hello. i've got 2 questions.

1) this is an 8 channel CCTV camera system. it has a separate 12V splitter type power adapter which powers all 8 cameras.




Power adapter rated output is 12V 3A. but each camera has a sticker which says "Input Rating 12V 0.8A". so when all the 8 cameras are working and drawing their max current, isn't it going to be 0.8A x 8 = 6.4A ? can someone elaborate. thank you.

2) I have a 5 way extension cord with these 5 devices are plugged in.



i'm trying to calculate the total current at the extension cord (assuming all 5 devices are drawing their max current). thank you.

 

Hi Auto,
Do the Camera's have nighttime IR emitters, as that Emitters can draw approx 0.6Amp.

The mains extension block should not be a problem.

E

 

@ericgibbs hi. yea they all have IR LEDs which come into action at night. cameras are working fine.
but my question is when all the 8 cameras are working and drawing their max current, theoretically it should be 0.8A x 8 = 6.4A ? but the factory provided power adapter has a output of 12V 3A.

the mains extension is a separate question. sorry if i didn't make it clear.
it has one TV screen and 4 wifi / internet routers plugged into it. i'm trying to figure out the total current at the extension cord assuming all 5 devices are working and drawing their max current. since they are in different voltages i'm having a trouble to calculate the total current.

thank you.

 

I will give you a little hint on the extension cord.

Calculate the wattage of each device, add them all together and compare the result to the wattage capacity of the cord.

Power = Volts times Amps

For example, if the cord can handle 10 amps that would be 10 x 230 = 2300 watts.

Your 12 volt 2 amp device would be 24 watts.

etc...

This assumes the amp rating of each of the lower voltage devices is the output amperage.

 

when all the 8 cameras are working and drawing their max current, theoretically it should be 0.8A x 8 = 6.4A ? but the factory provided power adapter has a output of 12V 3A.

That is correct. As to why they sent a 3A power supply you'll have to ask them. Either you have the wrong supply or the information on the cameras is not correct. 3 amps divided by 8 devices (cameras at max amperage) would require the cameras not to exceed 0.375 amps (375mA) (3/8 of an amp). That power supply will not provide sufficient power for 8 cameras - assuming the data on the cameras is correct.

By all rights a proper power supply should produce MORE than 6.4 amps. It should produce at least 9.6A to have sufficient head room so the supply doesn't overheat. A good rule of thumb is to double the amps. 6.4 x 2 = 12.8 amps. This case a 12 amp supply would be more than sufficient. Even a 10 amp supply will be plenty of power. Keep in mind you don't want to provide too much amperage availability as it's a waste of power.

 

12V 10A switching power supplies are common, cheap and efficient.

 

Keep in mind you don't want to provide too much amperage availability as it's a waste of power.

Say what?

 

12V * 6.4A = 76.8W
add 10% for losses and you get 83W.

do the same for all other loads... (add 10% to everything that is not already 230VAC load).
so here your total wattage is only some 200W. any power cord should handle that with ease.

 

Say what?

If you have a requirement for 5 amps you want a power supply capable for at least 7.5 amps. But to get a 75 amp supply (didn't forget the decimal point) you have a supply that far exceeds the needs of the 5A load. You have a lot of wasted power and money. It won't hurt the 5A device but it's just plain wasteful.

Ohms law says the 5A load will only draw the needed amperage. It will only draw 5A. Meanwhile you'll keep 70 amps in reserve just doing nothing but slowly emitting heat as waste energy.

 

If you have a requirement for 5 amps you want a power supply capable for at least 7.5 amps. But to get a 75 amp supply (didn't forget the decimal point) you have a supply that far exceeds the needs of the 5A load. You have a lot of wasted power and money. It won't hurt the 5A device but it's just plain wasteful.

Ohms law says the 5A load will only draw the needed amperage. It will only draw 5A. Meanwhile you'll keep 70 amps in reserve just doing nothing but slowly emitting heat as waste energy.

Seriously?

 

switching power supplies have different performance curves for different loads. larger PSU in general may have higher losses. but doing this kind of hair splitting on a circuit powered by mains, where actual load is only some 70W is not going to melt the glaciers or make power bill look any different

 

Hi Auto,
This edited sketch should explain the total loading on the mains extension block.

The transformer you have is not suitable to drive all the Camera's requiring 6.4Amps.
You require a 12V rated at least 8Amps.

In my camera system I use 3 * 12V 1.0A transformers to drive 3 cameras.

E

BTW: Some of the earlier posts have misinformed advice, take care.

Note: I see that panic mode beat me to it, while I was still prepping.

 

i do not know how discussion turned from 6.4A to 75A. that is making extreme examples with more than 1000% of reserve power. or going down to extremely low power device such as TV remote. choosing PSU that has 10-25% reserves is fine. using one that that has 300-500% reserve power is also ok but you are paying more for the PSU.

example RSP-2000-12 is 12V PSU1200W rate (100A).
https://www.meanwellusa.com/upload/pdf/RSP-2000/RSP-2000-spec.pdf

and when loads are extremely low, efficiency does drop. so instead of 92+ %, one gets as low as 80%. so 20% are losses. and since load is 12*6.4A=76.8W, and the losses are 15W. using PSU that has similar efficiency curve but rated for 150W would result in 8% loses or 6W. the difference is 15W-6W = 9W. so saving is real. but that is tiny saving that is spread over very long time and completely unnoticeable.

the big $$$ difference is in the price of PSU ad that is difference you pay up-front:
100A unit will cost some $800,
10A unit will cost $50.

 

choosing PSU that has 10-25% reserves is fine. using one that that has 300-500% reserve power is also ok but you are paying more for the PSU.

That's been my entire point.