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Charging a battery from well pump circuit (cycles on/off 120v)

Discussion in 'Power Electronics' started by AJ Peacock, Aug 25, 2019.

  1. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    Hi all,

    I'm planning a flagpole install in my front yard. I want to light the flag at night and don't like the solar options for my location. Nor is it possible to run power to this location. The flagpole will be about 10' from my well head.

    Here is what I'd like to do and I need some help.

    I plan to cover the well head with a large fake rock.
    Pull 120v off of the well wiring (wire nuts under well head cover).
    Charge a small 12v AGM (or other weather resistant battery) under the rock).
    Power a 12v LED flag light mounted in/on the rock (with a photo sensor).

    I have a good friend that is an electrician and can deal with the 120v.

    My question is how best to charge the battery considering the 120v power is only hot when the well is running.

    I'm not a complete Noob w/re to electronics, but I typically know just enough to get me in trouble!

    I was thinking a capacitor (or multiple) could be charged when the well circuit is energized, then feed a small 12v charger from the capacitor.

    Also, the well is 230v and has 3 wires running to it.

    I really appreciate any opinions/ideas.

    Thanks,
    AJ
     
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    You never said how much current the light needs and for how long.
    A capacitor can hold enough charge to activate a charger for a few seconds but a battery needs hours to charge.
    I doubt that the well pump runs long enough to charge anything.
    How about using a fairly large windmill generator to charge the battery?
     
  3. Alec_t

    Alec_t

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    Jul 7, 2015
    If you have two supplies going to the well, can't you use the 230V supply to power the light?
     
  4. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    Alec_t - The well is 230v and the pressure switch is double pole. So it is either all hot or not hot.

    Audioguru - Lights will likely be 8Watt/12v and either 2 or 3 of them. So either 1.33 or 2 amps. In the winter here, that would be 12-13 hours. So conservatively, 30amp hours usage/day. I haven't timed it, but I'd guess that when the well kicks on it runs for about 30 seconds. I really don't know how often per day it runs, maybe 3-4?

    My last option would be to snake a couple small DC wires through the same conduit, but I'm afraid that would be a bit of a challenge.

    Thanks,
    AJ
     
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    Your battery will never get charged since the charging power is only for very short time durations.
    Isn't it illegal to have low voltage wires in a conduit for the mains?
     
  6. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    I wouldn't doubt it and don't intend to do it (it would be tough anyway).

    Thanks,
    AJ
     
  7. dave9

    dave9

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    Mar 5, 2017
    You do not need to, nor should you, snake low voltage wire through the conduit. You can get away with just buying burial rated low voltage DC cable and make a new run out there parallel to the AC conduit. There are machines that take a spool of cable and dig a slit in the ground and place the cable.
    https://www.sunbeltrentals.com/equipment/detail/1151/0700035/4in-trencher-cable-installer/

    Otherwise, trying to charge capacitors, to charge batteries, from 30 seconds 3-4 times a day AC power, is unrealistic.

    Further, you can't use a "small AGM" battery. Per your upper figures, 2 amps x 13 hours = 26 AH, and that's not the battery capacity you need, rather you need much more than this so you don't deeply discharge it to result in a short lifespan. A typical recommendation for deep cycle batteries is don't discharge past 50%, so you'd want at least a 50AH battery.

    Anyway, 30s x 4 = 0.03 hours. You'd need approximately 900 amps delivered, and no cap charging losses, no charging regulator losses, and no battery charging (battery internal) losses. I bet your well pump wiring can't handle 900 amps or more, and the cost of the capacitors would be astronomical for what you're trying to do with them, and quite large too.

    I'd run the low voltage cable, back to an AC/DC PSU at the house, though you didn't mention the distance. This eliminates the cost of solar panel, battery (and replacement of battery again every few years), and battery charging circuit.

    A basic switchmode AC/DC, 12V ~4A PSU is not very expensive, so inexpensive that I'd go overkill and get a 6A or more rated PSU if the cost difference is only a few dollars which looks like the case, within this range costing about $15 on ebay. The biggest expense would probably be the trenching tool (or dig it by hand if you feel up to it (short distance), as burial grade 14/2 wire isn't expensive either, roughly 50 cents a foot in small spools.
     
    Last edited: Aug 26, 2019
  8. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    Dave9, that is what I figured. I was hoping I was missing something obvious.

    When I said 'small AGM' I was intending on something like that. I have several 'large' AGM's for my boat and my ham station (100+ Amp hours).

    I'd direct bury a low voltage except I'd need to go under a driveway and am not real anxious to deal with that!

    I'll probably end up with Solar, but I hate the thought of having a panel in the middle of the front yard. I can't set the panel off to the side because I'd have the same driveway issue as I have a circle driveway.

    The big issue with solar is that I have very large trees 70-90' all the way across from SE to SW of the flag location. That location gets very very little sun in the winter due to the trees and house and the Sun being so low in the sky.

    I'll keep scratching my head and will figure something out. Worse case is I'll just use Solar in the summer and not fly the flag at night in the winter. I've even contemplated getting a couple batteries and just swapping them every couple days during the winter. Another thought for the winter is to just run a low voltage from an outlet on the house and run it directly to the flagpole (the snow would cover it and I could protect it inside a piece of garden hose where it crosses the driveway (not much traffic on the circle in the winter as we use the side driveway to the garage.

    Thanks again,
    AJ
     
  9. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Why not ask him the best option to power your new flagpole?
    It may be cheaper and easier to run an ac circuit than dc because it likely requires larger expensive wire to overcome voltage drop. What you deem "impossible to run" may be easy for him.

    Btw, I'm sure he'll agree, that tapping power from the well head won't work.
     
  10. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    I did ask him. He is an electrician, not an electronics expert. He can wire a house or a business, generators multi phase machines etc. But he's never soldered a circuit board or done anything 'electronics related'. I've built a ton of circuits in my ham radio hobby but circuit design is definitely not in my wheelhouse. He said that it would be easy to tap into the power, but he didn't know the best way to charge a battery with power that cycled on/off like that, which is why I posted here. He also said we could pretty easily pull new wires under the driveway, but it would be sketchy because the driveway isn't in very good repair and there are tree roots etc.

    I think I have a plan of attack if nothing better comes along. I'll use a larger solar panel that will charge a fair size AGM under a fake rock. Landscaping/flowers etc. will hide it pretty well from the road. If in the winter it won't hold the battery up enough, I can either swap batteries every few days, or just drag an extension over and charge the battery. If the weather is super brutal, I can just pull the battery inside, pull the flag down at night, toss a couple logs on the fire and pour me a drink.

    Thanks,
    AJ
     
  11. Bluejets

    Bluejets

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    Oct 5, 2014
    Maybe place a standard mains flood light at the 230v location.
    The light will be quite capable of shining 10 ft or more if the correct lamp is selected.
    Not difficult to include an LDR there also.
     
  12. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    But it is only powered when the well is running (only 3-4 times/day for 30-45 seconds).

    AJ
     
  13. Bluejets

    Bluejets

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    Oct 5, 2014
    I would have imagined the control for the pump on/off would be located adjacent to/ if not actually on the pump motor itself (if not submersible for the latter).
    In which case there should be unswitched power available there.
     
  14. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Most wells have a bladder tank in or near the house with a pressure switch in (or next to) it to cycle the well motor. It may be possible to move the ps to the well head but I doubt it would work right. Not to mention it'd be more work than just running a new circuit.
     
  15. Tha fios agaibh

    Tha fios agaibh

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    600
    Aug 11, 2014
    Easy, but imho (et al) don't see it as feasible.

    On the other hand, Tree roots and rocky soil can be overcame.
    I have a circuit trenced all the way to my pond about 700ft away from the house amongst trees.
    Since your driveway needs work anyway, you may consider taking up a portion of it to rout circuit instead of boring under it.
     
  16. AJ Peacock

    AJ Peacock

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    Aug 25, 2019
    And it would freeze solid about halloween !
     
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