2140 ft pump motor control circuit via float switch..?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by ronan, Aug 6, 2014.

  1. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    I need to install a very long (2140ft distance one-way, X2) DC control circuit run through a float switch to control a 220 vac, 1.5 hp submersible water pump in a well pumping up to a gravity feed tank. Tentative planned installation is a wide angle float switch in the water tank, with a solid state relay of some kind at the well, a DC activated relay with a low input current for the long run. I was planning or hoping to use the solid-state relay to control the power relay/contactor to the pump.

    I have conduit installed already with three pull boxes to break up the pull distance plus it's on a steep slope so gravity is working in my favor when I go to pull the wire. I was figuring on a 24 volt power supply and was thinking of using 4 wire telephone cable and twisting wires together into two pair..? Basically looking for some relatively inexpensive wire that will get the job done. Any recommendations..?

    So far this is what I have put together from online advise from a few people more experienced in motor control circuits, one of which was a pump guy whom has wired up a couple systems similar to mine in length.

    Because of the long run and induction with AC the recommended advise is to use a solid-state relay that uses "logic level" input and high power output. It is recommended to use the solid-state relay to control the power relay/contactor as SSR's (Solid State Relays) tend not to be as good for switching inductive loads, such as pumps and motors.

    Possible relay for the job: Omron Corp. G3NA-210B-DC5-24, Info at:

    http://industrial.omron.ca/en/produ..._state_relays/panel_mounted/g3na/default.html

    I ran the wire run resistance on this calculator: http://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table
    And for 4300 ft (up and back) of 20 gauge AWG wire it is 44 ohms. 22 gauge wire is 69 ohms. I am just not sure of how to figure out exactly how little current is required to activate the relay? Any recommendations on the best wire to use for this?

    I was planning on the system using a 24 volt transformer run off one leg of the pump power supply I figured. I haven’t gotten to that part yet but I figured that’s not to complicated. Any recommendations?

    This set-up seems pretty simple to me. It is just a DC power supply, a Solid State Relay, and a contactor! Any similar or better options advise?

    One other thing that was mentioned was using a transistor-driven relay..? that required only a few milliamperes of current to activate the relay. I haven’t looked into that route.

    Any opinions on the differences regarding reliability and simplicity between using a solid state relay to control the pump motor contactor and using use a transistor-driven relay that required only a few milliamperes of current to activate the relay…? Is one system better over the other for a long switch circuit such as this using small wire? I’m just trying to nail down my best option? The transistor-driven relay route was mentioned to me while researching this. A recommended part number would be great if someone had one!

    Much thanks and appreciation for any advise
  2. Reach4

    Reach4 Well-Known Member

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    Location:
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    Regarding the worry about the drop in the control wire, note the resistance of the wire (even after accounting for resistance in both legs) is much less than the input impedance (72 kohms = 72,000 ohms). So that should not be a problem. At 24 volts, such a load is only about 0.33 milliamps.


    It is possible that some nearby power source could couple a voltage onto your wire. To minimize that, I suggest that you try to have your sense switch short out the control pair in the no-voltage condition, and to apply voltage in the other condition. This would mean that your float switch would be a SPDT (AKA form C) switch.

    I am not familiar with your relay brand. I am familiar with Opto 22. http://www.opto22.com/documents/0859_Solid_State_Relays_data_sheet.pdf

    Rather than making a DC power supply, you would have the option of using an AC-controlled solid state relay. One advantage of DC is that you could add a capacitor across the input of the relay if you ever detect a glitch. A capacitor would slow things down, depending on the value that you use. For either AC or DC you could add a resistor across the input. That would lower the effective input impedance, and would attenuate any coupling signals.
  3. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX
    You could use Cat5 computer cable, it is cheap and you can get shielded if you like. I would use shielded if the input impedance is really 72K ohms. Using a twisted pair can help for noise on the line.

    You can double up on the pairs if you need less resistance for the long run.

    For a run that long, a RF link may be a better / cheaper option.


    Good Luck on your project.
  4. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    Ok have a good idea for the system now. Any recommendations on a good source for some wire? The pulls will be in the six to seven hundred foot range! And we are talking 4300 ft total length so bulk supply is preferable. Thanks
    Also an RF link is more expensive when you throw in solar power, maintenance, and reliability. Two wires in the ground and a relay is pretty simple once it's set-up!
  5. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX
    500 or 1000 ft rolls will be your best bet for a good price. Don't forget a pull string or 2 extra.

    You can just find a place that has free shipping. There are plenty on the net. You may have some local places.

    BB stores carry cat 5. Maybe your local phone man has some used flooded 2 pair that you can get cheap, they use it for DSL.


    Good Luck on your project.
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,080
    Location:
    NW Ontario, Canada
    Small spools would mean lots of waste.
    Most BB stores only carry indoor grade, not outdoor burial flooded.
  7. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,353
    Location:
    Houston, TX
    Indoor grade may work in conduit. But the conduit may fill with water, so flooded cable would be more better.

    I am not a big fan of solid state relays for a application like that. With a wire that long, It will be picking up RF from every radio station in the world. RF suppression will be needed. Reach4 hit a bit on that problem, And the relays high impedance needs protection. A near lightning strike could wipe it out.

    Please do let us know how your project works out.
  8. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    If you didn't use a SSR what would you use..? I'm just leaning that way to keep the wire size down and for simplicity. I'm planning to use the solid-state relay to control the power contactor to the pump. As to what wire I'm looking for.... anything that is functional for this purpose and hopefully semi-economical. As to RF suppression that has been brought up to me a few times. Any recommendations on twisted vs straight, and shielded vs unshielded use in this application..? I can pick up Cat5 shielded for a decent price, and it's got extra wires should I ever get a wire failure in the future. Not set on it yet but I am considering it. It will have protectors on both ends and be in dry conduit 3ft underground.
  9. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,353
    Location:
    Houston, TX

    If you are using 24V then a normal relay will work. If you have a lot of voltage drop on your wire run, You can use a 12V or 6V coil relay.

    Simple and will work. No need for twisted pair or RFI protection. (Unless you have a antenna farm near by.)
    Last edited: Aug 8, 2014
  10. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,080
    Location:
    NW Ontario, Canada
    Buried conduit is always considered as wet and the wire choice should reflect that.
  11. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    Ok any recommendations for a normal 24 volt mechanical relay that will operate effectively with a 4300 ft 22 gauge wire switch circuit..? There is such a plethora of relays and crunching the numbers is kind of out of my field of expertise! Just considering my other options besides the SSR route..?
  12. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    First off thanks for all the input. I don’t dismiss anything out of hand, just gathering ideas. This is just a simple bang-bang (on/off) control loop! Nothing more I want to keep it as economical, functional and simple as absolutely possible. Just trying to determine which route is best to go with (advantages/disadvantages) a normal 24 volt mechanical relay or an SSR…?

    About RF interference…. Just how close to the radio station would one have to be to develop 1.8volts DC at 4ma on the wire to the tank and back..? I can’t see it being a serious issue for me. I’m in the boonies, but I'd still be interested in knowing.

    Overflow protection for this circuit is not an issue I am worried about. I’ve pumped out the overflow tank drain for years with the mechanical timer set-up. If it fails on I will catch it with a visual inspection.

    Sorry if I’ve come across as a bit slow I just haven’t mathematically analyzed circuits in so long that it’s made me lazy. I’m kind of like electricity I take the path of least resistance which was through this forum post.

    I came across this Signal Control cable/wire 20 AWG (10 x 30) Annealed Stranded Tinned Copper Wire, 2 Conductor Unshielded Multi-Conductor 300 Volt Consolidated Cable UL Style CM/CMG. And can pick up 2150 ft for around $200.00. Any reasons not to use this..? Keep in mind this is a personal homemade non commercial application. 4 conductor cable is not that much more expensive ether and gives me some back-up wires. It is close in price to Cat5 22awg wire.

    While I’m at it any help with picking a 220vac to 24vdc power supply to run the relays discussed in this post would be appreciated. I don’t know where to start in choosing one.

    Much thanks for the help
  13. DonL

    DonL Jack of all trades Master of one

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    Location:
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    The wire you want to use should be fine. Cat5 would give you 4 pairs that you can Parallel, if needed. I see that the price of wire is way up now.

    You can look up Ohms law, for voltage drop on the wire you plan to use. Post a link to the wire and I maybe could do the math.

    If you use a doorbell transformer, you can add a diode to use a DC relay coil, If you want to use DC. Or just use a wall wart.


    What is the rating for the load that you want the relay contacts to carry ?
  14. ronan

    ronan New Member

    Messages:
    10
    Location:
    California
    Hello again

    I’ve been tied up with other things with work and off this for a while now but I just wanted to say thanks to everyone for all your input on my project. I have everything but a few miscellaneous items rounded up now to do this project. Still trying to go the simplest route/ON OFF loop. I bought 4 conductor 22awg wire, full length/continuous piece roll. Two conductors for the circuit & 2 for future back-up/insurance.

    My last items are fuse protection & surge protectors. To be honest I don’t know diddly squat about Telcom and Movs protectors! What’s better Movs or Telco, proper sizing and help on how and where to incorporate those would be helpful. Again trying to go the simplest route possible here. Is it the same set-up on both ends..? Line to line and line to ground..?

    What would be a recommended fuse rating for the long 24vdc loop protection with my components?

    Thanks again

    Here are my system components below minus protectors and fuses:

    SSR Relay: OPTO 22 240D3 DC Control SSR, 240 VAC, 3 A
    http://www.coleparmer.com/Product/O...474-43?referred_id=5576&ProductID=EW-68474-43

    Normally closed model (low level) Narrow angle mercury activated float control switch normally open.

    Power Supply: 7.5 to 240 Watt, Single Phase, UL508!
    Idec PS5R Standard Series
    http://www.wolfautomation.com/produ...ingle-phase-ul508br-idec-ps5r-standard-series

    Power Relay: Enclosed Power Relay, 25A, 200/240VAC, DPST
    http://www.grainger.com/product/OMR...m/rp/s/is/image/Grainger/2XC19_AS01?$smthumb$
  15. DonL

    DonL Jack of all trades Master of one

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    Location:
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    Looks like you did do some homework. Nice work.

    The power supply is overkill, but is a nice one. If you set the power supply for 12 Volts You can use a 24V 1watt Zener diode and a 12V 1/2 amp Fast blow fuse that will blow if the diode shorts or hits its zener region.

    A mov may not be all that good for the low voltage protection. Zeners are good for DC protection. Many telco protector are made for AC because of ring voltage, but is better than nothing.

    Whatever you use, you should make them easy to replace.

    If you put a 12V electronic sounder across the fuse, It can alert you if the fuse blows.


    Good Luck on your project.
    Last edited: Sep 21, 2014
  16. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,353
    Location:
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