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Guest Post - Amps Times Volts Equals Watts
Amps Times Volts Equals Watts
By
Mrs. Cog
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It seems a bit backwards that we Cogs have spent this cold, snowy week immersed in learning about the pros and cons of solar energy. Too windy to cut wood and too wet and slippery to be outside except for chores, Cog began tackling the tricky issue of using a solar powered system as a backup power supply for our well. The devil is in the details he carefully explained. “Amps times volts equals watts.”
Gently teasing me about my status as a former urban princess, meaning one who expects to have things work at the flip of a switch and to pay someone to fix it when it breaks, Cog pointed out I came into this homesteading experience with little to no technical understanding of household systems. Electrical, plumbing and structural concepts were for the specialists, not homeowners who don’t even know that ‘amps times volts equals watts’.
Having relocated to our mountain in order to live a more self-sufficient lifestyle, it has not been lost on me that relying upon ourselves means becoming a generalist who can evaluate, design, build, and maintain many systems at a basic proficiency level. The learning curve has been steep and often comical as I have tackled becoming a gardener, cook, and herbalist. But these tasks have paled in comparison to the knowledge Cog teaches me about the modification and upkeep of our home. It has been particularly difficult for me to remember that amps times volts equal watts.
Why can’t I remember that? Amps are carefully considered when calculating the electrical surge needed to start an electric motor, a brief and sometimes very powerful draw of energy. Volts are kept in mind when powering the typical household device or appliance we use. We plug regular things into a 120 Volt outlet. The dryer, stove and well pump are each on a 240 Volt line, thus the funny plug on the appliance and the big clunky outlet it gets plugged into. I thought I finally understood it all since I had now scribbled it on a sticky: amps times volts equals watts.
So we simply needed to set up a solar collection system with enough watts to meet our goal, which in this case was to run the well pump. Although our well is shallower than others on the mountain it is still quite deep, nearly 250 feet down. Hand or simple electric suction pumps do not work at that depth. So during a long term power outage, when our backup generator runs out of propane, it would be wonderful to switch the well pump to solar energy for a sustainable water source. Easy-peasy because amps times volts equals watts.
As I asked more questions Cog vacillated between feelings of frustration and laughing out loud at my Star Trek impression of “Make it so Number One.” It seems that in my enthusiasm to find a quick and easy solution I managed to oversimplify the whole matter in much the same way people who are used to writing a check to pay the contractor often do when they don’t want their heads filled with details, but just want the damn thing to work. Still in the mindset I learned in Consumerism 101, Cog offered up “it’s not just about the watts honey.” No, it is! That’s what it says on my sticky: amps times volts equals watts!
It was during the back and forth with Cog as I continued my solar education that my talents as an expert word-maker-upper came into play. I discovered that the technical jargon could be altered to better describe the process or function, something which still makes us both laugh each time it is used. In this way we can smile over what was previously a dry and serious matter. In fact, the new lingo came about as Cog was showing me that while amps are all equal, some amps are more equal than others.
The exisitng very small solar setup.
To illustrate the problem Cog outlined this issue of amps as I grabbed a legal pad and began scribbling notes. The sun shines on the solar panels where energy is collected and funneled into batteries via a charge controller. The tricky part comes in converting that stored battery power to run a household electrical device. For that you need an inverter. Solar inverters are very touchy as to ‘watt’ quantity of amps you need to draw.
The motor in our well pump needs a swift kick of amps to get it started, a temporary surge if you will. Cog explained to me this electrical kick is called an “in rush” and he bought a pricey clamp meter to not only measure the current in a wire from the outside, but to measure the surge to start the pump. He was so funny, almost excited when the UPS guy brought his new toy. With this we would discover ‘which’ amps times volts equals watts.
As we tackled the measuring of the surge with Cog’s new “in rush meter thingy” we turned on various faucets to force the well pump to kick in. Move over Doc Brown because our well pump’s “in rush” of amps might as well have been 1.21 giga-watts after watching Cog’s reaction. For approximately 2/10ths of a second the pump required 57.5 amps to start the motor. Doing the math, 57.5 amps times 240 volts equals 13,800 watts. We’re gonna need a bigger flux capacitor.
Typical quality (and pricey) inverters provide around 4 to 5,000 watts of continuous power with maybe an 8 to 10,000 watt ‘surge’ capacity. So a quality inverter that could handle our well pump would be a seriously expensive upgrade. Thank goodness Cog is stubborn and continued making phone calls as he searched for answers to our new dilemma. He discovered a gadget called a “soft start” controller which basically stretched out the time of the initial energy surge required to start the motor, thereby reducing the amps needed all at once. I dubbed this the “in rush slower-downer.” Perhaps with this device we would need less amps times volts to equal fewer watts?
But alas, a subsequent conversation with an expert at the manufacturer of our well pump confirmed the well pump motor would not last long with the in rush slower-downer, aka the soft start controller, in place. The electronics and capacitors inside the ‘standard’ well pump motor require a massive jolt of amps to turn the motor over and overcome the water pressure already in the pipe running to the surface and onward to the house. Essentially it would quickly burn out the motor. With the solar collection system we were considering, sometimes there just aren’t enough amps <sigh>.
Cog did discover that the same company who manufacturers our well pump also offers deep well pump systems already set up for solar with a type of soft start device designed in. Unfortunately, the cost is on par with the flux capacitor inverter we would need for the 13,800 watt surge in our initial design. Watt to do, watt to do?
So, for the immediate future our backup water supply remains a clear babbling creek, inconveniently located several hundred feet down a steep and uneven logging road at the foot of our property on the edge of the mountain. While this actually helps comfort me in my process of emotional bargaining, consoling myself that we have alternatives in place should we need to actually become sustainably self-sufficient for a long period of time, we need to find a way to get our water to the top of our mountain. For now, the power to do that remains locked in the simple formula: amps times volts equals watts.
Mrs. Cog
11-27-2014
What's a watt?

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it's also assuming a short wire run, check a NEC table for the appropriate voltage drop.
Have you considered using a "ram"? My limited understanding tells me it will push up water to your cabin/home/off grid hideaway using the force of the brook/stream plus the ram itself. You may need to put in place a tank to hold some water but that may be less expensive than a more powerful inverter.
My neighbor tried using a ram to feed from a brook near his property. Nearly the same vertical lift I have of over 200 feet. In theory it will work. The cost and logistics are a bear. Try purchasing 600 feet of 2" plastic tubing plus tank plus pump plus associated pipes, fittings, couplings etc.
His problem was that when the rains came the nice little brook became a river and his pump and/or piping always washed away. He was fixing it two or three times a week. Plus the pipe, if it were to come up the logging road, would be even longer. If it were to head through the woods the shorter way there are some serious small cliffs and drop offs to overcome.
Just a thought ... by the way I do thoroughly enjoy your articles, thanks for writing/sharing.
Yes the wire size is right for a normal grid install, but when you are off grid, other methods can help.
Inrush current is a very common problem when off grid or even with generators supplying loads. It is money not well spent needing larger generator or inverter strictly to accomodate the inrush problem.
"It is money not well spent needing larger generator or inverter strictly to accommodate the inrush problem."
My feelings exactly and something I tried to explain to Mrs. Cog. That was when we got into the Amps Times Volts Equals Watts discussion. :-)
A very fine article, Mrs. Cog. Very fine...
Have you working on your Amateur Radio license yet?
Many thanks. :-)
I haven't yet tackled my HAM license with all our warmer weather projects this year. I have listened to some very interesting broadcasts from as far away as Uruguay on the short wave. We also recently acquired another older model pickup truck that came with a working CB installed.
Cogs
Amps and volts are inversely proportional. If your voltage is lower than normal you will pull more amps. Not having all the details is a disadvantage but the main reason for high starting amperage or inrush is due to starting up under a load and in your case it is water in the pipe. It might be impossible to have valves which would remove the head pressure so I suggest you look into installing some capacitors like you would see used to start an air conditioner compressor. They are inexpensive, easy to install but be careful as they pack a deadly kick. Read up on their use to start motors under load. Best.
I have a hunch that it'd be a bit cheaper and less headaches in the end to scrap the solar stuff. Thing is, if the whole damn system all goes south and they shut your electricity off, you might get a short while of use from that solar and you might not. If it goes on the blink, theres gonna be no delivery trucks running parts to you. No nternet to order them from, and no way short of actual barter to get anything you dont have stashed. And if you have enough stashed you better have a lots of weapons and ammo to keep onto it. I think a better investment would be a good education in how to live in a tent or on the go. Camp b the water and the food, etc.
Granted 57 amps is a lot for a starting capacitor, but did you consider going DC and putting a small battery in there?
A small Car battery will toss 300 Amps of DC starting current, and a smart controller will let you charge it and then
switch to using the power for feeding a inverter?
you still need the same inverter between the car battery and the burdened pump...DC to AC, pretty hefty transformer betwixt em and there's a difficulty in sustaining high AC amps from almost any dead DC source, not to mention the amp, watt and volatge loss that comes as that current spins about the coils and metamorphasizes to another phase...almost all solar feeds a DC car-battery complex to begin with. and even though 300 cold crankin amps is plenty if that pump were 12 volts, at 120 (and that's not factoring line/transformer loss)...well, do the math that Mrs. Cog provided and you'll see the difficulty. math is a bitch, patb.
in other words, tesla was a genius and edison was a salesman.
https://www.youtube.com/watch?v=OhEHB0a7Uyg
janus
um, that's why i said see if you can run the pump on DC, i don't know what's down there,a universal motor will
run DC as well as AC.
if it's a PV system charging a Battery.
PV -----> Charge Controller ----> battery pack 10 Lead Acid Auto Batteries doing 120 VDC ----> Pump
it's all DC, robust as heck.
Yup. If your gonna take out 13,800 watts at the back end in any combination of volts and amps for even a short length of time, you must put in 13,800 watts at the front end in any combination of volts and amps. Actually even more must go in the front end because of loss due to resistance and less than perfect conversion efficiency.
The math don't lie.
Something does not sound right. I have a 2.5 HP 240v single phase pump at 310 feet deep. It pumps 24 gal/min. While I'm getting ready to put a Godzilla sized inverter on it and run it off solar and battery backup - it has been run for 6 years on a cheap 8000w gas generator. At the time, I calculated 750 watts per HP times 2.5 then times two for surge = around 4000 watts. I bought the 8000W generator (10k surge) because it's the smallest gas generator that put out 240V. And it's been working flawlessly for years. I can fill my 5000gal tank in less than 3 hrs.
It doesn't make sense that your small pump requires such high current. I think you need a second opinion from someone else's clamp on current thingy. Those can be quite inaccurate unless you spend big bucks and even then I would be surprised if it was accurate measuring transients. My .02.
You will find that 750 watts per HP is not nearly enough for that pump motor, especially if it is a one phase and not three. Space and money restrictions make for inefficient designs. And the surge is 6-8 times run amps, not two. I"m not surprised the 8 kw genset runs the pump. It is the starting that is an issue, not the running. What size inverter are you going with?
If your well casing is 3" Grundfos might be your only quality choice. If 4" or greater there are other high quality submersible pumps available. We use rain water for the house and DC submersible for irrigation - the well pump is connected directly to PVs - when it sunny the cisterns are filled. Then a small pressure pump pushes the water to the greenhouse.
You need a larger capacitor above ground to start with your lower total available power(watts). And/or, you need a smaller output in-the-well pump which requires less starting input. Have you considered a storage tank above the house level which is filled by this lower output pump. Such water tanks are seen around most towns in the US. This way the pump is less expensive and needs less power as it slowly fills the tank, while the water pressure remains constant due to the height of the tank.
I am considering everything at this point. Money is always an issue.
Deep in the ol bag a tricks one might concider a wood gasifyer thingy. One 55 gallon drum and a twenty gallon with lid and stopper. It will run a genset well. Energy will matter a lot. That and a still as a set. Kinda covers a lot of bases.
I love this guy. Watch him all the time. Here is his gasifyer.
https://www.youtube.com/watch?v=yYGKn12Weu4&list=TLTDl-_YwJgUc
Yup Very studly. The truck is truly porta power. On ranch or wooded land very effective.
FWIW
I have a back up nat gas generator (GE 15kw). If we lose power it'll run half the house. The well required a 200 foot run out to the pump of a wire the size of a baby's arm.
If the generator fails (maybe no nat gas?) I have a Home Depot 'back up, back up' generator (thank you Burt Gummer) which does start the well pump. It is the Ridgid 10,000 starting Watts, 8,000 running Watts gas model. I tested it and feel certain that with our 5,000 gal holding tank, that at least we will die of thirst slowly.
See here about my Generac standby system.
http://twoicefloes.com/on-the-mountain/power-sources/standby-generator/
My backup to the backup to the backup is a portable generator.....but it is not of sufficient size to run the well pump. Regardless, I am trying to develop a system that will run on a self sustaining basis for months or years if need be. Generators require gas. Gas may become very expensive or very scarce. Or both.
its an uncomfortable thing to ask a man that just squeezed out his last tube of caulk, but....
Why the fuck didn't you just build the cabin next to the creek? Hillbillies hang thier hats down in the holler for a reason. Mostly thirst. Weld up a big ass wheel and start going by C.D. Miller.....
LOL
We did not built the place, but bought it from the man who built it 17 years ago. And we live on top of the mountain and the creek is on the side of the mountain accessible via a very steep and narrow logging road at least 200 feet in elevation lower than the house. Other than using a bulldozer to haul down building materials I have no idea how it would have been built down there other than spending $100k+ to build an all weather road to the creek.
But still, the very steep grade would mean you ain't going nowhere until the snow melts in the spring.
Pull the rope to start the generator. Pump a couple barrels of drinking water and fill the the tank for the livestock. Shut down the generator until it is needed again.
Much easier than investing in a complex system that will leave you mad and dry.
A generac propane generatpr might not be a bad idea to have to run your high inrush devices and for emergency power. In the distant past, I used a generator to get the pump started and then switched to an inverter for continuous use. The generac's are very reasonable in price too...
http://www.generac.com/
and one more equation for ya
$$$= volts x amps x time !!!
Hi Hulk,
Already did the Generac last year. The link to the write up with pictures is below. The alternative system we wish to install is for when the propane on hand runs out and the propane truck ain't coming unless we take out a second mortgage because all hydrocarbons have become very expensive after the petrodollar collapses.
Or something like that.
http://twoicefloes.com/on-the-mountain/power-sources/standby-generator/
Check out DC dynamotors too. I designed one up years ago and will dig up the parts list and schematic and get you a copy.
Well done CD !!! You just need to find that natural gas vein running under your property and you are set !!!
We live on the edge of the mountain. Literally the edge, with a cliff running along one property line and well over a quarter mile drop to the valley floor below. Interestingly there is a small hydroelectric plant down there which we can see when the leaves are down. Some day I shall rappel down there with a long extension cord and get me some free electricity. :-)
Here is the motor from the dynamotor
http://www.ebay.com/itm/Manta-2-10-hp-DC-motor-12-24-48-Volt-Etek-MT-Pat...
Here is the rappel kit!
http://www.attackopgear.com/Rappelling-Kits/ORS200.html
you will need a longer rappel rope though !!!
P.S. Going down is fun, getting back up is a real bitch !!!
LOL attack gear. This is how it starts... and before you know it, someone puts an eye out. Let's help keep Cog focused on the electrical please. ;-)
He started it !!!
Yeah....but you made me.
Big LOL here !!!
Look these up on ebay.... "Power Jack 6000w LF Pure Sine Wave Power Inverter", 24,000w peak for 10 seconds. Got one brand new at auction for $360, a magnitude of cost below others equivelant. Has a bunch of features that make it very attractive. Big inverters just idling consume significant amperage. This has a smart circuit that turns itself off if there is no draw and checks for draw automatically every 3 seconds with a very small draw circuit. If there is draw it turns itself back on. Chinese made, not fancy, been using it for about 6 months and am very happy with it. Even runs my small mig welder. Include schematics, parts list and has availability of parts if it needs repair.
You do need a battery bank which can be very expensive if you don't trouble to look for alternatives. About 80% of 'dead' vehicle batteries that are taken to recycling are recoverable and can last for many years if treated right. I spent several months researching and bought about $300 worth of power supplies and chargers and recovered 24 deep cycle batteries out of about 30 I tried for free. Near civilization you can get dead batteries for around $5 each at dumps or recyclers.
Cabling battery banks is also very expensive if you just go out and buy cables. The cables need to be heavy duty for the draw. I use AWG 2 size wire. For $100 you can get a chinese 16T hand hydraulic press for putting ends on battery cables and buy the connectors online to make the cables yourself. I managed to salvage enough wire off some old abandoned hoes to more than wire up my bank. Professional 20ft jumper cables are probably the cheapest way to buy this size of cable. Cut them up and put ends on them.
You also want some circuit breakers inline, all of which can be salvaged from derelict places.
With this inverter and 24 recovered batteries I can run everything in my house except for the hot water heater and dryer for about two weeks on a full charge. I cook with a small convection oven and/or induction cooktop, have half size fridge. Lasts about a week if I include my full size fridge and freezer.
The inverter has a 100a charger built in and can charge the bank in about 8 hours of running a 2kw generator. Eventually my system will be charged by micro hydro. Currently doing tests to see what I can get out of solar in my mostly wet/dark climate.
Lots of great ideas, thanks for sharing. Take it from and old sailor and mechanic, solder on your ends instead of crimping. If you use lots of flux it will draw the solder up into the cable and fill all voids in the connector so you will never have resistance issues between the cable and connector. Crrimp ends are great for quick repairs but be sure to use a liberal amount of dielectric compound between the cable and connector to prevent resistance problems. Good luck with your projects, energy is FREEDOM !
I assume you use a torch to solder those ends rather than a large heavy duty soldering iron?
I lightly crimp the end and then while holding the insulated end of the cable, put the terminal into the flame of a simple hand held propane torch ( the trick one with a piezo trigger that's good for starting fires in the wet ..) and heat the lug up until your thick solder starts easily flowing into the junction of the crimped end and the cable. Shocking how much solder you can pump in there. Do it right and the insulation won't even melt.
I just put the finishing touches on my micro nuke. Plan to hit the on switch this weekend as my uranium supplier in Ukraine has been offering some great deals and ships Fed Ex.
I keep ya'al in the loop here when we power up. Not sure if I'm ready to go full on reprocessing yet but obviously just like my hot rod Ford "there's nothing like an after market."
One way to get around high input current is to ramp up the pump motor with a device like this one.
http://www.ebay.com/itm/1-5-hp-variable-speed-controller-ac-drive-phase-...
... but ramping it up would shorten the life of the pump, according to the article. So, that was a possibility but means you'll have to replace the pump sooner.
No, ramping is different than starving the motor for current. It used on industrial motors everyday. Ramping involves controlling the frequency of the input wave form.
Link please to run a 3/4 HP 230 VAC submersible well pump motor that draws on average 7-8 amps continuous and 57 amps surge. I would love to see the solution because I looked into this and all I could find were very expensive variable frequency controllers.
Advanced Power Inc.
http://www.solarpumps.com/?gclid=CMTxoeyNnMICFVNp7AodSnoAWg
"Please give us a call and put our 25 plus years of experience to work for you today! Now with pumps to lift water up to 350 feet or flow up to 45 gpm on shallow wells. "
Please see the link above, they may help provide some answers to your questions.
Or, why not go with an all mechanical solution that can be easily maintained and/or repaired (think of the simple tools that allow the entire world to function, i.e., there are five main types of simple machine: levers, wheels and axles (which count as one), pulleys, ramps, and screws). I want things that I can look at and see how the individual pieces work together to accomplish a task/ function. Consider a windmill (all of the simple tools combined to work for you, form and function, simply and beautifully, grace in motion) for your water lifting needs, from either your well or the creek below your house. Windmills have been proven effective for a long time. No sensitive PV or other motherboard/circuitry/electronic whiz bangs required.
http://www.ironmanwindmill.com
I don't understand electronic gadgetry, for instance, I can take apart and rebuild an old 35 mm Nikon, and rebuild it with parts I manufacture but am totally lost when I open up one of the new-fangled digital cameras and see nothing but plastic circuit boards. It's a limitation, I know.
I do, however, see from your picture, that you probably have a steady supply of wind power at your location and also have room for a cistern under your house. From the cistern, a hand pump might work just fine for all of your needs.
I had excellent experiences with windmills generating electricity (no electrical engineer, me), too, both on small yachts and in a very rural place I have with a relative in Italy. This is our last turbine type: http://www.windturbinestar.com/mini-eolico-verticale-1kw.html for similar issues
but I agree with Pinche Caballero, a pure mechanical windmill might be much better suited to this task
I appreciate the info and have saved the link for later.
Thank you
http://www.automationdirect.com/adc/Shopping/Catalog/Drives/GS1_%28120_-...
GS1-21PO
This one is single phase in 3 phase out. I use it on my shop lathe. You can hook it up between neutral and any phase or between two phases to control the pump motor.
about $135