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Arri BL4 power


Alex Anstey
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Hi all,

 

I have an Arri BL4s with no battery. My basic physics is woeful and as a result I'm getting a little confused as to what to get and I'm terrified of destroying the camera! .

 

According to Jon Fauer's book, the camera takes 12v, 7ah.

 

So presumably I just need a 12v 7ah lead battery, the sort you can easily pick up for not very much money? The only alarm bells that are going off in my head revolve around the fact that any branded camera battery seems to cost a lot of money. Am I missing something, or would one of these cheap batteries provide the exact same power as one of the more expensive ones?

 

On another note, how important is the amp-hour figure (7ah)? If I had a 12volt battery which delivered 14ah for example, would that be a problem or would that fry the motor?

 

Any help gratefully received!

Alex

 

 

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He means 7A, which is an instantaneous rating. Amp-hours are a measure of battery capacity, not power drain. The 12V 14Ah would be fine and would theoretically run the camera for 14/7 or 2 hours, in practice rather less. But you'd just recharge it every day.

You could probably even run it off a car battery- the camera will do any voltage stabilising it needs itself- but they are rather large. In any case they're intended for starting a car and you don't need anything like as much oomph as that. The manual I have specifies at least 5Ah.

What you are paying for in a branded battery is fitting convenience, energy density, long life and a guarantee of performance. If you don't need them you can save a great deal.

Edited by Mark Dunn
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Cine specific batteries are great and very handy but expensive.

 

I'm no electrician, so there's my disclaimer, but I quite happily run my moviecam on sealed lead acid batteries and haven't had a problem so far. I did the same with my sr3 until I got the onboard batteries. Obviously I would recommend getting an electrician friend to check it out first- replacement parts from arri are very expensive if available at all

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Good to hear Charles, thanks for that!

 

I've had a look for cine specific batteries but finding any on the second hand market that are 12volts is proving difficult. They all seem to be 14v or higher.

 

I'm just desperate to run some film through the camera - it sounds like the sealed lead acid batteries will be fine for the time being!

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He means 7A, which is an instantaneous rating. Amp-hours are a measure of battery capacity, not power drain. The 12V 14Ah would be fine and would theoretically run the camera for 14/7 or 2 hours, in practice rather less.

 

That's not actually correct, Fauer was recommending the standard lead acid block battery of the time, which was 12V 7Ah. The 7 Amp-hour capacity rating is not essential, but a good base capacity. You can certainly use higher capacity batteries but that adds weight and expense without really being needed.

 

A BL4 doesn't draw 7 Amps, it's more like 2.5 to 3 at 24fps with a 400 ft load. On start-up there can be a current spike of up to around 10A depending on the load and condition of mag and camera. So if the battery has a fuse it needs to be at least 10A, preferably 15A.

 

The camera can accept slightly higher voltage, the rental house I work for used to usually supply 13.2V block batteries with nominally 12V Arri cameras and never had any problems.

 

I wouldn't worry too much about branded or cine specific batteries, cheaper brands should work just as well, they just might not last as long. A fused battery cannot damage a camera, as long as the polarity is right. Some people use things like power drill batteries, which can be quite cheap.

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Thanks so much Dom - that puts my mind at rest a bit.

 

Am going to have a go with a standard, fused 12v 7ah and see how I get on. It's good to know I can be a little flexible when it comes to voltage - opens up the second hand options a bit with the branded stuff if it comes to that.

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I think you can manage with NiMh tamiya batteries, for example those made for airsoft use. I use them with Konvas and Cameflex cameras and all kinds of accessories with either tamiya connectors or tamiya to 4-pin xlr adapters. the wires are quite short so you may want to make a extension for them. I recommend making a tamiya to 4pin xlr adapter with fuse holder and about 0.5m wires and making the other extension cords with tamiya connectors because they are much easier to replace and you can use factory made 4pin xlr cables also if needed, plus you don't have to change the battery connector. example of use: http://aapolettinen.blogspot.fi/2015/01/handheld-batteries-for-konvas-1-kcp.html

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