wiring question - relay schematic

Hi gang, I have a project in the shop, and I need some help wiring in a relay. The schematic can be seen here (the RH2 one)

I have a 12 volt circuit that is to control a 110V AC water pump. This is a stationary engine cooling pump, so when the power is 'on' to the ignition, I want the 110V AC water pump turned on.

I am trusting in the electical supply warehouse sold me the right relay. It is an IDEC # RH2B-V DC12V. The water pump is rated at 5.5 amps.

I need someone to use simple language to explain where the connections need to be made, such as where the 12V switch power and ground goes in, and how I should wire the 110V side. Thanks to all helpful people, ron

You want to wire your system the following way.

The input to the coil of the relay (input 13 to negative, 14 to positive) is 12v output from the engine. You have to make sure that it is the kind of output that is only available when the motor is running (ie not connected directly to battery).

Wire the 110v neutral directly to your pump. Wire the 110v hot to the contact 1 of the relay. Wire the motor's 110v input to contact 5 of the relay.

i

I have a little indigestion over this whole thing...

A bit of advice I got from the CEO of a leading IC manufacturer some years back is a lesson I've learned to live by: "Didn't read the data sheet? Then ye shall have no pie."

Sooooo.... I read the data sheet on this device. The contacts are rated at only 10 amps. This applies to a resistive load (lights or a heating element...). Inductive loads (motors, etc.) are a horse of a very different color. If the pump is rated at 5.5, the starting surge is probably a good deal more than 10. This suggests the life expectancy of the relay may be a bit in doubt.

Therefore, to make the best of things, since the relay has two sets of contacts, connect them in parallel. In other words, connect the 110 volt hot wire to both Pin 1 and Pin 4. Connect the power lead to the motor to both Pin 5 and Pin 8. This will effectively give you a 20 amp relay, which should last a LOT longer...

Jerry

Sorry about the posting time. PC clock is going bonkers. Sync'd time earlier and the sob changed on me...Paul

Umh. It seems to me that the pins 1/5, and 4/8 are the normally open and normally closed contact pairs, and pins 9 and 12 the moving contacts. I don't think you will ever make a connection between pins 1 and 5 or 4 and 8.

Jerry's idea to wire up both sets of contacts is a good one.

You will also need a diode across the coil to keep from inductive kickback from arcing the switch every time you shut of the switch. Since the relay the coil has a + and - marking this may be built into the relay, but I didn't find anything on the data sheet

so I'd put one in just to be safe. A 1N4004 diode should work and are generally easy to come by.

Here's my recommendation

Pin 14 to the +12 volt switch (as others have said make sure this is only on when the motor is running) Pin 13 to ground Pins 9 and 12 to the AC hot line Pins 5 and 8 to the motor. Connect the cathode of the diode (the end with the stripe or other indicator) to Pin 14 and the other end to pin 13.

Carl Boyd BSEE

Carl's right on the Pin 9 & 12 thing. I guess I was half asleep when I wrote my earlier post. I thought about the diode thing, but figured there was no need to complicate things. If the relay were being controlled by, say, a transistor, the diode would be essential. But the intent is to hook it directly to the ignition switch which is already hooked to the highly inductive (and low impedence) coil, etc. Any inductive kick from this little bitty relay won't have much effect on the overall circuit.

Jerry

What wonderful responses, this REALLY helps me out!

Regarding the diode, would it change your mind if I were to tell you that the 12V signal is coming from a simple 12volt relay that I have on the control panel which engages when the ignition switch is ON. Does that negate the requirement of the diode?

once again, THANK YOU! ron

I must have installed hundreds of Idec RH relays over the years. I'll agree with Jerry that the diode is uneccessary in this case and that the contacts are marginal for your load. But I'll also concur that by doubling up the contacts, and due to the fact that the switching frequency will presumably be very low, you'll be just fine.

Ned Simmons