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kelmonroe(at)COMCAST.NET
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 Posted: Thu Dec 03, 2009 5:12 am Post subject: Over-voltage relay |
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I have a CJ with a Delco 24V, 40A, alternator with integral voltage regulator on it. The system doesn't have any over voltage protection. Does anyone have an idea of what relay I should install? Thanks Kelley
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ChangDriver
Joined: 15 Sep 2007
Posts: 266
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| Posted: Thu Dec 03, 2009 12:04 pm Post subject: Re: Over-voltage relay |
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It is not that simple......I am sure if you look in the list archive, you will find Mark Bitterlich has done some very nice posts on the value of and design of a crowbar overvoltage protection circuit. Basically, you need a circuit that detects the overvoltage at a certain setpoint and opens the field to the alternator and keeps it open. No field voltage, no voltage out of the alternator.
Here is a useful link:
http://www.gatm.com/flying/electrical/phase_iv.html
Another option is to scrap the system you have and install a B&C system (system means, alternator, voltage regulator/protection, proper pinion gear, proper mounting plate for the alternator) that provides all the protection you may want or need. As you read in the above link, B&C has incorporated many safety features in their design. They also include a shear coupler between the engine drive gear and the alternator. In the case of an alternator bearing failure, the shear coupler fails instead of the pinion gear inside your engine.
Happy flying,
Craig W.
Craig W
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jblake207(at)COMCAST.NET
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| Posted: Thu Dec 03, 2009 2:22 pm Post subject: Over-voltage relay |
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Why would this system be any different than an over volt system on Cessnas, Mooneys, Pipers, etc?
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yakplt(at)yahoo.com
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| Posted: Fri Dec 04, 2009 3:12 pm Post subject: Over-voltage relay |
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There are many designs, and many ways to approach your goal.
You might consider "borrowing" the exact system B&C has set up for their small PMG altenator. You can just order their over-voltage kit for for their 10 amp PMG unit. This thing is a simple crow-bar circuit that when the voltage goes over about 30.5 VDC causes a circuit breaker to blow. This circuit breaker powers a relay. The relay opens, and disconnects generator output.
It would be very very simple to take this exact circuit and apply it to any alternator or generator out there. If you need help changing the design to meet your exact needs, feel free to contact me off-line.
Mark Bitterlich
--- On Thu, 12/3/09, Kelley Monroe <kelmonroe(at)comcast.net> wrote:
| Quote: |
From: Kelley Monroe <kelmonroe(at)comcast.net>
Subject: Over-voltage relay
To: yak-list(at)matronics.com
Date: Thursday, December 3, 2009, 8:11 AM
I have a CJ with a Delco 24V, 40A, alternator with integral voltage regulator on it. The system doesn't have any over voltage protection. Does anyone have an idea of what relay I should install? Thanks Kelley
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ollow target=_blank>www.aeroelectric.com
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yakplt(at)yahoo.com
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| Posted: Fri Dec 04, 2009 3:29 pm Post subject: Over-voltage relay |
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Which Cessna? Which Piper? Their systems all vary. In some Cessna's there is no disconnect, only an over-voltage warning light, with a module connected underneath the front panel. They rely on the voltage regulator completely, and if it goes bad, then the over-voltage light comes on and you turn the system off manually. This approach does indeed have advantages because the pilots brain is engaged as what the exact course of action should be. This assumes that the pilot knows the electrical system, what will happen if the light is ignored, and when it might be a good idea to simply ignore the light for a few minutes and leave the alternator turned on. On the other hand, you step up to a big twin like a Cessna 421 and they take a much more sophisticated approach to electrical management and electrical failures.
What it boils down to really is what approach you want to take, and this in turn is usually determined by what you are doing with the airplane and how much money you want to spend.
The person who posed the original question is flying an experimental airplane with a electrical system that differs from the original design. He expressed a desire for an over-voltage protection system. Indeed, one could take the over-voltage module out of a Cessna 180 and connect it to this alternator and make it work exactly the same. Nothing but a warning light.
Or, a person could design their own system and make it do anything they wanted it to do! I tend to favor that approach, but my field is Avionics to begin with, so it is obvious why I would want to design my own system to do exactly what I want.
Indeed, I have wired in an over-ride circuit into the stock YAK-50 design so that I can manually control the main contactor relay. Used incorrectly, I could blow fuses everywhere, but used correctly, it allows me to manually control the whole system and get me to my destination in an extreme situation. (No one flies this aircraft but me!).
Given the inherent danger of an over-voltage condition, I would want a system that:
1. Disconnects the source of the over-voltage automatically, with manual over-ride as necessary.
2. Lets me know about it with a warning light.
3. Is easy to fix and find parts for.
The complete B&C replacement system does ALL of that.
The B&C over-voltage crowbar circuit (alone) can be adapted to work and do all of that as well with a custom designed alternator package such as the gent in question appears to be using.
Or you can just start from scratch and design your own, which is not all that hard to do.
Best Regards,
Mark Bitterlich
--- On Thu, 12/3/09, jblake207(at)comcast.net <jblake207(at)comcast.net> wrote:
[quote]
From: jblake207(at)comcast.net <jblake207(at)comcast.net>
Subject: Re: Re: Over-voltage relay
To: yak-list(at)matronics.com
Date: Thursday, December 3, 2009, 5:20 PM
#yiv1616440324 p {margin:0;} Why would this system be any different than an over volt system on Cessnas, Mooneys, Pipers, etc?
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