Completely non-sketchy $20 2700V transistor breakdown tester (Emeco) - Page 1
Forum section: electronics / general

author: thm_w
author_rank: Super Contributor
timestamp: April 22, 2023, 12:55:51 am
content: https://www.aliexpress.us/item/1005004651567587.html- $20Neat mini multi-functional tester. Can be used to test:- FET/IGBT/transistor breakdown- zener diodes- LED forward voltage (the series string ones)- MOVsSpec:120V-2700V, 0.2mA-3.8mAThe calibration seems good for how cheap it is, I don't have a high-res meter on hand but the current into a short circuit is 3mA about as advertised. Voltage read was within 1V at 500V. You can test lower than 120V if needed, but that is the lowest open circuit voltage you can generate.Output is DC but pulsed. Have not checked the waveform yet.Inside:- 4-digit LED panel meter- Slim lipo cell (protected)- Flyback transformer w/ voltage multiplierTesting some stuff laying around here:- White LED reverse = 35V- 1N4005 diode = 1580V- 100V WIMA cap = 590V- IRFB3077 (75V FET) = 84V- 25V X7R 0805 = 358V! then it popped, short circuit. All the other tests were non-destructive at 0.2mA.Be SUPER careful when testing large capacitors, as the unit will charge them up to high voltages and only very slowly discharge them.A "discharge" button might be a nice feature to have, or a dedicated capacitor terminal with a built in resistor.The leads are silicone wire which is good. Croc clips are not exactly ideal. Not sure what I would replace it with though. Maybe a small plug in PCB, or ZIF socket?

author: pope
author_rank: Frequent Contributor
timestamp: May 02, 2023, 03:01:08 pm
content: nice ,thanks for the link

author: thm_w
author_rank: Super Contributor
timestamp: May 04, 2023, 08:26:43 pm
content: Here is the scope waveform:The device is set at 114V but you can see some 130Hz spikes going up to 137V.If you want a more accurate DC breakdown voltage, you can add a ~1uF cap on the output to smooth out the voltage. With this capacitance it takes about 5-10s for the high voltage to discharge to a safe level.

author: daisizhou
author_rank: Super Contributor
timestamp: May 05, 2023, 08:45:03 am
content: Is there a schematic for it?

author: Calambres
author_rank: Frequent Contributor
timestamp: May 05, 2023, 05:13:07 pm
content: Funny how Ali Express is selling you a device to check the fake components they also sell you.Just ordered oneSee:

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 05, 2023, 05:29:01 pm
content: That is a fully complete business model.

author: thm_w
author_rank: Super Contributor
timestamp: May 05, 2023, 09:46:50 pm
content: I like the youtube guy feels the need to hold on to the transistor while its being testedQuote from: daisizhou on May 05, 2023, 08:45:03 amNo, you could try emailing the address on the PCB.Or if you want I can take more photos. Its not terribly complex.

author: daisizhou
author_rank: Super Contributor
timestamp: May 06, 2023, 12:26:18 am
content: I can't see the exact model of the SOP14 chip.If you can hope to get a clearer picture

author: Someone
author_rank: Super Contributor
timestamp: May 06, 2023, 01:14:12 am
content: Quote from: thm_w on May 04, 2023, 08:26:43 pmThats a quick method to turn it into a death inducing widget, large capacitance + high voltage = high energy. The output needs a very limited energy to be safe, 3mA continuous is already a little iffy but 1uF takes it way off into dangerous.

author: thm_w
author_rank: Super Contributor
timestamp: May 08, 2023, 08:58:49 pm
content: Quote from: daisizhou on May 06, 2023, 12:26:18 amHere are some better photos.U1 - LMV324D1-D6 - U1M 1kV diodeQ1 - 2SD882

author: Fraser
author_rank: Super Contributor
timestamp: May 08, 2023, 09:23:25 pm
content: Just ordered one of these. Currently $13 but $16 delivered to the UK with taxes pre paid. Great value and an easy way to apply a useful high voltage to a DUTMy lab breakdown voltage tester is around 19” wide, 6” high and 10” deep…. Weighing about 15kg…… not exactly portable !Fraser

author: daisizhou
author_rank: Super Contributor
timestamp: May 09, 2023, 12:54:33 am
content: Thank you, looking forward to further user experience

author: tooki
author_rank: Super Contributor
timestamp: May 10, 2023, 03:27:15 pm
content: 2700V on a basic terminal block? Eww.

author: MathWizard
author_rank: Super Contributor
timestamp: May 10, 2023, 04:23:46 pm
content: Some LCD TV's output a few hundred volts, even just for strings of LED's. I can't remember what voltage CCFL tubes in TV's use, or Plasma TV's.But has anyone adapted a LCD TV PCB, to use for higher voltage testing ? Maybe change the output caps to something smaller, although I think some are pretty small already. And set some current limits.

author: thm_w
author_rank: Super Contributor
timestamp: May 10, 2023, 10:35:54 pm
content: Quote from: MathWizard on May 10, 2023, 04:23:46 pmCCFL might be good to 1200 or 1600V. Some have no output capacitance.You can get CCFL inverters for a few dollars, but you still have to add the enclosure, LED voltmeter, battery, high voltage diode, etc.

author: pope
author_rank: Frequent Contributor
timestamp: May 17, 2023, 09:01:23 am
content: Quote from: tooki on May 10, 2023, 03:27:15 pmYou mean it's not exactly safe, right?

author: Fraser
author_rank: Super Contributor
timestamp: May 22, 2023, 12:18:22 pm
content: My high voltage generator just arrived and, for the money ($13) it is great value. Perfect for the insulation breakdown tests I want to do up to around 1KV. For my tests I do not need my sophisticated lab gear, just a way to generate high voltages in a controlled manner. I could have built my own but at the price of this unit, that makes little sense. This unit could make the basis of a very neat high voltage tester field kit. Thanks to the OP for posting about this ‘gadget’.Fraser

author: Calambres
author_rank: Frequent Contributor
timestamp: May 22, 2023, 04:20:33 pm
content: Mine arrived a week or so ago. Works pretty well!

author: ledtester
author_rank: Super Contributor
timestamp: June 29, 2023, 05:22:39 am
content: Is there a battery in the device or can one be added? This page shows one underneath the PCB:https://www.iccfl.com/product_info.php?products_id=29787&osCsid=251g3gtsnkhbqruplo5jndsm93and also an email address: emeco_cn@163.com

author: Fraser
author_rank: Super Contributor
timestamp: June 29, 2023, 01:29:31 pm
content: The unit contains a LiPo pouch cell so is self powered and recharged using a USB charger.

author: Seekonk
author_rank: Super Contributor
timestamp: June 29, 2023, 01:57:15 pm
content: Reminds me of when I repaired car radios and amplifiers in the late 60's. Transistors were often in a series with each higher number being a higher voltage. I bought the cheapest low voltage TO-220 and selected them for breakdown voltage. A dab of paint would mark them. The very few with low voltage went into car radios and the rest went into home stereos. My home built used a scope. Every once in a while, I would see a strange anomaly on the smooth trace. I threw those out as I figures they might end up as a return repair.The meter on this one appears to be a discrete unit. I think I would add a switch to the voltage divider for a X10 reading. Most of what I do is lower volts.

author: Old Printer
author_rank: Frequent Contributor
timestamp: July 10, 2023, 02:03:18 am
content: Wacky shipping times. US to Us order July 10 - delivery Sept 10. China to US - delivery August 5th?? Same total cost $18.45 USD.

author: bateau020
author_rank: Frequent Contributor
timestamp: August 25, 2023, 05:57:48 pm
content: Just got one. Ordered a version with banana plugs, got the one with green "phoenix" connector, which is the most sold version it seems. Just be aware of it. It does look like I got an "original" Emeco, not a clone.My remarks:Pro:* Current setting is cautious. The actual current, when limited, is about 25-50% lower than set on the dial. The current spikes just before it goes into limiting are however pretty close to, but not exceeding, the set current. I like that. In the low setting (200uA), mine spikes to about 190uA, and settles at 140uA. Much better than my Brymen BM878 insulation meter, that has this the other way around. It's current spikes are 250% of the advertised 1mA limit (which is already too much for my taste).* Voltage reading is pretty close to what my other meters say.* The Volt meter autoranges: at lower voltages, the reading is XXX.X instead of XXXX. So this is not needed:Quote from: Seekonk on June 29, 2023, 01:57:15 pm* The battery charge circuit looks basic, but at least it's not a close-to-zero-cost trickle charger, it switches off when the battery is full. The absence of a properly placed lens or hole for the charge indicator led is not a problem: it is bright enough to be noticed.* The manufacturer does seem to improve the product over time: mine has a dab of silicone over one of the caps (C3) in the HV section, and some plastic coating in places, that did not seem to be there in earlier versions (example: the picture above).Con/remarks:* If you want to replace either the banana sockets or the "phoenix" connector with shrouded banana sockets: not enough space inside. Will have to do that differently.* The "phoenix" connector seems to be a low quality clone. I removed the non-used pin to increase spacing, but even the slightest contact of my correctly temperature controlled hakko desoldering iron to the pins melted the connector's plastic. Anyway, not a biggy, just be extra careful if you want to have a go at it.Fun:* You can use this tool to visually show the self healing of X2 caps. Just take an old Rifa cap, slowly crank up the voltage to make it spark (internally). The cap recovers, and you will see it spark elsewhere when you raise the voltage. Nice.

author: elecdonia
author_rank: Frequent Contributor
timestamp: August 25, 2023, 06:56:27 pm
content: QuoteCool! A device capable of destroying RIFA capacitors without generating smelly smoke!

author: kripton2035
author_rank: Super Contributor
timestamp: August 25, 2023, 07:33:43 pm
content: I bought one a few months ago, almost just when they went out.I bought a model without the battery, planning to power it with usb...alas ! this was a bad idea. I struggle to make this work, finally I plugged a battery and it worked fine.indeed a nice little device to test for high voltage.I use it mainly to test led strips.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: August 18, 2024, 08:12:16 pm
content: Also picked one of these up.. looks like there is some differences, in regards to the previous models in this thread.Fx.* Banana jacks* 40v to 3665v (its a screamer)* 0 to 5mA* Decimal tolerances (below 1000v / 999.9v)Model NY35, the older models seems to go from 120v to 2700v and 0 to 3.8mA, and volt reading in full digits.It is able (to an extent) to light up some of these quite old gas tubes, that I use for crude spectroscopy (atomic spectra-emission lines).It struggles to keep the charge on fx Mercury and Helium, while Neon lit up well.Neon_ - Mercury_Helium_The accuracy seems fine.Prices were around 18$ to 25$ incl. 25% EUVAT / Delivery (varies depending on sale, coupons, aliexpr.)Worth noting the listings on the unit above, claimed two LIPO cells, it ain't - just a single..will try to post some pictures from the internals.Its not that useful for such gas-discharge-tasks with so little ampere, I tend to use a rigged HV-tester which I can dial up from adj. powerbanks..

author: nidlaX
author_rank: Frequent Contributor
timestamp: September 02, 2024, 10:17:02 pm
content: Damn, one of these testers + that gas tube variety box would make for a great Christmas present.

author: tooki
author_rank: Super Contributor
timestamp: September 04, 2024, 06:08:23 pm
content: Quote from: DaneLaw on August 18, 2024, 08:12:16 pmNice pix! That's also rather daring of you, using 30V-rated banana plugs for nearly 4kV!

author: jewelie
author_rank: Regular Contributor
timestamp: May 31, 2025, 02:15:36 am
content: I got the same or similar one to you.I did a lot of successful testing of various transistors yesterday.Tonight... well, curiosity got the better of me.I made a 0.5mm spark gap between two sharp points theorising that it ought to spark at about 2000V or lower.So I tried it, at 50uA, gradually increasing the voltage until about 2000V -- success!(I immediately let go of the button once I saw and heard it working.)But after that, now the output, open circuit, is 0V.It's dead Jim.It's broke.I would have expected it to be fine with exactly this scenario?Is it my fault? Am I an idiot?

author: daisizhou
author_rank: Super Contributor
timestamp: May 31, 2025, 02:36:16 am
content: Don't worry, you can easily fix itFirst, disassemble and check various electronic ICs to see if the fault point can be found obviously.The step-up transformer is a component that is prone to failure.Disassemble it, separate the PCB, and measure the resistance value of the input or output

author: jewelie
author_rank: Regular Contributor
timestamp: May 31, 2025, 05:08:07 am
content: Resistance value of output 18Mohm one way, 15 other direction. Not shorted.Circuit doesn't oscillate, no soundTransformer I think is good.No voltage after transformer (not checked before it.)Diodes I think are good.Capacitors not shorted.Transistors good diode test, not shorted.Resistors I think are good.BUT!R41. Big resistor. I think should be 20ohms? Is that right? 18.4Mohms across R41! Open circuit?

author: daisizhou
author_rank: Super Contributor
timestamp: May 31, 2025, 06:11:30 am
content: Quote from: jewelie on May 31, 2025, 05:08:07 amThe best way to measure is to measure offline, which means to measure away from the original PCB circuit.It seems that R41 is very likely to be damaged, but it needs to be disconnected and measured to confirm it.The transformer may have a disconnection fault, which requires disassembly and measurement for final confirmation

author: jewelie
author_rank: Regular Contributor
timestamp: May 31, 2025, 08:39:14 pm
content: It was R41. Open circuit.I don't have any 20ohm 1%, only though hole 1/4W 10ohm 1%, so I've used two of those in series.Not much space due to voltmeter.Not my proudest bodge.Thank you for encouraging me to try to fix it!

author: thm_w
author_rank: Super Contributor
timestamp: June 02, 2025, 10:11:30 pm
content: Interesting that design seems to be more common now and maybe slightly cheaper, though more complex internal design.Its definitely more dangerous with the exposed banana plugs on the output..There are even TFT based units now:https://www.aliexpress.com/item/1005007922342860.html

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 03, 2025, 10:43:08 am
content: There are quite a few variants, also 4 banana-socket unitshttps://video.aliexpress-media.com/play/u/ae_sg_item/1758504002/p/1/e/6/t/10301/5000189656308.mp4?10v to 4kV & 0.01mA to 5mAPricewise quite close to the older units.. can be had on sale to a tad over 20 bucks incl. EUVAT & delivery.INternalhttps://ae-pic-a1.aliexpress-media.com/kf/Af46ef3cc49ad4b4ca7232cbc07070640p.jpgandhttps://ae-pic-a1.aliexpress-media.com/kf/A8a291ffc88c7486f80335b25fb74e3bbc.jpg

author: jewelie
author_rank: Regular Contributor
timestamp: June 03, 2025, 12:06:33 pm
content: That video gave me such anxiety. Both sets of hands in operation and far too near the terminals.

author: jewelie
author_rank: Regular Contributor
timestamp: June 03, 2025, 12:16:50 pm
content: Something I noticed on mine that seems different to the other models: a whole big bank of capacitors and high value (discharge?) resistors by the output terminals, though which it seems to discharge via the output terminals.Could this be why mine overshoots the voltage and current initially before very quickly hitting a steady state.Ignore the red circle (which marks R41, the 20ohm 1% 0207 that failed on mine), the capacitor and resistor bank are the two rows at the top.

author: elecdonia
author_rank: Frequent Contributor
timestamp: June 05, 2025, 04:54:23 pm
content: Quote from: Fraser on May 22, 2023, 12:18:22 pmI had the same thought when I first saw this item.I wonder how it compares to a traditional insulation tester, aka "HIPOT tester" or "megger?"These devices are commonly used to test the insulation resistance of mains-powered electric motors for leakage between the motor windings and the motor frame. HIPOT testers display "megohms of resistance" (up to thousands of megohms) while applying a user selected test voltage, often ranging in steps from 500V up to perhaps 2kV.I would use an item like this "Transistor withstand voltage tester" to measure semiconductor breakdown voltagesand alsoto test the insulation properties other items such as electric motors.

author: thm_w
author_rank: Super Contributor
timestamp: June 05, 2025, 08:02:48 pm
content: Quote from: jewelie on June 03, 2025, 12:16:50 pmCould be, but those capacitors are very low value (seevoltage doubler). If I test mine shorted into a DMM there is no current or voltage overshoot seen. Though I did not test into a scope, I'm sure there will be a small initial spike.Its possible the regulation circuitry on your unit is just not as well designed.Quote from: elecdonia on June 05, 2025, 04:54:23 pmYes works well for that.But if this is for anything other than hobbyist purposes, just get a real hipot tester.hipot usually has: trusted calibrated values, automatic output shutoff, automatic drain of voltage on output, etc.

author: jewelie
author_rank: Regular Contributor
timestamp: June 07, 2025, 11:36:04 pm
content: I went back in to replace my through hole bodge with a proper replacement 20ohm for R41.It worked initially, but has died again!Voltage stopped going above about 900V. Current (shorted through multimeter) no higher than 3mA.No oscillation sound.Then the voltage and current dropped to 0V again.Have tested R41, R42, the diodes, the transistor, the switch, etc.Doesn't seem to be battery (good voltage, plus same if plugged in.)Doesn't seem to be the built in DMM.I've lost patience with it now.It's not the safest circuit to be working.The fit is poor, as you can see the battery is getting sharp edges compressed into it.Maybe time for me to stop trying to fix it.Does anyone know of a model/version that works more reliably?(Sorry for the poor soldering!)

author: daisizhou
author_rank: Super Contributor
timestamp: June 07, 2025, 11:54:00 pm
content: Please note that this is only a high voltage tester, you cannot use it as a high voltage generator.Usually only suitable for small current testing, large current will inevitably lead to failureAs for batteries, especially this soft-pack polymer lithium battery,I usually regard it as a gift item, which cannot be used for a long time. If you want to use it for a long time, I suggest you change it to 18650 or 21700

author: jewelie
author_rank: Regular Contributor
timestamp: June 08, 2025, 12:12:55 am
content: Quote from: Fraser on May 22, 2023, 12:18:22 pmOut of curiosity, is yours still going?

author: jewelie
author_rank: Regular Contributor
timestamp: June 08, 2025, 12:13:55 am
content: Yes, only tiny currents!

author: jewelie
author_rank: Regular Contributor
timestamp: June 08, 2025, 03:02:04 pm
content: The internals of the one with discharge sockets look better to my eyes? Looks improved. Same main switching transistor but better layout with better separation and air gap on the HV side?(Taken from a teardown in an AliExpress review.)

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 04, 2025, 03:08:34 am
content: I just got the 3.7kV version, appears mostly identical inside to jewelie's one. I can confirm it also has the flaw of the potentiometer pins pressing against the highly flammable lithium battery, definitely check and fix before using! The display read a bit high out of the box, had to tweak one of the trimmers on the back side to get it to agree with my multimeter. The case is surprisingly sturdy for such a cheap device.Quote from: Someone on May 06, 2023, 01:14:12 am1uF at that voltage would basically be a microwave oven capacitor and would be about the size of the unit itself. Should need no explanation how bad of an idea that would be.The stock output capacitance is about 3nF. At maximum output voltage, that would be nearly twice the energy of a 15kV HBM ESD event. That and there being next to no series resistance likely explains the reported failure after shorting the output when it has a charge build up. Could probably be mitigated by adding a high voltage resistor in series at the right spot, I'm thinking between the positive terminal and the board, then move the meter sense wire so it reads the actual output voltage.

author: Someone
author_rank: Super Contributor
timestamp: September 04, 2025, 04:33:03 am
content: Quote from: NiHaoMike on September 04, 2025, 03:08:34 am61010 places the energy limit at 45 micro coulombs, so not much headroom. 3.7kV and 13nF is off into considered dangerous so adding a “small” 10nF capacitor is risky, let alone 1uF.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 04, 2025, 09:48:11 pm
content: How is it considered when there's resistance limiting how much current the capacitors can output? I'm thinking to add extra capacitance but behind the resistors limiting the output current.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 06, 2025, 11:47:20 pm
content: A bit of reverse engineering found that the midpoint of the output capacitance is used as part of the voltage multiplier. Disconnect that and replace with a 1nF, 3kV cap, now there's much less ripple. Still get a lot of overshoot at lower voltage settings, probably need to add a soft start circuit to solve that.I also added a 5V TVS diode across the 20 ohm sense resistor and rewired the output capacitor to the other side of the 20k output resistor. A few arcing tests at maximum voltage and current worked initially, but then the 20k resistor cracked. Still works, just with a little crackling noise from the broken resistor arcing. Probably have to replace with a string of lower value resistors to better withstand the transients.

author: MathWizard
author_rank: Super Contributor
timestamp: September 17, 2025, 05:48:59 am
content: So everyone's still ok ? Something like this worries me less than 600V vacuum tube radios and stuff, but the power's not much less than 600V @ 20mA. My CRT scopes also worry me way more than this. So how many Watts are bug zappers then, way less ?Someday I want to make a HV source for high resistance testing and leakage currents, or maybe there's a similar budget tester for that too. I'd add any cheap/easy safety mods too.Years ago I bought some large resistors and caps, just to make a HV probe, but I never got around to it, or needed it. I scrapped a Plasma TV once too, and have a lot of interesting caps from that, but I guess mostly way way to big for keeping the energy levels low.But I'm guessing building the circuits big and spread out, and point to point wiring, would make most aspects of a HV generator, pretty safe, just like in the old days around tubes.

author: thm_w
author_rank: Super Contributor
timestamp: September 17, 2025, 09:49:42 pm
content: A handheld bug zapper might be 1-2kV. But it has a large capacitor on the output, 22nF or more. You can calculate the stored energy (see a few posts above). This will have minimal output capacitance, unless, you connect it to a capacitor which when charged could be extremely dangerous.Main safety aspects I would say are: bleed resistors, covering circuits so they can't be touched (eg plexiglass), dead mans switch, lockouts, etc.