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Old 26 May 2014, 14:51   #1
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Solar Panel vs Bilge Pump - any experience?

Hello all,

Does anyone have any experience running a bilge pump on auto for extended periods of time (up to 2-3 weeks), to pump rain water out, using a solar panel charger to keep the battery topped up?

My boat is in a marina and will be left alone a fair bit, but I want the battery to be good to go at all times, and I also want the boat to not be full of rain water! Yes, I will get a cover ASAP too

I guess there are several parameters to consider (especially if the boat has / doesn't have a cover!) - but does anyone know if one of these has a fighting chance without a cover?

Solar Powered 12V 2.4W Battery Trickle Charger | Maplin
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Old 26 May 2014, 16:28   #2
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Codprawn used to discuss this regularly. The simple answer was no.

A more complicated answer would be - it depends! How sunny it is, where you mount it, how much it rains, the type of autoswitch, the size of pump, the size of the battery, other loads that might drain the battery etc...
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Old 26 May 2014, 16:36   #3
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Codprawn used to discuss this regularly.

...
I shocked the life out of poor old Codders last week. I had a couple of pallets booked for collection with Speedshift. I had the 'Grand Fromage' from Speedshift call to run a couple of collection details by me. The guy had no clue who he was talking to. I stopped him mid sentence, and said "hang on, you're Codprawn aren't you?" Codders was almost speachless.
He soon got back into his stride and we had a good chinwag.
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Old 26 May 2014, 16:42   #4
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Thanks, that all sounds sensible.

Thinking about it, would the size of the pump matter? Wouldn't a pump twice the power remove the same amount of water in half the time, making the energy consumption the same?
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Old 26 May 2014, 16:51   #5
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Wouldn't a pump twice the power remove the same amount of water in half the time, making the energy consumption the same?
Broadly yes... but not all pumps are created equal!

e.g. Sahara Attwood pump:
500GPH claims 1.5 Amps
750GPH claims 2.8 Amps
1100GPH claim 4 Amps
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Old 27 May 2014, 04:47   #6
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For the solar powered pumping alongside in the marina then the lowest rating would put little strain on the battery but more than match any rain water. On the other side, you want the largest capacity for when you are at sea and if having 2 pumps is not really viable then go for that option. The pump is only using the battery a few times whereas the solar panel will put at least 4 hours of charge on average on it.
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Old 27 May 2014, 09:43   #7
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Drain man
No power required?
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Old 27 May 2014, 10:04   #8
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Don't work unless there is considerable motion. I've tried them in sheltered harbour


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Old 27 May 2014, 10:06   #9
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I've wondered about this after once accidentally knocking the bilge pump switch from "off" to "auto" when putting the cover on. On my boat the pump bypasses the isolator switch, so even with all other electrics off the pump will still work.

Of course bit of rain and next time I went to launch & turn the key nothing more than a dull clunk! very frustrating.

I did think of getting a solar panel connected to the battery, but that involved being able to mount it securely (but removably) and there being more sun to charge the battery than rain to drain it, and leaving the console hatch open.

I'm just very careful to check the switch is off before leaving the boat, and leave the trunks down.
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Old 27 May 2014, 12:02   #10
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Assuming you used the 750 gph attwood cited with a 2.8 amp draw. That's 33 W, so that little 2.4 W trickle charger would need to run for 14 mins for every minute of pump usage. That's assuming perfect efficiency and actual sun.

If you get a bigger solar panel it'll for sure work. I would guess its going to need to be large enough to be valuable and then subject to theft though. Something in the 10 to 15W size would only need 2 to 3 minutes of sun for every minute of pump usage and would be much more likely to work out all summer long.
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