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Gazzar

Car audio permanent live - for memory and code

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Ages ago I wired my series with ISO plus for audio.

Including a permanent live for memory and code.

When the Landrover starts the voltage on this drops to 7 or 8 volts. This isn't enough to keep the key code. 

Does anyone have a clever way to keep the voltage at 12 ish volts? Maybe a rechargable battery the size of small thing?

I've checked across the battery when starting, and the voltage drop happens in the battery too.

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Some radios have a little capacitor on the positive wiring for this exact thing, should be fairly easy to sort? 

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Ummmm. I understand the theory, sheets of material with stuff between them, holds charge. But as to what I'd need? 

Clueless. Would there be one in a disco 1 loom?

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Don't know about the disco loom but basically any old capacitor (as big as possible preferably) will do. Just ensure it's rated for the voltage. Note electrolytics are polarised so go bang if you don't connect them the right way.

Shame you didn't ask when you were down here I've got loads sat around me.

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You could be swanky and put a diode before it so the starter can't pull the cap voltage back down.

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16 hours ago, Ed Poore said:

Don't know about the disco loom but basically any old capacitor (as big as possible preferably) will do. Just ensure it's rated for the voltage. Note electrolytics are polarised so go bang if you don't connect them the right way.

Shame you didn't ask when you were down here I've got loads sat around me.

Would something in a PC motherboard do?

There are some 12v bits in them, if I recall.

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Would this work?

IMG_20200329_122115.jpg

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24 minutes ago, Gazzar said:

Would this work?

IMG_20200329_122115.jpg

It would but it would be nicer if you had a higher voltage rating. Worst that'll happen is it'll go bang and cause brown pants, seat and possibly a crash :P. There's no harm in trying them out to see if it cures the problem. You can double the effective capacitance by putting them in parallel and if you wanted to "up" the voltage rating you could put them in series but it's not advisable long term.

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Is 16v not enough?  How does it work?

 

Do I put them across the earth and live? Ages since I did DC electrics, twenty years!

 

An afternoon in the workshop beckons....

 

 

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16v is quite low for a car as you can easily get 50v spikes after the starter disengages - I tend to aim for 2x the expected voltage, so for car stuff, 25v is a good start.

You jsut wire -ve to -ve and + to + across the wires near the stereo - if you get that wrong you'll get the aforementioned loud bang and replacement underwear!

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Most spectacular I've seen was a 1F (yes that is not a typo!) have a screwdriver dropped across it at full charge. Half the screwdriver got turned into a plasma. The other half narrowly missed the guys head and went through the ceiling tile!

Why the manufacturer didn't follow the request to put the terminals at either end I don't know.

  • Haha 1

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Skeptical about the diode - 600W is a fairly pointless figure to quote and I suspect if I chucked 600W through that diode continuously it would behave more like a fuse...

Compare it to a diode with a proper datasheet - the VS-20ETS16THM3 which is over a pound cheaper

That's got a continuous current rating of 20A and a peak of 300A, current is what matters on a diode in this situation. The Vrrm(max) maximum repetitive voltage is effectively it's breakdown voltage above which things go pop. Incidentally that one is automotive qualified too! Note for maximum current it should probably be attached to a heat sink / metal plate.

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10 hours ago, Ed Poore said:

Skeptical about the diode - 600W is a fairly pointless figure to quote and I suspect if I chucked 600W through that diode continuously it would behave more like a fuse...

Compare it to a diode with a proper datasheet - the VS-20ETS16THM3 which is over a pound cheaper

That's got a continuous current rating of 20A and a peak of 300A, current is what matters on a diode in this situation. The Vrrm(max) maximum repetitive voltage is effectively it's breakdown voltage above which things go pop. Incidentally that one is automotive qualified too! Note for maximum current it should probably be attached to a heat sink / metal plate.

Oh, that's getting complicated!

I'll think that through.

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Compare the pictures. The one I linked to is much beefier. The other one you linked is probably not much bigger than a standard through hole resistor. Can you imagine sending 600W through that continuously? Hence why it's probably a peak power rating.

Just look for one with 10+A continuous (or average) rating and you should be good. Farnell and RS are better for this kind of stuff because they have filters. Even if it's only to find a part number. 

I must admit I don't know what shipping is like since I've always had a trade account with them so it's always free and always next day.

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I think I'll be better served by making a device. Maybe an enclosure with connections that sits in the line.

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Against my natural instinct to pinch pennies,  I might open an account. I wonder if eldest has an account as an EE student?

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Might have but at least when I was at Imperial the department obviously had one but you had to fill out a form and stores would order it if it wasn't in stock already.

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When he wakes up, I'll ask.

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Is it worth putting a voltage stabiliser in this "thing"? Then I can use it to supply the clock.

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What do you need the voltage stabiliser for? Usually referred to as a voltage regulator. Does the clock require exactly 12V because I'd have thought it's tolerant of most voltages produced by a car - at least it should be.

The cap is there just to act as a battery (energy storage) for the radio. The diode as @FridgeFreezer said is to prevent it being discharged when the battery cranks over (energy will flow to the "lower" voltage so the cap will discharge into the battery).

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55 minutes ago, Gazzar said:

Is it worth putting a voltage stabiliser in this "thing"? Then I can use it to supply the clock.

Why would the clock need a voltage stabiliser? :huh:

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It's quartz, so shouldn't, but I presume the closer the input is to a steady 12v the better?

 

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31 minutes ago, Gazzar said:

It's quartz, so shouldn't, but I presume the closer the input is to a steady 12v the better?

Honestly it's not going to make a difference - it's a crappy clock anyway, voltage will really not make any difference! If you're worried, fit a head unit with GPS then the clock will always be right.

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