Ok, forgive me if this is a simple question, but I see that most resistors are rated using three criterea. Ohms, Watts, and Voltage. However, many distributors only provide the Ohms and the Watts in their specs. I'm looking for a source of 1/2W 1MOhm high voltage resistors(1-3Kv range). I've been able to find lots of resistors rated at 1/2W 1MOhm but without any voltage ratings. Should these by their nature be able to handle high voltages, or am I asking for trouble? Thanks for any help anyone can provide! Best, Pol
Given any two, you should be able to derive the third, since P = V*I in general and V = I*R for a resistor. This gets you to P = (I^2) * R which is useful here. So your 1/2W 1Mohm resistor can carry a current of I = sqrt (P/R) = sqrt (0.5 / 1 000 000) = 0.71 mA And the corresponding voltage drop is V = I * R = (7.1 * 10^-4) * 10 ^ 6 = 710 V What are you doing in the kV range?
I know a few sterois have high voltage resistors in them (mine does, it busted, I have yet to replace it), other than that...
Thanks for info, it's much appreciated. I'm using these in construction of a Tesla Coil pimary tank capacitor. I've got a bank(15x5) of small caps that are chained together in a series/parallel configuration that's going to provide 0.0106uf of capacitance at 10KV(AC). What I'm afraid of is that the capacitor bank is going to hold a very nasty charge for a very long time after power down(or accumulate a charge on its own), so I want to bridge each and every cap with a resistor to bleed the charge away shortly after the power is removed. Since the cap array as a whole will actually see well over 7.5KV once the resonance kicks in and the coils "couple" I want to make sure the caps can handle the extreme loads without fear of an "old" charge building up and killing me. Yes, I do know how dangerous this is, I'd expect it will be quite fatal in fact, thats the whole point of the resistors, an added safety. I know this doesn't exactly have anything to do with computer mods, but you guys are all so knowledgable, I really appreciate the advice. Your mathematics make sense, but why then do I see distributors listing voltage ratings for resistors that don't seem to correspond to those numbers? Or am I reading things/seeing things wrong? FYI, here's a link to what I'm putting together: http://deepfriedneon.com/tesla_f_mmc.html Best to all, Pol
Ok, maybe this link will help explain: http://www2.ozland.net.au/users/egel/resistor.htm So your resistor can have a breakdown voltage rating higher than R * sqrt(P/R) if it was designed for a high voltage application.
High voltage resistors are available and often look just like normal ones. I have used them for mains equipement. In the UK RS sell them but I know not about the US. >7.5 KV may be hard to come by.
For my MMC, I used 10M resistors across each cap. Normal voltage ones. The bank total is rated for 42000V which is about about 30000 RMS. On a 15/30 Franceformer, I get about 10-12 inches. Pretty good for a 3" secondary, a primary with way too little inductance, and a double static gap. Take a look here. Also, it doesn't matter too much because the main transformer's secondary winding acts as a direct short across the bank if you have it in parallel.
Capacitor voltages AC or DC? Wow, I knew I'd find at least one person who's done this hanging around Bit-Tech. First off thanks to everyone who offered advice, i have found a distributor for the resisitors I need. Since I found someone who's built their own MMC before(Multi Mini Capacitor bank for the uninitiated) I have one burning question. When I choose the capacitors for this, should I go by their rated AC or DC voltage? I know the primary coill circuit is AC, but since it's being used as a tank circuit, I'd hope the DC ratings would be acceptable(and I hope so, largely due to the cost). Thanks much for everyone's advice, and thanks much for any additional info. I knew the Bit-Tech community wouldn't let me down! Best to all, Pol ps: Sorry if this is considered off-topic, I'm not sure how much this place is supposed to stay in the realm of computer mods. But in my mind, keep it up, this place it great!
Yeah, go with the DC voltage. The RMS value is given on my caps for my next coil at 750V and a DC value of 3000V. They're usually within their tolerances running a RF current at the DC voltage. The best part about MMCs (besides the cost) is the fact that you can just take out a damaged cap and put a new one in, so even if one or two die, it's no big deal. But, are you using polypropylene capacitors? PP caps are self-healing.
