AC/DC

[Okeydokey]

I am looking for an AC  power supply to make redundant the need for batteries in my Pentax K-m camera,  I need a 6v - 6.5v power supply delivering about 3 Amps.  I read this stuff below and it might as well be written in Mandarin.  Can anyone tell me if this will do the job?  I have bought the bits to make up the interface, a bit of soldering is within my capability but need to power this now though a bit of bodge it and leg it.

Advert on Ebay reads:

This week I have an AC/DC Power Supply for sale.

It is in good clean condition, tested and working.

I think it was originally from a cordless telephone base unit.

Here are the specifications:-

Type  FW 7220       V24851-Z2618-A2-2

Input .................   230 V ~ 50-60Hz ~ 60mA

Output .............................. 6.5 V DC ~ 700mA

Made in Germany

Cable length is 72 inches          

 Barrel Pin Connector Diameter 2.5mm

 

My apologies for not be electronically or electically minded   I'm confident I can stick this whole thing together but my school lessons didn't go much further than eletrical analogies about water barrels filling with water and pipe sizes?

Many thanks

[steppenwolf]

Output .............................. 6.5 V DC ~ 700mA

You say that your require a 3 amp power supply (I am surprised at that as it seems a little high but I cannot confirm your requirement). However, the 700ma above means only  0.7 amp so this would not be suitable according to your requirement.

[Okeydokey]

Many thanks, I wasn't sure how many decimal places I should be moving the milli to the amp.  Makes sense now!

[JamesF]

I'm amazed it's not cheaper and less hassle to buy one off the shelf.  Or does nobody make one?

James

[Cornelius Varley]

3amps does seem to be a little high, but I've just looked at a Canon mains adapter and that one was 8v 3amps output.

[JamesF]

I was similarly surprised and checked my own Canon one which is not that different.  I presume the power is mostly for driving the lens motors.

James

[steppenwolf]

Really? Now that does surprise me! I guess there must be a reason but  you wonder how the tiny battery can have such a relatively long life in use. I don't necessarily agree with all the assumptions in this link but this article is very enlightening with both pieces raising a big a query over the 3 amp rating.

[Gina]

Seems to me that a decimal point might be missing

[Herbig]

Be very careful with this, if you are going to make it up yourself double check output, input and polarity, otherwise you could do irreparable damage.

[Okeydokey]

Not sure about the decimal point but interesting point never the less, (pun intended) thanks Gina:

From the Pentax forums, their world view:

'Let's use this as a start. Voltage is the amount of electric pressure in a circuit. 4 AA batteries in series will put out about 4.8 to 6 volts when fresh, depending on the chemistry involved, and the voltage falls slightly as the batteries are used. So 6.5 VDC (volts direct current) reflects the high end of those values. I would suggest that a power supply with an output between 6.0 and 6.5 VDC will do the job.

Amperage is the amount of current available. That last word is important. The official power supply can supply upto 3A (amps). It does not mean the camera's circuit uses 3A continuously. It uses only as much current as needed for the current operation. To play it safe, the power supply for this project should support output of at least 3A. Greater than 3A won't hurt anything; it just means the power supply won't work as hard'.

Other contributions to the same thread confirm 6.5V at 3A,  I am a simple man, very much the novice so I do take advice where ever I can find it.

[JamesF]

Amperage is the amount of current available. That last word is important. The official power supply can supply upto 3A (amps). It does not mean the camera's circuit uses 3A continuously. It uses only as much current as needed for the current operation. To play it safe, the power supply for this project should support output of at least 3A. Greater than 3A won't hurt anything; it just means the power supply won't work as hard'.

Other contributions to the same thread confirm 6.5V at 3A,  I am a simple man, very much the novice so I do take advice where ever I can find it.

Yes, the device is rated to allow a current draw of up to 3A.  In practice the camera may not use that much.  But the higher the current the "beefier" the components need to be, increasing the price.  So PSUs intended for a specific application are rarely made to be able to supply much more current than is required.

As I said earlier, I checked my own Canon PSU and it's not that different.  The voltage supplied is slightly higher and the current draw allowed slightly lower, but they're certainly in the same ballpark.  It's possible that some lens motors need that kind of power (not necessarily those in the kit lens) and perhaps also the display too.  Presumably they do have to be made on the assumption that someone will want to use them in the camera's most power-hungry configuration possible.

James

[Rooster]

Theres NO WAY on this planet that a camera needs 3 A  !!!!!!   I would say that a 700mA psu is more than ample (700ma = 0.7A)

Personally I would use an ammeter to measure the current drawn from the batteries... then you would KNOW for sure ! 

[Okeydokey]

If as JamesF suggests the current is driving the lens motor that is fine because I have moved to manual mode in every aspect of using the camera.

Strange how sure you are Rooster that 3A is excessive given the previous posts,  I'm only really after something that saves me 4 x 1.5V  AA batteries, in my simplistic view, that makes 6V, without the need to autofocus maybe I could get away with 0.7A, if the seamingly high levels of current are attributable mainly to this only.

Be really nice if this was the case, I have an AC-DC power supply unit at that level hanging around waiting to be used for such a project.

[TCWORLD]

Would something like this do you? http://uk.farnell.com/2334611

6V DC, 3A.

[Gina]

I have run Canon EOS DSLRs off a bench PSU which has digital voltmeter and ammeter.  The 1100D for example can draw up to 700mA in live view and AF with Canon lens, though normally in B mode with the shutter open capturing long subs it's more like 30-40mA.