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I am not understanding something fundamental to amperage:
Consider this adapter which outputs 12V 7A. It claims that several (eight, in this case) devices running at 12V 5A can draw enough power from this one 12V 7A adapter.
How is this possible? Wouldn't running two 12V 5A devices require an adapter with at least 10A output?
nipponese
Posted 2014-04-22T17:59:57.050
Reputation: 974
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Looks like the statement what the adapter can handle is 8 times the device "Foo" (some camera), and the device "Foo" has an input rating of 12V 5A possibly.
Looking at the data sheets, we have:
The input rating of 12V 5A that is
while the adapter's output rating of 12V 7A
For a idea how this may work out in practise:
Assume they specify "you can use the adapter for 8 FooCam", and they know that FooCam has a pan/tilt mechanism that needs 4.9A if the motor is blocked (broken camera mechanics), 2A if the motor is used in normal operation of pan/tilt, and 100mA if just providing an image.
Now, they can be pretty sure only one camera is moving a any given time, as multiple cameras are normally controlled by a single application controling only one selected camera at a time.
So normally, the actual current needed it 8*100mA + 2A = 2.8A at maximum, and we have enough power left for another moving camera, or even a camera blocking for a short time.
Volker Siegel
Posted 2014-04-22T17:59:57.050
Reputation: 1 188
The device in question won't work like a camera but require max power 100% of the time – Ramhound – 2014-04-22T19:26:36.170
@Ramhound The adapter is called "CCTV Surveillance Power Adapter (12V 7A) + 1 to 8 Power Splitter for Security Cameras" - which device are you refering to exactly? – Volker Siegel – 2014-04-22T19:29:09.327
The Gridseeds of course... – Ramhound – 2014-04-22T19:31:06.303
@Ramhound and where is the 5A specification from? Or even 5A continuously? – Volker Siegel – 2014-04-22T19:37:00.560
@Ramhound From the questions comments, we seem to agree it's not clear(?) Looking at GC3355_DataSheet.pdf, I see references to 5A at 1V, not 12V. – Volker Siegel – 2014-04-22T20:15:07.993
I agree the question is not clear and the information scattered. I just know the device is going to requires full power based on what it does – Ramhound – 2014-04-22T20:22:51.410
@Ramhound Yes, the PDF is clear about the current of 5A - but at a voltage fo 1V, which means the full power is 5W, not 60W (5A * 12V) – Volker Siegel – 2014-04-22T20:25:57.310
What is the difference between Core, PLL, and IO supply Power? – nipponese – 2014-04-22T20:38:06.230
1Core is what you are interested in. – Volker Siegel – 2014-04-22T20:46:05.800
I can't find the "8x 12V, 5A" claim. But you are probably right, the total maximal output power is 12V, 7A which can be split up using the cable. – Jasper – 2014-04-22T18:05:24.953
@Jasper Sorry, you're right, the claim is not specifically in that link, but this here http://highoncoins.com/litecoin-rig/how-to-make-stackable-tower-gridseed-rig-with-raspberry-pi-pre-built-cgminer/ (scroll down to 1 CCTV 12V 7A Power Supply)
– nipponese – 2014-04-22T18:08:31.930I don't see the claim that this can support 8 x 5A on the link you just pasted either. – Adam – 2014-04-22T18:12:42.727
@Adam The link claims it can support 10+: "I recommend 1 of these up to 10 Gridseeds, it can handle up to 20". This is the specsheet for the device https://github.com/gridseed/gc3355-doc/blob/master/GC3355_DataSheet.pdf (page 10)
– nipponese – 2014-04-22T18:29:57.097@nipponese - I see no evidence of that claim. I see no evidence it can support 8 devices at 12V/5A each device. Whom ever made that claim is mistaken. Its just not possible At least not with each device pull 5Amps each. – Ramhound – 2014-04-22T18:40:43.897
@Ramhound Just for the sake of clarity here: This guy (http://highoncoins.com/litecoin-rig/how-to-make-stackable-tower-gridseed-rig-with-raspberry-pi-pre-built-cgminer/) says "1 CCTV 12V 7A Power Supply: I recommend 1 of these up to 10 Gridseeds, it can handle up to 20" The Gridseed spec sheet states each device consumes 5a: https://github.com/gridseed/gc3355-doc/blob/master/GC3355_DataSheet.pdf
– nipponese – 2014-04-22T19:13:12.103Add all information in the question I hate have to go to external websites to answer a question because they are often dead in a year – Ramhound – 2014-04-22T19:29:04.727
1Looking at GC3355_DataSheet.pdf, I see references to 5A - but at 1V, not 12V! – Volker Siegel – 2014-04-22T20:16:22.693
1@VolkerSiegel Oh, duh. This is a good point. Sorry, I am new to this. – nipponese – 2014-04-22T20:35:05.460
I think the question as stated makes sense independend of that - all the device power things are in the comment, and not really part of the question. But this does need some cleanup... – Volker Siegel – 2014-04-22T20:43:47.190
So I think the question as refined in the comments is answered by "there was a confusion of two voltages, 12V and 1V - taking them into account it all works out"? – Volker Siegel – 2014-04-22T20:45:17.233