Grounding issue

[NED 209]

hi all. ive just finished isolating my alternator.

my car is a 24 volt landcruiser, so i installed a 12 volt alternator also.
now theres 2 power systems in the car, a 12v system, and a 24v system.

I need the 12v to run my computer and tripath amps. I was getting a whine though through the amp, so, I isolated the 12 volt alternator from the engine block.

it is isolated, but it didnt work. im still getting the whine through the amp.

I have a 10 amp ground loop isolator I bought on ebay. I read to install it on the power line between the battery and the alternator, but its a 90 amp alternator.

since the negative terminal on the alternator is connected directly to the negative terminal on the battery, and not grounded through the chassis, I'm getting really good readings of 14.5 volts, which is high compared to my other car at 13.5v

any ideas what to do to eliminate the whine? thanks for reading!

cheers,
ned .

[Perry Babin]

Both alternators need to be connected to ground.

A ground loop isolator isn't used in the B+/ground. It's used in the preamp line (RCA).

Have you checked the shield ground on the head unit?

[whizgeek]

is there big/good enough battery: you may need a decent load on the alternator. 14.5v is good for battery charging but seems a little high

[NED 209]

Hi, cheers for the replys.

Perry, im curious, why do both alternators need to be grounded to the chassis? im not an electrician im afraid, im still learning.

when you say B+ or ground, my isolator is designed to be used between the battery plus and the amplifier. i had a look just now, but its no longer on ebay nor do i have any email records of it, which is odd.

you think i should try an rca model isolator?

my 12v battery feeds a carputer, and an amp32 tripath amp.

the computer feeds the audio to the amp.

i tried the isolator on both the computer power line and the amp power line, but niether have any effect.

Whizgeek the battery is a healthy 70 amp car battery.

any suggestions appreciated,

regards,
ned .

[whizgeek]

i feel your frustration rising here...
cars are notorious for multiple noisy grounds, insulating everything is bloody hard work.
i presume the whine is engine speed related, so try disconnect the 12v alternator from battery to figure which one is the culprit.
I had an Alfa years ago, none of the metalwork seemed to be connected to any other panels, so everything electrical caused massive noise. even tail lamps.
Cant go messing with Toyota electrics...
From some vague memory Amp32 is almost immune to power noise, so its got to be grounding/shielding issue. Insulate everything.

[dangus]

Does the noise go away if you feed the Amp32 directly from a portable CD or MP3 player?

What if you substitute a real car amp? Vehicle power really isn't suitable for running electronics directly, not without special attention paid to filtering noise and protecting from transients.

Use a DMM on the AC range to check how much ripple is on the 12V supply to the amp and carputer.

[Perry Babin]

The alternators need to be grounded because that's the way they're designed to be used. The negative current path is through the case of the alternator. It would be nearly impossible to isolate the ground unless the alternator was specially designed not to have the case as ground.

The noise filters that go in the B+ line are not isolators. They are low pass filters that are used to block the higher frequency noise. They're RARELY of any use. If there is noise in modern systems, you typically have a defective component or the audio cables routed to close to some device that's producing a lot of 'electrical' noise.

The amp32 probably has no noise canceling system at the front-end like car amps. Install an RCA ground loop isolator between the amp32 and the carputer and the noise will likely disappear.

[NED 209]

Guys thats excellent thanks very much. I'll look into them all.

it is engine related yes / it increases with the revs

im not sure if it happens with an ipod attached to the amp32, im pretty sure it does.

im away for a few days so ill get onto it midweek.

cheers

ned .

[cdunginess]

Hi Dangus,sorry to have interrupted this thread but I noticed you are from bc more specifically Van Island.Me too.Your profile shows you're a techie and you've been on this board for awhile.I could really use some help with speakers I've designed,it may come down to testing.
The drivers I have are the scans 21W8555-1 the Excell W17E002 and the scan Rev tweet.I do have bass box pro and xover pro but have come to a point where I'm not sure that a passive x-over is the best choice.From what I know there is a nasty break up in the higher freq of the w17e so a filter will be required for that issue(I think).The problem I have is this modelling is too hypothetical without knowing the real life driver parameters(the person who sold me the w17s was able to provide the tested parameters for those drivers)So I'm now considering an electronic crossover.
Do you have the equipment to test the drivers mounted on a baffle,do you think this is the way to go?I'm very happy to pay for your time if you can help.
The cabinets are kinda funky, a tapered ellipsoid with truncated ends and a flat front for the baffle.The overall volume is 60 ltrs,I'll be looking at venting the lows and mids.
Thanks looking forward to hearing back

Craig