# 24V amp possibilites?



## Tirefryr (May 15, 2005)

I figured this is a great place to post this. Anyways. . . 

My current occupation involves a great portion of the automotive electrical field. I have access to a myriad of 24V alts, and I'm wondering how feasible it would be to make some 24V amps. I would love to have half the current draw, but I don't know about the 24V electronics and interference between them and the 12V system the other accessories would run on. I have a guy I'm coordinating with right now on the amplifiers, but I'd like to get some more input. Thanks!


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## MarkZ (Dec 5, 2005)

I'm not really clear on what you're asking exactly. Frankly, I don't think there's a major benefit to the 24v supply for the amplifier. The transformer is rated in VA (volt-amperes), so there's no real savings -- you double the voltage but halve the current. You're not really going to increase the amplifier efficiency a whole lot, except for minor resistive losses.

As for the alternators, if you can still deliver close to 100 amps (or whatever your particular 12v alt puts out) with the 24v alternator, then that'll be helpful. But only if there was a problem to begin with. For most audio systems in most cars not trying to win SPL contests, the 12v alt should be sufficient.

If you're asking HOW to modify existing amplifiers to accomodate 24v input, it pretty much means replacing the transformer, probably the MOSFETs, and possibly the filter caps. It's not a cheap endeavor, since it's a bit difficult to find SMPS transformers at a reasonable price.


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## chad (Jun 30, 2005)

I personally would like to see higher than 12V systems in cars. Not huge, but 36-48V would be cool.

Wire diameters would go down, percentages of voltage would loss would look way better. Lets say you want 2 36V batteries.... Go ahead, toss an ISO diode in there .7V loss at 36V ain't nothing compared to .7V at 12V (13.8V)

Granted transformers are rated in VA and AMPLIFIERS would not become that much more efficient. BUT there are WAY more HV FETS out thete than High Current FETS (something has to drive that transformer). I would see power supplies becoming cheaper and more reliable. Also, since the entire car is not rated in VA because it's DC it's straight amps. The whole car would run better, be lighter (less copper), and more efficient (except for the damn amps) 

Chad


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## MarkZ (Dec 5, 2005)

chad said:


> I personally would like to see higher than 12V systems in cars. Not huge, but 36-48V would be cool.
> 
> Wire diameters would go down, percentages of voltage would loss would look way better. Lets say you want 2 36V batteries.... Go ahead, toss an ISO diode in there .7V loss at 36V ain't nothing compared to .7V at 12V (13.8V)
> 
> ...


All true. But, for his application, would you even bother with 24v amplifiers? There really isn't much to gain, unless we're talking about amplification on the order of a few kilowatts here. Suppose he modded an existing amplifier to be able to accomodate the higher voltage. It could be slightly beneficial in the wiring loss and DCR losses of the transformer, as well as losses to the resistance of the FET itself. But you've also got to worry about the Vds of your FET (you still require a high current FET) and how close you're getting to the voltage rating of the filter caps.


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## MiniVanMan (Jun 28, 2005)

I agree that you'd only really realize the benefit of a 24 volt system in much higher wattage systems. You're daily driver could be that much more annoying pumping out 5000 watts rms. I think there's a niche market for it and it wouldn't be a bad idea at all, as long as you can provide the amplification. 

As for applying a 24 volt system to a 12 volt car, that can probably be accomplished with some sort of step down transformer between the battery and the 12 volt system in order to isolate it from the 24. Then tap your audio directly off of the 24 volts. Probably kind of messy, but if you can get it to work, I'm sure there's some money to be made.


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## phantoj (Jan 31, 2006)

One advantage to 24V is that you could build an amp with a respectable amount of power without having to step up the voltage at all.

On the current 12V systems, 20 watts RMS bridged is about the max without some kind of power supply. (Thus, the popular 20W/ch head units and the old 20W/ch "boosters") But with a 24V system, that 20W would be more like 80W, right?


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## MarkZ (Dec 5, 2005)

phantoj said:


> One advantage to 24V is that you could build an amp with a respectable amount of power without having to step up the voltage at all.
> 
> On the current 12V systems, 20 watts RMS bridged is about the max without some kind of power supply. (Thus, the popular 20W/ch head units and the old 20W/ch "boosters") But with a 24V system, that 20W would be more like 80W, right?


That's true. That's a bridged rating, which is fine for head units but still really small for aftermarket amps. But part of the problem with introducing more power to head units is heat. Seems like head units would be prime candidates for class D or class G amplification. Class D could be problematic with EMI in a HU (?), and class G is usually most efficiently applied with a transformer with multiple taps.


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## B&K (Sep 20, 2005)

MiniVanMan said:


> I agree that you'd only really realize the benefit of a 24 volt system in much higher wattage systems. You're daily driver could be that much more annoying pumping out 5000 watts rms. I think there's a niche market for it and it wouldn't be a bad idea at all, as long as you can provide the amplification.
> 
> As for applying a 24 volt system to a 12 volt car, that can probably be accomplished with some sort of step down transformer between the battery and the 12 volt system in order to isolate it from the 24. Then tap your audio directly off of the 24 volts. Probably kind of messy, but if you can get it to work, I'm sure there's some money to be made.


It is easier than that. Just run the two batteries to your alternator in parallel and run them in series to the amps. Only the amps would see the 24v and the alt would still see 12v only with a larger load since there are two batteries. They do this in bass boats all the time for the trolling motors.


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## Tirefryr (May 15, 2005)

Well, it takes an average of 1HP per 10 amps of current to drive your alt. I'm going to be needing in excess of 400 amps at times, and I've been paying attention to a lot of tractor alts I've been rebuilding recently. I really like the idea of having higher voltage with less current draw and smaller/less cable, and the fact that I don't particularly want to dedicate 40HP just to run the elctrical system. Now, I understand this draw will not be averaged, but I would like to strain everything as little as possible. The alts are cheap and easily implemented. I did not know how the 24V and 12V systems would interact in terms of intereference. That's my main concern as of now. 

As for the wiring, I had planned to keep the 12 volt stock alt and run all 12V off that, then use the 24V just for the amps. If need be, I could ditch the 12V altogether. The 24V tractors use a pair of 12 Volt batts in series, then just tap off one batt for 12V for the accessories, and the charging and starting system are handled by the 24V system. I know pretty much squat about the actual electronics side and how it works as far as the amplifiers are concerned, hence my questioning. Better to get multiple opinions and idea than just one. Thanks so far everyone!


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## chad (Jun 30, 2005)

Horspower transfers to watts in a linear equation, not amps. You will still pull the same amount of HP.

Chad


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## Tirefryr (May 15, 2005)

chad said:


> Horspower transfers to watts in a linear equation, not amps. You will still pull the same amount of HP.
> 
> Chad



I know it transfers to watts, but you can also transfer watts into HP, but I do understand what you are saying. Increasing the voltage will decrease the current, but I still have to input the same amount of power. Thanks for pointing this out. Can't believe I missed that.


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## GMo (Aug 9, 2005)

I think a 24V car circuit would be a good project, for audio mainly because of higher efficiency and lower temps.

Adjustments would have to be made to the input stage, diodes, collectors, and biasing/gain circuit. 

Your output stage could remain relatively unchanged.

And for our 12V car circuits, the car uses around 1HP for every 30A -50A of alt. output(depending on eff.).


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## MarkZ (Dec 5, 2005)

GMo said:


> I think a 24V car circuit would be a good project, for audio mainly because of higher efficiency and lower temps.


Why would the temps be lower? The amplifier's efficiency should remain about the same and the same amount of power would be consumed.



> Adjustments would have to be made to the input stage, diodes, collectors, and biasing/gain circuit.
> 
> Your output stage could remain relatively unchanged.


Not sure I follow. The amplifier proper will derive its power exclusively from the output of the power supply. The input stage, output stage, and the rest of the circuitry within the amp should remain unchanged. Only the power supply section needs to be modified -- transformer turns, Vds of MOSFETs, filter cap voltage ratings, etc.


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## GMo (Aug 9, 2005)

MarkZ said:


> Why would the temps be lower? The amplifier's efficiency should remain about the same and the same amount of power would be consumed.


If power was the heat related constant, then yes. But voltage and current have individual factors.
As one factor is increased passed it's regulated level, generally the supply efficiency and related component efficiency drops, generating heat.
If the more regulated factor (voltage) is increased and designed as such, efficiency remains higher due to current supply staying low.




MarkZ said:


> Not sure I follow. The amplifier proper will derive its power exclusively from the output of the power supply. The input stage, output stage, and the rest of the circuitry within the amp should remain unchanged. Only the power supply section needs to be modified -- transformer turns, Vds of MOSFETs, filter cap voltage ratings, etc.


You can't just change voltage limits and ratio multipliers without making some changes, but I'm obviously not talking about the comparator. P/S input.


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## MarkZ (Dec 5, 2005)

GMo said:


> If power was the heat related constant, then yes. But voltage and current have individual factors.
> As one factor is increased passed it's regulated level, generally the supply efficiency and related component efficiency drops, generating heat.
> If the more regulated factor (voltage) is increased and designed as such, efficiency remains higher due to current supply staying low.


What exactly is the source of this increase in efficiency though? A supply designed to accept 24v input will reduce resistive losses in the FETs, transformer, and all associated wiring. But in a properly designed amplifier, these reductions should be minimal. 

For example, FET drain to source resistance should be compensated for by adding parallel FETs. This shouldn't be overwhelming from a cost standpoint either, because with the 12v system you have the benefit of using low Vds FETs. Likewise, the transformer is rated in VA, so the increase in current is counterbalanced by the decrease in voltage. So basically you're left with wiring losses and transformer regulation losses, which should be minimal if the appropriate wiring and right transformer are used.



> You can't just change voltage limits and ratio multipliers without making some changes, but I'm obviously not talking about the comparator. P/S input.


But the amplifier is completely isolated from the supply voltage by the power supply section. Modifying the power supply to accept 24v will leave you with the same rail voltages. If preamplifier processors, like built-in crossovers, are powered off the 12v, then that'll have to be addressed too, but that's small currents. Regardless, there's no reason to modify anything in the signal chain between input stage differential amp to the output with the change in supply voltage.


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## Tirefryr (May 15, 2005)

Just to clear some things up, if I were to do this, I wouldn't be using any modified amplifiers. I would have custom built units just for 24V use.


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## nubz69 (Aug 27, 2005)

You could use it and build custom amps. If you could switch te 24V single rail into +/-12V dual rail then you would have lots of options. You could build yourself a nice ALEPH X amp to run your front stage.

Personally I think that the move from 12V to 48 by the industry is a good idea, especially for car amp designers. They will finaly be able to give us amps that should be cheaper and sound better


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