Cleaning a car's power supply

[agithegreat]

Now I don't mean with a bucket and sponge...

The car is a damn harsh environment to work with. I have a number of devices in the car (well soon to be in the car), which work from 10v right upto 15v (one) and 30v the other...

Now I'm suffering bad ground loops and background noise. If I turn off the engine and let it power from the battery it's noise free.
So does anyone have any suggestions on how to 'clean the supply'.
Current draw will be no more than 20a. Voltage can be variable (between 10 and 15).

I'm willing to build, experiment, blow things up, etc...

Using right now (noisily):
miniDSP 2x8 kit | miniDSP
eBay - The UK's Online Marketplace

[agithegreat]

Here's what i'm thinking so far...
With a double throw relay in place and some way of detecting a voltage below regulated 10v output, so it throws it over to just the battery... If that makes sense?
So when I have the engine running, the output is through the reg, when it's off it's just straight off the battery (obviously noise free ).
Would this work? Or is LTspice just simulating it will...
Also, any suggestions for a 'low volt' cutoff circuit. The regulated output will be on normally open and the battery, normally closed, so I can just 'disconnect' the reg when it's output is less than 10v. Or even input is less than 13v say...

[dangus]

The easy answer is to buy a supply made by a company like Melcher that is rated for vehicle duty. Maybe a more practical solution is to modify a car amp power supply to deliver a clean 12V (or whatever you need). To avoid reinventing too many wheels, choose a common amp where docs are available. "12V" on a car can range from 8V when starting to around 14V when charging, with spikes in the 10s of volts in either direction. You don't want anything connected to that 12V that isn't designed for the task.

Use a proper car amp with isolated switching supply. Car audio has been mature long enough that there are great deals on quality used amps. Check with auto wrecking yards; they may have stuff rescued from scrapped cars. Visit pawn shops at least weekly; good deals don't last all that long. It may be worth asking if they've got more stuff put away due to limited display space.

What's the source(s)? Do they have S/PDIF outputs? There's some inexpensive DACs on eBay, or the elv DAC.

[agithegreat]

Originally Posted by dangus

The easy answer is to buy a supply made by a company like Melcher that is rated for vehicle duty. Maybe a more practical solution is to modify a car amp power supply to deliver a clean 12V (or whatever you need). To avoid reinventing too many wheels, choose a common amp where docs are available. "12V" on a car can range from 8V when starting to around 14V when charging, with spikes in the 10s of volts in either direction. You don't want anything connected to that 12V that isn't designed for the task.

Use a proper car amp with isolated switching supply. Car audio has been mature long enough that there are great deals on quality used amps. Check with auto wrecking yards; they may have stuff rescued from scrapped cars. Visit pawn shops at least weekly; good deals don't last all that long. It may be worth asking if they've got more stuff put away due to limited display space.

What's the source(s)? Do they have S/PDIF outputs? There's some inexpensive DACs on eBay, or the elv DAC.

I actually have a bout 4 'broken' amps. With perfectly fine power supplies, SMPS style... However they all have too high voltage rails. 50v+.
If I could get this down to 30v I would be ok, then use a lin reg/another winding for the 12v.

I'm using a clarion drx9255 as a source. I don't really want to change this, if possible as it's a great unit.

Do you think it would be too hard to try and re-wind the outputs of an existing supply I have here?
I have 2x powerbass 3000d's. So the supply is good for over 3kw... The rail voltage is (from memory) about 120v though .
Or should I just try and find one more suitable?
I have a us amps merlin power supply too ( just over 50v a rail ).

Thanks for your help .

[marce]

I would aslo try and find the source of the noise... there may be other problems, but with the engine off it could be the alternator noise supression thats gone.

[theAnonymous1]

I've used a simple CLC filter before and it seemed to work well.

[agithegreat]

Interesting... That's the simplicity i'm after .
Got specifics? What value inductor did you use? How does it respond to transient loads?

[theAnonymous1]

Originally Posted by agithegreat

Interesting... That's the simplicity i'm after .
Got specifics? What value inductor did you use? How does it respond to transient loads?

I don't have a clue what the inductance value was. I just grabbed some parts out of my junk bins and threw the filter together without much thought. I got lucky and it cured the noise problem I had.

[jitter]

Originally Posted by agithegreat

Now I'm suffering bad ground loops and background noise. If I turn off the engine and let it power from the battery it's noise free.

Noise from a running engine is most likely caused by the ignition (I assume we're talking about a petrol engine). The pulsing high tension in the ignition is a great source of disturbance that a groundloop will pick up and inject into the circuits.

Eliminating the groundloops should be your first priority. Once that has been done, you may find that no further cleaning of the power supply is neccessary.

[dangus]

There's also noise from the alternator. Check for bad diodes. Improving the connection between the battery and chassis ground may help; clean the contacts, use a heavier cable, treat the connections with some goo that prevents corrosion, maybe use star washers to improve the contact.

You should be able to get a different voltage from a car SMPS just be rewinding the secondary, and adjusting the feedback voltage divider. If you're looking for a similar power output, use a larger gauge of wire on the replacement secondary, and maybe upsize the rectifiers and caps. If the power requirement is more modest, you ~might~ get away with leaving the windings alone and just reducing the voltage via the feedback control. Maybe. A "cheater" amp would be a good choice... one with low 4 ohm power rating but stable into a fraction of an ohm.

But I still think this is a bit like trying to train a cat to swim underwater and catch fish. Better to start with a seal or an otter. For the price of that 4 channel amp I got myself a scruffy but electrically fine made-in-USA Rockford Punch amp, a model with a lasting reputation for sound quality. I'm considering adding a couple of T-amps with a bypass switch for engine-off listening and movie watching.