Electrical Gremlins

[meddesign]

Looking for all good tricks to find Electrical Gremlins.  My voltage as read from my hand held gps will drop from 13.7 to 12.6 for a few seconds.  My encoder does not want to work at anything under 13.7. I just had the electric gear breaker trip  at end of  retract, had up light.   My electronic guru says bad grounds or bad circut brakers. My ammeter used to work much better.  1970 E with new zeftronics VR changed after my overvoltage would trip.  No overvoltage problems since unless that is what is causeing the alternator to drop out. 

 

Don B

[Jerry 5TJ]

Voltage Regulation During Flight

I recorded the voltage during a "typical" 45-minute flight in my M20C.  The DVM recorded 2 samples per second; there are just over 5000 points in the first graph.  

Overall comments

The generator is only "on line" when the engine is running >1600 RPM or so

The voltage is noisy even in steady state conditions

The voltage of the bus depends strongly on the applied load

If you look closely -- see the "First 5 Minutes" expanded graph -- you can see the mag checks which reduced the RPM from 1700 by about 100 RPM and the voltage about 1/2 volt.    After run-up, back to 1000 RPM and the voltage fell back to ~ 12 V.  

During flight I turned on various loads -- for example, at 15:44 local time I turned on the landing light (250W) and the voltage dropped.  At 15:49 I turned the landing light off and the voltage increased again.  

Background Information

Voltage was measured at the radio master bus 

The plane has original-type 50A generator

It has an original-style mechanical voltage regulator

I notice that the battery appears to be reaching full charge only near the end of 45 minutes of flight -- fully charged is a voltage of about 2.35 volts per cell for a lead-acid battery, or 14.1 volts.  

Does anyone think that changing to the newer solid-state type generator regulator (Zeftronics, for example) will improve this situation and reduce the noise "hash" seen here?

[meddesign]

As a follow up, my problem was traced to a bad crimp on the field wire of the alternator.   The wire was tight when pulled on but there was slight movement back and forth, which got worse when hot.  The encoder would not work because it is very old and the switching transistors do not have enough juice to switch when the voltage is low, because I added a splitter to allow my IFR GPS to have Baro.  input.  It works to the spec. of 10 V if there is no splitter.  I have to disconnect the splitter to certify my transponder and encoder on the ground.  I could add another encoder, but why bother, I now have a good alternator function blinking light, when my encoder stops working the GPS says out of altitude range and I know to check voltage on my handheld.  The Amp meeter still needs to be cleaned at the shunt and terminals to lower resistance, and then it should work.

 

 

[eaglebkh]

I have sort of an embarrasing story about my voltage issues.  At the beginning of this summer, I was having problems keeping my Aspen PFD alive due to low voltage.  The voltage reading on the Aspen was in the low 12's - low enough to make the Aspen switch to the internal battery.  My avionics guy couldn't figure it out, but thought it might be a regulator connection.  While I was inspecting the regulator, I realized the problem.  I had disconnected the scat hose coming from the exhaust manifold to the heater to prevent hot air getting into the cockpit.  Unaware, I had positioned the hose such that is was pointing right at the voltage regulator, making it heat up and throttle back the voltage.  The good news - it was an easy fix!

[carusoam]

Switching to the Zeftronics is easy and low cost.  Same footprint, same wire arrangement.  I did not have the tools to compare in detail, but the voltage regulation was on the money.  It also has a nice set of LED lights to help in troubleshooting.  I also noticed a curious additional circuit that can wired to a light on the instrument panel indicating that the generator has failed.

Have you opened the old regulator?  Springs and things and electrical noise makers.  It's hard to believe that thing even works.  And I thought magnetos were ancient technology.

[Jerry 5TJ]

UPDATE on Voltage Regulation During Flight

I posted about the voltage regulation (lack thereof, actually) on my mechanically regulated 50A generator last fall.  

Recently I did install the Zeftronics solid-state generator controller in place of the mechanical Delco-Remy.  That Delco-Remy original contained three relays -- one to shut down the system during overcurrent, the other two to bang on and off for under- and over-voltage control.   It was state of the art circa 1930.

I opened the Delco-Remy unit up; inside it was pretty clean but a bit rusty on the outside.  It still works (as well as it ever did); let me know if you want the thing.  

The new Zeftronics unit (almost) fit perfectly. I had to grind off a bit of the Zeftronics unit's mounting flange to clear a firewall bushing, and the two heavy gauge wires had to be rerouted.   Not hard at all.   About three hours total including getting it all signed off properly.

The results are good, very good.  The generator comes on line at ~ 1300 RPM now, and the buss voltage is a steady 14.2 +/- 0.04 volts above 1800 RPM.   That's a vast improvement on the wandering voltage and half-volt of noise seen in the graphs I posted. 

I'll take the same detailed data on a flight and post them soon for a "before and after" comparison. 

I am concerned that the Zeftronics unit may overheat, as there is no cooling air available at the upper end of the firewall.  Has anyone found heat to be a problem for these units?

[meddesign]

My sticker has curled because of the heat, but that is the only problem I have had.  It has been on almost 2 years.

 

Don B  70E

A&P

[carusoam]

I'm glad to hear you switched to the modern technology.  I look forward to the comparison graphs.  When I switched to the solid state version, I physically destroyed the mechanical device.  I figure it was the cause for the early demise of a handful of batteries, at least one generator and countless flights missed by the downtime it caused.....

Airflow may not be the best in that area, but I did not ever have electrical problems again.

I'm sure the old technology was well appreciated in 1930...  I wish there was as simple a solution for magnetos....

[Jerry 5TJ]

Last November I posted a chart showing voltage regulation (mostly it showed a lack of regulation) for my M20C's radio buss voltage.  Since then I replaced the original Delco-Remy mechanical regulator with a Zeftronics electronic generator regulator. 

It took several months for the test equipment and weather to all align properly. Today I took the "after" data -- the voltage regulation with the Zeftronics solid-state generator controller installed.

Attached are the two graphs overlaid.  In both cases I took about a 45-minute flight and recorded the radio buss voltage 120 times per minute with a DVM porting to a laptop.   The lower, noisy trace are the "before" data taken with the Delco-Remy mechanical regulator.    The upper, smooth trace is today's information, with the Zeftronics electronic generator regulator.

The electronic regulator is working far better than the Delco-Remy mechanical regulator.  Nothing else has changed, the same 50 Amp generator and the same radios are installed in the plane. 

The difference is marked.   In both test flights I switched on and off various loads -- radios, the 20A landing light, pitot heat -- while the DVM patiently took data readings twice per second.  In both flights you can see the run-up, followed by a period at idle RPM, then the take-off and flight, then the taxi in. 

Back when the Delco-Remy mechanical regulator was the latest thing, tube-type radios were king.  Those radios did not much care about a regulated voltage buss.  That is not true today; poor regulation of the supply can affect some equipment.   Poor regulation can also shorten battery life.  

[carusoam]

Jerry,

Nice to see the comparison of complete data sets.  Thanks for sharing.  It is interesting to see the entire flight (including run-up) as seen by your battery...Zeftronics give a real smooth control.

- a -

[m20edrvr]

I replaced the vibrating contact regulator on my 65e year before last, and replaced with a Zeftronics. At that time I also had the generator serviced/cleaned up.

A problem I have experienced, both before and after replacement, is that voltage will drop to 9.8-10.0V on final causing my GNS430 to trip and reset. I am seriously considering replacing the generator with a plane-power upgrade on annual to see if this fixes it.

Thoughts?

[Ned Gravel]

Quote: m20edrvr

I replaced the vibrating contact regulator on my 65e year before last, and replaced with a Zeftronics. At that time I also had the generator serviced/cleaned up.

A problem I have experienced, both before and after replacement, is that voltage will drop to 9.8-10.0V on final causing my GNS430 to trip and reset. I am seriously considering replacing the generator with a plane-power upgrade on annual to see if this fixes it.

Thoughts?

[danb35]

Quote: edgargravel

A generator will work when the battery is dead.  An alternator will not.

[Ned Gravel]

Quote: danb35

More accurately, most alternators won't start charging without some voltage on the bus.

[carusoam]

There are at least two other threads on generator and zeftronics replacement. 

Either way, the battery should last long enough to keep the electronics alive.  Seems like there is a significant other drain, or the battery is not holding much capacity.

As for hand propping 180 hp motors.  Has anyone done this succesfully?  I tried twice, then chickened out.......  That's alot of power, and a strong compression to overcome.

Best regards,

-a-

[N201MKTurbo]

I had an odd problem once with my Mooney, it mostly manifested itself while starting.

It turned out to be a grounding problem with the battery. The battery is grounded to the cross member that is bolted to the fuselage. The bad connection was where the cross member was attached to the fuselage. I had to remove the four bolts that attach the cross member. I cleaned the crud off of the mating surfaced and replaced the hardware adding star washers under the bolt head and nut to give a good electrical connection.

All of my electrical problems went away!

 

[Jerry 5TJ]

If the battery voltage on a six-cell lead-acid battery falls much below 10.5 volts when loaded and at normal temperature, there is just about zero capacity left.  If at the end of flight the bus voltage falls to that level on final with RPM above 1700 that implies either the system is not charging, or the battery is defective.   I'd guess the latter, but check all the key groundand wiring connections while you're at it.

The battery voltage should rise to about 14.2 to 14.4 when charging during flight.   If it does not, look at the charging system components -- generator,  generator controller, wiring.  

If you don't have a panel-mounted voltmeter, you can use one of those cigarette lighter mounted meters to watch the voltage.  Check EBAY or the local auto store.

[carusoam]

You can probably find your voltage reading on your portable Garmin (or other).  I have the 196 that has this feature, I bet the 696 still has it also along with XM, color, big screen and a few other nice things....

-a-