Van's Air Force
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Eliminate Master Contactor ??
- Thread starter RKellogg
- Start date
The Christen Eagle is setup without a master contactor, everything goes through a 20amp switch/breaker. It saves weight perhaps cuts down on electrical load and makes things a little simpler. The two drawbacks that I have identified (so far) is that if your starter contactor sticks, the starter will crank until the battery dies and if you do have a dead battery and jump the plane to start it, the charging current to the battery will exceed the 20amp breaker's capacity and it will trip when the rpm's are increased. Sounds like if you use several of them, this will not be a problem.
Bruce Green
Bruce Green
You can't run the starter load through those switches so you'll have the issue described above. Further, you won't be able to isolate power form coming into the cabin area.
The contactor draws about 0.7 amps at 14v. What is the weight delta between three beefy swithces and the contactor?
The contactor draws about 0.7 amps at 14v. What is the weight delta between three beefy swithces and the contactor?
How about a manual master switch? Harbor Freight has this........
http://www.harborfreight.com/catalogsearch/result?category=&q=battery+switch
Heavy Duty Battery Cutoff Switch
Item #66789
Only:$9.99
U.S. General #66789
This will carry starting load and also be able to switch it off manually if you need to isolate the battery load just like the master relay except it is a manual switch that does not use any power.
http://www.harborfreight.com/catalogsearch/result?category=&q=battery+switch
Heavy Duty Battery Cutoff Switch
Item #66789
Only:$9.99
U.S. General #66789
This will carry starting load and also be able to switch it off manually if you need to isolate the battery load just like the master relay except it is a manual switch that does not use any power.
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I am still a good ways from this point, however the same thought has crossed my mind, therefore I am interested in the replies.
After all, Aircraft Spruce sells a little item that is called a "PULL SWITCH" (part number: 16-140) for $ 9.50 that can pull 75 Amps. Anyway, I should think that one can use a device like this as opposed to the Master Contactor unit.
rocketbob
Well Known Member
Your starter will draw 300-350A initially.
No offense, but the idea of a Harbor Freight item keeping my plane in the air makes me very uncomfortable.
Wow! That sure is a lot of current all right.
However, if one kept the wiring for the Starter Contactor seperated from the other wiring, then that 300A to 350A should not be a factor.
So am I thinking about that correctly?
It sure is too bad that you could not look at the item before crossing it off of your list. They are sold by many other companies. Look in any off road racing magazine and you will find them, NAPA auto parts also sell them. You would find that they are made stronger than the normal relay used for most aircraft. The contact is copper and is held in place with a cam. And has a stronger release spring than most all solenoids used in our aircraft.
Any part that you purchase for your project should be judged for it's use.
No offense, but with your closed mind, you are best to build a 12.
I think it is time for a vacation from here.........................................
Ditto Neal's comments, plus ....
You asked for views. Here is another, though let me preface this with it is YOUR CALL. I offer the following for thought.
What is the real goal? Saving weight? The replacement items *probably* have similar weight. Also, by having a light meal prior to flight, maybe more weight could be saved.
(Yes, I know, every ounce counts in weight saving in plane building).
A *better* approach? This is one of those areas where the traditional approach is "tried and true" and I think that with the alternate approach there are some down sides ....
"Cranking amps" are quite high with these Lycomings. Probably in the range 400+. I think the Odessey PC680 delivers 680 amps for a while and under normal conditions around 450. Thus a BIG wire that will get HOT soon. Will your device handle 400 amps for 10 seconds ... 5 times ... within 3 minutes? (A hard to start engine)
Again, it is your plane so do what works for you but there are plenty of other places to save a pound or two that deviate from the "norm" or "tried and true" a bit less.
Personally, I would (and did) stay with the old relay/contactor approach.
You asked for views. Here is another, though let me preface this with it is YOUR CALL. I offer the following for thought.
What is the real goal? Saving weight? The replacement items *probably* have similar weight. Also, by having a light meal prior to flight, maybe more weight could be saved.
(Yes, I know, every ounce counts in weight saving in plane building).A *better* approach? This is one of those areas where the traditional approach is "tried and true" and I think that with the alternate approach there are some down sides ....
"Cranking amps" are quite high with these Lycomings. Probably in the range 400+. I think the Odessey PC680 delivers 680 amps for a while and under normal conditions around 450. Thus a BIG wire that will get HOT soon. Will your device handle 400 amps for 10 seconds ... 5 times ... within 3 minutes? (A hard to start engine)
Again, it is your plane so do what works for you but there are plenty of other places to save a pound or two that deviate from the "norm" or "tried and true" a bit less.
Personally, I would (and did) stay with the old relay/contactor approach.
Eliminate Master contactor ??
Thanks for the thoughtful responses! I have a new, broader perspective. Additional dialogue:
1. Ah, starter contactor sticking?I was not aware that this was a big problem. Personally, I have heard of no instances of this failure mode in either airplanes or surface vehicles. Certainly could happen. Suppose the Master Contactor could stick, too??? Maybe we need two Master Contactors in series to cover all eventualities.
2. One could further insulate always-hot wires coming into the cabin by running it thru a small diameter hose, as an additional measure. Opening the three ?master breakers? would shed all but this wire, hence the additional insulation.
3. Manual master switch sounds like a good idea, to the degree that it does not add additional failure modes, and the dreaded weight and complexity. Simple and direct is good.
4. I have been pleased with the quality/value of some Harbor Freight stuff. There is a lot that doesn?t get touched with a ten-foot pole. That doesn?t resolve the balance of trade issue, though.
5. Ah? ?tried and proven?? wasn?t that what they told the Wright Brothers about horses and buggys? In the final analysis, ?tried and proven? may not be the ?best? solution. Technology changes over time, thanks to guys who look beyond ?tried and proven?. Solid state relays sound promising, albeit not without drawbacks. Surprised nobody mentioned them?
6. Last time I looked the contactor was drawing 3 amps when engaged? ?? That is a significant penality for a device that can be replaced. Or was that the starter contactor?
So, gotta get this baby built, could have powered up the SkyView last weekend if I had resolved this point. Time forces the solution to (ugh?) ?tried and proven?. Guess it?s time to bolt those big, ugly, 1930?s technology contactors to the firewall and get on with life. Was hoping for a more elegant solution?
Thanks for sharing your insight and experiences!
- Roger
Thanks for the thoughtful responses! I have a new, broader perspective. Additional dialogue:
1. Ah, starter contactor sticking?I was not aware that this was a big problem. Personally, I have heard of no instances of this failure mode in either airplanes or surface vehicles. Certainly could happen. Suppose the Master Contactor could stick, too??? Maybe we need two Master Contactors in series to cover all eventualities.
2. One could further insulate always-hot wires coming into the cabin by running it thru a small diameter hose, as an additional measure. Opening the three ?master breakers? would shed all but this wire, hence the additional insulation.
3. Manual master switch sounds like a good idea, to the degree that it does not add additional failure modes, and the dreaded weight and complexity. Simple and direct is good.
4. I have been pleased with the quality/value of some Harbor Freight stuff. There is a lot that doesn?t get touched with a ten-foot pole. That doesn?t resolve the balance of trade issue, though.
5. Ah? ?tried and proven?? wasn?t that what they told the Wright Brothers about horses and buggys? In the final analysis, ?tried and proven? may not be the ?best? solution. Technology changes over time, thanks to guys who look beyond ?tried and proven?. Solid state relays sound promising, albeit not without drawbacks. Surprised nobody mentioned them?
6. Last time I looked the contactor was drawing 3 amps when engaged? ?? That is a significant penality for a device that can be replaced. Or was that the starter contactor?
So, gotta get this baby built, could have powered up the SkyView last weekend if I had resolved this point. Time forces the solution to (ugh?) ?tried and proven?. Guess it?s time to bolt those big, ugly, 1930?s technology contactors to the firewall and get on with life. Was hoping for a more elegant solution?
Thanks for sharing your insight and experiences!
- Roger
Roger, Please don't give up on your idea. I sent you a PM. Please read it before you decide your next step. There are many benifits to what you want to do as I explained in my PM. Just didn't want to post it here...... because from what I read, "no aircraft has ever had a manual master switch". The master switch by itself if left on will drain the battery dead just by the amount of current that it draws!!! If you ever open up a master sol. and look inside, then see how a manual master switch is built, you would understand.
If it fits in your project, A manual switch is the way to go....
If it fits in your project, A manual switch is the way to go....
L.Adamson
Well Known Member
My plane has a 30's technology constant speed prop, and the engine dates back to those days as well. They're simple, and they work. I don't see a better solution for managing high amperage such as engine starts. I still use relay/contactors for pushing higher currents in my business............even if they're stuck to a circuit board.
edit: addition...
No, I don't like ANY other ideas presented in this thread. We already know that the starter will pull far more amperage, than what's allowed through 20 amp switches. We know that it's still far too much for a 75 amp switch. An un-switchable starter cable could be a disaster in an airplane wreck, if you don't have the ability to disconnect it from the battery. These battery switches wouldn't be preferable either. The idea is to have the "master disconnect" just a very short distance from the battery. Once again, hot cables in a wrecked airplane with fuel draining around.........wouldn't promote pleasant thoughts. And a battery switch (as from Harbor Freight or elsewhere) wouldn't be possible to quickly turn off, unless you had a long lead coming through the panel area. Again,... the idea is to keep the "hot" lead, as short as possible!
edit again....
Okay, now I want to scare you. I installed a relay/contactor, that was part of the Bob K. alternator over voltage protection plan, that's now been eliminated. I left a few diodes on it, that were supposed to be removed for the application. Yet, it caused a direct short in a grounding cable that was either #2 or #4 copper. As I was sitting in the cockpit, the "aviation" insulation melted within mere seconds (no flames), and fell on my knee. The wire was melted almost completely through. All this within seconds, but I was quickly able to turn the "master" off. The plane wasn't yet flying at this point. It would be a rotten deal to have cable of this size, running through the airplane, with no way of removing the power.......for any form of simplicity.
L.Adamson --- RV6A
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kevinh
Well Known Member
I agree. For my day job work at an electric power train company (think cars, motorcycles, etc...). We are very-much in the 2010 technology and for the high current master going from the battery packs to the motor we use a contactor that looks very much like the unit I purchased from Van's.
Sticking contactors
Yes, they sometimes will stick or even not make good contact. I've opened up several that were having both kinds of problems and it always turned out to be one of two. The contacts inside the contactor are bridged by a copper disc. These contacts are a flattened area on the inside extension of the threaded lug on the outside of the case. Often when tightening the connections on the lug, too much torque is applied, which causes the contact on the inside to get cocked at a slight angle so that when the copper disc is pulled in by the solenoid it only makes contact on an edge rather than across the whole contact. This causes the contact resistance to be high causing it to get hot; this can both make it stick and also give poor cranking. On others I have seen where the solenoid override is insufficient and it makes poor or no contact. This is often due to wear on the contacts and the spring. The way it is supposed to work is that the armature of the solenoid moves down through the center of the contact disc while pushing it down with a spring. If the armature doesn't move far enough or if the spring has become weakened the armature can't put enough force on the disc giving a bad connection. Also it needs the spring force to move the armature back up to its released position. You can take one apart by patiently using a narrow screwdriver inserted under the the edge of the top portion where it is crimped around the bottom. By wedging the screwdriver under the crimp and prying it out you can eventually get the top loose and peer in to see how it works, and then fix it. I have fixed three by this method,both Master and Starter, and they worked better than when new!
Yes, they sometimes will stick or even not make good contact. I've opened up several that were having both kinds of problems and it always turned out to be one of two. The contacts inside the contactor are bridged by a copper disc. These contacts are a flattened area on the inside extension of the threaded lug on the outside of the case. Often when tightening the connections on the lug, too much torque is applied, which causes the contact on the inside to get cocked at a slight angle so that when the copper disc is pulled in by the solenoid it only makes contact on an edge rather than across the whole contact. This causes the contact resistance to be high causing it to get hot; this can both make it stick and also give poor cranking. On others I have seen where the solenoid override is insufficient and it makes poor or no contact. This is often due to wear on the contacts and the spring. The way it is supposed to work is that the armature of the solenoid moves down through the center of the contact disc while pushing it down with a spring. If the armature doesn't move far enough or if the spring has become weakened the armature can't put enough force on the disc giving a bad connection. Also it needs the spring force to move the armature back up to its released position. You can take one apart by patiently using a narrow screwdriver inserted under the the edge of the top portion where it is crimped around the bottom. By wedging the screwdriver under the crimp and prying it out you can eventually get the top loose and peer in to see how it works, and then fix it. I have fixed three by this method,both Master and Starter, and they worked better than when new!
Remote disconnect switch
If one wanted to save the .75 amps that a typical solenoid contactor requires, and keep the battery cable out of the cockpit, there is a proper way to do it. Then you get to answer the question for all your buddies; "What's that weird knob on your panel do?"
http://www.summitracing.com/parts/FLA-FR1003-2/?rtype=10
If one wanted to save the .75 amps that a typical solenoid contactor requires, and keep the battery cable out of the cockpit, there is a proper way to do it. Then you get to answer the question for all your buddies; "What's that weird knob on your panel do?"
http://www.summitracing.com/parts/FLA-FR1003-2/?rtype=10
