7.4V RC car battery for Arriflex S / B ST

[MattWalters]

Hi there, recently won an Arriflex ST body and motor w/ 2 lenses for 250 US appx - I think I did fairly well but welcome your opinions as I know these valuations fluctuate

my main issue now is actually testing to see it works, so I need a battery, I think from reading a few more forums that the 7.2V RC car batteries are ok

I've found some 7.4V ones which are closer to the actual original required voltage so I think thats even better, however, just wondering if theres any issue with the Mah as they vary wildly

I dont think there would be as diff Mah AA's can be used in electronics devices, but ive just once fried a very dear Super 8 camera by putting in 1.2V rechargeable AA's instead of 1.5V classic alkaline ones and now I'm super paranoid

any input is greatly appreciated thanks

[granfer]

The problem with RE-Chargeable batteries, of ANY voltage, in Super 8 cameras is that Super 8 cameras have no built-in protection against excessive motor current (AMPS). Re-chargeable batteries can deliver enormous currents if asked to, so if the motor of a Super 8 camera stalls or slows down significantly due to a mechanical or cartridge problem it will ask for more current to correct the problem. If that current gets too high or lasts too long the motor will FRY!!! Alkalines cannot supply the current, so no adverse effects.
If your Arri is designed for re-chargeable batteries then any type will not harm the camera so long as you keep the VOLTAGE below the rated voltage.

[bolextech]

You shouldn't have any problem with rechargeable cells but it's always safer to have a fuse in the circuit. A typical Arri ST motor draws 2.5A of current when it's running. The momentary initial current surge to get the motor started may be as high as 5A. Bear this in mind when choosing a battery system. Some cell types are better suited to high current drain than others. A 5A fuse will offer adequate protection.

Also, the majority of motors out there are the earlier type which were designed to work with 8 VDC. Starting with a pack that is nominally 7.4V might work fine but it won't last as long as a pack that has at least 8V to start with. Common battery packs based on nickel-type cells are nominally 8.4V and use 7x 1.2V cells. This gives you a little extra juice. Going too high is usually not recommended as it supposedly promotes accelerated wears on the rotor and brushes because of excessive sparking. I can't really confirm this from first hand knowledge but it seems to make sense.

Cheers,
Jean-Louis

[MattWalters]

Hi Jean Louis,

In this case do you feel that 8.4 is too much ? I know its quite dangerous to go above a certain voltage, but again, where is that line drawn is the question

I dont mind buying multiple 7.4's to have extra on hand incase one loses power too quickly

any thoughts are appreciated

[bolextech]

No, 8.4V is fine. It's what all the old NiCd based battery packs used.

As for a 9.6V pack, I would hesitate a bit because a fully charged pack when taken of the charger can have an output voltage of as high as 11V.

What I was talking about is running the motor off a 12V-14V supply all the time like I've seen some people do.
This I would not recommend.

Near the end of their production on this camera, Arriflex did have some newer designed motors which did run on 12V but these are not common and usually are clearly marked.

Cheers,
Jean-Louis

[MattWalters]

Excellent, in that case I guess I will be going with the 8.4, might just build one myself

thanks for your help on this one