Author Options:

Back-up power Answered

Hey there folks! Looking for some advise again. NH just went through the worst power outage in years (maybe history). 6 days without power has me thinking again. I have means of heat (wood stove) and means of cooking (propane) and lighting (candles and my LED projects), but the well pump is a problem. The need of water to flush the toilets came from the stream nearby, all well and good as it was, washing our bodies from buckets has to go. I have learned that my 220vac well pump actually draws it's power from 2 110 vac circuits. If I have this right (which is my first question, is this even possible) I only need a 110vac converter to run this off my batteries. Now, if I'm correct here (second question) a 4amp 220vac pump is 880 watts, then the draw from the 12vdc battery should be 74amps (give a few for losses maybe 80 amps). I only have 2 160AH deep cell batteries running currently. Am I looking at a reality of 2 hrs (half the draw) or 4 hrs use (full draw)? Or, is it even less.... Yup, that was a third question! I just bought a 2500 (5000 max) watt inverter intended for the shop and thought I would use this as my back-up for the winter. Am i even close here?


 we had 8 days instead of 7

I'm in total agreement with the disconnect. It has always been my intention to do so once I have accomplished what I'm attempting to achieve. No worries bro, I will protect my linemen! I believe I misunderstood you before, but now get it on the source of the 220vac. I will look into this deeper. I thought of a reason why the other circuits didn't work and just checked out my theory a minutes ago. I will test it this weekend. All circuits that ran were close or next to the supply breaker. All those that didn't were the same or more distance away. My thought is to move up the priority circuits next to the supply breaker (which happens to be at the top of the panel). I'm thinking that each breaker causes an amount of resistance (even if not turned on) and reduced my power enough not to run these circuits (located towards the bottom of the panel.

This makes sense to me and it's what I thought (but not knowing) was happening. Now comes the question.... If this is created from 2- 110vac sources (breakers), then is it possible to re-create the same with my battery back-up by supplying only 110vac back to the panel (with wattage being equal to the 220vac consumption)? Until corrected, I believe my well only needs 880 watts to run. 880 watts means 74amps at 12vdc. My batteries should give 170 amps before reaching cut-out. 2500 watt inverter.... Am I undersized???

You have it all backward . This is not created from 2- 110 volt sources, there is 2 - 110 volt sources created from 1- 220 volt source .
Your batteries will power your well pump, No sweat, However the voltage must be 220-240 there is no way to connect 2 - 110 volt circuits to = 220, the white wire is always there. If you join the black leg and red leg You short circuit the transformer, if you use both black or both red with both white then the wires go to the same place and is still 110 volts. 2500 watts is equal to 3 horsepower after electrical losses are satisfied. Your well pump is not likely that big, But some are.

Just completed the test run and here are the results; System is; 2 Werker Type 31 deep cycle batteries Run in parallel To a Cobra CPI 2575 2500 / 5000 max watt inverter Run through a 12g 5ft cord to the utility outlet next to the panel Main is turned off, utility is a 12g wire run through a 20amp breaker This gives me my back feed to power the panel. Basement lights YES! Florescent units run in pairs and 3 sets (wattage aprox. 170 watts) Water heater YES! Ondemand style needing little power to run (looked like 70 watts) Dining Room light YES! 4 CFL's 27(?) watts each Hallway upstairs light (standard 110vac 100watt can light) YES! Good news has now ended..... I ran each circuit that worked separately, then all together and they all worked. But all other circuits failed. I have a kitchen circuit run on 15amp breaker that should have operated a single CFL light (all other appliances unplugged) and it failed. Bath room circuit running 3 CFL's and it failed. Bedroom circut running the alarm clock only! That failed. I'm missing something here and I can not put my finger on it..... I ran one circuit at a time, when it failed, turned off (unplugged) everything possible in that circuit and tried again bringing up the least powerful item first. The failed areas just would not come up.... Any thoughts here? My mind is racing with possibilities, but a clear mind would really help about now......

in the battery cells are in series you divide the current by the amount of parallel batteries not cells

Big test comes tomorrow! Everything is here now and spent the day hooking it all up, including re-wiring the charge controller. I've come into yet another question for ya'll; Is there a basis on the RC rating? I seem to be in a conflict between batteries due to this. Are all RC ratings based on 25amp usage? My Werker batteries state based on 25amp usage. My Eveready (Pep Boys) does not state amperage.....

There's been quite a discussion here on my post and I wish to thank you all for your input. My inverter has not arrived yet, bummer, for I was hoping to experiment this weekend and learn the truth of my well power. I have returned to the basement and searched out all the wiring again to find the 220 vac line to the well. I can not find one. What I do have is 2 110vac breakers wired to 12g wire marked well and 1 runs directly to the control box (that gray box), the other runs through an outlet and ends in the same gray box. Today's quest (since the inverter is not here) is to volt test the incoming lines and test the out going to the well. I'll post up the results later.

discharging a battery fully is hard on a battery. even the best of deep cell units can only handle about 300 full discharge-charge cycles before being ruined.

if the battery is only for backup (not frequent use) then its ok (it got limited lifetime anyway so no justification to save cycles) but if there is a battery why not employ it for full time in some green project ?

yes it does hurt the battery. every full discharge charge cycle lowers the battery ah capacity. if you like, i can even post a graph

i meant something like this your battery is 50 AH. each too deep discharge takes away 0.5 AH. max battery life (in optimal other conditions) is 5 years you use the battery for backup only. you dischage it 10 times a year after year 1 its 45 ah at end of life (when it got high internal resistance and other problems anyway) it still got half its original capacity with less recent outages you use the battery less and it gets to end of life with higher capacity its not justified to save on discharge cycles cause youll recycle the battery anyway before you kill it too much with the discharges BUT isnt it just waste of battery to keep it for backup only ? you better use it all the time for a solar or wind project and do save discharge cycles

30% is enough to lower th ah. i think i will post the graph when i find it


9 years ago

I heard from a lot of relative in N.E. after the ice storm. Most modern gas furnaces have electric spark starters; my uncle has an old-school pilot light and his gas heat worked fine, while his neighbor froze... Although I have no idea how your pump is wired, it wouldn't be rated 220/240 unless the full voltage was needed. Of course, you cannot take a single 120 line and place it in series with itself and get 240V... ;-) That would result in a short. AFAIK, in the US the mains enter the house as 220-240V with a center tap. Half the 120V house wiring comes from one side of the 240V, half from the other...

if you use 2 isolation txformers then you can connet 120 V in series with 120 V. its essentially the same as 120 to 240 step up txformer

Yep. Additionally, this works with all true (isolating) transformers, not just "isolation transformers." Any combination (non-shorting, of course) of primary coils in either parallel or serial is OK, as is any combination of secondary coils. In fact, many transformers targeted for both the US and European market have a double-coil primary. For US use, each coil of the primary must be connected in parallel. If only one coil is used, the current rating of the trannie is halved. For Euros, the two primary coils are connected in series. There can even be crossover serial connections between primary and secondary (autoformers, etc.)

im a bit unsure about connecting secondary coils in parallel or more than 1 primary in parallel on same txformer isnt a difference of 1 turn in 1 of the coils equal to a shorted loop of wire ?

Good point. For parallel connections, they should be the same voltage and current rating--hence the "non-shorting" note (but that was confusing, and somewhat contradictory.) In a modern manufactured transformer you wouldn't see a loop count difference--at least for the same run.

i am not familiar with setups like yours (here everything is 240 V) but i guess what you have is like 240 V (red and black) with center tap (white) i think you can use 240 V power inverter and step down to 120 V txformer to provide the center tap (for the control circuit) or 120 V and 800+ VA step up txformer to provide the 240 V try to open and draw the circuit you have. itll then be easier to figure out how to use it and possibly rewire it to use 1 voltage only a water tank on the roof is great. it allows you to run the pump ocassionally and have water all the time

. As Yeasayer points out, that is not two 110V circuits. 110 is probably used in the control circuit, but the motor itself runs on 220. Unless you have some sort of weird setup. . Unless you want to install an elevated water tank or a large accumulator, you will need to run the pump all the while you are taking a shower or filling the bathtub. A gasoline/diesel/LPG/natural gas-driven generator may be a better option for extended outages.

Hi your well pump does not operate on 2 120 volt circuits, The motor start up capacitor and overload circuit may use 120 volts, (The long grey box Mounted near the well with an on off switch) The motor itself will have a Black wire and a red wire and a green safety ground. 120 volt circuits use a white neutral with either a black or red but not both. the white wire is a center tap in a 240 volt transformer output . some exceptions like a clothes dryer have a 120 volt drive motor and control system with 240 volt heating elements. this is why the color codes are helpfull.