I read the wattage of the HPS Light is just the wattage the light puts out, not what is actually required to run the equipment.

Hi Extinctx11! Here's the deal. A 400W HPS actually draws 400 Watts.....from the ballast! Total power drawn is 10 to 25% higher, with 10% for digital ballasts and 20%-25% for normal analog ballasts. So pratically speaking a normal 400W HPS/ballast combo draws about 500 Watts of power. 700 Watts comsumption for a 400W HPS is rediculous....perhaps you measuring device/techniques are showing their limitations. If not then something must be wrong, check the label on your ballast to see what it says. No way you can run a 650W HPS bulb on a 400W ballast without it going nova. Are you perhaps measuring not only the HPS but also additional lighting and/or ventilation? As it seems you are continuously measuring 200 Watts too many with both the 250 and 400. Right?

Im really happy you jumped into my post! I read ALL your logs man. You, Dier, and smokinvtec are my heros lol. In any case, since I made that post I went back and checked power consumption after 2-4 hours of running time. Apparently the HPS uses the power I mentioned.. but only for the first hour or so. After about 1.5 hours it drops... to about 3.5 amps. @ 122 volts thats 427 watts, which out of a 400Watt HPS I feel MUCH Better about that. Now I know I can run the 400 and the 250 at the same time and still be well within the 15amp breaker's limit with my fans. hows your grow going man!

the math goes like this. i got 2 150w hps systems, & the total power consumption of both systems are 188w each, which is labled inside the ballast box, (required by law to display these specs), they both also say what amps they use per given volts. mine says @ 120v = 1.56amps, the equasion is: (total watt / house volts), ex: 188w divided by 120v = 1.56amps. my dad is a 20+yr electrictian, & im experienced as well.

It might be stupid to even worry about but Im one of those people that HAS TO KNOW EXACTLY how much power I am using and what I am doing. Just like some people want to know their PH and some are like F#(*&@ it. Same with TDS- its just another measurement you may or may not take, I just happened to do it and am reporting my results!

i get what your saying, but whats listed on the product (ballast), has to be accurate, b/c thats the law for safety reason, like overloading a circuit. ive got those meters & more, & even my dad says they are not 100% accurate, b/c of lots of outside factors. anyway not trying to start any battle, just thought i would through in some of my 2 cents. i know how u feel, i like to know my power consumption too, b/c of power bill. peace out & good to see someone checking out something besides whats going on w/ their plants.

what do you know about converting Amps and volts depending on the houses wiring setup? My place has a huge wire that reads 120V, but the A/C breaker says 240V, but I Dont know if the amps I am reading has to be Multiplied by 240 or 120volts to get wattage, since it appears to be two 120V together, reading one of them says 10amps, do I multiply by 240 or what...

most houses will have 2 120v lines going into the main breaker box. not 100% understanding you but, Watts = Amps x Volts By dividing both sides of the formula by amps you get - Watts / Amps = Volts ... the amps / amps on the right hand side canceling each other out to leave volts. and by dividing both sides by volts you get - Watts / Volts = Amps ... the volts / volts on the right hand side canceling each other out to leave amps

If I'm not mistaking fuses and A/C breakers are triggered by current alone. The voltage is only mentioned to avoid sparking. Meaning, a 240 V 10 Amps fuse can be triggered with a 12 V power supply, if only the current exceed 10 Amps for a long enough time. Heat production in a wire is proportionally linked to Amps not Volts. This is why 240V AC power systems are more efficient and economical. Half the Amps for the same power = half the heat loss in the wires --> wires need to be less thick.