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Thread ID: 54689	2005-02-19 09:48:00	Build a DC-DC converter	george12 (7)	PC World Chat

Post ID	Timestamp	Content	User
326481	2005-02-20 03:59:00	The motors are powered off four 12v batteries - two in parallel, and those in series - to make 24v total at twice the current of one battery. Laptop is a good idea. But again, how on earth do I get the thing connecting at 1KM through hills and stuff!?	george12 (7)
326482	2005-02-20 06:40:00	The motors are powered off four 12v batteries - two in parallel, and those in series - to make 24v total at twice the current of one battery. Laptop is a good idea. But again, how on earth do I get the thing connecting at 1KM through hills and stuff!? www.interestingprojects.com The unit was purchased over the Net and promises a transmitter power of 1.5W, operating at a frequency of 1.2GHz. By my estimates, when the receiver is fitted with a reasonably high-gain antenna, this will provide a line-of-site range of more than 10 miles. Once the craft becomes autonomous, the value of such a camera is really rather limited -- but I may well use this same RF downlink to carry telemetry from the onbard flight control system. This will be invaluable during the testing phase of the project.	robsonde (120)
326483	2005-02-20 08:03:00	Sounds like you are planning to work the vehicle outside of visual contact conditions george, in which case you will be relying on the video feed to see where you are. What RF system were you planning on using? Cheers Billy 8-{)	Billy T (70)
326484	2005-02-20 10:26:00	Robsonde, looks good but I am on an extremely tight budget due to my age. Billy, I don't mind what RF system to use, I just need to find one I can use. Currently a webcam would be optimal as I can't afford a video camera :(. Edit: By the way, yes I am planning to use it out of sight range.	george12 (7)
326485	2005-02-20 19:49:00	Since it seems like you need non line-of-sight communications, there are immediate problems. The available free-to-use frequency spectrum that would permit streaming video bandwidth are all in the UHF or microwave bands, and these certainly will not "go round corners" at all. Only lower frequencies where propagation and reflection etc can occur will allow communications, but none of these free ones will have the bandwidth available for video. Generally you are looking at frequencies below 50 MHz for this. The (extreme) cost of obtaining your own spectrum space via a licence (even assuming any was available) would rule that out I suspect, you need quite a wide bandwidth.	godfather (25)
326486	2005-02-20 20:01:00	Billy, I don't mind what RF system to use, I just need to find one I can use. Currently a webcam would be optimal as I can't afford a video camera Well george, a web-cam is just a video source, so you will need a transmitter capable of handling a video stream, and for reliable out-of-sight operation at distances greater than 1 km you will need reasonable transmitter power on a frequency suitable for that purpose. UHF coverage might be a bit problematic for your needs, so I'd be looking at the lower frequenciy bands allocated for model control. Have a look via Google and see what options are out there. There is no point in trying to reinvent the wheel. Cheers Billy 8-{) edit: Oops, GF posted while I was away having brekkie! I agree with his bandwidth comment, so you may be looking at narrowband monochrome perhaps.	Billy T (70)
326487	2005-03-03 08:47:00	Built the DC-DC converter. Wasn't too daunting! Here's how I did it. www.jgi.co.nz/psu.jpg - the basic kinda block diagram I used a 5v linear regulator circuit using the LM 7805 voltage regulator plus an 8 amp transistor, I forget the model number. The PC draws around 3.5 amps from the 5v rail. For 3.3v, I used the LM350, 3 amp, (pc draws 1.5A from it) plus the supporting circuitry. I put the 12v rail straight through from the battery. The regulators make large amounts of heat, so I have heatsinks plus a 100mm fan on the PSU. The motherboard ignores the power_good signal, so I did too. I assume it checks the voltages itself. As for PS_ON well..... I ignored it. It produced disturbing but harmless results. Basically, the circuit delivers all rails constantly, whether the mobo is on or off. This leads to a very interesting setup. When I turn it off, the current usage drops to around 2.5a from the batteries, but some things stay running: Hard drive, all fans, power lights, video card - the screen stays on! Displaying the last image!. :o. But anyway, it's for my alarm system I'm building so it's on 24/7 - so the strange effects of being off won't matter. I power it from three random batteries in parallel at the moment, but I'll sort something better out soon. If anyone is interested and wants photos, I can do that if I find the digital camera, and dig up the software. By the way, the total cost of this PSU was only about $20! Plus some parts from an ATX power supply I had (heatsinks, case + fan, wires). And people say it's too hard!? But then I guess I really *should* have made it switching for efficiency. Meh, does the job nicely indeed. George	george12 (7)
326488	2005-03-04 03:31:00	And people say it's too hard!? But then I guess I really *should* have made it switching for efficiency. Meh, does the job nicely indeed. George Thing is George, you didn't actually build a DC to DC convertor at all, you built a simple DC linear regulator. That is a doddle and any keen amateur can knock one of those up using nothing more than the DSE catalogue for guidance. The problem with that route is the energy losses dissipated in heat, and for your mobile application battery power will be critical to operational life. However, if the present arrangement helps you to get the project operational to 'proof of concept' stage, you can start to refine the power source and computer to reduce the power requirements. FYI Jaycar currently have a 12V to 230V convertor (MI-5100) on sale for $54.95 incl. GST and that would power a laptop control system very economically and efficiently. As mentioned in a previous post, an old laptop could be found for peanuts, especially if the screen was stuffed. Cheers Billy 8-{)	Billy T (70)
326489	2005-03-04 03:54:00	:( My happiness smashed :( Yeah, but laptops can't have enough parallel ports, which my system is based on. I use about 3 at the moment. Next one I make will be switch-mode, thanks for all the help :).	george12 (7)
326490	2005-03-05 02:08:00	Well done, all the same George. ;) Even though your efficiency is less than 50%. It's interesting :( just how difficult it is to get efficient power transformation. :groan: The inverter/computer PSU combination is unlikely to be better than 60% or so. The inverter will be about 80-85%, but the PSU isn't designed for maximum efficiency (though it will still be quite a bit better than a collection of linear supplies). Something to bear in mind is that for each amp you pull at 230V AC from an inverter, the inverter will take about 20 amps from the battery. This does not give long running times for battery power. Lead acid battery ratings are "20 hour" ones ... so a 10 Ah battery won't provide 10 A for one hour... it will give 500mA for 20 hours. At 10A, it will be flat in a few minutes.	Graham L (2)
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