Setup for CHDK matrix bullet-time rig with Powershot A450 and A460 cameras - page 3 - Hotwire! Hardware Mods, Accessories and Insights - CHDK Forum
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Setup for CHDK matrix bullet-time rig with Powershot A450 and A460 cameras

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Offline Anaglyphic

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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #20 on: 22 / August / 2009, 14:00:50 »
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hey zcream,

I think what David was saying re: 6V SLAs was that you don't waste efficiency by dropping the voltage, you wire up the cameras in series, 2x25 vs. 1x50, so each will see Vbat/2=3V.
Since we cannot know all that there is to be known about anything,
 we ought to know a little about everything.
-- Blaise Pascal

Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #21 on: 22 / August / 2009, 14:17:38 »
you wire up the cameras in series

I was not saying that but did think it later.
I did not post that suggestion because I am not sure if it will work.

I guess I could try with my A460's some time.

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Offline Anaglyphic

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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #22 on: 22 / August / 2009, 16:35:53 »
Ah. Well there ya go, I stand chastised.   :-X  S'what I get for speaking for someone.

Still, logic prevails and I'm 95.975% certain it will work. The 4.025% is because that the first camera turned on in each series pair must be able to handle the whole 6V till the other camera starts pulling current. Since 2.5V and 6.3V (rated!) are the most common low voltage SMD electrolytics and the lowest-rated SMD film is I think 10V, and ARM processors by design can tolerate indefinite ~5V on every pin even if the core is running sub-volt... As long as you turn both cameras in the series set on within a few seconds, yea I'll call it 96%. Without stealing the schematics or disassembling the cameras in question and tracing the power traces it involves some faith and risk... so if you don't believe it, don't do it.

I don't think that this is any less safe than building a single 3s x 20p NiMH battery pack to power them all. Twenty cells in parallel will be impossible to charge correctly without precision cell selection, else it's only a matter of time before the individual cell imbalances will cause one of them to reverse polarity and vent. (Seriously, don't solder them up in more than groups of ...6? Well let's see you want to go for 20 in parallel for runtime so 7(x3=21) or 5(x4=20) but you're in to 2C-3C discharge rates if they really do draw that much current, so be careful and Google judiciously on battery pack construction or it's going to be one very expensive 10-use battery pack.)
Since we cannot know all that there is to be known about anything,
 we ought to know a little about everything.
-- Blaise Pascal

Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #23 on: 22 / August / 2009, 22:38:19 »
Well. That would be risky in case there was a voltage spike from the SLA. I will have 50-60 cameras connected and 30 of them will have 6+ volts on them. Hmm. Have to think about this.
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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #24 on: 22 / August / 2009, 22:42:12 »
From Wikipedia :-
>>
Over-discharging

A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the "good" cells will start to "drive" the discharged cell in reverse, which can cause permanent damage to that cell.
>>

It seems that reverse polarity will affect only 1 cell - and only 3 are in series. This would happen only if I let the cells discharge to that level. As I mentioned, I will use them for 10-20 shots in a day only so the odds of it happening are quite less..

LiON 18650 cells are also an option as they give 3.7V. Since I will connect them in parallel - and I have 10 of them already, there is no real problem of balancing as each will draw what it wants to draw. Balancing is more of a problem in series. Hmm.
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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #25 on: 23 / August / 2009, 05:57:17 »
Using a 6V battery, put a low-value power resistor in series with the supply and two 3V3 zener power diodes from the other end of the resistor to battery -ve.

The camera's DC input is connected across each zener.

Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #26 on: 23 / August / 2009, 07:00:00 »
I doubt the zener diodes will carry 10-15 A current. Are these not rated in ma ?
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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #27 on: 23 / August / 2009, 08:28:11 »
Are these not rated in ma ?

It would seem so.

Far easier to just use cameras that work off 6V.

They also require a lower current.




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MrSpoon

Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #28 on: 23 / August / 2009, 10:24:46 »
There's a lot of ways of splitting the 6v (rail splitting). Using two zener diodes for biasing wouldn't do as battery voltage has a *huge* tolerance, once the battery voltage fell below the zener breakdown voltage you'd lose biasing.

The easiest way would be to use two resistors to bias a transistor so that it's output is half the supply. Then one camera could be connected 'above' the output of the transistor and the other camera 'below' it.

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Offline Anaglyphic

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Re: DC Socket size on Canon Powershot models 1.1mm 1.3mm ??
« Reply #29 on: 23 / August / 2009, 12:40:42 »
LiON 18650 cells are also an option as they give 3.7V. Since I will connect them in parallel - and I have 10 of them already
!!! Sweet! Well you either build laptop packs or... very few people have the slightest idea what those are, and having 10? I'm guessing you're probably a CPFer. If so, what's your edc? Mine. :b

Anyway, yes, quite so, those would make a serious battery pack. But the monitoring and charging, unless you're pulling the pack apart each time and individually charging, you'll have to design a complete liion charging circuit and either breadboard or send it to a prototype house... although the massively parallel part would work to your advantage, especially if the protection circuit is on the cells already.

The easiest way would be to use two resistors to bias a transistor so that it's output is half the supply. Then one camera could be connected 'above' the output of the transistor and the other camera 'below' it.
No... no. A passives-only solution is the wrong approach for a battery application. Using a resistor divider would be very wasteful; you would have to allow for the maximum current or it would cause a voltage drop that would probably shut down the cameras at the worst possible time, right as they fire but before it writes the image to the card. And, when the camera(s) weren't pulling that much current, those resistors would be nice little radiators. The losses would be the same if you used 25 pairs or two high-wattage aluminium heatsinked ones and would account for over half of the energy.

The zener method would work, just as an overvoltage clamp, but you'd have to wire up a current limiting resistor and zener for each camera tap, or every-so-many cameras... going this route I'd use a PNP assist for heavy current work, running at ~50% of rated capacity. (and you'll still need heatsinks. Like the resistor divider approach it's not really battery friendly.)

Now using a divider as Vref for something more efficient, either a switcher or even an ldo analog regulator... but if you got to design and build circuit, why not go with a nano-picoamp voltage reference?
Since we cannot know all that there is to be known about anything,
 we ought to know a little about everything.
-- Blaise Pascal

 

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