Van's Air Force
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No power when master switch turned on
- Thread starter Wyo1971
- Start date
CHECK Master contactor
Wyo1971,
Does the master contactor energize (click) when you turn on the master switch? If not, measure the voltage from the POSITIVE terminal of the battery to the small white/orange wire that connects to the master contactor. It should be 12 volts with the master switch turned on. If there is not 12 volts, suspect a bad ground connection or bad master switch, or broken white/orange wire connection.
Is the battery ground wire connected to a non-painted point on the airframe?
Is there power at the accessory outlet between the seats?
Joe
Wyo1971,
Does the master contactor energize (click) when you turn on the master switch? If not, measure the voltage from the POSITIVE terminal of the battery to the small white/orange wire that connects to the master contactor. It should be 12 volts with the master switch turned on. If there is not 12 volts, suspect a bad ground connection or bad master switch, or broken white/orange wire connection.
Is the battery ground wire connected to a non-painted point on the airframe?
Is there power at the accessory outlet between the seats?
Joe
Last edited:
Hey Joe, is the accessory outlet powered with the master switch off?
I would think that using a test light would give a better indication of a bad ground.
The master contactor does not energize when the master switch is turned on. The voltage is 12 volts at the white/orange wire with or without the master switch turned on. The battery is grounded to a non painted surface, there is good continuity in the white/orange wire and good power at the power outlet between the seats. How do you tell if the master switch is bad?
The voltage was the same.
To Wyo1971,
Joe
What are you using for a voltage reference, positive or negative? I had suggested using the positive terminal of the battery for a reference. If you are using ground as a reference point, then there should NOT be 12 volts on the white/orange wire with the master switch turned on. The problem seems to be at the control board, either a bad master switch or a bad connection between ground and the master switch, or between the master switch and the white/orange wire. Make sure the control board is well grounded. Then remove the firewall-forward D-Sub connector from the control board. Turn on the master switch. Then measure the voltage between the POSITIVE battery post and pin 22 on the back of the control board (not the other half of the D-Sub that goes to the engine). As Harold suggested, a test light will be better for this test because it puts a load on the circuit. The test light should be on when the master switch is on. If not, then I would send the control board back to Van's. If the test light comes on with the master switch, then the problem is in the white/orange wire or the pin that connects to the control board.
Joe
LettersFromFlyoverCountry
Well Known Member
You mentioned the battery being grounded but you didn't mention the master switch ground. Did you check continuity between the airframe and the ground tab on the master switch? (Disclaimer: I'm not building an RV-12, so I don't know if they do things differently).
Thanks Joe for all of your help and time on this matter. I really appreciate it. When I used the positive side of the terminal I got 0 volts but using ground as a reference I got 12 volts at the white/orange wire with or without the master turned on. I ensured the control board was grounded good and then checked pin 22 of the firewall-forward D-Sub connector from the control board and got 0 volts. As suggested, I will go and get a test light and check all of this later today and let you know the results. An electrician I am not. Thanks again. Doyle
RV-12 is different
Bob Collins,
You make a good point. But the RV-12 is different. Instead of having discrete components, all of the switches and fuse holders and relays and resistors and connections and ammeter shunt and etc are soldered onto a multi-layered control board. That makes the aircraft easy to wire. It is similar to plug and play computer parts. But when things go wrong, it takes an avionics technician to repair.
Joe
Bob Collins,
You make a good point. But the RV-12 is different. Instead of having discrete components, all of the switches and fuse holders and relays and resistors and connections and ammeter shunt and etc are soldered onto a multi-layered control board. That makes the aircraft easy to wire. It is similar to plug and play computer parts. But when things go wrong, it takes an avionics technician to repair.
Joe
Bad master switch
Doyle,
You are welcome.
If I understand correctly, when the master switch is on, there is no voltage between the battery positive terminal and pin 22 of the firewall forward connector on the back of the control board. If this is true, then the problem is in the control board, either the master switch or a broken circuit board trace. It will not be necessary to repeat this voltage measurement with a test light unless you do not trust your volt meter.
Just to verify that the problem is not in the aircraft wiring, try grounding pin 22 on the end of the white/orange wire in the firewall-forward-wire-harness-D-Sub connector to see if the master contactor energizes.
Joe
Doyle,
You are welcome.
If I understand correctly, when the master switch is on, there is no voltage between the battery positive terminal and pin 22 of the firewall forward connector on the back of the control board. If this is true, then the problem is in the control board, either the master switch or a broken circuit board trace. It will not be necessary to repeat this voltage measurement with a test light unless you do not trust your volt meter.
Just to verify that the problem is not in the aircraft wiring, try grounding pin 22 on the end of the white/orange wire in the firewall-forward-wire-harness-D-Sub connector to see if the master contactor energizes.
Joe
vernhendershott
Well Known Member
Hi Doyle,
You might want to confirm that the diode is headed the correct direction as we had one here that ate two power boards before they found out that the diode was installed backwards. In this case it did smoke.
Best regards,
Vern
You might want to confirm that the diode is headed the correct direction as we had one here that ate two power boards before they found out that the diode was installed backwards. In this case it did smoke.
Best regards,
Vern
Good suggestion, Vern
Good point Vern. If that diode is backwards and one tries to test the master contactor with a grounded jumper wire, then that jumper wire could vaporize and cause a bad burn. To be safe, one could put a 5 amp fuse in series with the jumper wire.
Joe
Good point Vern. If that diode is backwards and one tries to test the master contactor with a grounded jumper wire, then that jumper wire could vaporize and cause a bad burn. To be safe, one could put a 5 amp fuse in series with the jumper wire.
Joe
conventional master contactor
Joe
Yes, the RV-12 uses a conventional master contactor. But according to the voltage measurements he has taken, the small solenoid terminal is not being grounded when the master switch is turned on. And that master switch is not readily accessible for testing, being buried in the control board.
Joe
I grounded pin 22 on the end of the white/orange wire in the firewall-forward-wire-harness-D-Sub connector and the master contactor did energize but no power to the control board. I stuck my nose to the backside of the master switch in the control board and it had that burnt electrical smell. I called Van's and informed them of the troubleshooting done and they said to send the control board back. They will send me another control board and ES Diode Master.
I want to thank you Joe for all of your help. I have been a regular follower of your posts and others and have gleened a wealth of knowledge from this forum that has helped me out time and again. Without this forum, I and others would be in a world of hurt. Thanks again!
Doyle
Testing the diode
Doyle,
It would be interesting to know if the diode caused the control board failure. Even if the diode was installed correctly, the supplier could have put that red band on the wrong end of the diode. A diode conducts electricity in one direction but blocks it from flowing in the opposite direction. The diode can be tested by removing it from the contactor and connecting the diode in series with a test light. The light should come on when the banded end of the diode is connected to negative and should not come on when the banded end is connected to positive. The new diode could be tested to be sure that it is marked correctly. This EAA Hints for Homebuilders movie explains how to test a diode.
Joe
http://www.eaavideo.org/video.aspx?v=63382258001
Doyle,
It would be interesting to know if the diode caused the control board failure. Even if the diode was installed correctly, the supplier could have put that red band on the wrong end of the diode. A diode conducts electricity in one direction but blocks it from flowing in the opposite direction. The diode can be tested by removing it from the contactor and connecting the diode in series with a test light. The light should come on when the banded end of the diode is connected to negative and should not come on when the banded end is connected to positive. The new diode could be tested to be sure that it is marked correctly. This EAA Hints for Homebuilders movie explains how to test a diode.
Joe
http://www.eaavideo.org/video.aspx?v=63382258001
Thanks for the link to the video Joe, that really helped explain how diodes work. I did not have a test light but I did borrow a good Ohmmeter and here are the results of the test per Van's procedures.
With Ohmmeter set on 2M with red test lead on end of ES Diode Master still connected to Master Relay and black test lead on disconnected end of ES Diode Master I get a reading of .0L. Reverse the leads and I get .991.
With Ohmmeter on diode setting with red test lead on end of ES Diode Master still connected to Master Relay and black test lead on disconnected end of ES Diode Master I get a reading of .0L. Reverse the leads and I get 552.
I guess that the ES Diode Master is working but not with the advertised numbers on the test procedure sheet. Maybe I shorted out something during my troubleshooting before I asked for help???
Doyle
Diode is good
Doyle,
I think the diode is good and did not cause the control board to fail. If the diode was shorted out, then there would have been sparks and smoke when you grounded the end of the white / yellow wire to energize the master contactor. So the diode is not shorted out. And it is not open either, judging by your ohmmeter readings. The only number that is out of the ball park is 552. Did you make a typo or misread the meter? I would expect a number between 0.5 and 1. Another test you can do is to leave the diode connected to the small terminal and connect the banded end of the diode to ground. The contactor should energize. However it is dangerous working around the positive battery lead. Making a mistake and shorting out the battery can cause bad burns. The best way to test the diode is with a 12-volt test light.
Joe
Doyle,
I think the diode is good and did not cause the control board to fail. If the diode was shorted out, then there would have been sparks and smoke when you grounded the end of the white / yellow wire to energize the master contactor. So the diode is not shorted out. And it is not open either, judging by your ohmmeter readings. The only number that is out of the ball park is 552. Did you make a typo or misread the meter? I would expect a number between 0.5 and 1. Another test you can do is to leave the diode connected to the small terminal and connect the banded end of the diode to ground. The contactor should energize. However it is dangerous working around the positive battery lead. Making a mistake and shorting out the battery can cause bad burns. The best way to test the diode is with a 12-volt test light.
Joe
Joe, the number 552 is correct. When I provided the numbers to VAN's they did not like the 552 either. I won't do anything else until I get a 12 volt test light. When I install the new control board and diode I want to make sure that everything is OK before turning on the master switch. Anything I can check prior to the new parts arriving? Thanks again for your time.
Doyle
Unreasonable number
When the meter is set for checking diodes, the meter displays the voltage that is dropped across the diode. For most diodes, the voltage dropped across them will be somewhere between 0.5 and 1, plus or minus. It is impossible for more voltage to be dropped across the diode than the voltage of the battery within the meter. If a meter has a 9 volt battery, then not more than 9 volts can be dropped across the diode. That is why the number 552 is unreasonable, even if the diode is defective, which I doubt. My mentor, Bob Nuckolls once said that he would pay $5 for any defective diode that was sent to him. I do not know if that offer still stands, but the point was that diodes hardly ever fail.
Joe
When the meter is set for checking diodes, the meter displays the voltage that is dropped across the diode. For most diodes, the voltage dropped across them will be somewhere between 0.5 and 1, plus or minus. It is impossible for more voltage to be dropped across the diode than the voltage of the battery within the meter. If a meter has a 9 volt battery, then not more than 9 volts can be dropped across the diode. That is why the number 552 is unreasonable, even if the diode is defective, which I doubt. My mentor, Bob Nuckolls once said that he would pay $5 for any defective diode that was sent to him. I do not know if that offer still stands, but the point was that diodes hardly ever fail.
When the new diode arrives, you could check it to be sure that the red band is on the correct end of the diode. It most likely is. But I know that you do not want to take a chance on having to wait a week or two for another control board.
Joe
Thanks for the clarification Joe. I have triple checked all of the wiring and everything looks good. I know that I will be a bit tense when I get the new board installed and turn the master switch on again.
Doyle
Bat relay incorrectly installed???
Perhaps you did NOT turn the Battery relay upside down, thus it will not work as far as I can see.
This it not clearly seen on the general layout drawings (OP-10), and certainly not the diagram below.
Looking forward the BAT terminal should be to the right (can not work if reversed, ref. Construction Manual page 5-18), and if you installed the optional "ES diode Master" (relay shown upside down on their drawing), it must be oriented according to their instruction too (red band towards BAT terminal).
Just a thought. Correct me if I am wrong guys...
Happy building!
TOM
Perhaps you did NOT turn the Battery relay upside down, thus it will not work as far as I can see.
This it not clearly seen on the general layout drawings (OP-10), and certainly not the diagram below.
Looking forward the BAT terminal should be to the right (can not work if reversed, ref. Construction Manual page 5-18), and if you installed the optional "ES diode Master" (relay shown upside down on their drawing), it must be oriented according to their instruction too (red band towards BAT terminal).
Just a thought. Correct me if I am wrong guys...
Happy building!
TOM
Agree with Joe (as usual). I wish more folks would close the loop with a final entry when an issue is resolved. It would help to inform the rest of the community.
