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Thread: I don't know my watts from my amps, help from those able please!

  1. #1
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    I don't know my watts from my amps, help from those able please!

    Okay, working on an article on keeping a water trough de-iced/ice free. Wanting to do it without plugging into the wall and increasing electric bill or creating a shock hazard.
    So, first thought, saw a you tube video on a guy that was aerating his pond using a 12 volt solar panel and a 12 volt bilge pump. He lets it shut down overnight and start on its own in the morning. Here it is. http://www.youtube.com/watch?v=AnqpDMzQcWo

    So, I can't let it shutdown at night because the amount of water is to small and it could freeze solid by morning. Thus I began thinking of a 12 volt battery charger, 12 volt battery of course and then the bilge pump.

    Here are the articles.
    Solar charger from Northern Tool - http://www.northerntool.com/shop/too...8565_200328565

    Bilge pump - http://www.ebay.com/itm/Marine-Boat-...f02880&vxp=mtr

    Battery - I currently have one somewhere. Not a deep cycle marine battery, but could purchase one if needed.


    Here is my problem. Because of freezing the whole trough overnight, I need to run off of the battery when the sun goes down or on cloudy days. With this current setup, am I drawing more from my battery than I am putting back? Every Saturday putting the 110v charger on the battery for a couple of hours wouldn't be bad, but I can't figure out if I am going to be doing a major overdraw on the battery (assume a typical car battery or deep cycle marine battery) If you need a specific cranking amp for this problem, tell me what size battery to purchase to make this operable.

    Okay, anyone, help?????????????? Thanks. Jon
    Jon

    God and family, the rest is icing on the cake. I'm so far behind, I think I'm in first place!

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  2. #2
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    jon, have you checked on how much electric you use with just a normal plugged in bilge? and they make heaters as well that claim to not use much electric?
    If in Doubt, Build it Stout!
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  3. #3
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    Only thing I can offer is this if it helps.
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  4. #4
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    Jonathan,
    A bilge pump of that size would run at least 48 hrs off a group 27 deep cycle marine battery,maybe more.With that solar panel you would have no problem and wouldn't have to use your battery charger .I'm not sure how a bilge pump would keep a watering tough from freezing.By the way on that ebay ad,they say 750 gph but are showing a 500 gph pump.
    Be nice to people on the way up,you'll see the same people on the way down.

  5. #5
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    The short answer to your question is NO, it won't work.

    P=I*E - Power (Watts) equals amperage times voltage.

    Your 2.2 amp 12 volt pump will draw 26.4 Watts, and your solar panel is only providing 15 Watts, so even on a sunny day you'd be drawing the extra 11.4 Watts from the battery.

    If you started with a fully charged battery, you might get an extra few hours of run time out of it, but not enough to be worth the $159.00 (plus tax and shipping) cost of the solar panel.
    Jim D.
    Adapt, Improvise, Overcome!

  6. #6
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    Jon, your answer is fairly complex and I will spend a little time coming up with an answer but it will depend on several things. the first one is the pump, how big a pump do you need. also the location you live in will have to be taken into consideration. you latitude and and longitude will effect the amount of daylight you receive in the winter on the average day in December. It may not require a large battery but should be one that is designed for frequent charging and discharging so an RV or marine battery might be a good choice. The panel in the movie is rated at 50 watts but that is on a good day. most of these panels are rated at a nominal 12 volts but they may put out 13 volts on a sunny day and 11 volts on a cloudy day. the rating is is watts a 50 watts panel like the one in the movie would produce roughly 4 amps at 12 volts since watts = Volts times amps. 50 Watts/12 Volts= 4 amps. If the pump was to draw 2 amps that would leave you with 2 amps to put back into the battery. Now that would work great any time after the vernal equinox until the autumnal equinox (thats summer time for you rednecks out there ) but not very good in the winter. According to a solar chart for Northwest Indiana you have about 9 hours of daylight in you area on December 20. In a perfect world that would mean that the batter would only have to run the pump for 13 hours and the solar panel would run the pump and charge the battery for 9 hours. So now all we have to do is increase the capacity of the solar panel to keep charge to battery and waalaa your in business You can do this by either getting another 50 watt panel and running it in parallel with the first one or getting a bigger one. Well it is almost that simple. This is a simple explaination as to how to do it. It would be nice to add in a charge rate regulator to make sure we charge to batteries properly I hope this has at least helped a little. BTW in a previous life I was an electrician on a submarine and although we didn't have solar panels we did have a lot of battery powered pumps etc.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
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  7. #7
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    Jim has it right for the base numbers. That solar panel only provides around 1.25 amps when its running full out. If you have any clouds or (worse according to a friend with solar panels locally) fog you can cut that by 30-60% during the "bright" part of the day and remember it only runs when the suns out so you ain't getting a whole lot of juice there.

    Some completely arbitrary math (that's close enough for estimating work):
    - you need 27 watts of continuous draw to run the pump (actually they say 2.2 amps and then 2.5 amps - so lets go with 30 watts just to be safer).
    - You should only drain a battery to around 60% (http://www.mpoweruk.com/performance.htm shows 80%, but I like a margin of safety and also you can see performance drops off horribly in cold weather, so there's that to. Lets go with 50% for more margin for lead acid and 75% for deep cycle)
    - You can get 35 amp hour lead acid batteries for somewhere in the $70-80 range or 200+ amp hour batteries for about twice that price (quick search found a 6v 224ah for $150 so you'd need two of those to get 224ah @ 12v - so the price/ah seems to be in the $1.5 - $2.0 range for standard commercial batteries).
    - so at 35 amp hours (decent car battery $70) you can run the pump for about 7 hours (35ah / 2.5amps * 50%) before recharging (14 hours and the battery is completely drained)
    - at 200 amp hours (2 deep cycle golf cart batteries around $300) you can run the pump for around 60 hours (200ah / 2.5amps * 0.75% its deep cycle so I'm giving it more slack, 80 hours and its completely drained).
    - The charger you have there will give you a peak of 15 watts when its sunny, picking an arbitrary day in Jan from the NREL PVWatts tool (which they appear bent on breaking grr) and doing a little math (which I won't bore you with because.. math) you get around 42-54 watts /day of power (depending on loss guestimates) or about 0.14 - 0.18 amps per hour.

    Put another way you need around 720 watts of power per day (2.5 amps * 12 volts * 24 hours) for that pump so working backwards that works out to something like 260 watts of solar array (figuring the 15 watt panel gave us 42 watts/day so we need 720/42 = 17.14 * as much charger * 15 watts = 257 watts of solar panel) to charge 2 * 6 volt deep cycle batteries (which gives you a day or so of buffer if there is a cloudy/foggy day). Yikes! That's getting into real money to even get close (quickly searching I found an RV kit for $1500 in that size range).

    The system that guy had is a 50 watt panel which should give you around 5-6 hours of runtime on the pump in the dead of winter. Looks like a panel setup like his goes for aorund $100 http://www.amazon.com/HQRP-Monocryst.../dp/B002WHUEKU

    Maybe something like one of these solar trough heaters would be more feasible:
    http://www.builditsolar.com/Projects.../SteveTank.htm
    http://www.builditsolar.com/Projects...rHorseTank.htm (v2)
    http://www.motherearthnews.com/diy/s...z10onzraw.aspx
    Looks like these guys sell premade versions as well: http://www.ranchtanks.com/


    Having used solar fence chargers in the same size I was curious about how they work. Turns out a 2 mile fence charger only takes 0.02amps, so there you go I guess.

  8. #8
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    Quote Originally Posted by Don Baer View Post
    According to a solar chart for Northwest Indiana you have about 9 hours of daylight in you area on December 20. In a perfect world that would mean that the batter would only have to run the pump for 13 hours and the solar panel would run the pump and charge the battery for 9 hours.
    Yeah unfortunately its not a perfect world.

    I used Jan 6th 1965 as a "sample" day (it looks vaguely close based on an eyeball scan of the pvwatts output for evansville indiana http://rredc.nrel.gov/solar/calculat...vansville.html (they only go up to 1977 in this version and the newer version with better data seems broken at the moment),

    For a 15 watts charger:
    1965, 1, 6, 08:00, 0.04
    1965, 1, 6, 09:00, 3.63,
    1965, 1, 6, 10:00, 4.31,
    1965, 1, 6, 11:00, 6.72
    1965, 1, 6, 12:00, 7.80
    1965, 1, 6, 13:00, 6.91
    1965, 1, 6, 14:00, 6.76
    1965, 1, 6, 15:00, 3.33
    1965, 1, 6, 16:00, 2.35,
    1965, 1, 6, 17:00, 0.14

    As you can see the actual power generated is pretty non linear throughout the day and we never actually even get to 15 watts (this is assuming a reasonable loss rate - assuming less loss the numbers look more like: ['0.05', '4.68', '5.56', '8.67', '10.07', '8.92', '8.72', '4.30', '3.04', '0.18'] - which is still leaves a pretty grim outlook price wise for doing something like this.

  9. #9
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    Quote Originally Posted by larry merlau View Post
    jon, have you checked on how much electric you use with just a normal plugged in bilge? and they make heaters as well that claim to not use much electric?
    My participants in my research are showing anything from $2.00 - $5.00 per day cost.
    Jon

    God and family, the rest is icing on the cake. I'm so far behind, I think I'm in first place!

    Host of the 2015 FAMILY WOODWORKING GATHERING

  10. #10
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    Quote Originally Posted by Ken Cook View Post
    Only thing I can offer is this if it helps.
    Thanks Ken, the difference is, with that system it isn't running 24 hours a day 7 days a week at a time. It runs and pumps water til the float valve sends the message that it is full so the pump shuts off and the batteries can recover. Is a cool system, actually have seen one in person.
    Jon

    God and family, the rest is icing on the cake. I'm so far behind, I think I'm in first place!

    Host of the 2015 FAMILY WOODWORKING GATHERING

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