Bow Thruster Battery Charging

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Baggy

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I'am thinking of adding a Bow Thruster with a dedicated battery to a 10mtr boat

To keep things simple, is their any reason not to charge the battery with just a 10/15 amp battery charger connected to a 375w inverter
 
There is no reason not to do so provided you remember to charge it enough that its always ready when needed - a simple and cheap alternative and fool proof way would be just to use a VSR off the house or engine bank to charge it whenever they are charging (alternator, shore power, solar etc)

A good quality one for marine use can be had for under £30 and then its just thin wiring between the two batteries (enough to handle the charge amps so unless you have a very big alternator probably only 4mm or at most 10mm wire not battery cable) and a very easy job to connect up
 
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Trident said:
There is no reason not to do so provided you remember to charge it enough that its always ready when needed - a simple and cheap alternative and fool proof way would be just to use a VSR off the house or engine bank to charge it whenever they are charging (alternator, shore power, solar etc)

A good quality one for marine use can be had for under £30 and then its just thin wiring between the two batteries (enough to handle the charge voltage so unless you have a very big alternator probably only 4mm or at most 10mm wire not battery cable) and a very easy job to connect up
Click to expand...

It needs to be a bit beefier than "thin" wiring! If the thruster is operated whilst the engine is running (a usual scenario) there could be a considerable current flowing in the wire from the alternator/main batteries.

A battery-to-battery charger would be a better idea.
 
"enough to handle the charge amps so unless you have a very big alternator probably only 4mm or at most 10mm wire not battery cable)"

As I said above - thin as opposed to heavy duty battery cable - the two examples I have of 4mm or 10mm would cover a 35 amp and 70 amp alternator respectively with say 10m of cabling to allow for an average sized boat (with under 3% voltage drop) - should have read charge amps though (now corrected)

A B2B charger is a good idea but much more expensive and if the OP is asking about plugging in a charger I assumed he's not looking to spend lots on a B2B charger
 
Thin wire can actually be a solution, if it's long enough and thin enough. It's an approach that's used industrially.
You have to do the maths and do it right.
Say you have 2 ohms of 10A cable, the bow battery would have to do all the real work, but the alternator would trickle charge it well enough.
If you don't take this approach, then when the bow battery gets old, the wiring needs to take the full wrath of the bow thruster.
Personally I think the B2B or A2B chargers are the tidiest solution, with stout buss bars a fair alternative.
 
Trident said:
"enough to handle the charge amps so unless you have a very big alternator probably only 4mm or at most 10mm wire not battery cable)"

As I said above - thin as opposed to heavy duty battery cable - the two examples I have of 4mm or 10mm would cover a 35 amp and 70 amp alternator respectively with say 10m of cabling to allow for an average sized boat (with under 3% voltage drop) - should have read charge amps though (now corrected)
Click to expand...

It's not simply the alternator output, it's the capability of the house bank or start battery to supply current. You recommended a VSR to supply current from the house or engine bank. My average-sized bowthruster takes a nominal 370A; it wouldn't surprise me if, in your suggestion, 100A or 200A could be drawn from the house/engine battery. 4mm or 10mm cable isn't big enough for that current.

Trident said:
A B2B charger is a good idea but much more expensive and if the OP is asking about plugging in a charger I assumed he's not looking to spend lots on a B2B charger
Click to expand...

You mentioned a VSR at under £30. Here's a battery-to-battery charger at under £30 which would do the job...

Votronic 12V StandBy Charger (Trickle Charger)

Edit: It's worth reminding the OP that if he decides to use a battery-to-battery charger, he needs to fuse the interconnecting cable at the bowthruster battery.
 
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Am I wrong in thinking that if the thruster battery can't handle the load and starts to try and take power from the house batteries or alternator, then either it will blow a fuse, designed to protect the wiring, or the VCR will switch off because the voltage has dropped below the threshold for "charging"?
 
Ian_Edwards said:
Am I wrong in thinking that if the thruster battery can't handle the load and starts to try and take power from the house batteries or alternator, then either it will blow a fuse, designed to protect the wiring, or the VCR will switch off because the voltage has dropped below the threshold for "charging"?
Click to expand...

If the engine's running, the VSR won't drop out. If anyone were to wire a supply from a VSR to the bowthruster with 4mm or 10mm cable as has been suggested, I'd hope they would have fused it in accordance with the wire size and so, yes, it would blow.
 
You are not wrong and a VSR is perfectly safe as I have said as it would blow a fuse if too much rampage was drawn . Obviously the Bow Thruster battery should be properly sized to run the thruster for anticipated use without running down . I have been running this set up for many years with no issues and never a fuse blown.
 
Ian_Edwards said:
Am I wrong in thinking that if the thruster battery can't handle the load and starts to try and take power from the house batteries or alternator, then either it will blow a fuse, designed to protect the wiring, or the VCR will switch off because the voltage has dropped below the threshold for "charging"?
Click to expand...
Probably.
The VSR won't switch of immediately.
The sizing of the fuse is not easy.
 
Yes, I understand the fuse blowing bit, but just as a hypothetical argument, if the VSR is installed next to the thruster battery, the the voltage drop along a long relatively thin cable, would would drop the voltage at the VCR and cause it to drop out, if the current was high, V= I x R and all that stuff.
This wouldn't be a sensible way to install a VCR, but I've seen a lot of not very sensible wiring on a boat in my time.
I don't want to get into an "anchor" thread, just thinking, all be it slowly.
 
I would firstly suggest to the OP that instead of fitting a bow thruster battery that he invest in heavy wiing and run the thruster off the engine start battery. If he chooses to go separate battery then use a VSR as suggested or even low loss diodes. However almost certainly the voltage of the thruster battery will drop so large current will flow from alternator (if it is capable) and engine battery. Volt drop in thinner cables will limit this contributory current which will on the one hand perhaps reduce thruster performance or on the other hand be a good thing to reduce current through VSR/diode. OP suggestion of a charger off an inverter is just going around in circles from DC to AC back to DC with inefficiencies at every step. ol'will
 
William_H said:
I would firstly suggest to the OP that instead of fitting a bow thruster battery that he invest in heavy wiing and run the thruster off the engine start battery. If he chooses to go separate battery then use a VSR as suggested or even low loss diodes. However almost certainly the voltage of the thruster battery will drop so large current will flow from alternator (if it is capable) and engine battery. Volt drop in thinner cables will limit this contributory current which will on the one hand perhaps reduce thruster performance or on the other hand be a good thing to reduce current through VSR/diode. OP suggestion of a charger off an inverter is just going around in circles from DC to AC back to DC with inefficiencies at every step. ol'will
Click to expand...

Wiring will have to be fairly heavy, I think that my bowthruster spec. mentions a max. current of around 330-360A. I'd need to check but think even 95mm2 cable would have a voltage drop of 6%-8% for a battery mounted 7.5-10m from the bowthruster. Fairly expensive as 20m 95mm2 cable must be close to £500.

I just had a quick look at my manual and it suggested at least 122mm2 for 7.5 - 10m distance.

PVB's suggestion of a £30 Votronic 12V StandBy Charger (Trickle Charger) would merit further consideration. You need lighter cable plus an extra battery but not that expensive. Certainly much cheaper than £500 for heavy cable (though untinned variety would be less than £500).

You also get some useful redundancy as there's an extra battery if the starter battery failed somewhere remote (though it would probably be less hassle to parallel the domestic bank temporarily).
 
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I'm just about to have a bow-thruster installed, so I'm very interested in hearing the various possibilities there might be.

I don't have strong views about it, but had come to the provisional conclusion that, despite the cost, running heavy cables was the solution that was (given my own circumstances and constraints) the most reliable, simple, effective and safe option.

One factor influencing me is the idea that with a bow battery and small cables, its either going to have to be a very big heavy battery (right where I don't want it), or I'll risk running out of power for the thruster when I might need it.

Mistroma said:
Wiring will have to be fairly heavy, I think that my bowthruster spec. mentions a max. current of around 330-360A. I'd need to check but think even 95mm2 cable would have a voltage drop of 6%-8% for a battery mounted 7.5-10m from the bowthruster. Fairly expensive as 20m 95mm2 cable must be close to £500.

I just had a quick look at my manual and it suggested at least 122mm2 for 7.5 - 10m distance.
Click to expand...

Interesting, as the manual for the bow-thruster I'm about to install suggests rather smaller cables than that. Nominal current draw for mine is 315A (about 10% lower than yours) and for 7m to 14m combined cable length Side-Power suggests a minimum 70mm2 cable, and recommends 95mm2.
 
LittleSister said:
I'm just about to have a bow-thruster installed, so I'm very interested in hearing the various possibilities there might be.

I don't have strong views about it, but had come to the provisional conclusion that, despite the cost, running heavy cables was the solution that was (given my own circumstances and constraints) the most reliable, simple, effective and safe option.

One factor influencing me is the idea that with a bow battery and small cables, its either going to have to be a very big heavy battery (right where I don't want it), or I'll risk running out of power for the thruster when I might need it.



Interesting, as the manual for the bow-thruster I'm about to install suggests rather smaller cables than that. Nominal current draw for mine is 315A (about 10% lower than yours) and for 7m to 14m combined cable length Side-Power suggests a minimum 70mm2 cable, and recommends 95mm2.
Click to expand...

I have just dug out the documentation for my MAxPower CT80 in case my memory had failed me.
Datasheet says 446A at 10.75V (4.79kW) Possible advertising people wanted to get close to claiming 5kW :D

Installation guide does say 360A and recommends 120mm2 cable for 15 - 20 m runs
It also says 95mm2 is OK for 10 - 15m runs (i.e. 5 - 7.5m from battery)

I guess that your figures aren't very different for 315A vs. 360A and less than 15m cable run.
 
Mistroma said:
I have just dug out the documentation for my MAxPower CT80 in case my memory had failed me.
Datasheet says 446A at 10.75V (4.79kW) Possible advertising people wanted to get close to claiming 5kW :D

Installation guide does say 360A and recommends 120mm2 cable for 15 - 20 m runs
It also says 95mm2 is OK for 10 - 15m runs (i.e. 5 - 7.5m from battery)

I guess that your figures aren't very different for 315A vs. 360A and less than 15m cable run.
Click to expand...

I've had another look, and despite the 315A 'Nominal Current Draw', the recommended fuse is ANL 250A. I read elsewhere that ANL fuses are 'medium blow' and 'around one second protection'. Presumably therefore the 315A is a momentary draw on e.g. start-up, and draw will fall to below 250A in sustained operation.
 
Baggy said:
I'am thinking of adding a Bow Thruster with a dedicated battery to a 10mtr boat

To keep things simple, is their any reason not to charge the battery with just a 10/15 amp battery charger connected to a 375w inverter
Click to expand...
Is there any particular reason you are considering a bow thruster in a 10 meter boat?
 
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