1975 Piper Seneca II alternators and voltage regulators
Hello all, I am having a huge issue with my electric on the right side of the plane. My system is only producing 13volts off the back of the alternator when everything is hooked up. When everything is disconnected I have 14v at idle and 24volts at 1500rpm and that’s at the back of the alt. When it’s all connected up normal I only get 13v off the back of the alt and 12.3 at the buss. I ran a new field wire to the voltage regulator and same thing. I bypassed the master and the alt switches and the same thing. For whatever reason when it’s hooked up normal all I can get is 13v off the back of the alt. I understand that there is a diode prior to the buss that will shave off about .7v which is why I am getting 12.3 at the buss. I have new regulators and I actually swapped them and the problem followed. I need to add that when connected normally my ammeter/load meter shows zero. I checked connections on the back of the alt and made for sure that they were tight. I have one battery lug that’s tight, one field lug with a 4inch strap on it that are both tight. I know that the alt gets the grounding from the block of the motor. There is also an AUX lug with nothing connected. Are there any test that I can run that I have not covered? Or does anyone have any ideas?
Thanks
Tim
Comments
With the engine OFF, ignition OFF (mags grounded) carefully measure the voltage from engine GND to the Alternator Field terminal with the Master and ALT switches ON. Also, measure (using the same GND) the bus voltage under the same conditions. What are those readings?
DJ
Ok I will do that and update asap. Thank you
Tim,
you lost me. How are you getting 24 volts from a Seneca II electrical system? Believe they switched from 12V to 24V halfway through the Seneca III deliveries.
Bob
we disconnected everything from the alternator and hooked up directly to back of the right alternator. The reading started at 14V at 900rpms and when we moved forwards with the testing we moved the rpms up to 1500rpms and the readings was at 24volts at the back of the alternator
this is a 12volt system that needs to be recharging at 14volts. I am getting only 13volts from the alt after its all connected resulting in 12.3 at the buss
In the original post you stated that you swapped the regulators and the issue followed? If thats the case, have you and your A&P adjusted the reg? It does sound like it's trying to work, as it's giving you 14V at idle and goes up with RPM, that's good with no reg in the system. Be careful doing that, the higher voltage can damage things.
Tom Jackson
PA28RT-201, N3022U
Tappahannock, VA (KXSA)
A&P/IA, Private Pilot, IR/A
Yes sir we had everything disconnected when performing that test straight off the back of the alt. Also we have tried to adjust the reg. With that test we set up some test leads that go from the back of the alt to a volt meter that was ran inside the plane for me to evaluate as my A&P adjusted the regulator from inside the nose. With this being done my cigarette lighter volt meter started at 12.3v and the hand held volt meter from the alt started at 13v. As he adjusted the reg there was never a change in voltage at either device. We will be doing the suggested test from djspathis this afternoon.
I hope you find it, but I'm stuck on the the issue following. That indicates to me that it's not an issue with the airplane, it's in the reg. Your field wiring is good, as it energizes the alternator-if bad you wouldn't even see the lower voltage you're seeing.
I'd really suspect that you received a bad regulator. I assume the left side is normal, except with the regulators swapped?
Tom Jackson
PA28RT-201, N3022U
Tappahannock, VA (KXSA)
A&P/IA, Private Pilot, IR/A
Ok, my A&P spoke with mike from aero tech who overhauled the alts. He asked for us to do some certain test. He said that we need to prove that the gear is not slipping on the alternator by applying a load to the alt and reading the current. When we tested off the back of the alt before we didn’t have any load on it. When the reg asks for more from the alt (more load) then the slipping of the gear clutch could be happening. So we ran a test set up like this. Everything disconnected except the battery … we used the battery to create a load so we don’t blow any avionics up. There is a diode between the battery and the load/ammeter. We didn’t remove the diode, hooked up to the alternator directly we had all the CB’s pulled out, we got 13.2 before the diode with 0 on the ammeter. 12.4 after the diode with 0 on the ammeter. We then took a measurement on our meter for current and was getting 5amps after the diode into the ammeter but the ammeter is still showing 0. Tomorrow we will report back to mike from aero tech and go from there. We didn’t have time for any other testing , so sorry but we do intend to do the suggested testing next. Yes the left side is working perfectly. Have I mentioned that ALL OF THIS WAS WORKING PERFECTLY BEFORE MY ANNUAL!!!!!!!????????????
When we swapped regulators the left side was still perfect.
The whole thread is a little bit confusing we're both alternators overhauled at the annual?. Get a very sensitive ohm meter and measure your field resistance in the alts, and compare the left and right sides. Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Here’s a quick update. Both alternators and gear clutches were overhauled in January 2024. The regulators were replaced in the2023 annual. With 20hours put on the alts since January 2024. My annual was up in July. I had planned to use the plane in august and September so I put the plane in annual at the beginning of June. It took this guy 3.5 months to get the annual done and obviously I was not happy. After this annual the left side is working but the right side was not producing power. My A&P that did the annual told me that he isn’t very good with electrical on planes and suggest I find someone that is good with avionics and wiring to troubleshoot the problem. I was glad to move on from that A&P anyways and found a very reputable A&P that does all the trouble shooting for J&G Aviation. We have now tested at all locations in the in the wiring diagram and isolated everything possible. Upon speaking with Mike from aero tech which is who overhauled the alts, suggested that we do a current test at the buss with only the battery connected to create a load to prove weather or not the gear clutch is slipping or not. We did the test but because of the complicated location of a diode we didn’t bypass the diode as suggested by mike. We were only getting 5amps after the diode. My A&P replaced the Diode just to make sure that the diode wasn’t bad. We will be doing that run up to test on Tuesday to see if that new diode changes anything. We don’t really expect a change but hopeful. If we don’t see a change then we will remove the alternator and test the gear clutch for slippage or is the alt not producing.
Hi,
Did the original shop use a ground power unit? Wondering if they fried something in the OV system or regulator.
When you mentioned you "swapped the regulators and the problem followed" I assume you really meant the problem remained on the right side?
When you disconnected everything and got the right alternator to 24V at 1500 rpm how did you power the field? The regulator OV relay should have come on at 17V
If the shop you did not like left a ground power unit on as well as the alternators it might cause some problems. For example, if the GPU voltage was below ship set point then the regulators would be continually feeding current into the field and the field would heat up with no rotational cooling.
I don't think it is the clutch as the voltage would be correct with no current - especially with both engines running and the voltage would only drop out at higher draws
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Ok, for the 24v at 1500rpm test the only thing that was connected was our meter. We ran a wire from the battery term on the back of the alt into the copilot seat, then we ran a wire from the field term on the back of the alternator into the copilot seat. Then we got into the plane and started just the right side and got 14volts at idle and 24volts at 1500rpm. We then left those wires connected to the back of the alternator and connected the battery wire of the aircraft and the field wire of the aircraft back up to the alternator along with our testing wires. That’s when we couldn’t get more than 13.2 on our test wires and because of the diode it passes through we only got 12.3 on the buss. We separated the 2 alts from each other so we could get exact measurements from the right side. We ran a battery and field wire directly the wires that bring it inside to the buss and bypassed the Voltage regulator and pulled all of the CB’s so it would blow anything up. Also yes you’re correct about the swapping of the regulators. When we swapped the regulators the problem remained on the right side. I just wish that I could find an A&P or a shop that specializes in Piper Seneca’s.
@empannin , you mentioned a GPU,,, you know when we did a run up on the motors to tweak the overhauled fuel injection system, that guy said that they ran the battery down too much and had to a gpu to kick it off. Hummmmmmm that’s very interesting. Everything was hooked up normal. How would that mess up the alt?
If they left the alternator switches on the regulators could be feeding voltage to the alternator fields. There probably would be no current if the voltage was greater than 14V but if it was low then the regulator would try and energize the field of the alternator to raise the bus voltage.
Since the alternator is not running it dumps all the current and heat into the windings.
This would also be the case if they ran down the batteries with the alternator's on. The regulators would use the ship battery to try and get voltage out of the alternators. Maybe the only left the right one on?
If the field wiring was damaged then the behavior might be unpredictable.
GPU's can also be set for the wrong voltage (24V vs 12V) and have poor regulation of voltage as well as AC ripple with a cheap supply.
If a shop ran my battery down I would send them links to ordering (and paying) for a new one.
If this is the shop that "does not understand electricity" then anything is possible....
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Ok, here is an update, J&G Aviation pulled the alternator and tested the alternator and found that the coupler IS slipping. WOW with about 20 hours on it, you wouldn’t think. So now we are filling out warranty information sheet out with QAA.com to see if they will warranty this coupler. Ill keep you updated
Fone;
Glad to hear you're on the right track! Could not agree more with all the excellent advice you received above.
Charging systems are not very complex. They consist of a battery, alternator, regulator, wiring and an overvoltage relay. Except for the OV relay, they are identical to automotive charging systems.
Run lots of ground tests before you take it up.
Keep us updated!
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
still waiting on everything to come in and be installed. I suspect it being completed this week.
Good afternoon everyone and thank you for everyone’s fantastic feedback. The slipping coupler on the alternator was definatly the problem. Just wanted to let y’all know.
Fone;
Great to hear! Congrats on finding the source of the problem, and thank you for following up with us!
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area