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ACL II at 75fps, power requirement.


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#1 Gregg MacPherson

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Posted 20 September 2011 - 08:09 PM

I have an ACL II with the latest electronic base and latest Thomson chrystal controlled motor. All in as new condition. I ran some tests with scrap film and this brought up some questions about the supply voltage needed at high speeds.

With 1.9ah NiCad batteries discharged to 12.9V I can run at 50fps, but we don't get to speed at 75. My guess is it's somewhere between 50 and 75fps. The sync light stays on. The loaded battery voltage at 50/75 fps was 11.5/11 V.

So I tested with a 12V car battery. This battery had 12.35V and then 14.16V with the engine running (alternator charging). On its own, 12.35V the battery would not run 75fps, but at 14.16V it did fine. The current draw at 24/50/75 fps was 1.6/5.7/7.6 amps.

I didn't try the NiCads freshly charged yet.

- Does anyone know what the current is supposed to be at different speeds? My ACL I was supposed to have about 1amp at 24 fps.
- Are people using special batteries for higher camera speeds? The (ACL 1.5) user manual talks about higher capacity batteries being useful if doing a lot of high speed, but it's still a "12V" battery.

If we go to a high capacity high discharge NiMhi then I think we can maybe solve the supply problem. But I want to see if the current I measured is ok.

Any ideas anyone?
Cheers
Gregg.
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#2 Gregg MacPherson

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Posted 29 September 2011 - 07:30 PM

This may be useful so I'll report on progress with this.

From the previous owner I got that Visual Products had serviced the camera about 2 yeras ago, when they optimised the clearnces for minimum camera noise, with the current draw being higher but still "within limits". I don't yet know what those limits are.

Andrew Zorawski at AZ Spectrum had upgraded the motor electronics previously so I sent him a detailed email. I got really good ideas back from him. I didn't ask him yet if I could paste his reply here, so I'll summarise:

- Recommends for 75 fps a battery of at least 4Ah and up to 15.6V, a cable no longer than 1.5m.

- The proper current for the 74fps motor just with the camera body (no magazine) with 12V battery is:
24fps - 0.8A
50fps - 1.8A
75fps - 2.7A

- If you already have good batteries, make sure the motor is well positioned on the camera. By slightly loosening 3 fixing screws, run the camera at 24fps and gently push the motor and check if the current is decreasing in some positions. Sometimes the motor is too firmly pressed against one side. If this happens please put a spacer on the one side; important is correct coupling between the motor and the camera by a rubber disk.

- Can try to put no more than one drop of oil ( can be auto oil 40/30) on the motor's bearing (on the camera side).

- Can try to adjust the motor drivers by two potentiometers at speed 24fps. Potentiometers are located at the bottom rear of the motor electronics box. Turn these a small amount to minimise current and motor noise. Remember to note the origional position so changes can be undone.

- If these things don't help then the problem is with the camera body or magazines.

Cheers
Gregg.
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#3 Daniel Klockenkemper

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Posted 01 October 2011 - 10:04 PM

Gregg,

Thanks for sharing this information. My ALC 2 has the late, mirror-parking motor; I don't know what the power draw is, but it reaches speed at 75fps in under 1 second with a 12v 4.6Ah NiMH battery pack, so I'd guess that the draw is under 4.6A (which is borne out by the figures you quote). With an old NiCad pack, the sync light never went off at 75fps.

Regards,

Daniel
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#4 Chris Millar

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Posted 01 October 2011 - 11:37 PM

The (ACL 1.5) user manual talks about higher capacity batteries being useful if doing a lot of high speed, but it's still a "12V" battery.


They could be talking about putting 12v batteries in parallel ...

Every battery has an internal resistance that forms a simple voltage divider the lower the resistance of the load relative to others means proportionally more and more voltage dropped over this internal resistance which equates to less over the load itself (where you want it).

75fps is a proportionally lower resistance in this case - fire it up and measure the voltage across the terminals when it's running, you'll see it drop below spec pretty fast.

anyhoo - so if you were to put two 12v batteries in parallel, 12v would still be your terminal voltage but the internal resistances would have halved (although there is no ohmic connection, they form a node of common potential inside which equates to a parallel resistance at the connected terminals).

Your battery got twice as big also (it's also going to last twice as long ...)

In a nut shell: the bigger the battery (relative to others in its type), the better

NiCd's have relatively low internal resistance - which you've already seen the effects of Posted Image

Another option would be to get a battery of higher voltage and regulate it - get ready to dissipate some heat though
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#5 Gregg MacPherson

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Posted 02 October 2011 - 03:15 AM

They could be talking about putting 12v batteries in parallel ...

anyhoo - so if you were to put two 12v batteries in parallel


Reading the ACL 1.5 manual, Eclair had a 4Ah battery for cameras that ran a lot a higher speeds. It had a different casing, connectors and charger.

I had thought of hooking a couple of the 1.9Ah batteries up in parallel. I'll give it a go. But I'm getting the idea that with the tweaking for noise this camera has a higher than average current draw at high speeds. I think Andrew's idea of using a 15.6V battery sounds good.

Looking forward to switching to NiMhi when I can afford it.

Cheers
Gregg
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#6 Chris Millar

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Posted 02 October 2011 - 04:29 AM

By using a 15.6V battery you're just upping the voltage that will get divided back down to somewhere near the 12v you need.

By adding them in parallel it'll work for slower speeds also without fear of cooking anything.


It'll likely be fine either way though ;)
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#7 Gregg MacPherson

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Posted 23 January 2012 - 07:59 PM

I was a bit slack on solving that problem and reporting back. There are some ideas arising that may be usefull for camera users who are technically minded.

My new tests were done in warmer temperatures. I think the camera is almost new and set up with close tolerances and these factors may have been a small contributor to the previous result (failing to run at sync at 75fps).

For the new test I made a couple of changes but unfortunately I didn't test the changes individually so can't confirm which was the most significant.

Firstly, I checked the potentiometers that adjust the motor drivers. The paint spot seal was cracked and one of the pots had (been) rotated a tiny amount, judging this just by the brocken paint being out of register. So I tried to put the pots back as they were when they were spoted with paint. Also I had a look (@24fps) at the variation in noise and amperage while making small adjustments to the pots. Changes in noise were noticable but small, changes in amperage were very small.

Second, I took the motor off, checked the alignment to the rubber drive block carefully and remounted it. Carefully rensioned all the screws about the same.

Third. I used the on off switches on the body rather than the handgrip (later I tested 75fps with the handgrip switch and it still was OK)

I used the very short onboard battery cable and used a less than full 1.9Ah NiCd battery starting at 12.7V no load voltage.

RESULTS:
Ran fine at 75fps with lots of stops and starts for 180' , the length of the test roll. The sync light showed a nice quick start up. I then checked the no load bat voltage, was 12.34V. Ran another 180' the same way, all good, maybe the sync light showing a slightly longer start up. No load voltage then was 12.26V. Could have continued with more tests with this battery.

I ran a test with a battery that had a no load V=12V and I could not get speed @75fps.

CONCLUSIONS AND IDEAS:
Don't know what the dominant factor is out of temperature, tight mechanism, motor alignment, motor driver pot adjustment. I owe some thanks to the AZ Spectrum man for his ideas.

Not sure if I will make a higher voltage battery for high speed as per his recomendation. I may just make a jumper cable so I can double tha capacity of my normal batteries. Switching to NiMhi will be a great move also.

I read recently in the Eclair list in the Topica forum someones experience with high speed with ACL II with the latest motor. He said that voltage had to be over 12V.

If anyone has any of the following that they can share please contact me:
- Owner manual for ACL II
- Circut diagrams for ACL II.
- Workshop service/repair manuals for ACL I or ACL II

Cheers,
Gregg
<viz@xtra.co.nz>

Edited by Gregg MacPherson, 23 January 2012 - 08:02 PM.

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#8 Chris Millar

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Posted 23 January 2012 - 08:28 PM

Gregg didn't realise you're in NZ

I'm currently in Auckland...
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#9 Gregg MacPherson

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Posted 23 January 2012 - 09:19 PM

Gregg didn't realise you're in NZ

I'm currently in Auckland...


Hey Chris,
I'm also in Auckland. Ping me on the email above. Maybe we could meet or corro' about film making or cameras.

Cheers,
Gregg.

PS.
Further to the 75fps problem solving. Re the tests I did measuring current with a multimeter. I'm wondering if the multimeter leads are a bit fine and affected our result.
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