I want to install an amp in the trunk of my 70ss to power a 10" sub. I also have a factory looking engine compartment, so I don't want a big red power wire hooking up to the battery. Would it be ok to hook the power wire to the starter? Does anyone have any other suggestions? Thanks.

The starter will work fine. Just make sure you route it away from any heat source.

The starter will work fine. Just make sure you route it away from any heat source.
And put a fuse in line, preferably close to the starter :thumbsup:

just run a battery in the back in the trunk thats what im thinking if doing with the 64

And put a fuse in line, preferably close to the starter :thumbsup:

Ever seen what happens when you don't? :eek: :eek: I worked in a cutom autosound shop for several years when I was in high school. Some numbnuts brought his car in that he had wired (first red flag!!). I sat down on the door sill to take a peek under the dash. Guess what happened?!? His amp wire under the threshold shorted out! It burned a "track" all the way back to the amp. Scared the #$*#$*@#% out of me! One minute I'm minding my own business, the next the car was filled with smoke!

Thanks, I'll definitely use a fuse!

One idea is to use a black wire or cover the wire with a factory looking wire loom. You may be able to run the wire behind the drivers side fender so most of it will be hidden. I would use a coat hanger to run the wire.

I think you are suppose to hook it up straight to the battery because the battery filters out some of the engine noise but i'm not 100% sure.

I think you are suppose to hook it up straight to the battery because the battery filters out some of the engine noise but i'm not 100% sure.


Yes & No... the battery is a giant capacitor, and does filter out some noise. The primary reason is that some of the higher power amplifiers can suck upwards of 30A + for brief moments, and the only wiring in the vehicle able to handle this additional load is what YOU have installed. If you think about it... what other circuits in the vehicle have 30, 40, or 50 Amp fuses?? Probably none. Direct to the battery (or the starter post via 00g/heavy cable from the battery) is the only path in the vehicle that will supply those kinds of demands.

The very best way to avoid "noise" is to follow a few simple tips:
#1 - Good grounds! Use the same guage wire for the Neg. (amplifier power connection) as you are the Pos/feed. Keep it as short as practical, and have bare metal-to-metal contact to steel.
#2 - Cable routing. Run the power wiring down one side of the car, and your audio/signal feeds down the other. Keep them physically separated as much as possible. If they do have to cross eachother, do it at a right-angle.
#3 - Mount the amp to a sheet of plywood/insulator. Keep the amplifier chassis isolated from the vehicle ground plane.

Your positive connection should be at the + post of the battery, and fused within 12" of connection. Any wire between the battery + and the fuse is a potential "toaster". I understand your desire for "cleanliness" and connection to the starter post is a good way of concealment, but pleeeezzzeee install a weatherproof fuseholder close by on this line if you go this route!

This is the way I see it. When the engine is running the current for the amp is supplied by the alternator. If the amp is connected directly to the battery or if it’s connected to the starter, the current flow will be from the horn relay to the battery through a 10 gauge wire and a 14 gauge fusible link. While the battery does offer some filtering an automotive audio amplifier will have power input filtering and power supply isolation that should eliminate most noise. The negative effect will be a reduced battery charge do to lower voltage at the battery. The higher the current draw of the amp the lower the voltage at the battery. The best place to connect the amp is the horn relay.

The starter and battery are connected with a pretty heavy piece of wire, usually about 1awg or better. So, it really does not matter if you connect to either one when the wire you are connecting is much smaller.

A big NO to the horn relay unless it is a pretty small amp. Most decent amps require their own 10awg or heavier wire connected directly to the battery. You can not connect the amp wire to a spot in the car that is wired with a 10awg which is already loaded with all the other car loads and expect that existing wire to also handle the amp load. A lot of amps require a wire heavier than 10awg too.

If the charging system is not keeping the battery charged after the amp install then the charging system needs to be updated.

To add to Johns post. Make sure that the ground wire is extended throughout the car. You can not connect a 8awg ground wire from the amp to the body if there is only a crappy 12awg wire going from the body to the battery at the front of the car. The best way is to make sure the ground straps that go engine to firewall are installed with clean ends and in good condition. The big power wire from the battery to the engine will take care of the rest of the ground path.

Peter

I am using a small 100 watt amp, so the wire size I'm using is 12 awg. I also have the same size ground wire. Thanks for all the advice, I think i'm going to go ahead and hook it to the starter.

The output of the alternator is connected to the horn relay. When the engine is running that is the most direct connection to the source. When the engine is running the alternator is providing all the cars electrical requirements not the battery. The only connection the battery has to the alternator is the 10 gauge wire from the horn relay that also has a 14 gauge fusible link on the end. If the amp is connected to the battery the alternator will supply it through the above mentioned wire while recharging the battery. Because of the increased current through that wire the voltage at the battery will be lower, depending on how much current the amp draws, resulting in a lower charge.

Of course if you turn on the amp with the engine not running the amp will need to be supplied by the battery through the same, horn relay to battery w/fusible link wire.

Upgrading the wire size from the horn relay to the battery is an option. However you will need to increase the size of the fusible link, In event of a short circuit will it still be the week link, or will you burn up other wiring before it?

If I were going to add electric fans or a high output audio amplifier or any other high current load. I would use a relay with an oil pressure switch or an RPM switch that would disconnect the power until the engine is running. I would connect all added loads to the horn relay with circuit protection. If needed install a higher output alternator and a larger wire from the alternator to the horn relay. Leaving the battery to do the job it’s designed for, store energy for starting. The 14 gauge fusible link will keep the battery from feeding short circuits. It along with the 10 ga wire will recharge the battery only, not try to supply the current needed for addons that are connected directly to the battery.

I have two big amps in my 67. I purchased a fuse block that has big (#0) clamps on the input bus. I cut the battery lead to the starter, near the firewall mounted fuse block and passed the two cut ends through the metal bus. You MUST make sure the fuse block has a HUGE metal bus for the battery to pass through to the starter without a voltage drop. Then it taps off the big metal bus to three fuse protected clamps for up to #8 wires for the amps. Make sure you follow all of the advise you have goten here so far or you will have a dead battery. The fuse blaock is for stereo amp usage is is all enclosed and protected. You can't see it if it's installed in the pocket to the left of the battery.

Don't do this if you don't know what you are doing (Poof/Bang).

Chuck

Chuck, What fuse block are you using and do you have photos of the mounting in your car ?

Elree, in this case it's a small amp and would probably work off the horn relay. In my other car I installed a #4awg for the amp directly from the battery. In that case, I'd have to run 4awg from battery to the connection point and from the alternator to the connection point. The way it is, the electrical system with 8awg charging wiring is keeping up just fine so it will work up to the point you install so much amp you overpower the charging system.

You are right that the horn relay is the closest source to the alternator but big power amps need the battery to provide extra power during the peaks in the music (typically strong bass notes to the sub). These peaks can draw more current than what the alternator can supply. Yet, the alternator will keep up between the peak current draws to keep the battery charged.

Also, I would need a pretty big relay to switch that 4awg wire using a oil pressure switch. It's just not practical. For electric fans, however, it would work good. Another bonus would be taking the fan load off the battery until the engine is running. But then, I used the keyed power source that is only on when key is in the on position to run my fan relay so the fan is off when I'm cranking the car.

As I said, go to the battery and then upgrade the charging wiring and alternator if it can't keep up.

Peter

You are right that the horn relay is the closest source to the alternator but big power amps need the battery to provide extra power during the peaks in the music (typically strong bass notes to the sub). These peaks can draw more current than what the alternator can supply. Yet, the alternator will keep up between the peak current draws to keep the battery charged.


To expand..
In some of the more "serious" competition audio systems I did we went as far as either installing a dual-output alternator with a small second battery (just for the audio gear), or upgrading the standard alternator with a 100A+ (police/ambulance duty) unit using a battery charging isolator (RV stuff), with a couple of Marine deep-cycle batteries in the trunk!

It's no joke about some of these audio systems... Think "Doc Brown and Back to the Future"... 1.21 gigawatts.... 1.21 gigawatts!!

Chuck, What fuse block are you using and do you have photos of the mounting in your car ?

Sure Mike, I have the reciept at home. I got it on line. I am in chicago until Sunday. Please send me a PM to remind me and I will send the info and a piture when I get back to the Bay area (if this snow ever quits.... ARGHH).

Chuck

It never is as simple as stating "do it this way or that way" is it! My recommendation was prompted by the usual method of adding electric equipment "I'm going to hock it directly to the battery" assuming the battery is the source of the cars electrical energy. I've seen it many times when trouble shooting auto electrical problems. In this case there was no mention of increasing the size of the wire from the alternator to the battery. The factory configuration is good for charging the battery and running the low amp factory accessories. I personally am not a fan of larger wiring from the battery. That's why I recommend connections to the horn relay on Chevrolet cars built in the 60s - 70s time period,

Sure connecting to the battery for amps 200 to 600 watt is better, bigger than that when you mount batteries in the trunk. I have had no problem with a 100 watt amp getting power from the horn relay.

I do understand the fluctuating power demands of audio amplifiers, isn't that the reason for the big, 1 - 10 farad, caps mounted along side the amp?

"It's no joke about some of these audio systems..." Like the Rockford Fosgate 15 kilowatt amp just 25 grand. Rockford Fosgate you can buy better but you can't spend more.

Don't think anyone has hit the million watt (Megawatt) or billion watt (gigawatt) mark yet. But if they did, you can bet someone in a rice burner would have one and be driving down the road with volume at max.

It never is as simple as stating "do it this way or that way" is it!{/QUOTE]

That's why I said use the battery unless it is a small amp. I then said I believe a larger amp should go to the battery and the charging system upgraded as necessary.

The larger amps should have the same size power wire from the amp right to the battery which means the charging wiring from the horn relay to the battery would have to be upgraded if you connect there. So then, what is the difference between there or using the battery??

[QUOTE]That's why I recommend connections to the horn relay on Chevrolet cars built in the 60s - 70s time period

Well that sounds a lot like a "do it this way" statement.

Peter

This is a far more complex subject than most in the hobby world know. I have a brief summary and then an explanation below (I have kept it as short as I could).

The executive summary is:
1. The alternator is always putting out more voltage than the battery when the car is running thus it is doing all of the work.
2. Since the battery and alternator are in parallel so they will work together if you exceed the capability of the alternator.
3. At the point the alternator is heavily overloaded the voltage of the entire system begins to drop and the battery will increasingly take over the load as the voltage drops below 12.6V. This is rpm dependent as alternator output is determined by RPM.
4. Batteries look better to amplifiers as a source of power due to better internal Z. The internal Z gets worse with battery age.
5. The wire that is run to the amplifier in the trunk is more of an issue than where the wire is hooked to in the front of the car (comparing alternator regulation point, or horn relay buss to the battery)
6. The return path for the current (negative or ground) is of equal importance to the positive run of wire. The alternator references it's voltage regulation to the metal body of the alternator. Since it is bolted to the engine block the block becomes the real ground for the electrical system of the car.

Best Practice Installations:
1. Use a number of smaller wires in parallel (rather than one big wire) to run from the front of the car at the regulation point of the alternator, since it does all the work, to the rear of the car.
2. Running a separate set of ground wires to the block is as important as the positive wires.
3. Use a good amplifier
4. At higher power levels (above 300W) use a capacitor very near the amplifier per the manufacturers recommendations.

One caveat here. If you want to run your 500W boom box woofer at full tilt with the car not running you need to provide an alternate path for the current as the battery is going to have to do all the work. Thus one of the previous posts suggestions to have a battery in the trunk connected to the alternator by an RV battery switch (ORing function) is the correct one. At that point you would also need to increase the size of the wire from the alternator to the horn relay with a suitable fusible link to match.

An explanation, the more complex stuff:

Amplifiers draw current in proportion to the power they are driving. With no sound they draw little current with boom box sounds they draw a lot of current. Thus as the sound changes the current required changes. As the current changes become larger the voltage drop on the wires that feed energy to the amplifier can affect the amplifiers performance.

Over all Voltage drop is caused by two terms: resistance which is a direct current term (DC) and "Z" which is the symbol used for impeadence which is an alternating current (AC) term. Both of these terms depend on wire size and run length.

Example,
Amplifier in a trunk, wire run from front of car, either battery or horn relay.

Estimated length of the wire is 3 meters (9.75 ft) to get to the trunk.

To calculate the AC term, Z, we first need to know the inductance, L, of the wire and to this end we use a web calculator in the first citation below,

A 2 AWG wire will have an inductance, L, of 3.523 micro henries
and
a 10 AWG wire will have an inductance, L, 4.636 micro henries.

This assumes a permeability of 1, which is free air but since we run our wires next to a ferrous material in our cars (steel) the value of inductance is greater than the simple calculation shown here.
Citation: http://www.consultrsr.com/resources/eis/induct5.htm
Citation: http://en.wikipedia.org/wiki/Inductance


Using the formula (2 * pi * frequency * henrries) we get Z,
2*3.14*1000*3.523e-6 we get 0.0221 ohms of Z for 2 AWG
2*3.14*1000*4.636e-6 we get 0.0291 ohms of Z for 10 AWG
Citation: http://en.wikipedia.org/wiki/Reactance
I chose to use 1000 Hz as it is where most good power amps are rated, e.g. 200W into 4 ohms @ 1000Hz RMS (notice RMS: root mean squared) not peak power, music power, etc.
Capacitance is the inverse of inductance. Capacitors can be used to counteract the effect of inductance (to a point). That is why we put them in the trunk where the amplifier is. It counter acts the inductance effects of the wires.

Now the DC term:

The DC resistance of the wire is:
2 AWG is 0.001563 ohms per 10 feet while
10 AWG is 0.009989 ohms per 10 feet.
Citation: http://academic.evergreen.edu/projects/biophysics/technotes/fabric/wire.htm
(my daughters College)

In this case two 10AWG in parallel would be better than one 2AWG from the AC view and DC view (as the reactive and resistive component cuts in half for two wires in parallel, cuts to a third for three wires etc.). A lot easier to run and probably less $ too.

Less ohms is better. The AC portion of the ohms (power loss) dominates not the DC. Use a run of two or three 10 AWG in parallel and you will get better results than one 2 awg.

The other issues of source Z and load Z have to do with the alternator regulator design, the design of the battery and the design of the amplifier.

Batteries exhibit a better source Z than an alternator as the control system electronics in the alternator do not have a fast response time (thus they are high Z at higher frequencies).
Citation: http://www.telepower.com.au/INT95b.PDF (for batteries).
Citation: http://lees.mit.edu/lees/dperreault/ConferencePapers/cpConvergence00p583.pdf


Cheap amps do not have a lot of capacitors on the input and need more external caps to work well in applications where the amp is far from the source of power. As a overall statement there are three types of amplifiers: linear, switching and some that use both techniques. The ones that use switching and linear combination and some of the switchers will actually draw more current as the input voltage goes down making things worse when the alternator is not active.

There are incredible capacitors available>
http://www.cdiweb.com/datasheets/cet/PowerStorP_Specs.pdf
Never use a battery in the trunk (unless you have to as stated above) as batteries age much more quickly than capacitors.

Sorry that this is so long...

Ron

What I mean by the statement, It never is as simple as stating "do it this way or that way" is it, Is that no one. including myself, asked for additional information like: What size is the amp? Do you have factory gauges and do you want the amp gauge function as designed? What size is the alternator?

A small amp will work fine wired to the horn relay. A 500- 600 Watt or larger amp can be wired from the horn relay if using a second battery mounted in the trunk. This would leave the wiring, that the amp gauge needs for correct operation, unchanged. If the connection is made at the starter where will the circuit protection be located? If it's a fuse and is mounted by the starter it will be a pain to replace when it blows, also the wiring will be by the hot exhaust. There are many variables that need to be considered.

The bottom line is there is no one way that's correct and all others wrong.

Ron;

That is a lot of good info but I believe calculating the Z of the wire as you did is somewhat misleading. Have you run tests to determine this is really the case. I do not believe that big power amps will draw current on the 12V feed wire at the same frequency as the music.

The power circuit for a high power linear amp goes something like this: filter - DC switcher (probably something like 100khz) - filter - amplifier output section

The design of the filter section after the switcher should keep the voltages fairly constant. A switcher runs using feedback to keep the voltage constant even as the input voltage changes.

So, audio frequencies should not be measurable on the DC input of the amp.

Then, the input filter to the switcher should keep the switcher frequencies from getting into the DC input of the amp so they also should not be measurable on the 12V power.

I can see the voltage dropping and rising with the power output of the amp, not on the frequency output of the amp which are quite different things. A constant test power output would produce no AC components on the 12V power.

Elree, I think we are agreeing, there are many ways to do it and the best or simplest way depends on a bunch of factors that need to be considered. Even then, there may be a few ways that all work pretty much as good as each other.

Peter

Ron;

That is a lot of good info but I believe calculating the Z of the wire as you did is somewhat misleading. Have you run tests to determine this is really the case. I do not believe that big power amps will draw current on the 12V feed wire at the same frequency as the music.



The power circuit for a high power linear amp goes something like this: filter - DC switcher (probably something like 100khz) - filter - amplifier output section

The design of the filter section after the switcher should keep the voltages fairly constant. A switcher runs using feedback to keep the voltage constant even as the input voltage changes.

So, audio frequencies should not be measurable on the DC input of the amp.

Then, the input filter to the switcher should keep the switcher frequencies from getting into the DC input of the amp so they also should not be measurable on the 12V power.

I can see the voltage dropping and rising with the power output of the amp, not on the frequency output of the amp which are quite different things. A constant test power output would produce no AC components on the 12V power.

Elree, I think we are agreeing, there are many ways to do it and the best or simplest way depends on a bunch of factors that need to be considered. Even then, there may be a few ways that all work pretty much as good as each other.

Peter

I took a Apline MRP-F350 amp with a set of Focal 165VR speakers and ran some tests, so yes I have some tests to back up what I am saying. The tests below were all powered from and HP6030A Power supply using remote sensing at the battery terminals of the amplifier. So the input was held constant at 13.8 volts.

You are correct; amplifiers won't draw current at the same frequency as the music as the current is filtered (averaged) by the PSRR (Power supply rejection ratio, also called audio susceptibility). In class D amps, where the switching supply and the amplifier are merged into one circuit (switching amplifier) the input current to the amp and the output voltage to the speaker look like this (this is Devil with a Blue Dress On by Mitch Rider):

http://i274.photobucket.com/albums/jj264/bikeron_2008/Alpine%20Amp%20tests%20for%20wire/tek00011.png
Blue trace, Ch2, is the input current AC coupled at 1 amp per division, the violet trace, Ch3, is the output voltage to the speaker at 10V per division. The top window shows a period of 2 seconds of music and input current, the bottom is an expansion of the area in the cursors.


Except at low frequencies (like 30Hz):

http://i274.photobucket.com/albums/jj264/bikeron_2008/Alpine%20Amp%20tests%20for%20wire/tek00007.png
The blue trace, Ch2, is the input current, AC coupled and the violet trace, Ch3, is the output voltage to the speaker. Focal 165VR speakers.


At high frequencies the effect is less:

http://i274.photobucket.com/albums/jj264/bikeron_2008/Alpine%20Amp%20tests%20for%20wire/tek00006.png
Blue, Ch2, is the input current to the amplifier, but is 200mA per division not 1A/div as shown. Violet, Ch3, is the output voltage to the speaker. 20.3W RMS into 4ohms, Focal 165VR speaker. This shows input current at 1000Hz. Notice that the input current is twice the frequency of the sound output.

Peter, notice that at any normal use of an audio amp you do see lots of AC artifacts in the input current as shown above. Music causes a very complex input current waveform as in oscillograph one above that has lots of high frequency components.

In class D amps notice on the 30Hz and 1000Hz oscillographs that the input current frequency is double the audio frequency. So it is even worse from an impedance perspective.


The reason most of the amplifier manufacturers say to hook to the battery directly is that the ripple from the alternator (alternator whine) is not rejected properly by the amplifier but if you hook to the battery the lower Z of the battery (which acts as a capacitor {filter}) and eliminates that problem.

However if you hook to the battery you won't get the full 14.2V that the amplifier needs for working at it's full power rating. So then in order to eliminate the alternator whine you need at least a capacitor at the amplifier and perhaps a filter.

In addition, Alpine says to use the body as a ground and to tie all audio grounds at one point, meaning radio, preamps etc. which is the point you attach the amplifier ground to. This means you go to all sorts of effort to fix half of the pipe that supplies energy to the amp and you hope for the best in the other half.

Looking at the another way; if the wires and their reactive properties were not a problem, we had no AC artifacts to deal with, there would be no reason to sell $100 capacitors to overcome this problem. This is a real problem.

I am going through all this right now as this stuff I used for the test is going in my Chevelle. I'll post how I finally wind up doing it.

Ron

That is some interesting stuff. The last plot clearly shows that the current input to the amp is tracking the instantaneous power output of the amp. It is odd though that the same effect is not shown in the middle recording.

That is a digital amp though so I'd be curious if a linear amp (ie class AB) will exibit the same characteristics. The power supply supply filtering after the switcher in a linear amp might filter the instantaneous power draw and make the current follow the avg power output. Then again, with the power supply being a high frequency switcher it may exibit the same results.

Have you figured out how big a capacitor you would need to filter out most of the current ripple the amp has?

Peter

Peter and all,
I am trying to post stuff as I get to it; but I have other things that I need to attend to in my Lab so it can take me a while to get the info out.

The test I'm reporting now was done to see how well an amp would reject alternator noise. Alternator noise varies as the RPM of the engine changes. I show two examples below, one from a Suzuki Vitara car (the last one) and one from an article cited below (the middle oscillograph)
See:
http://www.eetasia.com/ARTICLES/2005OCT/C/2005OCT_SPE2.HTM

As an informative aside:"The output-voltage waveform of an alternator is not so flat. Figure 4 (the second one below) shows that the rectified sinusoidal waveform has a ripple voltage or ripple current associated with it. This ripple can be quite large, even when we include the 1F capacitance of the battery. The peak-to-peak ripple voltage out of an alternator can be as much as 4 to 6V at high output currents."

I'm trying not to go overboard on this and say that we need to get rid of 4 to 6 volts of ripple. So I used the ripple that we see in the Suzuki example, about 0.080 AC peak to peak volts superimposed on the 13.8 volt DC input to the amp.

Then I measure how much of that 0.080 Volt signal gets to the speaker output of the amplifier with the speaker hooked up to that output. The ratio of the output to the input is the power supply rejection ratio, which we state as decibels, = log (Vout/Vin) * 20.

This is a tricky measurement to take due to the single ground structure of consumer audio systems. If you want details on how it was done and what the test set up looks like send me a PM and I will elaborate further and send pictures. I used the same amp and speakers as I posted before, with the addition of an Alpine Radio, CDA9884, as the termination of the audio input of the amp.

Below is a plot (first graph) of the power supply rejection ratio of the Alpine amp taken with a Network Analyzer.

The plot shows the attenuation (in decibels) and phase shift (in degrees) across an audio frequency band of 20Hz to 50KHz. At low frequencies the amp can't get rid of the noise on the +13.8V input as well as it can at 1.6KHz and as the frequency rises above 1.6KHz the ability of the amp to reject supply noise declines again.

Now none of this matters if you can't actually hear any of the noise in the speaker. In order to find out if the amp would power the speaker over this frequency range (to determine that the noise could be heard) I listened to the speaker as I was running this test. I could hear (in both ears) the superimposed AC from 340Hz to about 6KHz. I'm 54 yrs old so what would a 17 year old hear?

This brings us to the next point; the nonlinear response of the speaker. It is much better at pushing out air at 1KHz than at 100Hz. So even though the amp is better at getting rid of the input noise at 1 KHz you can still hear it! You have to consider your ear and the speaker(s) used!

Four learnings come from this:

1. If you want to minimize background noise from your speakers (alternator whine, MSD box, fuel injector drivers) you need to run the power leads directly from the battery (which is equal to a 1 farad capacitor). You would not run the wires from the alternator regulation point (horn relay).

2. If you want the rated power from the amp (which needs 14.4V) you would have to attach the power wires to the alternator regulation point (horn relay) and put up with the alternator whine.

3. When you have the amp cranked up and it draws larger alternating currents (as shown in my previous post) the music output level will be modulated by the voltage change that appears at the input terminals (see my previous post on wire resistance and inductance) to the amp, causing inter-modulation distortion. The further the battery is from the amp (the longer the wires) the worse the effect.

4. The speaker matters too!

How to solve all these issues?

Putting a battery in the trunk seems to be the most practical, as a no maintenance, sealed, motorcycle battery (YTX24HL-BS, from Koyo/Powersonic about $70) is lower cost than the 1 farad capacitors they sell at the audio stores ($99.99).

I have found capacitors from a half to 30 Farads on the web from prices of $55 to $1000. None of them are properly specified (ESR and ESL), so how much good they actually do is not known.

As my next experiment I will take the amp and see the ripple voltage levels on my Chevelle and see if there is a filter design that would help get rid of the bulk of the noise without affecting the input voltage too much. This will require some simulation work so expect a few weeks before I post again.

Ron

A little more work done in evaluating the noise in the Chevelle"s electrical system.



http://i274.photobucket.com/albums/jj264/bikeron_2008/Battery.png

The oscillograph above, shows the battery voltage on my Chevelle during normal operation. I'm not sure what causes the variation in voltage, maybe the MSD box during capacitor charge up (the MSD box power is taken right across the battery terminals).
The waveform shows variations of 150 to 200 millivolts at the battery (not counting short transients).

http://i274.photobucket.com/albums/jj264/bikeron_2008/Batterywfan.png

The oscillograph above, shows the battery voltage when the electric fan is on. The waveform shows variations of 150 millivolts at the battery (not counting short transients).

http://i274.photobucket.com/albums/jj264/bikeron_2008/20Aloadadded.png

The oscillograph above is the voltage transient that occurs when a 20A load (like the electric fans) turns on at the horn relay (point of regulation of the alternator). The waveform shows variations of 750 millivolts (1V) at the battery (not counting short transients).

http://i274.photobucket.com/albums/jj264/bikeron_2008/20Aloadrelease.png

This oscillograph, above, is the voltage at the horn relay when the 20A load is switched off. The waveform shows variations of 750 millivolts at the battery (not counting short transients).

http://i274.photobucket.com/albums/jj264/bikeron_2008/2.png

The oscillograph above, is at the horn relay at 2600 rpm with the 20A load active. The waveform shows variations of 1500 millivolts at the battery (not counting short transients).

The 12SI alternator is worse than the Suzuki example I had shown previously (80 millivolts) as the Delco is at 1500mV! In fairness I was trying to perturb the system in the Chevelle to show me the worst case variation, so the Suzuki example is probably not the worst case variation that would occur in iit's electrical system.

Now that I know the magnitude of the disturbance, 1500 mV, the frequency range, 300Hz to 12KHz I am going to look at an effective filter design. I will also consider ground loops as I can't see that it is practical to ground the radio, amplifier and Ipod power source all at the same spot.

Remember that in testing the Alpine Amp in the previous post we found that 80 millivolts on the +12 could be heard out of the Focal 165VR speakers.

The conclusion is that taking the power from the alternator regulation point is the wrong thing to do as it has about 10 times more noise than the battery.

More posts after some filter simulations. If anyone wants to know how the set up was done let me know.

Ron