Good. The Lamarsaurus is very susceptible to field resistance and the Hartzell troubleshooting chart will be useful, but I agree there is some weird de-phasing between current and voltage, if you are indeed measuring bus voltage.
I have some voltage/amperage indication issues on an EDM930 primary engine monitor, installed on a Socata TB20.
The values are all over the place, and I don’t even know where to begin to find the cause.
Can it be a battery issue? Or maybe the alternator or something wrong with a regulator somewhere? The engine starts normally and I cannot see any other abnormal behavior on the 5 years old battery.
It’s true I have added a lot of consumers on the avionics bus lately, on a system that maybe wasn’t designed for so many instruments.
AlexTB20 wrote:
The values are all over the place, and I don’t even know where to begin to find the cause.Can it be a battery issue? Or maybe the alternator or something wrong with a regulator somewhere? The engine starts normally and I cannot see any other abnormal behavior on the 5 years old battery.
It looks like the voltage is going down when the current is going up and vice versa. I suspect a problem with the voltage regulator.
I have posted this a while back before the Covid madness started and forgot to press the ‘watch thread’ button… Sorry for this, maybe @Peter can move it there.
A lot of answers received and I will probably start by disconnecting the ALT breaker and measure the cables’ resistance, then measure voltage with a multimeter in various places to confirm the EDM readings… maybe a simple contact spray will solve an erroneous reading.
As @Airborne_Again noticed, there seems to be a relation between voltage and current (when one goes up the other goes down), is this a clear indication something must be wrong with the voltage regulator?
I’ve read the alternator is most probably an old 60s design for cars and Peter said the regulator should be a Lamar PWM. Most probably I would want to replace these anyway. Are the any new, alternate parts on the market?
A modern, solid state version regulator 10 times better and an alternator half the size of the original must already have appeared by now for sure…
CPA (Cessna Pilots Association) recommends Zeftronics as being heads and shoulders above OEM regulators/ACUs, and strongly recommends using them whenever replacing a regulator. I’ve had one on my C172 for ages and they are very reliable. They make models for most SE GA aircraft, but I don’t know if Socata is on the list. Type in the p/n from the TB20 parts catalog and see if something comes back.
If it helps, my plane is low tech. I just have an amperemeter. As I had an alternator failure in the past, I have the habit to look carefully at the indicator. Because of the very low consumption during flight (low tech I said) the pin is really near 0.
But just after starting the engine, as you just draw on the battery, pin goes frankly on positive way. This summer, I was surprised, when I switched on the alternator, the pin stay several minutes before moving (like it need to warm) but after that it worked. I flew nearly 5 months with this phenomena. (Never accept strange things in aviation) during a flight the pin was moving from + to 0… a bit like you and finally definitely to 0. I came back without alternator (I already did it).
The trick was a bad connection to the regulator…. since that time I have also a car tension indicator as a 12v plug. With this plug I can read the voltage to confirm charging is ok.
In your case such easy 12v socket lighter plug can help you to understand if it is becoming from your EDM or not. If not, bad connections can be on alternator or regulator.
Hope you will find
I was unable to find the exact issue so far.
I think the best thing to do is to replace everything, since they would need replacement anyway sooner or later.
Is the Zeftronics the best choice as a voltage regulator? I wasn’t able to find the exact model for a G1 TB20, 14V.
I am sure after 40 years there must be more robust and modern units out there to replace the original parts. Any suggestion for alternator, voltage regulator, filter, etc. would be greatly appreciated.
Yes, Zeftronics seem to be recommended regardless of plane brand. The Mooney crowd loves them too.
