Bowthruster battery charging

mrplastic

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I have decided to fit a Bowthruster and wonder if anyone is able to offer advice on the electrical supply. I currently have a factory fitted windlass which has sizeable cables running from the engine bay area directly to the windlass relay. I am wondering whether I can piggyback a suitable battery onto these cables for the bowthruster, maybe fit a battery to battery charger to maximise the charging to the new battery. It seems a simple solution but not sure if its workable!

Any thoughts?

Many thanks in advance

PS HAVE NOW READ EARLIER POST WHICH HAS ANSWERED MY QUESTIONS!
 
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jwilson

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I contemplated similar to give a (probably similar) factory-fitted cable-fed windlass it's own small starter type battery in the forepeak. A small one for weight. My windlass has been changed to run with engine off, it was originally set up to run only with engine on, but it's useful sometimes to run it without the engine.

I was just going to let the heavy cables feed a VSR to charge the battery when the engine was running (or on shorepower charger). Given the cable size there should be very little voltage drop at charging currents. Did the same in a big van a few years ago to charge a very large battery for lights/tools/inverter in the load space, and it seemed to work fine.
 

jwilson

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I contemplated similar to give a (probably similar) factory-fitted cable-fed windlass it's own small starter type battery in the forepeak. A small one for weight. My windlass has been changed to run with engine off, it was originally set up to run only with engine on, but it's useful sometimes to run it without the engine.

I was just going to let the heavy cables feed a VSR to charge the battery when the engine was running (or on shorepower charger). Given the cable size there should be very little voltage drop at charging currents. Did the same in a big van a few years ago to charge a very large battery for lights/tools/inverter in the load space, and it seemed to work fine.
 
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homer

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I fitted a battery in the bow for the bow thruster (about 85Ah starter type battery as I recall) and ran a light cable (about 1.5 mm2) from the house batteries which are in the stern. When the bow thruster is running, the resistance (and, hence, voltage drop) along the light cable is such that the current is limited to a couple of amps and so the cable is not overloaded. When the bow thruster is not running, the light cable trickle charges the bow thruster battery from the house batteries. After a couple of years (with no problems), I decided to fit a VSR into the charging cable so that the house batteries could not be discharged by the BT battery (not that they ever had been - just being cautious). MUCH cheaper set up than a DC to DC charger.
 

CLB

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I fitted a battery in the bow for the bow thruster (about 85Ah starter type battery as I recall) and ran a light cable (about 1.5 mm2) from the house batteries which are in the stern. When the bow thruster is running, the resistance (and, hence, voltage drop) along the light cable is such that the current is limited to a couple of amps and so the cable is not overloaded. When the bow thruster is not running, the light cable trickle charges the bow thruster battery from the house batteries. After a couple of years (with no problems), I decided to fit a VSR into the charging cable so that the house batteries could not be discharged by the BT battery (not that they ever had been - just being cautious). MUCH cheaper set up than a DC to DC charger.

But resistance equals heat. I would not be happy with your system. If the bow thruster battery became low, what's to stop large currents trying to get along the thin wire when you operate the bow thruster? Sounds like a fire risk to me,
 

mattnj

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I fitted a battery in the bow for the bow thruster (about 85Ah starter type battery as I recall) and ran a light cable (about 1.5 mm2) from the house batteries which are in the stern. When the bow thruster is running, the resistance (and, hence, voltage drop) along the light cable is such that the current is limited to a couple of amps and so the cable is not overloaded. When the bow thruster is not running, the light cable trickle charges the bow thruster battery from the house batteries. After a couple of years (with no problems), I decided to fit a VSR into the charging cable so that the house batteries could not be discharged by the BT battery (not that they ever had been - just being cautious). MUCH cheaper set up than a DC to DC charger.

That's a bad idea, nothing to stop lots of current going down the cable and bad things happening....you need to limit the current that cable can get....from memory take a look at an lm317 one of those and 2 resistors and you can limit the current electronically down that cable....then it's a good idea..
 

Aurai

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Should it help

I would be very happy to detail the set up I use, and was guided towards. Yes to forward battery, but wired in to Echo Max unit.

http://www.xantrex.com/power-products/power-accessories/auxiliary-battery-charger.aspx

protected by suitable Circuit Breaker and then wired back to midship House Batteries on "light" wires saving the cost of heavy duty battery cables, running half the length of your boat. Full spec on request.

I do understand that if you already have the heavy cables reaching forward, that it seems a shame to change them, mine were not high quality and scrap value offset some of the cost!

Thank you.
 
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My 'factory fitted' set up uses a 135Ah battery in the bow which serves both the windlass and the bow thruster. That battery is charged by the main engine alternator system with a third output from the splitter device that separates the starter and domestic charging circuits. When on shore-power, again a third outlet from the mains charger runs to the bow battery. All cables are significantly 'heavy duty'.

Incidentally, when I came to change that battery, I rather expected I would need a starter type - high current, short draw etc, but two independent major suppliers to the marine world both advised a leisure type. So that's the way I went and two years later, it doesn't seem to have been a bad choice.
 

Fendant

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I retrofitted a bow thruster and have a separate AGM 90Ah, which is kept up by a Sterling Bat-Bat charger.
Easy to install and all Batt's monitored via a Philippi BCM Battery Monitor.
I did not touch the windlass circuit which is connected to the 350 Ah house batteries.
 

homer

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What stops a large current going down the charging wire is the resistance of the wire itself. I did the calculations and it can never exceed a safe level. Of course it does dissipate a bit of heat but precious little and bear in mind that that is spread along the entire length of the 10 metres or so of wire. In practice, there is no dsicernible increase in temperature at all. Putting a fatter cable and a resistor in would concentrate all the heat in one place - a worse system in my view.
 

homer

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I should have mentioned that there is also a fuse in the circuit which would blow if the maximum safe current were exceeded - which it it is not.
 

lw395

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What stops a large current going down the charging wire is the resistance of the wire itself. I did the calculations and it can never exceed a safe level. Of course it does dissipate a bit of heat but precious little and bear in mind that that is spread along the entire length of the 10 metres or so of wire. In practice, there is no dsicernible increase in temperature at all. Putting a fatter cable and a resistor in would concentrate all the heat in one place - a worse system in my view.

I have not done the sums, but I expect you are right.
It might be nice to add a fuse, to cope with the fault conditions of a flat thruster battery?
Crossed posts :)
 
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