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Thread: Inverter for AC powered backup sump?

  1. #1
    DIY Member RinconVTR's Avatar
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    Default Inverter for AC powered backup sump?

    We have a VERY active sump during peak times and estimated water flow exiting the 3/4hp Simmer far exceeds what the battery back up pump can handle. (Estimated at 3000gph at peak using simple pit volume and time calculations) So I want to install a more powerful backup pump, which brings me to AC powered pumps or water power pumps.

    I am not a fan of the water powered pumps, so I see inverted DC power from 2-3 batteries to power a separate AC backup pump as a practical and very reliable solution. There are RV type inverters with built in chargers that would seem perfect. Also, the AC pump would obviously have its own float, which I would set just above the primary high float level which would kick on the backup for any reason the water exceeds the primary float level, automatically. No manual effort.

    This system would replace the current Basement watchdog set up, so I would lose the nice alarms. But as long as there is AC power, the backup would forever have power from the inverter and built in charger. Finding an alarm for the backup pump is a small issue, IMO.


    Comments?

  2. #2
    DIY Member RinconVTR's Avatar
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    Another idea is to keep the Basement watchdog and add a water powered backup. I'd tie the Watchdog in to the main discharge, and use the backup discharge for the water powered pump. Together, they would keep the sump pit from over flowing during peak demand, plus I'd keep all the alarms built into the Watchdog.

  3. #3
    DIY Senior Member CarlH's Avatar
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    Personally I would avoid an inverter if possible. There are efficiency losses from the inverter as well as needing to size the inverter large enough to handle the start up current needed by the pump motor. Without doing any research and throwing and a SWAG, I would say that an inverter for this purpose would be expensive enough to make you consider other options. IMHO if you are going with a battery backup, it is best to stick with a DC pump.

    Also, you might try a different method to determine you peak volume. You should be able to estimate your pump volume using the specs for your pump and the actual rise. When you are at peak volume, time how long you pump runs in a minute. You might do this over several minutes rather than a timing in a single minute and then do the math.

    The other thing to consider with the battery backup is how long it will keep the pump running during a power outage. This alone may make you consider adding the water powered backup.

  4. #4
    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by CarlH View Post
    Personally I would avoid an inverter if possible. There are efficiency losses from the inverter as well as needing to size the inverter large enough to handle the start up current needed by the pump motor. Without doing any research and throwing and a SWAG, I would say that an inverter for this purpose would be expensive enough to make you consider other options. IMHO if you are going with a battery backup, it is best to stick with a DC pump.

    Also, you might try a different method to determine you peak volume. You should be able to estimate your pump volume using the specs for your pump and the actual rise. When you are at peak volume, time how long you pump runs in a minute. You might do this over several minutes rather than a timing in a single minute and then do the math.

    The other thing to consider with the battery backup is how long it will keep the pump running during a power outage. This alone may make you consider adding the water powered backup.
    Thanks for the reply, your thoughts about the inverter are spot on. An A/C pump with 2 large batteries would only last 8 hours at best and cost would be equal to a high flow water powered pump.

    A note about my peak demand, the 3/4 HP Simmer pump I have says it pumps 4100 GPH, but thats just a spec. My calculations were done on a repeated basis, not just once over a period of a few minutes. The pump at peak ran every 12 seconds for more than an hour, and thats with a Hi-Low electronic switch installed giving me more depth to pump vs using the OEM switch. 3000 GPH is a rounded up number that I feel I need to match just for peace of mind.

    Regarding the water powered pump, I am going to install one this Fall when things are dry. With the battery back up and the water powered pump, I will feel really good about leaving the house for long periods of time during the spring and summer.

    FYI - for those shopping for a water powered sump pump I found two high volume water pump manufactures. One clearly stands out as being better and its made in America. Its called the Water Cannon and their web site is www.tanecorp.com and the other option is called basepump. The water cannon is better built and has better specs over the basepump. I will post pics and such when I get it installed.
    Last edited by RinconVTR; 08-09-2010 at 02:17 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    why not just connect those "2 or 3 batteries" to the DC powered pump. ITS charger should keep the batteries fully charged, and an alarm is a simple addition if yours does not already have one. I can visualize a 3/4 hp AC pump draining the batteries very quickly.

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    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by hj View Post
    why not just connect those "2 or 3 batteries" to the DC powered pump. ITS charger should keep the batteries fully charged, and an alarm is a simple addition if yours does not already have one. I can visualize a 3/4 hp AC pump draining the batteries very quickly.
    I cannot find any DC pumps with capacity at or near 3000 GPH (the peak flow rate I want to match when the power goes out) and that would last more than 8 hours on 2-3 batteries. I think the draw of such a pump would be nearly the same as the small backup(not my main 3/4 HP pump) AC pump driven by an inverter and the same two batteries.

    On that note, there are some DC systems I found using dual DC pumps that work with their $2500+ system cost! (obviously, I dont consider that an option)

  7. #7
    DIY Senior Member CarlH's Avatar
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    It does sound like you have a lot of water coming in. I know you are asking about pump advice, but I'm going to throw out some other suggestions. Have you considered trying to improve the situation from the outside? Things like extending downspouts farther from the house, and extending the sump discharge line. Landscaping improvements. Overhangs to reduce rainwater collection in welled exits, etc.

    Next time you at one of those peak conditions, test you current backup system. Pull the plug on your primary pump and see how the battery power solution performs. Use the results of that experiment to determine how it holds up and if you really need a higher capacity backup. I think this would be the true test to see how you stand with a battery backup setup. You might need to add more batteries for your desired run time.

    No personal experience with them, but it seems that Simer pumps don't have the best track record. From what I can tell, they were due to switch failures. As long as your upgrade is a reliable switch, you may have made major improvement by not using the Simer switch. Even so, you might want to have a spare for your primary pump on hand. Something like the Zoeller N98 might be better option. It is 1/2HP, and nearly same capacity as your 3/4HP Simer.

    Another thing you can do is to get out your pencil, paper, and calculator to determine how much water is discharged with each cycle of the pump based upon the calculated volume of water using the diameter of the sump and the difference between the pump on and pump off height of the water. You'll have to look up the formulas. Or you could bucket fill the sump to see how much is pumped with each cycle. Add enough water to get it to cycle once, and then start filling and keeping track of how much water you need to add to get it to cycle. This with the shortest cycle interval will give you your actual flow rate. To use the rated flow rate of the pump to estimate the actual flow rate you would need to know how much time the pump is on during a specific time period. The on time divided by the off time will determine the percentage of the rated output the pump is pumping. That assumes the factory numbers are accurate.

  8. #8
    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by CarlH View Post
    It does sound like you have a lot of water coming in. I know you are asking about pump advice, but I'm going to throw out some other suggestions. Have you considered trying to improve the situation from the outside? Things like extending downspouts farther from the house, and extending the sump discharge line. Landscaping improvements. Overhangs to reduce rainwater collection in welled exits, etc.

    Next time you at one of those peak conditions, test you current backup system. Pull the plug on your primary pump and see how the battery power solution performs. Use the results of that experiment to determine how it holds up and if you really need a higher capacity backup. I think this would be the true test to see how you stand with a battery backup setup. You might need to add more batteries for your desired run time.

    No personal experience with them, but it seems that Simer pumps don't have the best track record. From what I can tell, they were due to switch failures. As long as your upgrade is a reliable switch, you may have made major improvement by not using the Simer switch. Even so, you might want to have a spare for your primary pump on hand. Something like the Zoeller N98 might be better option. It is 1/2HP, and nearly same capacity as your 3/4HP Simer.

    Another thing you can do is to get out your pencil, paper, and calculator to determine how much water is discharged with each cycle of the pump based upon the calculated volume of water using the diameter of the sump and the difference between the pump on and pump off height of the water. You'll have to look up the formulas. Or you could bucket fill the sump to see how much is pumped with each cycle. Add enough water to get it to cycle once, and then start filling and keeping track of how much water you need to add to get it to cycle. This with the shortest cycle interval will give you your actual flow rate. To use the rated flow rate of the pump to estimate the actual flow rate you would need to know how much time the pump is on during a specific time period. The on time divided by the off time will determine the percentage of the rated output the pump is pumping. That assumes the factory numbers are accurate.
    Thanks a lot for the additional advice, it was however nearly the exact steps I took before arriving at my status today. The outside is graded well, if not over done. I have only 1 downspout that drains more than 10ft from the house, the others along with the sump discharge actually discharge at the end of my lot via underground PVC pipe.

    I do have a back up main pump on stand by but it is another Simmer, a 1/2 HP version. Their switches (also under the Flotec name) are absolutly GARBAGE! You're right!!!

    The battery backup has not been tested at peak because I tested it during a few mild flow times and all it did was hold the level steady, running non-stop during the 20-30 minute tests. In all honestly, I didnt test exactly how long it would run, I didnt think I needed to knowing it was working hard just holding a steady level during the "mild" tests.

    In short, I think I am very well set up for every possible emergency situation except when I would be out of town and I've taken every step possible trying to find possible causes for the extreme flow at "peak" times. And its this peak time situation that I want to over come. With the combination of the battery back up and a water powered pump installed (probably in Fall) I will exceed any peak flow I can estimate.


    Edit: I read some concerns about water use and cost, and I used an extreme example of the water powered pump running non-stop for 10 hours @ 15 GPM. Milwaukee water cost on average is $3 per 1000 gallons, which is very near the national average.

    10 hours = 600 minutes.

    600 minutes @ 15 gallons per minute = 9000 gallons

    9000 gallons at $3 per 1000 = $27

    $27 (max) for peace of mind during a very rare emergency? Sign me up.
    Last edited by RinconVTR; 08-10-2010 at 07:59 AM.

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  10. #10
    General Engineering Contractor ballvalve's Avatar
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    At 3000 GPH I would fill in the basement with dirt and build a garage for storage. Probably pay for the garage in electricity cost in a few years. Or at least build a nice pond and get some ducks and geese to help pay for that burden of a basement. Sorry for the dark advice, but that is a crazy cross to bear.

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    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by ballvalve View Post
    At 3000 GPH I would fill in the basement with dirt and build a garage for storage. Probably pay for the garage in electricity cost in a few years. Or at least build a nice pond and get some ducks and geese to help pay for that burden of a basement. Sorry for the dark advice, but that is a crazy cross to bear.
    Again note I'm rounding up and being liberal with my numbers for the sake of keeping up during peak demand (typically 4-8 hours at most) and no power. The common flow rate I see is very similar to running two garden hoses into the pit around 35gpm or 2100 GPH (which I could simulate by borrowing the neighbors hose! hmmmmm), and that flow rate is actually reflected in the video above. I dont have the highest calculated flow on video, but was calculated to be around 2500. I use 3000 as a liberal number to plan for worst possible case.

  12. #12

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    I saw your video of your sump pit. Although what you have is working, given the amount of water you are dealing with I think you should approach is differently. Cycling the pump like that wastes electricity because of the startup draw required by the motor and the short cycling generates heat and excessive wear on the pump.

    First I think you need a much bigger pit. Something like 3 feet by 5 feet. This will give the pump a longer cycle time. Next I would get a pump that is close to your normal flow rate as far as GPMs go. Ideally you would want it slightly under so it never shuts off. Then I'd get a second pump that can handle peak capacity. This pump would only cycle occasionally during normal whether to remove the excess water the first pump could not keep up with - maybe once every 10 minutes or possibly longer. During rainy weather it would run more, but your cycle times would still be longer that what you have now. You could also add a pump alternator and a 3rd pump to alternate between the second and 3rd pump buying you even longer cycle times and in the event any of the pumps failed you would still have enough pumping capacity to avoid a flood.

    As for power backup I'm not totally opposed to the ac inverter approach but I think its more expensive than you are figuring on. And there is some loss thru the inverter - between 5% and 15% - but you can take that into consideration when buying the batteries. Inverters aren't cheap though. Xantrex makes a 2400W modified sine inverter for about $1000 that switches between battery and utility power for you and charges the batteries. It is unlikely you will be able to go with a smaller inverter because of the startup power required for the pumps. The batteries will also be expensive. For each hour of 1000w of continuous power you would need 1 Triojan T105 battery at about $150. Four hours would set you back $600 if the pumps drew 1000w continuous. The pumps most likely draw less, but you would need to figure out how much less.

    Anyway just thought I'd share my thoughts on your problem.

    -rick
    Last edited by drick; 08-13-2010 at 08:29 PM.

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    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by drick View Post

    First I think you need a much bigger pit. Something like 3 feet by 5 feet. This will give the pump a longer cycle time. Next I would get a pump that is close to your normal flow rate as far as GPMs go. Ideally you would want it slightly under so it never shuts off. Then I'd get a second pump that can handle peak capacity. This pump would only cycle occasionally during normal whether to remove the excess water the first pump could not keep up with - maybe once every 10 minutes or possibly longer. During rainy weather it would run more, but your cycle times would still be longer that what you have now.
    -rick
    While I dont think its feasible to increase the size of my pit (a big job on any day, but also the pit is located within a small closet within a finshed basement and would require major work beyond the pit area itself!) however I do like the idea of adding a pump that matches "normal" flow and a second to help during peak demand. My only downfall would be space. I have looked at smaller pumps before, in effort to reduce electicdraw, but I found reducing the HP doesnt always equate to a good reduction in amp draw. The Simmer 3/4 draws about 7 amps, while their 1/2 HP still draws 6.

    Still, I will be looking into adding 2 small pumps to replace the single large one. I like this idea, a lot.

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    FWIW, 1hp=746.x W. My guess is those numbers are peak, not constant.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Engineer Furd's Avatar
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    746 watts is, by definition, one electrical horsepower. Since electric motors are not 100% efficient the electrical needs of any motor is in excess of the calculated electrical horsepower.

    For example, my table saw has a motor rated at 1-1/2 horsepower yet it draws 14.8 amperes at 115 volts for 1,702 watts. If it were 100% efficient it should be 1,119 watts using 746 watts per horsepower.

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