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Post by David Murray on Mar 5, 2008 22:18:30 GMT -5
I'm trying to use a 7805 voltage regulator to get 5V from the 12V system on my car. It seems to get hot pretty fast. I haven't let it stay on more than about 4 minutes and my infrared thermometer is already reading 140 degrees. Not sure how hot it will actually get, or at what point it will burn up. Anyone know? Is there a better way to get 12V (possibly as high as 14V on occasion) down to 5V?
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Post by jsaily on Mar 7, 2008 10:01:14 GMT -5
David, you should use a large heat sink with your regulator if you wish to get high currents with large voltage difference. Your regulator must now dissipate to heat the 7V x current. What's your application and current demand?
It's better to get a step-down switcher for the task. I just bought some MC34063-based from Sure Electronics in eBay. These are perfect for the task and don't get hot (and are cheap!).
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Post by David Murray on Mar 7, 2008 16:02:30 GMT -5
There shouldn't be more than a few hundred miliamps draw on it. Here is the project: www.flickr.com/photos/david_murray/It is to run some guages in the electric car's instrument cluster. However.. I think I've found an alternative solution that is very cheap. I went on ebay and bought some car chargers that output to USB for $1.00 (plus $3 shipping) This will probably do what I want even better.
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Post by jsaily on Mar 7, 2008 16:58:07 GMT -5
Wow... But you'll need hefty heat sinks for hundreds of milliamps with 7805 and 12V input. You could also consider the more intelligent regulators with thermal shutdown.
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Post by Jeff Ledger on Mar 11, 2008 18:07:16 GMT -5
David,
Curious: what type of motor are you using?
HP?, 3PH? Voltage?
Jeff
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Post by David Murray on Mar 12, 2008 8:38:50 GMT -5
I'm not running any motor from the regulator. If you are talking about for the drivetrain in the car, see here: galaxy22.dyndns.org/ev-talon/I have pretty much every specification you could want on the front page.
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Post by MadModder on Mar 12, 2008 16:10:19 GMT -5
I would use an LM2596 switching regulator. I'm using one to get around 7 volts från 30V. I draw one amp from it, and it's cold to the touch without any heatsink whatsoever. A few more components required though.
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