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| Voltage rating of 1W 10M carbon film resistors ? |
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| lordvader88:
I figured I'd use the max continuous voltages, to be safer. I've seen 300-500V for 10M I'll try 9x10M and just to be extra careful. I don't have to hold the probe, or the meter or anything, just flip a switch and see. I have a few TV flyback, but I'm not messing with them until I have a real HV probe, or real HV resistors. But soon I want to experiment, I've never tried anything with HF/HV except plugging in a plasma ball. |
| JS:
--- Quote from: MasterTech on August 26, 2018, 09:27:24 am --- --- Quote from: Jwillis on August 26, 2018, 03:01:00 am ---There are high voltage 1/2 watt carbon film resistors.Here's a few datasheets to look at.https://www.vishay.com/docs/31036/hvwmvw.pdf , https://www.vishay.com/docs/31039/bt.pdf,https://www.vishay.com/docs/30260/hvr2537.pdf . Or try a thick film planar https://www.mouser.ca/datasheet/2/427/fhvr-230664.pdf. Or https://www.vishay.com/docs/28907/vr25vr37vr68.pdf --- End quote --- The only true carbon resistor there is the Vishay series T and B, easily recognizable for its size, 44.5mm for a measly 7.5kV max, but useful for their power handling capability. The MHV, HVW series is really misleading saying "carbon film" at first but specifying "Element: metal alloy" later, it is pictured below. The HVR is also metal film. One important caveat. Max working voltage does not consider in these resistors creepage distances, or any ambiental factors like humidity or pressure. So although it is not stated in the datasheets most of this resistors are for use in oil or potted assemblies if those voltages are to be applied. This is specially true for the VR series (very small for the rated voltage) and the MHV, MVW, HVX that are uncoated. The FHV series however is fine for air use. Again this depends on particular conditions, like impedance of the source voltage and max voltage applied. Here is a bunch of VR68 and MHV resistors, --- End quote --- I wouldn't use any kind of HV circuit without some kind of conformal coating, good clean and a few layers of spray insulator applied should give a better rigidity over plain air on a PCB. I see how in some low leakage applications that could be a problem but at that point the voltage rating of the resistors is the least of your problems, and usually end with much bigger resistors anyway just to be safe. If you feel lucky, I've heard about people melting old acrylic parts into thinner to use later as HV insulation coating. JS |
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