Lighting safety + ventilation questions

[bajabudz]

Hello,

My growspace is 2x2x5' and I just bought a 150hps light (2100k light + digital ballast + cooltube). I read about needing a contactor/timer relais for using HPS lights since there is an inductive power load instead of a resistive one. While buying my equipment at a local growshop I asked the vendor if I needed a contactor to use my HPS lights. He said that contactor's aren't needed for a 150hps, and he advised me to buy a digital timer from Primera-Line Digital Weekly Timer DT | Primera-Line Adapter | brennenstuhl® (20$), which I did. I'm getting kinda mixed information about this. Everyone agrees for higher watt HPS lights you definately need a contactor but I can't seem to find conclusive material about 150hps, and the salesman seemed to be quite sure it wouldn't give me any problems security wise. As you can see the reason I'm making this post is to receive 100% correct information which will ease my mind about a possible safety hazard regarding the HPS and won't keep me guessing.

The second question I'm having is how much CFM my exhaust fan needs to properly ventilate my growspace (2x2x5) with a 150hps in it. I read the topic about this from 420magazine and they said the air needs to be refreshed 3 to 5 times every minute. So 60 to 100 CFM exhaust + passive intake should do the trick?

Thanks in advance and friendly greetings

 

[Stealthboat]

Not sure about the whole contactor deal, but I know the rule of thumb is 50 watts per square foot, so 2x2 = 4 square feet or 200W. I'd add in a few CFL's with that HPS and things will look really nice (if you have room and the means). Yup the best ventilation will be dumping all the air out every minute or two, so your grow tent volume is 2x2x5 = 20 cubic feet, and 20 ft^3 every 2 minutes would equal out to a CFM of roughly 600 (20ft^3 x 30 cycles/hour [@ 2 min intervals]). But that's the max you would ever need, 600 CFM. you can get away with one half that strength so roughly 300 CFM. If you have to use ducting though, be aware that each bend in the ducting will reduce the air flow by at least 10%. Carbon filters will also reduce the air flow by 20% at least. So adjust accordingly.

 

[Dan Ultra]

If you have a digital ballast then you dont need a contactor relay timer. You only need that for magnetic ballasts.

 

[bajabudz]

Not sure about the whole contactor deal, but I know the rule of thumb is 50 watts per square foot, so 2x2 = 4 square feet or 200W. I'd add in a few CFL's with that HPS and things will look really nice (if you have room and the means). Yup the best ventilation will be dumping all the air out every minute or two, so your grow tent volume is 2x2x5 = 20 cubic feet, and 20 ft^3 every 2 minutes would equal out to a CFM of roughly 600 (20ft^3 x 30 cycles/hour [@ 2 min intervals]). But that's the max you would ever need, 600 CFM. you can get away with one half that strength so roughly 300 CFM. If you have to use ducting though, be aware that each bend in the ducting will reduce the air flow by at least 10%. Carbon filters will also reduce the air flow by 20% at least. So adjust accordingly.

Shouldn't the air get refreshed 3 to 5 times per minute instead of once every 2 minutes? According to your calculation, where you mixed up CFM(inute) and CFH(our), my room should need to get refreshed 600 CF per Hour which means 10 CFM (600 / 60 = 10). Seems kind of low or did I get misinformed?

E.g. in your growspace according to your grow journal you have 4.5'x4.5'x7 which is 142 cubic feet. Your inline fan is 590 CFM so the air in your grow space gets refreshed 590/142 = 4.15 times per minute.

If you have a digital ballast then you dont need a contactor relay timer. You only need that for magnetic ballasts.

I've read posts about people using 250w with digital ballast and digital timer coming back from home and seeing their house on fire because their timer caught fire. And I'm 100% sure people with 1000watt+ definately need a contactor, even if they have a digital ballast. Don't spread this false information, some people might take it and might suffer serious consequences cause of it.

 

[Stealthboat]

More air flow will always help. Yes the 1-2 times per minute is the ideal setting, so right now my fan is on roughly ~33% power so the CFM is somewhere around 200. So 200CFM / 142ft^3 = 1.4 minutes per air dump, still very good air flow. Sorry my math when stoned gets confusing lol. I bought a bigger fan because they are more efficient on lower speed settings and also slightly less noisy than buying a 200 CFM fan and running it at full speed, don't want the jet engine sound lol. You know what you're doing though, you seem to know what's going on.
I bought some electronic timer for my 1000W rated ballast and 600W bulb/hood, it's some Chinese thing for $15 but it's been doing fine for me. I wouldn't trust those little $5-$10 timers you can get and Walmart, Target, etc. Buy something decent off ebay.