DC Load - I need some guidance - Page 1
Forum section: electronics / testgear

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 10, 2024, 04:56:25 pm
content: Hi,I'm looking to finally get an electronic DC load. Previously, I've used power resistors, but it's cumbersome. I then started researching and I realized that there were programmable loads with a great deal of features that would be very handy today, and others that would probably be great tomorrow.Regardless of where I go, I find praise and criticism for both. There's always someone who finds them utterly useless, noisy, etc. My primary need is to test out both linear and switching power supplies, but battery testing and simulating noisy loads and how they affect other parts of a circuit is also very relevant.I originally began looking at Rigol DL3021 and Sigilent SDL2021X-E. I thought I had decided on the SDL2021X-E, simply because the software seemed better, and it wasn't as noisy as the Rigol (I have a Rigol scope, and even though I love it, it drives me nuts sometimes).Now, of course, as always, doubt sets in. And while perusing other loads at other dealers, I stumbled upon B&K Precision 8550, which for some reason seemed very attractive to me. It also boasted more features/better software, larger LCD and seemed more practical on the whole. Except for the backside, which has none of the connectivity of Rigol/Sigilent. I don't have any need for it now, as a USB stick with preprogrammed routines will work fine, but who knows.Price wise of course, the 8550 is in a totally different bracket than SDL2021X-E. Forking out for the latter is still a large investment to me, but I'm also not foreign to spending bucks to get good stuff that will last and still prove useful 10-20 years on, as my projects and knowledge evolve.Then, I read that B&K is simply ITech, only overpriced, and that's that. I know there are hundreds of threads like this, and I've tried my best to google around in the last couple of weeks, but right now I feel pretty stuck. Any advice or input would be greatly appreciated.

author: 2N3055
author_rank: Super Contributor
timestamp: June 10, 2024, 06:30:42 pm
content: Quote from: mvno_subscriber on June 10, 2024, 04:56:25 pmYou might be overcomplicating things.General loads (all of the ones you mentioned are in that category) are very useful tools. But also limited.They are useful for :- static loading of voltage/current sources for purposes of thermal testing- for testing/measuring battery capacity- for testing of solar panels I/V curves- for dynamic load testing where switch between two currents and look for load/unload response.- for testing large LEDWhat you cannot do with them is using them as a load while performing any kind of frequency response analysis. Or use it as a load while measuring PSU noise and ripple.They are also limited in speed of load change, not very good at low currents (because that is not what they were designed for.).Honestly, all of the ones mentioned can do the job. I personally have Maynuo 9812 that have "LED mode" that changes control loop response. Unit is a bit old fashioned UI on the device. It has very powerful software for the PC though.If I were you I would choose by price and ease of driving.

author: nctnico
author_rank: Super Contributor
timestamp: June 10, 2024, 07:10:19 pm
content: Quote from: mvno_subscriber on June 10, 2024, 04:56:25 pmThe B&K Precision 8550 is a rebadged Tonghui DC load.I have been looking at a DC load myself and settled on a Korad KEL2010 (after testing it thouroughly). After a fix to swap the fan and move the mains transformer away from the analog circuitry, the KEL2010 also works well for currents in the single digit mA range.See these threads:https://www.eevblog.com/forum/testgear/dc-load-korad-kel2010-or-tonghui-th8402a/msg4969006/https://www.eevblog.com/forum/testgear/korad-kel2010-multicomp-mp710771-review/msg4975759/

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 10, 2024, 08:09:00 pm
content: Quote from: 2N3055 on June 10, 2024, 06:30:42 pmThis I don't quite understand -- when in transient mode, switching between currents, or in list mode, wouldn't that be useful for measuring PSU ripple and transient response? B&K has features specifically made to test DC power supplies as well (sweep mode, load regulation test).Also, with regards to low currents - mA resolution are from 0.05mA to 1mA in CC mode, depending on model. In my world that's low current. Or am I not reading the specs correctly?

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 10, 2024, 08:11:50 pm
content: Quote from: nctnico on June 10, 2024, 07:10:19 pmNot sure if that is meant as a bad thing or not, as far as I read in the threads you provided, Tonghui is seen as an ok brand. Buying Korad, Tonghui or Rigol from AliExpress is not any cheaper than buying RND, B&K or Rigol here at home, when considering shipping and taxes (except you don't get any proper warranty or support!).When it comes to having to modify the unit in order to make it work properly; that's not for me. I need a device that works well, with good support and firmware upgrades.

author: 2N3055
author_rank: Super Contributor
timestamp: June 10, 2024, 08:46:39 pm
content: Quote from: mvno_subscriber on June 10, 2024, 08:09:00 pmI said FREQUENCY response (Bode plot) not transient. Transient load test is included in my list of PROs..No, you cannot really measure PSU ripple with active load connected. Apart from load injecting it's own noise, load is active device that is "hunting" PSU output on a switcher, depending on how fast the load is.. Waveform on output of the switcher might not necessarily be the same as if there was a passive resistive load on the output. Of course, you can get some results and it might be good for comparative purposes (comparing a good one to bad one), but for real low noise or really accurate results you use passive resistive loads.Also, resolution is not same as accuracy, and using anything at 1% of full range and expect accurate results is not good practice. If load has 3A range, 30mA is 1% of full scale..For less than 50mA you need device made for that range to be able to get accuracy..... Again, you can test, but accuracy won't be what you expect.Funny thing is that at these low currents it is easy to load with simple resistors too.

author: nctnico
author_rank: Super Contributor
timestamp: June 10, 2024, 09:09:14 pm
content: Quote from: mvno_subscriber on June 10, 2024, 08:11:50 pmThe latter is why I bought the Korad load from Eleshop which is a European test equipment distributor which offers hassle free returns. In the end there is no substitute for doing your own suitability tests.QuoteI get that. And in that case I'd recommend to look at loads from GW Instek or Chroma. These are a serious step up in price though (and may not have banana jacks on the front panel) . Also take fan noise into account. Last month I used a Chroma DC-load at a lab but the fan didn't turn off which is annoying when testing light loads which normally wouldn't need the fan to be on. In my opinion finding a DC load which really ticks all the boxes is surprisingly hard.

author: temperance
author_rank: Super Contributor
timestamp: June 10, 2024, 09:11:34 pm
content: @ntcnicoQuoteIn an other topic you stated to not buy any low cost equipment anymore? Or was it only to stir up a conversation with someone else on here? If there is equipment which you can't trust it must be Korad. The loop compensation / MOSFET drivers might be just some copy paste and guesswork.

author: nctnico
author_rank: Super Contributor
timestamp: June 10, 2024, 09:17:18 pm
content: Quote from: temperance on June 10, 2024, 09:11:34 pmIf you read the threads I've linked to, you'll see I have considered a whole bunch of DC loads from many brands and then sifted towards the ones which are obtainable and which ones fit the requirements. If a cheaper piece of equipment fits the requirements and passes thourough functional & fitness verification, I have no problem with it. Especially when there are next to no other alternatives. Where it comes to Korad and DC-loads: Korad has been in the power design business for a long time so I don't think they copy & paste but actually do know how to design the analog section properly themselves and optimise for cost (both in part choice and procurement). The board layout for the KEL2010 has been done with great care; the person who did the layout this wasn't riding his/her first rodeo so to say. Its just that they placed the mains transformer in a less optimal place which could be a choice driven by the mechanical design.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 11, 2024, 06:05:55 am
content: Quote from: mvno_subscriber on June 10, 2024, 04:56:25 pmYou mention testing batteries and power supplies, which is also something I often use my electronic load for, but even my unit (ET5410) that maxes out at 150V/42A_420Watt.I'm hitting the ceiling quite often in some tests, not least in regards to high drain Liion & LIPO cells/packs, and they will only get more potent in the years to come, but since you are highlighting models that peak at around 200Watt..I guess that is enough for you?I went for one of these unitshttps://tinyurl.com/yeyr6p6snumerous years back from a European warehouse.(CZ Banggood)..Its quite feature-packed, not least with the price in mind, which back then was around 150$ (on sale incl. 25%VAT & delivery).It got 12 main categories..https://tinyurl.com/3mk3dvymwith submenu'es.https://tinyurl.com/4jjdp82vIt's more or less done what I needed over the years, but I haven't dug down into the more advanced settings which can be quite cumbersome to adjusthttps://tinyurl.com/4kf3k3m9- though most of it' you can also control through numerous PC programs and terminals.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 11, 2024, 09:32:38 am
content: It's easy to get sidetracked by all the different specs and apparant shortcomings. As mentioned by others, I guess I have to be more precise as to what I'm looking for.So here's a try, in no specific order:Adjustment: 1mA resolution is plenty good enough for meCurrent ripple: 10mA constant ripple current sucks. I would prefer better, but in worst case I guess I can compensate with static loads as long as I know it's there.Software: This is important to me. Buggy software is a no-go, because I'd end up not trusting the instrument. And getting really frustratedFeatures: Static and dynamic loads are important. Also, being able to whip up a CSV (or whatever format needed), pop it into the USB port and execute it is a bonus I'll appreciateI/O ports: I guess it's nice to have. But no requirement, really.Screen: I like to be able to view graphs on an LCD. There should be a real good reason if I'm to go for something with text only.Build quality: I expect it to last 15-20 years at a minimum. Anything less would indicate a faulty design and I'd feel uneasy. Cheap plastic etc is ok, I'm not too picky about it as long as it works.Power: 200W is plenty. 150W would work too.Seller: I prefer to buy from reputable sellers. Elfa Distrelec, RS, local companies. Maybe I'd try Batronix, but I prefer sellers that offer DDP shipment. I have an assumption that makes everything warranty and repair related stuff much easier?Price: The B&K 8550 is really a bit more than I feel comfortable with, unless it's super duper cooler than the competition. The Rigol DL301 / Sigilent SDL2021X-E are also expensive, butseemto be a good balance between price and functionality

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 11, 2024, 02:18:56 pm
content: Quote from: mvno_subscriber on June 11, 2024, 09:32:38 amYou keep referring to this Siglent SDL2021X-E in numerous posts.. Im not familiar with that model and I guess your a thousand too high.Have you examined a bit, perhaps watched or read a few reviews of modern programmable electronic loads.?

author: ftg
author_rank: Frequent Contributor
timestamp: June 11, 2024, 03:05:38 pm
content: I have a Korad KEL103 at the office and it has served my needs well.Which has been mostly testing and sweeping <30W DC-DC converters I have designed.I don't really use any factory provided software, as it can be controlled via Ethernet, so we have some inhouse software to control it, a lab psu and multimeters to get some repeatable pretty pictures of converter efficiencies.For measuring ripple I use a pile of switched TO-220 power resistors to have stable loads.Ofc this is not really convenient for larger loads.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 11, 2024, 05:22:36 pm
content: Quote from: DaneLaw on June 11, 2024, 02:18:56 pmOops, yes, sorry. For some reason these model numbers get fuddled around in my head. For clarity, here are the datasheets of the loads I'm considering:ManufacturerModelDatasheetSigilentSDL-1000X serieshttps://siglentna.com/wp-content/uploads/dlm_uploads/2024/05/SDL1000X_DataSheet_DS0801X-E01F.pdfB&K Precision8550https://bkpmedia.s3.us-west-1.amazonaws.com/downloads/datasheets/en-us/8550_Series_datasheet.pdfRigolDL-3000 serieshttps://beyondmeasure.rigoltech.com/acton/attachment/1579/f-0778/1/-/-/-/-/DL3000_DataSheet_EN.pdfI've mostly discarded Rigol, as it has a fan that is constantly on. I hate that. Also, the Rigol business model of having artificially crippled units with payable unlockables is something that makes me feel kind of cheated.Sigilent seems to have good models that are easily hackable when the time comes. However, there is a huge price gap between different models that don't really offer much extra (and the insides are identical, as far as I could tell). So a bit like Rigol, however not as bad.B&K seems to have the most features software-wise, for example frequency sweep to check for PSU ringing, load regulation testing and CC/CR/CW mode in battery testing. It doesn't have USB or LAN, however. Not that it matters much to me, but is somewhat puzzling. Weight is also low compared to the others, which makes me suspect more fan noise. Or cheaper build.Dave did a teardown of the Rigol -- Sigilent and B&K is much more difficult to find. I've located some scraps of information on this forum, but nothing that really tells me much. I do wonder if the added price of the B&K translates to better build (and/or less current ripple?).

author: nctnico
author_rank: Super Contributor
timestamp: June 11, 2024, 05:37:35 pm
content: AFAIK the B&K 8550 is a very new model so it is no surprise very little information can be found. Regardless your choice, my advise is to prepare a testplan which is relevant for your usage scenarios and test a DC load. You could test a few and keep the one you like most and return the others. Test equipment sellers won't mind at all as this is common among their customers.

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2024, 07:39:21 pm
content: Quote from: mvno_subscriber on June 11, 2024, 05:22:36 pmhttps://www.eevblog.com/forum/testgear/siglent-sdl1000xsdl1000x-e-electronic-load/Defpom teardown vid is reply #80

author: Martin72
author_rank: Super Contributor
timestamp: June 11, 2024, 09:08:12 pm
content: You can choose from:https://www.batronix.com/versand/last/SDL1020X-E.htmlEasily make this:https://www.batronix.com/versand/last/SDL1030X.htmlI've been working with it a bit, it's making a good impression so far - but I'll do a proper test with it when time finally allows and post it in the forum.I have all the resources for it, I still have to get a battery, if you want to determine the ripple of the load, a regulated power supply makes little sense as a source.When I have that, I'll get started.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 12, 2024, 08:21:29 am
content: I took the plunge. I ordered the B&K 8550. I just knew that if I had ordered the Sigilent, I wouldn't stop thinking about the features set of the 8550. It fits me and my needs - hopefully.If any are interested, I can post back when I get around to using it (not this week, but maybe next), since there is very little to find online about this load. If there are specifics you'd like to know, post here and I'll whip up some images and/or videos when the time comes.Right now I'm just empty inside after having spent all that money, but I know I'll appreciate it in due time

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2024, 08:29:46 am
content: Quote from: mvno_subscriber on June 12, 2024, 08:21:29 amI would highly appreciate it if you can share your experiences with the B&K 8550 . Actually I have been trying to buy the Tonghui version but didn't want to risk ordering it from Asia so I'm (still) really curious about how it works.

author: 2N3055
author_rank: Super Contributor
timestamp: June 12, 2024, 01:25:33 pm
content: Quote from: mvno_subscriber on June 12, 2024, 08:21:29 amNobody pointed you to this topic:https://www.eevblog.com/forum/testgear/bk-8550-electronic-load-current-ripple/Also what applications?I'm looking at datasheet and it has nothing that my old cheap Maynuo does not have. And Maynuo PC app is more powerful..Anyways, good luck and like Nico says, let us know how it goes...

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 12, 2024, 08:49:18 pm
content: Quote from: 2N3055 on June 12, 2024, 01:25:33 pmYes, I did find it so I've come to peace with the 10mA current ripple which seems to be standard for DC loads in this price range. I'll still have to use static loads for some testing, so I'll bunch together my existing set of power resistors and make something nice out of them for complementary testing.Regarding applications, my first will be a power supply I'm building. I want to stress test the supply with regards to heat, current limiting, short ciruited outputs, see whether certain usage patterns may couple into other parts of the circuit, noise levels at different combinations of draw and how it will cope with long term abuse. I'm pretty sure I'll find a bunch of other uses as I get into it as well.Quote from: 2N3055 on June 12, 2024, 01:25:33 pmWith PC connection, I guess the sky is the limit. For me, I prefer my bench to be PC-free -- I want all my equipment to stand on their own. Less mental interference. It's my hobby, and I have more than enough computer usage at work. So having a full blown interface in the unit is something I'm willing to pay for.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 12, 2024, 09:26:24 pm
content: Aint it more or less the same fundamental tests, that go again across many of these programmable electronic loads.# CC# CV# CR# CP# Trasnsient# List/Aut.# Battery# LED-DR# SCAN/SWEEP# SHORT# CC+CV *# CR+CV *# CP+CV *// Looks like there are some specific features on some models, even though the testnames vary greatly from brand to brand on what each vendor calls a given mode, while in practise being more or less the same.The stacked CC/CP/CR+CV (*) feature, where it flips when a max-criteria is met, does not seem that common, GW Instek's more expensive loads seem to have it (PEL3000/5000), and some of the models from East Tester but most don't.

author: bson
author_rank: Unknown
timestamp: June 12, 2024, 11:06:43 pm
content: Quote from: mvno_subscriber on June 11, 2024, 05:22:36 pmI've had a B&K 8600 for about 6 years now with no complaints. If I were looking today however I'd probably get the Siglent SDL-1020X. The main reason is its LXI-11 LAN support for remote instrumentation, and 200W (even the 150W of the B&K 8600) is plenty for anything I ever need. Otherwise I just don't see much difference spec-wise between the B&K and Siglent units. With LAN a GPIB port isn't needed, IMO, so I'd just buy the much better bang for buck Siglent.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 13, 2024, 10:19:50 am
content: Quote from: DaneLaw on June 12, 2024, 09:26:24 pmHmm, I thought Sigilent didn't have sweep functionality, did I misread the data sheet??The devil is in the details here. With Rigol and Sigilent, my impression is that the battery tester feature only supports CC (that was Dave's gripe with the Rigol. I checked out their firmware revision history and it seems that hasn't changed) - whereas with B&K, you have the same CC/CR/CW as in all the other modes. There might very well be other differences too.(Also, the B&K looks way sexier IMHO)

author: tautech
author_rank: Super Contributor
timestamp: June 13, 2024, 03:02:43 pm
content: Quote from: mvno_subscriber on June 13, 2024, 10:19:50 amMaybe.SLEW is mentioned on P14https://int.siglent.com/u_file/download/23_10_09/SDL1000X_programming_guide_E02B.pdf

author: nctnico
author_rank: Super Contributor
timestamp: June 13, 2024, 09:29:13 pm
content: Quote from: Martin72 on June 11, 2024, 09:08:12 pmWell, for 50Hz ripple, a decent power supply should have a low enough ripple & output impedance to test. It would be interesting to know whether the Siglent loads have the 50Hz current ripple or not.

author: Martin72
author_rank: Super Contributor
timestamp: June 13, 2024, 10:05:04 pm
content: We will see.My fear is that when two regulated systems "meet", this can lead to interactions.I also have a few linear "iron" power supply units, but they can only handle a maximum load of 3A, which is not a lot.

author: nctnico
author_rank: Super Contributor
timestamp: June 13, 2024, 10:13:50 pm
content: Quote from: Martin72 on June 13, 2024, 10:05:04 pmYou won't need a lot of current to show the DC load regulation ripple. 100mA is more than enough; otherwise you'd likely be swamping the ripple you want to measure.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 14, 2024, 06:19:48 am
content: I got the unit yesterday. I won't be able to test it properly before next week, but wanted to hook it up and just fiddle around a bit. Now, two things struck me, one of which I'm not sure what to do with.1. The fan is always on. It's not super loud. It's a bit quieter than my oscilloscope (Rigol). It sucks, but I'll probably be able to live with it. Most likely I'll have my scope powered up whenever I use this thing anyway.2. There's a really high pitched noise coming from the unit. It's higher than your average CRT monitor whine. It's almost not a sound at all, and more a sensation. It's very fatiguing, almost nauseating. I downloaded a random FFT app on my phone, it registered a 15Khz spike at startup (which is clearly audible, sounds like something charging up), but then nothing. The nauseating sound has higher pitch than that, how much higher I'm not sure, but I assume it has to be quite loud for me to actually hear it. I mean, I guess I have a good ear, but I am 41 and have no illusionsI hope then that this whine is a fault, or that it will pass (is it possible?). If not, I'm not sure if I'll be able to live with it. Crossing my fingers 🤞🤞

author: 2N3055
author_rank: Super Contributor
timestamp: June 14, 2024, 07:41:00 am
content: Quote from: mvno_subscriber on June 14, 2024, 06:19:48 amThat whine is either coming from PWM for fan or from a switcher PSU. If it is there it won't get tired and go somewhere else....

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 14, 2024, 07:56:46 am
content: Quote from: 2N3055 on June 14, 2024, 07:41:00 amIs there anything I can do to dampen it without meddling with its insides? Could it be its placement somehow acoustically amplifies the sound? I find it difficult to imagine that this is how it's supposed to be.

author: 2N3055
author_rank: Super Contributor
timestamp: June 14, 2024, 08:10:16 am
content: Quote from: mvno_subscriber on June 14, 2024, 07:56:46 amI don't know. First you need to realize where is comes from.If it comes from fan PWM, you have actual fan being a speaker....It might change as fan RPM change.If it comes from PSU, then it is some component that is making a noise. A inductor, transformer or something else magnetostrictive or piezoelectric (like ceramic capacitors for instance)..It might as well be a standard thing on these.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 14, 2024, 06:39:44 pm
content: Quote from: 2N3055 on June 14, 2024, 08:10:16 amTried loading it with 150W to make the fans spin up, and spin up they did. Still the same whining, though. Had ringing in my ears 15 minutes after I turned it off. I'll call for a replacement unit on monday, this has to be defective. Right now it's a health hazard.That said, I really like it so far and I don't want to let it go. It has already gotten a place in my heart! Let's hope a new unit will fix things.

author: Martin72
author_rank: Super Contributor
timestamp: June 15, 2024, 10:44:17 pm
content: QuoteThese are usually inductors such as core chokes or transformers.The wire windings are relatively loose around the core and start to vibrate when current flows, this is transferred to the core and the whole thing forms a small "loudspeaker".We impregnate our coils/transformers under vacuum, which reduces the vibrations enormously.What you can do "privately" and afterwards is to localize the sounding component and cover it with e.g. silicone.

author: 2N3055
author_rank: Super Contributor
timestamp: June 15, 2024, 11:08:04 pm
content: Quote from: Martin72 on June 15, 2024, 10:44:17 pmI also have heard elkos and ceramic capacitors "sing" quite nicely...

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 15, 2024, 11:12:45 pm
content: Shame with the whine, as it is such relative things that one would expect are sorted out the more expensive units from certain brands - Tonghui rebadge or not.Where did you purchase it from? did it seem new when it arrived (like you were the first unboxing it) if not, it could indicate that its solely this unit, and some other buyer has been there with a "no thx, you're going back" and the reseller is trying their luck to find it a new home.Are the 4mm protruding input jacks on BK8550 of the 8mm grade with 2mm wall-thickness or is it the 6mm that are common on many power supplies with 1mm thickness?On East Testers programmable loads, it looks to vary depending on wattage and could look like its the 6mm wide/1mm metalthickness on ET5420 (2ch 20A pr. channel / ET5411 1ch 500V/15A) while 8mm/2mm metal-thickness on the 40A load (ET5410).https://cdn.globalso.com/easttester-cn/fu3.jpgBK8550/TH8401 does look good, kudos for both sense & 4mm input jacks at the front.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 16, 2024, 12:11:16 pm
content: Quote from: DaneLaw on June 15, 2024, 11:12:45 pmI bought it from Elfa Distrelec. Funny you should mention if it had been a return item, I did wonder if it had been opened before when I unpackaged it, there was something.. but everything seemed well packed inside.Regarding the banana jacks, I wasn't quite sure I understood the question, but with threads the outer diameter is 8mm (see pic). Feels pretty solid.The knob that is screwed on also feels decent. Weighs in at 27g on my generic kitchen scale.

author: Martin72
author_rank: Super Contributor
timestamp: June 16, 2024, 12:26:54 pm
content: Every DC load or power supply unit should have such combined 4mm/screw terminals.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 16, 2024, 06:31:36 pm
content: I wonder if something else is up with this unit. On the back, it has a BNC out to connect a scope. From the manual: "Connect an external voltmeter or oscilloscope to display the input’s current."I've never used such a feature before and I couldn't find anywhere what it's supposed to read, but I assumed maybe 1V per amp or something? Anyway, its output is a third of that; 333mV per amp (on scope set to 1X = 1M input impedance). Is that normal? I've tried two different cables, same result, and double checked that my scope is not defunct.Am I doing it wrong?

author: nctnico
author_rank: Super Contributor
timestamp: June 16, 2024, 06:37:12 pm
content: Quote from: mvno_subscriber on June 16, 2024, 06:31:36 pmThe Tonghui manual says it is a 0V to 10V output with 10V being full scale. So if the range (full scale) is 30A then the output will be 10/30 = 333.3mV/A which is exactly what you are measuring.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 16, 2024, 06:49:01 pm
content: It shows 333mA regardless of range (3A/30A). But clearly, 333mV per amp. I guess that's ok then. Is such a weird scale common on these kinds of instruments?

author: nctnico
author_rank: Super Contributor
timestamp: June 16, 2024, 07:15:49 pm
content: Quote from: mvno_subscriber on June 16, 2024, 06:49:01 pm0V to 10V is a common output range for monitoring / control purposes. But you can choose a custom probe attenuation factor to compensate on an oscilloscope. More advanced multimeters also allow to use math to scale a reading.

author: Martin72
author_rank: Super Contributor
timestamp: June 16, 2024, 09:06:15 pm
content: Quote from: 2N3055 on June 15, 2024, 11:08:04 pmWith ceramic capacitors, you can try to replace them with MIL types - under no circumstances should you blindly replace them with supposedly better film types."Singing" electrolytic capacitors:Anyone who has always wondered why many (switching) power supplies have their electrolytic capacitors glued to a mostly white viscous mass, well this is the reason.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: June 16, 2024, 10:35:22 pm
content: Quote from: mvno_subscriber on June 16, 2024, 12:11:16 pmYes, the circumference of the 4mm socket.6mm -4mm = 1mm sides.8mm - 4mm = 2mm sides.If its Elfa Distrelec Norway, then contact them and explain the whine-issue, and your concern if itis a brand-new unit, and you wanna return it for another..One of the benefits of purchasing from local resellers.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 18, 2024, 09:46:57 am
content: A quick update: I contacted Elfa yesterday, and today they're sending a replacement unit.This is why I always buy big things from local sellers, even though it sometimes is a bit more expensive (which, in today's world, it seldom is anyway).Crossing my fingers the new unit is better. Will come back to this thread when I've installed the new one.

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: November 05, 2024, 08:33:09 am
content: Realized I hadn't posted anything here; I haven't had the opportunity to test the load thoroughly enough. I've only used it for testing power supplies and discharging batteries so far.What I can say is that, with regards to ripple, it self reports a ripple of about 5mVpp. When analyzing with a scope, it seems to be about 3-10mVpp depending on the circumstances. I suspect the last digit on the display of the load has limited precision.Just thought someone might find it interesting.

author: nightshift8000
author_rank: Newbie
timestamp: January 22, 2025, 10:03:33 pm
content: Quote from: mvno_subscriber on June 18, 2024, 09:46:57 amHi,I'm currently considering buying a 8550, so I am wondering if the replacement unit also had the noise issue? Can you share your experiences?Thank you

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: January 23, 2025, 09:11:00 pm
content: Quote from: nightshift8000 on January 22, 2025, 10:03:33 pmThe replacement unit didn't have the noise issue, so I'm happy.In general, the unit is relatively quick to start up (roughly measured 11 seconds, which I've understood is good compared to the competition), the display is bright and very readable. Menus are nothing fancy, but very responsive, no input delay. Numbers are easy to read, menus are *mostly* self explanatory (I had to read the manual to understand how it saved my settings in between uses, but apart from a few quirks it's very ok).You can choose between using a wheel to move and adjust parameters, or by keying in exact numbers. I use both.I haven't tried using USB or remote control. I've used it for testing power supplies and batteries. It has a decent set of options for my use, and plenty for future endeavours.All in all, I enjoy this piece of machinery! If there is any specifics you'd like to know, I'd be more than happy to check it out for you.