07-02-2008, 04:03 PM #1
'95 SLT750 Electrical Question - Battery Drain - NOT caused by MFD
I recently acquired a 95 SLT750 that has a battery drain issue when the engine is off. If I leave it sit with the engine off for 10+ minutes, I get the LoPwr message on the MFD and the battery will not start the machine again.
The machine has NO electric bilge pump....just the siphon style.
The previous owner disconnected the MFD and the battery drain did not go away. I have it disconnected now, so all of the testing done below was done with the MFD disconnected. Therefore, the MFD is not the cause.
The battery was charged a couple weeks ago and has been sitting in the garage. I put a voltmeter on it today and it read 13.00 volts on the bench. I installed the battery in the machine, and upon connecting the second cable, I get a spark - indicating there is a load. Based on the size of the spark, I suspected a decent sized load, and the source of my problems.
I put my ammeter in between the cable and the battery post and measured a current draw of 15+ amps! (Not milliamps!).
After looking at the schematic and reading several posts on this site, I suspect a bad regulator/rectifier (LR21 for this machine). I pulled the electrical box apart and checked resistance between ground at the LR21 and the negative battery cable, as well as the engine block. 0.0-0.2 ohms....no problem there.
I then disconnected the yellow wire and red/purple wire that runs from the LR21 to the circuit board. Doing this eliminates the 15+amp draw that is draining my battery. I then reconnected the red/purple (which I believe is how the LR21 senses battery voltage and charges the battery) and still no issue - no draw. Therefore, the draw is only occurring when the yellow wire from the LR21 is connected.
So, I removed the LR21 from the box and measured resistance between it's yellow wire and the aluminum plate that comes out of it (it's ground) and it's basically a dead short (< 1 ohm). Since I thought there may be a diode in there, I measured resistance both directions and it's shorted both ways.
It sounds to me like a pretty cut & dry example of a bad LR21, but I'm not 100% sure. I don't even mind spending the money to replace it. I just don't want to replace it and then find something else is the cause and have to re-order and wait for more parts to come in.
Can anyone confirm my diagnosis??
07-02-2008, 07:30 PM #2
is the Lr21 very hot to the touch huh? something has to be very hot (grounding out) to the touch.............................
07-02-2008, 08:11 PM #3
I'm not sure if it gets hot. It's out of the machine right now. I guess I can put it back in tomorrow and check it. I didn't leave it hooked up for long (just a few seconds at a time) and I didn't have the box open when I measured the current draw, so if it did get hot, it would have had time to cool down before I got my hands on it.
One thing I can do is open the yellow wire and put my ammeter in there. I'm pretty sure it will read the same 15amps there.
If the yellow on the LR21 is shorted to ground all the time, you can follow the path from the battery through the breaker, and then up the red/purple wire through the stator charging circuit, out the yellow of the stator charging circuit and then to the LR21 and to ground (with the alleged short).
The more I think about it, the more this has to be the problem.
Anybody with me on this????
07-02-2008, 08:24 PM #4
The yellow wire comes from the stator. Does your drain dissapear when you disconnect it from the electrical board?
It should also have no voltage on the yellow from the stator wire unless the engine is being cranked. If you have voltage there and it's tripping the regulator it may be the cause of your trouble.
07-02-2008, 08:52 PM #5
Didn't check to see if there is voltage on the yellow wire from the stator. I can do that tomorrow too.
Just to be clear, there is a yellow wire coming from the stator. There is also a yellow wire going to the LR21. These two yellow wires are "connected" via the spade connectors on the electrical board.
You want me to check to see if I have voltage between the yellow wire from the stator and ground (with the circuit open), right?
If you follow the wiring diagram, I'm baffled as to how the yellow wire from the stator would not have voltage on it unless the battery is disconnected?
I'm looking in the 1992-1998Factory Manual on page 7-55 (1995 SL750 - since I can't find the diagram for the 95 SLT750, I assume these are close with the exception of the power trim and the LR23 on the SL vs. the LR21 on the SLT).
So, PH2OCRAFT, follow along with me on this theory......if you look at that wiring diagram on 7-55, and you start at the positive battery terminal, you go to the starter solenoid with a red wire. You come off that red wire with another red wire and go to the breaker. Then you leave the breaker with two red/purple wires. One heads to the stator charging circuit (at about the 5 o'clock position)...that's the one I'm interested in. If you look close at the diagram, you can follow that circuit around the stator windings counter-clockwise until it exits on the yellow wire coming from the stator charging circuit (at the 9 o'clock position). It then heads straight to the LR21 (with one tap going off to the MFD presumably for RPM).
Correct me if I'm wrong, but I don't see a break in that circuit anywhere and the stator winding is (should be) a continuous circuit (I think), so from what I'm seeing, I think I should read +12V at the output of that yellow stator charging circuit wire any time the battery is connected.
Am I missing something???
07-02-2008, 09:05 PM #6
I don't have a manual with me but as I remember it.
The red/purple is full time power to the regulator. When the yellow trips the regulator it delivers power to the orange wire out of the regulator.
The yellow will not open the regulator until you're cranking.
I know this is the way it is with the Domestic engine, can somebody confirm this of the Fuji??
What does the orange wire go to?
If it's the trim, you know the orange should only have power while cranking or running.
I suggest removing the yellow from the stator so you know wether or not it's keeping the regulator open. If the regulator shuts down and you have NO power to the orange with it disconnected, look at the stator.
If you disconnect it (yellow wire from the stator) and the regulator still allows power to the orange wire, you know it's junk.
07-02-2008, 09:07 PM #7
One more thing...on another post http://greenhulk.net/forums/showthre...ghlight=stator by andy95'slx780, he mentions the resistance through the stator charging (aka lighting) circuit (red/purple to yellow) should be 0.6 ohms. This is incredibly close to a dead short, which again makes me think if you put power from the battery into one side of it, it should come out the other.
Please let me know if I am completely missing the boat (no pun intended).
07-02-2008, 09:10 PM #8
ph2ocraft....just to be clear, I have an LR21, which does NOT have the orange wire.
I only have three wires on the LR21. Yellow (coming from the stator), ground, and red/purple coming from the battery so the LR21 can "sense" battery voltage and determine how much current to send to the battery.
That red/purple at the LR21 is the same one that goes to the stator charging circuit. It splits out of the breaker and goes to both locations.
07-02-2008, 09:13 PM #9
MMMnnnn, I just don't have access to a wiring diagram and can't open the pictures on my phone but you're making sense if that's the case.
It sure was nice when they went to the LR23 and newer.
07-02-2008, 09:23 PM #10
I'm not doubting you about the LR23 being nice, but right now, if my LR21 is bad, I'm loving it. I can get a new LR21 for $21. An LR23 is $86. Sometimes, you just gotta love, "old school."
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