REVIEW - Lambda/EMI BOS/S bipolar operational PS or "40 pound OP AMP" - Page 1
Forum section: electronics / general

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 02:34:56 pm
content: I didn't know such a thing existed untilthis postby JackOfVA. His test setup used a Kepko BOP and I googled it to see what it was. A bipolar operational power supply that is 4 quadrant so it can dynamicaly source or sink power. Check the adata sheetout for all this thing can be used for and the specs. I found this one on ebay by searching "operational power supply" and it is new in box with manual and schematics. My second offer of $250.00 was accepted which was about half the buy it now price. EMI is no longer in business but TDK/Lambda service is still aware of them and sent me all the marked up schematics and cal procedures that the techs used on these units. This unit does not have the programming interface card option and even though I have the schematic for it, I dont have the code so it will be easier to drive it with a function generator. That is realy the reason I bought this to begin with, give my function gen some horespower.This unit is capable of +/-20V and +/- 10A Bandwidth 20kHz full power at -3db. slew rate at max load 1.6V/µs 0.8A/µsMore posts with some testing will follow.EDIT: One sold and then I bought the last one.There are2 morenew but without manual and original packaging from the same seller. (remember I only payed about half the asking price. YMMV)Massive original box it came in.Front panel with rack mount ears on... and removed.A 40 pound Op Amp... The only damage was a popped bezel that easily glued back in place.Rear connections cover all available controls.Overall view.Main control board.Back of front panel.Power supply.(2) 40000µF caps.Main transformer.Secondary transformer.Bridge. What are the notches in the caps about?Heatsink and power board.Power board.120mm fan at end of heat sink. Yes it is noisy!fiberglass surround of heat sink for isolation/cooling air guidance.End view of beefy heatsink.AC in, thermal switch, and heat sink isolation block.Virgin manual and schematics.

author: Monkeh
author_rank: Super Contributor
timestamp: November 08, 2012, 02:46:54 pm
content: Very nice.However. Who wants to contribute to the 'Get robrenz a new camera' fund?

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 03:13:39 pm
content: Quote from: Monkeh on November 08, 2012, 02:46:54 pmMy camera is fineyou are seeing extremely bad editing practices on my part on some of the pics

author: saturation
author_rank: Super Contributor
timestamp: November 08, 2012, 03:23:21 pm
content: Wow. Didn't know of such units either, just read the thread and the material here. Most excellent. Great score. It appears very well made, all USA? Making me think reaaaaaaaaaally hardIts versatility is astounding, alas I have a setup doing many of its capabilities with individual instruments, but not as powerful. All through hole construction makes it very serviceable. Looking forward to more details.This is likely a unit that brought up a query on the Array eload thread about using 4 quadrant supplies as an eload, and this unit certain can do.

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 03:37:47 pm
content: That query was me.Yes USA mfg and no unobtanium.Some quick no load tests.currentcurrently the gain setting for external input is 2x Remember its only rated for 20kHz, the 50 and 100 are just to see what it would do. The output starts to have a substantial offset at 100kHz. It also shows some offset at the low millivolt input level.Edit: Blue trace is the FG input to the BOSS, Yellow trace is BOSS output.

author: T4P
author_rank: Super Contributor
timestamp: November 08, 2012, 04:17:33 pm
content: Those aren't notches and they're not caps eitherThose "notches" are probably intentional by the manufacturer so that if it blows it's gonna disperse the energy and not catch fire then blow up, well i'll bet it's a MOV

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 04:27:55 pm
content: TheKepko BOP manualgives immensly more information about considerations involved in using this type of unit than theEMI BOSS manual. These are designed for primarily resistive loads. Driving any significant capacitance or inductance can cause high frequency oscillations. I hope to learn what the tuning differences are on the units sold for inductive or capacitive loads are (not both in the same unit) so I could modify this unit to be switchable for the three modes of tuning.

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 04:32:50 pm
content: Quote from: T4P on November 08, 2012, 04:17:33 pmThey are notches/slots, and they are .01 1.5KV caps across each diode of the bridge. straight from the schematic.

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 04:40:24 pm
content: Quote from: saturation on November 08, 2012, 03:23:21 pmShipping a 50 pound package to the federated states of Micronesia is going to be expensive

author: oPossum
author_rank: Super Contributor
timestamp: November 08, 2012, 05:31:54 pm
content: The notches are a spark gap. Prevents high voltage from damaging the cap. They are (were?) a common ordinary part.

author: SeanB
author_rank: Super Contributor
timestamp: November 08, 2012, 06:12:14 pm
content: Those are spark gap capacitors, designed to flash over at a predetermined voltage. 1.5kV in your case. They are used to clamp transients, though on that bridge they are not much use, probably were a item they had in stock in 100k lots.So now you have a audio amplifier capable of driving a 0.1R speaker load, or a 200W DC servo motor.

author: Monkeh
author_rank: Super Contributor
timestamp: November 08, 2012, 06:23:45 pm
content: Quote from: robrenz on November 08, 2012, 03:13:39 pmAh, so the noise and low resolution are artistic?

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 07:06:54 pm
content: Quote from: Monkeh on November 08, 2012, 06:23:45 pmYes, it requires special techniques like take a high res photo with camera set to available light and tremble when you take the shot. Then slightly rotate the photo in a crap photo editor, crop it, resize it, use MS paint to join two photos side by side, save it as a Jpeg, resize that photo. I think the results speak for themselves,

author: Monkeh
author_rank: Super Contributor
timestamp: November 08, 2012, 07:13:41 pm
content: Quote from: robrenz on November 08, 2012, 07:06:54 pmOkay, opening a new fund: Get robrenz a photographer.

author: robrenz
author_rank: Super Contributor
timestamp: November 08, 2012, 09:29:30 pm
content: Quote from: SeanB on November 08, 2012, 06:12:14 pmNot until I find out what is different on the units made specifically for driving an RL load without oscillating. Ditto for the units sold specifically for RC loads. I don't know what the threshold is for capacitance or inductance on this unit before it causes trouble. The Kepko BOP manual (link in post above) somewhat discusses it but I have not had a chance to try to digest it.

author: JackOfVA
author_rank: Unknown
timestamp: November 09, 2012, 12:24:29 am
content: Nice unit - if I didn't have three Kepco bipolar supplies I would be tempted. And my Kepco fans are loud as well.If you drive an inductive load, adding series resistance will often keep you out of trouble. These supplies are like any op amp and can be unstable with certain loads.

author: poodyp
author_rank: Regular Contributor
timestamp: November 09, 2012, 01:18:12 am
content: I once saw a unit like this (but much,muchsmaller), meant to literally be an "op-amp in a box", complete with a diagram of an op-amp on the front, and binding posts at the + and - inputs, outputs, and offset adjustment.

author: robrenz
author_rank: Super Contributor
timestamp: November 15, 2012, 07:35:37 pm
content: This Agilent power blog entryshows how CV, CC, and CR is accomplished on a electronic load. The BOSS can sink in CV and CC as is, but I will need to add an external circuit to have it do CR. I just need to find how constant power works now.

author: robrenz
author_rank: Super Contributor
timestamp: November 24, 2012, 10:03:26 pm
content: Ok, I tried to be nice and let others have a chance. But I bought the last one for $175.00 and $29.88 shipping. Now I have 400W source or sink that can run in series at 40V @10A or in parallel at 20V @ 20A. The kepko manual covers the connections for series and parallel connections that allow them to behave as a single op amp with one input.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 25, 2012, 02:33:12 pm
content: err Rob... schematics please!nice unit i give you 80% for photography(alot better than "credit")

author: robrenz
author_rank: Super Contributor
timestamp: November 25, 2012, 11:23:35 pm
content: Mecha,I will email them to you. I recieved them in a email from TDK lambda tech and the file is over 3 meg even zipped so I cant post it. I dont think I can split up a single pdf with adobe pdf reader.

author: robrenz
author_rank: Super Contributor
timestamp: November 28, 2012, 12:43:48 am
content: The twin brother showed up today.The top unit is in CV mode sourcing 1A at 0 volts. The current is going thru the fluke reading 1000mA agrees with the source unit readout. The middle meter is reading the source voltage at 0 to 0.1mV and agrees with the source unit readout.The bottom unit is in CC mode sinking 0.9A. at 0.01V (acting as an Eload). The left meter is reading the sinking unit voltage at 0.094V and agrees with the sinking unit readout.I could not figure out how current could disappear so I reversed the roles of the two units and the top unit current readout still agrees with the fluke and the bottom unit still read 0.9A so I just need to recalibrate the meters on the second unit.

author: saturation
author_rank: Super Contributor
timestamp: November 28, 2012, 08:10:31 pm
content: I wish I had the room or less PSUs [ I bought 3 Power Designs precision suppies plus 3 others I already have..] to make room for this but oh well, the BOSS is in good hands! Thanks for waiting. It certainly simplifies having added high power PSU to use and a CC eload to use as needed. Given the specs too it could make for one interesting music amplifier too.Quote from: robrenz on November 24, 2012, 10:03:26 pm

author: robrenz
author_rank: Super Contributor
timestamp: November 29, 2012, 04:53:42 am
content: You have one more PD than I do.Like I need another power supplyMy brain hurts after using one BOSS as an Eload hooked to the other BOSS acting as a power supply. After much head scratching I think i understand. I hooked up one as a CV source and the other as a CC sink and it behaves as expected. Crank in some negative current and it loads the CV source. And like a good CV PS it will deliver the current at almost zero volts. But if I crank the CV supply to the negative voltage quadrant, the current value and direction remain unchanged. If I understand correctly the roles just reversed and the CV BOSS is now acting as the Eload to the CC BOSS. No wonder these things are called bipolar.Now I short the output of a Power Designs 2020 power supply and it takes 1.4mV to drive the full 2A. Then remove the short and set it at zero volts and load it with a CC BOSS at the full 2A and the voltage at the PD output is -0.8mV (suppied by the BOSS?) then dial in 0.8mV on the PD supply and the voltage on the PD output is 0V, seems to make some sense. I am measuring the current with a Fluke 87 and the fluke and the PD current meter agree at this point. Now I turn the current limit down to 1.5A on thePD meterand the Fluke and the BOSS meter stay at 2A. Now the voltage supplied by the BOSS rises to drive the .5A difference.So if I understand, a 4 quadrant bipolar supply can act as an Eload but it is different in that it is a current source and sink where it will pull current out of a supply if necessary to maintain the set current where a regular Eload is only a dynamic resistive load.Feel free to set me straight, I am still trying to digest this.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 01, 2012, 05:23:32 am
content: nice pictures and reviews Rob. this thread is bookmarked for my laterrevisionreferencecheers.

author: Unknown
author_rank: Unknown
timestamp: December 01, 2012, 12:22:53 pm
content: Quote from: robrenz on November 29, 2012, 04:53:42 amElectronic loads can work in constant resistance, constant current or constant voltage mode. Not all loads may have all modes. The main difference between a four quadrant supply (no need to add bipolar, four quadrant already means any combination of neg/pos voltage and current) and electronic load is that an electronic load can't source current or voltage, only sink it. If you short a load, the current will be zero. If you short a four quadrant power supply, it will source the set (negative) current.

author: robrenz
author_rank: Super Contributor
timestamp: December 03, 2012, 07:13:47 pm
content: Thanks Mecha and alm.More tests in trying to understand how the Power Designs PS when in current limit can read less Amps than the in circuit Fluke. Please comment.I take the total test leads and fluke ammeter loop that I am using to connect the PS to the BOSS and short the banana's that plug into the BOSS. I then dial in the compliance voltage necessary to drive 2.000 amps on the PS which is 184mV. So that is the voltage drop of the leads + Fluke shunt. I leave that voltage setting on the PS.Plug those banana's into the BOSS and dial -2.000A in CC mode. Fluke reads 2.0A, PS meter reads 2.0A. Voltage reading at the PS terminals is 182mV and reading at BOSS terminals is 0.0mV. No voltage is being supplied by the load and there is no excess voltage available from the PS because it is set to the exact voltage drop of the test/meter connection. So the BOSS in this state is acting as a close to zero ohm short.Now turn the current limit of the PS down until it reads 1.5A on its meter. Fluke and BOSS still read 2.000A, Voltage reading at the PS terminals is -0.862V and reading at BOSS terminals is -1.039V a difference of 177mV which is the leads/fluke voltage drop. The PS has a diode between + and - output to shunt reverse voltage input which is letting the -.862V pass but the diode is dropping approximately 0.7V itself. To test that I turn the power supply off and drive 100mA into it and the voltage drop across the PS output terminals is 0.700V.Here is my take/guess after experimenting with 2 regular power supplies a diode and 3 ammeters. (It initially looked like I found a way to make current flow bidirectionally thru a diode)When the PS is supplying 2A in CV mode with only compliance voltage the BOSS is sinking 2A and supplies no voltage. The compliance voltage of the PS has the protection diode reverse biased. 2A is circulating thru the PS and BOSS.Now set PS to 1.5A in Current limit mode. PS ammeter reads 1.5A and BOSS and Fluke meter read 2A. 1.5A is now circulating thru the PS and BOSS. but an additional current loop of .5A is now circulating thru the protection diode and the BOSS. The Fluke/BOSS meters are reading the sum of the two loops (1.5 +0.5) and the PS meter is reading the 1.5. The BOSS has to now source the 0.5 amp instead of sinking so the voltage polarity flips to - 0.862V which is the voltage drop of the PS protection diode plus the 177mV needed for the voltage drop of the leads.Is this correct?

author: saturation
author_rank: Super Contributor
timestamp: December 03, 2012, 07:48:23 pm
content: Hi robrenz,Yes, I think so. I haven't commented as of yet as I needed the time to read your setup thoroughly, but in general, and depending on what your 4Q PSU is designed to do, the PSU could provide the balance of current that the DUT does not provide to insure the dialed in current remain constant. However, you may be able to defeat it so you can sink purely from the DUT. It can create a bit of a headache if you want to determine a DUT's real capabilities, without the PSU compensating. For example to test a battery's AH, once the knee of the discharge curve occurs, which signals a rapid deterioration in output current, the PSU may begin charging the battery at that point, when you really want it to fail. Also, an eload can be programmed to terminate the test and disconnect the DUT once a low-end cutoff voltage is reached, and you'll have to figure a way to configure a 4Q supply to do the same.Quote from: robrenz on December 03, 2012, 07:13:47 pm