Standard metal film resistors, how do they cope in HV applications
gargamel, Sun Nov 29 2015, 11:11AMHi there,
I'd like to use some common 1% metal film resistors in networks for bleeder/balancer in an MCC cap or as voltage devider for measurements.
They are specified with 300V continous and 500V breakdown voltage (for 1min).
My device wont run for thousends of hours, but I want reliability.
How do you deal with that, how far would you push them?
Re: Standard metal film resistors, how do they cope in HV applications
Sulaiman, Sun Nov 29 2015, 04:10PM
it depends upon your attitude;
the resistors are rated for 500 V intermittent so you can use that figure reliably, intermittently
or you could de-rate them to 100 V, requiring five times more resistors, is the extra cost & effort worth it ?
and consider what may happen if one fails in an mmc balancing situation,
plus heat dissipation will be 1/5 per resistor.
(Read a resistor datasheet to realise that it is not advisable to use resistors near their rated power dissipation)
personally I use VR37 resistors because they have never failed me and I bought a lot e.g.
but I'm sure others are similar.
Sulaiman, Sun Nov 29 2015, 04:10PM
it depends upon your attitude;
the resistors are rated for 500 V intermittent so you can use that figure reliably, intermittently
or you could de-rate them to 100 V, requiring five times more resistors, is the extra cost & effort worth it ?
and consider what may happen if one fails in an mmc balancing situation,
plus heat dissipation will be 1/5 per resistor.
(Read a resistor datasheet to realise that it is not advisable to use resistors near their rated power dissipation)
personally I use VR37 resistors because they have never failed me and I bought a lot e.g.
but I'm sure others are similar.
Re: Standard metal film resistors, how do they cope in HV applications
Patrick, Sun Nov 29 2015, 05:36PM
I'm glad someone asked, I'm getting ready to do the same, but maybe with carbon composistion for 30 to 60 seconds at a time. I just need a temporary load to pull the HV down to its real value.
Patrick, Sun Nov 29 2015, 05:36PM
I'm glad someone asked, I'm getting ready to do the same, but maybe with carbon composistion for 30 to 60 seconds at a time. I just need a temporary load to pull the HV down to its real value.
Re: Standard metal film resistors, how do they cope in HV applications
Wastrel, Sun Nov 29 2015, 07:46PM
Resistors tend to have a lower resistance close to their maximum voltage rating. AoE mentions this I think.
Wastrel, Sun Nov 29 2015, 07:46PM
Resistors tend to have a lower resistance close to their maximum voltage rating. AoE mentions this I think.
Re: Standard metal film resistors, how do they cope in HV applications
Hydron, Sun Nov 29 2015, 08:30PM
If you size your bleeder/balancer resistor right for a MMC you shouldn't end up worrying too much about dissipation - voltage rating will be the biggest issue. I'm not sure how much you can push them - for a MMC bleeder you'll be solidly in the intermittent operation regime, so start with that figure.
Different resistor technologies are more or less resistant to pulse loading - I think carbon composition is particularly good actually. The internet will tell you all about it.
This video is worth watching, points out some pitfalls of pulse loading resistors:
Finding pulse energy ratings can be a pain, but some brands publish them (normally energy rating up to a certain duration, then a multiplier of continuous rating for longer pulses), so keep looking if at first you don't succeed :P
Hydron, Sun Nov 29 2015, 08:30PM
If you size your bleeder/balancer resistor right for a MMC you shouldn't end up worrying too much about dissipation - voltage rating will be the biggest issue. I'm not sure how much you can push them - for a MMC bleeder you'll be solidly in the intermittent operation regime, so start with that figure.
Different resistor technologies are more or less resistant to pulse loading - I think carbon composition is particularly good actually. The internet will tell you all about it.
This video is worth watching, points out some pitfalls of pulse loading resistors:
Finding pulse energy ratings can be a pain, but some brands publish them (normally energy rating up to a certain duration, then a multiplier of continuous rating for longer pulses), so keep looking if at first you don't succeed :P
Re: Standard metal film resistors, how do they cope in HV applications
Patrick, Mon Nov 30 2015, 06:45AM
I went through my previous work a few years ago, I don't know if this pic helps others, and I cant fin my original thread, but heres a pic.
Patrick, Mon Nov 30 2015, 06:45AM
I went through my previous work a few years ago, I don't know if this pic helps others, and I cant fin my original thread, but heres a pic.
Re: Standard metal film resistors, how do they cope in HV applications
gargamel, Mon Nov 30 2015, 09:25PM
Thank you for your answers
Well, in my case the cap should be charged an kept at a high voltage for some seconds or in worst case minutes. In my case it's about DC.
I dont like carbon, for they are mostly 5%.
My thoughts are to push them only to 200V, use some more and sleep well ;)
It's just a matter of space and a little more soldering...
gargamel, Mon Nov 30 2015, 09:25PM
Thank you for your answers
Well, in my case the cap should be charged an kept at a high voltage for some seconds or in worst case minutes. In my case it's about DC.
I dont like carbon, for they are mostly 5%.
My thoughts are to push them only to 200V, use some more and sleep well ;)
It's just a matter of space and a little more soldering...
Print this page