Point of having 2 solinoids on engine?

[legoman67]

Our mercruiser 255MIE's have one solinoid mounted above the flywheel, and the offset starters that came with the engine had a built in solinoid unit. We had to change from offset to inline starters, and got the starters from our old engines rebuilt, which only had a single solinoid system. Anyways, the solinoid mounted on the engine does not seem to function, I know they are only 20$ or so, but it just seems like a redundant system, and things would be simpler without it. Can i safely just take it out of the system?

 

[chiefalen]

Re: Point of having 2 solinoids on engine?

Are you talking about the slave solenoid ? Do you know what it does?

You want to hot wire the battery straight to the coil don't ya. Hah !

I remember you tried to ask about short cuts before.

 

[CharlieB]

Re: Point of having 2 solinoids on engine?

The smaller solenoid/relay is used to carry the load/operate the starter solenoid.

The long wire run from the engine bay to the ignition switch, adds a potential for voltage drop and an increase in current flow, (also known as HEAT).

To prevent a possibility of fire caused by toasted wiring in the harness or near the ignition switch, the use of this 2nd starter relay came about.

 

[chiefalen]

Re: Point of having 2 solinoids on engine?

Woa a second the slave doesn't do that, it's called a slave cause it captures the current and cuts all current to everything but the starter and coil.

It's important in cars cause it cuts all current to radios, ac, lights, and only allows the starter and coil to draw current.

Same in boats. You want only the starter to get juice and the coil. Thats why the wiring is the way it is.

It is the only solenoid that does that.

Now understand young man, no hot wiring the boat !

Sheech 16 he knows everything. But i have been keeping up on his progress and it is impressive.

 

[Fishermark]

Re: Point of having 2 solinoids on engine?

Chief - the "slave" solenoid is just there because of the long run from the ignition switch. Nothing more, nothing less. It is not found on cars - or at least not any cars I am familiar with. Charlie B has it right. (Although I think the biggest issue is simply getting enough juice to the starter solenoid, not the heat generated... but that's a possibility too.) The solenoid is just a switch. The ignition switch being energized causes the slave solenoid to be energized which causes the starter solenoid to be energized - each with a progressively larger gauge of wire.

 

[Don S]

Re: Point of having 2 solinoids on engine?

it's called a slave cause it captures the current and cuts all current to everything but the starter and coil.

It doesn't do that at all. It's in the yellow/red wire and can't capture anything.
CharlieB, and Fishermark are right, it's only there to make it easier on the wiring for long runs on bigger boats.

I've installed many slave solenoids/relays on older models, especially 27 to 28 foot models with flybridge or dual stations, not equipped with them, just because of the long run of 16ga. wire. With the neutral safety switch and several plug in connections, it didn't take much corrosion to prevent the starter solenide from engaging. It takes a lot more amperage to pull in the starter solenoid than it does to engage a small solenoid or relay.

 

[legoman67]

Re: Point of having 2 solinoids on engine?

ya, it ony interupts the yellow and red(on their way to the starter solinoid), and the only other thing on that circuit is the circuit breaker.

yes im only 16, and yes i jumped into a twin engine 29' boat restore head first. Im not trying to take shortcuts, hotwiring the coil was what i did when i ran the engine on the ground, becuase i didnt have a full engine run stand to plug into. It just seems pointless to me to have a solinoid soley for the purpose of activating another solinoid.

Alright now, here is the real problem with the slave how it is.

When i give the starter solinoid 12 volts directly it opens and the engine starts(every time), when i give the slave the power, the starter does turn but very slowly. Its also very random, and only 1 out of 3 times giving the slave power does the starter actually turn at all.

Anyways, if its really nessicary ill put a new slave solinoid on it. Are they anything special? or just a regular solinoid?

 

[abj87]

Re: Point of having 2 solinoids on engine?

Anyways, if its really nessicary ill put a new slave solinoid on it. Are they anything special? or just a regular solinoid?

If it wasn't needed would mercruser bother to put one in???
Not only does it allow lighter wiring to the ignition switch but is probably wired to provide 12v to the coil during cranking as well.
Not any old solenoid will work it needs to be a marine ignition protected unit.

 

[Fishermark]

Re: Point of having 2 solinoids on engine?

Yes, buy a new slave solenoid and put it on. I think it is an odd way of doing things too... BUT that's the way they designed it and with the 16 gauge wire it is a good idea to put it back in instead of trying to bypass it.

Not only does it allow lighter wiring to the ignition switch but is probably wired to provide 12v to the coil during cranking as well.

It has nothing to do with the full power to the coil during cranking. As mentioned, it simply is a way to get a heavier gauge of wire to activate the starter solenoid. The starter solenoid will provide power to the coil - regardless of the slave solenoid.

 

[abj87]

Re: Point of having 2 solinoids on engine?

Yes, buy a new slave solenoid and put it on. I think it is an odd way of doing things too... BUT that's the way they designed it and with the 16 gauge wire it is a good idea to put it back in instead of trying to bypass it.



It has nothing to do with the full power to the coil during cranking. As mentioned, it simply is a way to get a heavier gauge of wire to activate the starter solenoid. The starter solenoid will provide power to the coil - regardless of the slave solenoid.

Thats what the "I" termanal is for. I guess it depends on the application because thats the way mine is and its factory.
it looks like this right?

 

[Don S]

Re: Point of having 2 solinoids on engine?

Thats what the "I" termanal is for. I guess it depends on the application because thats the way mine is and its factory

.

Why is this so complicated. The above solenoid is NOT needed. Just a solenoid to engage the starter solenoid. The slave solenoid can be one of very small size, does not need to engage the ignition or anything else.
The smaller solenoids take little amperage to create more amperate to the solenoid on the starter.
With a 29 ft boat, use them or you will be getting into the engine compartment to jump the starter because your slightly corroded wiring will not engage the starter solenoid. It will the slave, just not the start solenoid.

It's amazing how people that don't understand the system and process can say it's not needed and actually give reasons and alternatives.

 

[JustJason]

Re: Point of having 2 solinoids on engine?

When i give the starter solinoid 12 volts directly it opens and the engine starts(every time), when i give the slave the power, the starter does turn but very slowly. Its also very random, and only 1 out of 3 times giving the slave power does the starter actually turn at all.

Anyways, if its really nessicary ill put a new slave solinoid on it. Are they anything special? or just a regular solinoid?

To test the solenoid correctly, you need to have a DMM and know how to do a voltage drop test. You can read about that here.

http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103

You should keep the slave solenoid, and not bypass it. It keeps all of the "high current" on the engine side of the boat, and not the boat side of the boat. (if that makes any sense to you)
It's always best to go OEM..... But if you have a Napa autoparts near you bring in your old one and have them match it up to something. If you asked them for an old Ford fender mount solenoid that would work fine.

Woa a second the slave doesn't do that, it's called a slave cause it captures the current and cuts all current to everything but the starter and coil.

Chief....... what are you smoking tonight man?? Where/how did you come up with that line??

 

[dan t.]

Re: Point of having 2 solinoids on engine?

this may not be relivant but we used to wire up our oval track cars this way, the reason for this was so you could remove the starter without unhooking the battery there being no power there unless the slave solinoid was engaged

 

[Don S]

Re: Point of having 2 solinoids on engine?

this may not be relivant but we used to wire up our oval track cars this way, the reason for this was so you could remove the starter without unhooking the battery there being no power there unless the slave solinoid was engaged

Different concept, the start battery cable would still be live with a mrine slave solenoid.
Here is a basic Mercruiser wiring diagram of how the slave solenoid is wired in. It's not there for any reason than to stop higher amperage loads of the starter solenoid from over loading the long runs of light gauge wire in bigger boats. That's it, nothing fancy, nothing spectacular, if you want throw the thing out, it won't hurt anything. Except the starter might not engage because of poor connections due to long runs.
It's only there to make things work more consistantly and more often, and it does. If you are around it on a lot of different boat. (like I am).
If you have an 18 foot boat, you probably wouldn't ever have the problem.

 

[JustJason]

Re: Point of having 2 solinoids on engine?

this may not be relivant but we used to wire up our oval track cars this way, the reason for this was so you could remove the starter without unhooking the battery

Eaghhh... your missing the point a bit. Main power still goes to the starter motor. The slave solenoid only allieviates the load on the keyswitch and the boat side wiring..... and that's it.
1 thing everyone has to remember, is that the entire power package get's delivered from Merc to the boat builder as a complete package... as in that slave is in there from Merc. Everything in the power package is done by Merc in such a way that the installer of the package has very little to do in terms of the wiring on the "Engine side" of the boat.
They do this on purpose.
When a boat breaks down.... 1/2 the time the owners go cussing the manufactorer of the power package up and down, when in fact the breakdown is due to wiring in the "boat" that has little to do with the engine. And Merc knows this.
Merc does not choose and install ignition switches (key switches) in boats. (except of course for the product lines Brunswick produces).
The only thing the slave solenoid does is make starting the boat more reliable.

Just like the kids song "the leg bone is connected to the knee bone"....

This is how it works.

You start with 12+VDC at the battery.

12+VDC runs up a small gauge wire (usually 14-16AWG) from the engine up to the helm... to the keyswitch (this wire is run by the boat builder)

A wire then runs back from the keyswitch to the slave solenoids IGN terminal.(a wire installed by the builder to)

The slave solenoid is usually internally grounded to the block itself, without an external wire. Some however do use a wire on the GND terminal that runs to the block.

Another wire, coming out of the "Engine side" harness connects to the main input side of the slave solenoid. (that wire is put there by Merc)

On the output side of the slave solenoid there is another wire in the harness (again from Merc) that runs from the output side of the slave to the START terminal on the main starter solenoid. This wire is usually a bit heavier at 10 or 12 AWG.

So when you turn the keyswitch, the keyswitch activates the slave solenoid, which passes power along to the starter solenoids START wire.... not the main power wire.
And that is all there is to it.

If you ask why it sounds redundant... here is why.

with DC electric systems.... especially in low voltage systems such as a 12VDC system. The entire system is suspectable to voltage drops.

Anything from a rotted wire, to a bad crimp or connecter, to rusted terminals acts as a giant resistor and eats up voltage.

(i always get crucified on this next part)

When voltage drops, demand for current goes up. Current... not voltage... is what fry's keyswitches, solenoids, starters, and the wires themselves.

Voltage drops do naturally occur over long runs of wire to. Especially if the wire is thin and does not have many strands to it. The less inductive a wire is... the more the voltage drop will be over a given length of wire.

If you take a starter motor solenoid, just the solenoid and not the starter itself. It does take a few amps of current to kick out and hold out that bendix gear.
It's designed to work on 12+VDC.

Now if you have 25ft of power wire to the keyswitch, and 25ft back to the starter. Your talking about 50ft of 16 gauge that needs to carry 5 or 6 amps... it's not going to work for very long.

Now if your using that same 50ft of wire to power a slave solenoid. To get the slave to click it only takes a couple of milliamps.... and it will work just fine on less than 12+VDC. (although even slaves have a minimum voltage threshhold.... but it's much lower than a starter) There is less current traveling up and down the wiring in the boat, and less current going through the keyswitch. The wireing, and the switch last a lot longer.

Why is this so complicated

Haha... i know what you mean.

hopefully this uncomplicates it for a few people.

 

[JustJason]

Re: Point of having 2 solinoids on engine?

Dam Don ya beat me to it.... it took longer for me to type than it took for you to post a pic. I need to get cracking on my pic's more often.

 

[dan t.]

Re: Point of having 2 solinoids on engine?

good wiring diagram Don, very obvious how it works.