Re: 912UL electrical problem
No particular experience with Rotax but...
Looks like it is either the regulator or a wire that samples the generator output is broken/missing. The DC output of a generator should NEVER be so high as it will destroy the battery.
Ariel
Re: 912UL electrical problem
Carl,
Properly regulated voltage should run no higher than 14.1 - 14.5 volts at any time including after startup. That should be your standard.
Make sure your charging/regulating wiring is secure and correct - no loose screws or connections. Make sure that master switch is not at fault. I know you have checked some already but make sure nothing was overlooked.
If everything is secure and no cracked wires (sometimes a break can occur under the insulation) - I'd be concerned about the health of the regulator.
Running an over voltage can be hard on radios, etc. - and it doesn't have to take long to do the damage.
As always - be sure your gauge is reading correctly - plugging a second one into the system to check might not be a bad idea.
If you are a buy and fly guy - might be worth having a Rotax repairman or a qualified A & P take a look at it - I hate replacing parts just to find out what it isn't either - can get kinda pricey.
Sincerely,
Dave S
KF7 Trigear
1 Attachment(s)
Re: 912UL electrical problem
if the voltage is really going that high there must not be any overvoltage protection or crowbar installed . if anything is wrong with the stator the voltage wont be high . the regulator is pretty much the only thing that can fail and cause the overvoltage . if the alternator switch wont turn off the alternator its either a switch or a relay thats no good . first things first , you have to figure out how your ship is wired since your not the builder . good luck
Re: 912UL electrical problem
Thank you all for the suggestions re: my elec problem. I'm based out in the boonies so I
unfortunately can't turn to an AME for help & don't have spare gauges for testing. This
engine has 360 hrs on it & I've had it for the last 100 - electrically trouble free until
now.
Thnx for the diagram Chuck. The one in my manual is different - I'll try to figure out the
diffs. I checked the ground common to both the Amp meter & voltage gauges in case it was
causing a similtaneous false reading on both dials, ie, just an indication fault - not the
case. I had done some work on the engine last winter & had disconnected the yellow leads to
the rectifier- regulator (RR) - (the "G" connections on the RR) & may have crossed wired
them when re-connecting (not critical, I understand). In any case, I've confirmed the
continuity of that circuit. I didn't disconnect the other RR leads.
More info: the voltage is normal at 2000 RPM (14V), but increases linearly as I increase the
RPM. At 3000 RPM it's at 16V. Above 3000 RPM it increases to the gauge limit (above 16V -
18V extrapolated). As mentioned before, after a few minutes it returns to normal readings (14V).
The over-voltage may re-occur during flight, but rarely.
I gather that the capacitor (22000uF, 25V, according to my diagram) is the RR's protection.
There isn't one, so I've got one on order. All other wires look fine & the ones I've tested
for continuity are good too.
I've flown with this problem for approx 20 hrs, but am loath to fly the machine now that I
understand the potential consequences (more work to replace a burnt out dynamo than just
changing the RR). Also, it seems to be getting worse. Looks like I may have to bite the bullet...
Re: 912UL electrical problem
Before you buy new parts you might want to take a garden variety voltmeter and corroborate your readings (hate to buy new parts and find out it was the gauge).
1 Attachment(s)
Re: 912UL electrical problem
Hi, I have attached a pdf of an article that might be of use. I did allot of looking for info when I was having a charging issue.
Re: 912UL electrical problem
Problem fixed.
I replaced the rectifier-regulator, which fixed the problem of the occasional over-voltages on my 912UL.
BTW, I learned from a Rotec tech that turning off the Master swit (engine running) is NOT a good idea. I did this a few times to try to "cool" my voltage problem, but he said that this creates an overload on the rectif-regul, which may damage it.
Many thnx to all who took the time to help me out - I learned a lot.