12V -> mini-USB, 2A converter, *not* in cigarette lighter format?

[icon]

Hi

A mate is trying to plug a Tom-Tom sat nav into his motorbike and I foolishly said I'd help him. I'm trying to find something that will convert 12V into 5V, at 2A, with a mini-USB plug on one end and two trailing wires on the other. There are loads available built into cigarette lighter plugs, so I might end up buying one of those and taking a Dremel to it but before that, can anyone point to a better solution (UK preferred...)?

Cheers
John

[rr100]

No need to spin the power tools, the "cigarette lighter plug" ones are really easy to adapt, at least the cheap regularly sized-ones.
Unscrew the tip and it will fall apart, leaving you with a small PCB you can use directly in your project or take advantage of the case and solder your cables directly to the PCB (don't forget to add a cable fuse if needed because you'll be bypassing and throwing away the fuse).

Example here: http://www.penguin.cz/~utx/hardware/Hetai_HD-818/
scroll down to "Dedicated car charger teardown" look on the right, there's black and red cables coming from the right - you can just connect there. You can throw out all the metal parts that connect to ground and +VCC but again take care of the fuse, simplest with some in-line fuse holder.

[SeanB]

If you go the dismantle route on a cigarette lighter power unit use a 5A automotive blade fuse in the power lead and add a 1000uF 5V capacitor across the input, along with a 1N5403 diode as reverse voltage protection. Makes the output more stable and reduces radiated noise from the unit. Wherever you mount it ensure it is well encapsulated, preferably inside a small metal case, to protect it from water and provide heatsinking.

[RJSC]

If you go the dismantle route on a cigarette lighter power unit use a 5A automotive blade fuse in the power lead and add a 1000uF 5V capacitor across the input, along with a 1N5403 diode as reverse voltage protection. Makes the output more stable and reduces radiated noise from the unit. Wherever you mount it ensure it is well encapsulated, preferably inside a small metal case, to protect it from water and provide heatsinking.

5V electrolytic across the input ?

You mean a 5v capacitor across the output, or a 16V (at least, better 25V or 35V) capacitor on the input?

[SeanB]

25V, missed the 2.......

Though I do actually have some 100uF 6V capacitors that are double the size of a 1000uF 25V unit.

[icon]

Great! Thanks for the tips, I'll get on ebay...

Regards
John

[Fingerpuppet]

I was thinking of doing this exact thing... Dashcam tucked away behind the mirror, usb mini b cable slips up under the headliner to the texas instuments eval board with all the fixin's already attached in the reference design...

http://www.ti.com/lit/ug/slvu163/slvu163.pdf        <---$10

...and then wired to the 12v supply for the map lights (which powers off after 30 seconds when the car is locked!)

I'm just not sure about fuse selection and if I'll need additional input or output capacitors or if I have any inrush problems or any noise due to the non-isolated design, and heat... oh, that relentless summer sun car heat... etc.

Am I a fool, or does this look acceptable?  (I just HATE the idea of hard-wiring in a piece-of-crap car lighter adapter above the headliner... their teardowns are NOT confidence inspiring)

[rr100]

I don't see anything particularly bad in the pictures from the teardown I mentioned above (and the board is quite typical for a charger of this size/type).
Is just a straightforward use of the 34063; you can just buy or find around the house a bunch of those (chargers) and have a look, I'm sure you'll find one you consider acceptable (you might want to change some caps or redo one or two solder joints but really not that much that can go wrong).

Depends on your load as well, if around 1-1.5 amps not only the ventilation might be a problem but also the voltage drop across wires/connectors. But lower than that should be no problem. If paranoid use a small (but not extremely fast) input fuse and put everything in a metal box...

I would worry more about the camera, because those are using quite a bit of juice and in my experience always run hot, if you want some decent quality video.

[mariush]

I recently bought one of those car adapter chargers (it was under 2-3$ at a sale) and made a video about it here:



In the video I've replaced the 34063 with a ncp33063 (same thing, just lacks inverting mode i think) because I either shorted the original chip or it was damaged in the first place.

Since the title of the thread has 2A in it, I guess I should point out that most car adapters using mc34064 or similar chips aren't capable of actually doing 2A, and some don't have components optimized for high currents... for example mine was more "tuned" for 9-10v rather than 12-24v (it was more efficient with lower voltages, up to about 400mA)

There are cheap buck regulators that can do 2A or more without any problems, like those LM25** you can find on eBay. You just have to package them in a small box and you'll be fine. If you want to, you can replace the capacitors with some high temp ones (Panasonic FR series for example, 8-10k hours at 105c depending on capacitor size) and the buck regulator itself should handle summer heat under a car windshield just fine if you add some heatsink to it.

later edit:

Here's 2 pictures of the charger I opened up in the video .. output cap is just something I had around (the original one exploded when i powered it up, as the original damaged mc34063 passed the input voltage directly to the output)

[SeanB]

My one went up into the lining by the light. I added a wire down to get a switched 12V supply for it, and fed it up the A pillar to into the lining to get power. Ground was there for the light, so all I did was wrap it in some plastic card and tape it closed with a backup cable tie as well. I later had to fix it when the capacitors vibrated the solder off, and the inductor did the same. New capacitors and leaded solder and a little glue it went back in and still works. I wrapped it in a little foam to reduce vibration and this does not seem to impair the unit, it runs quite cool ( best advantage of SMPS over linear) and works well. I took the camera and made a mount that screws into a tapped hole in the rear view mirror mount ( plastic moulded over a zinc casting, holds threads quite well) and has some small neodymium magnets that mate with small steel washers to hold the camera, much smaller than the cup mount it came with.