Multiple 5v relays inline

[Guitarnerd]

Hi. I have a project where I'm using 6 5v pcb coil relays so that one power source will switch all 6 at one time. I usually use the pre-made boards but have a space constraint so I thought I'd be able to just use the switch coils by themselves. I tried one and it worked fine so I wired up all 6 and things got a little nuts. The relays would not switch and my volt meter was reading around 0.6v where the supply voltage was a little over 5v. I'm clearly doing something wrong but not sure what that is. Any guidance would be greatly appreciated.

 

[Bluejets]

Place coils in parallel, use a power supply sufficiently sized for all 6 coils (plus about 50% margin to allow for inrush current).
No idea where you are measuring power or how your connections are made so supply a photo and a pencil sketch of everything.

 

[Guitarnerd]

This is an example of what I'm getting.

 

[Guitarnerd]

This is an example of what I'm getting.View attachment 65575

I'm very confident that my power supply is more than enough to power these 6 coils.

 

[Martaine2005]

What PIN numbers are you connecting to?.
Perhaps you have a current limit set too low for 6 coils on your power supply?

 

[danadak]

This is correct way to wire these for operation off 5V.



Your nominal current is ~90 mA / relay, so 450 mA required by supply.

What exactly is the supply, eg. schematic ?

Note there should not be an inrush current per se as they are inductive in
nature, question is are they low Q so current transient pretty damped....
But there is a minimum V, I needed to get them to turn on. And then holding
V, I is lower.

Regards, Dana.

 

[Guitarnerd]

What PIN numbers are you connecting to?.
Perhaps you have a current limit set too low for 6 coils on your power supply?

I was running from pin 9 on a Leonardo board.

 

[Guitarnerd]

This is correct way to wire these for operation off 5V.

View attachment 65578

Your nominal current is ~90 mA / relay, so 450 mA required by supply.

What exactly is the supply, eg. schematic ?

Note there should not be an inrush current per se as they are inductive in
nature, question is are they low Q so current transient pretty damped....
But there is a minimum V, I needed to get them to turn on. And then holding
V, I is lower.

Regards, Dana.

That all makes sense to me. The power supply is a OneSpot, so, 9vdc 1700mA. I have it passing through a voltage regulator that drops it to about 5.5vdc. I had the negative tied to the regulator and the positive coming from pin 9 on an an Arduino Leonardo. Maybe, as noted by Martaine2005 the pin can't push enough voltage to it?

 

[bertus]

Hello,

The relays can not be driven by an arduino pin.
You will need a buffer between the arduino pin and the relays.

Bertus

 

[Bluejets]

Also, some relays will have a freewheeling diode installed and incorrect coil connection will cause the diode to short the supply.

 

[danadak]

You have to read datasheets and their pin ratings to succeed at designs.

From the data sheet look at pin and max allowed current in the MCU supply
rail ratings :

 

[Guitarnerd]

So, I'm thinking about adding a7th relay that triggers from the arduino and that one relay will switch power to all the others. That should work, right? The arduino can switch one relay at 5v 72mA for the one relay, can't it?

 

[danadak]

See the DC current in the previous post ratings ?

And the logic level specs on a pin -



You have to switch the one relay with something like this -



Diode 1N4007 or equiv. Transistor 2N3904, 2N2222.......

 

[Guitarnerd]

See the DC current in the previous post ratings ?

And the logic level specs on a pin -

View attachment 65603

You have to switch the one relay with something like this -

View attachment 65605

Diode 1N4007 or equiv. Transistor 2N3904, 2N2222.......

Thank you. I was looking at something that looks very similar. I was planning on this without the indicator leds.

 

[danadak]

One correction to the earlier post, since you need to drive ~ 450 mA,
a 2N3904, 2N2222 not adequate as the base drive to get the transistor
is ~ 45 mA, too much for the MCU GPIO pin.

Either use a logic level MOSFET (preferred) or a darlington TIP type transistor,
either in a TO220 type package. Say 60 - 100V breakdown to give you plenty
of margin.

Regards, Dana.

 

[Guitarnerd]

One correction to the earlier post, since you need to drive ~ 450 mA,
a 2N3904, 2N2222 not adequate as the base drive to get the transistor
is ~ 45 mA, too much for the MCU GPIO pin.

Either use a logic level MOSFET (preferred) or a darlington TIP type transistor,
either in a TO220 type package. Say 60 - 100V breakdown to give you plenty
of margin.

Regards, Dana.

Like these?

Amazon.com

 

[bertus]

Hello,

Mouser has stated the mentioned part as obsolete.
You could use one from this page:

https://eu.mouser.com/c/semiconductors/discrete-semiconductors/transistors/mosfets/?package%20%2F%20case=TO-220-3&transistor%20polarity=N-Channel&vds%20-%20drain-source%20breakdown%20voltage=60%20V&vgs%20th%20-%20gate-source%20threshold%20voltage=2%20V&instock=y

Bertus

 

[danadak]

Like these?

Amazon.com

Overkill on current rating but should be OK.

This should be interface (ignore MOSFET part number). Note change the 100K from
gate to ground with 10K. To minimize effects of noise pickup at gate thru parasitic C
coupling.



Regards, Dana.

 

[Bluejets]

Op still has not supplied the detail on each relay.

 

[Guitarnerd]

I'm almost done with my project and all the guidance has been a tremendous help. Thank you all!