Alex Tsekenis

There are really tiny PCs, smaller and lighter than the board in your link. Anyway, if its for an academic exercise then you should go with something more DIY. There is an intermediate solution, embedded development platforms. You can try googling that. I have asked an ex-lecturer of mine, he is a Professor of DSP in the uni of Manchester UK. He really knows his subject and he should be able to reccommend a better board than I would. http://www.eee.manchester.ac.uk/aboutus/staff/show.html?ea=patrick.gaydecki I will post his reply here once I get it. From experience I would suggest not to get too DIY with hardware and to focus on what I think will be the main focus of your application, image processing. So for RX/TX I would go with a ready module and interface that to the rest of the system. For example, http://www.radiocrafts.com Maybe these specific modules don't offer such long range, but you should look for a such level of integration. Regards, Alex

Daylight bulbs are amazing, a pure bliss to the eye in an electronics lab. The only issue is that the eye is not so sensitive to that light so maybe you need a few more tubes. If I have daylight tubes on and then change to warm white my eyes hurt. I think they are great, you should try them maybe on a bigger scale. I even convinced Intel Corp. to change the ones in my area. :D

And the smaller IGBTS...I also have these in half-bridge style with two devices per package. Bear in mind, some of the smaller IGBT units have one of the two unit toast. This is a SIEMENS BSM75GAL120DN2 http://www.infineon.com/dgdl/75gal120dn2.pdf?folderId=db3a304412b407950112b4095b0601e3&fileId=db3a304412b407950112b431af4e5520 These are 1200V 105A or 210A pulsed. The dual units are identical in terms of package with I think a bit lower specs. Let us know when you have seen them so we can remove the pics to save space. Also let me know if you need higher res pics. Regards, Alex

Riccardo, Here are some pics of the single big IGBTS. They are these: http://www.mitsubishichips.com/Global/content/product/power/powermod/igbtmod/hmd/cm400ha-34h_e.pdf 400A 1700V and 800A pulsed. Regards, Alex

I would recommend a micro PC motherboard and a high resolution usb camera. You can do all your software development on a very high level language like C# under Windows embedded. Regarding RX/TX, I am sure there are long range modules that can plug say in your serial port. Same for GPS modules. How does that sound? Do you prefer a more DIY approach? What were the issues you were thinking of? That is a great idea btw, congratulations! Now you need to find a way to get those firemen to move their... Regards, Alex

I hope the inventive idea is not the IR thermometer :-\

When we say infra-red, we mean all the frequencies below what the human eye can see. That is very wide band of infinite frequencies or wavelengths. The IR receiver or transmitter in a remote control system use very different wavelengths than an IR thermometer. For this very simple reason, you cannot use either a receiver or a transmitter for this. IR thermometers that you can buy in shops use a very different kind of sensor, called microbolometer. If you want a reasonably accurate thermometer to measure say the temperature of a wall, than I can reccomend the Fluke 62 http://cgi.ebay.co.uk/New-FLUKE-62-Handheld-IR-Infrared-Thermometer_W0QQitemZ390093115750QQcmdZViewItemQQptZUK_BOI_Electrical_Test_Measurement_Equipment_ET?hash=item5ad35c9166 Alternatively, you can use the TPA81 sensor module (requires microcontroller and programming). This is an array of 8 thermopile elements in a row. You can use it to measure temeprature of objects nearby, very low accuracy but it is great if for example you have a robot and you want it to follow a candle flame. http://www.robot-electronics.co.uk/htm/tpa81tech.htm Hope this helps. Alex

Hi, Taking the worst case, where you have 2 turns 0.5m dia. , your coil will have an inductance of about 4uH. I have assumed an ESR of 50mOhms including connectors. Once you trigger the IGBT, assuming no voltage drop there, you will get 340 Volts across your inductor. Current will start rising but not linearly due to the discharging capacitor and resistor in the path. The peak current when it occurs will be when the inductor voltage is 0 volts and it will be about 800A. This is the worst time to switch off the IGBT. If this happens, whatever current is flowing tin the coil will appear across your diode, coil and resistor and it will be a bit less than 800A due to the diode drop which will be significantly more than 0.6 Volts at that current. So do you need a bigger diode? Probably. The issue here could be thermal runaway of the diode once you reverse bias it again as it could be too hot by the end of the coil discharge period (starting from when you switch off the IGBT) when it is in forward bias. This could destroy the diode be excessive leakage current , in the region of uA for this diode. One thing you can do, is add a resistor, say about 0.6Ohms in the path of the diode. That will limit the current to something that the diode can cope with. This question really has no easy answer, certainly beyond Ohm's law. At these currents even the ESR of the capacitor and the resistance of your cables will have a dramatic effect. Very low level circuit analysis is needed and good knowledge of IGBTS and Shottky diodes. The narrower the ON time for the IGBT, the easier it will be for the diode. You can control the peak current by varying the ON time. I tend to use an isolation transformer everywhere that I can as it saves lives. Now, you can use one during development and then use a pulse transformer or an optocoupler to trigger the IGBT. I will take a picture of the IGBTs and half-bridges soon and post it here. They are packed away in storage atm. I seem to have a picture of the IGBTs and other power modules before cleaning them to store them(attached), I will have a look in storage and give you part numbers very soon. Regards, Alex

I see. Much better now. Yes that will complicate driving the IGBT but not too much. It comes down to whether you want electrical isolation of the control circuit or not. For example, if your control circuit is powered by some lab bench power supply that has earthed negative terminals then you will trip the safety relay. If it is a self-contained unit then no problem. One more point, why do you include the transistor in the current loop that is created when you switch off the coil? Why not have the diode's anode connected to the collector of your IGBT? Regards, Alex PS: I happen to have some used Mitsubishi IGBTs rated at 800A if I remember correctly and some SIEMENS half-bridges again IGBT rated at 300A I think. Let me know if you are interested.

Hi, Find a cheap 9V, 10VA or so transformer (maybe one of those that you can choose the output voltage), connect all the bulbs in parallel and then to the transformer. Merry Christmas! 8) Alex

See attached diagram with notes. This is definitely a coil gun. ;) You have already connected the ground to mains and broken the isolation the 12V transformer provides by grounding the 1000uF capacitor. If I were you I would use an isolated control section powered from the 12V trafo and leave the high voltage side floating. I have serious fears that your power section in the red circle will blow up. What is the NMOS you are using, which one? It is connected wrong. Anyway, I doubt it would be able to withstand such voltage and current. In this sort of application you can use a thyristor. To trigger it you can use an optocoupler or relay to maintain isolation between the control circuit that you have greater chances of touching and the power circuit. What is the inductance and ESR of your coil? The free-wheeling diode D7 might not be able to withstand the back-EMF when the capacitor is drained. My point is that you should get mathematical with C1, D7, Q2 and L1 maybe run a simulation too. Alex

I think a posting rule on minimum required posts will be very effective, say 10 posts required for Sell/Buy and 5 posts for HV. Spammers dont have the time to post 5 times to get one advert out. Maybe it is worth seeing how this is managed in other forums too.

Yes an isolating transformer will limit the current for several reasons. However you should consider that only if you require electrical isolation in your system. It is an overkill otherwise. 100W is a very big transformer to use. you can power your TV at the same time as charging the capacitor ;D To calculate the resistor's rating you need to decide on how fast you want to recharge the capacitor and to what extent. The RMS values of voltage and current will need to be calculated from the voltage and current waveforms and multiplied to give you a power rating. The resistor used will still need to be able to cope with the current surge that is why I suggested a wirewound resistor. I bet a 10W 220 Ohm resistor: http://uk.farnell.com/welwyn/wh5-220r-ji/resistor-10w-5-220r/dp/9507817 would be up to the task with a lot of margin. Regards, Alex

Maybe if you placed a rule on the system that doen't allow you to post there if you have say under 10 posts?

Agree with Hero. I am posting to advise you not to give away great ideas for free :) Regards, Alex

The power dissipated would be for a fraction of a second and it will repeat every time you want to recharge. The rectified UK mains voltage should be about 340 Volts peak. To limit the maximum input current to 1.5 A you could use a 226 Ohm resistor or the closest E series equivalent. Very crude calculation ignoring diode drops and capacitor ESR but the tolerance of the resistor isn't any better. What do you mean by transformer? I thought you wanted to charge a capacitor off mains? Maybe you mean an isolation transformer? - Edit - I see why you though of transformer. No, you dont need a transformer. A much much smaller wirewound resistor would be able to handle the power for this short duration. Regards, Alex

Hi Riccardo, You must use a resistor. The series capacitor would also be discharged at the beginning thus acting like a 'short circuit'. Although the capacitor would present capacitive reactance as you say, at switch-ON the waveform is a 'step' signal going from 0 to whatever the mains voltage is at that time. A step signal is made up from infinite sinewaves at higher frequencies. As you might be aware, capacitive reactance is inversely proportional to frequency so like I summarise above, the capacitor will behave like a short circuit due to the higher frequency components. That said, if you choose your capacitor values wisely, you should be able to distribute the charging current across several mains cycles by managing the voltage each capacitor sees across it at each given time. A resistor is easier to calculate in this respect. So, use a resistor. I have seen people use ligh-bulbs to charge capacitor banks for rail and coil-guns if thats what you are after. What capacitance do you want to charge? P.S. I just saw Her'os reply. An idea would be to use a relay to exclude the resistor from the circuit once the capacitors have been charged not to waste energy. Regards, Alex

Oh that's not good. :-\ To whom?

Hi Hero, Too poor for any real PCB contouring in my opinion. But great for drilling afterwards. I found a great page that shows the capabilitities of this method using magazine paper and a laminator. The 25

Come on now... Maybe it blends well with flux fumes. :P MrUmunhum - Any local store will have stripboards or matrix boards, from China, England/ Europe, some 'Arab country' or maybe from America who knows. Just ask in local shops. I assume that this is for a simple electronics project. I always recommend to people to not use stripboards and use matrix or tripad boards instead. Stripboards are too error prone, unreliable and dangerous if you are building some high power circuit. Regards, Alex

Hi Hero, 25

Ah...do you think I have gone soft gogo? :'( Once you have built a dozen PCBs on your own, your priorities might change from pride#1 to repeatability and quality#1 which is still pride from a different viewpoint. The ideal would be to get professional quality at home but that requires a big investment in equipment and space. What you say that you need 100s of PCBs to be cheaper is a misconception from my experience. There are companies that specialise in bulk orders and others in prototypes. For example, a 18x10 cm board with 4 layers, plated-through vias, silver plating, black soldermask and white silkscreen on both sides with the smallest pitch being 0.2mm was about 25