Powering 20 5vdc relays...

Projects General Guidance
1

Experts,

Going to re-engineer a standard PDU by using the good old blue relays to switch 120v to sockets on the PDU. The uC will send signal to trigger the relays, but I need to not drive relays with the uC (obviously). How to switch them?

Given current assumptions:

  1. 5Vdc relays seep to draw 41mA to 90mA, depending on what you read.
  2. Would be happiest with an IC that can handle more than just one output, for cost and space.
  3. Assuming NO, I don't want to 'cut it close' with current ratings of xistors/MOSFETs.
  4. MOSFETs in this range are almost $2 each, so trying to figure a cheaper way.

Hope this is the right forum... Ideas?
TIA!

2

If the 5v relays have a coil resistance of ~70 Ω almost any transistor will work, ex: 2N2222.

There is a ULN2803 that can drive 8 relays.

You can use a TPIC6B595 POWER LOGIC 8 BIT SHIFT REGISTER that can drive 8 relays and take serial Arduino data sending parallel 8 bits to the relays.

3

Those are fabulous choices! Thanks! I figured I was stuck with MOSFETs...

larryd:
If the 5v relays have a coil resistance of ~70 Ω almost any transistor will work, ex: 2N2222.

There is a ULN2803 that can drive 8 relays.

You can use a TPIC6B595 POWER LOGIC 8 BIT SHIFT REGISTER that can drive 8 relays and take serial Arduino data sending parallel 8 bits to the relays.

4

FETs are of course, the preferred option nowadays - all the digital electronics you use are based on them rather than bipolar transistors and FETs are of course, the devices in the TPIC6B595 which is by far the best way to drive multiple relays for 5, 12 or 24 V. No other components needed (not even the "kickback" diodes). :grinning: