two bilge pumps, two float switches, add to same original circuit

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Sep 17, 2014.

  1. sdowney717
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    sdowney717 Senior Member

    I want to add a second bilge pump to the same circuit.

    However running into trouble with the manual turn on by a single switch, the circuit will complete a path so that one float switch would then run two pumps at same time, not good.

    This diagram works but leaves the other pump not able to turn on using the same manual 'on' helm switch.

    Is there a solution? Do not want to run a new wire bundle and a seperate helm switch. I do want both pumps to turn on from one switch and run independent using their own float switches.

    Here is a schematic

    FS = float switch
    BP = bilge pump

    Bat = power source to pump

    [​IMG]

    this pic shows dashed wire, but that means the float switch turns on both pumps. the float switch is rated 20 amps, the pumps are 15 amps each.

    [​IMG]
     
  2. sdowney717
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    sdowney717 Senior Member

    Haha, one solution is run strings with pulleys to float switches. Pull strings together, pumps turn on. Tough for me to conceptualize the wiring, but will be simple maybe for some one else.
     
  3. gonzo
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    gonzo Senior Member

    The second diagram is correct. The pumps and switches should be connected in parallel.
     
  4. Grey Ghost
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    Grey Ghost Senior Member

    Rule makes 35, 37, and 40 amp float switches. (super switch)

    I know I've had a pump that has more than one + input wire too, one for the float switch and one for the switch. That would work for this I think.

    I wonder if it would be better to keep it as two separate circuits though. (Even running an extra wire.) That way if a short happens or a switch fails only one pump is knocked out.
     
  5. AndySGray
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    AndySGray Senior Member

    Or you could just wire a double pole switch.

    I personally like the momentary type i.e. you have to manually hold the thing but can't accidently leave on.
     
  6. AndySGray
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    AndySGray Senior Member

    The switch is generally termed a DPST (Momentary) and all that means is that there are two switches inside a single body (Double Pole DP) and there is only one set of contacts i.e. Off - On (Single Throw)

    On - Off - On
    would be like the 2 position switch you find on Nav/Off/Anchor hence Double Throw DT i.e. you DONT want a DPDT

    Wire both commons to +ve and each output to a single pump but there will be no cross feed when the switch is open.

    Bad Diagram but ;-
     

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  7. AndySGray
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    AndySGray Senior Member

    Oh yes and you need 3 fuses

    one for each float switch (after the wire splits) at e.g. 15A (maybe 20A or a slow blow 15A)

    and a 35A before the manual switch as it draws double for 2 15A pumps.
     
  8. latestarter
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    latestarter Senior Member

    If your dashed wire was via a relay/solenoid which is only on when the manual switch is on it could solve the problem.

    Check with someone who is experienced first as I have no knowledge of boat electrics, just working from first principles.
     
  9. CDK
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    CDK retired engineer

    Instead of hard wiring, insert a diode in the switch wire to each pump, cathode side to the pump. Both pumps then work independent on their float switches, the manual switch controls both.

    Check the actual current consumption of your pumps. The 15A rating is for the fuse, the pump will draw less than half that. If you cannot find 8 or 10 A diodes, use a bridge rectifier instead.
     
  10. sdowney717
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    sdowney717 Senior Member

    Someone shared another schematic for me that works using a relay.

    [​IMG]


    I thought about diodes etc.. but could not imagine how to wire? Could you share that?
     
  11. CDK
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    CDK retired engineer

    Like this:
     

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  12. sdowney717
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    sdowney717 Senior Member

    Thanks, Interesting!

    So the diode blocks the flow.

    I assume there is no connection where the cathode of the right side diode wire crosses across the wire line for the left side diode?

    What type diode can handle this current? Do you have a suggestion to use?

    Using the relay from the other schematic all you need is two cube 40 amp relays which are easy to get.

    The idea of a manual switch for an emergency type pumps is mostly in case the automatic side fails. And to test to see if the pumps run.
     
  13. sdowney717
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    sdowney717 Senior Member

    http://www.ebay.com/itm/2-X-VISHAY-...224?pt=LH_DefaultDomain_0&hash=item56629d5f80

    Would something like these work?
    What about voltage drop in the forward direction? Losing volts to a bilge pump means losing GPH capability. Likely not to matter too much as the float switch is direct wire.

    These have a 70 amp rating with a high surge capacity (1250 amps) which for motors you would want. How much power surge would a bilge pump draw on startup?
     
  14. CDK
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    CDK retired engineer

    "I assume there is no connection where the cathode of the right side diode wire crosses across the wire line for the left side diode?"

    Yes, in ancient times and Omega sign was made on crossings without a connection. Now we place a dot on crossings that are connected, because 9 times out of 10 a crossing is just a crossing.

    There is a small voltage drop across a diode, just about 5% in a 12V system.
    The Vishay diodes are OK but a bit large. As I wrote in post #9 you can also use a bridge recifier. The side marked - goes to your switch, the AC sides go to your pumps.
    You actually use only 2 of the 4 diodes; 20 Amp types have a central mounting hole and "faston" tabs so they're easy to install without any soldering involved.
     

  15. sdowney717
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    sdowney717 Senior Member

    Nice idea. I do have some 30 amp bridge rectifiers from Radioshack.
    And I have a 50 amp bridge rectifier I got off Ebay.
     
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