Charging 24v Batteries Without Electricity

Hi,

We will be going to a place where a generator will run for only two hours of the day.

We are shooting with 2 s16mm cameras and I'm wondering if anyone has any idea of alternative methods of charging and where we could get them from.

We will have vehicles close by, so we have a car battery for a possible unit of some sorts (I was told about a 300w power inverter but not sure where to find one?)
Any advice would be greatly appreciated.

Thank you,

Sally Low

>>We will have vehicles close by, so we have a car battery for a possible unit of some sorts (I was >>told about a 300w power inverter but not sure where to find one?)

Sally, I apologize for sounding like one of the listmums, but if you had included your location as they request (and basic work description but I think it's safe to guess you're an AC), I'd have a better idea of how to advise you.

In the US, you can get consumer quality inverters in the 300 watt range from just about any car parts store, Wal-Mart, etc. that plug into the 12 volt DC cigarette lighter or power point in just about any vehicle. They can be hardwired directly to the battery for a more reliable connection. If you go with a Wally World one, or get another consumer version, buy two, one to use, one for a spare, they're cheap (less than $100). The US ones obviously put out regular 60HZ, 120VAC. Most (all?) professional quality chargers are multi-voltage, multi-frequency, either automatically or with some sort of option switch. All but some very expensive inverters don't have accurate frequency output. That conceivably could bite you if you tried to run anything directly off the inverter that is sensitive to line frequency. For instance a small AC powered Obie light wouldn't be "flashing" at a flicker safe rate.

The better, more industrial strength ones are sold through electronics distributors, one of the brands I've bought in the past is Tripp-Lite, I have a Tripp-Lite that is at least 20 years old that still works 100%. I did get a 350 watt one for a client in an emergency a couple of weeks ago from Radio Shack that looks (and worked) like a pretty decent unit. It served its purpose, it ran the mission critical part of a radio station studio complex for 8 hours off the manager's Mercedes SUV (parked in the driveway idling) . Their backup generator had failed after 6 hours in a lengthy power outage, I got them back on the air with one of my inverters running off my van. The manager then went out and shopped for a permanent one for her station and replaced me after a couple of hours, paying me my consultant rate to sit in the reception area while drinking Starbucks coffee and chatting with the receptionist was getting expensive quickly. :-)

Hal Smith
Engineer and Somewhat DP
Edmond, OK

>>In the US, you can get consumer quality inverters in the 300 watt range...

Just a note... I have tried to use the Arriflex charger for the 12 volt SR batteries with a budget priced inverter with no success. The Arri charger wants to see a cleaner AC signal than the low-priced inverters put out. I've also had similar problems with a Victory battery charger. The invertors sold by Xantrex and others put out a very clean 60 Hz signal and can be used with anything that plugs into 120V AC/60 Hz. They cost much more, though. Around $1000.

Rod Williams
Motion Picture and HD First Camera Assistant
Petaluma, California
U.S.A.

In my experience, most switchmode (100 - 250 volt AC input) battery chargers require a pure sine wave inverter for the charger to function properly. Some of the cheaper modified sine wave inverters will be virtually useless for battery charging.

My 2 bob.

Angelo Sartore
1st. AC
Melbourne
AUSTRALIA

Angelo Sartore writes :

>>In my experience, most switchmode (100 - 250 volt AC input) battery chargers require a pure sine >>wave inverter for the charger to function properly. Some of the cheaper modified sine wave >>inverters will be virtually useless for battery charging.

Something's going on here that's deeper than just switchmode. I run different switchmode chargers off of inverters all the time, including a Sony FP charger. I also run all sorts of gear with switchmode power supplies off inverters. If there is a specific charger or two out there that don't like inverters it isn't solely because of their being switchmode that causes them to dislike square wave inverter outputs, a switchmode supply itself is a square wave oscillator followed by rectification and filtering. I suspect overly obsessive-compulsive engineering by someone in Germany.

Hal Smith
Engineer and Somewhat DP
Edmond, OK

>> Something's going on here that's deeper than just switchmode.

Yeah I think so too .. there are very few switch mode devices that won't work with even the most shoddy square wave inverter (and I have the grottiest 1Kw Inverter in the landrover). Are we talking about the 12V onboard batteries for the SRII here. Because if I remember correctly (and I owned one) that charger was always a bit "Odd" and that the new ones are way better.

But advice wise .. Lots of leisure batteries .. All well charged before you leave and then you can attach the inverter to them and charge your onboards. When the generator is on for two hours then you put everything on charge from the same outlet.

The other bit of advice is that if you are using an "Unreliable" power supply it's better to have at least some lead acid batteries because they do not have to "Cycle" with an uninterrupted power supply. There are a few chargers that discharge the battery and then put it on charge for 8 hours and then stop .. if you disconnect the power then the cycle starts again. At least if you have lead acid batteries then you can "TOP UP" a half charged battery.

Justin Pentecost
Specialist Camera Assistant
London
07973 317 241

I've had the same issue with my Victory Block batteries on a camera truck installed inverter.

Calling Victory they had no idea, saying it might be a situation where the inverter is too small to handle the blocks...but, come on, I have a 1500 watt inverter! We have run 1.2K HMI Pars from it. Also, all forms of chargers for power tools, laptops, printer, etc... seem to have no problem with the power produced by this inverter...only the battery chargers on the Victory brands.

Now, I am pretty sure it’s something to do with the sine wave or some such thing...does anyone know how to rectify this situation with an added capacitor or some simple circuit filter circuit?

Cheers,
Jeff Barklage, s.o.c.
www.barklage.com
view reel on web: www.reelsondemand.com
USA based DP

I've had this inverter for 10 years, and it has run many different chargers:

http://www.antonbauer.com/battery_belts.htm#mobile

http://www.xantrex.com/web/id/16/p/1/pt/10/product.asp

It's made by Xantrex, but I bought it from Anton Bauer. They used to sell it with an Anton Bauer label on it. I'm not sure what they mean by "modified sine wave," but it works.

It has a cigarette lighter plug, but the manual says to wire it directly (through a fuse) if you want more than 150 watts.

Pat Blackard
Gaffer/DP
Austin, Texas

Pat Blackard writes :

>>I'm not sure what they mean by "modified sine wave," but it works.

Modified sine wave means they've made an attempt to have the output look more like a sine wave (to a first approximation, a sine wave is a smoothly curved wave, no sharp corners) and less like a square wave (sharp corners on the output waveform). Doing that reduces harmonics (same thing as musical overtones) on the inverter's output. In lay terms it "cleans up" the output. It's the excessive harmonics on square wave output inverters that is bothering fussy switchmode chargers.

Modified sine wave inverters internally generate a stepped or pulse duration waveform that then has some filtering applied to it which smoothes the output to a sine wave approximation. (filtering somewhat like my previous post suggests trying on inverters with trashy output). The reason inverters generate either a square wave or some form of stepped or PDM wave is that means the internal power electronics are either on, or off, which is much more power efficient than a true sine wave generator would be. A true sine wave generator would have to basically be some form of amplifier with a maximum theoretical efficiency of 66% (a Class B linear amplifier).

Hal Smith
Engineer and Somewhat DP
Edmond, OK