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Bow thruster with relay for charging ?


moiuk

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There seems to be a relay in the charging circuit for my bow thruster batteries, with the 12v line going up to the starter control panel.  

 

The charging circuit is wired into the starter battery/alternator.

 

Can anybody guess/or know how this is likely to be set up without me trying to follow all the wires back?

 

If it is responding to ignition on, then I would expect this to make sense so that the bow thruster batteries will charge when the engine is running, but this would also be bad because operating the bow thrusters will also draw some current from the starter batteries (especially if the bow thruster batteries are older and hold less charge than the starter battery).   If this is the case, then would it make more sense for the bow thruster charge to be connected to the domestic bank?

 

What would be the normal way of configuring it?

(I do not trust that it has been wired with very much thought).

Edited by moiuk
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had a further thought after posting, that the 12v signal wire could be connected to the bow thruster panel, and be charging when bow thruster is off and isolated when bow thruster is on. This would then make a lot of sense, but would require me knowing this so that I switch the thrusters off after use to allow them to charge ?

 

Anybody done this?

Edited by moiuk
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14 minutes ago, moiuk said:

There seems to be a relay in the charging circuit for my bow thruster batteries, with the 12v line going up to the starter control panel.  

 

The charging circuit is wired into the starter battery/alternator.

 

Can anybody guess/or know how this is likely to be set up without me trying to follow all the wires back?

 

If it is responding to ignition on, then I would expect this to make sense so that the bow thruster batteries will charge when the engine is running, but this would also be bad because operating the bow thrusters will also draw some current from the starter batteries (especially if the bow thruster batteries are older and hold less charge than the starter battery).   If this is the case, then would it make more sense for the bow thruster charge to be connected to the domestic bank?

 

What would be the normal way of configuring it?

(I do not trust that it has been wired with very much thought).

Presuming the BT batteries are in the bow and the alternator and engine battery are in the stern, the long run of relatively thin wire bow to stern (x2) helps to limit the maximum current that can be taken from the engine battery when the BT is being used.
 

Not an entirely elegant way of doing it, but seems fairly common.

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10 minutes ago, nicknorman said:

Presuming the BT batteries are in the bow and the alternator and engine battery are in the stern, the long run of relatively thin wire bow to stern (x2) helps to limit the maximum current that can be taken from the engine battery when the BT is being used.
 

Not an entirely elegant way of doing it, but seems fairly common.

Yes the bt batteries are in the bow and alternator is in the stern.

 

So, I don't need to worry about too much current flowing down the much thinner wires from the starter battery? Even when they have a higher capacity and voltage? 

 

10 minutes ago, nicknorman said:

Presuming the BT batteries are in the bow and the alternator and engine battery are in the stern, the long run of relatively thin wire bow to stern (x2) helps to limit the maximum current that can be taken from the engine battery when the BT is being used.
 

Not an entirely elegant way of doing it, but seems fairly common.

Not sure i understand the need for the relay in this case? Is there any need to isolate the bt bank from the starter battery when the engine is off?

Edited by moiuk
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20 minutes ago, Tracy D'arth said:

Relay energised from the D+ , warning light, connection. With relay closed bow battery connected to starter battery.

OR

VSR between bow and starter battery, the easiest way.

How can I check which of these it is?  Assuming I have understood what you mean, my relay is either a voltage sensitive one OR energised from the ignition panel being 'on.

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6 minutes ago, moiuk said:

Yes the bt batteries are in the bow and alternator is in the stern.

 

So, I don't need to worry about too much current flowing down the much thinner wires from the starter battery? Even when they have a higher capacity and voltage? 

 

Not sure i understand the need for the relay in this case? Is there any need to isolate the bt bank from the starter battery when the engine is off?

Take a moment to consider how long you operate the BT for. A few seconds every few hours. The starter battery is probably 110Ah so perhaps 50A for 5 seconds (0.07Ah) per usage isn’t going to make much of a dent even without that current mostly coming from the alternator. When the BT is not actually running, the BT battery voltage will be fairly close to the engine battery voltage and the current flowing will be proportional to the voltage difference divided by the resistance of the round -trip wiring. Ie not a lot

 

Regarding the relay I suppose it protects against a scenario of a lot of BT usage (and bearing in mind the slow recharge rate due to the wiring resistance) flattening the large BT batteries, following by stopping the engine. With the flat BT batteries in parallel with the starter battery, over time (over night or longer) the fairly modest current flowing from the engine battery into the BT batteries could accumulate to quite a lot of Ah and thus a low engine battery which could fail to start the engine.

7 minutes ago, moiuk said:

How can I check which of these it is?  Assuming I have understood what you mean, my relay is either a voltage sensitive one OR energised from the ignition panel being 'on.

VSR doesn’t have a control wire. It just has connections to the 2 batteries and a local 0v wire. Whereas a normal relay has an additional connection to switch it on or off (ie 4 connections). Plus it will likely have some markings or branding on it.

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10 minutes ago, moiuk said:

How can I check which of these it is?  Assuming I have understood what you mean, my relay is either a voltage sensitive one OR energised from the ignition panel being 'on.

No not the "ignition " but the warning lamp connection to the alternator D+ which is live only when the engine is running and charging the batteries. What type of relay is it? 2 big terminals, or 2 big and 2 small ones?

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How good to see somebody getting some actual help with a bowthruster rather than the forum 'elders' questioning the wisdom of the first time poster who asked for help with theirs earlier today.

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12 minutes ago, Tracy D'arth said:

No not the "ignition " but the warning lamp connection to the alternator D+ which is live only when the engine is running and charging the batteries. What type of relay is it? 2 big terminals, or 2 big and 2 small ones?

2 big and 2 small terminals.

 

Yes that makes more sense to have it tied to the alternator d+ so that it is only on when the alternator is charging.

18 minutes ago, nicknorman said:

Take a moment to consider how long you operate the BT for. A few seconds every few hours. The starter battery is probably 110Ah so perhaps 50A for 5 seconds (0.07Ah) per usage isn’t going to make much of a dent even without that current mostly coming from the alternator. When the BT is not actually running, the BT battery voltage will be fairly close to the engine battery voltage and the current flowing will be proportional to the voltage difference divided by the resistance of the round -trip wiring. Ie not a lot

 

Regarding the relay I suppose it protects against a scenario of a lot of BT usage (and bearing in mind the slow recharge rate due to the wiring resistance) flattening the large BT batteries, following by stopping the engine. With the flat BT batteries in parallel with the starter battery, over time (over night or longer) the fairly modest current flowing from the engine battery into the BT batteries could accumulate to quite a lot of Ah and thus a low engine battery which could fail to start the engine.

VSR doesn’t have a control wire. It just has connections to the 2 batteries and a local 0v wire. Whereas a normal relay has an additional connection to switch it on or off (ie 4 connections). Plus it will likely have some markings or branding on it.

with the relay, yes your explanation makes sense. My bt batteries are currently flat, so overjigyt I coukd have the issue that my starter would also be flat without it.

 

With the  current flow, my concern is that the lengthy cables are not rated for large current flows. This is more a concern for me than the draw from the connected starter battery.  It almost needs a second relay attached to the bt on/off control panel.

Edited by moiuk
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1 minute ago, moiuk said:

2 big and 2 small terminals.

 

Yes that makes more sense to have it tied to the alternator d+ so that it is only on when the alternator is charging.

So its an ordinary relay, you understand how it works to charge the batteries and how it isolates the bow batteries from the start battery now?

Can I help you further before I fall asleep?:closedeyes:

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7 minutes ago, Tracy D'arth said:

So its an ordinary relay, you understand how it works to charge the batteries and how it isolates the bow batteries from the start battery now?

Can I help you further before I fall asleep?:closedeyes:

yes I get this bit now, last concern is the potential current flow from the alternator powering the bt when the bt batteries are not able to?

 

Please feel free to sleep of course?

 

I should add, the reason why my bt batteries are empty is because the negative charge cable had been disconnected  from the starter battery and left lying loose on top for some reason?  Can't explain why somebody would have done that.  

Edited by moiuk
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Just now, moiuk said:

yes I get this bit now, last concern is the potential current flow from the alternator powering the bt when the bt batteries are not able to?

The alternator will supply what it can, the current to the bow will depend on the state of charge of the batteries and the volt drop in the long cable run there and back. The volt drop will be high with the thruster running. That is why you need batteries at the bow.

Its not a problem, you will not damage the alternator. If the batteries are too discharged the thruster will not run properly until they are charged.

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3 minutes ago, Tracy D'arth said:

The alternator will supply what it can, the current to the bow will depend on the state of charge of the batteries and the volt drop in the long cable run there and back. The volt drop will be high with the thruster running. That is why you need batteries at the bow.

Its not a problem, you will not damage the alternator. If the batteries are too discharged the thruster will not run properly until they are charged.

Thank you, concern aliviated. All should work safely.

 

This will also explain why the thrusters seemed to be working, but not really moving the boat. Hopefully with them getting good charge i will see a  noticeable difference in their ability to move the bow. Still confused why the charge cable was left disconnected....

Edited by moiuk
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I have a relay between my start and BT batteries (located at the bow) from the same alternator (or mains battery charger). Once the start battery is at 13.6v the relay switches the charge to the BT batteries and then once the charge reaches 13.6v at the BT batteries the relay switches the charge back to the start battery.

 

It's a good system because your start battery is generally fully charged anyway so most of the time the BT batteries are getting the charge. Also it means the domestic battery bank has its own dedicated alternator which isn't shared and so nothing is interfering with domestic battery charging.

Edited by blackrose
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1 hour ago, moiuk said:

This will also explain why the thrusters seemed to be working, but not really moving the boat. Hopefully with them getting good charge i will see a  noticeable difference in their ability to move the bow.

 

1 hour ago, The Happy Nomad said:

How good to see somebody getting some actual help with a bowthruster rather than the forum 'elders' questioning the wisdom of the first time poster who asked for help with theirs earlier today.

 

Except the OP is now in the situation where the bow thruster doesn't work because its dedicated batteries are flat, and there is too much volt drop in the charging line to power it directly from the start battery.

So this is the time where the forum 'elders' have a point. If the OP can steer his boat without needing to use the bowthrusters (much), then he won't be dependent on what is always going to be a less than satisfactory charging setup.

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7 hours ago, David Mack said:

 

So this is the time where the forum 'elders' have a point.

Put simply no.

 

They are seeking help. No lectures about 'you should be able to steer without one' are required when they probably already know that.

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8 hours ago, David Mack said:

 

 

Except the OP is now in the situation where the bow thruster doesn't work because its dedicated batteries are flat, and there is too much volt drop in the charging line to power it directly from the start battery.

So this is the time where the forum 'elders' have a point. If the OP can steer his boat without needing to use the bowthrusters (much), then he won't be dependent on what is always going to be a less than satisfactory charging setup.

Trying to run bow thrusters from the engine start battery at the opposite end of the boat is never going to work unless the cables are massive, the volt drop is simply too great.

But with sensible size cables the bow batteries will receive a sufficient charge to fully charge the batteries.

Volt drop is directly proportional to current, so a lower, charging only, current incurs a lot less volt drop than there would be with the large running current of the bow thruster.

This is why there has to be batteries in the bow in the first place.

 

The bow batteries frequently suffer due to being neglected and too deeply discharged by over use of the bow thruster without them receiving a full recharge.

The steerer maneuvers the boat into a mooring with the bow thruster, and stops the engine. This leaves the bow batteries partially discharged, possibly for a long time, a sure fire way of sulfating lead acid batteries.

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13 minutes ago, Tracy D'arth said:

The steerer maneuvers the boat into a mooring with the bow thruster, and stops the engine. This leaves the bow batteries partially discharged, possibly for a long time, a sure fire way of sulfating lead acid batteries.

An extremely pertinent point.

Maybe the recommendation should be "run the engine for at least one-hour after the last use of the BT"

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3 minutes ago, Alan de Enfield said:

An extremely pertinent point.

Maybe the recommendation should be "run the engine for at least one-hour after the last use of the BT"

Indeed, or even consider at the outset fitting one of the , admittedly more expensive, hydraulic systems?

 

Howard

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40 minutes ago, Tracy D'arth said:

The steerer maneuvers the boat into a mooring with the bow thruster, and stops the engine. This leaves the bow batteries partially discharged, possibly for a long time, a sure fire way of sulfating lead acid batteries.

Clearly this is a potential issue, however in reality it is often the case that a boat being manoeuvred into an awkward berth at a marina, will subsequently be plugged into shore power. Provided the boat is reasonably well equipped and set up, the built in charger (Combi or whatever) will then charge the BT batteries...
Provided the BT charge isolation relay is a VSR! (which we know isn’t the case for the OP).
 

A boat being moored on the towpath really doesn’t require a BT to be operated.

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10 hours ago, moiuk said:

This will also explain why the thrusters seemed to be working, but not really moving the boat.

Not necessarily. There could be leaves, plastic bags and crud blocking things up for example. The bow thruster will still whine, but little thrust generated. The shear pin that protects the thruster if the prop gets jammed could have been broken. Again, motor noise, but no thrust.

Jen

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10 hours ago, moiuk said:

Thank you, concern aliviated. All should work safely.

 

This will also explain why the thrusters seemed to be working, but not really moving the boat. Hopefully with them getting good charge i will see a  noticeable difference in their ability to move the bow. Still confused why the charge cable was left disconnected....

Get the BT batteries' fully charged by an external source, before relying on the alternator charging.  This will be much quicker, and enable you to check the condition of the batteries.  The combination of large capacity batteries and thin charging cables, and a surprisingly low alternator output, (think 5-10 amp rather than the 50-90 amp alternator rating) then you may require in excess of 60 hours engine run time.

 

Bod.

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4 minutes ago, Alan de Enfield said:

Try telling that to tow-path moorers.

For some it seems to be the only way they can 'get off' the the side.

Yes but that is on leaving the mooring (after which lots of engine running) rather than arriving (after which many hours of no engine running).

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