Power supply for automotive use

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Im planning on building a rally computer, and im looking for a robust power supply/filter to use in the car. Input voltage, idealy is 12V, but can be between 7 and 14v depending on conditions, and probably very noisy due to the operation of the car.

If anyone has something suitable could you post me a link?

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Hi,

Not sure where you're located, but you could try these people who are based in the U.S:

http://www.lindelectronics.com/

My last company used about 12,000 of their DC-DC converters to power Panasonic laptops used within vehicles. Very well made and utterly reliable over 4 years of use (and still going). Odd connectors though so if you go for one of these make sure that you get the input / output cables at the same time.

HTH

Robin

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Nice, but I'm looking more for schematics for a power regulator/filter then a premade unit.

This is going to be my first project with a microcontroller, and my electronics theory isn't very strong at the moment =) Basicly, I just want something that will run well for now, so I can concentrate on the software side of the project.

thanks

richard

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I think you will find that good power in a car is going to be the most difficult and vexing part of your project.

Go electric!
Happy electric car owner / builder

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This I have noticed already. Working on my desk is fine with a decent PSU, but I know how much the power fluctuates in my car, let alone the noise.

Are the sample designs that WebBench at National Semi worth investigating for this purpose? And for digital, is a switching regulator a valid choice?

Sorry for the dumb questions, but my prior experience with electronics has all been audio/analog related.

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Our rally computer power source was simple. We have a metal case, so we used it to heatsink a pair of 7805s. An antiparallel diode protected us from negative transients. The input to the 7805s had about 100 uF across it, and we backed up the clock for those brief instances of lost power with a 9V alkaline. The inputs from the car and the alkaline were isolated from one another with a pair of diodes. Our display used power hungry LEDs so we had a separate 7805 for them, but with no backup. And, of course, a fuse on the 12V input. We didn't use a switcher because there was no switcher cad back in 1980.

Since the 9V battery was used only briefly and occasionally (accessory power went off when starting), it lasted quite a while.

For digital, a switching regulator is a valid choice. But most newcomers find the linear regulator to be a quicker implementation. If you use an LCD and a modern CMOS processor, yours won't run as warm as our Z80 and LEDs did.

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I used a National simple switcher LM2574 and a polyswitch & diode in series and a 21V MOV in parallel.

The main reason I used a switcher was the lcd backlight led - it draws >100mA. Otherwise you could use a linear reg specified for auto use - see National Semiconductor.

Apart from the obvious voltage sags when the car starts, you have to cope with impulse noise and possibile alternator load dumps. The MOV and polyswitch should cope with most issues.

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Wow...

im glad im not alone building a computer for my car =)

My current plan is to have a 6 digit display for driver and 2 for navigator, built from 7 segment LED modules, so I would like to have a filtered power for the CPU, and a seperate power section for the wheel probes.

Space is not a huge concern at the moment (i hope) so disapating the regulators heat into a metal chasis is already part of my plan.

If anyone has links to a similar project, I would love to take a look at how it was designed/built =)

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IMHO LF50 is a good solution. Even if the battery dropped down to 5.5V (during pulses like engine starting etc.) you'd still get 5V on the output. It's a low drop stabiliser, very good. It's got overcurrent protection (you can short circuit it if you want without harming it) and it costs just a little above a 7805. IMHO better that 7805.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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daqq wrote:
IMHO LF50 is a good solution.

I searched looking for additional information on "LF50" but didn't find anything that looked like a regulator.
Do you have a link to such info?

Thanks

I'll believe corporations
are people when Texas executes one.

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Google for LF00 - it's a big series of chips, click the very FIRST link - http://www.ortodoxism.ro/datashe... . LF40 gives an output voltage of 4V, LF120 12V etc.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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Thanks daqq.
I am working to a car system (but police car drive siren & blue light) and have the same problem with the power.
LF50 shut down when power if > 16v. well I am not sure it is a good idee for this application 30V peak it is quite commun and if you must protect power input to this, use a LM78xx most robust+ some condensator to save power when Vbat is lest than 5V (few millisecund).
Thierry

Thierry Pottier

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Don't forget to put protection on all in- and outputs too. Spikes and noise don't only occur on the power feed ;)

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Why have a separate power supply for the wheel sensors?

I use proximity sensors that are only two wires for my wheel sensors, these are current limited by a 100R resistor. If you are going to use hall effect sensors, you could use a separate regulator for these but you'll still need something like a SA5.0 transzorb and a polyswitch to take care of induced transients and short circuits.

Best to keep power disipation down to a minimum - even if you have a large heatsink. You also have to be aware of vibration, so don't think of using a single sided pcb unless you go to extra lengths to cope with the vibration.

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seperate PSU for the sensor's as they need power (or at least the ones I have investigated so far do) and from other projects that mixed digital and analog, its always been advised to have seperate power rails for each.

This will be used for TSD rallies, not stage/performace events, so I dont think vibration is as much of a concern, but I might be wrong on that.

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I recently did a TSD rally computer using an ATMEGA128. Backlit LCDs were used rather than led displays. The operation was based on the ALFA computer.

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jayjay1974 wrote:
Don't forget to put protection on all in- and outputs too. Spikes and noise don't only occur on the power feed ;)

Is there a "simple" way of protecting inputs/outputs from spikes/transients?

Phil.

"If they did that in Manchester, they'd be chinned"

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Kartman wrote:
I recently did a TSD rally computer using an ATMEGA128. Backlit LCDs were used rather than led displays. The operation was based on the ALFA computer.

:D

I have been talking to Spamiam, and it turns out you guys are responsible for my insanity already =)

My plans are much lower though, I want to start with a basic correctable odometer function, probably with a secondary function for KPH and display of the RTC time. This is my first project after "hello world" so I'm trying to set my sights low, but I think that if it works, then I will add more functionality as i learn more (both in programming/design and rallying)

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Spamiam will be able to help you with the calculations etc. I basically got Spamiam's circuit, tarted it up, did a pcb design and put it all in a nice box.

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If its the same one as on his webpage, that is a very nice design.

With regards to input protection, is there a benefit to using optoisolators? or will the parts you mentioned give better results?

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I did a car computer for my car using ATmega64 and 128x64 PLED display. For the PSU is used normal 7805 regulator and 12V input voltage was filtered with coil, capasitors and protection diodes.

Low-voltage side is then filtered with 100uF and 100nF capasitors.

It has been working very well now for 9 months and I have not found any problems with noise. Though I have not checked 12V line with scope to see how noisy it is.

Some pics here : http://j-ware.no-ip.com/gallery/view_album.php?set_albumName=carcomputer

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Most automotive designs I know of do not use optos. The car is all metal, so galvanic isolation is not required.

Optos aren't quite the 'magic bullet' you'd hope they are - they still need ESD protection and over voltage protection.

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That's a neat layout, looks quite smart. I like the use of a radio chassis for the unit.

I like the use of lego... Is that eletrical "grade" :lol:

Phil.

"If they did that in Manchester, they'd be chinned"

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Quote:
I like the use of lego... Is that eletrical "grade"

Yeah :) In the beginning I just aligned those masks using only my eye, but then I build that aligning tool.
It helps a lot in mask aligning. I wish I could have a light-table someday, would help even more.

Legos are great for prototyping :)