Battery simulators NGM202 vs BCS6401 - Page 1
Forum section: electronics / testgear

author: Geofrey
author_rank: Contributor
timestamp: June 13, 2024, 11:34:49 pm
content: Hi,I've been around here for quite some time (at least 5 years according to my own profile) but this is my first post. I usually get all the info I need and much more from existing posts, but not this time.I design embedded products with lithium batteries, DC-DC converters, MCU and various energy sources. I am not involved in production, but I also do after sales services like diagnosis and repairs. So far I've managed reasonably fine with entry and (lower-)mid level equipment but I am looking to simplify my test setups and gain time during development, test and validation. My bench setup is currently :-PSU : Multicomp MP710087. That's a Farnell re-badge of the Owon P4603. I found that out when I was looking for a way to 0 the current readback. It turns out even maxing out the calibration setting, the best I could get is a ~80mA dead zone, as I need to draw 81mA from the PSU for it to regulate to a 1mA setting and/or read 1mA. That's a serious inconvenience and would not recommend this PSU. I also have a couple more very basic PSUs, one linear, one switching.-electronic load : Maynuo M9812. It has an approximately 1.6mA offset, but I am happy with this instrument-DMM : BM789, UT191, EX330, a couple more basic ones, a couple of current clamps-scope : DS1054Z-time reference : Leo bodnar mini GPSDO. I am using it for RTC trimming.So what I want my future new expensive piece of equipment to do ?- Allow me to test hardware and software for charge and discharge at various battery/voltage level, both at stable and dynamic voltage SoC, repeatably, without spending hours getting batteries to necessary level (so yeah a battery simulator)- Safely power up early stage prototypes at low current < 10 mA, or whatever is enough to turn on the MCU but very unlikely to damage anything- Do the first power tests with confidence that the glitches and oscillations are not PSU induced. I spent way too much time debugging early software and hardware that turned out perfectly fine when run with batteries instead of my PSUs.- Not worry about burden voltage or cable losses, not doing test lead swaps on powered EUT to be able to measure from A to µA when doing low power mode tests. Nor jumpstart the board with a cell and flying leads while the electronic load is connected to the battery terminals for charge tests- Be PC controllable for automated tests, including hardware in the loop software test. Right now, due in part to long battery cycle times, doing a good (but not complete) coverage for software validation on actual hardware takes a week, running in parallel in 4 samples of each product variant.- Last for a long time, if the equipment is good, it is likely I will keep it for 20+ yearsI've narrowed down my search to the R&S NGM202 and the B&K BCS6401.The BCS6401 can sink 10A vs 6A for NGM202 and is substantially cheaper. Both points are nice but not essential.The NGM202 can source 12A vs 10A (I don't care at the moment), has better resolution (but not really better accuracy), seems a lot better at logging (500Ksps vs 30Ksps, 800Mo internal memory + external memory ability vs 1024 sample points), has touchscreen and eyecandy UI, a free PC software that someone here described as outdated and incomplete vs no PC software at all, but both take SCPI commands anyway.Based on specs I am leaning towards the BC6401, but I have found 0 review, teardown or anything. I am also wondering if I would miss any of the things the NGM202 brings over. I guess the 500ksps sampling would be better to find glitches and bugs or do MCU run/sleep time analysis, but would not help with fine analysis of 100KHz switching DC-DC converter. And I should be able to add a Joulescope to the BCS6401 for even faster sampling at 2Msps and 300KHz bandwidth, at a slightly reduced accuracy. Anyway, is anyone with experience with battery simulators willing to share their thoughts and advice ? That's my first time spending that much on TE, so I am not sure what to expect.I also considered but eliminated :Keysight E36731A : the battery simulator part is a nearly 1000€/year PC licence. Supposing they even maintain it for 20 years that's 20k€ extra. No thanks.Keithley 2281S : only 1A sink. I can live without the battery simulator sinking the 8A max I am doing up to now, but this is too limiting.GW Instek PPH-1506D / PPH-1510D : 3.5A sink per channel, but only CH1 can simulate batteries so no paralleling to get higher than that, slower regulation, a bit less accurate, less expensive but not exactly cheap either, so buy cheap buy twice is not an option.I attached a brief comparison table on the points that matters to me.Cheers

author: pdenisowski
author_rank: Super Contributor
timestamp: June 14, 2024, 09:07:13 am
content: Hi Geofrey. If you have any specific questions about the NGM, please let me know. I've also made a couple of videos about it, and they cover battery simulation and fast logging as well.Quote from: Geofrey on June 13, 2024, 11:34:49 pmThe NGM has a VNC or web based remote user interface: there's no special software for running or controlling it. We do provide some GUI based scripts that extend the functionality of the NGM for certain special applications, but all of the base functionality is controllable remotely via a web browser or VNC client. If there is an issue with any of the scripts, please let me know and I'll talk to the developer directly (he's very responsive to change requests).https://www.rohde-schwarz.com/us/application/ngm200/Obviously I'm biased towards my own company's productsbut having used it extensively, I do think the NGM would meet your requirements very well.

author: Geofrey
author_rank: Contributor
timestamp: June 14, 2024, 11:37:19 am
content: Hi Paul, thanks for your reply.Do you know what is the bandwidth in fast log mode ? Does fast log have an impact on the quoted accuracy numbers ? Does it add noise to the measurements ?If I understood your video well, fastlog through SCPI sends the binary data (that's already something like 16 Mo/s of raw data I guess). How does decode to .csv works in that case ?I noticed that every battery simulator is working on an open voltage + internal resistance model. This is good enough for most applications in the 10-95% SoC range (at least for lithium based batteries which I am the most familiar with) but on lithium cells (or at least the one we use), the voltage after stopping a complete discharge can significantly creep up for 10+ min. LiFePo can also have a more complex behavior near 100% SoC. Are there solutions for a more realistic simulation at the extremes of battery SoC ? Even if PC controlled ?What kind of delay would be a SCPI loop for implementing a custom model ? A get latest U and I values followed by a set updated U and I targets loop, if it is not something inadvisable or risking to degrade the PSU.I am not sure I will ever have the time to dive into these kind of things, but knowing the hardware is capable of this if the need arises would be nice.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 14, 2024, 02:08:22 pm
content: Quote from: Geofrey on June 14, 2024, 11:37:19 amI'm not completely sure what you mean by "bandwidth", but max logging rate is 500,000 samples / sec (at least that's in units of Hz)Quote from: Geofrey on June 14, 2024, 11:37:19 amNo to both, at least in my experience. I'll ask the product line if we have any numbersQuote from: Geofrey on June 14, 2024, 11:37:19 amIf you're streaming binary FastLog data over SCPI your program will need to do the conversion to .CSV. I can either post or PM you the format and how to convert it - it's pretty straightforward. The other method is to do the conversion on the NGM using the built-in utility and then transfer the csv file.Quote from: Geofrey on June 14, 2024, 11:37:19 amEverything is possible via PC controlAll the battery simulation control parameters and current values can be set/read via SCPI. I'm not sure I entirely understand the scenario, but I think what you're saying is that after the battery reaches some low SoC (and is functionally "empty"), the VoC slowly moves up for a while. In this case, I would simply use SCPI to slowly increase the power supply output voltage. If the supply output voltage became high enough that current started flowing again (monitoring via SCPI), then I would revert to battery simulation again, either with the original model or a different "low SoC" model. Sorry if I'm misunderstanding the question.Quote from: Geofrey on June 14, 2024, 11:37:19 amAbsolutely would not damage or degrade the PSU - lots of customers do exactly this. I'll need to check on how quickly this can be done via SCPI, although I suspect the limitation will be the network (Eth/IP/TCP) and not the instrument.

author: Geofrey
author_rank: Contributor
timestamp: June 15, 2024, 09:33:22 pm
content: Thanks for the detailed answers.By bandwidth I meant like for scopes, which typically have a bandwidth lower than the sampling rate to avoid aliasing. I would like to know if fast log mode is susceptible to aliasing. Or maybe that is not applicable to the logging of a PSU, or the values logged are the average since last log point, can you clarify ?I am pretty convinced the NGM202 is very good, now I need to decide if it 2850 € ex VAT better than the BCS6401

author: pdenisowski
author_rank: Super Contributor
timestamp: June 16, 2024, 10:24:30 am
content: Quote from: Geofrey on June 15, 2024, 09:33:22 pmIt's a good question: I haven't seen power supply logging specified in terms of bandwidth - it's basically simply taking N samples per second and as long as Nyquist is being observed (and I'm sure it is), then there won't be any issues with aliasing. In the specification sheet we specify logging rate and voltage / current measurement accuracy (which is the same as the readback accuracy), so this would necessarily include any other effects as well.*I did some looking around and I couldn't find a benchtop power supply manufacturer who specifies logging accuracy in terms of bandwidth - most also seem to say it's the same as readback accuracy (and several don't specify it at all).

author: Geofrey
author_rank: Contributor
timestamp: October 04, 2024, 08:37:50 pm
content: So I finally went with the BCS6401. Sorry @pdenisowski, the NGM202 looked really nice, but the price and 3+3A max instead of 5+5A definitely played a part in the decision.I did also consider a pair of Otii Ace Pro. I had a nice demo from Qoitech. This seems quite capable also, but the extra software licensing model broke the deal. At least it is quite usable without extra license (that was not the case on the non Pro models) and there is a perpetual licensing scheme available, but the battery simulation software is one of the extras, automation is the other. The battery part I can understand, even if that puts the solution right between the BCS6401 and the NGM202 in terms of cost, but 50€/month or 2500€ perpetual for automation which is something you can relatively easily achieve through SCPI commands on every other instruments is a bit meh. The Otiis also need to be tethered to a PC to work, that can be an hindrance.About the BCS6401, it's not really perfect : ergonomics and usability could be improved. A small non touch screen is not the best. The UI is responsive enough but quite slow to navigate. The worst part is that there is no way to set an arbitrary SoC to go to on your battery profile, neither you can freeze the profile to that SoC. The only option is to reset to the first point of your battery profile. So if you want to simulate end of charge, you need to import a profile starting at 90% SoC and going upwards. If you want to do a full discharge, another profile starting at 100% and going downwards. Want to do a full charge ? Another profile. Work at mid SoC : yet another one. I find that pretty insane.It's also not silent. Okish at low currents but loud as soon as the first fan speed step up, which happen when one of the channels cross 1A.The crossover between low and high current ranges is at 5mA, and it's a 1000x step in current readback resolution. Given that, the readback resolution is a bit poor in the 5 to 100mA range.All being said, I decided to keep it. Having the source+sink capability is really nice, and SCPI commands should let me use some scripts to improve on the usability.I did manage to connect it to HKJ's TestController software. For the moment I did the configuration files for basic readback only. I will push it as soon as I get the time to make it a bit more complete.

author: Kean
author_rank: Unknown
timestamp: October 05, 2024, 01:45:46 pm
content: Congrats on the purchase. Let us know how you find it after you get to know it better.Just for reference, BK Precision products are almost always rebadges. I believe that the BK BCS6401 is a rebadged ITECH IT6412.Seehttps://www.itechate.com/en/product/dc-power-supply/IT6400.htmlI looked at a few options over the last few years, but all were out of my price range. I almost bought a refurbished Keithley 2281S, but missed out after overthinking the purchase.Early last year I managed to snag a 2nd hand Keithley 2306 on eBay at a good price, and I could not get it to reproduce the described fault (over temp warnings). It just needed recalibration, which I did myself. The fans are horribly noisy though, and I've yet to write any scripts to properly simulate battery SoC.On a day to day basis, I use a pretty simple "battery simulator" (2-quadrant PSU) that I designed myself - although that is limited to 9V 1A source, and 300mA sink. It has a SCPI-like USB serial interface, and no other UI other than a couple of status LEDs. Accuracy is pretty low, but it is more than good enough for my typical "long term" testing, and more importantly for automated firmware and manufacturing testing. And it is very cheap to build, so I have half a dozen or so.

author: Geofrey
author_rank: Contributor
timestamp: October 15, 2024, 08:45:44 pm
content: Thanks Kean. The ITECH IT6412 certainly looks very similar, and the series shows interesting different combinations of voltages/currents. And yeah, when you need a fleet of device and have the time for a side project, DIY is compelling. Actually the first electronic project I did was a high current (60A charge, 40A discharge) battery tester/cycler, with the ability to set arbitrary current cycles, to evaluate cells on a realistic use case, including high power regen peaks. Full of flaws, which is not surprising considering it was my first ever electronics design and was self taught on this field. No way I could afford anything off the shelf at that time. I'm still using 25A/25A cheaper BOM derivatives now, 10 years later, 24/24h 7/7d for more basic cycle life assessment of cells following different use profiles.I completed the device file for HKJ's TestController, with enough stuff to do SoC and iR curves with it.Note to users : as is, the 4th command in a row in a script get ignored, unless a delay is added after the 3rd command. For example :Code:=setVoltage(ps,4.2)=setCurrent(ps,1.5)=setResistance(ps,0)#delay 0.5=setOn(ps,1)is ok, but without the #delay 0.5, =setOn(ps,1) is ignored.