Bilge Pump

[MargeandParge]

A Numpty question from me.

Just about to rewire our bilge pump directly to a battery bank. " which one domestic or engine ?:.

Kindest Regards Marge and Parge 

[dom]

It's far from a numpty question. It's a bit of a perpetual debate, with no definitive answer.

Do you have a mooring wth shore power? And is there a float charger on either/both banks?

[ExSurveyor]

I would tend to go for the domestic bank as it is usually larger.

My primary one is on the domestic bank, I have a second backup pump, set slightly higher, this is wired to the engine battery. Belt and braces. I am also on shore power with a decent charging system.

[Smoggy]

The bank with the biggest capacity so it will keep going longer when you're not there seems a no brainer to me, fused of course and before isolators.

[Turnoar]

Based on the amount of rain we seem to be getting I would fit another bilge pump and wire one to domestic and one to engine. Best regards Noah.

[Vaughan]

Sorry, but I disagree with comments so far.

The bilge pump should be connected to the starter battery as, in theory, this battery is fully charged at all times. Just as it would be in your car.

If you connect it to the domestics and the fridge then runs the batteries flat in the night, then it also kills the bilge pump.

In fact, these small submersible bilge pumps take a very small amount of current and can run for 24 hours without hurting the batteries.

The bilge pump should also be wired so as to by-pass the battery master switch. 

[dom]

12 minutes ago, ExSurveyor said:

I would tend to go for the domestic bank as it is usually larger.

That tends to be the best option in many cases, and the batteries generally have better deep cycle resistance than the engine battery.

The flip side is, left for longer periods, you're going to kill more batteries with most domestic banks if the pump runs the batteries too low.

The "best" option is on any bank with support from a mains charger, or solar panel. With a 100w solar panel, simplistically speaking, you'll add roughly two hours pump running for an hour of sunlight.

 

[ExSurveyor]

4 minutes ago, dom said:

The flip side is, left for longer periods, you're going to kill more batteries with most domestic banks if the pump runs the batteries too low.

A small price to keep the boat afloat for longer though.

[dom]

Excuse the hasty sketch, but can anyone with an electrical understanding see why this isn't feasible?

You'd probably want to use germanium diodes or whatever the latest option is these days to minimise drop.

[Islander]

Schottky diodes would be better with a lower forward voltage drop. Often found on solar suppliers. If you want to spend lots of money an fet charge splitter would probable do a nice job as it will have virtually no loss.

Personally we use the traditional technique of using the engine battery.

Colin 

[dom]

17 minutes ago, Islander said:

Schottky diodes would be better with a lower forward voltage drop.

I may well be over-thinking the drop and in reality, it'd probably only lose you a short amount of running time.

Just seems like such an elegant solution to me. Ordinarily, it'll draw from the higher voltage bank, or share the load across both. In a critical situation, it'll use all the capacity in both banks.

 

[grendel]

starter battery as it is the one on a 50W solar panel (both batteries are also charged when on shore power), so the solar is a backup should the shore power run out of credit, or get unplugged.

as its a monocrystaline solar panel, I have seen it start charging at 5.30am on a dull day, which was exactly why I got that one, also when moored up and not on shore power I see the starter battery at 14.1 volts- ie float charging.

[Smoggy]

I have the double diode trick between my engine accessory feeds to a relay so whichever is turned on the engine bay fan runs and depth sounder fires up.

It's a good idea for bilge pump.

[dom]

14 minutes ago, Smoggy said:

I have the double diode trick between my engine accessory feeds to a relay so whichever is turned on the engine bay fan runs and depth sounder fires up.

It's a good idea for bilge pump.

Seems well worth trying - having all your battery capacity available for the pump in the worst case scenario can only be a good thing.

The only thing I'd probably do after connecting it all up is to pull each fuse in turn and bridge it with an ammeter, just to confirm there's no residual drain.

[MargeandParge]

Thanks for all the replies looking to me like two pumps is the easiest and safest option. 

Kindest Regards Marge and Parge