Running small relays... Voltage drop.

[rbrooks]

I have a couple of small Radio Shack 5v relays that I'm running with an Automation Direct 5v supply. Whenever one relay is energized, the voltage drops considerably (results in 2.5-3v).

I can't believe there's that much drop across the coil. Is there anything I can do for this, or are discreet supplies or a bigger supply needed?

 

[BobK]

How much is the coil supposed to draw, and what is the power supply rated at?

Bob

 

[gorgon]

The drop is over the power supply, reducing the output. Have you tried to measure the resistance of the coil? Small cheap 5V relays can easily draw from 40 up to 100mA.

TOK

 

[rbrooks]

Well it's a 3.2a power supply, draw on the coil I will have to double check. Just seems like a lot of voltage to drop for one small relay.

 

[gorgon]

Could also be your cable connecting the relay. Is it flimsy? Do the load switched by the relay also load the power?

TOK

 

[rbrooks]

It's a pretty stout wire, for the application. It's also only about 5" long so there shouldn't be much else.

The only other thing this power is doing is running through 4 249 ohm resistors across the load side of four other SSRs. It's all either being switched or switching these relays, it's not providing power for any other items.