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  #21  
Old 06-23-2011, 09:38 PM
Bill Wightman's Avatar
Bill Wightman Bill Wightman is offline
 
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Nice work Paul. I like your "set it and forget it" ideology. That's pretty much the way Boeing did the 777 (except we've got like 16 levels of redundancy). And like the Triple, your critical buss gets fed automatically if either of the feeds fail. Boeing calls those things "transfer busses".

Well done!
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  #22  
Old 06-24-2011, 12:10 AM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by Ironflight View Post
Steve - I am with Walt (obviously) on using a switch alone when you can instead of a switch and a relay. I've just seen enough relay failures, and fewer switch failures. You need to make sure that your switch is adequate for the job, and if it is - get rid of one failure point!

Paul
I've had several switch failures in my RV. Switches that carry incandescent lighting loads (landing, taxi) or strobe power supplies are highly stressed, and I will be using relays for these types of loads in my Rocket. When/if the relays fail, they are easy to replace... even in flight.

This may be the fault of the switches (search the aeroelectric list for my failure analysis).

The only conclusion... design for maintenance. If you have to fix something (and you will), make it accessible. Everyting breaks eventually. I don't even know if you can crawl into an RV-3!

V
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  #23  
Old 06-24-2011, 03:55 AM
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Quote:
Originally Posted by Walt View Post
I just think switches are more reliable than relays, so if I can use a switch I will.
Quote:
Originally Posted by Ironflight View Post
Steve - I am with Walt (obviously) on using a switch alone when you can instead of a switch and a relay. I've just seen enough relay failures, and fewer switch failures. You need to make sure that your switch is adequate for the job, and if it is - get rid of one failure point!

Paul
Paul/Walt, Thanks. I'll review that decision of mine once more. The switch is already man enough to take the load. I'm using Eaton toggle switches.

Quote:
Originally Posted by Walt View Post
I also just noticed the 60 amp ANL, if you're using a 60A alternator I would suggest stepping that up to an 80 ANL to prevent nuisance blowing of the ANL.
Walt,
I'm not so sure that 60A ANLs with a 60A alternator are such an issue. My understanding is that the ANL current limiters are very slow blow that can take a good deal more than the rated current indefinitely. According to the Bussman ANL spec sheet even a 50A rated ANL will take 100 seconds to blow when exposed to about 110A. See the chart below. If anyone understands the logic behind the rating scale for ANLs I'd be keen to learn.

I'd also be interested in hearing from folks that have had nuisance trips on 60A ANL/60A Alternator combos and solved it by uprating to an 80A ANL.




The above is cut from http://www.cooperindustries.com/cont...S_2024_ANL.pdf

Thanks again,
Steve
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Last edited by shuttle : 06-24-2011 at 07:04 AM. Reason: fix spelling!
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  #24  
Old 06-24-2011, 07:01 AM
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Quote:
Originally Posted by shuttle View Post
Paul/Walt, Thanks. I'll review that decision of mine once more. The switch is already man enough to take the load. I'm using Eaton toggle switched.



Walt,
I'm not so sure that 60A ANLs with a 60A alternator are such an issue. My understanding is that the ANL current limiters are very slow blow that can take a good deal more than the rated current idefinitely. According to the Bussman ANL spec sheet even a 50A rated ANL will take 100 seconds to blow when exposed to about 110A. See the chart below. If anyone understands the logic behind the rating scale for ANLs I'd be keen to learn.

I'd also be interested in hearing from folks that have had nuisance trips on 60A ANL/60A Alternator combos and solved it by uprating to an 80A ANL.


Thanks again,
Steve
Steve,
After a review of the ANL chart above I will agree with you, stay with the 60A. My hanger mate blew an ANL after installing a plane power alternator, but I'm not sure what size it was but I'll find out (I was thinking it was a 60 but I'll double check).
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  #25  
Old 11-20-2012, 09:17 AM
humptybump humptybump is offline
 
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Quote:
Originally Posted by Ironflight View Post
use a switch alone when you can instead of a switch and a relay. I've just seen enough relay failures, and fewer switch failures.
Paul, I am trying to address my new electrical design and agree it would bve nice (and easier) to use a switch rather than a switch+relay.

I want to have my 60A feed from the alternator/battery spit to essential and non-essential buses.

What source and what switch have you found for 20A or 40A circuits ?

Also, you use "twin-pack diodes" - could you share the MFG and part # ? I have not been able to figure out how to size these diodes.
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  #26  
Old 11-20-2012, 10:39 AM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by humptybump View Post
Paul, I am trying to address my new electrical design and agree it would bve nice (and easier) to use a switch rather than a switch+relay.

I want to have my 60A feed from the alternator/battery spit to essential and non-essential buses.

What source and what switch have you found for 20A or 40A circuits ?

Also, you use "twin-pack diodes" - could you share the MFG and part # ? I have not been able to figure out how to size these diodes.
I'm traveling right now Glen, so don't have the part numbers for the diodes - but I know that Christer at Steinair does - give him a call!

As for large-capacity switches, well - if you're trying to switch anything 20 Amps or larger a relay is probably more appropriate. I prefer not to use relays any more than I have to, as I said, but for large loads, you are kind of stuck. I really prefer not to have relays in my critical path to get power to essential loads - the fewer active components between your source and critical loads, the better.

Paul
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  #27  
Old 11-20-2012, 11:19 AM
humptybump humptybump is offline
 
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Thanks Paul.

I agree to the desire for switches over relays. What was confusing me in the RV-3B diagrams and photos was I did not see any relays for the buses and I did not see any large breakers. What I did see was one or two primary switches and lots and lots of individual component breakers.

I must have missed the point of protection for your essential bus. That is what has been confusing me on most of the threads.

Once I have the fundamentals down, I will write it all up with diagrams and share it back on VAF.
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  #28  
Old 11-20-2012, 12:57 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by humptybump View Post

I must have missed the point of protection for your essential bus. That is what has been confusing me on most of the threads.
.
True - that was a system's level architecture drawing - not a wiring diagram that showed all components.
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  #29  
Old 11-20-2012, 01:47 PM
humptybump humptybump is offline
 
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So, for the actual implementation, did you find a hi current switch or did you use a relay ?

I've found a suitable relay but not a suitable switch at the bus current loads.
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  #30  
Old 11-20-2012, 01:49 PM
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Andy Hill Andy Hill is offline
 
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Given the expertise here, here is our proposed more "minimal" RV-3 Elec layout:

No Master (Electrical) Relay, may include a mechanical battery isolation sw. Start Master sw is to remove a single point failure leading to activation of the Starter. Comments welcome
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