Deo joseph
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Relays

Sat Apr 01, 2017 4:56 am

Hi..
I am using pi-3 to control electrical appliances like fluorescent lamps (inductive load).
Anyone please suggest me which relay should i use?
Requirements:
DC controlled relay(5-12V), AC switching(230VAC/20A)
I need a industry standard highly reliable Electromagnetic relay..

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Re: Relays

Sat Apr 01, 2017 6:09 am

Deo joseph wrote:Hi..
I am using pi-3 to control electrical appliances like fluorescent lamps (inductive load).
Anyone please suggest me which relay should i use?
Requirements:
DC controlled relay(5-12V), AC switching(230VAC/20A)
I need a industry standard highly reliable Electromagnetic relay..
Whatever realy board you pick, make sure it can be switched by the Pi's 3.3v GPIO pins, or you'll find they don't work. There are 100's that are made for the Arduino and other 5v microcontroller platforms which dont work on the Pi.

Getting one to switch 20A will be an issue too. Are you really sure you have that much lighting? That's a large factorys worth.

The sparkfun "Beefcake" relay is the only one that springs to mind that will switch 20 amps @ 230v, however it's a 5v system, so you will need some additional circuitry to make it work reliably on a Pi.

You may want to look for USB switching units. These are mostly plug and go, no soldering, etc. some even have standard 13A mains sockets.

-Gordon
--
Gordons projects: https://projects.drogon.net/

pcmanbob
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Re: Relays

Sat Apr 01, 2017 10:47 am

Deo joseph wrote:Hi..
I am using pi-3 to control electrical appliances like fluorescent lamps (inductive load).
Anyone please suggest me which relay should i use?
Requirements:
DC controlled relay(5-12V), AC switching(230VAC/20A)
I need a industry standard highly reliable Electromagnetic relay..
If you need industry standard relay than I would suggest building your own relay driver board to drive the relays you want , non of the ready made boards will have industry standard relays they will just use small pcb relays that are not designed to switch that sort of load.
this is the sort of relay you will need to switch that sort of load http://uk.rs-online.com/web/p/non-latch ... s/8278541/ you will not find this sort of relay on a ready made board.
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Deo joseph
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Re: Relays

Tue Apr 04, 2017 4:02 am

Thank you..

Deo joseph
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Re: Relays

Tue Apr 04, 2017 10:17 am

What if i make use of this relay.. http://www.digikey.com/product-detail/e ... -ND/404546 for my project..

PiGraham
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Re: Relays

Tue Apr 04, 2017 10:32 am

Deo joseph wrote:What if i make use of this relay.. http://www.digikey.com/product-detail/e ... -ND/404546 for my project..
No, definitely not. That has a 12V coil that draws 1.9W you can't drive that from GPIO.

Deo joseph
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Re: Relays

Tue Apr 04, 2017 10:42 am

Ya not possible from GPIO pins..If i use a driver IC TPL7407L..?

pcmanbob
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Re: Relays

Tue Apr 04, 2017 10:50 am

Deo joseph wrote:Ya not possible from GPIO pins..If i use a driver IC TPL7407L..?
Yes you could use that relay if you used aTPL7407L to drive it but you would need a 12v dc power supply to power the relay coil.
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PiGraham
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Re: Relays

Tue Apr 04, 2017 10:51 am

You might find something here
http://uk.rs-online.com/web/c/relays/so ... 4294535071

At 3V 10mA Pi gpio could drive one of these directly. If you need to control more than one use some other switching device, like a ULN2804 driver or some discrete transistors.

Deo joseph
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Re: Relays

Tue Apr 04, 2017 10:55 am

Thank you..That was a great help!

Deo joseph
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Re: Relays

Tue Apr 04, 2017 10:56 am

One more question do i need to use optocouplers is it necessary?

pcmanbob
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Re: Relays

Tue Apr 04, 2017 11:10 am

PiGraham wrote:You might find something here
http://uk.rs-online.com/web/c/relays/so ... 4294535071

At 3V 10mA Pi gpio could drive one of these directly. If you need to control more than one use some other switching device, like a ULN2804 driver or some discrete transistors.

If you are going to use a driver chip I would recommend the ULN2803A its 3.3v input compatible so you can drive it directly from the gpio .
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Deo joseph
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Re: Relays

Tue Apr 04, 2017 11:35 am

pcmanbob wrote:
PiGraham wrote:You might find something here
http://uk.rs-online.com/web/c/relays/so ... 4294535071

At 3V 10mA Pi gpio could drive one of these directly. If you need to control more than one use some other switching device, like a ULN2804 driver or some discrete transistors.

If you are going to use a driver chip I would recommend the ULN2803A its 3.3v input compatible so you can drive it directly from the gpio .

But ULN2803A requires more current which the board is not able to supply when we are using 48 digital I/O pins

pcmanbob
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Re: Relays

Tue Apr 04, 2017 11:52 am

Deo joseph wrote:
pcmanbob wrote:
PiGraham wrote:You might find something here
http://uk.rs-online.com/web/c/relays/so ... 4294535071

At 3V 10mA Pi gpio could drive one of these directly. If you need to control more than one use some other switching device, like a ULN2804 driver or some discrete transistors.

If you are going to use a driver chip I would recommend the ULN2803A its 3.3v input compatible so you can drive it directly from the gpio .

But ULN2803A requires more current which the board is not able to supply when we are using 48 digital I/O pins
was only a suggestion instead of the ULN2804 which 6-15v input
you never mentioned driving 48 I/O pins if you are going to drive 48 relays you will need more I/O any way and a separate psu to power them
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PiGraham
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Re: Relays

Tue Apr 04, 2017 12:02 pm

pcmanbob wrote:
PiGraham wrote:You might find something here
http://uk.rs-online.com/web/c/relays/so ... 4294535071

At 3V 10mA Pi gpio could drive one of these directly. If you need to control more than one use some other switching device, like a ULN2804 driver or some discrete transistors.

If you are going to use a driver chip I would recommend the ULN2803A its 3.3v input compatible so you can drive it directly from the gpio .
Good point.

PiGraham
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Re: Relays

Tue Apr 04, 2017 12:09 pm

Deo joseph wrote: But ULN2803A requires more current which the board is not able to supply when we are using 48 digital I/O pins
Pi gpio, the signals you control with software, can only handle small currents (16mA each), and the dhip can only handle a small total over all gpio. Those SSRs take 10mA input. A limit of 51mA total means you could brive only five SSRs at once.

You can draw power from the power pins (3.3V pins) up to the limit of the regulator. That will be much higher than the gpio 50 mA and you could use a driver chip powered from those pins to drive more SSRs. This topic suggests a limit of 250mA. I don't know if that's correct. You should check if you neds lots of channels, but IF it's right you could drive 25 SSrs because the you will need tiny currents from the gpio to drive the darlingtons and they will handle the 10mA x 25 which the 3.3V pins can supply.

Deo joseph
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Re: Relays

Tue Apr 04, 2017 12:14 pm

OK.. Thank you for all your inputs..

Deo joseph
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Re: Relays

Thu Apr 06, 2017 3:38 am

hi..
with all Your inputs i am planning to go ahead with my project..
this is what i am doing..
Pi-3>> I/O Port Expander (MCP23017)>>Relay driver(ULN2803)>>Relay(G7L-1A-BUBJ-CB-DC12)>>AC Lamps

G7L Specs:-
Coil Voltage: 12VDC , Coil Current: 158 mA
Switching voltage: 250AC , Contact Current Rating: 30 A

is that right or do i miss anything?
Please guide me in choosing the power supply unit..that can power up 2 Pi-3 board and 48 Relays..
(Fixed dual voltage DC power supply 5V and 12V so that i can power up pi board and relays )

pcmanbob
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Re: Relays

Thu Apr 06, 2017 8:30 am

make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.
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PiGraham
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Re: Relays

Thu Apr 06, 2017 9:26 am

pcmanbob wrote:make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.
A PC ATX PSU could do the job at the lowest price. Here's one:

http://www.ebuyer.com/255700-ace-black- ... ace40012cm

DC+3.3V +5V +12V1 +12V2 -12V +5VSB
Output 18A 20A 8A 13A 0.3A 2A
Max  400W  
I read that as 5V 20A and two 12V 8A + 13A which is plenty.

Deo joseph
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Re: Relays

Thu Apr 06, 2017 9:47 am

pcmanbob wrote:make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.

Why 7A at 5V ??
The Pi-3 board needs only 700mA and Maximum current i can draw from board is 50mA..

SteveSpencer
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Re: Relays

Thu Apr 06, 2017 9:58 am

Hmm. If the Pi3 only needs 700mA, why is the recommended supply for it a 2.5A one?
Steve S
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pcmanbob
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Re: Relays

Thu Apr 06, 2017 10:00 am

Deo joseph wrote:
pcmanbob wrote:make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.

Why 7A at 5V ??
The Pi-3 board needs only 700mA and Maximum current i can draw from board is 50mA..
opps my bad, should have been 5A this allows for anything you might add to the usb. you could probably get away with 2A per pi so total 4A at 5v if you are not going to plug any thing else in to the usb, and 700ma is at idle if you are running programs on it you may need more. also you may need 5v for any attached electronics they will need power form some ware.
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PiGraham
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Re: Relays

Thu Apr 06, 2017 10:06 am

Deo joseph wrote:
pcmanbob wrote:make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.

Why 7A at 5V ??
The Pi-3 board needs only 700mA and Maximum current i can draw from board is 50mA..
No, the 50mA is a limit on the switchable gpio pins, not the board. You can draw more than 50mA from the 5V/GND pins, maybe 250mA

PiGraham
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Re: Relays

Thu Apr 06, 2017 10:16 am

pcmanbob wrote:
Deo joseph wrote:
pcmanbob wrote:make sure you use a ULN2803A the A is important as this version has diode protection built in to protect the transistors from back emf from the relay coils.

As for the psu I would think you will need to build one as you will need 7-8A at 12v and 7A at 5v, I doubt you will find one on the shelf to do that.

Why 7A at 5V ??
The Pi-3 board needs only 700mA and Maximum current i can draw from board is 50mA..
opps my bad, should have been 5A this allows for anything you might add to the usb. you could probably get away with 2A per pi so total 4A at 5v if you are not going to plug any thing else in to the usb, and 700ma is at idle if you are running programs on it you may need more. also you may need 5v for any attached electronics they will need power form some ware.

48 x .158A = 7.58A, say 10A for safety.
The gpio expanders will need a supply (3.3V) but there are only three of them and current is minimal if they only drive the darlingtons, so could probably run from Pi 3.3V output.
5V 2.5A for one Pi3B (allows for typical USB peripherals).

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