controlling multiple relays

Forum 2005-2010 (read only) Hardware Interfacing
1

I have project where I am controlling 6 relays that need 5V each to "switch on".

My question is this:
Since I may need to supply 5V to 6 relays at one time, I am assuming the arduino cannot handle this, so does that mean that I am going to have to make 6 separate 5V power supplies for my project? or is there a more effective way to cut up a large amount of electricity into 5V "pieces"
I also cannot use batteries for this project.
can someone point me a good direction?

thanks

2

First we would have to know the current demands of each of the 5vdc relays, do you have a spec sheet for the relays? If not too high then it is possible that the Arduino's 5vdc power could be used. If the total current requirements for all 6 relays (assuming that there is situations where all five must be activated) is too much for the Arduino's internal power limits then ONE external 5vdc supply would work fine assuming it's maximum current capacity is equal or greater then the demand for the 6 relays, there is no need for 6 separate 5vdc supplies.

The biggest problem is the Arduino's 5vdc current capacity is different and much less when being powered from the USB cable Vs using an external power pack plugged into the Arduino.

Anyway see what you can find out about the relay's coil resistance or current requirements, the best solution will follow having that information.

Lefty

PS: I've asked this question before but not received an answer yet. What is the 5vdc current limit of the standard Arduino board when using just the USB cable? 100MA?, 500MA? I assume the answer lies with the FT232R USB controller chip and what it asks for in additional 5 volt current if any from the PC's USB controller?

3

thanks retrolefty!

I think it would make more sense for me to use one seperate 5V power supply to power them, I really appreciate you clearing that up for me!

anyways here's the spec sheet for the relay that I'm using 677-OJE-SH-105DM:

but it kinda looks like russian to me. But using a 5v power supply makes sense if I can decipher this data sheet
thnx

4

okay looks like 91.0mA per relay so that's 546mA total ...
so I'd need a separate 600mA 5V power supply for the relays
does that sound right?

5

It appears that the current requirement for your relays is 91 ma each, or just over 1/2 amp total for all six. So a 1 amp 5vdc external power supply should work well. Also be aware that you will need some kind of switching transistor between the Arduino output pins driving these relays as the current limit for a output pin is 40ma or less.

Lefty

6

I have ordered transistors and diodes following an online tutorial for using relays but I forgot that I would have to have external power for more than one relay, now I clearly understand and know what I need.

Thanks again lefty

7

Good. I did a little research on the FT232R USB convertor chip's web site and it appears that while the chip has 'hooks' to make additional USB current avalible, however the Arduino's simple design does not utilize this feature so the on board 5vdc current limit is 100ma total, so an external power source is required for anything requiring over that amount, minus what the Arduino board itself requires.

Good luck

Lefty