originally?

Everything is working ok. I found it by accident because I felt like when I got home from the lake when I hook the battery up to the charger that it shouldn't need much charge but it does in most cases so I figured I would see what voltage the battery is getting while running.

spurrinit
07-10-2012, 08:16 AM
Does anyone see any problem or danger with running a new heavy guage wire from the back of the alt to the positive post on the battery? The only thing I can think of is that my ammeter on the dash might give a false reading.

JimN
07-10-2012, 08:43 AM
Everything is working ok. I found it by accident because I felt like when I got home from the lake when I hook the battery up to the charger that it shouldn't need much charge but it does in most cases so I figured I would see what voltage the battery is getting while running.

In that case, the wire you need to look at is the charging lead from the alternator. They don't usually make that one very long because high current over long wire requires heavier gauge. If the current is extreme, the wire will become warm/hot and if it gets too hot, it can affect the other wires in the bundle, possibly catastrophically. Pull the charging lead from the alternator and inspect/clean the terminal- if the wire looks like the insulation has expanded or is still at the end, make sure it's not because water got in and corroded the wire. The other end would either be on the starter or the solenoid- inspect it there, too, making sure nothing is loose. Also, make sure the ground cable on the engine is clean and tight, as well as the battery cables at the battery. If these are dirty, and it won't necessarily look that way without removing them, it can definitely affect the voltage/current during cranking.

Do you always connect it to a charger as soon as you get home? Why- do you often leave it for long periods without using it? If so, I would recommend disconnecting the battery cables, rather than putting a charger on it- a trickle or float charger would be a better choice.

spurrinit
07-10-2012, 09:03 AM
In that case, the wire you need to look at is the charging lead from the alternator. They don't usually make that one very long because high current over long wire requires heavier gauge. If the current is extreme, the wire will become warm/hot and if it gets too hot, it can affect the other wires in the bundle, possibly catastrophically. Pull the charging lead from the alternator and inspect/clean the terminal- if the wire looks like the insulation has expanded or is still at the end, make sure it's not because water got in and corroded the wire. The other end would either be on the starter or the solenoid- inspect it there, too, making sure nothing is loose. Also, make sure the ground cable on the engine is clean and tight, as well as the battery cables at the battery. If these are dirty, and it won't necessarily look that way without removing them, it can definitely affect the voltage/current during cranking.

Do you always connect it to a charger as soon as you get home? Why- do you often leave it for long periods without using it? If so, I would recommend disconnecting the battery cables, rather than putting a charger on it- a trickle or float charger would be a better choice.

I was expecting the orange wire to from the back of the alt to go to the breaker and solenoid but it appears to go to the dash ammeter and then come back to the breaker and solenoid. This seems odd to me because of the size of the wire and the distance that it travels. BTW the harness looks factory and doesn't look like it has been tampered with. I am going to check all connections again and see if I can't find anything. I'm thinking about running a heavy guage wire from the back of the alt to the positive side of battery.

Thanks again for your help.

SilviaMan
07-10-2012, 09:32 AM
Use your meter to find the voltage drop.
measure: Alternator (+) to the (+) post of the battery.
measure: Alternator case (-) to (-) post of the battery.
I would like to see less than .5vdc on both of these. if one is higher than that it will tell you which side has the voltage drop.
If its on the positive side then start moving back from the battery testing each connection until you have less voltage drop it will help identify the connection or section of wire that has the problem. pretty much the same thing to check the negative side.

TRBenj
07-10-2012, 10:08 AM
This sounds like a normal "issue" for the stock PCM wiring. An ammeter needs to be in line with the alternator and before any other loads (alternator-->ammeter-->load), otherwise it is useless. The length of wire required to run from the engine compartment to the dash and back is what causes the voltage drop... that and probably some suspect connections at both ends. If you bypass the ammeter, it will shorten the loop and lessen the voltage drop... but it will also make your ammeter useless since it will no longer read the current being pulled from the alternator.

The wire running from the alternator to the dash and back is sized such that it can handle the full rated output of your alternator. IIRC, that orange wire is usually 10awg, which can handle 55A. I believe the stock alternator is either 35A or 45A. Going to a larger wire would be fine, and would reduce the voltage drop at the dash and battery.

spurrinit
07-11-2012, 07:56 AM
I was able to do some testing yesterday and what I found was that, just like TRBenj said, the voltage drop was on the positive wire running from the alt to the dash ammeter and back to the 50 amp breaker. When measuring the voltage drop it just got continually bigger the farther away from the alternator. There was no voltage drop on the neg side. I also measured resistance again and was getting around .2 ohms through the positve side of the circuit. It helps when you set your multimeter to the right setting! :D

I took every connection loose in the orange wire to the dash and the red wire back and cleaned them up with a wire brush. After doing that I was able to get 14.1 volts at the battery leaving me with a .7 voltage drop which I can live with.

Thank you to everyone for your help. Hopefully this thread will be able to help someone out in the future.

Philscbx
07-13-2012, 01:59 PM
I took every connection loose --
cleaned them up with a wire brush. --
-- get 14.1 volts at the battery leaving me with a .7 voltage drop which I can live with.That's Great - Worthy process to add to any manual saved to file.