Mosfet R/R Causing Battery Drain - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 11-10-2011, 10:43 AM Thread Starter
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Mosfet R/R Causing Battery Drain

I've suspected I had a battery drain for the last little while and checked into it recently.

I pulled the positive leads off the battery. I have two, the main one, and a separate one for the new Mosfet R/R. Set up my multimeter in series with the leads and battery and noticed a draw coming from the Rectifier lead.

What would potentially cause this? I wired the Rectifier according to the instructions provided. So the positive and ground are connected directly to the Battery.

Is it normal for a Mosfet R/R to draw current?

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

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post #2 of 7 (permalink) Old 11-12-2011, 07:26 PM
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I don't know exactly how the MOSFET R/R works, but I never did like MOSFET anything. One more reason I lost interest in amateur radio. Kind of like everybody wanting to put LED everything on bikes. What's wrong with regular bulbs? The VN750 came with old technology that works. I know it works, because I have put 150,000 miles on it without a failure.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
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post #3 of 7 (permalink) Old 11-12-2011, 07:58 PM
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Quote:
Originally Posted by Roach View Post
I've suspected I had a battery drain for the last little while and checked into it recently.

I pulled the positive leads off the battery. I have two, the main one, and a separate one for the new Mosfet R/R. Set up my multimeter in series with the leads and battery and noticed a draw coming from the Rectifier lead.

What would potentially cause this? I wired the Rectifier according to the instructions provided. So the positive and ground are connected directly to the Battery.

Is it normal for a Mosfet R/R to draw current?
No it is not normal for them to be a current draw,do you have the headlight relay jumpered also or did you put it back in the circuit like it was before.the mosfet should only work when ac current is coming into it from the stator ,your new RR may be faulty,it doesn't matter if it is a mosfet or shunt type ,it should not draw current with the key off.

One possible solution is run the battery positive lead thru your ignition switch ,thereby disconnecting it from your battery with the key off.Which should solve your problem if it is working properly otherwise.

Quote:
I don't know exactly how the MOSFET R/R works, but I never did like MOSFET anything
The same reason a lot of kids won't eat Brussel Sprouts,they don't know what they taste like ,they just don't like 'em




If you see it on my bike I did it
VROC#30324
92 vn750(sold)
Current ride 05 1500 Classic FI
lovin' the new scoot



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Last edited by denny6006; 11-12-2011 at 08:04 PM.
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post #4 of 7 (permalink) Old 11-14-2011, 09:47 AM Thread Starter
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Quote:
Originally Posted by denny6006 View Post
No it is not normal for them to be a current draw,do you have the headlight relay jumpered also or did you put it back in the circuit like it was before.the mosfet should only work when ac current is coming into it from the stator ,your new RR may be faulty,it doesn't matter if it is a mosfet or shunt type ,it should not draw current with the key off.

One possible solution is run the battery positive lead thru your ignition switch ,thereby disconnecting it from your battery with the key off.Which should solve your problem if it is working properly otherwise.
I have done nothing with the headlight relay yet. Actually since I never had the bike running before installing the new rectifier I'm not sure what the normal headlight function is like. It's off when I turn on the bike, and lights up after the engine is started.

I thought about wiring it through the ignition. But the whole point of wiring it directly to the battery was to have as little resistance as possible. I've also thought about a relay that could get a signal when the key is turned on and allow power to flow.

But my main concern is figuring out why it's drawing current if it's not supposed to.

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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post #5 of 7 (permalink) Old 11-14-2011, 11:32 AM
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Quote:
Originally Posted by Roach View Post
I have done nothing with the headlight relay yet. Actually since I never had the bike running before installing the new rectifier I'm not sure what the normal headlight function is like. It's off when I turn on the bike, and lights up after the engine is started.

I thought about wiring it through the ignition. But the whole point of wiring it directly to the battery was to have as little resistance as possible. I've also thought about a relay that could get a signal when the key is turned on and allow power to flow.

But my main concern is figuring out why it's drawing current if it's not supposed to.
Your head light as working as it should,that's odd if you didn't use any part of the original harness.If you did use part of the original harness that went to the R/R your current draw may be in the headlight relay which is internal to the JB.



Check this thread out and see if you wired it this way or used any part of the factory R/R harness ,If you did ,you may need to do it like this without hooking up the head light relay to the charging system and jumper the relay at the Junction Box so it will come on as soon as you turn the key on rather than waiting for the engine to crank.Your Junction box may be the culprit instead of the R/R. and if you take the headlight relay out of the circuit until the key is on, you may lose the current draw with the key in the off position.
https://www.vn750.com/forum/showthread.php?t=20056




If you see it on my bike I did it
VROC#30324
92 vn750(sold)
Current ride 05 1500 Classic FI
lovin' the new scoot



Quote:
"When all is said and done,usually more is said than done" UNK
Click on one x and drag to the other to read between them.

Psalm 40:1...
XI waited patiently for the Lord; and he turned unto me, and heard my cry. X
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post #6 of 7 (permalink) Old 11-14-2011, 12:43 PM Thread Starter
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Quote:
Originally Posted by denny6006 View Post
Your head light as working as it should,that's odd if you didn't use any part of the original harness.If you did use part of the original harness that went to the R/R your current draw may be in the headlight relay which is internal to the JB.



Check this thread out and see if you wired it this way or used any part of the factory R/R harness ,If you did ,you may need to do it like this without hooking up the head light relay to the charging system and jumper the relay at the Junction Box so it will come on as soon as you turn the key on rather than waiting for the engine to crank.Your Junction box may be the culprit instead of the R/R. and if you take the headlight relay out of the circuit until the key is on, you may lose the current draw with the key in the off position.
https://www.vn750.com/forum/showthread.php?t=20056
Ok, this is odd. I did not use any of the original harness, and I wired everything just as mentioned in that post except for a jumper to the headlight relay.

Without that jumper my headlight should not come on at all, correct? The relay shouldn't be getting a signal unless someone tinkered with it previously.

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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post #7 of 7 (permalink) Old 11-14-2011, 12:57 PM
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Since the Mosfet R/R measures the voltage from the output instead of a separate sense wire like the original R/R, it will draw a little bit of current from the battery when the engine is off. But it should not be much - less than 10mA. It should not matter if the bike is regularly used, but will drain the battery if not (winter). How much current did you measure?
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