Considerations when running of DC power

[James d Page]

Hi,
Are there any conciderations when running of DC power apart from the obvious that the voltage shouls be in range 11.5V to 17V and beable to give the 60W or so power. for example of a car, and I take it of the DC is out of voltage range for the camera an inverter to get AC would be a bad idea.

Thanks

James

 

[Nathaniel Haban]

I think you might be over-complicating things a bit. I believe (anyone feel free to correct me if I'm wrong) that car outlets like cigarette lighters are 12V. Basically, this:
http://www.walmart.com/ip/FAST-TRACK-XO-Vision-DC-to-AC-300W-Power-Inverter/17057038
plus this:
http://www.red.com/store/power/product/ac-power-adaptor-150w-epic
and you're good.

 

[Gerald Menclik]

What I don't get, can't you just take the 12V output from the car and power your Scarlet? Just a little bit soldering for the right cable?

 

[Nick Pasquariello]

What I don't get, can't you just take the 12V output from the car and power your Scarlet? Just a little bit soldering for the right cable?

People have. I forget where on the forums I saw it, but someone was talking about doing exactly that for their Scarlet about a month ago. So, I can't tell you any specifics, but I can tell you it's been done.

 

[Nathaniel Haban]

What I don't get, can't you just take the 12V output from the car and power your Scarlet? Just a little bit soldering for the right cable?

I want the original poster to promise he won't do this. I'm not trying to pick on anyone by saying that, but jerry-rigging your own power supply, when you can buy an inverter for 10 or 15 bucks, is not worth it. When you're talking about a $10,000+ investment, go with what's better and safer, not marginally cheaper.

 

[ericyoung]

What I don't get, can't you just take the 12V output from the car and power your Scarlet? Just a little bit soldering for the right cable?

In theory yes. But you must make sure to wire the Red end correctly (TWO pins are positive and TWO pins are negative - according to the manual) to avoid damaging the expensive power board on the camera.

Also, don't stop and start the car engine while the camera is connected. And never rev the accelerator if the engine is running.

Nathaniel's inverter and Red's AC power both have voltage regulators which will help protect your camera, but still don't stop/start/rev the engine while powering the camera/inverter.

 

[James d Page]

Thanks,
The car was just an example that will be a convent power source. My understanding is that the batery is nomaly a nice 12.8volts, goes up a volt or two when the engine is running. but I was not aware of it overvolting by the 50% to exceed the 17V maximum of scarlet, that would not be good for all the car systems let alone 12V devices pluged in.

I had heard it was a bad idea to plug a solidstate DC power supply into an inverter as unless it is a more expensive one with a true sinosodal AC output it will make a modifed square wave with just the same RMS and peak voltages as true AC plus lots of noise and harmonics from voltage pumping.

off the car (or other DC source) assuming there is not a large overvolt, on reving, under volt on starting then bar some voltage ripple where would the problems arise?

 

[Pax]

Car DC voltage can vary wildly between 0V-20V, so I would never advise anyone to use it directly into a DC device that doesn't regulate voltage itself. DC-AC car invertors, phone chargers, and USB chargers regulate the outgoing voltage and have fuses that will at least blow when their incoming voltage hits +20V. Get a good invertor rated for more wattage than you need. If you have the budget, you could put a battery like the AlienBees Vagabond Mini between the camera and the car, and turn the car off when shooting- it's a 130 Watt-hour battery with charger built in, and can handle up to 120W continuous load. Another good thing to know (if you don't know!) is most invertors produce AC either using sinewaves or modified (non) sinewaves; non-sinewave invertors can damage photography strobe gear, and can sometimes cause electrical interference and audio hum.

 

[Michael McCune]

And we all know that auto electrical systems now are not simple now and surprising ($$$) damage can be done to the computerized systems if one applies their electrical creativity with a little too much enthusiasm.

Carts? If well designed, could work well in some mobile situations: shelves with plenty of room for a full car battery, proper voltage regulation (gotta have it), distribution cables to various other pieces (monitors, recorders, etc.). Might double as a dolly if the wheels are suitable.

Or a carry-on bag or case with wheels to consolidate and transport various power units, including an extension cord to use local AC.

 

[ericyoung]

Thanks,
The car was just an example that will be a convent power source. My understanding is that the batery is nomaly a nice 12.8volts, goes up a volt or two when the engine is running. but I was not aware of it overvolting by the 50% to exceed the 17V maximum of scarlet, that would not be good for all the car systems let alone 12V devices pluged in.

I had heard it was a bad idea to plug a solidstate DC power supply into an inverter as unless it is a more expensive one with a true sinosodal AC output it will make a modifed square wave with just the same RMS and peak voltages as true AC plus lots of noise and harmonics from voltage pumping.

off the car (or other DC source) assuming there is not a large overvolt, on reving, under volt on starting then bar some voltage ripple where would the problems arise?

You want to use a true sinusoidal output inverter.

The camera is expecting either a very constant DC voltage from the AC/DC mains supply designed for the camera, or a gradually decreasing one (like a camera battery), it won't have been designed for a randomly swinging, possibly spiking and noisy one such as a car battery under load or being revved. At the very least you will be stressing the power board of the camera, at worse you will exceed it's design parameters and fry the board. In fact, now I come to think about it, if the engine is running, you probably should go the inverter and AC/DC mains adapter route because of engine noise interference.

 

[Jim Collins]

Do not connect anything valuable to a car electrical system that hasn't been designed for it. An automotive load dump event can produce surges of over 100V and huge currents that will literally vaporize anything that hasn't been built to take it. There are components available that will arrest the surge but even they allow about 40V to get through. Best to let your $40 inverter handle it.

 

[Gerald Menclik]

I want the original poster to promise he won't do this. I'm not trying to pick on anyone by saying that, but jerry-rigging your own power supply, when you can buy an inverter for 10 or 15 bucks, is not worth it. When you're talking about a $10,000+ investment, go with what's better and safer, not marginally cheaper.

I know what you mean, but inverting the 12V up to 110V or 220V here in Europe and then transforming down again .... ??? and there are circuits available to protect the stability of the voltage ...