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Topic Options
#217156 - 11/21/14 08:56 AM Master solenoid diode installation
Norm Offline
New Member

Registered: 09/13/13
Posts: 3
Loc: Quesnel BC Canada
Hello Everyone
I have a 1958 172 and have been working on a sticky master solenoid. The one that has been in it forever is a Cutler Hammer (Eaton). I cleaned it out as there was sticky oil in the bottom of it that made the solenoid very slow to come on in cooler weather. It works fine now, however my AME says that I should have a diode installed to protect against spikes. He says it should be installed from the small master switch connect post to ground. Ive been looking on line and have become more and more confused as diagrams seem to differ as well as the reason for even installing a diode. Could someone point me to a good diagram or offer some advice on this subject? ThankYou
Norm

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#217180 - 11/21/14 09:57 AM Re: Master solenoid diode installation [Re: Norm]
multisync Online   content
Pilot in Command

Registered: 08/28/12
Posts: 481
Loc: CA
The coil in the solenoid is a large inductor. When the master switch is turned off the current through the inductor (solenoid) quickly disappears. This causes a large voltage spike backwards across the solenoid. The diode shunts (limits) this voltage so it does not get to your avionics and also lengthens the lifetime of the master switch contacts.

Be sure that the cathode (end with the white bar) is connected to the battery and the anode is connected to ground (current flows from anode to cathode). If you get it backwards the battery will be shorted directly to ground and the diode with blow as soon as you turn on the master switch.

http://www.bandc.biz/continuousdutycontactor.aspx

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#217181 - 11/21/14 10:19 AM Re: Master solenoid diode installation [Re: multisync]
Pedals2Paddles Offline
Second in Command

Registered: 10/17/14
Posts: 126
Loc: USA
Yep, that's all there is to it. If you're getting confused, it is probably because you think it should be more complex than it is. Which is true for most things... But this is really that simple. A diode from the coil + terminal to ground, done.

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#217254 - 11/21/14 05:49 PM Re: Master solenoid diode installation [Re: Pedals2Paddles]
Norm Offline
New Member

Registered: 09/13/13
Posts: 3
Loc: Quesnel BC Canada
Thanks guys....I think I have it straight now!

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#217273 - 11/21/14 06:50 PM Re: Master solenoid diode installation [Re: Norm]
Peedie Montgomery Offline
Platinum Pilot

Registered: 02/06/10
Posts: 3466
Loc: Hickory, NC
That's what I love about this site, so much great help from so many smart people. Money to buy more 100LL.Fly Safe and Often
_________________________
Ya'll Fly Safe and Often

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#217292 - 11/21/14 09:37 PM Re: Master solenoid diode installation [Re: Peedie Montgomery]
atticwing Offline
New Member

Registered: 11/01/14
Posts: 9
Loc: Chandler, AZ
Good info -- I think I'm going to like it around here...

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#217320 - 11/22/14 07:47 AM Re: Master solenoid diode installation [Re: atticwing]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 7724
Loc: Slidell La
If you have any solenoid sticking master or starter, being 58 version I would recommend replacement. I keep a spare starter solenoid on my shelf NIB all the time.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#217325 - 11/22/14 09:08 AM Re: Master solenoid diode installation [Re: vettdvr]
Norm Offline
New Member

Registered: 09/13/13
Posts: 3
Loc: Quesnel BC Canada
A spare or even a jumper would be a good idea. The solenoid was in very good shape inside, all parts in good condition. Ive never seen another solenoid that actually came apart, I couldn't resist looking inside it! The old girl doesn't have a starter solenoid, just the ancient pull start, so I'm OK there

Norm

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#217327 - 11/22/14 09:45 AM Re: Master solenoid diode installation [Re: Norm]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 7724
Loc: Slidell La
Originally Posted By: Norm
A spare or even a jumper would be a good idea. The solenoid was in very good shape inside, all parts in good condition. Ive never seen another solenoid that actually came apart, I couldn't resist looking inside it! The old girl doesn't have a starter solenoid, just the ancient pull start, so I'm OK there

Norm


You are right I forgot some of the early models you could open and clean out.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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