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 | | From: | Jonski | | Subject: | 12v regulator for Rio Jukebox in vehicle? | | Date: | Fri, 07 Jan 2005 15:40:17 +1300 |
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 | Does anyone have a cheap, simple circuit for limiting the output
voltage from the car's cigarette lighter to 12v?
I have a Nomad Jukebox MP3 player, which needs a 12v supply. I am
worried that plugging it directly into the car's 12v outlet will fry
it. I just want something that clamps the voltage so that if it goes
over say, 14v the excess will not cause the player to go all crisp and
smokey ;-)
Would a zener work? Or do I need to go as "complicated" (relative
term) as a voltage regulator? It seems that these all need an input
voltage somewhat above the output voltage.
I bought a selectable-output-voltage power supply from DSE, but
opening the case shows that when I select 12v out it bypasses the
regulator inside the case and gives me whatever the car puts on the
accessory socket.
I found the following calculator on the web
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2
and put in the following:
Vz = 12 V
P = 0.01 W (in the zener) (Can this be less, say 0.005 W?)
Vin = 14 V (is this a good number?)
it gives me
R = 2k4 ohm (so make it 2k7 ohm)
I don't know what the Jukebox draws, but it won't be more than 500 mA,
probably less than 250 mA. Let's see... It uses 4x 1700 mAH NiMH
batteries and runs for a claimed 4+ hours. 1.2 V batteries give me
8.16 VAH. So at 12 V, it'll be drawing 170 mA. Give or take. Hmmm... a
HDD spinning up to start will consume 4.5 W. Is this gonna be a
problem? I operate the Jukebox with batteries in, so I wonder if it
will draw from them if the external supply can't hack it? Or will I
turn the supply resistor into popcorn?
So I can put in a load resistance of Rl = 0.04 kohm, giving
Il = 300mA
Do these numbers look right? Just get a 12 V 400 mW zener (eg 1N759)
and whack in a 2k7 1/4 W resistor for R in the circuit?
I'm hoping that this works. If so, it means I spend <$1 instead of the
$30 I spent for the do-nothing converter.
Any comments welcome!
Cheers
Jon
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| | From: | PC | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Fri, 7 Jan 2005 20:50:41 +1300 |
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"Jonski" wrote in message
news:a7nrt0961jk6mlmn1bvgmjhpjvt8ekncis@4ax.com...
> Does anyone have a cheap, simple circuit for limiting the output
> voltage from the car's cigarette lighter to 12v?
>
> I have a Nomad Jukebox MP3 player, which needs a 12v supply. I am
> worried that plugging it directly into the car's 12v outlet will fry
> it. I just want something that clamps the voltage so that if it goes
> over say, 14v the excess will not cause the player to go all crisp and
> smokey ;-)
>
> Would a zener work? Or do I need to go as "complicated" (relative
> term) as a voltage regulator? It seems that these all need an input
> voltage somewhat above the output voltage.
>
> I bought a selectable-output-voltage power supply from DSE, but
> opening the case shows that when I select 12v out it bypasses the
> regulator inside the case and gives me whatever the car puts on the
> accessory socket.
>
> I found the following calculator on the web
> http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2
> and put in the following:
> Vz = 12 V
> P = 0.01 W (in the zener) (Can this be less, say 0.005 W?)
> Vin = 14 V (is this a good number?)
> it gives me
> R = 2k4 ohm (so make it 2k7 ohm)
>
> I don't know what the Jukebox draws, but it won't be more than 500 mA,
> probably less than 250 mA. Let's see... It uses 4x 1700 mAH NiMH
> batteries and runs for a claimed 4+ hours. 1.2 V batteries give me
> 8.16 VAH. So at 12 V, it'll be drawing 170 mA. Give or take. Hmmm... a
> HDD spinning up to start will consume 4.5 W. Is this gonna be a
> problem? I operate the Jukebox with batteries in, so I wonder if it
> will draw from them if the external supply can't hack it? Or will I
> turn the supply resistor into popcorn?
>
> So I can put in a load resistance of Rl = 0.04 kohm, giving
> Il = 300mA
>
> Do these numbers look right? Just get a 12 V 400 mW zener (eg 1N759)
> and whack in a 2k7 1/4 W resistor for R in the circuit?
>
> I'm hoping that this works. If so, it means I spend <$1 instead of the
> $30 I spent for the do-nothing converter.
>
> Any comments welcome!
>
> Cheers
> Jon
Jon
Go to Dick Smith Electronics and get an LM 317T (Cat # Z6541) 3 terminal
regulator.
Have a look on their website for the LM 350 for a sample circuit.
They will provide up to 1.5 amps and are adjustable 1.2v to about 1.2v below
applied (battery) volts.
You may have to add a heat sink and take the appropriate anti spike and
insulation measures.
Cheers
Paul.
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| | From: | EMB | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Sat, 08 Jan 2005 08:47:18 +1300 |
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| PC wrote:
>
> Go to Dick Smith Electronics and get an LM 317T (Cat # Z6541) 3 terminal
> regulator.
> Have a look on their website for the LM 350 for a sample circuit.
> They will provide up to 1.5 amps and are adjustable 1.2v to about 1.2v below
> applied (battery) volts.
Giev that it's internal battery voltage is only 4.8V you'll probably be
able to use an input of 9-10v sucessfully - which makes the drop via the
regulator much less of a problem - a 7809 would then do the job.
--
EMB
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| | From: | Radio-nut | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Fri, 7 Jan 2005 20:34:39 +1300 |
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| Hi Jon
The best way to build a stable 12V supply for the car is to use a LM7812
voltage regulator 3 pin chip.
Very simply the car lighter socket (+) connects to one pin
The lighter socket (-) connects to pin 2
The MP3 Player connects to pin2 (-) and the other remaining pin, giving a
stable 12v output.
A couple of caps are used to make sure the thing is stable. A bit of metal
to dissipate the heat and your in business
http://ourworld.compuserve.com/homepages/g_knott/elect127.htm
http://homepages.which.net/~paul.hills/Circuits/PowerSupplies/PowerSupplies.html
http://www.electronicsinfoline.com/go.php?out=http://www.spelektroniikka.fi/kuvat/regu.pdf
http://cache.national.com/ds/LM/LM340.pdf
Good luck
Mike
"Jonski" wrote in message
news:a7nrt0961jk6mlmn1bvgmjhpjvt8ekncis@4ax.com...
> Does anyone have a cheap, simple circuit for limiting the output
> voltage from the car's cigarette lighter to 12v?
>
> I have a Nomad Jukebox MP3 player, which needs a 12v supply. I am
> worried that plugging it directly into the car's 12v outlet will fry
> it. I just want something that clamps the voltage so that if it goes
> over say, 14v the excess will not cause the player to go all crisp and
> smokey ;-)
>
> Would a zener work? Or do I need to go as "complicated" (relative
> term) as a voltage regulator? It seems that these all need an input
> voltage somewhat above the output voltage.
>
> I bought a selectable-output-voltage power supply from DSE, but
> opening the case shows that when I select 12v out it bypasses the
> regulator inside the case and gives me whatever the car puts on the
> accessory socket.
>
> I found the following calculator on the web
> http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2
> and put in the following:
> Vz = 12 V
> P = 0.01 W (in the zener) (Can this be less, say 0.005 W?)
> Vin = 14 V (is this a good number?)
> it gives me
> R = 2k4 ohm (so make it 2k7 ohm)
>
> I don't know what the Jukebox draws, but it won't be more than 500 mA,
> probably less than 250 mA. Let's see... It uses 4x 1700 mAH NiMH
> batteries and runs for a claimed 4+ hours. 1.2 V batteries give me
> 8.16 VAH. So at 12 V, it'll be drawing 170 mA. Give or take. Hmmm... a
> HDD spinning up to start will consume 4.5 W. Is this gonna be a
> problem? I operate the Jukebox with batteries in, so I wonder if it
> will draw from them if the external supply can't hack it? Or will I
> turn the supply resistor into popcorn?
>
> So I can put in a load resistance of Rl = 0.04 kohm, giving
> Il = 300mA
>
> Do these numbers look right? Just get a 12 V 400 mW zener (eg 1N759)
> and whack in a 2k7 1/4 W resistor for R in the circuit?
>
> I'm hoping that this works. If so, it means I spend <$1 instead of the
> $30 I spent for the do-nothing converter.
>
> Any comments welcome!
>
> Cheers
> Jon
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| | From: | rastus | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Fri, 07 Jan 2005 20:46:07 +1300 |
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| Radio-nut wrote:
> Hi Jon
>
> The best way to build a stable 12V supply for the car is to use a LM7812
> voltage regulator 3 pin chip.
> Very simply the car lighter socket (+) connects to one pin
> The lighter socket (-) connects to pin 2
> The MP3 Player connects to pin2 (-) and the other remaining pin, giving a
> stable 12v output.
> A couple of caps are used to make sure the thing is stable. A bit of metal
> to dissipate the heat and your in business
The LM7812 has a dropout voltage of between 2 and 3 volts. This means
that the output voltage cannot get to 12 V in a lot of cases with a
supply voltage of 12 - 14V.
You must use a low dropout voltage regulator for this application.
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| | From: | Dave - Dave.net.nz | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Fri, 07 Jan 2005 15:56:14 +1300 |
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| Jonski wrote:
> Does anyone have a cheap, simple circuit for limiting the output
> voltage from the car's cigarette lighter to 12v?
> Any comments welcome!
Sorry, can't help you with this, but something semi related, that I have
done in my own car, is take a DSE solar panel->cig lighter car battery
charger, re-wired the output to go to a cig socket, and am running a
laptop off it... The laptop is just sitting there streaming MP3s to a
USB FM sender...
Now, I have no idea what it is doing to the battery in the laptop, but
it is keeping it charged enough that it hasn't turned off in three
weeks(since I turned it all on), the laptop also has wifi to connect to
my wlan in the house, and thanks to adding a bit more ram, able to play
SVCD/VCD back "ok".
The laptop is a Pentium 233(overclocked to ~263{3.5x75}) running Win2k
with 128MB ram, got it free(was thrown out) so is of no real concern if
it dies.
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| | From: | KewlKiwi | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Sun, 09 Jan 2005 22:26:57 +1300 |
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| Jonski wrote:
> Does anyone have a cheap, simple circuit for limiting the output
> voltage from the car's cigarette lighter to 12v?
'Just built two such units using an LM2940 low drop-out reg (DSE have
it) for front and rear camera modules.
Each unit has one of the above regs, 1x 63v, 0.47uf electro on the input
and 1x 63v 47uf electro on the output. (Which could be paralleled with a
smaller tantalum cap, see the datasheet)
Dropout voltage is (typically) 0.5 volts i.e. it will still work down to
12.5 volts from the cars electrics.
Wiring it up is simplicity itself...
-----------
| |
12v unreg in---------| LM2940 |------------------------- > 12v reg out>
| | | |
| ----------- |
0.47 + | + 22uf (min)
- | -
| | |
ground-----|--------------|-----------------|--------ground
Extract from datasheet:
"Designed also for vehicular applications, the LM2940/
LM2940C and all regulated circuitry are protected from reverse
battery installations or 2-battery jumps. During line
transients, such as load dump when the input voltage can
momentarily exceed the specified maximum operating voltage,
the regulator will automatically shut down to protect
both the internal circuits and the load. The LM2940/
LM2940C cannot be harmed by temporary mirror-image insertion.
Familiar regulator features such as short circuit and
thermal overload protection are also provided.
LM2940C 1A Low Dropout Regulator
Dropout voltage typically 0.5V @IO = 1A
Output current in excess of 1A
Output voltage trimmed before assembly
Reverse battery protection
Internal short circuit current limit
Mirror image insertion protection
P+ Product Enhancement tested"
To be on the safe side, unplug or switch it off when starting.
Bob
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| | From: | Jonski | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Mon, 10 Jan 2005 08:17:22 +1300 |
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| On Sun, 09 Jan 2005 22:26:57 +1300, KewlKiwi
wrote:
>'Just built two such units using an LM2940 low drop-out reg (DSE have
>it) for front and rear camera modules.
>Bob
Thanks Bob, this looks like the go!
Cheers
Jon
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| | From: | Daver | | Subject: | Re: 12v regulator for Rio Jukebox in vehicle? | | Date: | Sat, 8 Jan 2005 18:02:31 +1300 |
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| Voltage regulators may not work as the input voltage may not be high enough.
However as with many things it is likely the ipod will accept a lower
voltage openning the door to a lower regulated voltage. Also if the 12volts
is based on a plug pack it is probably operating atmore than 12 volts
anyway.
"Jonski" wrote in message
news:a7nrt0961jk6mlmn1bvgmjhpjvt8ekncis@4ax.com...
> Does anyone have a cheap, simple circuit for limiting the output
> voltage from the car's cigarette lighter to 12v?
>
> I have a Nomad Jukebox MP3 player, which needs a 12v supply. I am
> worried that plugging it directly into the car's 12v outlet will fry
> it. I just want something that clamps the voltage so that if it goes
> over say, 14v the excess will not cause the player to go all crisp and
> smokey ;-)
>
> Would a zener work? Or do I need to go as "complicated" (relative
> term) as a voltage regulator? It seems that these all need an input
> voltage somewhat above the output voltage.
>
> I bought a selectable-output-voltage power supply from DSE, but
> opening the case shows that when I select 12v out it bypasses the
> regulator inside the case and gives me whatever the car puts on the
> accessory socket.
>
> I found the following calculator on the web
> http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2
> and put in the following:
> Vz = 12 V
> P = 0.01 W (in the zener) (Can this be less, say 0.005 W?)
> Vin = 14 V (is this a good number?)
> it gives me
> R = 2k4 ohm (so make it 2k7 ohm)
>
> I don't know what the Jukebox draws, but it won't be more than 500 mA,
> probably less than 250 mA. Let's see... It uses 4x 1700 mAH NiMH
> batteries and runs for a claimed 4+ hours. 1.2 V batteries give me
> 8.16 VAH. So at 12 V, it'll be drawing 170 mA. Give or take. Hmmm... a
> HDD spinning up to start will consume 4.5 W. Is this gonna be a
> problem? I operate the Jukebox with batteries in, so I wonder if it
> will draw from them if the external supply can't hack it? Or will I
> turn the supply resistor into popcorn?
>
> So I can put in a load resistance of Rl = 0.04 kohm, giving
> Il = 300mA
>
> Do these numbers look right? Just get a 12 V 400 mW zener (eg 1N759)
> and whack in a 2k7 1/4 W resistor for R in the circuit?
>
> I'm hoping that this works. If so, it means I spend <$1 instead of the
> $30 I spent for the do-nothing converter.
>
> Any comments welcome!
>
> Cheers
> Jon
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