MargeandParge Posted May 28 Share Posted May 28 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 Quote Link to comment Share on other sites More sharing options...
dom Posted May 28 Share Posted May 28 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? 1 Quote Link to comment Share on other sites More sharing options...
ExSurveyor Posted May 28 Share Posted May 28 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. 1 Quote Link to comment Share on other sites More sharing options...
Smoggy Posted May 28 Share Posted May 28 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. 1 Quote Link to comment Share on other sites More sharing options...
Turnoar Posted May 28 Share Posted May 28 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. 1 2 Quote Link to comment Share on other sites More sharing options...
Vaughan Posted May 28 Share Posted May 28 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. 5 Quote Link to comment Share on other sites More sharing options...
dom Posted May 28 Share Posted May 28 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. 1 Quote Link to comment Share on other sites More sharing options...
ExSurveyor Posted May 28 Share Posted May 28 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. 1 Quote Link to comment Share on other sites More sharing options...
dom Posted May 28 Share Posted May 28 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. Quote Link to comment Share on other sites More sharing options...
Islander Posted May 28 Share Posted May 28 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 1 Quote Link to comment Share on other sites More sharing options...
dom Posted May 28 Share Posted May 28 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. 1 Quote Link to comment Share on other sites More sharing options...
grendel Posted May 28 Share Posted May 28 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. 2 Quote Link to comment Share on other sites More sharing options...
Smoggy Posted May 28 Share Posted May 28 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. 2 Quote Link to comment Share on other sites More sharing options...
dom Posted May 28 Share Posted May 28 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. 2 Quote Link to comment Share on other sites More sharing options...
MargeandParge Posted May 28 Author Share Posted May 28 Thanks for all the replies looking to me like two pumps is the easiest and safest option. Kindest Regards Marge and Parge Quote Link to comment Share on other sites More sharing options...
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