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Old 26 August 2011, 15:25   #1
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How much Battery Drain

Hi,
I have wired my bilge directly to my battery due to her being kept on a mooring, my question is how much battery drain will their be?

She has one of these small Rule 500 computerised bilge pumps and a small solar pannel attached to the battery but I am unsure how powerful (not very) battery is 85ah and fairly new.

Any advise would be much appreciated.
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Old 26 August 2011, 15:50   #2
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Hi and welcome to the forum. This pump draws around 2 amps. Given average lead acid battery efficiency you are likely to get around 30 hours or so from a reasonably fully charged condition. At 500 gallons per hour you'd be looking at shifting 15000 gallons of 'oggin or rainwater. Your solar panel will probably take up the slack on that in reality unless you have a very leaky boat IMHO.
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Old 26 August 2011, 16:05   #3
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The rule 500 will never pump 500gal/hr installed (or any other centrifugal pump for that matter). As soon as there is even 0.5m of head on it the output will drop to maybe 300gal/hr. 2m of head and you are likely down 200gal/hr. Both will depend on installation tubing type, length, etc.

2amp draw sounds about right though.
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Old 26 August 2011, 16:07   #4
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Thanks, so in basic terms she should be ok, I intend to get a bigger pannel later in the year, I dont want to paddle out and find a flat battery but had to do something to shift all the rain water, we get a lot of it down here.
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Old 26 August 2011, 16:16   #5
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Jack, I've known centrifugal pumps whack out 200 tons per hour! Admittedly not little fella's made of plastic.........
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Old 26 August 2011, 16:58   #6
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Hi I keep my Ron on a swing mooring. I changed back from a rulematic 1100 back not a basic pump and float switch. The former pulses every 5 secs of it feels resistance it pumps till it's dry and on and on! Where as the pump on works when water level actuates the float. I was
Going to the boat after 2weeks an the battery wad flat and the boat full
Since I change mo probs. I also fitted a 10 watt solar panel. Very pleased can go 5 weeks and all dry. Hope this helps.
Cheers
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Old 26 August 2011, 17:02   #7
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Courageous' numbers are a bit optimistic! If any rubbish gets in the pump strainer, or the output hose is not perfect size/kinked etc. In those cases, the pump continues to work at the same power but moves less liquid. Lets say it only actually moves 1/2 what you expect (I don't know how Rule pumps specs compare to reality), but the pumps I buy in my dayjob usually are optimistically named.

If you regularly let your battery discharge by as much as 30 hours at 2 A (ie. 60 Ah) on an 85 Ah battery it won't last long (especially if it is a normal battery rather than a deep cycle). Normal advice is not to discharge by more that 50%. Lets assume that your battery is 85% charged when it starts (after a long trip it might be more than this, but lets play safe). That means you have 35% of its capacity before you reach its limits. That is 30 Ah which at 2A for the pump is 15 hours of pumping.

So that is 3750 gallons. Assuming your boat is kept in Cornwall as per your profile, then the annual average rainfall is about 1m (bear in mind this is average so some years will be worse than others) and the worst months are about 0.12m. For simplicity lets assume your boat is rectangular 5m x 2.3m and so in a year will gather 11.5 m3 of rain. If you add in lets say 1 gal per day of spray or slight leaks coming aboard then you will have an annual total of about 3500 US Gallons of water coming on board!

So that says your battery, should manage about a whole year pumping out your boat. But there are a few other things to think about that will zap the battery:

(1) temperature. the battery works less efficiently at cold temps, but self discharges faster at high temp!
(2) the natural self discharge of the battery which will be about 40+% per annum at UK temps - so about 3-4% per month.
(3) the automatic sensor in your pump draws power even when off (compared to a float switch system which does not). It uses something like 1% of the rated current to check if there is any water to pump. So that is 0.02A which sounds tiny, but that is 0.48 Ah per day.

If you are lucky your solar panel will top up the losses. But you don't say which panel you are using and I expect you will be lucky to get an average of 0.1 Ah from small panels in typical UK sun unless you have an expensive panel and mount it at just the right angle etc. If your boat is only afloat in summer then you are getting over 150 hrs of sunshime a month, so probably about enough to make up for the losses above. But in the depths of winter you are getting 50 hrs a month of sunshine at best - and of course that corresponds to maximum rainfall too.

All together if it was me I wouldn't be leaving it without at least a quick run and checking the battery voltage for more than 4-6 wks during the summer; and probably wouldn't leave it for more than a couple of weeks in winter.
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Old 26 August 2011, 19:14   #8
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Jambo, I had the same problem in one of our hardboats, almost sank until we went back to a float switch and solved the problem.

Palwort, that is pretty in depth, I am going to use your methodology to work out the size of the solar panel I need if you don't mind.
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Old 26 August 2011, 19:21   #9
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Quote:
Originally Posted by Courageous View Post
Jack, I've known centrifugal pumps whack out 200 tons per hour! Admittedly not little fella's made of plastic.........
All bilge pump ratings are for zero head. As soon as they have to pump uphill (i.e. in any kind of real world installation) the output declines. Smooth bore hose helps as well as keeping the hose runs modest.

I would upsize the solar panel before worrying too much about pump size in a RIB. Its not like it can completely sink.
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Old 27 August 2011, 12:34   #10
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Ok, I have ordered a 10w solar panel, and intend to swap over the bilge pump for a "normal" pump. I never leave the boat for more than 2 weeks at a time so for the time being she should be ok. At the end of the season I will trail her to and from so I won't need to keep the bilge on all the time.
Thanks for the help.
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