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Help with sub-system - 12V bow thruster

alistair1537

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Dec 28, 2019
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Hi

So, I have a bow thruster fitted to the barge - powered by 12V battery in the bow - charged via the engine alternator...

I also have my water tank forward in the bow and I was wondering...Could I use the 12V battery of the Bow thruster to power the water pump? Obviously, yes - but I do not wish to run the engine to recharge the battery for the small amount of work a water pump requires - so, I'm thinking about a separate solar kit specifically to charge this battery. I see 100W kits for around 100 quid with the controller included. Are there any concerns about this setup i need to factor in? All help appreciated.

Cheers

Alistair
 
I see 100W kits for around 100 quid with the controller included. Are there any concerns about this setup i need to factor in? All help appreciated.

Those kits usually come with those cheap $5 PWM charge controllers. Get a separate panel and spend a bit more for a better MPPT charge controller. The Victrons are pricey, but are made for the marine environment. What you want to do sounds like no problem, but answer Supervetch's question, and what your thruster and pump might draw and for how long, to see if 100w is not enough, or too much.
 
What battery chemistry? How large a battery bank is this?

SLA battery that came with the Barge - I imagine it's in the 100-150Ah range - also, I'm unsure as to what the designated use is - like a start or deep cycle, but I imagine with the duty cycle of bow thruster work it's rarely under too much stress?
 
Those kits usually come with those cheap $5 PWM charge controllers. Get a separate panel and spend a bit more for a better MPPT charge controller. The Victrons are pricey, but are made for the marine environment. What you want to do sounds like no problem, but answer Supervetch's question, and what your thruster and pump might draw and for how long, to see if 100w is not enough, or too much.

I don't mind the PWM controller, it's proven tech. I'm not looking for bang for buck here, the duty cycle will be low for the entire system - so price is the issue - Also, I'm not strictly "Marine" being in fresh water so that concern isn't a major factor? When I'm underway and the bow thruster is being used, normal engine charging will recharge, it's more of when I'm moored up, using the water pump for showers etc. that I will rely on the 100 watts to trickle the battery.
 
I've seen bow thrusters that use 650A, so I wouldn't conclude it's not under too much stress.

For perspective, a 150Ah battery will take 3-4 days of clear skies and dawn to dusk exposure to fully charge the battery from a 100W panel.
 
Look around the battery box in your engine bay & you may find a small DC-DC charger. If so, the bow battery is not charged directly by the alternator but as a slave from the engine starter battery. If that's not the case (such as on an older barge with a "split-charger") then you might want to consider making that upgrade first.
Then the power your pump takes out of the bow battery will be replenished from the engine battery even if the engine is not running so you won't excessively drain the bow battery between moves.
The other point is that with a DC-DC charger from the engine battery to the bow battery, if you want to fit any PVs, you should wire them to charge the engine battery (& it will look after the bow battery). That way you keep both batteries charged with a single PV system.
 
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