Controller ratings questions

khargy

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Feb 4, 2011
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I've been playing around with some DMX and RGB controllers for awhile, but I haven't been able to figure this out:


If I look at a controller like the following: http://www.holidaycoro.com/3-Channel-DMX-RGB-Controller-p/26.htm


It says "2 Amps per channel". To me that would be mean I can have 2 amps on Red, 2 amps on Green and 2 amps on Blue. So if my LED strips is set to "White" that would be 6 amps. Well now, if I understand things correctly, the common line has 6 amps on it. Is the correct and is that ok? Or do I need to assume I can only use 2 amps total for the RGB so like .67 amps per color?
 

David_AVD

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With smaller channel count controllers, the maximum permissible current draw is usually the channel's maximum current value multiplied by the number of channels. eg. 2A per channel, 3 channels and a 6A total.

When you get into higher channel counts on a single controller, the maximum permissible current draw is often less than the individual channel value multiplied by the number of channels. eg. 2A per channel, 24 channels, but only 20A total.

This lower overall limit is usually due to the practicalities of running that much (total) current through the circuit board tracks and the power input terminals.

In reality, most Christmas light displays don't turn on all channels 100% at the same time, so the lower total current capability doesn't tend to be as much of a problem as you'd otherwise think.
 

fasteddy

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Yes you are correct on the rating of 2amps per output for the controllers.

But

The load is determined by the lights you are using so the 2 amps per channel would mean you could load up that channel up to 2 amps, Now depending on what lights and how many you use will determine what cable would be the best fit.

For example a 5 metre strip of dumb RGB strip with 30 x 5050 RGB LEDs per metre will draw aprrox 0.2 amps per metre per colour, this means that each 5 metre strip will draw 1 amp per colour for a total of 3 amps. This 3 amps will return back down the shared common wire. So you would have to ensure your cable used is rated to take that common return load.
14/020 4 core alarm/security cable is used because it has a rating of approx 4.5 amps per core, this allows you to run one whole strip. Others use the 6 core 14/020 alarm/security cable because this way you can triple up your common return wires so that you can carry more return current.
 

khargy

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Ah great, that was my next question :) Does anyone use cat5 in the example you just mentioned (0.2 amps per metre per colour)? What the rating for a single wire? A pair?
 

fasteddy

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khargy said:
Ah great, that was my next question :) Does anyone use cat5 in the example you just mentioned (0.2 amps per metre per colour)? What the rating for a single wire? A pair?
I do not use CAT5 for power and I also dont recommend it for most installations, there are some exceptions, the reasons being that most people will use solid CAT5 cable due to its cheap price which is not the best solution because solid core is designed for permanent installations, so you may not have many issues the first year but after that you could expect to start seeing issues with brocken cores the more the cable is disturbed
If you then went to stranded CAT5 then you are paying a lot more and CAT5 is designed for approx 1 amp per core, so then this makes using 4 core and 6 core alarm/security cable a good option as it is stranded and has a higher current carrying capacity than CAT5
 

fasteddy

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This cable is 34 strands x 0.178 which is equivalent to 18 guage per core so approx 7.5 amps per core depending on your installation, so this cable is a great choice with plenty of current capacity. The description says it is for in wall installation, but being stranded this would be far better than using solid core.
The larger the headroom you have between the load (amps) and the current rating of the cable will mean you will suffer from less voltage drop for a similar length of cable with a smaller guage cable.
 
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