Help me understand 'Amp Draw'

[Ereefic]

I've got a PFO 250w HQI ballast, not sure what brand the actual ballast is, but i'm goint to use an Advance M80 for my question because the #'s are similar.

On my ballast box, it says 5.5amps

I've looked up the specs. for the Advance M80 and this is what it says under 'line current':

Operating - 2.6amps (Is this when bulb is fully operational?)
Open Circuit - 5.5amps (What does this mean?)
Starting - 2.2 (As soon as it turns on?)

What I want to know is, when is the ballast drawing 5.5amps? What does 'open circuit' mean? I thought ballasts drew more amps when starting up? Please help me understand this.

[BeanAnimal]

A ballast is in theory a perfect current source. As the load resitance goes up, so does the current.... without getting very techincal the ballast operates by changing voltage depending on the bulb state.

If a bulb burns out, the ballast "sees" an infiniate resistance (open circuit). This cuases the ballast to send more voltage down the line. The higher voltage being pushed from the output side of the transformer causes the input side of the transformer to DRAW more current from the mains.

So to answer your question... the 5.5 amps will be drawn anytime the bulb is removed or burned out. Running a tar ballast without lamps plugged in will also give you the same result.

[Ereefic]

Thanks BeanAnimal. So this should be correct then:

The ballast fires up and draws 2.2amps. When the bulb is up to temp./warmed up, it is drawing 2.6amps. And the ONLY way this ballast will draw 5.5amps is if the bulb burn out or there is no bulb screwed in. And running 3 of these only on a 15A circuit should be fine and not trip a breaker, UNLESS all the bulbs are burned out and it fires all 3 at the same time.

I understand those #'s will change a little, but that's pretty close.

[BeanAnimal]

Well.....

a 15A circuit should be run at no more than 12A (80% lodaing max, according to the NEC). More than that and you will have nuisance tripping problems. But yes you should be OK.

Be aware that each ballast will have a significant inrush current when you turn the switch on, this could easily be 10A or more per ballast. Usually the inrush is not enough to trip the breaker, but with ALL 3 at the same time, it may.

Remember those ballasts have big IRON core transformers and fairly large caps to charge. When you flop the power on, the entire transformer core needs to become saturated with electrons (FLUX) as does the coil wrapped around it. At the same time the output caps are sucking as much current as they can trying to come to a full charge. Thats the sharp "hummmmm" ghag lasts half a seconf or so when you power them up.

Bean

[manderx]

the 5.5 amps will be drawn anytime the bulb is removed or burned out

are you sure about this? i've seen the SLS rep post that it's perfectly ok to run only 1 lamp in a dual ballast. i wouldn't think drawing 5.5 amps would be covered by 'perfectly ok'. plus wouldn't it pretty much overheat and burn up? all that juice has to go somewhere.

[BeanAnimal]

Several things to consider...

Electronic Ballasts are different than Magnetic Ballasts. Some electro ballasts can sense the "open circuit" and shut down the driver. This thread regards MAGNETIC (TAR) ballasts.

Secondly, there is no such thing as running 2 bulbs on 1 ballast.

A "DUAL MH BALLAST" is 2 magnetic ballast setups in one box. That means 2 transformers, 2 caps, etc.

So yes I am 100% sure.

[robsmith32]

Manderx, i'm not sure about the sls dual ballast, but the csl dual i just sold, had power switches on each side., so yes, no problem running 1 bulb on a dual ballast.

[Horace]

I do not know the internal workings of these ballasts, but it doesnt make a heck of alot of sense to me that the ballast would be using any power if the bulb was burned out. If the bulb is burned out that means there is an "open" in the circuit. If there is an open in any circuit current stops flowing completely. Voltage remains the same though. Its a simple formula... Current = Voltage/Resistance. Therefor if resistance is infinite current = 0. How exactly do these ballasts not follow this simple law?

[BeanAnimal]

Honestly I don't want to sound rude... but there is a lot of "guessing" going on here and not a lot of knowledge. The correct answer has been provided. Come on guys... lets not make this confusing.

A Magnetic Ballast CAN NOT RUN TWO MH BULBS and do so safely or well. The ballasts reacts to the current draw of the bulb (limits it) to regulate the bulbs opartaing characterisitics. THAT IS WHAT A BALLAST DOES. IN other words the characteristics of the ballast must be matched to the bulb it designed to drive. This means the starting voltage and current, drive voltage and current, and open circuit voltage and current must be matched to the BULB. If one bulb were to become weak or burned out, it would take the other bulb with it. You will only find single bulb MH (or an HID/ARC) type bulb) ballasts, it's that simple.

Horace, it does not make sense to you because you don't understand the internal workings of a ballast. The job of a ballast is to drive a bulb. As the resistance in the circuit goes up, the ballast reacts by driving the circuit harder. An "open circuit" is one of infinite resistance.

Please see the terminology used to designate the current draw on the ballast; it is called "OPEN CIRCUIT" current (or voltage) for a reason.

I am fully aware of what OHM'S LAW is...

The ballast is not breaking ohms law. When the ballast sees an "open circuit", it drives the outputs high to try and ignite the bulb. Remember there is a multi winding xformer, an ignitor and a cap.

Definitions:
Open Circuit Current: The RMS current measured at the input terminals of a ballast with lamp removed or inoperative.

Open Circuit Voltage(OCV): The voltage across the output terminals of a ballast when no load is connected (RMS, unless otherwise stated)

BTW you may want to note that every wall wart in your house draws current even if nothing is plugged into it....

Enjoy

[Horace]

<a href=showthread.php?s=&postid=7429983#post7429983 target=_blank>Originally posted</a> by BeanAnimal
Honestly I don't want to sound rude... but there is a lot of "guessing" going on here and not a lot of knowledge. The correct answer has been provided. Come on guys... lets not make this confusing.

A Magnetic Ballast CAN NOT RUN TWO MH BULBS and do so safely or well. The ballasts reacts to the current draw of the bulb (limits it) to regulate the bulbs opartaing characterisitics. THAT IS WHAT A BALLAST DOES. IN other words the characteristics of the ballast must be matched to the bulb it designed to drive. This means the starting voltage and current, drive voltage and current, and open circuit voltage and current must be matched to the BULB. If one bulb were to become weak or burned out, it would take the other bulb with it. You will only find single bulb MH (or an HID/ARC) type bulb) ballasts, it's that simple.

Horace, it does not make sense to you because you don't understand the internal workings of a ballast. The job of a ballast is to drive a bulb. As the resistance in the circuit goes up, the ballast reacts by driving the circuit harder. An "open circuit" is one of infinite resistance.

Please see the terminology used to designate the current draw on the ballast; it is called "OPEN CIRCUIT" current (or voltage) for a reason.

I am fully aware of what OHM'S LAW is...

The ballast is not breaking ohms law. When the ballast sees an "open circuit", it drives the outputs high to try and ignite the bulb. Remember there is a multi winding xformer, an ignitor and a cap.

Definitions:
Open Circuit Current: The RMS current measured at the input terminals of a ballast with lamp removed or inoperative.

Open Circuit Voltage(OCV): The voltage across the output terminals of a ballast when no load is connected (RMS, unless otherwise stated)

BTW you may want to note that every wall wart in your house draws current even if nothing is plugged into it....

Enjoy

First off Bean, Chill out.....

I am not saying your wrong, like I said, I am not aware of all the internal components of a MH ballast. However, I AM an electronics technician and do fully understand how all the various electronic components work, I am just not aware of which ones are inside the ballast.

Just curious but how is the ballast reacting to the change in resistance? You say "drive the bulb harder" but what exactly is increasing, the voltage or the current?

[BeanAnimal]

I am chilled... your the one who quoted ohms law in response to a factual reply regarding the OPs question :)

No worries... just trying to keep the thread on track and the information is simple as possible. The waters are starting to get muddy with "that does not make sense to me" or "my ballast fires two bulbs, so you may be wrong" stuff. I am not taking it personal but rather want to keep it factual. MH ballasts are the topic of many a question here.

The answer to your new question is somewhat complicated depending on the type of discharge lamp (low pressure, high pressure, metal replacement, etc)

By definition the ballast limits current. However, depending on the lamp type, voltage may need to be altered as well. Probe start, pulse starts...etc. The Open Circuit Voltage is typically the starting voltage and is much higher than the operating voltage. This is provided in different ways, either by an ignitor, or seperate transformer (or seperate taps).

To be dead honest, a ballast epxert would be able to explain the details of each type of ballast with better clarity than me stumbling through it. Suffice to say that curernt (and sometimes frequency) are controlled to keep the bulb operating in it's normal range. Voltage is changed to start the bulb. A peek at the ANSI ballast specs would offer some insight.

There is a person here at RC who knows a LOT about ballasts, I just can't remember his name off hand. I will search around and see if I can come up with it. He would be able to fill in the gaps and make us all smarter :)

[HippieSmell]

This link may be useful.
http://www.venturelighting.com/TechCenter/Glossary.html

[manderx]

Secondly, there is no such thing as running 2 bulbs on 1 ballast.

A "DUAL MH BALLAST" is 2 magnetic ballast setups in one box. That means 2 transformers, 2 caps, etc.


um, yeah, what exactly made you think i was talking about running 2 bulbs off 1 core/cap?. not really sure how it could have been read otherwise since i assumed everyone here knew what a dual ballast was. a dual ballast (with 1 power cord/1 switch), with only 1 socket/lamp connected means that one ballast is firing a lamp and the other ballast does not, and is therefore an 'open circuit' by the definition you gave.

so then what you are saying, is when people only run one of the ballasts in their dual ballast box (which the sls rep said was perfectly ok for ballasts that don't have the optional individual switches), one is drawing (using the above numbers given) 2.2 amps and the other is drawing 5.5. of the 2.2 amps, most of that is going to the bulb itself, some wasted by the ballast as heat (which is very noticable) and whatever emf it puts off (more of an issue for electronics from what i understand). then on the 'open circuit' ballast, all 5.5 amps is being used by the ballast, presumable the only place for *all* that energy to go is heat/emf. but it doesn't seem to do this since it doesn't get crazy hot when you run it like this, which i have done a few times for various reasons with my old sls dual m80, which is why i asked if you were 100% sure.

[BeanAnimal]

]um, yeah, what exactly made you think i was talking about running 2 bulbs off 1 core/cap?. not really sure how it could have been read otherwise since i assumed everyone here knew what a dual ballast was.Most people have no idea what a dual ballast is, other than the fact that it fires two bulbs from one "box". Your comment was fairly ambiguous and could have been taken either way. I took it as a lack of understanding what goes on inside a dual ballast (not becuase I thought you were stupid, but because the average person has no idea).

a dual ballast (with 1 power cord/1 switch), with only 1 socket/lamp connected means that one ballast is firing a lamp and the other ballast does not, and is therefore an 'open circuit' by the definition you gave.Exactly, one of the internal ballasts is running open circuit. AGAIN depending on the ANSI ballast type, this could mean different "modes" of operation. An electronic ballast my shut down in this scenario.

so then what you are saying, is when people only run one of the ballasts in their dual ballast box (which the sls rep said was perfectly ok for ballasts that don't have the optional individual switches), one is drawing (using the above numbers given) 2.2 amps and the other is drawing 5.5. of the 2.2 amps, most of that is going to the bulb itself, some wasted by the ballast as heat (which is very noticable) and whatever emf it puts off (more of an issue for electronics from what i understand). then on the 'open circuit' ballast, all 5.5 amps is being used by the ballast, presumable the only place for *all* that energy to go is heat/emf. but it doesn't seem to do this since it doesn't get crazy hot when you run it like this, which i have done a few times for various reasons with my old sls dual m80, which is why i asked if you were 100% sure. [/B] In essence that is what I am saying.

The "open circfuit current" figures will vary from ballast to ballast. For open circuit voltages and current draws, you may want to ask SLS for the specs on their units.

When sizing lighting branch circuits, these are the figures that an electrician or engineer would use, not the bulb wattage or steady state current draw of the ballast.

Enjoy

[manderx]

maybe there's some 'power factor' magic causing it to have an apparent draw of 5.5 amps, even though it's not actually consuming much or anything?

[Spuds725]

Do you think they would put that info on the ballast, if it wasn't an actual current draw??

Time to get an amp meter and check (and stop speculating)... ;)

[BeanAnimal]

Dunno what kind of majic that could be.... 5.5A is 5.5A :) Thats a LOT of imaginary power compared to 2.2A of real power. Maybe if we hooked enough of em in series we could lower the electric bill :)

[Ereefic]

Answer me this, why would the 250w HQI draw almost double the 'open circuit' amps of the 400w HQI?

[BeanAnimal]

It's all about the ballast configuration. How far apart are the operating and open circuit figures on the 400?

[Drakis]

higher voltage = less current

[Drakis]

The 400w is most likely operating at a higher voltage thus drawing less current

[manderx]

Dunno what kind of majic that could be.... 5.5A is 5.5A

not if it has a really low power factor in the 'open circuit' state.

dugup on wiki:
By definition, the power factor is a dimensionless number between 0 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load.

but the wires still have to be able to carry it i think, which is why the electricians need to account for it.



/really surprised someone who knows-the-know hasn't stumbled across this thread to set us straight...

[BeanAnimal]

I understand REAL and REACTIVE power. However, in either case current still flows. The only difference is how your meter deals with it. Normal Power Factor (NPF) ballasts come in around .79... High Power Factor (HPF) Ballasts come in around .9.

HPF draw less current to do the same amount of work. In theory a capacitor will charge 90 degrees out of phase and thus consume no real power....

In any case 5.5A of reactive (imaginary) power is a lot...

Still looking for the ballast expert :)

[PaulErik]

The PFO 250-watt dual and single ballasts use the Advance ANSI M80 ballasts.

The open circuit current is when the lamp fails to light or the lamp is not installed. Ballasts use little power (wattage) if an open circuit is present but the amp draw will greatly vary depending on how the ballast is setup and designed.

The capacitors function depends on the ballast circuit type. A typical North American magnetic metal halide ballast is a Constant Wattage Autotransformer (CWA) type. This type of ballast always has two coils. The primary (first) coil transforms voltage (step up transformer) and the secondary coil is used in conjunction with a capacitor to regulate/limit arc current. The capacitor is also used for power factor correction and is always connected in series on the load side in the circuit.

The Advance HQI (ANSI M80) is not like typical North American MH ballasts. It is a High Reactance Autotransformer (HX) type. This type uses the primary coil for voltage conversion and the secondary is solely used for limiting arc current. The secondary coil is just a simple reactor/lag ballast. A capacitor is usually used but not required for operation. The capacitor is only used for power factor correction and is connected between the line in (power) and common in (neutral) side of the ballast.

The capacitor in both circuit types is used for power factor correction. The ballast causes a lag (hence the lag ballast name) in the input voltage by up to 90 electrical degrees and capacitor is used to correct this as much as possible during standard operation.

The CWA ballast will have a lower open circuit amp draw because if the lamp is not present or the lamp simply fails the ballast circuit is incomplete and the capacitor can not function.

A High Power Factor HX ballast will have a greater open circuit amp draw because the capacitor is still present and functioning in the circuit. The capacitor value is carefully calculated to correct the power factor when the ballast is fully operating. When the ballast has no load the ballast consumes a small amount of power but then the capacitor over corrects the power factor.

Here is an example of the same ballast with different configurations.

250-Watt High Power Factor HX Ballast (high reactance ballast equipped with a power factor correction capacitor) Spec:

Input Voltage: 120V 60Hz
Power Factor: .90 Min
Operating Current: 2.59A
Open Circuit Current: 6.06A
Starting: 2.86A
Input Operating Watts: 287W Nominal

250-Watt Low/Normal Power Factor HX Ballast (high reactance ballast without a power factor correction capacitor) Spec:

Input Voltage: 120V 60Hz
Power Factor: .40 Min
Operating Current: 5.90A
Open Circuit Current: 0.40A
Starting Current: 8.73A
Input Operating Watts: 287W Nominal

Without a capacitor the ballast will draw more (starting and operating) current because the power factor is so low. With the capacitor the draw is lower starting and operating wise but will over correct the open circuit amp draw making the power factor way off resulting in an excess draw but both setups will consume the same amount of power (wattage). The power factor will differ depending on the ballast design and the state the ballast is in (starting, operating and open circuit).

When calculating power usage / wattage (power the electric company charges) with resistive loads you have to factor in the power factor.

Hope that makes some sense.

[PaulErik]

Ereefic,

The 400 HQI uses less amperage during an open circuit than a 250 HQI is because they use a different ballast circuit type. At the moment the 400 HQI is a CWA or CWI ballast circuit (depending on the vender and supplier).

[BeanAnimal]

Paul thanks for dropping in and explaining what I would have stumbled through :)

I know that a cap can have an ofset of 90 degrees but was not aware that it was sized to "offset the offset" of the coil and thus bring the power factor back closer to 1.


I would have only been able to draw the parallel to a class A amplifier... and not done a good job of it.

Bean

[hahnmeister]

"When calculating power usage / wattage (power the electric company charges) with resistive loads you have to factor in the power factor."

-Paul Erik

And I remember certain people saying all that matters for an electric bill was watts... I knew there was more to it than that.

[BeanAnimal]

Paul.... the info on your site is wonderful! Could I convince you to move it to a site that does not have popups and forced advertising?

The whole deal in PDF would be great too!

[BeanAnimal]

hahnmeister in nost homes the power factor averages out pretty close to what the meter is calibrated for. Your good old spinning meter does a fairly decent job at measuring the true power usage.... newer digital meters have had a rough time getting it right (that is why the didn't appear on the scene until recently.

Commercial power is however a different story. Because large industry and buildings have large motors and a lot of HID lighting, they have serious power factor problems. The power company may even install large banks of capacitors to correct the power factor (and ensure that the meter bills correctly).

The funny part is that YOU the customer PAY for losses on the neutral line between you and the transformer. The power company does not mind a bit when THEIR side of the meter is messing up the PF... they only get concerned when your side messes it up in your favor.

If you remember the big brown that let to a blackout out several years ago(2003 I think) ... it started in the RUST BELT and was due to a voltage sag (due to demand) and the large steel mills and auto assembly lines drawing a LOT of reactive power from the lines. The rolling brownouts made hte problem worse. The increased current usage due to the voltage sag in conjucntion with the now severely messed up power factor created by the electric furnaces and large electric motors created a problem. The operators at a power plant in ohio made some bad decisions based on assumed power real power useage and did not consider the reactive power component of the problem. Down went part of the Eastern grid. (21 plants went offline I think).

Not that any of that has anything to do with the conversatio... but it does make a good read about real and reactive power :)

[hahnmeister]

PaulErik, your info has been key in putting several 'myths' to rest with regards to halide lighting (the whole SE vs DE debate for instance). I wonder if your website couldnt be expanded into wiring and circuits for the use of people to minimize their electrical bills with the equipment that they have. Some arguments that have come up have been 110v vs 220v wiring (does running 220 and using 220v ballasts lower your use?), splitting up circuits into multiple lines for less draw on each wire, and 'balancing' the loads of the circuits on the poles of the circuit breaker to reduce use.

Bean and I have gotten into it in the past because my impression was that adding more lines/splitting up circuits/ running 220v ballasts instead of 110v COULD lower your bill...and Bean has the 'wattage is all that matters' opinion.

[hahnmeister]

Bean, do you remember where that thread was where everyone was arguing about this stuff?

[BeanAnimal]

Have no idea what it was titled.... my contention was that in most homes it does not matter, as the resulting power factor that is the sum total of all usage is about the same. I also said that balancing the draw from each 110 leg is a good idea.

The other contention was wire resistance and the savings running 220V.... omething that again is not likey to show real world saving due to the number of variables involved. Of course ANY TIME you move up in wire size and down in total ampacity, the resistance becomes less of a factor.

Remember in single phase power that the loss on the utility side of the neutral is payed for by the customer (the loss on the hot legs by the utility). Did you ever notice the serive drop conductors neutral is rather undersized. If your drawing 50A off of both legs, the meter reads 50A. If you draw 50A off of one leg, and 25A off the other, the meter reads 50A. So getting the legs balanced is a good idea. 220V is "balanced" to begin with... so it makes it a bit easier.

I can see this is headed into a deep discussion about PF, power generation, RMS voltage, and the actual functionality of electric meters. Something I honestly have no interest into delving into for the purpose of proving that a balanced electric service is a good thing, or that running 220V will not save you money.

[PaulErik]

I have to correct myself I meant to say when calculating power usage / wattage (power the electric company charges) with inductive (not resistive) loads you have to factor in the power factor.

My personal site has not been updated in many years. Once time permits I’ll be making a new site with a lot more information and without the forced advertising.

You can save a few watts if you use 220/240 volts with HID (Metal Halide) lighting. If you take a common multi-tap magnetic (120V, 240V) ballast and just wire the ballast to 240V you will not save any power really.

The good thing about 240 volts is it meets the Open Circuit Voltage (OCV) requirement to most European and some North American metal halide lamps. This allows you to use ballasts that just regulate/limit arc voltage (Reactor/Lag type). No voltage conversion is needed eliminating the need for two coils and in turn it will operate more efficiently. Reactor/Lag 240V ballasts are not very common in North America because ANSI (American National Standards Institute) specifies a minimum OCV of 250 volts for most North American pulse start type metal halide ballasts.

A common North American Constant Wattage Auto Transformer (CWA) multi tap 400W metal halide ballast uses approximately 455 watts nominal. Using a Reactor (R) 240V ballast uses approximately 430 watts nominal. You would save 25 watts per fixture/set up. The efficiency difference between the ballast types goes up with wattage. A 1000 watt metal halide setup would save approximately 55 watts per fixture/set up. The system wattage will vary. The figures above are based on manufacturers electrical data sheets.

[BeanAnimal]

Paul, that is the wattage wasted in the second coil as heat and EMI/RFI?

[rcmike]

I have a question that may be related to this. I have been told that you can run 250 W bulbs on a 400 W ballast if you change to 250 W capacitors. Is this true? If so what does it do to power consumption and bulb life? This is a standard magnetek ballast I am talking about.

[PaulErik]

Each coil will waste power to heat and EMI/RFI.

You can not use a 250-watt ballast capacitor on a 400-watt ballast and safely operate a 250-watt lamp. You can add another capacitor to a 400-watt CWA ballast to limit more current. This is only used to dim the lamp that is designed for that ballast.

This is typically only used in the commercial lighting field. The lamp has to be ignited at full power for at least 15 minutes before being dimmed. This is done by connecting the addition capacitor to the circuit when the lamp is fully on. This only allows two level dimming.

[rcmike]

That is kind of what I thought but I wanted to check.

Thanks!

[hahnmeister]

"The good thing about 240 volts is it meets the Open Circuit Voltage (OCV) requirement to most European and some North American metal halide lamps. This allows you to use ballasts that just regulate/limit arc voltage (Reactor/Lag type). No voltage conversion is needed eliminating the need for two coils and in turn it will operate more efficiently. Reactor/Lag 240V ballasts are not very common in North America because ANSI (American National Standards Institute) specifies a minimum OCV of 250 volts for most North American pulse start type metal halide ballasts."

-Paul Erik

I thought this might be the case...220s have less conversion to do...so they are more efficient. Kind of like a DC converter plug/brick...it wastes so much energy in the conversion. I knew there was a reason why I bought my new 1000watt HQI ballast in 220 instead of 110 (besides 1000 HQI ballasts only being made in 220 because of the extra demand of HQI).