MOSFET R/R installation location - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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Where does this wire go?
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post #1 of 6 (permalink) Old 09-03-2014, 11:27 PM Thread Starter
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MOSFET R/R installation location

So tired of the VN750 charging system fragility that I'm willing to give the MOSFET R/R a try.

Already put in a TPE stator and did the "tuxedo" mod: the old stator was toast, and the frelling engine is NOT coming out of the frame again until it's time to do an overhaul. Reason I think I need a new/better R/R? Voltage across a new AGM battery occasionally drops below 11.0 at idle when the engine is warm (after a 70 mph dash down the highway). Tried bypassing the headlight relay (moving the blue wire to the unused slot in the junction box 8-pin connector, which is the standard setup for other than U.S./Canadian VN750s anyway): no change, other than headlight now comes on when the key switch is ON (as expected). When the engine and electronics are cold, I get 12.9V at idle, 14V+ at 1,500 RPM and above.

The installation location shown in the sticky post is underneath the side cover. At the risk of being too obvious, it gets HOT down here in Texas. The R/R has cooling fins on it for a reason. Is there enough air flow under the side cover to keep the electronics sufficiently cool when ambient temperature is north of 100 degrees F? Installation locations that seem pretty good to a person living in a place with 80-90 degree summers are suspect down here :-(. Unless the size of the new R/R is an issue, I'm tempted to go with the original relocation mod location (near the passenger foot peg, which is where my current "stock" R/R is mounted).

Thanks in advance for sharing your experience/advice.
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post #2 of 6 (permalink) Old 09-03-2014, 11:42 PM
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First, I see no reason not to mount the MOFSET R/R behind the cover... the first 3 installs were in Texas, Florida, and Gerogia in this very spot, and have been running with out issue for 3 or so years now (if not more). Secondly... I don't know where people are getting this misinformation about the Blue Wire Bypass saving the battery voltage. The "Blue Wire Bypass" is for troubleshooting a faulty headlight relay inside the junction box. Bypassing the headlight relay has ZERO effect on how much draw the headlight is putting on the charging system.
Correct me if I am wrong here, but we have only one battery, and every piece of electronics feeds off of the one Battery. No matter what circuit you move the headlight to, it still draws power from the same battery as before.
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post #3 of 6 (permalink) Old 09-04-2014, 08:22 AM
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2x on the side cover. It's a good spot but, the passenger foot peg is easier. The MOSFET doesn't get nearly as hot either so hot spot on the passengers leg should not be a concern.
Have you already got one? If not, I have one to get rid of.
Pm me if your interested.
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post #4 of 6 (permalink) Old 09-04-2014, 08:25 AM
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+1 slim

also will add that in the stock location (under battery box) is also very hot, probably hotter than inside the left cover. that is just inches above the goats belly.

I am sure there is more than enough air flow inside the left cover for the R/R to be happy. its NOT a sealed area after all.

2005 VN750

Sold 11-27-17
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post #5 of 6 (permalink) Old 09-04-2014, 11:54 AM Thread Starter
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ACK to all earlier postings: won't worry about the "under side cover" installation location. kanuck69: already ordered a "super kit" from RoadsterCycle, otherwise, I would have been happy to take your MOSFET off your hands -- sincere thanks for the offer. As an aside on the "hot spot on the passenger's leg" comment... What passenger? :-).

Update on post-headlight-relay-bypass status... I rode the bike into work this morning. Got a steady 14.1-14.3V across the battery within a few seconds of pulling away from a stop, and at all other times while moving. EXCEPT (and here's where it gets interesting), the turn signals appear to drop the voltage across the battery by approximately 0.4V, and the brake lights drop it by 0.9-1.0V. At idle (stopped at intersections), this makes for an uncomfortably low voltage reading, occasionally dipping below 12.0V. Is this normal?

On a conventional (stock) R/R, how is the brown "load sensing" wire supposed to work? Any way to test that functionality? Obviously, this will be OBE when the MOSFET R/R gets installed, but inquiring minds want to know :-).

On the matter of the "blue wire bypass", in theory, this should make for an easier MOSFET R/R installation because I won't have to worry about splicing in the yellow relay "engine is running" wire into one of the stator leads, yes? Beyond that, even if the relay load is negligible, it isn't zero, so completely disabling it should help.
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post #6 of 6 (permalink) Old 10-16-2014, 08:17 PM
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Quote:
Originally Posted by slimvulcanrider View Post
Bypassing the headlight relay has ZERO effect on how much draw the headlight is putting on the charging system.
Correct me if I am wrong here, but we have only one battery, and every piece of electronics feeds off of the one Battery. No matter what circuit you move the headlight to, it still draws power from the same battery as before.
You're correct that won't affect the headlight draw, but it should eliminate the relay which does draw power to keep the relay energized.

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