# HMI strike amperage

4 replies to this topic

### #1 Matt Irwin

Matt Irwin
• Basic Members
• 389 posts
• Cinematographer
• Los Angeles

Posted 20 January 2006 - 09:12 PM

Hey guys,

Does anyone know how many amps it takes to start (for example) a 1200w HMI on 110v? Is there a general rule to determine this (like # amps per 100w or something)?

Thanks,
• 0

### #2 Tim J Durham

Tim J Durham
• Sustaining Members
• 742 posts
• Director
• East Coast, Baby!

Posted 21 January 2006 - 01:00 AM

Hey guys,

Does anyone know how many amps it takes to start (for example) a 1200w HMI on 110v? Is there a general rule to determine this (like # amps per 100w or something)?

Thanks,

That's 10 Amps, right? 1200w/120v = 10 Amps.
• 0

### #3 Jim Murdoch

Jim Murdoch
• Guests

Posted 21 January 2006 - 02:26 AM

Hey guys,

Does anyone know how many amps it takes to start (for example) a 1200w HMI on 110v? Is there a general rule to determine this (like # amps per 100w or something)?

Thanks,

The lamp current is limited by the ballast, either by a large iron-cored choke or an electronic current limiter. Generally with an iron-cored choke ballast they draw less current at startup, and as the voltage across the lamp drops with warmup, the current increases.

An electronic ballast tends to draw much the same current whatever stage of ignition the lamp is at.
However, the power supply of an electronic ballast can draw a massive whallop of current at switch-on, as it charges up its main filter capacitor bank. Some generators take great exception to this.

Or are you thinking of Incandescent lamps, perhaps? Generally they tend to draw a massive current when the filament is cold, which falls away rapidly as it reaches normal operating temperature. However, most generators seem to be able to handle that.
• 0

### #4 Robert C. FIsher

Robert C. FIsher

New

• Basic Members
• 8 posts
• Electrician
• Los Angeles, CA

Posted 22 January 2006 - 03:19 AM

The lamp current is limited by the ballast, either by a large iron-cored choke or an electronic current limiter. Generally with an iron-cored choke ballast they draw less current at startup, and as the voltage across the lamp drops with warmup, the current increases.

An electronic ballast tends to draw much the same current whatever stage of ignition the lamp is at.
However, the power supply of an electronic ballast can draw a massive whallop of current at switch-on, as it charges up its main filter capacitor bank. Some generators take great exception to this.

Or are you thinking of Incandescent lamps, perhaps? Generally they tend to draw a massive current when the filament is cold, which falls away rapidly as it reaches normal operating temperature. However, most generators seem to be able to handle that.

It really depends, if you are pluging into the wall then you need a wall circuit that can handle the current the lamp will draw. In the case of a 1200W HMI I would say it draws 12-14 amps under normal conditions. The reason the current may be more than the calculated current is the inefficency of the ballast and power factor of the ballast. Now when using this same 1200W HMI on a generator it changes things especially if the generator is a small one. Large generators don't have a problem but if you are running the 1200 off a 2500W generator then the inrush current of the lamp comes into play. A 1200W HMI will draw 2-5 times the running lamp current for the second after you hit the go button on the unit, so this would kill the 2500W genny. I would use a 5500-6500W genny and then you could run 2 1200's if started one at a time. Also the larger the generator the more inertia the armiture has so it can take larger loads momentarily. Incadescent lamps also have large inrush currents a 5k will draw 2-4 times that when you switch it on so now that can be 200 amps for about 1/2-1 second until the filament heats up, after that it's only 43 amps. Lamps up to 1000 watts have less inrush current for less time because the filament resistance is less.
• 0

### #5 Matt Irwin

Matt Irwin
• Basic Members
• 389 posts
• Cinematographer
• Los Angeles

Posted 22 January 2006 - 03:07 PM

Wow, thanks for the replies guys.

Robert, you told me exactly what I wanted to know. I was on a shoot running a 1200 off of a 3k genny and upon firing the light, the genny choked but kept running and the 1200 fired properly. That's pretty much what prompted the question. Thanks again.
• 0