Seeking second opinion on fuses/breakers for solar pump

Hi folks,
It is a pleasure to become aquatinted with this forum.

I have a relatively simple solar pump to set up. I've had some assistance from a solar "expert" but some of what he's told me doesn't make sense. He's hard to get a hold of, and I have to make purchase decisions as soon as possible. So I thought this would be a good place to seek a second (or more!) opinion.

Attached is a diagram that shows the set-up I have in mind.

Attachment not found.

Assuming everything else in the set-up is correct, my question is simply about the breakers he has suggested.
You'll see there is a 40A between the AC/DC converter and the selector switch. There is also a 15A between the panel and the selector. And then there is a 30A from the selector going out to the bilge switch.

The bilge switch is rated to 20A
The Dankoff 1408 is rated to have a max running amps of 12.3A
The selector switch can handle some hundreds of amps (I forget exactly, but it's VERY high).

The LCB is either going to be one or other of these two:
http://www.solarconverters.com/index.php/products/83-power-pump-tracker-linear-current-booster/118-ppt-12-24-15
or this one
http://www.solarconverters.com/index.php/products/83-power-pump-tracker-linear-current-booster/121-ppt-12-24-30

(I am awaiting confirmation as to which one I require. I figure it's the 15A version).
Unfortunately the Dankoff LCB is rated to 10A max, and they figure my application will draw around 11A. That's the reason for going with an LCB from Solar Converters Inc.

The question I have is regarding the breakers. Two of them seem redundant to me. The 40A and 15A.
I would have thought the 30A was enough, and that this should in fact be 15A. That's the one in the diagram between the selector switch and the bilge pump switch.

The diagram does the LCB as just an option. But it will in fact be installed right away. I just haven't updated the diagram to reflect this.

Am I thinking along the right lines with the breakers, or is the advice I already received actually accurate? (if so, why?)

With much thanks,

J

Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Seeking second opinion on fuses/breakers for solar pump
    Solaris wrote: »
    Hi folks,
    It is a pleasure to become aquatinted with this forum.
    I have a relatively simple solar pump to set up.
    Am I thinking along the right lines with the breakers, or is the advice I already received actually accurate? (if so, why?
    With much thanks,
    J

    OK, I see no batteries in this setup, is that right?

    The choices made by the switch are pump off, pump driven by PV, pump driven by mains CC, pump driven by both.

    One problem comes immediately to mind: When the switch is in the Both position and the pump is not running, you will be feeding up to 45 volts from the panels back into the 24 volt output of the CC. That could well damage it. A diode would fix this.

    Second, you may need some circuitry to keep the pump from trying to run when the current from the panel is not high enough to allow the pump to start. A lot depends on how it behaves when fed too low a voltage. This will be potential problem even with the LCB unless the LCB includes a low voltage cutoff.

    Even with the LCB transforming excess voltage to additional current, your single 300W panel at high noon still may not be able to provide full 12A 24V to the pump. If this is OK and it will just reduce its output, fine.

    The 15A breaker is there to protect a damaged panel from exposure to high current from the CC if it is on. (Switch in the 1+2 position.)
    The 40 A breaker is there to protect the CC from a short circuit on its output.
    The 30A breaker is there to protect the pump and the wiring going to it.
    They are all doing different jobs and need to be located in different places and have different settings.

    No indication on the otherwise pretty complete diagram of the wire sizes. I will give him the benefit of the doubt that they will be right.
    SMA SB 3000, old BP panels.
  • Solaris
    Solaris Registered Users Posts: 4
    Re: Seeking second opinion on fuses/breakers for solar pump

    Thanks for the detailed response.

    Yes. No batteries. Pump comes on with sun and goes off with lack of sun. PV direct.

    The LCB handles low voltage cut off. Although even without it, the dankoff slow pump just sits there until it has sufficient current is there. It's designed for direct PV source.

    I shall assume 30A is low enough to protect pump.

    Regarding the diode. I think this is a good idea. Any pointers on what I need to buy, and from where? (online is easiest for me)
    Ideally the switch won't be put to Both but it should be protected in case someone does that. I wasn't able to find a selector switch that was only 3 way. So settled on a 4 way.

    Regarding wiring size. I am yet to figure that part out. Correct wire for PV to mounting box was already supplied. But the rest was to be figured out once we knew the distances to the tank with its bilge switch. Should know that shortly.

    Cheers,

    J
  • Solaris
    Solaris Registered Users Posts: 4
    Re: Seeking second opinion on fuses/breakers for solar pump

    I have an updated wiring diagram, based on the original one I put together and posted.

    The LCB is wired in there now.
    It seems a diode will not be necessary. There is no intention of putting the selector to 1&2.

    I have now put all the breakers into a breaker box in the diagram.

    The panel produces 300W and the system will (according to Dankoff) draw about 11 amps. Which comes to around 264 watts. Even if it goes to 12 amps, we're looking at around 288 watts, are we not? They advised this panel will be sufficient to power the pump on its own. Hope they are right about that.

    If anyone feels inclined to look over the current wiring diagram, I'd appreciate any input on errors or omissions.

    With thanks...

    J

    Attachment not found.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Seeking second opinion on fuses/breakers for solar pump
    Solaris wrote: »
    The LCB is wired in there now.
    It seems a diode will not be necessary. There is no intention of putting the selector to 1&2.

    I believe that there are two ways to get from the 1 position to the 2 position. One way is via OFF, the other way is via 1+2. Are you sure nobody will turn the switch the wrong way? Can you add a mechanical stop to prevent that?
    SMA SB 3000, old BP panels.
  • Solaris
    Solaris Registered Users Posts: 4
    Re: Seeking second opinion on fuses/breakers for solar pump
    inetdog wrote: »
    I believe that there are two ways to get from the 1 position to the 2 position. One way is via OFF, the other way is via 1+2. Are you sure nobody will turn the switch the wrong way? Can you add a mechanical stop to prevent that?

    Yes, my thought exactly. I'll have a small metal bar bolted in below the switch knob to prevent it being turned downward.