EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: graybeard on March 07, 2021, 11:42:01 am
-
I have been shopping for an electronic load for my home lab and I noticed one key specification that seems to be missing from the specifications from all of them is the isolation voltage. This is the ability to operate above and/or below earth ground.
To be fair many power supplies do not specify this either. However it is an important specification because the power source you may wish to test with your electronic load may be operating well above earth ground.
For both power supplies and loads this is usually limited by the isolation of it's AC power supply or isolation of the isolation computer communications circuitry.
(http://diver.net/eevblog/isolation_voltage_small.JPG)
Chris
-
A first hint would be the IEC EN 60950, which is valid for PSU for electronic devices like computers- I dont't know inhowfar lab PSU and electronic loads fall into this category.
There also the isolation withstanding voltage is specified, as far as I remember (because this is also valid if you do recurring security checks for equipment) it is 500V DC or higher.
IEC/EN60950 has recently be replaced by another version, I would have to look that up.
-
A first hint would be the IEC EN 60950, which is valid for PSU for electronic devices like computers- I dont't know inhowfar lab PSU and electronic loads fall into this category.
There also the isolation withstanding voltage is specified, as far as I remember (because this is also valid if you do recurring security checks for equipment) it is 500V DC or higher.
IEC/EN60950 has recently be replaced by another version, I would have to look that up.
I'd be more cautious and assume 48V in case no isolation voltage has been specified. On the cheaper loads it is likely that there is no isolation barrier between the control circuitry and the DUT so all the buttons and knobs can be connected directly to the input voltage.
-
I glanced at the user manual of the Kikusui electronic load I was using, and the isolation voltage specifications exist.
-
A first hint would be the IEC EN 60950, which is valid for PSU for electronic devices like computers- I dont't know inhowfar lab PSU and electronic loads fall into this category.
There also the isolation withstanding voltage is specified, as far as I remember (because this is also valid if you do recurring security checks for equipment) it is 500V DC or higher.
IEC/EN60950 has recently be replaced by another version, I would have to look that up.
I'd be more cautious and assume 48V in case no isolation voltage has been specified. On the cheaper loads it is likely that there is no isolation barrier between the control circuitry and the DUT so all the buttons and knobs can be connected directly to the input voltage.
Yes, on second thought you are right- I thought primarily of devices that are powered from 230V AC (or similar), so the isolation is measured from the input pins to every conductive part of the device itself when you are doing security measurements.
But yes, some of the smaller "PCB-only" loads that are battery-powered or having a USB connector may not necissarily need this level of protection, since there is no PSU with mains/AC input inside.
-
For the record: I'm not referring to the PCB-only loads but also the low cost ones from Array, BK precision, GW Instek, Rigol, Siglent, etc for which the isolation voltage is not specified in the datasheet.
-
That's one of the things I liked about an old acdc EL-300 electronic load that I rescued from the scrap pile recently.
It is actually powered by the current that it is sinking! It doesn't have to be plugged in at all (the only thing that needs AC power is the fan!)
So you could float this thing on a Van der Graaf generator if you wanted, at least with loads that don't need the fan! :D
-
My Aim-TTi LD400P has isolation spec'd at +-300V, with that clearly marked next to the terminals so I don't forget.
-
After some questions to the factory about missing specs in datasheets and manuals SDL1000X models of later construction now sport a new front panel with a +240VDC MAX to Ground.
Although documentation does need updating..........
(https://www.eevblog.com/forum/testgear/the-missing-specification-from-electronic-loads/?action=dlattach;attach=1189710)