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emarald 2nd May 2002 01:13 PM

missing toroid
 
HELP... i got this car amp from a friend but the single toroidal transformer is missing, now i need to know the spec of the missing component +- ...its a 2 channel amp, bridgable with 500watt max output, fuse is 10 amp single,(could be wrong), also former has two secondaries. I intend on using the amp to drive a single 12 woofer rated 500w max..any ideas ANY cos i went to a place and the guy wanted to give me a 35-0-35 unit @ 500VA, only it was about 5 times to big to fit.......

Jocko Homo 2nd May 2002 02:10 PM

May have 2 secondaries, but probably several primaries. Those amps use swithcing supplies which is why a conventional one won't work.

Jocko

emarald 2nd May 2002 02:23 PM

6 connectors
 
ok the board has 6 solder connectors i assumed that one set was primary and the other two sets were the secondaries, also this is a pwm setup..if that helps

AudioFreak 2nd May 2002 03:04 PM

these transformers usually have 2 x primary windings and are designed to operate at higher frequencies which allows them to be much smaller .... it is near enough to impossible to speculate what the transformer from here with more details of the surrounding circuit.

Holger Barske 2nd May 2002 06:11 PM

I agree, it is impossible to determine the specs without knowing a few things: what kind of switching reg is used: boost, flyback, half bridge, etc...? What is the switching frequency? Won't be easy to answer without a schematic.

Aud_Mot 3rd May 2002 02:21 AM

Your only realistic hope is to get information from the manufacturer.

Even that may be difficult. Car electronics designs can vary greatly, even within the same make & model.

Some reasons:

a) They are built with price point being the dominant design goal. Tech support can be an expensive feature.
b) They can be built by several different "turn key" factories, using different parts and designs. Again within the same make & model.
c) Their switching power supplies typlicaly use IC's that cannot be identified.
d) Car audio tends to be more disposable than regular audio. "It's not worth fixing it, sir."
e) Car stereo is notorious for exagerating the true power output, thus making any backwards engineering exercise difficult.

Most people would be suprised how of much the above applies to higher end car stereo brand names.

Taking on the challange of you original post could be a very good exercise in learning how switch power supplies work.

Good Luck,

Aud_Mot

emarald 6th May 2002 03:44 PM

why more than one primary?
 
confused?, why is there more than one primary, my thinking was that it operates like a normal ac PS although at a higher freq. like 50khz or so, or is there dc involved or just what is this toriod doing there? and how is it doing it cos now i'm gonna wind my own %^&xyz*&^ toriod,,,i mean its just a coupla wires around a doughnut...

mrfeedback 6th May 2002 04:52 PM

Don't Bother To Make A Replacement
 
You have two primaries because the normal arrangement is to have two transistors alternately switching current into their respective primaries from the common 12v supply, thus giving pseudo AC excitation.
You will need to find an original to copy, because of windings polarity and turns ratios considerations, and wire sizes, and torroid core material.
If you get any of it wrong you are likely to let the smoke out.
Much easier to track down the right dealer, warranty service center or manufacturer, and just buy a new one.

Eric.

AudioFreak 7th May 2002 12:03 AM

Quote:

confused?, why is there more than one primary, my thinking was that it operates like a normal ac PS although at a higher freq. like 50khz or so, or is there dc involved or just what is this toriod doing there? and how is it doing it cos now i'm gonna wind my own %^&xyz*&^ toriod,,,i mean its just a coupla wires around a doughnut...
I would strongly suggest that you do not try to wind your own transformer for this application unless you can obtain a datasheet or technical specs. The problem is, if you do not get it right, you will almost certainly do more harm than good. I assure you, it is far more complex than just 'a couple wires around a doughnut' you need to know winding ratios, core type, frequency, polarities and a host of other specifications.

The problem with car amps is that there is no ac to work from so the power supply must use the +12V from the car and convert it into +/- rails of a higher voltage. This is usually done by switching the dc thru transistors (such that current flow is in alternate directions) at high frequency which feed alternate windings of the primary the effect of this is that the output from the secondary is indeed high frequency square wave AC.

emarald 7th May 2002 08:08 PM

ok my research basically comes up with the same thing, now lets say i decide to go beyond the rectifiers and based on the specs in my first post, what dc voltage will i need for this amp to work?


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