i need help of this Relay circuit.

[xiaobai00]

need help from u guys, please. A million thanks if can help. =(

i have problems of this circuit layout.

1) what's the purpose for dotted line between pin 12 to 11? But the ic is ULN2003. Is the dotted line meant to be repeated the circuit as in pin 10?
2) Is the relay RL7 example is included with the switch (S7)?
3) Do relays have ohms reading, example 200ohm, 12V? I dont understand well, sorry.
4) What is the meaning of N and PH bottom of the image?

**broken link removed**

 

[mneary]

You will find most excellent advice here .

 

[xiaobai00]

please post if you know anything. Thanks alot =(

 

[mneary]

Your improved questions are helpful.

1) The dotted line may indicate a repeated circuit; hard to tell in this context.
2) I think S7 is a switch and isn't part of a relay.
3) Yes, that's a normal relay specification.
4) Neutral, Phase

 

[xiaobai00]

i need a majority views of this. =(

Heard what my teacher told that S7, the switch is included in DPDT relay. True or False?

if 12V DPDT relay, and the coil resistance is more than 200 ohm, lets say more than 800-900 ohms can able to use in the circuit?
P.S i couldnt find exactly the requirement of relay, 12V and 200ohm DPDT relay. How?

Thanks alot for point 4. =D

 

[mneary]

It's clear to me that the two unmarked NO and NC pairs linked by a dotted line are the DPDT relay contacts and S7 is a switch. You can only confirm for sure by looking at the actual appliance. A vote won't help.

 

[Azaruk]

The dotted line, imho, does indeed indicate that the relay circuitry is copied onto those pins.

A relay coil will show resistance when measured with an ohm-meter.

All "S" identifiers are switches. The other contacts shown are the relay contacts. The switches are seoarate components and are not physically part of the relays.

"N" indicates the Neutral side of the mains supply, while "PH" indicates the Live side of the mains.

Remember, when working with ciruits connected to the mains supply to be careful! Also, ensure that any metal chassis or casing is adequately earthed.

I hope this has been helpful.

 

[ljcox]

i need a majority views of this. =(

Heard what my teacher told that S7, the switch is included in DPDT relay. True or False? False. If S7 was a contact on Rl7, the relay could not operate.

if 12V DPDT relay, and the coil resistance is more than 200 ohm, lets say more than 800-900 ohms can able to use in the circuit? Yes.
P.S i couldnt find exactly the requirement of relay, 12V and 200ohm DPDT relay. How?

Thanks alot for point 4. =D

This is not a good design since the relay has low and high voltages on its contacts. Therefore you will need a relay that has good isolation between the contacts. Otherwise, there could be a flash over from the contacts with the mains connected to them to the 12 Volt contacts.

 

[Azaruk]

The coil resistance of a relay simply gives an indication of the current you can expect to be drawn by the circuit when the relay(s) are energised. (A simplification, I know, but in this case, that's all that is required). A higher resistance = less current, but CAN lead to a slower response time. For switching appliances, relay closure speed will not be an issue.

 

[xiaobai00]

for S7, switches, may i know what is the type of switches? Otherwise i wont know what to buy when asking the staff in any electronic store.

For relays, switches only contain NO, NC and CO, right? There's no include with switch indicates with "S", right?

my question is does relay resistance ohm important? I couldnt manage to find the exact relay required for this circuit, 12V, 200ohm.

 

[Hero999]

please post if you know anything. Thanks alot =(

It can take a couple of days for someone to reply to a thread and you only waited less than an hour! Please try to be more patient, if you don't recieve a reply within a week then try bumping the orignional thread and adding more information.

 

[Azaruk]

The switch (S8) is a single-pole toggle switch, rated for mains voltage. The current rating should be adequately rated for the maximum current drawn by the appliances. (S8) is, in effect, a master switch.

The other switches can be much smaller as they only activete the relays. They couild be miniature toggles, slide or rocker switches, low voltage, low current.

For complete safety, consider changing (S8) to a double-pole switch, one pole for (PH) the other for (N), so that mains voltage is completely isolated from the circuit when switched off.

The relays are 12V coil with two sets of change-over contacts. Commonly referred to as double-pole, double-throw.

 

[xiaobai00]

May i know ohm value is important to relay? I couldnt manage to find 200 ohm for DPDT relay.

 

[Sceadwian]

It's important for driving it. If you have a 5 volt supply to drive the relay and the relay requires 100ma's for switching the 200ohm resistance is only going to allow 25ma's which means the relay won't trigger. So it really depends on the voltage you're going to trigger the relay with and the current required by the relay to switch.

 

[ljcox]

May i know ohm value is important to relay? I couldnt manage to find 200 ohm for DPDT relay.

The important issue is what voltage is required to operate the relay. The coil resistance is not important.

According to your circuit,you have a 12 Volt supply, so buy a relay that is specified to operate on 12 Volt.

 

[Sceadwian]

ljcox, coil resistance is important if the voltage of the relay and the driving circuit aren't the same. If he has a 5 volt relay he can still use it, as long as he puts in a current limiting resistor to drop the other 7 volts. Providing a higher voltage than rated for the relay for brief switching periods can actually cause the relay to switch faster and is still safe provideing too much power isn't provided.

 

[ljcox]

Agreed, but I was trying to keep it simple. He seems confused enough already.

EDIT:
Xiaobai00, The ULN2003 can sink up to 500 mA. So the resistance of the relay coil will not be critical. But, as Sceadwian wrote, you will need a resistor in series with the coil if the relay operates from less than 12 Volt.

Pin 9 of the ULN2003 must be connected to the +12 Volt supply in order to protect the transistors from the back EMF of the relay coil when it is released.

Tell us the details of whatever relay you intend to use so we can advise you further.

What is its operate voltage and coil resistance.

You could use two 5 Volt relays in series. This has the advantage that the high and low voltages are separated. If you want to do it this way, let me know and I'll post a circuit.

 

[xiaobai00]

thanks guys for info. i will post up the picture of relay i bought.

 

[xiaobai00]

and now one problem that is confusing me about switches indicated with "S". May i know what kind of switch in order to ask from the staff in any store.

 

[xiaobai00]

do u guys have the datasheet of DPDT relay? So that i may know which pin is for NO, NC, CO as well as the coil. Total pins it have 8 of them .