Bow Thruster and Similar switched electrics

[Genoa]

… I am replacing some snazzy electronic controls for a bow thruster and want to take an electric positive from the engine area that is live only when the engine is running. Where would you take it from?
this is not the 60amps to drive the thruster, but for a relay to ensure the engine is running before any action takes place?
please don’t say the starter button on the controls… that is to difficult to run a cable from.
engine bay preferably….
tia

 

[mjcoon]

You don't really mean "starter", but surely "power" or what would be called the ignition switch on a petrol engine. But strictly that does not guarantee that the engine is running; it might not start! So perhaps you want the generator/alternator output? Or follow the connection from the power-on switch to the engine bay and connect to that?

 

[Genoa]

You don't really mean "starter", but surely "power" or what would be called the ignition switch on a petrol engine. So perhaps you want the generator/alternator output? Or follow the connection from the power-on switch to the engine bay and connect to that?

that second half of this statement is exactly right. Alternator out is probably the right place. I have 2 alternators on one engine, is there a preference? The fisrt sentence though is a bit pedantic. I did mean starter button, eg the one that spins up the engine, but that would be wrong because it returns to ground when the engine is running.

 

[BabaYaga]

want to take an electric positive from the engine area that is live only when the engine is running. Where would you take it from?

I am controlling a relay (for parallel charging purpose) by a feed from alternator D+, which is the charging light circuit.
The relay only closes when the alternator begins to generate power, so I think that would be suitable.

 

[Stemar]

I am controlling a relay (for parallel charging purpose) by a feed from alternator D+, which is the charging light circuit.
The relay only closes when the alternator begins to generate power, so I think that would be suitable.

That's the one - it's how I did it on Jissel. Take the feed from the alternator terminal, the warning light (alternator side or anywhere in between that suits.

 

[Mister E]

What about using a split charge relay as used in campervans. Some of them are rated at over 100amps.
These will only supply power with the engine running.
The newer ones are voltage switching and connect to the starter battery.

 

[Genoa]

What about using a split charge relay as used in campervans. Some of them are rated at over 100amps.
These will only supply power with the engine running.
The newer ones are voltage switching and connect to the starter battery.

Not sure I understand how, if it is connected directly to the battery it is only live if the engine is running. Please educate me….

 

[Mister E]

Not sure I understand how, if it is connected directly to the battery it is only live if the engine is running. Please educate me….

It is voltage sensitive, sensing the higher charging voltage .

 

[Stemar]

Just a thought - is it a good idea to have the bow thruster controlled by whether or not the alternator's charging? An engine failure - or just a poor contact on the alternator - approaching a dock could put it out of commission just as you've lost the flow of water over the rudder as well. At least fit an override to give "last chance" manoeuvrability.

 

[BabaYaga]

It is voltage sensitive, sensing the higher charging voltage .

But what happens with the voltage level and how does the relay behave when the 60A thruster load comes on?

 

[Boathook]

But what happens with the voltage level and how does the relay behave when the 60A thruster load comes on?

I thought you had made a typo with 60 amps and see that it is what the OP quoted. I'm wondering what size BT it is as 60 amps seems very little.
I'm with Stemar and would like the BT to work regardless as to whether the engine is running.

 

[mjcoon]

Just a thought - is it a good idea to have the bow thruster controlled by whether or not the alternator's charging? An engine failure - or just a poor contact on the alternator - approaching a dock could put it out of commission just as you've lost the flow of water over the rudder as well. At least fit an override to give "last chance" manoeuvrability.

Only the only time I was given the job of parking a yacht with a thruster the conditions were very benign but I switched it on regardless. But by the time I felt I needed a burst it had quietly switched itself off due to lack of use...

 

[BabaYaga]

what size BT it is as 60 amps seems very little.

Agreed.
Just wanted to question the idea of using a VSR when a large current is drawn, as it seems likely that the voltage level will be affected.

 

[Mister E]

The voltage should only drop if the starter battery is not charged or the alternator is low power.

 

[BabaYaga]

The voltage should only drop if the starter battery is not charged or the alternator is low power.

I have no experience of using a BT, but from what I have seen it is often used in close quarter maneuvering, when engine RPM is rather low and alternator output likely also low.

 

[ean_p]

isn't the real question why you would want to unnecessarily complicate your system in this way? What meaningful advantage does it bring for you?