Postby carfreak » August 4th, 2010, 11:18 pm
An Explanation of the T15KW and an Interview with Amp Designer Anthony D'Amore
Intro
A lot of hype about technologies has floated around in recent years, most notably from the automobile world. With cars being a main focal point in American society, these technologies have become synonymous with energy, monetary and environmental savings. In automobile hybrids, most of these savings result from advanced electronic hardware.
Interestingly, at least one of those electronic technologies has made its way into car audio. Rockford Fosgate has developed a new concept in amplifier design, which they unveiled at the 2006 Consumer Electronics Show in the form of the attention-getting T15kW. The gist of this amplifier is to store ungodly amounts of energy, enabling it to produce 15,000 watts at greater than 100 percent efficiency. In other words—achieving the impossible. With our curiosity piqued, we went directly to the source, the Rockford Fosgate engineer responsible for the T15kW, Anthony D’Amore, for a little insight on this seemingly impossible achievement.
Some have reviewed the specifications of the T15kW with hybrid technology (HT) without understanding what the technology is. This causes them to refer to Ohm’s Law (circa 1827) and immediately say this amplifier is either impossible or trying to break Ohm’s Law. Ohm’s Law has been correct for 179 years and I’m sure it will remain correct for many years to come. This technology in no way breaks Ohm’s Law.
The real law that we need to talk about is the first law of thermodynamics, or Conservation of Energy. This states that energy cannot be created nor destroyed; additionally, you can only get the same amount of energy out of a system as the amount of energy that was put in. This is true for every amplifier, including the T15kW.
Here’s a quick review of what “efficiency” means, as I will refer to it later. (Efficiency = Power Out ÷ Power In.)
Let us take a typical Class A/B amplifier for example. Say it puts out 200 watts RMS and it takes in 300 watts to do this.
EFFICIENCY = 200 ÷ 300 = 0.67 OR 67%.
How do we know how much power it took in? This is where Ohm’s Law is helpful. We knew it took in 23.8 amps to do this at 12.6 volts.
23.8A X 12.6V = 300W
Conservation of Energy does not say “Power In Equals Power Out.” It says “ENERGY IN EQUALS ENERGY OUT.” What’s the difference? “Power” alone tells us nothing about length of time; “Energy” does (Energy = Power x Time). When you get your electric bill in the mail they don’t charge you for how much “Power” you used, they charge you for how much “Energy” you used, hence the unit “Kilowatt x Hours.” A kilowatt-hour is a lot of energy and I doubt we will ever see the unit used in mobile audio. When referring to the T15kW, though, we could use the unit kilowatt-second, meaning 1 kilowatt for 1 second. However, there is already a unit of measure for energy that is commonly used in the audio world: the joule. A joule is to energy like the gallon is to water. It is a quantity of energy and is defined as 1 watt-second or 1 watt for 1 second. OK, I know that is a bunch of info, but it’s necessary to really understand the topic.
I suppose we should talk about storing energy now, as in a capacitor. The formula for how much energy a capacitor can store is: (1/2 x C x V2). Which reads 1/2 times the capacitance (in farads) times the voltage squared. As an example, let’s find out how much energy is stored in a 1-farad capacitor that is connected to the +12V system.
(1/2 X 1 FARAD X 12 X 12) = 72 JOULES OR 72 WATT-SECONDS
If you are still with me, now we have the basis to discuss the operation of the T15kW and its hybrid technology.
Power-Energy
You cannot put out more power than you take in, or can you? The answer is YES YOU CAN, for periods of time. The HT system in the T15kW stores a huge amount of energy, well into six figures of joules. It is capable of this by using the latest technology in capacitors designed for use in hybrid vehicles and large wind-turbine electricity generators. The operation of the system is somewhat analogous to the operation of a hybrid vehicle. During some conditions, a hybrid car runs on just electric power; other conditions, on just gasoline power; and under “full throttle” conditions, on both systems. The T15kW has two systems in a way. It has the high-voltage system, which is stored in the amplifier, and it has the 12-volt system from the vehicle. When the T15kW’s output power is low, it uses power from the high-voltage system to run the amplifier and very little energy from the 12-volt system trickles in. When output power is relatively high, it uses the high-voltage system along with some energy from the 12-volt system to keep the high-voltage system charged. When it is at “full throttle,” it uses both systems to their capacity to supply the output devices with the maximum amount of energy possible.
So how can this work and why doesn’t it just “run out” of energy? The key is that music is very dynamic, meaning it has loud times, like a kick drum, and relatively quiet times, like … well, like anything that is not loud. During loud times, the system releases energy for instantaneous efficiency of well over 300 percent. During quiet times, it absorbs energy; the instantaneous efficiency at this point could be as low as 0 percent. HT is an energy management system. The “average” efficiency is still similar to other amplifiers. But, you must read the last two paragraphs to understand the big picture. The system in this amplifier was designed so that it could play typical music continuously at 15 kilowatt levels. After all, this is an audio amplifier we are talking about and audio amplifiers were intended to play music. With the HT system inside, the T15kW plays music like no other amplifier before it.
The question has been asked, “What about a sine wave, like for an SPL competitor?” The T15kW has plenty of energy to get through a three-second sine wave burst. However a five-minute “death match” competition is not the T15kW’s forte. Who wants to torture their investment like that anyhow?
Efficiency
So why would I design such a system? First of all, this amplifier will make your ears smile when you hear it. Or you’ll be smiling from ear to ear. So we’re talking sound quality. Secondly it has the ability to deliver incredible amounts of dynamic power. But maybe more importantly, when getting into the multi-kilowatt range, the power delivery from the 12-volt system becomes more and more inefficient. The HT system in the T15kW solves this though current-averaging to help with efficiency. Let’s talk about why current-averaging is useful.
Ohm’s Law states that power, and in this case power lost, equals current squared times resistance. Let us take a case with any typical amplifier playing music or a sine wave burst for a period of time where half of the time is loud and half is quiet, just to simplify the situation. Let us also pretend that during the loud times the amplifier draws 1,000 amps and during the quiet times it draws 0 amps. Suppose for a moment that during a loud time, 1,000 amps of current are being pulled on a 12-volt system through a 10’ run of 1/0-gauge cable. Standard resistance for this length of 1/0-gauge cable is about 0.0012 ohms. Using the previously stated formula for power lost, 1,000 amps times 1,000 amps times 0.0012 ohms equals 1,200 watts!!! So during this loud time 1,200 watts of power is being lost on that cable alone, and of course during the quiet time 0 watts of power is being lost since the current being drawn at that time is zero. With that said, half the time 1,200 watts are being lost and half the time 0 watts are being lost, for an average loss of 600 watts.
Now let us take that same example with HT’s ability to current-average for the same period of time. So instead of drawing 1,000 amps when loud and 0 amps when quiet, it draws 500 amps continuously. If we put that number into the formula for power (loss) we will see something interesting. Five hundred amps times 500 amps times 0.0012 ohms equals 300 watts loss in the cable. The losses are cut in half! So while the “average” efficiency of the T15kW amplifier itself may be similar to other amplifiers, it makes the entire system from battery to amplifier outputs much more efficient.
I hope this helps explain the technology—it is REAL, and it does work. —Anthony D'Amore
An Interview with Rockford Fosgate engineer Anthony D'Amore
Car Audio and Electronics: How did the initial idea of the hybrid amplifier evolve?
Anthony D’Amore: There were several things that took place for me that led to the design of this technology. My father has had multiple heart attacks and, during one episode, had to be shocked repeatedly by a defibrillator to bring him back. I remember being in the waiting room thinking about the defibrillator and what a great machine it is. How can a portable device with a very small battery system deliver such huge bursts of power? I knew the answer to the question, but the real question was: Could I use it in amplifier design? A couple of years later I found myself days before the annual Rockford Corporation Sound-Off, which is an SPL competition for employees. At this point I was the defending champion for three years and wasn’t sure how I was going to outdo my performance from the previous year. I had an old 1980 Datsun station wagon that I used specifically for these events. It had only one battery and a 60-amp alternator, so I could not rely on that system for any serious power.
But I thought, I need a lot of power for a short period. I went to work on building an amp just for this. It consisted of a power supply that converted 12 volts to 140 volts and a dozen motorcycle batteries to hold the charge. I didn’t have any Mosfets on hand that would handle the heat, so a couple of colleagues I and designed a system to liquid cool the devices. We got it finished just hours before and didn’t know what it was going to do, so we had the amplifier connected to an Audio Precision test system DURING the competition. After several rounds of competition and adding ice to the cooling system, my team of madmen and I walked away as victors and the prototype amplifier, dubbed the “D’Fibrillator,” belted out 15,030 watts RMS while keeping its cool! That set the mark, and now we just had to figure out how to turn it into a useable amplifier that could sustain music at these levels; and enjoying music as much as we do, the amplifier had to sound great doing it.
CAE: The foundation of the hybrid amp appears to be its energy storage ability, the capacitor. What industry was the capacitor technology sourced from and what was its intended use?
AD: The capacitors in the T15kW come from the power industry, as in power generation, transmission and distribution. The intended use for these capacitors is for very large wind-turbine energy generators, like the type seen around Palm Springs, CA. They are also finding homes in hybrid vehicles.
CAE: What was so special about this technology that made it suitable for the hybrid amp?
AD: The great thing about these capacitors is their ability to store so much energy in a small package. (Each capacitor used in the T15kW holds about 5,500 percent more energy than a common electrolytic capacitor of the same physical size.) This, along with their very low ESR (equivalent series resistance), made them a good match for something that is charging and discharging them repeatedly.
CAE: What’s the difference between adding a large capacitor inline with the power supply and that energy being stored in capacitors within the amplifier? Couldn’t the same results be achieved?
AD: The difference is huge! The equation for energy is 1/2 times C times V2. We can see by the equation that the voltage term is SQUARED, making it the most powerful part of the equation. It is difficult to store large amounts of energy with only 12 volts. More importantly, by having the energy stored on the other side of the amplifier’s power supply, the amplifier can control the energy coming in and out of the capacitors as in how much and when. By doing this, we are able to achieve “current-averaging,” whereby the amount of current that comes from the vehicle’s electrical system can be averaged over time. By averaging the current over time, the power losses in the power cables from battery to amplifier and within the amplifier’s power supply are greatly reduced.
Traditional amplifiers work like this: When the bass line hits, the energy that feeds the speakers is more or less coming straight from the vehicle’s electrical system. No matter how big the amplifier is, if the vehicle cannot deliver the power, neither will the amplifier. The hybrid technology in the T15kW works like this: When the bass line hits, that energy comes from the AMPLIFIER. At a more convenient time, like after the bass line, the energy can go from the vehicle, back to the amplifier. By doing this we have an amplifier that can deliver MORE power than the vehicle can supply for periods of time. Since music is very dynamic in nature, having relatively loud and quiet periods, the T15kW can play music continuously in this manner. Putting capacitors inline with a traditional amplifier will not produce the same results.
CAE: Is there a set limitation for current draw from the vehicle’s electrical system predetermined by the amp? Does this equate to a percentage of its maximum current consumption?
AD: Yes and yes. The amplifier has a very sophisticated power supply that sets this limit. In the T15kW, that limit is set to approximately 350 amps. This value was chosen based on average modern music containing around one fifth of the amount of power of a continuous sine wave.
CAE: Are there any hurdles with the technology that need to be overcome before hybrid amps become part of the Rockford Fosgate lineup?
AD: One of Rockford’s biggest challenges is not with the technology itself but rather educating our customers on the benefits of the technology. The primary focus of the T15kW is to demonstrate and promote this technology. Without hybrid technology, a stack of traditional amplifiers as powerful as the T15kW would not be possible to use in a vehicle without doing very extensive electrical system upgrades. Once this technology is understood, it will be easier for Rockford to introduce products containing the technology into the marketplace.
CAE: With smaller amplifiers drawing minimal amounts of current, at what power level does this technology start to make sense, both in terms of performance and cost?
AD: That really depends on what the “acceptable” amount of current consumption is. For aftermarket systems it may around the 1,000-watt level. If it were for an OEM customer, however, they may like to see a 200-watt amplifier that only requires six amps. Typically, the technology will reduce the peak current to one fifth that of a traditional amplifier. I should also mention that the technology has to do with the power supply portion of an amplifier and not its output section topology; thus, it could be used in Class A/B, B/D, D, etc., platforms.
CAE: Will amplifier size ever be an issue with this technology? Are there any other limitations?
AD: The capacitors used are a new technology for the capacitor manufacturer as well. The applications they were used in before the hybrid amplifier were not as size sensitive as car audio is. We are working with the capacitor manufacturer on development of devices that have form factors better suited for use in mobile amplifiers. The size-per-watt of the amplifier shouldn’t change much due to the technology. As an example: The T15kW is no doubt a huge amplifier, but an equivalent stack of amplifiers and batteries to do the same job isn’t any smaller.
CAE: How were you chosen to take this idea and bring it to life?
AD: It started with me on the quest for more power on my own time. Luckily for me, I work for a company that is a leader in the industry and is always working to stay on top. As such, research and development exercises like this are always in the works. Sometimes they don’t work out, but sometimes you end up with something killer! Such as the 3Sixty.
