Api 312 power consumption

Hi

What would be the biggest power one single channel will need? I need to figure out a transformer ta would fit one single channel, without being overly overrated. Is it safe to figure out about 100 to 150ma at worst? Along with the phantom power, maybe 10 to 15ma. Does it sounds about right?

Yes, thats plenty.
My 312's consume about 70mA P/C

Thanks. Is it safe to assume that:

DC Watt for the phantom power is about, in the worst case, 10ma x 48v = 0.48W x 2 = 0.96W AC
DC Watt for the bipolar rail = about 80ma x 15v = 1.2W x 2 = 2.4W (Do I need to take in count the negative rail ??)

So 0.96W + 2.4W = 3.36W. 1W = 1VA so I need about 4VA. If I need to include the negative rail, so it would be about 6.8VA.

I should be allright with a 15v dual rail, 10VA toroidal from Antek, then. Right?

Deepdark said:

Do I need to take in count the negative rail ??

Click to expand...

Yes, yo do!

1W = 1VA

Click to expand...

No, it's not! W is active power, VA is apparent power, var is reactive power. Draw a square angle triangle and all that,
while all are volts X amps there are different timing consideration. VA is the volts your DMM reads times the amps your DMM reads (proper reading of course, sometimes TRMS needed, doesn't make much sense in DC). W is the used power in the system, referred as how much heat a resistive load will dissipate, independently if DC or AC. The var is the geometric difference between them and refers to the power that goes in and out of the system but never gets used. If your load isn't linear (guess what, it isn't) this last one stops making sense and there are others ways to call it.

Thanks. Is it safe to assume that:

DC Watt for the phantom power is about, in the worst case, 10ma x 48v = 0.48W x 2 = 0.96W AC
DC Watt for the bipolar rail = about 80ma x 15v = 1.2W x 2 = 2.4W

So 0.96W + 2.4W = 3.36W. 1W = 1VA so I need about 4VA. If I need to include the negative rail, so it would be about 6.8VA.

I should be allright with a 15v dual rail, 10VA toroidal from Antek, then. Right?

Click to expand...

So, for a single channel, 10mA for the phantom, 80mA for each rail.

10mA x 48V = 0.5W
80ma x 15v x 2= 2.5W
(2.4W+0.5W) x 1.5* = 4.5VA

* YMMV, rule of thumb numbers depend on the person holding the thumb...

  You are missing here the losses on the PS, and some cases you might want to be able to handle, I guess using the 10VA is the way to go unless some other constrain. That 1.5 can change, depending hugely on the PS design, there are some decent spread sheets out there to help with that, I guess 1.5 is the smallest number I'd use for a quick calculation, it might be short in some cases, if the PS isn't that efficient or you are over estimating your filter caps, for example.

JS

Should I'd be better off to go with a way overkill 25VA power transfrmer? Just to be sure...

another question about the overall consumption. I need to select a fuse. Basically, we know about how, at full load, the api will consume. 80ma/rail + 10ma for phantom power = 170ma per channel, right? From there, how do I select the right fuse? Things to take into consideration:

I use a 25VA power transformer (I know it's overkill, but it's way easier to get than a 10VA).  I guess it's safe to keep the 25VA to feed up to 3 channels, after that, I shoudl jump to the nearest easily available power transformer (50VA).

Thanks guys for your time  ;D

Deepdark said:

another question about the overall consumption. I need to select a fuse. Basically, we know about how, at full load, the api will consume. 80ma/rail + 10ma for phantom power = 170ma per channel, right? From there, how do I select the right fuse? Things to take into consideration:

I use a 25VA power transformer (I know it's overkill, but it's way easier to get than a 10VA).  I guess it's safe to keep the 25VA to feed up to 3 channels, after that, I shoudl jump to the nearest easily available power transformer (50VA).

Thanks guys for your time  ;D

Click to expand...

  It's ok, if a 25VA is easier to get and fits your case nothing wrong with it.  If a 100VA ends being more practicall for some reason (ie. you have a spare one already) it's ok too.

  Fuses is a complete different topic. You must have one directly from the mains connection, so worst case you don't have fire, 25VA, 120V, I guess a slow 250mA would do, if it's fast you will probably need a higher rating. Remember fuses are rated as I^2*t (current squared times time, but we usually only mention the current) and curves behave a little different at each end. In practice, the fuses for this applications are cheap, so we tend to start with a smallish rating and expect it to blow during firsts tests, and increase, one step at a time till it doesn't blow, at least till you get the hold of it. For this application I like a screwed fuse holder, conventional glass fuse, there are 2 standard length, whatever it's easier to source, I like the longer ones if they fit the case.

  Would be wise to have extra fuses in the rails themselves, but here options are wider, as the protection could be electronic, resettable polyfuse, pcb holders for glass fuses, etc. Here, about 50% over the rated current of the rail, fast blow, to protect greater damage in case of failure in some circuit. In dual rails is also wise to have some mechanism to turn off the other side if the other fail, si you don't end up with only one rail since some circuits might be damaged for such situation.

JS