that is what i want, that should help with the temps and evenly distribute power consumption.
It's a fairly simple matter to use a relay (or two) to make a switch that will transfer the output of a single ballast to run one of two lamps.
However, keep in mind that the cost of the relays, timer (and power supply for the relay coils if a low voltage coil relay type is selected) may exceed the cost of a second ballast!
The main design constraint is that HPS ballasts have an igniter which sends a 1.5-4kV (at quite low current) pulse to the lamp to strike the arc. Most relays are not rated for that much voltage.
If you use a relay that can't provide 4kV worth of isolation between the contacts, the igniter pulse could jump between the contacts and not make it to the lamp tube, preventing the tube from striking.
So, for this design exercise, I've used two separate SPDT relays:
The wiring from the ballast, through the relays and on to the lamps will need about 25mm distance between uninsulated connections (air has 10kV dielectric strength per 25mm).
AC power connections to the timer and ballast are omitted in this dwg for clarity. Relays shown have AC mains voltage coils, but relays with 12V coils are much more common and much cheaper. If low voltage coil relays are used, you'll have to organise a low voltage power supply between the timer and the relay coils.
I do think it would be more reliable in the end to just use two ballasts, but this ckt will do the job.
I assume this can be done again to no ill effect if needed.
No need to assume- it'll be fine.
Yep, it's mould, caused by keeping the RW too wet.
Any thoughts that you have for improvement would be much appreciated.
Yep, you're going to need a
lot more ventilation capacity than 50CFM. Plan on 1CFM per cubic foot of room volume.