Electronics > Beginners
Using Ch1 + (inv)Ch2 on hot side vs unhooking mains ground
Brumby:
--- Quote from: Jwillis on August 13, 2018, 01:07:18 am ---I'm not sure why you need to see mains ...
--- End quote ---
This is my question also.
Mains is typically rather low impedance, capable of delivering significant energy. This low impedance means it is going to take a lot to cause any significant impact on the delivered mains - aside from higher frequency EMI.
I simply must ask "Do you really need to see the mains waveform?"
lordvader88:
Never mind all that, wow differential probes are super expensive.
Back to plan A for now, get another 30-40 feet of wire and finish the MOT isolation transformer using 2 primaries on the same core.
bitseeker:
Yes, they can be super expensive, especially from the A-brands. The EEVblog HVP-70 is made by Sapphire, the same company that makes them for Keysight, LeCroy, etc. So, it's a good value as compared to what you'd pay with one of those other brands on the cover.
However, MicSig came out with some that are even more affordable. Their DP10013 is 100MHz and up to 1300V. However, it's a x50/x500 probe (unlike the x10/x100 of the HVP-70). So, the attenuation of the MicSig is higher, but also lighter on the budget. I wish they'd come out with a lower-voltage (500-700V is plenty for SMPS) probe that was also x10/x100.
https://www.ebay.com/sch/i.html?_nkw=micsig+dp10013&_sacat=0&_sop=15
https://www.ebay.ca/sch/i.html?_nkw=micsig+dp10013&_sacat=0&_sop=15
Note that the voltages produced inside an SMPS can be well over 300VDC, even when connected to 120VAC in North America. Be careful when probing, even with a DMM, as a slip in the wrong place could make for a very bad day.
james_s:
Yes the DC bus is typically 330V whether the input is 120V or 240V, except in very small power supplies.
I'm still not sure why you want to probe the mains side, I have the tools to do so safely, but I can't think of many reasons to try.
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