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Troubleshooting: No power

flylow

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I was troubleshooting no power to my radio and ICS, but now I have no power at all to my aircraft. My electrical is all in the wing root but the battery is under the seat (electrical will be moved this winter, but it's almost summer flying...).

I'm not sure if I shorted something out. When I flip the master switch, I don't hear the solenoid and nothing comes on. I checked the voltage on either side of the master solenoid, and it seems fine (12.5ish either side). There is power to the master switch, but I don't know if the switch is working.

As you can tell, I'm not an electrically minded person so any help is appreciated.

Thanks
 
Check your ground cable where it attaches to the airframe. I'm guessing it attaches to the seat frame. I've had that happen on mine, and everything is completely dead when the ground is lost.
 
if you show power 12v at master switch with it ON, then the other wire that it connects to is not going to ground like it should.

edit: providing you have solenoid, and not fuses for main power buss

pictures would help
 
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Thanks for the responses. I'll check the grounds.

Here's some pictures Mike. I know the wing root wiring needs to go.




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If your reading voltage on both sides of the solenoid, the solenoid is open, assuming your reading across the solenoid.
 
Cruiser- I think you are on to something. With the switch off, I shouldn't get any voltage across the solenoid. With the switch on, thats when I should see power on the side that goes to the starter solenoid. Seems like the contractor is closed to let the power go across to the starter post, but maybe I'm confusing terminology.


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So far, I’ve found a poor connection from the solenoid to the master switch (butt connector coming loose). Still troubleshooting.

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I provided info on determining whether the master solenoid is open or closed. If you read voltage across your master solenoid it is open. Your volt meter touching both big connections on the solenoid and you see 12 volts, plus or minus, the solenoid is open. Loosen all of those screws on that electrical panel, apply your favorite anti corrosive remedy and see if things improve. A squirt into each wire terminal and a repress would not hurt either.
 
Also, when you check your main ground (I still think that's your problem), just because it's tight doesn't mean its good. Take it off and scrape/brush it clean. At minimum loosen it a bit, twist it back and forth and then crank it down tight. When mine acted up it was completely tight but had no continuity due to paint and arcing.
 
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Is there a fuse between the master and the little terminal on the solenoid that actuates it?
Mine has pretty wimpy blades that hold the fuse in and they are easily corroded. Occasionally I shine these up with 1000 grit sandpaper.
 
Should NOT be fuses/breakers anywhere in a master circuit! Can't stress that enough!

Basic circuit: Battery cable from battery positive to the one big post on master solenoid marked 'battery'. The other big post on master solenoid is connected to the start relay and main bus. Since you have only one small terminal on your master, check to be sure the solenoid is marked 'continuous duty', not 'intermittent duty'. The small terminal is connected to one pole of the master switch and then from the switch to ground.

When the master switch is turned on, the wire from the small terminal is connected to ground. This allows current to flow from ground, through the closed contacts on the master switch, to the small terminal on the solenoid, through the coil, through an internal jumper to the large terminal connected to the battery positive. The magnetic field developed in the coil will pull the contacts closed connecting the two large terminals.

If you flip the master switch on and don't have power or hear the solenoid actuate, you need to check the circuit from the small terminal on the solenoid, all the way to ground. Connect the ground lead on a voltmeter to a good airframe ground. I'm assuming that you have a clean solid ground connection from battery to airframe. With the master switch off, there should be 12 volts at the small solenoid terminal. with the master switch on, the volts should go to zero. If they do go to zero, there is a problem with the solenoid. If they don't go to zero there is a bad master switch or a bad ground connection for that switch.

Web
 
What weenie said. To make it easy, if there is 12 volts both sides of that solenoid, the ground side is simply open. Your wire has either come disconnected, or there is a lot of corrosion under a ground lug somewhere.

Think about it - a wire with 12 volts on it cannot be connected to the airframe ground. Period. Put a jumper on it to test, then go clean the ground lugs.
 
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Dang...tried to edit but deleted...so here it is again

1951 Supercub. Fused between battery and master..been there for almost 70 years. I know more about brain surgery than electricity but is this a concern??..wirewienie?


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That circuit is a completely different design. The 'master' circuit on the original Cub type aircraft did not use a master solenoid. That master circuit is just one pole of a two pole switch. Pushing the toggle up or down will supply bus power by connecting the bus directly to the battery through the switch and one of the two fuses.

Yes it's been around for 70 years but I don't think it's a particularly safe design. It's hot all the time (unless the battery is disconnected) and it's parked just a few inches away from the right fuel tank. So it's an owners call to keep using it. I always recommend changing over to a master switch/solenoid circuit if you are doing a rebuild or major repairs.

Web
 
Flynlow, if you a have a “one wire” solenoid, it should be wired the same as #24107 shown below. The coil is internally energized from the batt connection. The master switch grounds the coil, as shown, to complete the circuit and close the coil. Reconnect your battery as normal. Take a short jumper wire and jumper from th small connection to any convenient ground. The negative battery terminal will work fine. The solenoid should close. If it does not, replace it. If it does, replace the master switch.
 

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Good idea. Those toggle switches fail with regularity. I have had the one in your photo fail. Tough to replace, unless the panel can be swung inboard from the wing root.
 
I have also concerns with the proximity of the switch to fuel tank. Doesnt seem like a huge project to relocate...probably $30 project for s good Texas A&P


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I have also concerns with the proximity of the switch to fuel tank. Doesnt seem like a huge project to relocate...probably $30 project for s good Texas A&P


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yup... have known many that have died in otherwise survivable crashes, from a fire starting up in wing root, because of the sparks/gas... ALL electrical get moved from the wing root in every rebuild I do...
 
Thanks for all the help.

It is a continuous duty solenoid. You can’t see the other post. I figured out all of my confusion. The master switch doesn’t ground the system. It’s wired differently. The landing light CB is tied to the master switch and to the landing light solenoid. Both of the posts on the master solenoid came to the master switch. And the master switch doesn’t go to a ground. I’m rewiring it like the PA18 schematic.






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I have experienced this twice now and would like to avoid a third experience. When temps drop to 20F or below I have experienced odd electrical characteristics. I have confirmed viability/continuity of the breaker, single pole single throw switch, battery voltage 13.12VDC and all checks out just fine. When temps are above freezing, no issues ever. So problem I exeperience is when it is real cold and plane sits outside for a few hours. I go to turn master switch on and nothing happens. Master relay does not engage and no power supplied to main bus. Starter push button is somewhat tacky. Only thing I can think of is that the master relay somehow has water/condensation inside and when it freezes it prevents relay from engaging. The remedy is to hand start the engine, go fly with cabin heat on and after 5 minutes of flying or so the electrical system comes alive. So to summarize, no problems ever when temps above freezing. Problem has occurred when temps were well below freezing and cabin area unheated for 2 or more hours. I am going to replace the master relay/solenoid and observe any symptom changes.
 
I have experienced this twice now and would like to avoid a third experience. When temps drop to 20F or below I have experienced odd electrical characteristics. I have confirmed viability/continuity of the breaker, single pole single throw switch, battery voltage 13.12VDC and all checks out just fine. When temps are above freezing, no issues ever. So problem I exeperience is when it is real cold and plane sits outside for a few hours. I go to turn master switch on and nothing happens. Master relay does not engage and no power supplied to main bus. Starter push button is somewhat tacky. Only thing I can think of is that the master relay somehow has water/condensation inside and when it freezes it prevents relay from engaging. The remedy is to hand start the engine, go fly with cabin heat on and after 5 minutes of flying or so the electrical system comes alive. So to summarize, no problems ever when temps above freezing. Problem has occurred when temps were well below freezing and cabin area unheated for 2 or more hours. I am going to replace the master relay/solenoid and observe any symptom changes.

Judging from the "Location" noted on your post, moisture in an electrical component seems pretty likely.

MTV
 
I live in Unalaska but do most of my flying in SE AK. Unfortunately no place to store a cub in these parts. The recent issue occurred at 4,500 feet MSL outside Juneau with OAT of 0 F.
 
Click......click click click click...nothing. Hmmm?

Many years ago local mechanics had a pet fix besides replacement. Some would drill a vent and dry on the hangar's furnace then reseal with glue. Some suggested leaving them unsealed so they could evaporate the insulating moisture. Others said leave the master on while pre-flighting and it'd warm up and work. I used to buy new ones at M&O auto supply and keep a spare. And carried a small jumper cable with clamps just in case it was too cold to fuss with fixing.

What's the latest on how to deal with it?

Gary
 
I had my starter contactor stick last week on a cold day. I assumed moisture in it too or something broke. When it worked again the next day after it got warmer, ice seemed most likely to be the cause. I bought a new starter contactor but haven’t installed it yet. And prophylatically I am putting in a new continuous duty master contactor too.
 
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