Looking for a DC load - Page 1
Forum section: electronics / testgear

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 08, 2018, 10:02:49 pm
content: The time has come for me to look into purchasing a DC load. I've always been enamoured with the Maynuo models, as they seem to provide fair quality for a reasonable price. Normally I'm hesitant to hook up unknown Chinese designs to mains, but I feel the Maynuo models have been proven to be reliable. Looking at the current range of Maynuo offerings, something like the M9711 or M9811 seems to be interesting.However there are two issues that lead to me to looking at other alternatives. Most Maynuo models only go up to 150V. Normally I don't work with anything near that, but I can imagine wanting to work on nixie tube power supplies in the future. Considering these are typically 160V to 170V, the aforementioned models won't do. The M9812B solves the voltage problem, but this doubles the cost of the unit and I'm not sure the added benefit is worth that.Another quibble is that the models don't speak SCPI, but Modbus instead. Even though I could probably figure out how to get that working, it'd be easier to have something that just speaks SCPI. It's my intention to also use the unit in an automated testing setup, so having a way for the load to talk to a computer is important. The Maynuo models are supported by LabView, but I currently prefer to use Visual Studio to cobble together scripts.I've looked at the Rigol loads, but I don't think they're mature enough to be real contenders. Other options are much more expensive and that's more than what I would want to spend on a DC load right now. I looked at Arrow loads, but I'm not entirely sure of their construction and reliability. Maybe the wisdom of the forums can help me find a suitable device for me needs.*3,5 digit or better on voltage and current*SCPI*200V or higher should be enough for nixies?*Fair quality and doesn't burn my house down*Ideally near 300 euro, say 500 euro max*Available in EU region, importing should not be an issue

author: SWR
author_rank: Regular Contributor
timestamp: April 09, 2018, 08:26:41 am
content: How about $42?https://www.aliexpress.com/item/150W-DC-Digital-voltmeter-Constant-Current-Electronic-Load-200V-20A-Tester-Discharge-meter-car-battery-Capacity/32822372034.html?spm=a2g0s.9042311.0.0.A1xP2J... allthough it's some-assembly-required (I had to 3D-print my own housing for it, but it works as advertized).

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 08:42:01 am
content: Quote from: SWR on April 09, 2018, 08:26:41 amNo SCPI means no integrated testing. It's also a bit more hobby grade than what I'm looking for. I've looked at a ZKE EBC-A05+ too, but I think I'd rather spend a bit more on something I can depend on a bit more.

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 09:14:53 am
content: Quote from: Mr. Scram on April 08, 2018, 10:02:49 pmI am afraid that name of such DC load is "Unobtainium". In case it is just for hobby, you shall lover specs. If it is money-making instrument, then you shall reconsider price limit. I would go for one of Maynuo models you mention. In EU region also check B&K Precision offering.Arrayand tekpower.us has some "good specs, low price"DC loads, but I have no idea how good they are, nor is there any shop selling them in EU.

author: ElectronicCat
author_rank: Regular Contributor
timestamp: April 09, 2018, 10:24:56 am
content: You might be interested in a similarthread I started on the topic. I eventually resorted to building my own based on a design byScullcom Hobby Electronics. The version I built only goes up to 100V/9A but you could probably modify it to do a higher voltage relatively easily. It ended up costing me about £100 in parts plus another £100 for the PCBs and various hardware (heatsinks, connectors, enclosure, power supply).

author: Performa01
author_rank: Super Contributor
timestamp: April 09, 2018, 01:22:08 pm
content: Array 3710A, 3711A; 0-30A, 360V, 150/300W.I've had my department at work purchasing them a couple years ago and we've never run into issues, so I can recommend them.Btw, Gossen Metrawatt sells them as SSL150 and SSL300.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 01:39:00 pm
content: Quote from: Performa01 on April 09, 2018, 01:22:08 pmAre those the same units as Gossen Metrawatt sells or are they cosmetically very similar? Because I wasn't too sure about the brand, but if the former is true that seems to be a stamp of approval.Of course, they look like they got run over but something's got to give. I can't quite find what protocol it speaks, I'll need to investigate a little further.

author: BillB
author_rank: Unknown
timestamp: April 09, 2018, 01:48:35 pm
content: If you are looking at Array, check out the "new?" 3715:http://www.array.sh/yq-3715E.htmI almost pulled the trigger on this one, but scooped up an Itech 8511+ for a good deal. Had I to do it over again, I probably would have given this one a shot.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 01:51:27 pm
content: The Gossen Metrawatt have what seems to be a proprietary but well documented protocol. I'm not sure the Arrays are exactly the same.https://www.gossenmetrawatt.com/resources/la/ssl/ssl-sb_gb.pdf

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 01:55:40 pm
content: Quote from: BillB on April 09, 2018, 01:48:35 pmThat one explicitly does speak SCPI and also has an excellent voltage range. It looks like a turd compared to many other units, but I guess it's not a fashion show. It looks like it's a proper contender.

author: BillB
author_rank: Unknown
timestamp: April 09, 2018, 02:00:45 pm
content: Yeah, I don't know what it is about DC loads, but UI doesn't seem to be at the top of the list for anybody making one, except I guess for Rigol, but then again their UI is.One other point, is that the Arrays are a little more compact, size wise. It was a factor for me, as my bench is space limited. The Maynuo/ITechs are a little on the long side.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 02:59:17 pm
content: How relevant is remote or four wire sensing? In hindsight it's the one thing my power supply doens't have that could have been nice, though even very serious tools don't seem to bother with it.

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 03:07:28 pm
content: Quote from: BillB on April 09, 2018, 02:00:45 pmSeems, this is some kind of curse for electronics manufacturers. Usually you get only one of: 1) good electronics & function 2) good software & UI 3) good look. There's indeed exceptions but unfortunately they are not so common

author: BillB
author_rank: Unknown
timestamp: April 09, 2018, 03:16:01 pm
content: Quote from: Mr. Scram on April 09, 2018, 02:59:17 pmOh yeah, forgot about that. I don't think that Array model has remote sense, which of course, might be important to you depending on your use case and how accurate you want your measurements. The Maynuo/Itechs do have remote sense, which I must say, is a nice feature.

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 03:19:54 pm
content: Quote from: Mr. Scram on April 09, 2018, 02:59:17 pmFor DC load I would say remote sense is a must. If you work with hi-power logic (boards) that can draw significant current, then remote sense for power supply will not hurt as well. For 60V 2A supply I would not bother about remote sense, but I would definitely get 30V 20A supply with remote sense. My 2 cents.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 09, 2018, 03:30:23 pm
content: Quote from: ogden on April 09, 2018, 03:19:54 pmYes, it seems to make more sense with more current. My most powerful power supply can provide 10A at 30 volt or 5A at 60 volt with the two channels combined, but I'm typically nowhere close to that. It's mostly microcontrollers and other frugal stuff, though my interests may very well shift. I can see myself working on something like motor controllers. I could of course always add another power supply.

author: nctnico
author_rank: Super Contributor
timestamp: April 09, 2018, 04:12:56 pm
content: Quote from: Mr. Scram on April 09, 2018, 02:59:17 pmRemote sensing is only necessary if you need the load to measure the voltage accurately.

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 04:55:38 pm
content: Quote from: nctnico on April 09, 2018, 04:12:56 pmI doubt you want to measure voltage inaccurately.Definitely you want DC load to show correct power dissipated, but in case you have let's say 10A current, you could lose quite lot in the leads. In result DC load says it is 20Watts, but together with losses in the leads it could be even 21W or whatever. Obviously your efficiency calculation will be way off. So you shall measure actual voltage on your supply terminals, recalculate power. What if you shall do measurements for range of input voltages and output loads? In result your programmable DC load is no better than those chinese loads for 20 bucks because you are doing everything with your multimeter and calculator anywayp.s. Perhaps DC Loads w/o remote sense have lead resistance correction function, but I have no idea.

author: BillB
author_rank: Unknown
timestamp: April 10, 2018, 01:41:40 am
content: I'll also add that my ITech 8511+ supports both "frame" and SCPI protocols, but the accompanying software doesn't use SCPI, and I've haven't found much more documentation about the interface. Might be worth investigating if you're considering the ITech variants.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 10, 2018, 01:32:52 pm
content: Quote from: BillB on April 10, 2018, 01:41:40 amThe B&K website tells me that Itech is somehow associated with them or a subsidiary, which isn't bad news at all. The manual does mention SCPI, but leaves the exact commands undocumented. I don't think SCPI is standarized enough to just be able to jump in. Let's see if I can dig up more.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 10, 2018, 01:49:03 pm
content: Quote from: nctnico on April 09, 2018, 04:12:56 pmThat's the idea. I want to initially do efficiency tests without mucking about too much with additional multimeters. In hindsight I maybe should have bought a powersupply that is capable of remote sensing. It wasn't exactly the cheapest supply either, but I hadn't really considered it at the time of the purchase.I can always stick a multimeter on the supply end if I'm really worried about accuracy, but I think I'd rather have it sorted on the load end. That eliminates the Arrow units, unfortunately.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 10, 2018, 01:58:35 pm
content: Quote from: Mr. Scram on April 10, 2018, 01:32:52 pmThere we go:http://www.itechate.com/Upload/File/20150806155656.pdf

author: BloodyCactus
author_rank: Frequent Contributor
timestamp: April 10, 2018, 02:02:59 pm
content: Quote from: Mr. Scram on April 10, 2018, 01:32:52 pmB&K just slap their name on the ITech models. B&K didnt design or develop it. ITech are not a B&K subsidiary. B&K also resell ITech power supplies as well.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 10, 2018, 02:10:02 pm
content: Quote from: BloodyCactus on April 10, 2018, 02:02:59 pmSure, but it at least tells me it's not the most questionable Chinese junk around.

author: MarkL
author_rank: Unknown
timestamp: April 10, 2018, 02:54:55 pm
content: I like the Array 3723A. Max envelope is 200V, 30A, 350W. The CC, CP, CR, CV loop response is excellent.http://www.array.sh/yq-3721e.htmIt has sense inputs, and they're on the front which is very much appreciated (but not standard spacing, oops).It speaks SCPI via an isolated RS232 port (no ridiculous converter dongle), and has an optional GPIB card, which I have on my units.The fans are variable speed.The quality is surprisingly good. I bought two of them after evaluating B&K and TTI. The only downside is it's higher than your stated price target @ USD$769. There are some other models in their 372x series at higher and lower prices. Here's one distributor with posted pricing and discounts:https://www.circuitspecialists.com/programmable-dc-electronic-loads

author: BillB
author_rank: Unknown
timestamp: April 10, 2018, 02:58:19 pm
content: Quote from: Mr. Scram on April 10, 2018, 01:58:35 pmGood find.There are some threads here discussing the relationship between BK/ITech/Maynuo. Apparently, the design is from the same primary designer moving to different companies. We have BKs at work, but for the home/hobbiyist, I'm perfectly comfortable with ITech's quality vs BK given it is a fraction of the price.The only problem is that for the voltage, you'd need to step up to the XX12B versions, and the Maynuo is cheaper than the corresponding ITech, but I don't know if the older Maynuo supports SCPI. Now you're in the $500+ price range which opens the door to alternatives like the Array 3723A mentioned by @MarkL.

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2018, 10:56:41 pm
content: Quote from: Mr. Scram on April 08, 2018, 10:02:49 pmIf it is that close, I might put a 40 volt shunt regulator (precision power zener diode) in series with the load and use a small preload to keep the shunt regulator operating correctly with no load from the DC load. Of course now you cannot pull the load down below 40 volts.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 11, 2018, 12:34:27 am
content: Quote from: MarkL on April 10, 2018, 02:54:55 pmThe price of the 200V Array 3722A model actually looks interesting, but that one's much more expensive elsewhere. I don't think I'm prepared to spend >600 euro on a DC load right now.

author: bicycleguy
author_rank: Frequent Contributor
timestamp: April 11, 2018, 01:47:41 am
content: Quote from: MarkL on April 10, 2018, 02:54:55 pmThat looks nice. Trying to research a little found this guy a while back complaining about input capacitance of the Array 3711A:https://www.eevblog.com/forum/testgear/digital-load-recommendations/msg1367620/#msg1367620I don't understand how this could be. How could you do transients and pulses? I realize it's a cheaper model. Any comments?Also looking at the manual for the 372x series I have a question. What happens on your 350W model if you setup say 20A and put in 36V=720W. I think it says it current limits after a time period? What does that mean exactly? Can it handle higher watts for a short time?

author: MarkL
author_rank: Unknown
timestamp: April 11, 2018, 05:51:17 pm
content: Quote from: bicycleguy on April 11, 2018, 01:47:41 amThe 3723A has 2.2uF in series with 3 ohms across the terminals (measured with an LCR meter; I didn't open the unit). It hasn't gotten in my way for anything I needed. However, if for example, you were doing CV transients with low load currents it could be a factor.The 150uF forrestc is mentioning in the 3711A is approaching two orders of magnitude larger. I would probably have his same complaints in scenarios with rapidly changing voltages across the input terminals. If you were doing purely current transients/pulses with little to no change in voltage I would think the input capacitor would not be a major factor.In that thread they are also saying the 3711A is a rebadge. I don't think the 3723A is, or at least I've never seen one branded differently. It seems to be a new/different design than the 371x series.QuoteA quick test with a 60V 9A supply shows that it will sustain 369W for at least 3 minutes (that's how long I waited), and anything at or above 370W for 5 seconds with current limiting to keep it under 410W. After 5 seconds the overload protection turns off the input and needs to be manually reset.But I should add this is hardly an exhaustive test and there may be other edge cases on how it decides to do the protection.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 11, 2018, 05:53:17 pm
content: Quote from: David Hess on April 10, 2018, 10:56:41 pmThat's an interesting thought. I haven't been able to come up with another case the past few months that requires a higher voltage and I doubt I'll be deep into nixies any time soon. The solution is a little finicky, but it does mean buying an affordable load without worrying too much about edge use cases that are out of reach.

author: David Hess
author_rank: Super Contributor
timestamp: April 13, 2018, 08:39:37 pm
content: Quote from: Mr. Scram on April 11, 2018, 05:53:17 pmIt is what I did in the past when faced with the same conundrum. Ordering $20 worth of big zener diodes or power transistors (or both) to make what is essentially a shunt voltage regulator or precision power zener diode was a lot more palatable then buying or even renting a DC load for what was likely a one time test.If the required power dissipation (of the shunt) is not too high and the precision is adequate, then some inexpensive power zener diodes may be suitable. If high frequency performance must be preserved, then bypass the zener diodes or precision shunt regulator with capacitors.

author: bicycleguy
author_rank: Frequent Contributor
timestamp: April 13, 2018, 09:56:42 pm
content: Mr Scram,Don't want to hyjack your thread but you seem to be vague about what you want and I am clueless so would an e-load work for these use cases or more specifically how good and what spec e-load:1. Making VI curves of a 300W max, 40V open circuit, 9.7A short circuit solar panel.2. Designing, testing and debugging a MPPT (max power point tracking) DC-DC converter for above panel.For the MPPT task would it introduce more problems for a noob than using resistor banks?

author: woody
author_rank: Frequent Contributor
timestamp: May 02, 2018, 12:00:16 pm
content: Quote from: Mr. Scram on April 11, 2018, 12:34:27 amYesterday I got a 3721A fromhttps://labtronix.co.uk/drupal/shop/electronicload/el3723aWith USB interface, shipping and Paypals' stiff exchange rate it translated to €589,- ex. VAT.If you leave off the USB interface I recon that the 3723A will cost about the same, just under €600,-Not affiliated and I do not have the device yet, so cannot tell you more than that he guy running the shop is responsive.

author: colorado.rob
author_rank: Frequent Contributor
timestamp: May 07, 2018, 03:34:02 am
content: Who sells itech in the US? I'm looking for the IT6400 series, and only seen them available in Europe and AU.

author: BillB
author_rank: Unknown
timestamp: May 07, 2018, 04:00:06 pm
content: Quote from: colorado.rob on May 07, 2018, 03:34:02 amTequipment.net carries ITech but I don't see the 6400s. Maybe contact them to see if they can get one?