HID Lighting Contactor Relay Circuit & Lamps

Thread Starter


Joined Oct 5, 2009
This project is in two parts;
I would be very grateful for help in either or both parts.

Please ask for clarification if you need it.

I have a 1000w digital HID (High Intensity Discharge) lighting ballast:

- can I run more than one light if I can make the load "appear" the same?
for example, if I had two pairs of lamps - each pair running in series,
would that work? (I am more worried about what I believe the ballast does which is sending out many pulses per second might not feed all the lamps.)


(ignore dots, used as spacers)

- I have one lamp outside for security and one inside my workshop for lighting.
I can manually pull the lead out
(from the mains side of the ballast first, not the lamp side of the ballast, which I understand is dangerous)
and switch over lamps while keeping just one ballast working.
I want to do this automatically as my entry/exit times are the same.

I want to use a contactor relay connected to a mains timer. I also want to use only one ballast. Is there a way to safely switch over the operating lamp from the ballast end?

..............................................................................----lamp 1--
---240v--BALLAST--- (project/timer/contactor relay)-----
..............................................................................----lamp 2--

(ignore dots, used as spacers)

Many thanks for looking in; I appreciate any help.
Last edited:


Joined Apr 2, 2009
U know something, when it comes to HID, I would take a lot of precaution.

Dangerously high Voltages. Do it at your own risk, I do not advice, but I would do it just for the heck of it :p

A few things first I would consider ( I am not saying to do this but what I would take as precautions since I have meddled with HID's)

One is to check that does the ballast works without a load, meaning does it shut down if the bulb is disconnected. If so live switching is off. besides HV switching relays or semiconductors is hard to find. Thinking of the HV do you really know how much voltage is used to drive these bulbs, if so I don't think that you would consider a live HV switching
Secondly is it safe or that the ballast can withstand sudden load changes without blowing the power drivers.:D

If all above fails, I still have a way of doing what you intended but is tricky, and have to use a few relays and a time delay relays too.

Once my shema is posted, others might find a way to simply it down, cause I always does. :D



Thread Starter


Joined Oct 5, 2009
Hi R!f@@/Rifaa

Thanks for your reply, I seriously appreciate it.

I need to find out the differences between a digital and 'traditional' ballast,
to see whether what I want to do is applicable to both devices.

Thanks for the heads-up about the high voltages, for some reason, that had escaped me, I knew but forgot. :(

What I had thought of so far was a PIC controller to do this: (with appropriate relays)

1 - turn the ballast mains supply off
2 - wait 5 seconds
3 - disconnect lamp 1
4 - wait 1 minute
5 - connect lamp 2
6 - wait 5 seconds
7 - light lamp 2
8 - wait x hours (with lamp 2 on)
9 - turn the ballast mains supply off
10 - disconnect lamp 2
11 - wait 1 minute
12 - connect lamp 1
13 - wait 5 seconds
14 - light lamp 1
14 - wait x hours (with lamp 1 on)
15 - goto 1/repeat

But this would still need high voltage relays at the lamps...

Your thoughts would be extremely appreciated.



Joined Apr 2, 2009
Not bad if I do say so my self.
U got the whole idea.

A little change in the timing is OK, If u got the pic to time appropriately then normal relays will do just fine.

no. 4 wait 1 minute - not necessary, if u disconnect the power the ballast will discharge with in seconds. So 3-5 sec will be OK.
no. 6 wait 5 sec, ---no need, u can power up after lamp is connected.
Same goes for 11 and 13.

As for digital ballast, it's not exactly digital, ballast consist of the inductor and the caps.
It's the driving method that varies, but digital as u say are trouble some, it has protection to safe guard the inverter. So if live switching is not used then u have no worries

To switch the lamps, U will need contactors which rates the insulation voltage at kilo volts, or u have to use two separate relays to switch each wire of the bulb separately, to keep them from arcing if two contacts of the same relay is used to switch the wires of the bulb together. Get it?

Get the contactor or more relays.
And get the PIC programmed for the timing.
The GPIO pin no.s will depend on the amount of relays you find.

I will draw up a schema after you give me the full spec of each relay or contactor you find with the driving voltage of the PIC you use.