Do you have experience with high voltage resistors THT? - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 05, 2021, 11:10:32 am
content: I find Vishay have VR37 series High Voltage Metal Glaze Leaded ResistorsAre really cheap and are in stock (what is also important these days)They have Umax. = 3500 VDC compared to common few hundredI want them mainly for mains ZC detection to MCUIs there any trap or I can sleep well with them?

author: TimFox
author_rank: Super Contributor
timestamp: September 05, 2021, 01:45:59 pm
content: The maximum voltage rating is good, so long as you also obey the maximum power rating: 3500 V at 100 k (minimum available resistance in this series) is 122 W, but the power rating is only 0.5 W.Above 25 megohms, the voltage rating dominates over the power rating, but the series only goes to 33 megohms.Also note the 700 V insulation rating (through the coating around the resistor to anything touching the surface).

author: bdunham7
author_rank: Super Contributor
timestamp: September 05, 2021, 02:11:25 pm
content: I've been using the very similar HVR37 series in applications like HV dividers and such even when they might be 'overkill' because I'm more comfortable with the specs,. In mains-sensing, this would make me more comfortable as well, especially the 10kV pulse withstand.. They also seem to have a low voltage coefficient. The differences between VR37 and HVR37 seem slight, the HVR37 description refers to a flame-resistant lacquer and they are a bit bigger. They both have the 700V insulation limit (never noticed that before) but hopefully your PCB design doesn't run traces under your HV resistors or anything like that. Where I use them I have thousands of volts so it becomes obvious you have to keep stuff away. Where mains are concerned, you should treat it as if it were thousands of volts--because it might be someday! So VR37 is probably a much better choice than something with a 300-500V rating.

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 05, 2021, 02:28:55 pm
content: 230/400V mains have a 2.5kV surge level (what shall every device withstand) so it is still in continuous rating, which is niceI can see why they have just 700V insulation limit. That enamel coating is easy to damage. And every little scratch can easily compromise it when another component touches.But I plan to have them far from everything, no traces near

author: Benta
author_rank: Super Contributor
timestamp: September 05, 2021, 04:47:15 pm
content: I've used Vishay VR37 and VR68 for mains applications with good results. Quality and reliable, absolutely no issues.

author: sandalcandal
author_rank: Unknown
timestamp: September 05, 2021, 07:27:41 pm
content: Have used 80x10Meg HVR37 resistors to make a DIY EHT probe based on the April 2010 Silicon Chip magazine article. Was going to pot it but never did. Seems to work fine for >30kV.Also started but did not finish a HV oscilloscope probe project using HVR37 resistors potted in paraffin wax. I don't recall breakdown being an issue.

author: BrokenYugo
author_rank: Super Contributor
timestamp: September 05, 2021, 07:49:10 pm
content: I rebuilt the HV divider in an old oscilloscope with VR68 resistors and it seems to work, given those are 10 kV resistors with like 1200 volts across the whole chain.I don't think there's a trap with these like the SMD parts that require potting to meet their HV specs.

author: CaptDon
author_rank: Super Contributor
timestamp: September 06, 2021, 10:08:38 pm
content: We built high voltage ion sources for the 'anti-static' ionizers used in electronic manufacturing.We had a constant problem of arcing even though we used potting and overkill on physicalspacing. Lesson learned...... DO NOT touch the bodies of those resistors with bare fingers!!!!!The contaminants in body oils will fluidize in the potting and come back to haunt you!!! Wehad dozens of these devices returned from the field. We were a contract manufacturer forthe anti-static fan devices. Employees who eat potato chips for lunch and then return to theassembly area without washing hands, wearing gloves or finger cots cost us a bunch of moneyas a manufacturer!!! You can't watch every monkey in every show!!