Cheap 100:1 2KV Oscilloscope probes - any experience ? - Page 1
Forum section: electronics / testgear

author: Miyuki
author_rank: Frequent Contributor
timestamp: March 20, 2017, 11:10:23 am
content: HelloI want to ask if you have any experience with cheap high voltage probes from ebay. Will they really work to 1200-1500V ?I need them for smps diagnosis, yesterday I kill some 600V ones, yes they really die at higher voltage(there was some 1100V peaks and it hold it for short time then to spark gap)

author: amspire
author_rank: Super Contributor
timestamp: March 20, 2017, 11:36:57 am
content: I have some Hantek T3100 100:1 100MHz 2KV probes that were pretty cheap, but you have to look carefully at the voltage derating. At 1500V, the maximum frequency is 2MHz. At 20MHz to 100MHz, the maximum voltage is about 400V.If you are talking about a waveform with a lot of transients or noise, there may be a significant high frequency component. You can get the Hantek probes for about US$20.

author: Andy Watson
author_rank: Super Contributor
timestamp: March 20, 2017, 11:39:08 am
content: I have an Isoprobe II 100:1 which I have used with 2.4kV signals - and I'm very happy with it. Sold (a year or two ago) under the name of Multi-Contact.http://ec.staubli.com/AcroFiles/MA/SZ_RZ043_de-en-fr.pdf

author: HighVoltage
author_rank: Super Contributor
timestamp: March 20, 2017, 02:41:57 pm
content: I am using the TestTec series HVBandwidth: 300MHzInput Voltage Max: 2.5kVTest Probe Attenuation: 100:1For simple applications, this probe works very well.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: March 20, 2017, 06:11:02 pm
content: Have 2x Testec TT-HV 250 100:1Attenuation Ratio: x100Input Impedance: 100M?, 4 pFBandwidth: 300 MHzRise Time: 1,2 nsCable Length: 1,2 mCompensation Range: 10..50 pFMax. Input Voltage: 2500Vp CAT I, DC incl. Peak AC (deratingwith frequency)Scopes unburned so far.Edit: Note, I used theseonlywith low-energy HV as per CAT I spec!"Measurement Category I:This category is for measurements of voltages from specially protected secondary circuits. Such voltage measurements include signal levels, special equipment, limited-energy parts of equipment, circuits powered by regulated low-voltage sources, and electronics."

author: Someone
author_rank: Super Contributor
timestamp: March 20, 2017, 10:17:06 pm
content: Quote from: amspire on March 20, 2017, 11:36:57 amAnd the associated derating of the voltage! Even these cheaper products are very clear about their limitations:http://www.hantek.com/Manual/T3100_Probe_Manual.pdfAbove just 10MHz its only a 500V probe.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 20, 2017, 11:03:54 pm
content: I tried some cheapo ones. Video below. I ended up making my own. The ones I made I trust.https://youtu.be/v1jJ1Z_fgFU?t=184Home made ones are herehttps://youtu.be/z7rnifjWd_U?t=531

author: alm
author_rank: Super Contributor
timestamp: March 20, 2017, 11:48:07 pm
content: Not sure if a circuit with high voltage transients that have already killed a probe is the place to use a cheap probe of dubious safety. Note that a fault in the probe could easily kill a scope or injure a person.I would trust Testec more than random Chinese eBay probes. Some of the old Hameg probes looked very similar to the Testec ones, so at least at some point they made probes for reputable manufacturers.Are we talking about the primary side or the secondary side of a high(ish) voltage power supply? Because if it is primary, you should probably use a probe rated for CAT II at the appropriate voltage.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 21, 2017, 02:41:00 am
content: Quote from: alm on March 20, 2017, 11:48:07 pmKill a scope for sure. That's why I had the spark gap, the buffer amp and then another high speed clamp when I ran that cheapo probe.

author: Miyuki
author_rank: Frequent Contributor
timestamp: March 21, 2017, 09:13:19 am
content: I use cheap probes with cheap scope so if something fail no big deal (can be also easily repaired), in worst case I have old analog scope, it have valve input buffer with insane input voltage ratingsBut this spark gap wit buffer amp and clamp is good ideaWe are talking about primary side, in this this case it was PFC with 410V output and aux supply powered from this voltage, flyback topology with 1000V clamp, it operates at low frequencies 40-60 kHz

author: David Hess
author_rank: Super Contributor
timestamp: March 22, 2017, 08:16:20 pm
content: They work fine however be aware that they cannot be used safely at high voltages with AC coupling.If a x100 probe has a 100 megohm input resistance which is all of the common inexpensive ones, then it has 99 megohms in series with the oscilloscope's input resistance of 1 megohms. But when the oscilloscope's AC coupling capacitor is included, the capacitor will charge to the voltage at the probe's tip and the input voltage rating of the oscilloscope will be exceeded by several times causing high voltage breakdown in the oscilloscope possibly damaging it.Better x100 probes have a shunt resistor preventing this problem and can be identified by a lower input resistance specification.

author: Miyuki
author_rank: Frequent Contributor
timestamp: March 23, 2017, 09:06:55 am
content: Quote from: David Hess on March 22, 2017, 08:16:20 pmOh that is important info thanksSo I ordered two Hantek T3100

author: ziakansi
author_rank: Newbie
timestamp: March 11, 2024, 11:47:31 am
content: Hello FolksI found this discussion quite useful. I am using T3100 Probes. Since, it is 100:1, so it should attenuate the voltage by the factor of 100. However, in my case it does not perform attenuation and gives me output as 1:1. I ordered four probes and all has the same output. Am I missing something here?Please guide me how can we get the correct attenuation.

author: wasedadoc
author_rank: Super Contributor
timestamp: March 11, 2024, 01:05:34 pm
content: Quote from: ziakansi on March 11, 2024, 11:47:31 amSounds like you are missing the required 1 MOhm "load" on the probe output. What are you connecting the probe to?

author: G-son
author_rank: Regular Contributor
timestamp: March 11, 2024, 05:42:15 pm
content: Quote from: amspire on March 20, 2017, 11:36:57 amI read somewhere that this derating is because the current flow through the capacitance of the probe cause a significant power loss = heat in the probe at high frequency. Is that the only issue?I'm thinking if it's only heat we're worried about we should be able to more or less ignore the derating if we only get short high frequency, high voltage transients, with plenty of cooldown time between - but things tend to be more complicated than they seem so it might not be that simple.