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graemefrew(at)gmail.com
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 Posted: Tue Dec 30, 2008 2:38 am Post subject: More Nanchang VR Stuff |
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Hi All,
This Nanchang voltage regulator stuff is very topical for me right now. I have a syndicate member stuck in the middle of the South Island of NZ with our CJ that keeps blowing the main power 50 amp fuse. He has had an avionics guy scratching his head over the system for two expensive days now and they are no closer to a solution. I've had no end of problems with my VR so my engineer cobbled together a VR using a Harvard part as a start point. It has worked flawlessly for two years but now it seems we have a major problem. I've sent the avionics guy all the electrical diagrams I have from the CJ manuals and he doesn't seem to be any closer to pin pointing the problem. I was advised through this list a couple of years ago to chuck the VR over my left shoulder and fit an alternator. At the time it seemed like an expensive solution but right now it is a path I wish I had gone down. In my humble opinion an alternator seems like a good long term solution if you are having electrical trials with your CJ. Hind sight is a wonderful thing.
Happy New Year from those of us first to see it in.
Regards to all on the list.
Graeme
[quote][b]
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yakplt(at)yahoo.com
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| Posted: Tue Dec 30, 2008 5:53 pm Post subject: More Nanchang VR Stuff |
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Graeme, here is a trick that should be helpful in troubleshooting your 50 amp fuse problem. Pull the fuse, now take a 28 volt light bulb.... preferably somewhere around 50 watts or so. If you can not find one like that, substitute two 12 volt bulbs in series. Bottom line is that with say 50 watts worth of light bulb, your current draw will be roughly 2 amps. Take the light bulb and connect it with wires in PLACE of the fuse. This will LIMIT THE CURRENT DRAW TO 2 AMPS MAXIMUM! This way the power can be turned on and LEFT on, without blowing anything. When the short circuit occurs that has been blowing the fuse, the light bulb will come on ... full brightness. You can then turn off, disconnect, isolate other circuits one at a time until the light bulb goes out. Using this method you can shake, rattle and roll all the wiring just having someone eyeball that lightbulb as you do it.
This method works on ANY kind of problem with a short circuit where a fuse or circuit breaker is blowing as soon as you apply power. Most technicians look at a light bulb as a simple way of checking for voltage, as in a "idiot light". Rarely do they also realize it can be used as a current limiter, and that the total current draw allowed is simply a matter of using different wattage bulbs, using the standard formula of: I = P/E
Mark Bitterlich
N50YK
From: Graeme Frew <graemefrew(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Tuesday, December 30, 2008 5:36:06 AM
Subject: More Nanchang VR Stuff
Hi All,
This Nanchang voltage regulator stuff is very topical for me right now. I have a syndicate member stuck in the middle of the South Island of NZ with our CJ that keeps blowing the main power 50 amp fuse. He has had an avionics guy scratching his head over the system for two expensive days now and they are no closer to a solution. I've had no end of problems with my VR so my engineer cobbled together a VR using a Harvard part as a start point. It has worked flawlessly for two years but now it seems we have a major problem. I've sent the avionics guy all the electrical diagrams I have [quote][b]
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yakplt(at)yahoo.com
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| Posted: Tue Dec 30, 2008 6:03 pm Post subject: More Nanchang VR Stuff |
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Oops, I forgot to mention. Blowing the 50 amp main fuse is pretty rare. I would offer this one test before using my message describing the light bulb test method. Turn the generator off. Start the engine. Run the engine up to 60% or more. Now turn the generator on. Does the fuse blow? Hopefully not. Slowly bring the generator down to idle and watch the current. If at idle you see massive neg. current and the fuse then blows, you have a reverse current issue. When the engine is not turning the generator fast enough, or the generator is not turning at all, there is a direct current path to ground from the battery to the generator. This is true of ANY aircraft using a generator! In every case, there is a reverse current cutout relay to prevent this. In the Russian aircraft this is the 200 relay. I have no idea what it is on the CJ, but there HAS to be one. If this relay sticks closed, or gets spot welded closed (happens with old relays) then as soon as you turn on the aircraft master, the 50 amp fuse will blow. Every time. Turning off the generator might not be a good test if the relay has frozen closed. In this case you need to disconnect the generator wiring. Turn on the electrical master. The fuse should not blow. See if battery voltage appears on the generator PLUS wire that you now have disconnected. If it does... your reverse current relay is stuck closed. Also try starting and running it with the gen wiring disconnected. If none of that works, go back to using the light bulb for troubleshooting. If this reverse current relay is stuck closed, it might also have smoked the generator, but not all the time. It might survive.
Mark Bitterlich
N50YK
From: Graeme Frew <graemefrew(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Tuesday, December 30, 2008 5:36:06 AM
Subject: More Nanchang VR Stuff
Hi All,
This Nanchang voltage regulator stuff is very topical for me right now. I have a syndicate member stuck in the middle of the South Island of NZ with our CJ that keeps blowing the main power 50 amp fuse. He has had an avionics guy scratching his head over the system for two expensive days now and they are no closer to a solution. I've had no end of problems with my VR so my engineer cobbled together a VR using a Harvard part as a start point. It has worked flawlessly for two years but now it seems we have a major problem. I've sent the avionics guy all the electrical diagrams I have [quote][b]
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