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bamafrankie
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83 Posts
Discussion Starter #1
I recently replaced the r/r on my 2003 vn750. I checked the stator with a meter and it checked good. my question is this I can jump start the bike with a riding lawnmower battery but when I pull the jumper cables off it goes dead. the battery on the bike is bad( only has about 10.8 volts. does the bike have to have a good battery to run even if the charging system is fine.
 

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Prowling Tiger
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2,048 Posts
Yes! Needs at least 12 volts to think about starting. This bike relies heavily on a good battery and charging system. Charge the battery first, then try to jump or when it does start, get the RPMS up to 2500 to get the charging system fully running.
 

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bamafrankie
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83 Posts
Discussion Starter #3
I was wondering if the bike was like a car they will stay running of the charging system once you jump it off. I read a thread by another member and I went and disconnected the bullet connectors from the stator and cranked and checked voltage at the connectors and I have 20plus volts ac at fast idle on all three leads. the connections were a little corroded so I cleaned and reinstalled. the reg/rectifier is new from rmstators just installed Friday. I guess I need to replace plug at the r/r it came with a new one was just saving it cause I was thinking of moving my r/r again to up near the radiator.
 

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Registered
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8,253 Posts
Might test the AC volts at higher RPM, but 20 sounds pretty low for AC volts. Should see a minimum of 40v AC, I think.
 

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Registered
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207 Posts
I recently replaced the r/r on my 2003 vn750. I checked the stator with a meter and it checked good. my question is this I can jump start the bike with a riding lawnmower battery but when I pull the jumper cables off it goes dead. the battery on the bike is bad( only has about 10.8 volts. does the bike have to have a good battery to run even if the charging system is fine.
Frankie, your experience is normal. The bike dies when you remove the jumper cables because the voltage regulator shuts down if it see less than ~12VDC on it's sense line. This is different than in a car because of the way our charging system works. The car alternator uses a variable field current in the rotor to regulate output voltage, and once the engine is started you can remove the battery and the regulator receives it's sense voltage from the output of the alternator. Conversely, our stator/regulator combo continues to use the battery as a reference voltage.
 

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bamafrankie
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83 Posts
Discussion Starter #6
Thanks for the info I checked the stator and the voltage is a little above 20ac at idle but when I try to rev to 3k rpm the motor dies, reckon the battery is to week but the voltage is picking up before it dies a about 1k

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Prowling Tiger
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2,048 Posts
Thanks for the info I checked the stator and the voltage is a little above 20ac at idle but when I try to rev to 3k rpm the motor dies, reckon the battery is to week but the voltage is picking up before it dies a about 1k

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What's the voltage at the battery? It should be around +12VDC at idle and shoot up to ~14VDC at higher RPM.
 
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