Solenoids (NOT a Jimny question)

I know that some knowledgeable people watch this forum!

My 3.0 Litre Mercury engined power boat has a double solenoid system fitted to the starter mechanism.

Its all 12 volts and a slave solenoid mounted to the side of the engine "fires" the main solenoid sitting on top of the starter motor. Mine has gone intermittent and looking on the Internet this is a common failure.

It looks to me that there is probably a back EMF or pulse spark from the main solenoid that is burning the contacts of the slave solenoid. Is there any simple way to add in some spark supression that will increase the life of the replacement slave solenoid I have coming in the post. The Internet suggests the live of the slave solenoid is a short one! Its a 12 volt system, would an suppressor capacitor from an old style ignition system help, reverse diodes? neon arrestor?



Martin

Hi Martin

"From what I remember" from my electronics training, the best solution for that would be to use a Diode. That is commonly used in relays to extend their live spam. I actually think that most new ones come with one integrated already. The only problem is to find one that can take the current that will flow in it.
How many amps is the battery installed on the boat?

Hi,

I assume you mean that you have a relay connected so as to energise the starter solenoid?

As in the last post, a simple diode wired so the cathode (positive/banded) end is towards battery positive will do the trick. A 1n5401 5A diode is rated to carry 200A spikes, so it should be ok.

I would have thought a 30A relay would last years switching the solenoid coil unprotected though, it is all that most cars use.

Fitted a new solenoid and took apart the old one. Looks like its been overheating rather than arcing??