High running voltage

[Russ46]

Hey guys, so I installed a volt meter in my 1997 challenger and when I'm running around 6000rpm its reading like 17 volts!

When I installed the meter I found a spare wiring harness under the dash that had a terminating cap on it so it wasn't being used for anything, it is an orange and a black wire so I used that to power my volt meter and depth finder. But now I am noticing some pretty high voltages when running in high rpms. Is this normal? Is my voltage regulator faulty? Do you think there is potential to damage the MPEM using it like this?

 

[Sfx27]

If I'm not mistaken your magneto charges your battery at higher rpms. The 17 voltages just means its charging your battery.

 

[Russ46]

If I'm not mistaken your magneto charges your battery at higher rpms. The 17 voltages just means its charging your battery.

You dont think 17 volts is excessive though? From what I've read it seems like there shouldn't be more than about 14.5 volts from the engine?

 

[Sfx27]

You are correct should be 14.2- 14.4. I'd try to check the voltage coming off the magneto

 

[Russ46]

You are correct should be 14.2- 14.4. I'd try to check the voltage coming off the magneto

I just ordered a new rectifier. The voltage coming off the mag would be AC and I am guessing it is fine because when the boat idles it was making around 13v, seems to me the rectifier just failed and it isnt regulating voltage anymore.. will replace it and share the results!

 

[ronmold]

Have you checked your new volt meter? 13 seems a little high for idle. 17 is too high and will cook your battery after a bit. You should never have a 4 volt swing on a properly running system. I believe the rectifier/regulator magneto system on the Rotax works like most outboards & motorcycles with a fixed strength spinning magnet, where after the rectifier turns the AC into DC, a sensor circuit in the regulator side monitors the voltage and if it rises above a certain level, usually 13.8-14.2, a variable shunt is introduced across the + & - leads which, with the help of the battery always taking current and acting as a load, the resistance of the stator windings (under the flywheel) causes the voltage to drop until it's below the threshold. If your regulator is bad the battery is left trying to do the entire job, although poorly, of reigning in the excess voltage. In this condition if a battery lead would come loose at higher RPM's your voltage could go well past 20-30 volts, not so good for the MPEM.

 

[Russ46]

Have you checked your new volt meter? 13 seems a little high for idle. 17 is too high and will cook your battery after a bit. You should never have a 4 volt swing on a properly running system. I believe the rectifier/regulator magneto system on the Rotax works like most outboards & motorcycles with a fixed strength spinning magnet, where after the rectifier turns the AC into DC, a sensor circuit in the regulator side monitors the voltage and if it rises above a certain level, usually 13.8-14.2, a variable shunt is introduced across the + & - leads which, with the help of the battery always taking current and acting as a load, the resistance of the stator windings (under the flywheel) causes the voltage to drop until it's below the threshold. If your regulator is bad the battery is left trying to do the entire job, although poorly, of reigning in the excess voltage. In this condition if a battery lead would come loose at higher RPM's your voltage could go well past 20-30 volts, not so good for the MPEM.

Sorry I lied, just checked again and with it running on the trailer at 3000rpm it reads 12.8 volts. So i trust it. I just replaced the rectifier and topped up the water in the battery, added about 2oz water to each hole. Will report if it is fixed tomorrow!

 

[Russ46]

So now my voltage is max 14.5 volts so I'm happy with that. My 3000rpm bog is better now too but it still struggles to rev past 5000 rpm