Steady 12V from car cig lighter socket - how to?
john_s
Posts: 369
Here's another task that I'm putting for open discussion.
This time I need to "reliably" obtain around 12V / 2A from my car's cigarette lighter.
To accomplish it I came up with the following circuit that should provide something not exceeding by much the expected 12VDC from the said source.
I plan to implement it inside the "standard" cig-plug and welcome any complains or suggestions
Thanks,
John
This time I need to "reliably" obtain around 12V / 2A from my car's cigarette lighter.
To accomplish it I came up with the following circuit that should provide something not exceeding by much the expected 12VDC from the said source.
I plan to implement it inside the "standard" cig-plug and welcome any complains or suggestions
Thanks,
John
569 x 313 - 6K
Comments
-Phil
"reliably" under what conditions ? "around" is also vague.
The serious systems, that mean reliable, include cold cranking in their conditions, which can go to ~4V IRC.
Those systems have Switch Mode solutions, and the best use the dual-inductor approach, which allows Vin to pass across Vo.
There, you can get 12V out from 4~20V in.
-Phil
BTW, it is not just automotive that has a 'nominal voltage'. Try putting any battery on a voltage meter that has some precision and you will see new alkaline cells are more than 1.5 volts, those 1.2 volt NiCads are something much higher when fully charged.
In sum, the nominal volts is just a rough estimate of the voltage at the level where most of the power is delivered.
If you have devices that you desire to protect from either low or high voltage, you have to actively regulate. And if you are going to put a voltage regulator in a car, it should be at least able to handle 60VDC spikes and provide some sort of low-voltage dropout feature.
Use 2013 solutions, not 1963 Popular Electronics solutions.
And that 12VDC TVS is doomed to self destruct in short-order... it should be 14.2VDC or higher.
In practice the big drop-outs are when operating the starter and most people expect that drop (headlights
dip).
I think a reasonable compromise can be achieved using filter components, but I'd add a fairly large DC choke and lots of
capacitance to help cut out big spikes and noise (possibly an oversized cigar plug is needed!). With the choke you
can contemplate a proper 15V crowbar circuit (zener+transistor) to kill transients (the choke limits the current unless
its a consistent 15V+). And finally LDO 12V regulator at the end. Or even 10V - many applications that need more than 5V
will actually work with 10V I reckon.
The DC-DC converter is a good approach but they don't overload gracefully, whereas a filter+linear regulator can fare
better on inrush currents.
Some of the eBay LM2596 buck regulator modules might just fit inside a cigar plug?? Then you'd have to go for 10V out,
but they are good to a few amps and cheap and chips.
My goal is to provide a certain safety built into a regular lighter plug rather than to design a complete DC PSU.
I've decided to add 2 (?) inductors and increased the TVS to say 17V.
Is temporary dropout to 10v OK?, or is it 12V (±0.1v) constantly a must?
P.S ground is not -12V, it's 0.
voltage is like a waterfall, your schematic is from a 12ft height to 12ft below sea-level = 24ft fall (24v)
However, I'm adding some extras and that's why I need an additional protection not to blow my circuitry during say 40V surges expected from automotive lighter socket.
While you have specified the voltage for your capcitors, you haven't specified the actual capacitance. With a good LDO regulator, you won't need huge capacitors in line. Consider using one if space is at a premium.
Inductors, capacitors... at some point you really are going to have to do the maths for a real filter design or this will just be junk.
See:
Load_dump
autotransients really informative
High-Frequency Automotive Power Supplies
Duane J
u1 = 100nF
Thanks - a very informative reading and I start to feel more and more like a "rocket surgeon"
I wonder how can one compare all that info to a single fuse to be found - or most of the time NOT - inside those lighter plugs....
Things like Cell Phones have well designed regulators that can take the abuse from the car.
Others just don't care. The sheep will just replace the thing that went bad anyway.
BTW, 0.1uF??? I don't think this will be even noticed by a several amp 50V pulse.
Duane J
If you really need reliable 12.0 volts under all conditions, you might consider (don't laugh) a step up converter plus a step down converter. Sounds a bit silly, but boost up to ~18 volts then back down to 12.0. Numerous threads here about various units, cheap on Ebay.
Step down 3A buck regulator for (you guessed it) a buck: http://www.ebay.com/itm/1-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-S3-/200967073436?pt=LH_DefaultDomain_0&hash=item2eca922e9c#ht_4708wt_1206
Step Up 6A $5: http://www.ebay.com/itm/150W-DC-DC-Boost-Converter-10-32V-to-12-35V-6A-Step-Up-Voltage-Charger-Power-/400555361933?pt=LH_DefaultDomain_2&hash=item5d42f5c68d#ht_10000wt_1004
http://www.linear.com/solutions/1666
Yes I know the V in is max at 36V but its gonna take OV as well as UV on the automotive power rail .
small current but > http://www.pololu.com/product/2096/
under 5 USD .
http://parts.arrow.com/reference-design/B0F31F194C9F938C5BDF73D18B8713AB
and the fine people at EEV have this http://www.eevblog.com/forum/projects/sepic-or-buckboost-for-cleaning-up-12-volts/
Does automotive industry care of what's out of there?
I'm talking an "average" car
btw. that other circuit that I wanted to protect from voltage surges is the 5-12V LiPo charger http://www.adafruit.com/products/280
Now that IS some really good stuff !
Probably just a fuse, nothing else.
Remember their initial use was for lighting cigarettes and over the years transformed in to accessory power port but that was never official.
It's it time for a new standard for power ports on cars?, sure regulated 5v & 9v would be nice.
Tony there was gonna be a SAE update to a 48ish V system . Thinner wires and less amps to drive our power stations on wheels . less copper in the car . lighter Ect
http://www.automotive-eetimes.com/en/german-carmakers-agree-on-48v-on-board-supply-charging-plug.html?cmp_id=7&news_id=222901632
http://en.wikipedia.org/wiki/42-volt_electrical_system
Like all good ideas ...... most never come to a head
Why the Fraggin! Bork do you want to pack it into the most unreliable connector ever made?
Junk the idea of putting the stuff inside that, and instead find some space under the dash to stuff everything.
Also, the cigarette lighter is protected by a fuse, and may or may not be connected through the ignition system.
Really advanced cars can have a sensor to measure the battery voltage even when the ignition is off, and switch it off if the voltage falls below a predetermined level.
If you want any electronics to survive in a car, don't bother building a PSU yourself, just buy something that has already been designed and tested for this environment.
The charging voltage can get as high as 14.4V. If that is to be dropped to 12V, while at the same time delivering 2A, you're talking about getting rid of nearly 5W of heat.
But I still need to plug it in .... into lighter socket
Now we are talking heat dissipation... and that was NOT my primary objective at all - just an over-voltage protection to meet 12V max requirements of said LiPo charger that has none built-in.
-Phil
The real goal is to protect my Microchip MCP73861/2 inside adafruit LiPo charger http://www.adafruit.com/datasheets/mcp73861.png that only allows:
Absolute Maximum Ratings†
VDDN...............................................................................13.5V
I figure that a $3 KIS-3R33S switcher tuned to provide 12VDC / 2A nearly steady from car lighter socket voltages should do the trick.
All that of course after my original / dreaded F + L+C+D+TVS circuit placed inside the lighter plug
the datasheet Says 5-12V so feed it with 5 .
I strongly suspect that the automotive DC electrical environment is the MOST severe for digital electronics. And that cigarette lighter plug was merely intended for a cigarette lighter... nothing else.
Honking horns, switching on/off headlamps, brake lights, hi/low beams, and archaic turn signal flashers all come into play. A lot of variation in inductive transients and old-school switches.
++++++++++++
My own preference is to find a good set up that isn't junked up with excessive redundant parts. I am not sure you need a 2 amp fuse. I wonder if the coils are going to make things better or worse, and a 100nf capacitor is going to do next to nothing for a 2 amp load.
A. Do you really need to provide a 2 amp load.
Parallax uses LDO regulators that provide up to 1 amp LM2940 that can be gotten in 9 and 12 VDC and with a few extra parts will do the whole job. That 2 amp specification creates problems.
B. Do you really understand that transient filtering and voltage regulation?
These are separate topics from an electronic design point of view. But the makers of voltage regulators know that automotive electronics is a huge market for them, so they have create newer and better voltage regulators just to sell to the auto industry. That LM2940 has reverse polarity protection as well as LDO, and several other features.
C. Transient filtering has improved greatly, but typical schematics on the internet often show notihg of such details that are included in good products.
I remember when everyone wanted a computer noise filter with an MOV in it. These weren't the best solution ... they just worked one time and burnt up. Now MOVs are used with a replaceable fuse so that the device can be revived for another use and so that the failure can be confirmed. And we have an array of diode device that can take big joltz that happen is micro-seconds. The best real world solutions are to know where the hits are coming from and why you choose a particular protection.
Modems, Antennas, and other long wire connected items need lightning strike protection. Electronics on automotive supplies have to deal with the alternator/voltage regulator setup and the starter/solenoid step up creating most of the trouble. Also, the ignition if you have an older distributor or your coil wires are defective.
There are a lot of different topics in this mixed bag. And if you drive a 1953 Chevy pickup, you are going to have much more to deal with than a 2013 Lexus.
In sum, it isn't just a 12VDC battery that is in play.
And if you just happen to have a CB radio in your car, it is another roll of the dice.
This may be a Star Drek quote, but nonetheless;
D@mn the Primary Objective!
Everything you do electrically have effects and side-effects.
What good is an otherwise 'perfect' PSU if it melts the insulation on the wires next to the metal body of the connector?
Or the heat builds up inside the connector, and finally destroys the PSU itself?
As for using the lighter socket at all...
I meant it when I called it the worst connector ever.
It's even worse than the SCART connector!
At least the SCART connector isn't plagued with vibration, heat and temperature fluctuations... excessive condensation...
For anything that needs a stable power, please find another connector and install somewhere in the dash.
Personally, I'm considering something like these for use in my car:
http://no.mouser.com/ProductDetail/Conxall-Switchcraft/17282-2SG-300/?qs=sGAEpiMZZMv5iorFleMzWtfrGD80OuoBFZcD6wmO%252bvE%3d
It'll mean having to hack apart some adapters to fit a new plug, but...
At least I'll know that it'll stay plugged in!