Using a 240v switch on a 12v circuit

[Tony Brooks]

41 minutes ago, bizzard said:

I think they're really only used for switching a light on in the bathroom as they are probably micro switches and might burn out putting DC through them. I would use a relay with it which will do the actual switching of the pump. The pull switch just energizes the relay.

I agree. The Gulper motor is likely to be fairly inductive so would produce high voltage surges upon switching off, quiet apart from the fact DC arcs do not self quench every one hundredth of a second.

[Robbo]

50 minutes ago, bizzard said:

I think they're really only used for switching a light on in the bathroom as they are probably micro switches and might burn out putting DC through them. I would use a relay with it which will do the actual switching of the pump. The pull switch just energizes the relay.

+1

Edited December 17, 2018 by Robbo

[alan_fincher]

1 hour ago, Kendorr said:

I'm about to wire in my gulper pump, it's fuse rated at 5 amps. I intend to use a pull switch which is shown in the pic. I have the neutral going direct to the pump and the positive will go in at L1 and out at COM.

The switch has 10AX on it. Am I right to assume this is a 10 amp switch and as such will be fine with the 5 amp fuse fitted to the pump?

 

Thanks, Kevin

Although it has 10AX on it, I'm doubtful that is a genuine 10A switch.

Its use is clearly for small mains lights at 230V AC, so it has no need to be high power.

I've owned a boat that used one of these to work a shower pump.  It really wasn't up to the task, and had to be replaced.

I'd advise against putting a DC inductive load through it.

Edited December 17, 2018 by alan_fincher

[Kendorr]

Thank you for the replies, I'll put it back in the house electrics box!!

That is until I can figure out what sort of relay to use and how to wire it in.

Kevin

[Robbo]

8 minutes ago, Kendorr said:

Thank you for the replies, I'll put it back in the house electrics box!!

That is until I can figure out what sort of relay to use and how to wire it in.

Kevin

Car ones are perfect for job.  Like https://www.halfords.com/workshop-tools/garage-equipment/fuses-electricals-fixings/halfords-hef555-relay-12v-40a-4-pin

 

[Kendorr]

26 minutes ago, Robbo said:

Car ones are perfect for job.  Like https://www.halfords.com/workshop-tools/garage-equipment/fuses-electricals-fixings/halfords-hef555-relay-12v-40a-4-pin

 

Thanks Robbo, from what I can see, my positive feed will go to the pull switch and then through to the relay, pin 87. The positive will then come from pin 30 down to the pump?

 

[Robbo]

23 minutes ago, Kendorr said:

Thanks Robbo, from what I can see, my positive feed will go to the pull switch and then through to the relay, pin 87. The positive will then come from pin 30 down to the pump?

 

Pump side...

pin 30 to fuse/box battery

87 to pump (positive),   pump negative to battery

 

Switch can be done various methods, this is one way...

86 to negative

85 to switch

positive to switch (positive can be taken from pin 30)

 

 

 

[Kendorr]

38 minutes ago, Robbo said:

Pump side...

pin 30 to fuse/box battery

87 to pump (positive),   pump negative to battery

 

Switch can be done various methods, this is one way...

86 to negative

85 to switch

positive to switch (positive can be taken from pin 30)

 

 

 

If I've understood you, my diagram should be correct?

[Robbo]

pin 30 should be too the distribution board and 87 to the pump.

Edited December 17, 2018 by Robbo

[Robbo]

This is what I mean....   87 and 30 are swappable, but the switch needs to be fed from the fuse board side.   The cable to from the switch (from 87/85 pins) doesn't need to as thick as the cable from the board to the pump as pumps like to fed by decent size cable but it needs to within the ratings of the fuse at the distribution board.  ie. if the fuse is 10amp, this bit of cable (and switch) needs to be rated above 10amp.

 

Edited December 17, 2018 by Robbo

[Kendorr]

15 minutes ago, Robbo said:

This is what I mean....   87 and 30 are swappable, but the switch needs to be fed from the fuse board side.   The cable to from the switch (from 87/85 pins) doesn't need to as thick as the cable from the board to the pump as pumps like to fed by decent size cable but it needs to within the ratings of the fuse at the distribution board.  ie. if the fuse is 10amp, this bit of cable (and switch) needs to be rated above 10amp.

 

Got you, thank you so much for the help.

Kevin

[Robbo]

2 minutes ago, Kendorr said:

Got you, thank you so much for the help.

Kevin

The cable from 86 to ground is part of the "switch" circuit so this doesn't need to be as thick either.

[jonathanA]

Just for accuracy, of course the relay, battery  and pump negative are all connected with wires not using the boat hull as “earth return” as in car wiring. 

 

Sure we all knew that but just worth mentioning....

Edited December 17, 2018 by jonathanA

[Flyboy]

On 18/10/2015 at 17:03, Neil Smith said:

That saved me a question as I want to use a 240v light switch for my whale gulper.

 

Neil

I am going to use an ac light switch for the whale gulper.

 

Neil

I've got a 10 amp 240v light pull switch on my Whale Gulper 220. It was fitted by the boat builder and still works fine after 10 years.

[jonathanA]

8 hours ago, alan_fincher said:

Although it has 10AX on it, I'm doubtful that is a genuine 10A switch.

Its use is clearly for small mains lights at 230V AC, so it has no need to be high power.

I've owned a boat that used one of these to work a shower pump.  It really wasn't up to the task, and had to be replaced.

I'd advise against putting a DC inductive load through it.

Actually the AX rating means the switch is rated for reactive loads like fluorescent lighting (although still mains voltage)

 

ive been using an architrave light switch for our gulper for over 8 years and it’s fine so given a pull switch is less than £2 from screwfix I’d keep it simple and use one rather than bugger about with a relay at 2 quid you could buy two and still save money compared to buying and fitting a relay 

 

others will disagree, but your choice - KISS principle applies...

Edited December 17, 2018 by jonathanA

[ditchcrawler]

All my switches are 240 AC rated

[alan_fincher]

11 hours ago, jonathanA said:

Actually the AX rating means the switch is rated for reactive loads like fluorescent lighting (although still mains voltage)

 

ive been using an architrave light switch for our gulper for over 8 years and it’s fine so given a pull switch is less than £2 from screwfix I’d keep it simple and use one rather than bugger about with a relay at 2 quid you could buy two and still save money compared to buying and fitting a relay 

 

others will disagree, but your choice - KISS principle applies...

Yes,

They are cheap, and may well keep going a long while.

 

Just it's fairly annoying if they pack up when you are in the shower trying to use it.

But it's only ever happened to me once, so perhaps I've been unlucky.

Most people seem to be using a rule of thumb that 10A AC equates tosafe use at 5A DC. Given the load is a motor, I think that's pushing things a bit, but as you suggest you may get away with it for years, and maybe lucky it willnot fail eventually.

[GUMPY]

All the 12v switches on Loddon are repurposed 230v ones, they were all fitted in 1994, am I due for total imminent switch failure?

Hope not.

[BEngo]

The 1989- 1990 Crabtree ones in Jarrah are still going so I expect you'll be  OK for a few years yet.  Mind you, modern Chinese made stuff is nothing like switchery used to be.  These days even MK is pretty nasty by 90's standards.

 

N

[Robbo]

Here's an exciting youtube video of the DC vs AC switching...

 

[alan_fincher]

1 hour ago, Robbo said:

Here's an exciting youtube video of the DC vs AC switching...

 

 

This one may be even more pertinent?
 

 

[Robbo]

3 minutes ago, alan_fincher said:

 

This one may be even more pertinent?
 

Ofcourse alot higher voltage so the arc would be a lot more, at 12v it be a arc nothing to write home about, not even at christmas.

[Jen-in-Wellies]

Mains AC switches move the contacts apart over a relatively short distance and rely on the 100 times a second drop to zero to quench the arc between the contacts. Switches designed for DC move the contacts a much larger distance apart as quickly as possible to quench the arc. This is more expensive and harder to manufacture than an AC switch. For higher current DC I have used a 12V 16A DC rated automotive switch in a mains pattress blanking plate, drilled to take the switch. Still looks nice and neat. Alternatively, an automotive relay can be used as described by others. I did this on the bilge pump, where a separate float switch was rated for 2A, but was much cheaper than the high current switches.

 

Jen

[Tony Brooks]

Rather a late comment bit I thought DIN 30 was a live feed into a relay etc. and if so the relays in the diagrams are the wrong way round. Not that this will make any difference in this application but these relay are available with a surge quench diode in parallel with contacts and if I am right then when one of those is wired as shown the diode would be destroyed. Really happy to be proven wrong about this.

[Jen-in-Wellies]

33 minutes ago, Tony Brooks said:

Rather a late comment bit I thought DIN 30 was a live feed into a relay etc. and if so the relays in the diagrams are the wrong way round. Not that this will make any difference in this application but these relay are available with a surge quench diode in parallel with contacts and if I am right then when one of those is wired as shown the diode would be destroyed. Really happy to be proven wrong about this.

Yes, 30 should be to the 12V supply. 87 to the load. See here and here. My understanding is that there can be diodes fitted across the relay coil, 85 and 86 sometimes, in which case these should be connected the right way round, rather than between 30 and 87. The high current pins are only important for polarity if you are using both 87 and 87A, the normally open and normally closed outputs, in which case, unexpected things would happen.

Jen

Edited December 18, 2018 by Jen-in-Wellies