Alternator out warning board

[bking]

Learjetter,

I placed an order with Computer Components but they only had 1 in stock with a 3 month wait for the second relay. I searched the web and found another for $225.00 along the 4 resisters at Wilco.

Long story, but I also found a new surplus PC board for $175.00. After finding the board, I decided to make up a new unit and ordered all new diodes and the MS terminal boards.

The only 2 items that I could not get in the correct part numbers were the fuse blocks and 7 position bottom terminal strip and, according to Cessna, they are no longer offered. That said, I found similar components with the same ratings and also have them on the way.

I should have less than $700.00 total in parts for a new board. New surplus and "as removed boards" were running from $2,600.00 to $4,100.00 so, I'll have some fun and save a few coins.

If you could post a photo of your board it would be great and thank you,

BK

[hayesjaj]

This is incredibly useful info, thanks all. I'll likely need to do this on my 73G restoration. Would anyone be interested in an aftermarket cover for this unit? My cover is missing and I'll probably need to get some metal bent for it...may as well make a few.

[MD83driver]

Originally Posted by bking

Learjetter,
Long story, but I also found a new surplus PC board for $175.00.
BK

When you found this board, was there a part number associated with it? I am in the process of rebuilding mine. Thanks

[bking]

I have attached a list of the components, part numbers and vendors I used to replace my assembly and so far, the Alt Out warning light hasn't been flashing.

[MD83driver]

Thanks you for posting that information. I bought the 300-884 Relays a couple of months ago and they actually arrived yesterday. I bought the rectifiers and some diodes. I will use your list to collect the rest.

I have been thinking about why there would be so much trouble with these alternator lights if both regulators are set to the same voltage, either 27.7 or 28.8 volts. One possible area for this is since these are not paralleled in real time by the regulators, there is potential voltage drop from the rear to the front, thereby the incoming voltage from the rear would then be less that from the front. Just spitballing.

[mshac]

Originally Posted by MD83driver

I have been thinking about why there would be so much trouble with these alternator lights if both regulators are set to the same voltage, either 27.7 or 28.8 volts. One possible area for this is since these are not paralleled in real time by the regulators, there is potential voltage drop from the rear to the front, thereby the incoming voltage from the rear would then be less that from the front. Just spitballing.

You hit the nail on the head. You can install my 400-Series voltage regulator upgrade, and in all cases so far, the flashing alternator lights stay dark. Adding true paralleling alternators equalizes the load between front and rear.

I'm not clear what Cessna engineers were thinking when they designed the Skymaster's voltage regulation system, but it may have to do with the fact that the engineers at Pawnee (Cessna's single engine factory) had never built a twin before (and would never build another).

[Dan schultz]

Getting close to having my bird in the air. Been working on my Alternator warning system. Neither alt light would come on. My parts airplane, N3CY, had a AMF Portter Brumfield JRE1AD1 24v 10a reed relay on the board for the front alternator. While waiting for my 300-884 relays from computer components I acquired a number of the JRE1AD1 relays and installed them as depicted in the photo for the front and rear.

The front alt out light immediately worked rear did not. After hours of looking at the manuals, trying this and that, could not figure out why the rear large diode had battery voltage on both sides. The front alternator only had 5 volts on the anode side and the rear diode had 24 volts on the anode side with no alt light on the panel. Finally after looking at the tracks on the back of the pc board, where the relays are soldered in use opposite sides of the relays for the front compared to the rear. I unsoldered the rear relay repositioned it back in with the lettering upside down, and now I get 5 volts on the anode just like the front and the rear alt light is now on. Using a bright lite to light up the photocell on the panel increases the intensity of the alt lights making them easier to see. What a PINA.

Front alternator reed relay shown in pic.

Now to get my starter adapter back together to see if the lights go out with the alternators running.

Dan
67S

[Dan schultz]

Received my 300-884 reed relays Thursday from Computer components, I bought 4 at 90.00 each, about six weeks wait. Installed one for the rear alternator, right side of board, it all works fine now with the AMF relay installed on the left side.