Maximum Number of Zones

[HereComesTheRain]

Yeah, that is expected behaviour when using fairly long wires (as you have on the breadboard) and not using decoupling capacitors on all the 5v connections.
I would start by putting a capacitor (e.g. 0.1uF) on every hc595 between pin 16 (5v) and pin 8 (GND).  
On the breadboard itself between 5v and GND I would use a 47uF (more or less).

For more info see this and this
 

--Gerard

Hello Gerard

Thank you for the information.  It's makes sense.

"a capacitor (e.g. 0.1uF) on every hc595 between pin 16 (5v) and pin 8 (GND)"

So I would insert the capacitor in the same holes as the  hc595 pin 16 and pin 8?

UPDATED:  I installed four 0.1uF, one for each hc593, wired everything back up, powered everything up and tested.  Results are the same.  Unplugging and plugging the USB irrigation enclosure fan triggers the RELAYS.

You said "On the breadboard itself between 5v and GND I would use a 47uF (more or less)."

What volt 47uF would you recommend? (20v, 30v 50v or more)

Do I install two 47uF on the BREADBOARD, one on the TOP POWER RAIL and one on the BOTTOM POWER RAIL?

Speaking of BREADBOARD the GND of the TOP POWER RAIL is connected to the GND of the BOTTOM POWER RAIL and each POWER RAIL has an independent power supply. (Pi powers TOP RAIL, 2nd power supply BOTTOM RAIL)  Will adding one or more 47uF to the BREADBOARD cause a problem?

I am wondering if this would happen if the Pi was being powered by a better power supply (brick style) rather than a small wall wart (charger style)?

What does this say about the APC UPS?  I would have thought that the UPS and its battery would buffer any power fluctuations.  Is this a noise issue?

Can you recommend a book for someone wanting to learn the basics but not interested in becoming an EE?

Thank you again for your time and assistance.