Merc trim solenoid - potential hack for longer life?

[Mad Props]

Thoughts welcome....

I took apart my old trim solenoids because I tested them and was getting very high resistance across the main terminals. I ordered new ones so I figured I'd investigate what the inside looked like... they are surprisingly repairable... in fact, I posted a video on my YouTube channel on how to test them and fix (at your own risk)... I don't plan on using the fixed ones, just keeping them in my tool box as backups.

all that being said, I noticed the failure mode of BOTH my solenoids was heavy pitting and carbon buildup on the copper studs and disk.
this is because these solenoids are making and breaking contact on a high current inductive load. When you open a switch on a motor or coil, you get significant arcing because the coil in the motor produces high voltage spikes... these spikes cause arcing at the contacts which constantly erodes and contaminates the contacts.

industrial motor contractors get away with this by using better plating, snubber diodes, and or sacrificial discharge tips on the contacts.

from what I can tell, mercruiser has done nothing to mitigate the issue.

my idea is to place a fly back diode from the ground terminal to the positive trim motor terminal on each solenoid.

They work by conducting the motors dissipating current thru the diode back to the motor positive wire...

it works like below (from wikipedia, check wikipedia page for further reading on flyback diodes)


hope this makes sense...
as far as the diodes I'm using, I happened to have some 1n5822 diodes in my parts bins. Pretty much anything would work as long as its reverse voltage is higher than 40v or more and its max instantaneous forward current is over 80amps or so as there will only brief current spikes.

hope this makes sense... i might be way off base, but it should work and at least give me quite a bit more life from my new trim solenoids for the cost of 2 20 cent diodes.

 

[achris]

Should work. Nice thought.

I use a flyback diode on the solenoid for the second battery in my vehicle (across the coil side, to protect other on-board electronics that are sensitive to spikes, not the solenoid). Hadn't thought too much about the trim solenoids, by yeah, good idea. :thumb:

Chris.....

 

[Mad Props]

Glad to see someone agree, especially chris! LOL..

I wish the solenoids had a clear case so I could see what they look like with and without the diode. I bet those things look like a fireworks show without it.

 

[harringtondav]

Cool. Reminds me of the condenser in old breaker point ignitions.

I have a Gem Remotes controller on my marine rail lift. The 'up' contacts in the 3P 240V motor contactor weld failed after LT 100 cycles.
​​​​​​
I'll call Gem and see if a capictor or diode will reduce the arching.

 

[achris]

Cool. Reminds me of the condenser in old breaker point ignitions.

I have a Gem Remotes controller on my marine rail lift. The 'up' contacts in the 3P 240V motor contactor weld failed after LT 100 cycles.
​​​​​​
I'll call Gem and see if a capictor or diode will reduce the arching.

Can't use a diode in an AC situation, and a capacitor is usually used for starting. About all you can do is put in a bigger contactor.

Where's ya signature?

Chris

 

[TurtleTamer]

I switched the solenoid on my starting circuit from the trim type to a remote Ford one, I think for an '88 Thunderbird if I'm not mistaken. It is much beefier and works great. Wouldn't be hard to modify the mounting bracketry on the Powerdyne trim assembly to accept them, though the use of a diode is a lot less intrusive,and it is uncertain how long the Ford solenoid will last under continuous duty like raising/lowering an outdrive vice quick bumps to turn over the starter.

 

[Mad Props]

Cool. Reminds me of the condenser in old breaker point ignitions.

I have a Gem Remotes controller on my marine rail lift. The 'up' contacts in the 3P 240V motor contactor weld failed after LT 100 cycles.
​​​​​​
I'll call Gem and see if a capacitor or diode will reduce the arching.

Yep.. Chris is right... AC is a little different... Its got is "ups and downs" BA DUM CHHH!

AC is bad because as Chris said, you can't really do much to suppress the arcing, however, its good because AC crosses the zero point (0 volts) twice every cycle, either at 60Hz or 50Hz depending on where you live. So in AC, the arcing is self extinguishing (usually why switches are rated to much lower voltages in DC versus AC.

So yeah, your motor contactor is going to just need to be beefier unfortunately.

 

[Mad Props]

You know what... I take that back.. I dunno why I totally forgot about TVS diodes. They are used to suppress transient negative and positive voltage spikes, so they would be perfect for a motor contactor. They are basically to back to back zener diodes. The one below would suffice for a motor contactor. You would place one in parallel with the switch across each leg of the hot wires (L1 to T1 and L2 to T2.).

They are also dirt cheap.

https://www.digikey.com/product-detail/en/littelfuse-inc/1.5KE480A/1.5KE480ACT-ND/2699807

 

[harringtondav]

So yeah, your motor contactor is going to just need to be beefier unfortunately.

Thx Mad

I called Gem (good outfit). They said the contactor shouldn't have failed with my set up. I fessed up that I failed to plug an extra cable stress relief, and had an ant farm in my control box. The larvae apparently prevented full pull-in. Once arcing started, down hill fast.

 

[Mad Props]

Thx Mad

I called Gem (good outfit). They said the contactor shouldn't have failed with my set up. I fessed up that I failed to plug an extra cable stress relief, and had an ant farm in my control box. The larvae apparently prevented full pull-in. Once arcing started, down hill fast.

Yep, usually the number 1 reason AC condensor contactors fail.. Spiders, ants, and bees think that little cavity makes a nice warm dry spot, till they get fried lol.

I'm thinking if I get bored tonight, I may sacrifice one of my old solenoids and try to make a cross section of it so I can video it with and without the diode. Basically for my own fun, but if it shows anything cool, I'll put a video up.

Stay tuned! lol

 

[achris]

Just remembered MOVs. Good for catching AC spikes. Not so good for stopping ants though. :faint2:

Nice signature harringtondav

 

[Mad Props]

It works! I took one of my old "refurbished" solenoids and cut a cross section into it so I could see what goes on when it opens and closes. No shortage of sparks when no protection! And then I decided to hook my oscilloscope and capture the voltage spikes with and without the flyback diode.
With flyback diode ~9V
Without flyback diode >400V! No wonder the contacts get pitted destroyed.

 

[achris]

Guess I'm going out and buying a handful of diodes this morning. :facepalm:

 

[harringtondav]

And then I decided to hook my oscilloscope

Damn man! Oscilloscope!? I thought I was ahead of the curve with expensive, rarely used tools and equipment. You just knocked me off my high horse. I don't do electronics, so I've never given a scope a thought....think my neighbor has one...hmm. If I can't figure it out w/my multimeter/amprobe and capacitor tester, I hold up the white flag.

Will you please reply with Google searchable p/ns for the diodes? I've copied you diagram, and its in my manual. My starting slave solenoid is the same part as my trim solenoids. But I'm guessing the current draw on the starter's pull-in coil doesn't warrant a diode. Accurate guess?

 

[Mad Props]

This is probably way overkill but it's so cheap, why not...
https://www.digikey.com/product-detail/en/diodes-incorporated/6A10-T/6A10DICT-ND/8819

also, I completely plan on this going on the starter solenoid too.. most likely suffers the same fate...for 50 cents, why not..

 

[Mad Props]

Also, double check your diode orientation... ask me how I know :facepalm:

 

[Mischief Managed]

Thanks for the awesome tip. I just ordered a hundred of these DIODE GEN PURP 1KV 6A R6 on ebay for 10 bucks. I will probably only use 30 or so. If anyone on here wants some, PM me with a mailing address and I'd be happy to send some out via snail mail. Figure it's the least I can do considering all the help I get here.

 

[hoowahfun]

Man...very cool, nicely done.

All this talk of diodes and oscilloscopes makes me wish I paid more attention in my Electrical Principles class back in college. Cool stuff, but over my head lol.

 

[Mad Props]

Lol.. I'm actually a mechanical engineer but I find electronics really interesting... that and I have way too many hobbies
but anymore, a decent understanding of electronics is a good tool to have in your belt.

 

[kenny nunez]

One of my friends who has a shop had a couple of new Sierra solenoids that did not work. I took them home and found the problem. The copper contacts on the inside were not thick enough to be contacted by the plunger. I slightly bent the contacts down then they worked perfect. Then I tried it on an older solenoid with the same results after cleaning the contacts. Needless to say I am not an engineer either but like to experiment with things like that. The diode trick is really impressive.