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rowlandcarson(at)gmail.co
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 Posted: Mon Aug 13, 2012 11:34 am Post subject: crowbar component location for rotax installation |
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I'm checking through various parts of my circuit diagram and after looking at the crowbar circuit (for the Rotax integrated alternator - LAA mod 10404, issue 5, Jul 2003) I have a query.
How does one know when the crowbar has operated?
Would it be a good idea to put a warning lamp across the 5A breaker to show when it has popped?
It seems OK to me (as a disciple of Bob Nuckolls) to have the whole crowbar circuit close to the alternator, in the engine compartment and thus the 5A breaker not accessible in flight. But I'd like to have some positive indication if it ever has to do its job.
Any thoughts or prior art?
in friendship
Rowland
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budyerly(at)msn.com
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| Posted: Mon Aug 13, 2012 1:44 pm Post subject: crowbar component location for rotax installation |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Rowland,
Just a quick thought over about 10 panel installations:
I use a perihelion design OVP which is a fancy resettable crowbar (see periheliondesign.com) It kills the control circuit (C terminal) in the Rotax or the field in a standard internally regulated external alternator ending the power. It can be hooked to a relay to kill the feed leaving the regulator to run away if you so choose. Perhaps still powering some non overvoltage critical items.
You can use the somewhat crude but effective Knuckolls crow bar to kill a relay and allow a double pole relay to light a light bulb on the panel. When the relay opens, the contact from the panel side could light a light. I suggest an in line fuse to prevent full bus voltage from being unprotected. Eric Jones at Perihelion Design has done this for us in the US but his gear may not be permitted in the UK.
As for the alternator light, it is basically the most worthless tool in the shed (in my opinion)
It only lights if the regulator is working properly and the alternator does not produce current. Engine off/battery and alternator switch on.
It operates on the concept of comparing the control voltage to the output voltage. As the alternator sits quiet at engine off, the light gets power from the control through the battery of course. The bulb lights up (note that the alternator must be a light bulb and not an LED as current goes two ways) as the L or light side of the regulator is essentially grounded. As the alternator begins to produce power, the voltage of the output equals the control voltage and the light extinguishes as it has +12 on each side (slightly less as diodes are involved) and the bulb is out.
Should your regulator fail, the light is inop. If only one or two diodes of the triple diode rectifier fail, the light may dimly light as the alternator is in an under voltage condition. I have seen this only one time in my whole life. Normally your first indication of a failure of your regulator is your low battery warning light if you have one. That is why I preach that one must have an ammeter and voltmeter to determine his electrical systems health.
Now if the alternator circuit has high resistance going from the bus to the C terminal or otherwise is running below bus voltage, the voltage regulator will cause an overvoltage condition, completely undetected unless you have an OVP circuit. Knuckolls came up with a handy kill mechanism to protect the circuitry. Just not very elegant.
This is why I went to the Eric Jones/Perihelion Design unit. It costs about $100 with shipping and is worth every penny. One LED and one reset button (though I wouldn't reset and overvoltage condition normally).
Best Regards,
Bud Yerly
Europa Tech Support
Custom Flight Creations, Inc.
www.customflightcreations.com
(813) 653-4989
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