New Battery solenoid not working

[n1410d]

Ok this is a perplexing one. I decided to replace the Battery solenoid that is mounted to the front of the battery box. The one I removed was working, but there was a lot of rust around the base of the posts. Both the old and the new solenoids are the round type (New one is Lamar p/n X61-0028). Both have the two large posts for the Battery in and power out. The old solenoid just had a single small post for the wire running from the switch. The new one has two small posts, one for the switch and one for airframe ground.
I installed the new solenoid and wired it up just the same as the old one had been. I also put a jumper from the ground post to the airframe just to test the system before I fabricated a grounding wire. Switched on the master and........nothing.....I jumped from the positive on the battery to the switch post on the solenoid and it closed and powered up the system. Removed the jumper went back and tried the switch again and.....nothing.
In desperation I removed the new solenoid and replaced it with the old one and it worked just fine.

Obviously there is something different about how this new solenoid is wired internally. Any ideas???

Patrick
Grand Prairie TX
C-170A
N1410D

[blueldr]

Any master battery solenoid is simple as can be. Just ring it out with a VOM and find which terminals do what. Maybe you're in a little over your head. Get an electrician to give you a hand.

[canav8]

Check to make sure there is a good ground.

[n1410d]

I've wrung out the system and the wiring checks out. As I said the only thing I've changed is the solonoid. Old one works, new one does not. I've tested the new one and the unit itself is fine. It just doesn't play well with the airplane.

Patrick Mahaffey
Grand Prairie TX
A&P CFI
C-170A
N1410D

[Metal Master]

Obviously there is something different about how this new solenoid is wired internally. Any ideas???

Patrick
Grand Prairie TX
C-170A
N1410D[/quote]
The pictured Lamar switch is an open terminal switch. That means that it is not internally wired to anything. The two small Lugs are each end of the coil. One end has to be connected to ground the other to power. This way the switch can be used with either a ground connection at the control or with a battery connection at the control.

Lamar relay resize.jpg (32 KiB) Viewed 7678 times

If the master switch provides a ground for the master relay then one of the small lugs get connected to the Battery (Larger lug that the battery is connected to)lug on the side of the relay. Then the other Small lug is connected to the wire that is providing the ground from the master switch providing a ground to the switch. In the attached picture here the wire providing ground from the master switch on the instrument panel would be connected to the small lug on the right of the picture. The diode only prevents arcing at the switch. The battery would be connected to the Large lug on the left and the buss would be connected to the Large lug on the right.

Lamar wired for Positive coil end.jpg (7.49 KiB) Viewed 7678 times

If the master switch provides 12 volts to the master relay then then the hot wire wire gets connected to one of the small lugs. The other lug then gets connected to ground (The Base of the relay) providing a current path through the coil when the master switch is turned on and provides power to the other lug. This is not common as power then has to be present at all times at the instrument panel master switch.. The new Lamar relay can be wired so that either side has the battery connected to it so the relay can be used in any configuration left to right upside down or right to left.

[blueldr]

If I'm not mistaken, doesn't the master switch just provide a ground for the solenoid coil? I don't have a schematic, but my memory may be off too.

That solenoid shown looks like a starter solenoid to me, and would be designed for intermittent rather than full time operation.

[GAHorn]

bluEldr, that is correct. As Jim (Metal Master) points out, the cockpit switch only provides a GROUND for the relay/solenoid.
The internal (electromagnet) coil needs power from the hot (battery) side terminal of the relay, while the cockpit master switch grounds that coil, thereby activating the relay.
This was discussed and illustrated very nicely at the recent addition to the library: http://cessna170.org/forums/viewtopic.php?f=28&t=11992

[170C]

These 170's are too simple compared to all that heavy iron you usually are working on Pat Good luck with getting it to operating correctly. Let us know how you solve the issue.

Frank

[n1410d]

GREAT!!
Thanks for the helpful information. Makes perfect sense now. Always great to ask the brain trust on here before letting the smoke out of something on the airplane.

Cheers

Patrick Mahaffey
Grand Prairie TX
A&P, CFI
C-170A
N1410D

[n2582d]

I asked Lamar what the differences were between the X61-0028 offered at Aircraft Spruce and P52-0034-1, the Lamar contactor called out for by Cessna. Here's their reply:

The P52 number is a Cessna proprietary kit which includes instructions and a small jumper wire. The X61-0028 does not come with the instructions and jumper wire.

So one pays Cessna an extra $60 for a jumper wire and instructions (which can be found in SEL 24-02).

[blueldr]

If you're into saving money and aren't too worried about lineage, any auto supply can provide a suitable solenoid for use as a master solenoid for a lot less money than aviation sources. All you need is enough information to know what to ask for.

[GAHorn]

They used to be $17 at NAPA (in 2005), but now they're $40.
http://www.napaonline.com/Catalog/Catal ... 0311519496

[n2582d]

While attending an IA renewal seminar today in Santa Clara I talked with the Lamar representative, Jim Errington. He confirmed that the contactor included in Cessna's P52-0034-1 "kit" is indeed X61-0028. Here's a picture of a corroded contactor, caused by moisture ingress. (The outside copper ring makes contact with the main terminals.) To prevent this sort of corrosion he recommended sealing the contactor with PlastiDip.

To check if your contactor is corroded measure the voltage at each main terminal. The max. voltage drop allowed between the two main terminals is .2 volts.