Whats the Maximum average power draw of this class D amplifier? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: March 24, 2022, 05:46:39 pm
content: Hi,Whats the Maximum average power draw of this class D amplifier?http://www.fullfataudio.com/products/ffa-8000/We want to know what power will be drawn from our mains generator, which is pure sine output, 240VAC.

author: SeanB
author_rank: Super Contributor
timestamp: March 24, 2022, 06:08:02 pm
content: Flat out up to 44A, assuming your generator voltage droops down and does not drop below the cut off voltage at the power connection at the amplifier at full load. They say 32A, 2 16A connections, which I assume are parallel and to the same phase, at 240VAC, which is around the 8kW mark, and which, for a class D amplifier, will be pretty close to 90% efficient.However this is a peak, likely lower, unless you are doing area denial weapons again. In that case assume you will need 12kVA of alternator power, to allow for the peak current, and for whatever you are using to generate the sound. I highly doubt they will survive long periods of operation on full power though, perhaps half an hour and then lower output, or they will go into thermal protect mode.

author: Faringdon
author_rank: Super Contributor
timestamp: March 24, 2022, 06:42:51 pm
content: Thanks very much is it true that generally, the power draw of these in actual use tends to be "maximum/8"?..So in other words, 1kW?I mean, it seems unlikely that they have a 8kW offline SMPS in there to supply the Class D's?What power level of offline SMPS do you think might be in the enclosure?And this one would use a 250W offline SMPS inside it?..http://www.fullfataudio.com/products/ffa-2004/The bottom of this page gives some power levels per channelhttp://www.fullfataudio.com/products/...but i am not sure what this means in terms of the supplying offline SMPS in the case?The FFA8000 is only 50cm x 50cm x 9cm....i cant see there being two class D stages and an 8kW offline SMPS inside there..?...I mean , you are plucking a bass guitar at a festival........theres no way you are continuously plucking......the maximum average power must be very low?.....i reckon youre talking a 500W offline SMPS inside that FFA8000?...ie max power/16

author: dmills
author_rank: Super Contributor
timestamp: March 26, 2022, 02:43:26 pm
content: Depends on what time you are integrating over....It will manage 8kW for likely a few hundred ms to a few seconds on a hit, but will thermal limit if it is sustained, and note that because the amp drives a reactive load that supply is quite likely two quadrant.Generally the 1/8th figure is a long term (and what that means varies!) thermal limitation, but think seconds not ms.The usual expectation is that you are running these things off the grid or off relatively large rotating machines which can indeed hit 32A for a second or so, long term most program audio has about a 10dB crest factor so for the purpose of figuring power bill figure on 1kW, but for the purpose of sizing the peak current for a burst figure on 32A which your generator has to be able to supply without sagging the amp into shutdown.I would quite happily run that on a 13A socket because the time constants mean that my LONG TERM RMS current will be way below anything to cause the circuit protection a problem, and 32A is well below the 5*32A that will take the magnetic side of a MCB.You may need type C breakers to avoid tripping out on startup however, some designs (Old Crest looking at you!) have notoriously heavy inrush requirements.I would note that the headline figures assume a 2 ohm load on each channel (or a 4 ohm load bridged across both), if you are running higher then that (And nobody much likes doing the 2 ohm thing if they can avoid it) then your power requirements drop significantly.Oh often the power factor varies in 'interesting' ways with the program content as well, a standard PFC voltage loop is just too damn slow to track the audio.....