Wiring question...

Options
couchsachraga
couchsachraga Solar Expert Posts: 84 ✭✭
I'm trying to wire in a solenoid that will control a diversion load (excess PV to water heating element). The Midnite Classic 200 has the capability, and I'm comfortable wiring it up.

BUT

I also have been planning on wiring up a "water is at low temp" circuit to keep the water from freezing (long story I'll eventually write out here).

So, my question:
Is there a problem with using the same solenoid? One the low temp side I don't see a problem - it's actually another solenoid (that is controlled by a "standard" 24v AC controller), so if those wires get energized it is not a big deal (esp. while the other solenoid is open). I'm assuming (always unsafe to do...and hence my post) that if wired correctly (+ to +, - to -) that the voltage will be the same (to trip the solenoid), and the solenoid should only pull enough amps to have triggered itself anyway. BUT, is there a problem on either end with the charge that controls the solenoid "back feeding" (in other words putting 12v to the Midnite)? Or do I need a diode or something in the circuit on each side of said solenoid to be safe?

For the curious, this is a solar thermal (hot water) tank with two coils in it - one heats it (thermosiphon from outside on the ground), the upper one "cools" it - I'm using the tank as a "heat bank" to help heat the place when I"m not there (and therefore use less propane). Still very much getting the kinks out, but so far the concept is working at least.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...

    Let's just see if I understand what you're trying to do.

    You have a solenoid that you want to be controlled by two different sources: output from the AUX of the Classic and another trigger. Your concern is that if this is done in parallel Voltage from the other source could back-feed to the controller and cause a problem.

    If so and if I recall correctly the Classic should have a relay on its output, not drive anything directly. (The old MX60 is like this; 200 mA for a relay and nothing more.)

    The relay solution should work fine. The Classic triggers a relay in its key parallels the switching of the other source. If need be that can also be relay controlled.

    Does that make sense?
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    It does; but also realize that the "relay" and the "solenoid" in this case are the very same thing.... The load allowed to the heating element is the same either way, I'm not concerned with that, it is how the "switch" is powered. I think a diode on each side should protect things just fine (as well as fuses of course!!). I'll have to double-check that the output of the Midnite will be enough to trigger the solenoid in question (which is an insulated continuous duty 65 amp 12v unit (load is 25 amps)). Otherwise I'll have to add a relay (yet another, but smaller, solenoid) to control that (just like I have on the other side where a 24v AC relay is controlled by a Johnson Controls unit that will turn "on" or "off" at whatever set points I choose (in this case if the lower part of the domestic water tank gets to 35 degrees i want it kicking on regardless of whether the batteries are fully charged or not). If time allows tonight after the kids are in bed I'll try and type something up so folks can poke holes in the plan we've been working on and are finally installing (and fixing;) ).
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...
    It does; but also realize that the "relay" and the "solenoid" in this case are the very same thing.... The load allowed to the heating element is the same either way, I'm not concerned with that, it is how the "switch" is powered. I think a diode on each side should protect things just fine (as well as fuses of course!!). I'll have to double-check that the output of the Midnite will be enough to trigger the solenoid in question (which is an insulated continuous duty 65 amp 12v unit (load is 25 amps)). Otherwise I'll have to add a relay (yet another, but smaller, solenoid) to control that (just like I have on the other side where a 24v AC relay is controlled by a Johnson Controls unit that will turn "on" or "off" at whatever set points I choose (in this case if the lower part of the domestic water tank gets to 35 degrees i want it kicking on regardless of whether the batteries are fully charged or not). If time allows tonight after the kids are in bed I'll try and type something up so folks can poke holes in the plan we've been working on and are finally installing (and fixing;) ).

    No the relay and the solenoid can't be the same thing. That's the point.
    If you are talking about using a relay (not a solenoid - they are different things) to switch something on/off they can be paralleled on the key (the switching part) but you do not want the coil operated by two different power sources exactly due to your concern about one interfering with the other.
    You do not want to use a diode as that will drop Voltage, possibly too much.
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    Ok, say I use a relay to control the solenoid (which seems a bit redundant to me, but I'm no electrician!), and BOTH relays trip on at the same time (both trying to power the solenoid). Is that OK, or not so much? In my (admittedly simple) mind it gets back to the same problem as before, and the reason for a diode or something similar to keep voltage flowing one-way.

    It is all 12v DC...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...

    I think I have to draw a diagram to demonstrate my meaning.
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    And to be clear... when I'm talking about a "solenoid" I'm talking about a continuous duty, 12v, high amperage one of these:

    https://www.youtube.com/watch?v=WBUhQfZUo54

    So small current from Midnite triggers connection for much larger current for opportunity load.

    I'm not sure if that clarifies things on my end, but I"m very curious what you're trying to articulate so I can get this right, as well as learn a bit more. I'll likely bug an electrician friend of mine as well, though he's more of a solar AC (grid tie) guy.
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    To clarify things further (maybe;) )

    From the Midnite Classic 200 manual:

    The Classic includes two auxiliary ports which can be configured to become inputs or outputs. These aux ports can be used as a secondary power supply to be used for accessories such as vent-fan, anemometer and generator starter or even and anemometer. The Aux output is limited to 200ma or less per channel. These aux ports if used correctly could extend the system life. Here is an explanation of how they work.
     An internal, re-settable Positive Temperature Co-efficient (PTC) fuse protects the AUX internal components from overcurrent or a short circuit.
     AUX 1 consists of either RELAY or LOGIC operation depending on the user selection function.
     AUX 2 could be set to become an INPUT or OUTPUT. One at a time this port could be reading
    the state of a device connected and takes an action from there.

    This mode will turn Aux 1 on when the Classic gets within a certain range of the voltage set points for each charging stage (V High) and turn Aux 1 off when it gets to a low set point (V Low). These set points are user adjustable and will allow the Absorb, Float and EQ timers to continue to run. You will adjust these set points to negative numbers and the numbers are an offset from the voltage set point. For example a -.2 would turn Aux 1 on 2 tenths of a volt below your set points. This mode will allow you maximum diversion while maintaining your 3 stage charging. It also allows you to set a delay time in seconds the Classic will wait before turning Aux 1 on after reaching the V High set point. It also allows you to set a hold time in seconds the Classic will wait before turning Aux 1 off after reaching the V Low set point.


    So in my mind as long as the output (200ma) is enough to close the solenoid, I'm OK. If not, then I have to introduce a 200ma relay....
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    And just to post 3 times in a row... quick research on continuous duty solenoids leads me to believe I'll be getting a relay... seems 0.700 Amps is standard for what is needed to close them. Oh well... more wiring!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...

    This is what I was indicating.
    The relay on the left is controlled by the MidNite Classic. The one on the right is controlled by something else. The parallel keys will energize the same load as an 'either' switch. This allows total isolation of the two controls and also offers the ability to change current type and amount and/or Voltage.

    It is possible you could do this with one relay and two diodes to prevent back-flow of Voltage from one control unit to the other, but not knowing the internal circuitry of either control device I can not say for sure how well it would work.
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    Perhaps it is because I can't read diagrams very well, but I do not follow how that functions as an "either" switch - to me it looks like of the Classic triggers that relay, it signals the load (a solenoid) to shut providing power. If the "other control" does the same thing, it also works. BUT, what if they both close at the same time? Would the "control voltage" from one not potentially go back to the other relay? I only see the yellow boxes and black lines well on my screen though... but faintly see pink and white outlines... so I could easily be missing something!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...
    Perhaps it is because I can't read diagrams very well, but I do not follow how that functions as an "either" switch - to me it looks like of the Classic triggers that relay, it signals the load (a solenoid) to shut providing power. If the "other control" does the same thing, it also works. BUT, what if they both close at the same time? Would the "control voltage" from one not potentially go back to the other relay? I only see the yellow boxes and black lines well on my screen though... but faintly see pink and white outlines... so I could easily be missing something!

    Nope; the relay coils are 100% isolated from each other unless they are powered by the same source.

    If both close at the same time there is no variation in power supplied to the load nor is there any interaction between the outputs to the relays from the controls.
  • couchsachraga
    couchsachraga Solar Expert Posts: 84 ✭✭
    Options
    Re: Wiring question...

    First off, THANK YOU for taking the time yet again to help. You do a lot here and we don't say THANK YOU enough.

    Secondly, I'm still confused... but it may be the wiring in my head (planned wiring) that is the problem.
    If a + connection goes from the OUTPUT of the Classic relay TO the load (Solenoid), AND a + connection goes to that same terminal (output from the OTHER relay), are they not both attempting to power said Solenoid?

    I do understand, and see that each relay is independently powered (and one in fact is AC and the other DC), and that the load it self is unaffected by all of this.

    I'm ASSUMING (never safe) that since the + will come from the very same supply to each of the relays, then it likely (hopefully) doesn't matter that it rejoins itself on the + terminal of the Solenoid (if both relays are closed)... which was (sort of;) ) my original question.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
    Options
    Re: Wiring question...

    You can use a single relay as Marc's Cariboocoot's drawing...

    If the output is a grounded/open connection (common on many controllers), just place the one side of the relays to +12 volts (should have a small fuse too for safety) to the coil, cathode towards relay. And then wire the relay output to the controller.

    If you have multiple drives, you can place between the coil a diode in series and the controller output. The diode will allow "wire "OR"ing of multiple drivers (each with its own diode isolation).

    You may also need a diode snubber across the coil (a diode "reverse biased") contacts. This helps prevents the coil from generating 100's of volts when the controller output turns off:

    http://en.wikipedia.org/wiki/Flyback_diode

    Get a manual from the equipment supplier (or application data sheet)--It should go into the details of what sort of voltage/current levels the controller will support.

    There are latching relays from BlueSea (motor inside that drives contacts?):

    http://www.bluesea.com/products/category/Solenoids/ML-Solenoids

    There are also solid state DC relays too:

    http://www.power-io.com/products/hdd.htm

    The solid state relays (many times?) need a big heat sink/good air circulation to lessen the chances of overheating.

    Regular DC mechanical Solenoids (high power contactors) seem to use ~6-12 watts of power to "hold"... For low power systems, that may be a significant load, and certainly too much power for a typical Charge Controller to drive with its Aux outputs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Options
    Re: Wiring question...

    I think what may be confusing you is that the power for the load on the relay contacts does not come from the Classic AUX port. It can and should be entirely independent of it. That is how you can use the Classic to control virtually any Voltage or current. In other words the AUX output may be 12 VDC @ 200 mA but the relay keys can be connected to, say, 120 VAC and handle 15 Amps (depending on the relay used of course).

    The other method, with diodes on the (+) output of the Classic AUX and other control to operate one relay from two sources may also work. I think the Classic has a SS relay driver in it, but I've no idea how isolated it is from backfeeding Voltage from another source.

    Lots of ways to do it, as always. The devil is in the details, as always.