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Discussion Starter · #1 ·
I am considering adding a subwoofer amplifier. But not if my Prius electrical system is already maxed out with my xd800 amp. So I was thinking a good test would be to hook my fluke 179 meter to the amp input terminals and crank some tunes to see if the voltage drops. BTW what is best way to attach the multimeter to the amp… just jam in with the power cable?

And how to interpret results? How low for how long would be a concern?
 

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Your meter likely cannot measure the transient current and/voltage fluctuations to accurately measure this. If you have output level goals and are limited on power run class d amps and use higher efficiency drivers. I'm sure plenty of prius owners have figured out roughly how much power you can pull from the car, google it.
 

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I am considering adding a subwoofer amplifier. But not if my Prius electrical system is already maxed out with my xd800 amp. So I was thinking a good test would be to hook my fluke 179 meter to the amp input terminals and crank some tunes to see if the voltage drops. BTW what is best way to attach the multimeter to the amp… just jam in with the power cable?

And how to interpret results? How low for how long would be a concern?
I just use one of these:

Amazon.com: Dual USB Car Charger,4.8A Output,Cigarette Lighter Voltage Meter Compatible with Apple iPhone,iPad,Samsung Galaxy ,LG ,Google Nexus,USB Charging Devices,Silver


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307681
 

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first, it's great that you are thinking about this & asking these questions.
second, with the multimeter tool you are mentioning.... it cannot read fast changes in voltage or current, so you will need to be doing things in the time periods of lets say ~5seconds at a minimum. so message here, is that music is not a good option, it draws fast current peaks, and you will likely miss those and get inaccurate results.

how to test
the general concept would be the following..... you need a way to draw different (known) levels of current from your electrical system, for example..... 10A for 5 seconds, 20A for 5 seconds, 50A for 5 seconds, 100A for 5 seconds, etc. Then while you are pulling the current.... you can measure the voltage at the battery or alternator. You really need a high current, current probe for this in addition to your multimeter. otherwise you will not be able to determine what the current is......
how to interpret results
Once you collect some data, see what current level causes the voltage to go down to ~12.7V - 12.9V. Let's say that is maybe like ~80A current draw for 5 seconds? (i am making this up)
Once you hit that point, you know your alternator/electrical system is struggling to keep up, and that's how much current your stock electrical system can provide safely/reliably, without degrading life of battery/alternator, etc.

You would need to keep in mind also,..... other electrical loads in your car will need current, so thing like heaters, defoggers, headlights, etc. you need to understand how much current those items require as well and hopefully balance this with your amplifier's current draw requirements.

Hope that helps.
 

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Discussion Starter · #6 ·
I am hearing the message that music is probably too dynamic to measure reliably. But music is in fact the load that I need to test. This car is generally considered to be able to deliver about 80A including accessories, and has a fusible link at 100A. The XD800 amp is rated to output 800w, and assuming an efficiency of 80% that means using 1000w or about 75A at 13.5V.

So if the amp is producing rated output it is sucking down basically all the power the car has.
BUT actual music at actual listening levels is going to use less. The amp channels driving the tweeters are surely not using as much as the mid bass for instance. Then there is crest factor and the fact that I won’t listen at peak levels all the time. I wouldn’t be surprised if I am maxing out at 40A or less from the amp, and have 30A that could drive another amp. Or maybe the xd800 is underrated on a per channel basis and can steer the power to the subs and use the whole rated 75A.

I guess the real question boils down to how much power is the amp using when music clips the subwoofer channels. If I am near 80A then I have no spare power for another amp. I suppose I could do this test with pink noise but that seems a bit of a tweeter danger. I do have large 4 ohm resistors which I could use to replace the tweeters for the test.

And I don’t have a clamp meter. I should probably get one.

Still there is the issue that I don’t listen to pink noise so that doesn’t say much about power reserves that would be available during actual music.

So far what I am learning is that Current into the Amp is worth measuring, at steady state conditions. Voltage at the amp while playing music would be the other way of seeing how much reserve is available.
 

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Discussion Starter · #7 ·
I just use one of these:
I have a hardwired voltage meter already at the front of the car. But under any significant power draw, the voltage at the amplifiers in the back are going to be different. I also think these hardwired meters are not fast enough to see what happens on transients. My Fluke multimeter has a bar graph updated 40 times a second that might be enough to see transients if I put it right on the amp terminals.
 

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you have many good questions.

Do you have an alternator? I suspect no.....? Can you explain the electrical system topology? where does the "12V" system get it voltage? what is normal voltage? Is it the same as a system with an alternator? Prius may be an extra special creature.

now...... How do you know your car's electrical system can only supply 80A? what conditions does that 80A apply? idle? fully charged battery pack? constant 80A is available all the time? what's the source of that info? did the source test the the system themselves?... i personally would be wondering those types of questions.

it sounds like your topic changed direction from how do i measure my car's OEM electrical system capability to ..... how do i measure what my amplifier will consume/require....
so i think you are totally right, you will be maxing out your electrical system if it indeed can only supply ~80A. that's true, its reality. You amp will draw that 80A, right before it clips. but will will be for short durations while playing music.

Anywho.....To measure the power consumption accurately on an amplifier with music, you need better tools. oscilloscope, voltage probes and current probes are needed. and this power level will change depending on the type of music you are playing.... so you would need to measure multiple types of music and characterize performance. It's safe to assume that if you have things dialed in correctly you could be drawing 80A spikes of current when the bass hits.

If you have things wired with the correct size wires, you should not see any voltage drop at your amplifier. Or very minimal voltage drop, like 0.1V
 

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A prius uses a step down converter to bring the voltage of the motor battery down to 14v for the car electronics. If you pull more amps than the converter can output, you'll have 2 situations. 1) the converter and battery don't have enough capacity and the voltage of your car system dips low and/or 2) the battery has enough capacity to prevent voltage from dipping below 12.5, but there is no left over power from the converter to charge the battery back, and eventually you are at point 1).

Either way, your battery stays in a constant low capacity state or it is heavily drained and charged. Meaning you'll be replacing a lot of batteries and often. And probably also a broken over worked converter.

You can look into installing another converter or replacing the existing one with a higher output, if they exist. In either case, you'd need another 12v battery as well to handle the additional load. You'd have to read up on if two converters could be installed and share the same load. It may not be possible, in which case you could isolate the amps on their own converter/battery source.
 

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Discussion Starter · #11 ·
I got a Klein CL800 clamp meter and did some tests with real music. My system currently has no subwoofer. I have my levels set conservatively so turning it all the way up is just a little less than what I would really want.

Using the clamp meter and a DMM for voltage, both set to read max values, I only read 10-12 amps max at about 14 volts on the power supply wire. So only using about 150 watts total. Reading voltage and current on one of the mid bass drivers was about 40-50 watts which Is consistent with 150 total.

I am sure I could push much more power with pink noise, gain tweaks, and better measurement but this experiment does give me some confidence that I have power reserves to drive a subwoofer at typical listening levels.

I am now thinking of replacing the xd800/8v2 with a MMATs 6150 (4channel plus sub) by using a passive crossover to drive the tweets and mids from one channel, to get more sub power. That amp is capable of using more power than the car will deliver, but in actual use I wont be driving it constantly.

I like the idea of having only one amp box so the subwoofer and full range channels can share the same power supply. Not to mention less power splitter hardware.
 

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I got a Klein CL800 clamp meter and did some tests with real music. My system currently has no subwoofer. I have my levels set conservatively so turning it all the way up is just a little less than what I would really want.

Using the clamp meter and a DMM for voltage, both set to read max values, I only read 10-12 amps max at about 14 volts on the power supply wire. So only using about 150 watts total. Reading voltage and current on one of the mid bass drivers was about 40-50 watts which Is consistent with 150 total.

I am sure I could push much more power with pink noise, gain tweaks, and better measurement but this experiment does give me some confidence that I have power reserves to drive a subwoofer at typical listening levels.
So you want it louder? Is that what you are saying?
40W to a bass drivers would have to be making a hell of racket.
 

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If it is something like “the Pixies” with a wall of sound it will be useful.

If it is thumping music it is still probably valid as the DMM will likely catch the current going in fine.
It has chokes and the current usually goes in at a more smoothed rate than it leaves to the speakers if it is a quality amp.

Itis worth a try with your “normal music”, and pick noise and some exemplar like ”The Pixies”.
 

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My thought was pink or white noise would effectively be all octaves or frequencies playing at once, like a 20 to 20k sine wave. This would allow you to test a worst case scenario.
Do you mean this is unrealistic as music would never draw this much current?
 
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