Water pressure switch on 24v system

SystemSystem Posts: 2,511 admin
Norm. open on at 30 off at 50 or 60
Where can I find them?
Thank You

Comments

  • System2System2 Posts: 6,290 admin
    Re: Water pressure switch on 24v system

    Existing is Square D, without the voltage rating
    And is going through 4 contacts better than 2 ?
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Water pressure switch on 24v system

    Mark,

    You will need a switch rated for the current and voltage, at DC, for your needs... AC is much easier to switch that DC because DC sustains arcing much better than AC--hence a similarly rated DC switch (even at a lower voltage) will be much heftier than the same AC switch.

    For inductive loads, on the motor side of a DC switch, you can place a reverse biased diode from the negative to the positive lead (i.e., diode does not conduct electricity when power is on).

    When the switch is turned on, the power goes to the motor--current flows and all is normal. When you turn off the power, the DC motor turns into a generator (plus wiring inductance) and it tries to keep the current going. This can cause several hundreds of volts across the switch and create an arc--which will continue to flow current as the switch contacts are moving apart--quickly ruining the contacts. The reverse biased diode (properly rated for voltage and current) will supply the current into the motor until it stops turning--helping to prevent arcing.

    In the end, if you do not use a pump switch rated for the DC voltage/current--it will not last long unless you use it so power a separate relay which is rated for the power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Water pressure switch on 24v system

    The word I got once from a Square D rep (speaking on his own however!) even though the Square D P switches are not specificaly dc rated, he would derate them to ~1/4 their amperage ratings. I run one on my 12/24vdc shurflo at 30-50 psi and have had no probems.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Water pressure switch on 24v system
    BB. wrote: »
    Mark,

    You will need a switch rated for the current and voltage, at DC, for your needs... AC is much easier to switch that DC because DC sustains arcing much better than AC--hence a similarly rated DC switch (even at a lower voltage) will be much heftier than the same AC switch.

    For inductive loads, on the motor side of a DC switch, you can place a reverse biased diode from the negative to the positive lead (i.e., diode does not conduct electricity when power is on).

    When the switch is turned on, the power goes to the motor--current flows and all is normal. When you turn off the power, the DC motor turns into a generator (plus wiring inductance) and it tries to keep the current going. This can cause several hundreds of volts across the switch and create an arc--which will continue to flow current as the switch contacts are moving apart--quickly ruining the contacts. The reverse biased diode (properly rated for voltage and current) will supply the current into the motor until it stops turning--helping to prevent arcing.

    In the end, if you do not use a pump switch rated for the DC voltage/current--it will not last long unless you use it so power a separate relay which is rated for the power.

    -Bill

    Where can I find the DC pressure switch and dioed ?
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Water pressure switch on 24v system

    I don't use well pumps... So the best I can do is direct you to our host's page:

    http://store.solar-electric.com/dsp-11023.html
    Heavy duty Pressure Switch, "GSG". Rated up to 2HP for AC, about 10 amps @ 24 VDC.

    Note - although these pressure switches are rated for DC, we really recommend using them with a pump controller. Switching DC voltage eats up the contacts pretty fast at full load.

    Class 9013 Type GSG pressure switches are two-pole devices for controlling electricity-driven water pumps.

    A pump controller--you can check with your pump manufacturer or supplier and see what they offer...

    Or you can go to a large supply house like McMasters or Grainger and look for a 12/24 volt relay...

    Regarding the diode--DigiKey.com is a good web based electronics supplier if you don't have any small shops near your place. Look for a standard diode one that is rated at 100 volts (couple times the input voltage) or more reverse voltage, and 20 amps (larger than your rated pump current) or more forward current... 1 part should cost around $1.00 each... Make sure you use a circuit breaker or fuse to protect the diode and well pump... Don't want to have 1,000 of amps from your battery going through a short somewhere.

    Solar Guppy and others here have done a lot more than I regarding well pumps, switches, and controllers... I am sure that they can give you better advise than me.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Lefty WrightLefty Wright Posts: 111Solar Expert ✭✭✭✭
    Re: Water pressure switch on 24v system

    Try your local well driller or pump shop. Or if you have a farm and ranch type hardware store or a place that sells irrigation equipment they should have a pressure switch with a DC rating.

    The pressure switch on my pressure tank has AC and DC ratings.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Water pressure switch on 24v system

    Here's one,,http://www.recycledgoods.com/itemdetails.aspx?productID=31422

    Here's anonther: http://store.solar-electric.com/dsp-11022.html

    tony
  • System2System2 Posts: 6,290 admin
    Re: Water pressure switch on 24v system

    I checked our well house today. We use NASON SQ and NASON SQ3 Pressure switches with contactor relays on our D.C. pumps. They aren't exactly what you asked for but have the advantage of kicking the pump on after only a 2 PSI pressure drop instead of waiting for your pressure tank to be nearly empty before the slow DC pumps even get started trying to catch up. They do fail from time to time in either open or close position and I'd recommend a backup high pressure shut off.
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