In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

This is not a good idea, as you'd need a capacitor the size of atlantis
plus the V_out would ramp down not stay steady. If youre deterimned to
do this you could just wire the lighter to an always on fuse,
disconnecting the old feed. But this wont really work either, since
system v drops heavily during cranking.


NT

wrote in message
ups.com...
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

This is not a good idea, as you'd need a capacitor the size of atlantis
....

That reminds me of the power supply I made for my first high level language
computer - a UK101 - a kit that involved soldering hundreds of connections
by hand. I decided I wanted to make the supply really smooth, so I put a
10,000 microfarad capacitor across the outlet. It was big, but it would run
the TTL based computer for several seconds after I disconnected the power.

Colin Bignell

The message . com
from contains these words:

This is not a good idea, as you'd need a capacitor the size of atlantis
plus the V_out would ramp down not stay steady.

If he stuck a diode in the feed so it wasn't trying to backfeed the rest
of the car and provided the drain on the socket wasn't too high he'd get
away with it.

--
Skipweasel
Pay no attention to that man behind the curtain.

wrote:
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

This is not a good idea, as you'd need a capacitor the size of atlantis
plus the V_out would ramp down not stay steady. If youre deterimned to
do this you could just wire the lighter to an always on fuse,
disconnecting the old feed. But this wont really work either, since
system v drops heavily during cranking.


NT

Indeed. One reason that aircraft used to use (and may still do) rotary
converters so that huge electrical drains like lowering undercarriages
or flaps do not result in instrument blackout. A big heavy rotor
spinning at many thousand RPM stores a lot more energy than the same
sized capacitor.

Which leads to a potential third suggestion. And auxiliary 12v (or less)
battery with a low Vf diode in series with it (shottky) that powers the
phone..and is recharged at a slightly lower voltage from the main battery..

In fact thats a very nice case for a 3 cell lithium battery. With the
diode it will never get overcharged.

The Natural Philosopher wrote:

Indeed. One reason that aircraft used to use (and may still do) rotary
converters so that huge electrical drains like lowering undercarriages
or flaps do not result in instrument blackout. A big heavy rotor
spinning at many thousand RPM stores a lot more energy than the same
sized capacitor.

This is completely wrong. Although aircraft certainly did (and some
still do) use rotary converters, they didn't use them to supply the
high power loads. The high power system was fed by engine generators
(DC, then later AC) at 100V and above and the rotary inverters were
used to supply the older 28V standards for existing instrumentation
systems. Nor do these rotaries have particularly massive rotors with
appreciable stored energy in them.

I posted a summary of aircraft electrical power to this ng a while ago.
http://groups.google.co.uk/group/alt...a7213ccfd91f85

wrote:
The Natural Philosopher wrote:

Indeed. One reason that aircraft used to use (and may still do) rotary
converters so that huge electrical drains like lowering undercarriages
or flaps do not result in instrument blackout. A big heavy rotor
spinning at many thousand RPM stores a lot more energy than the same
sized capacitor.

This is completely wrong. Although aircraft certainly did (and some
still do) use rotary converters, they didn't use them to supply the
high power loads.

I never said they did.

If you READ what I said, the rotary converters are there to keep the
INSTRUMENTATION running when the BIG power stuff ****s the batteries.

The high power system was fed by engine generators
(DC, then later AC) at 100V and above and the rotary inverters were
used to supply the older 28V standards for existing instrumentation
systems. Nor do these rotaries have particularly massive rotors with
appreciable stored energy in them.


Thats is almost exactly what I SAID ****wit. However the rotaries have a
lot more energy in them than a bank of similar weight capacitors.

I posted a summary of aircraft electrical power to this ng a while ago.
http://groups.google.co.uk/group/alt...a7213ccfd91f85

Yawn.

In message .com,
writes

The Natural Philosopher wrote:

Indeed. One reason that aircraft used to use (and may still do) rotary
converters so that huge electrical drains like lowering undercarriages
or flaps do not result in instrument blackout. A big heavy rotor
spinning at many thousand RPM stores a lot more energy than the same
sized capacitor.

This is completely wrong. Although aircraft certainly did (and some
still do) use rotary converters, they didn't use them to supply the
high power loads. The high power system was fed by engine generators
(DC, then later AC) at 100V and above and the rotary inverters were
used to supply the older 28V standards for existing instrumentation
systems. Nor do these rotaries have particularly massive rotors with
appreciable stored energy in them.

So, an Austin Allegro with an APS tied to the roof rack then ...

--
geoff

In article . com,
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated

Wouldn't it be easier to either re-wire the cigar lighter to the ignition
circuit or provide a second outlet so wired?

--
*Speak softly and carry a cellular phone *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article . com,
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated

Wouldn't it be easier to either re-wire the cigar lighter to the ignition
circuit or provide a second outlet so wired?

--
*Speak softly and carry a cellular phone *

Dave Plowman London SW
To e-mail, change noise into sound.

Thanks for your replies, I hadn't realised it would have to be that big
so I think I will take Dave's advice and hook it into the ignition
circuit instead.
Regards
Trevor Smith

No ammount of rewiring the sockets will get round the fact that voltage
on the main bus drops to a few volts during cranking

This is the scheme I used for the radio and
GPS in my last but one car. The NICAD supplies the voltage when the
supply is less than 9volts and even when the main battery is removed.
The Nicad trickle charges through the 330R resistor



SUPPLY LOAD
----------|-------||--------------
/ |
\ 330Resistor |
/ |
\ |
|-------||----+
|
-------
--- 9 VOLT
------- NICAD
---
------
---
|
|
GROUND

In article . com,
dcbwhaley wrote:
No ammount of rewiring the sockets will get round the fact that voltage
on the main bus drops to a few volts during cranking

So what? It's unlikely the phone needs more than 10 volts.

--
*All generalizations are false.

Dave Plowman London SW
To e-mail, change noise into sound.

So what? It's unlikely the phone needs more than 10 volts.

--
But the main bus voltage can fall below 6 volts when cranking the
engine, especially if it is very cold.

On Thu, 28 Sep 2006 12:49:04 UTC, "dcbwhaley" wrote:

This is the scheme I used for the radio and
GPS in my last but one car. The NICAD supplies the voltage when the
supply is less than 9volts and even when the main battery is removed.
The Nicad trickle charges through the 330R resistor

I have a Pama handsfree kit that does exactly that....
--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith


If you dig-out your old school physics books you'll find that CV=IT so
for particular values of load current (I), hold-up time (t) and
acceptable voltage droop (V) you can work out the size of C ... but much
more practical to feed the phone kit from somewhere else.

Dave

Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

Wire it direct to a permanent live with its own fuse, much easier than
having to hide a "coke can" somewhere!!

Staffbull wrote:
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

Wire it direct to a permanent live with its own fuse, much easier than
having to hide a "coke can" somewhere!!


Trouble having to remember to switch it off when I leave the car,
memory not as good as it used to be. No I will wire it into a ignition
feed as I only really need it when driving not parked up with the
engine off. Thanks again for the feedback.
Trevor Smith

Staffbull wrote:
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

Wire it direct to a permanent live with its own fuse, much easier than
having to hide a "coke can" somewhere!!


Trouble having to remember to switch it off when I leave the car,
memory not as good as it used to be. No I will wire it into a ignition
feed as I only really need it when driving not parked up with the
engine off. Thanks again for the feedback.
Trevor Smith

Trevor Smith wrote:

give the phone kit enough juice to keep it powered up during
the time it takes to start the engine

I'd use 3 capacitors in parallel. 22uF (which is probably adequate),
then a 1uF and a 100nF all in parallel, because I'd be worried about
filtering high frequency electrical noise from the starter. Feed them
from a diode.

If 22uF isnt enough, then either fix the engine to start more quickly,
or parallel up another one. As we don't know just how much the
bluetooth gadget draws for current, it's not practical to calculate
this beforehand.

wrote in message
ups.com...

I'd use 3 capacitors in parallel. 22uF (which is probably adequate),
then a 1uF and a 100nF all in parallel, because I'd be worried about
filtering high frequency electrical noise from the starter.

Does that actually work? My rather simple understanding of capacitors was
that if you stick them in parallel, they just behave like one larger one. Or
is the resistance of the wiring somewhere providing a useful effect?

cheers,
clive

Clive George wrote:
wrote in message
ups.com...

I'd use 3 capacitors in parallel. 22uF (which is probably adequate),
then a 1uF and a 100nF all in parallel, because I'd be worried about
filtering high frequency electrical noise from the starter.

Does that actually work? My rather simple understanding of capacitors
was that if you stick them in parallel, they just behave like one larger
one. Or is the resistance of the wiring somewhere providing a useful
effect?


More that the coiled up-ness of the big capacitor puts substantial
inductance in series with it. Also electrolytic capacitors have a
measurable internal resistance.


cheers,
clive

The Natural Philosopher wrote:

More that the coiled up-ness of the big capacitor puts substantial
inductance in series with it.

DC Volts + Inductance ?

Not really an issue is it.

Also electrolytic capacitors have a
measurable internal resistance.

Yes, to a DC voltage a Capacitor has infinite resistance because it is
open circuit!

I presume the OP was querying strapping 3 capacitors of the same value
in parallel i.e. 3 x 22 uF instead of a single 66 uF cap.

--
http://gymratz.co.uk - Best Gym Equipment & Bodybuilding Supplements UK.
http://trade-price-supplements.co.uk - TRADE PRICED SUPPLEMENTS for ALL!
http://fitness-equipment-uk.com - UK's No.1 Fitness Equipment Suppliers.
http://Water-Rower.co.uk - Worlds best prices on the Worlds best Rower.

On Thu, 28 Sep 2006 16:21:10 UTC, "Pet @ www.gymratz.co.uk ;¬)"

wrote:

The Natural Philosopher wrote:

More that the coiled up-ness of the big capacitor puts substantial
inductance in series with it.

DC Volts + Inductance ?

Not really an issue is it.

Also electrolytic capacitors have a
measurable internal resistance.

Yes, to a DC voltage a Capacitor has infinite resistance because it is
open circuit!

His point, I think, is that an electrolytic capacitor does not have
infinite resistance. (actually, no capacitor has infinite
resistance....)

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

In article ,
"Pet @ www.gymratz.co.uk ;¬)" wrote:
Yes, to a DC voltage a Capacitor has infinite resistance because it is
open circuit!

Eh?

--
*If love is blind, why is lingerie so popular? *

Dave Plowman London SW
To e-mail, change noise into sound.

wrote:
Trevor Smith wrote:

give the phone kit enough juice to keep it powered up during
the time it takes to start the engine

I'd use 3 capacitors in parallel. 22uF (which is probably adequate),
then a 1uF and a 100nF all in parallel, because I'd be worried about
filtering high frequency electrical noise from the starter. Feed them
from a diode.

If 22uF isnt enough, then either fix the engine to start more quickly,
or parallel up another one. As we don't know just how much the
bluetooth gadget draws for current, it's not practical to calculate
this beforehand.


But it's possible to make some reasonable estimates. Assume that 2V
droop is the max acceptable and that the load current is 10mA ... CV=IT
will tell you that 66uF will give about 13mS hold-up ... it would be a
rare car that starts in 11mS ;-)

As somebody else has suggested the best way is to wire it from somewhere
else or take a diode to a small rechargeable battery and power it from that.

Dave

On 27 Sep 2006 15:57:13 -0700, "Trevor Smith"
wrote:

In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position.

Well it would do that.

snip

Any advice would be appreciated

Forget the capacitor idea it's ridiculous. Rewire the socket or add
another one suitably fused directly back to the battery. Or you could
just not use the phone while driving or alternatively chuck the whole
lot away and use a phone box.


--

In message . com,
Trevor Smith writes
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which
means it turns off when you turn the key to the start position. I would
like to put an electrolytic capacitor across the terminals of the
socket to give the phone kit enough juice to keep it powered up during
the time it takes to start the engine but I'm not sure how they are
rated, ie: a high number uF a lower number. I know the current that the
kit draws will be needed to get the right capacitor for the right time
but I haven't checked this yet, and I wouldn't the formula to work it
out any way so I was going to go for the biggest.
Any advice would be appreciated
Regards
Trevor smith

Buy Drivel's rusty old Prius

it's got a big battery in it

--
geoff