Do you have numbers for the efficiency difference? Can you get them?

Don't waste your money on an electrician. 240volt units run exactly the same as 120. It's only motors and compressors that run cooler and more efficiently.

ramsay22,

Were you told you were going to get "better light output and reduced energy costs" if you bought this ballast? I wouldn't be surprised if they told you that you can cut your current consumption in half with 240 volts. I often find I cannot stomach reading the selling points on most of the web-based "grow sites".

rob_thompson is correct. The only advantage of 240v is that some motors will have more torque available. One other exception occurs if you are wiring up a parking lot with HID lighting. There you can benefit from 240 or 277 volts - the advantage being a decreased voltage drop in long circuit runs.

Could you possibly post a link to this deception? I could stomach one look.

Zink

You do save power costs with 240v, particularly on magnetic ballasts. Check the stats on a GE transformer label: you can save 18%. But that is if you are really at 240v. In most cases, you have 230v or 220v etc., so would not save as much.

240v does not run exactly the same as 120v. For one thing, 240v has twice the current-carrying capacity and so has less resistance. For another, the bulbs typically run at over 300v, so takes more energy to increase from 120v than from 240v.

With electronic ballasts, you still save some with 240v, how much would depend on the circuit design (which varies a lot more than magnetic ballast design).

Those who lack knowledge ought to show more respect.

Just to be more precise, Lermer is almost right. It does not "take more energy to increase from 120 than from 240" - what it takes, is more windings of copper wire, and this results in slightly greater losses in the iron core and copper windings. Because you have to provide a bigger "electrical leverage", and due to facts of life with electricity, increased leverage comes with the cost of higher losses.
Losses in copper/iron systems increase by the square of the current, so if we need twice the current, losses are 4 times as much, in proportion. That means that for instance a 400 watt ballast might lose 20 watts if using 240V but will lose maybe 80 watts if using 120. (double current means 4 times the core loss) That might mean an extra 60 watts of loss, or 15% of the 400 watts. (this is where the 18% figure from lermers post comes from - he is providing a simplified almost correct explanation, and is pretty knowledgeable, although always verify everything for yourself independently). However, the TOTAL HEAT, will be still either 420 watts one way, or 480 watts the other way - both ways still put out lots of heat to get rid of, and the savings in electricity by using 240v are only justified for a very large operation, and probably only if u are handy with doing the wiring urself - it is actually very easy, easier to wire, than for example do plumbing.
For instance, if my setup called for 6x 400 w ballast, i would consider running 240, because it would only take one half of the amount of wire, and standard house wire will handle up to 300 volts. For instance 15 amperes of 240v would supply the 6 ballasts above, whereas if i was running 120 volts, i would need 15 amperes TIMES TWO, or double the amount of wire. The space on the electrical panel would be exactly the same - 2 separate 15 ampere breakers in one case, and 2 ganged 15 amp breakers in the other case. But the ganged breakers would be served by one cable, and the separate breakers would be served by two cables. so 240 v will give a neater job, because it uses one half of the amount of cable, if u have a large enough operation, and there might be a 15% savings in electricity, but the TOTAL HEAT will still be huge, and the lamps will still all be just as bright. The price of 240 v electrical plugs, and 240v electrical receptacles is MUCH more than 120v plugs and receptacles, but now it becomes a question of what are you growing and will your growing profits easily cover these costs. In terms of hiding this electrical useage from "the man" - that's another story, especially with modern meters that the utilities want to install - "smart meters" that determine exactly at what point ur power is being turned on and off, and very easy to spot a large indoor operation that is being turned on and off always at the same time every day, or a consistent on and off pattern of significant amperes.

Here is a link that might be useful: the explanation about efficiency, voltage, copper, and iron.

so basically i don't understand why we have to live in fear of "the man" for growing something that is nowhere near as destructive as just alcohol or cigarettes. if i grow any contraband, i go to jail, lose my job, marriage, family, etc., but the purveyors of alcohol get rich beyond your wildest dreams, and all you're left with is a hangover - compared to the hugely satisfying sleep u get with a completely natural product supplied by nature, without any fermentation necessary, easy to grow, and u will not get blind if u make a mistake, and u do not wake up all cranky, or with a shot liver, requiring a liver transplant, like some famous baseball player.

Say what? I guess I am a bit confused as to what new properties of electricity are being heralded here. I used to design power supplies for fun. And, ever since my "Transformer Technology" course from my 2nd year Electrical Engineering course at the University of Louisville was complete, I have spent the subsequent years reading technical research and specifications for my knowledge and pleasure. When I give information here I feel obligated to be accurate, and not to misinform in any way, and will post corrections if I am wrong. When I see misleading information posted as facts, I feel compelled to offer correct data (with educational explanations if possible). So I am re-posting the data from the manufacturer.

From the GE 2008 HID catalog:
>>> MAGNETIC BALLASTS - 400 watt
Probe Start Power Consumption:
120v, 208v, 240v, 277v - All use 446w
Pulse Start Power Consumption:
120v, 208v, 240v, 277v - All use 443w

I found the same results in the Advance, Venture, and Sylvania catalogs. Each similar ballast had consistent power consumption between available voltages the wattage used remains the same whether 120v or 240v. Data from manufacturers, if available, is always very good, since they are legally held to certain standards. On the other hand, third-party resellers such as the overabundance of "Grow Sites" I see on the web, can spin and hype to their hearts content. AND THEY DO!

To The Question of Respect
I certainly do respect the others in this forum and try to show that by illustrating facts the best I can. My postings here DO NOT have an underlying purpose to pepper someone less knowledgeable with slick sales hyped re-interpretations of product specs to eventually lure folks into e-mailing me. You should tell folks when you are actually selling the very products you are advising on. That is truly disrespectful to others, if not devious. This forum is a community conversation  NOT a marketing opportunity! You, Mr. Lermer, often try get people to email you at your sales address. If any one wonders, one can look you up online. One of your articles (which has recently been removed, it seems) stated that the orange light pushes the blue light out of the sun! Another touted that different wavelengths travel at different speeds. What a total misunderstanding of physics you have. I did not write this particularly to put you down, or to mess up some future sales transaction, but I think you should admit your other quest here  to sell products.

-- ramsay22
I guess now I am definitely interested in seeing a description of why running the ballast at 240v is more efficient that 120v. Do you have a link with any specifications or explanation from the actual manufacturer? If not, just post the "third-party who is responsible for this" link

Zink

this means basically if u have a larger operation, that would for instance utilize 2 x 15 amp of 120v breakers, and u are starting from scratch, 240 volts is preferable in order to save on the amount of cable running from the distribution panel to the growing facility, but u will pay more for the connectors. 14 gauge cable costs less than a dollar a metre,
so a difference of 40 metres and 80 metres amounts to a paltry 40 bucks, not really worth the bother if zink's figures are right. it sounds like with zink's background, he must know what he is talking about, we are talking science here, which always has an absolute answer, and if he actually designs power supplies, then i would go by what he is saying.

The copper losses of the transformer, with double the voltage, U need half the winding, which means resistance is one half, and current is one half, the proportionality suggests that the copper loss is one half due to R being one half, and the I component will make the copper loss one quarter - i don't understand why the copper losses do not make a significant difference. I didn't study power supplies, just first year physics only, then MD. my interest in growing cannabis for my medical patients.

For the same amperage draw, at 240V a smaller diameter circuit wire may be permitted - thus the circuit is a little less costly. However that is not the main advantage.

If the same diameter wire were used on both 120v and 240v,
the 120v circuit would have more resistive losses in the wire. This consumes more energy unnecessarily.

The ratings for magnetic ballasts include only the ballast and not the wire (as in the real world).

Also the factory tests probably feature a cooled transformer, as in street or parking lot lights which have heat-dissipating aluminum housing exposed to wind. The transformer runs cooler when powered by 240V because the primary current in the transformer is halved. So if the transformer were not cooled (as is often the case in applications), heat would build up more in 120v. The heat increases resistance, which lessens efficiency.

Heat shortens transformer life, by melting the resins (causing the plates to vibrate, interfering with the electro-magnetic lines of force) and degrading coil wire insulation (creaing micro-shorts). Over time, the 120v transformer will consume ever more energy (because it tends to run hotter). The ratings given are just the initial ratings and not an average over the life of the transformer.

I was a ham radio operator before most people here were born. I've been involved professionally with transformers since 1981. I didn't know the field of indoor growing was like the Olympics, where only amateurs can enter.

I think lermer wins this one.
Also the point about heat kills electronics is also right.
The only mistake is about Olympics. If I could do anything even one tenth as well as the poorest Olympic athlete I'd be singing Hallelujah at the top of my lungs. Amateurs (cough cough cough ha ha ha - sure, and I've got a bridge in brooklyn to sell u) But I disagree with lermer that different wavelengths of light travel at different speeds - that only happens when light enters a prism or something, but through a vaccuum they only go at one speed) Also, white paint reflects heat the same as mylar does, I checked the internet for that too. As far as CMH goes, there is no reason anyone should be running regular MH anymore, CMH is way better.

Lermer wins again. Heat kills electronics. Your HID lamp has a steady state voltage of 300v. 240v is already almost there, so ur ballast is much more efficient running 240v. this does not apply to an electronic ballast, only the copper/iron type, which i prefer, because CMH and HPS both run well on a copper/iron HPS ballast. the most important losses are called the copper losses, which increase as the square of the current. if the current goes up by twice, the copper losses are four times. this equals heat, 4 times more, which is waste, and kills electronics. No one should be running regular MH anymore. Spend a little bit more upfront, and get CMH lamps that last longer and grow better.

Great forum guys I'm shocked to find this on houzz.com. however I have 240v technically 115 volts on each pole so 230 volts and my 1000w digital ballasts are running at 7.6amps like it's a 120v I've tried various styles of grow lighting turned it up to 1000w can't identity what the heck is going on.

Is it because I'm not running on full 240v the problem