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Wiring a Relay - Help Please


bargebird

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I have read on here that its a good idea to wire a relay to the domestic water pump to stop the pump's own micro switch from wearing out.

So I have now got a standard 30amp automotive relay with the terminal numbers-:

30 - 85 - 86 - 87

Can anyone tell me which wires I connect to which terminal?

I use a Par-Max 3 pump and have the necessary connectors

but no idea how to wire it to which cool.png

Thanks as always

 

Jules

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Does this help?:

 

 

 

Terminal/Pin number Connection

85 Coil

86 Coil

87 Normally Open (NO)

87a Normally Closed (NC) - not present on 4 pin relays

30 Common connection to NO & NC terminals

 

http://www.12voltplanet.co.uk/relay-guide.html

 

Richard

 

MORE: 85 and 86 are the coil - the bit you power to switch the relay

 

30 and 87 are the bit that gets switched on when you power the coil (on 85 and 86)

Edited by RLWP
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So at the moment, +12v will come into the pump switch, go out of the pump switch to the pump motor, and then on to the -ve.

 

You have to break into the wire between the switch and the pump motor, ie cut or disconnect it. Wire the switch side of this wire to the coil (85). Wire 86 to -ve. Wire the pump motor side of the wire mentioned above, to 30. Wire 87 to the incoming +12v (in addition to the existing connection from +12v to the switch.

Edited by nicknorman
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We LOVE this kind of question

 

Richard

 

Next, we will start an almighty falling-out over wire sizes, voltage drop, appropriate fuse sizes, the need for the relay, pump out toilets, immigration and cheese. It's just how it is here

 

Where do you stand on custard?

Edited by RLWP
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Next, we will start an almighty falling-out over wire sizes, voltage drop, appropriate fuse sizes, the need for the relay, pump out toilets, immigration and cheese. It's just how it is here

 

 

and snubber diodes, don't forget those.

 

MP.

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I have read on here that its a good idea to wire a relay to the domestic water pump to stop the pump's own micro switch from wearing out.

 

Can we rewind a bit? Can someone explain this please?

 

Why would the pump's switch wear out? What is a micro-switch anyway? I thought a domestic water pump had a pressure switch?

 

My previous pump lasted 5 years (liveaboard use) and when it eventually failed it wasn't because of the switch. The "new" pump is now 5 years old and still going strong (hope I haven't spoken too soon).

 

So what's with using a relay?

Edited by blackrose
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Can we rewind a bit? Can someone explain this please?

 

Why would the pump's switch wear out. What is a micro-switch anyway? I thought a domestic water pump had a pressure switch?

 

My previous pump lasted 5 years (liveaboard use) and when it eventually failed it wasn't because of the switch. The "new" pump is now 5 years old and still going strong (hope I haven't spoken too soon).

 

So what's with using a relay?

 

Oh Mike - I've been biting my tongue not asking that question!

 

I suppose that the best thing to do would be to use the pressure switch to power a relay to turn on the pump. That's what NickNorman described. It would take switching the motor current away from the pressure switch

 

None of our pumps do this, and they don't get the use that yours does. As a piece of empirical evidence, your experience says the relay isn't needed

 

Richard

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Pump switches can "wear out" because each time the switch contacts open, the inductance of the motor tries to keep the current flowing which leads to arcing of the contacts. Over time the contacts can burn and oxidise until they no longer work. However, it is quite feasible that something else will fail in the pump first. However, that was not what the OP was asking and since she had already got the relay it was a moot point.

 

A pressure switch comprises a diaphragm and plunger that moves as the pressure changes, operating a microswitch. The latter component is just a standard thing that is a switch operated by a small amount of travel, with built-in hysteresis.

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As a piece of empirical evidence, your experience says the relay isn't needed

 

Richard

I'm sure the life of the switch will vary with the make and model of the pump. And also the supply voltage (ie any wiring voltage drop) since a reduced voltage will result in the pump taking more current and thus more arcing when the contacts open. But certainly our pump doesn't have a relay and has survived 4 years of leisure use so far. But as we both said, that wasn't what the OP asked.

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Interesting, thanks for the explanations. While I'm not necessarily against modifying "industrial design", I also can't help thinking that if the modification was necessary or even beneficial, then perhaps it would already have been included by the manufacturer.

 

Do any pump manufacturers include a relay as part of the design?


But as we both said, that wasn't what the OP asked.

 

No, but it is what I asked.

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Do any pump manufacturers include a relay as part of the design?

 

Don't know - and you are entering into the fascinating world of value engineering. Does a customer want to pay less for a pump that doesn't last as long, or more for one with a relay that lasts longer. And if so, how much?*

 

What's the optimum cost/life span ratio for a manufacturer?

 

I suspect that, when you get seriously into this, you buy pumps, separate pressure switches, relays, construct a circuit with appropriate boxing, wire diameters, fusing, connectors and so on...

 

Embrace the 'what' Mike, the 'why' is just sooo complicated

 

Richard

 

*Actually, I think I've answered my own question. Yes - people are prepared to pay for the simplicity of an integrated pump/pressure switch over the cost of the separate components

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With over 30 years working on electrical system within NB's.

 

It is normally the pump which dies first not the switch.

 

And I have never fitted a relay to any from of pump other than a toilet as supplied.

 

Keith

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A bit off topic since the OP was talking relays but one of my (elderily) pumps did in its' micoswitch. Contacts shot. I thought relay but put a diode on the new switch instead. Eight years on I'm not sure if it helped.

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It is best to use a relay adjacent to the pump, if the pump is a long way from the switch, as you can eliminate problems with voltage drop.

Just use the larger size cable to feed the pump motor via the relay contacts and smaller cable, via its own fuse, for the switch/pressure switch/relay circuit.

If you really want to get complicated you can have circuits that enable the pump from different locations.

You should still put a large diode as a back emf suppresser across the relay contacts as the cheaper relays still will burn out the contacts, in the same way that the microswitch in the pressure switch will burn out without one.

The pump suppliers save you at least 20 pence by not fitting one!

As others have stated - any switch or relay operating an inductive DC load will last much longer with a diode fitted

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I have been using a simple, non-diode, automotive relay on my water pump (two switches) for about 15 years. No sign of contact burn out yet. It is , I see, to recall, a 40 amp one though, not 10 amps.

 

Edited to add that I did it because I am using ordinary domestic light switches as pump switches so would be asking for contact problems if I let those handle the motor current.

Edited by Tony Brooks
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With over 30 years working on electrical system within NB's.

 

It is normally the pump which dies first not the switch.

 

And I have never fitted a relay to any from of pump other than a toilet as supplied.

 

Keith

 

I've had a microswitch in a pump die. I replaced the microswitch which fixed things for a bit, but the pressure switch cut-in and cut-out pressures started varying wildly, so I installed a separate adjustable pressure switch. That also uses a microswitch, and since I anticipate not having to replace it, I installed a relay to protect that microswitch, The pump whose microswitch failed is still going fine, controlled by the external pressure switch and relay, four years later.

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Don't know - and you are entering into the fascinating world of value engineering. Does a customer want to pay less for a pump that doesn't last as long, or more for one with a relay that lasts longer. And if so, how much?*

 

What's the optimum cost/life span ratio for a manufacturer?

 

I suspect that, when you get seriously into this, you buy pumps, separate pressure switches, relays, construct a circuit with appropriate boxing, wire diameters, fusing, connectors and so on...

 

Embrace the 'what' Mike, the 'why' is just sooo complicated

 

Richard

 

*Actually, I think I've answered my own question. Yes - people are prepared to pay for the simplicity of an integrated pump/pressure switch over the cost of the separate components

 

Maybe the money's better spent on a larger accumulator?

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Maybe the money's better spent on a larger accumulator?

Everything has a downside! Larger accumulator means less likely to notice a slow leak, longer periods when the supply is at the lower end of the pressure range (also of course longer periods when the supply is at the upper end of the pressure range, but that is no help if you only want to run off a small amount of water) and cost-wise it's probably less good value for money than a relay. Down-side of a relay is probably just the hassle of fitting it, can't think of any once it's installed.

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