Quick question about automotive relays on boat

[stuhaynes]

Automotive Relay 24V 40Amp 5Pin Changeover With Bracket - Genuine Tyco Part. Just ordered from fleabay.

I believe the coil terminals are 85 and 86. Are these relays positive / negative sensitive? Does it actually matter which way they are connected? Common sense would seem to suggest it does matter to prevent the relay trying to fly the wrong way!

Without digging over old ground about my water pump switch failures, I've had another one. The external switch I fitted to replace the bad one on the water pump was fine for everything but the auto washing machine. With the sort of extended running that the washer requires to operate, the (250VAC 22Amp) microswitch is overheating, hence the relay, suggested by Elton in an old thread.

Thanks in advance.

 

[NickRobinson]

A single throw, purely electromechanical (no semiconductors) relay will 'pull in' whichever polarity is used, I think.

Nick

 

[Billjratt]

+1 and well-mentioned about the semiconductors, as some devices have an internal diode across the coil to suppress back-emf.
Some relays have a diagram on the cover, or the cover can be popped off for a look.
If there's a diode leave it connected and observe correct polarity as it will prolong the life of the contacts used to energise the relay.

Question - is the automatic washing machine using the waterpump which is driven by a relay and microswitch? ...and the microswitch is overheating???

Or is this another system altogether?

 

[nigelmercier]

I believe the coil terminals are 85 and 86. Are these relays positive / negative sensitive? Does it actually matter which way they are connected? Common sense would seem to suggest it does matter to prevent the relay trying to fly the wrong way!

Do you mean this one? If so, connect to the coil either way between 85 and 86. However, if I was using it I would put the +24 on 85 and 0V on 86, so they "look right" with the positive voltage at the top.

Terminal 30 is the switch common (C), 87a is normally closed (NC), 87 is normally open (NO). Terminal 87 is the one that makes with C when you energise the coil.

 

[stuhaynes]

+1 and well-mentioned about the semiconductors, as some devices have an internal diode across the coil to suppress back-emf.
Some relays have a diagram on the cover, or the cover can be popped off for a look.
If there's a diode leave it connected and observe correct polarity as it will prolong the life of the contacts used to energise the relay.

Question - is the automatic washing machine using the waterpump which is driven by a relay and microswitch? ...and the microswitch is overheating???

Or is this another system altogether?

I don't think that there is a semiconductor. There is no mention in the spec. Then again ebay is not big on stuff like this and I don't know enough to judge. The micro switch was connected to the last pump, the relay is being added to save the micro switch when connected to the other pump. Hope the following reply makes it clearer. I know that this all sounds confusing, it's doing my FHI!

Do you mean this one? If so, connect to the coil either way between 85 and 86. However, if I was using it I would put the +24 on 85 and 0V on 86, so they "look right" with the positive voltage at the top.

Terminal 30 is the switch common (C), 87a is normally closed (NC), 87 is normally open (NO). Terminal 87 is the one that makes with C when you energise the coil.

Yes, it's exactly this one. The idea is that I will use the external pressure switch to energise the coil (about 150Milli amps I think) on the relay, and that way relieve the current on the micro switch. If it works, given that my pressure switch has failed 4 times in the last year (I reported 5, but when the pump came back from repair the last time, last week, the original PS was still fitted). If this does work it's going to save lots of people lots money and total aggravation.

I ought to point out that I have a second pump, the one that came back last week which we're using now). I'm trying to get the mod finished before it fails again. The previous record was 7 days.

Also worth mentioning that the cost of the parts at RS components including VAT and delivery was just over £20. Bought the lot, including P&P and VAT for a fiver. Beats £120 for a new pump if warranty expired!

Thanks for the help so far.