Alternating Alternator Lights

[jimmuse]

I acquired a 75 G and have noticed the alternator lights flickering in flight (one to the other). I know I have seen discussion of this problem somewhere, but a search of this site didn't come up with it.

Is this the same problem solved by swapping out voltage regulators?

My mechanic is chasing this problem on 3 Skymasters.

Jim

[kevin]

Search the board with the keyword "voltage", you will find a number of things. Also, specifically check out this thread about my own troubles in this area.

http://www.337skymaster.com/messages...hlight=voltage

There is a good message from Bob Cook in there about what to check for, as well as a message from Gmas about alternator drive couplings. I would check connections etc at Bob describes first. For me, it was loose diodes.

I believe that Peter's board (www.skymaster.org.uk) has some material on this as well.

Good luck Jim! (Always wanted to say that. Mission Impossible fan...)

Kevin

[Mark Hislop]

Jim:

I had the same problem on my 73 P. I found a modification, done on a Form 337, that allows you to swap out the original voltage regulators to regulators from 400 series Cessnas. These new regulators are wired together to give a truly paralleled system, thus both alternators are always sharing the load. I got the info and paperwork from CPA.

I agree with Kevin though, first make sure all of the rest of the charging system components....alternator diodes, brushes, connections, couplings, etc are as they should be. The paralleled regulators are, in my opinion, the way the system should have been designed in the first place, but the modification shouldn't be used to cover up another problem.

Mark

[jimmuse]

Mark,

I got the same info from Tom at CPA. I figured that would probably be the solution, but will check other stuff first.

Thanks

Jim

[Bob Cook]

There is nothing wrong with the existing system if it is in good shape.

For the cost of parts replace the diodes and capacitors on the front firewall.

2) make sure the switches (field) have low resistance. this includes field circuit breakers.
3) make sure all connections are tight.
4) test each alternator for full load capacity individually during flight.
5) make sure couplings are not slipping.
6) make sure the cables going to the battery are <copper>.
7) make sure battery is in good condition.

Recommend getting an EI volt metter and current shunts for future troubleshooting and monitoring.

To set the system up .

1) make sure battery in full charged condition.
2) use cart to start aircraft.
3) set regulator on front engine for exactly 28.4 volts. (check manual as there are two volt settings depending on regulator).
4) once stabalized disconnect front and do same with rear.
5) once rear is set then go back and parrellel both alternators.
6) check current on both alternators.... they should be the same. If not slightly increase or reduce rear regulator voltage (slowly) and wait for 15-30 seconds to stabalize.
7) There should be no flickering and the alternator outputs should be the same.
8) I adjusted mine and has remained perfectly stable for past TWO years and current balance is within 1 amp !!!!!

parrellel regulators from the 400 series aircraft work fine as well but why spend 300 dollars or more when in fact the problem lies elsewhere.

Cleaning the system up prior to changing regulators is mandatory anyway.

BTW run both engines around 12-1300 rpm for balancing. Double check higher rpms momentarily to insure the alternators are putting out at this rpm.

When you start the engines the battery is depeleted and the alternators are then charging the battery and throwing off the meter readings while charging occurs.

fyi

Bob

[jimmuse]

Bob,

Will do.

And thanks,

Jim