Overvoltage...question for Todd (or anyone else in the know)

[Michael]

My EDM 700 has been stopping its scroll of data on the battery voltage page, and flashing. When this happens it is reading 29.1-29.2 volts. I assume this means the voltage is too high? I replaced the voltage regulator a few months ago and was wondering what the problem might be. I've been pushing the "step" button and things go back to normal until it stops again at some later time.

Any ideas?

Michael

[Todd Peterson]

There's two things to consider. The first is that any of the limits on the EDM 700 can be adjusted up or down. On some of our airplanes I have adjusted the upper CHT limit from 460F to down around 405F. That way if I happen to miss a hot cylinder it will automatically tell me I have to make an adjustment. Same can be done I'm quite sure with the voltage.

Second thing is that there may be a problem that needs looking into. It seems to me like you have a 1979 airframe which would have the over voltage relay incorporated in with the voltage regulator. This should protect your electrical system if in fact the charging voltage is too high. Of course this presupposes that the voltage regulator unit is properly working. Does the amp meter in the engine cluster also show an excessive charge? If it does then that combined with the EDM 700 would most certainly indicate a problem. If it is normal then it could also be the EDM 700 itself.

If you could get a mechanic to check the voltage while the aircraft is running it would tell you wether you actually have a problem or not. If the charging voltage is within the normal range then it would be the EDM 700. If the voltage is in fact to high then the first thing I would do is carefully check all the wiring connections on the alternator. I have seen it where a single strand of wire from the battery post has reached over and touched the field post. Both terminals should have rubber boots to help insulate them. If everything there is ok then I would probably swap out the voltage regulator and see if anything changes. If it corrects the problem I would think that the former regulator may not have been a good one. Doesn't happen often but it does happen.

You might also want to take a look at your battery. I'm not sure if a shorted cell would do that but I think it might be a possibility. If the over voltage problem does actually exist and you have a good battery it will most certainly mean your battery will need to be serviced.

[Michael]

Thanks Todd, I'll have someone check into the problem as you suggest. What is the recommended charge voltage for a 28 volt system? Is 29.2 way out of the ballpark?

Michael

[Todd Peterson]

I can't remember exactly what the EDM 700's have been showing the the 24 volt aircraft. It seems to me like I have been seeing 28 volts on those that I have flown.

Can anyone out there with a 24 volt system and an EDM 700 say what they are running?

[kwmoore]

Mine reads right around 28 volts (1978 182Q).

[witrakw]

ditto, on the 28 volts

bill

[Michael]

Turns out EDM 700 is reading about a half volt high. I'm going to leave it as it is and keep on flying.

Michael