How to wire a warning light?

[rosie]

My MD7 has Martec fresh water cooling where the coolant is circulated by an electrical pump. I would like to install a warning (buzzer/light) which will operate if the pump fails to run. The pump is supplied by 12v fused from the engine battery via the engine control panel and the circuit is completed with an earth to the engine block. Can any forum electrical wizard suggest a simple solution?

 

[andy_wilson]

Do you want a warning if the pump stops, or if the temperature rises (which would be useful if the pump runs but water supply is blocked partially or fully)?

 

[petersto]

I presume your boat has a temp. guage and what you want is a flow switch from RS. There was a novel way of wiring it up in either the PBO or ST a couple of months ago. Let me know if you would be interested and I will dig it out for you.

 

[rosie]

Hello Andy. I already have a coolant overheat warning as part of the engine control panel. This operates some time after the pump stops!! I had this problem recently as a result of some dodgy connections to the pump and it occurred to me that a "pump not running" warning would avoid the inevitable overheat. The pump is said to be extrememy reliable and I have renewed the connections, nevertheless I thought a simple indication that the pump has stopped(for whatever reason) would be a useful mod.

 

[aluijten]

Although simple, it's not exactly cheap. But it might make you happy:

http://www.sailorssolutions.com/index.asp?page=ProductDetails&Item=FS200

Cheers,

Arno

 

[rosie]

Re: How to wire a warning light?Re Josi

Thanks. I hadn't thought of a flowswitch, but from a quick look they seem expensive. I was thinking of an electrical warning of no volts to the pump (if that is not mutually exclusive!!). I would appreciate info on PBO / ST articles.

 

[aluijten]

Re: How to wire a warning light?Re Josi

It's not so complicated to do this:

You will need:
a 12 (car)relay
a 12 volt buzzer
a warning light (optional)
some wire to hook things up

The relay must be of the type that switches over. This means if no voltage is applied then there must be two switch points connected and when the voltage is applied another contact is made and the original is broken.

Now connect as follows: the coil in the relay is parallel to the pump, so when the pump runs there is 12 volts on the coil. Thsi means that the relay will click as soon as the pump starts running.
The switch inside the relay is connected as follows: one of the switch points (the common point) is conneced to the + of the battery via the engine switch (do NOT use the supply cable of the pump!) the contact point that is broken when 12 volt is supplied to the relay coil is connected to the + of the buzzer and the warning light. The - of the buzzer and the warning light is connected to the - of the battery. Note that most waring lights do not have a + or -. In that case just use one for the relay and the other for the - on the battery.
That's all.
I imagine you can buy the stuff at the Halfords.

Cheers,

Arno

 

[brianrunyard]

Re: How to wire a warning light?Re Josi

The problem with this setup is you are only checking if the 12v supply is present, not if the pump is actually running.
A flow switch or a pressure switch that operates on a fairly low pressure would be better.
The type of pressure switch used in washing machines might be a posibility, it's a diaphragm switch that operates at quite a low pressure.

 

[rogerthebodger]

Re: How to wire a warning light?Re Josi

This is the kind of flow switch I am using
http://rswww.com/cgi-bin/bv/rswww/search...e&Nr=avl:uk

 

[rosie]

Re: How to wire a warning light?Many thanks

Many thanks for your responses. I have decided to go the flowswitch route (from RS). When I finish the job I will post result in case anyone else is interested.

Cheers!