Recommendations for lab psu that can sink current - Page 1
Forum section: electronics / testgear

author: Psi
author_rank: Super Contributor
timestamp: August 12, 2015, 09:18:54 am
content: Hey,Does anyone have a recommendation for a midrange lab psu that can sink as well as source current.It needs to go down to 0V and have adjustable current limit.Max current doesn't matter too much, 3A is fine. Even 2A would be ok.Max voltage maybe 20v or so.Any ideas? Would prefer a brand that has at least some reputation as being ok.

author: AndyC_772
author_rank: Super Contributor
timestamp: August 12, 2015, 09:33:18 am
content: If you have the desk space for it, an HP 6632B. They're silly money new, but come up regularly on Ebay.It's 20V, 5A, can sink as well as source, and has impeccable start-up and turn-off characteristics. It's also extremely (electrically) quiet, and has an accurate voltmeter and ammeter built in.

author: tooki
author_rank: Super Contributor
timestamp: August 12, 2015, 09:45:52 am
content: <n00b tangent>Why would one need a PSU that can sink current?</n00b>

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 12, 2015, 09:47:35 am
content: I'm guessing it means act as a dummy load.

author: sorenkir
author_rank: Regular Contributor
timestamp: August 12, 2015, 10:17:10 am
content: Hameg R&S HM8143 (or older model HM8142, less power).Michel.

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 12, 2015, 10:19:37 am
content: Quote from: tooki on August 12, 2015, 09:45:52 amOne good application is to absorb current routed back to the supply via clamping diodes on an I/O pin. For example, good design practice for automotive products is to ensure that any external I/O connections can tolerate being connected to the 12V supply.Another application is to absorb energy from a regenerative ("four quadrant") motor drive when it slows down or rapidly reverses. This is a quite common requirement for servomotor drives.

author: AndyC_772
author_rank: Super Contributor
timestamp: August 12, 2015, 10:28:58 am
content: If a device is powered from a rechargeable battery, and incorporates its own charging circuit, then it's really useful to have a supply which can simulate the battery in both the charging and discharging conditions.For example, suppose you're developing a product that's powered from a 7.2V Li-ion battery pack. You set the 6632B to 7.2V, and connect it to the battery terminals. When you switch on, the product is powered, and the displays on the PSU show exactly what voltage and current is being delivered.Then, connect the external power source which will be used to recharge the battery pack. The 6632B keeps the terminal voltage at 7.2V, but will now sink current instead. Its display shows the charging current as a negative value.

author: w2aew
author_rank: Super Contributor
timestamp: August 12, 2015, 01:22:33 pm
content: Quote from: Psi on August 12, 2015, 09:18:54 amThere are several models of the 2400 series Source Measure Units (SMUs) from Keithley that will sink 3A current - such as the 2420, 2425, 2430 and 2440, as well as the new graphical 2460. Each can operate in all four quadrants (+/- Voltage, +/- Current). They can be setup in constant voltage mode (with current sourcing or sinking and measuring), or constant current mode (with voltage measuring).

author: edavid
author_rank: Super Contributor
timestamp: August 12, 2015, 02:37:39 pm
content: HP 6825A power supply/amplifier is a classic.

author: dadler
author_rank: Unknown
timestamp: August 12, 2015, 04:55:11 pm
content: I have a 66312A, bought for peanuts on eBay.http://www.keysight.com/en/pd-1000001616%3Aepsg%3Apro-pn-66312A/40-watt-dynamic-measurement-dc-source-20v-2a?cc=US&lc=engIt can source (up to 2A), and sink current (up to 1A)--although the sinking of current is not regulated, it is measurable.These were meant as sources/monitors for cell phones and have advanced analysis features-they are almost like a power supply with voltage/current oscilloscope features.I've found mine to be quite accurate/precise in both measurement and power delivery--although I don't use it that often. It has many, many features that are only accessible via GPIB/RS232. I bought it mainly as a curiosity and it's fun to play with.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: August 12, 2015, 05:20:23 pm
content: Gossen Metrawatt SLP and SSP "Konstanter" are very good (switching mode) supplies that work perfectly well as current sinks.The regularly appear at moderate prices on eBay at least here in Germany:http://www.ebay.de/itm/Gossen-Metrawatt-Konstanter-SLP-240-20-Labornetzteil-/131576406262?hash=item1ea290a0f6Then again, in NZ or Oz they are probably not easily obtainable...

author: Kevin.D
author_rank: Frequent Contributor
timestamp: August 12, 2015, 05:25:08 pm
content: HiHow much current sinking might you need ? I read sourcing up to 3A, do you need 3A sinking as well. ?What make/model is your current bench supply since Some makes have an active pull down (Used to discharge any large output capacitor quickly) this can sink perhaps up to few 100mA .Another possibility If your bench supply has Remote Sensing capability then you can try something along the lines of my quick example below. Sinking capability here is limited by power dissipation of Q1, this should work down to a minimum voltage of ~1.2V (the 2 Vbe drops of the pnp Darlington, alternatively you could use a pnp/npn compound pair here (pnp Sziklai pair) to get this down to a min of ~ .6V ).ps(I haven't done spice here but to ensure stability You may need to ensure there is always some small load present on the output by adding a small preload resistor at Rload or in parallel with D2). One obvious thing lacking with this simple circuit is you can't current limit set the current your sinking so it's only good for C.V mode sinking, adding CC sink limit control requires much more circuitry, I wasn't sure if that's a feature you wanted. ?Regards

author: eas
author_rank: Frequent Contributor
timestamp: August 13, 2015, 12:36:32 am
content: I think the HP 6632b was superseded by the 66332a. There may be important differences between the two, but otherwise, looking for both increase your chances of getting a good deal. I got a 6632b for $100, and others have reported similar scores, but I haven't seen a price that good for a couple of months.There are newer Agilent supplies targeting the same niche that come in a narrower, more bench friendly chassis. The 66309, 66311, 66319, and 66321 are available in B and D variants (D has a built in DVM). I've seen working examples go for $200 or less.Keithley also has the 2303 and 2304. I've seen a number go for under $150, and I got a working 2304 for under $100. The front panel display and controls on these are kind of cheap.None of the above come standard with front-panel connections, though I think they are an option on some of the HPs.The keithley SMUs seem pretty sweet, but I doubt they'd fit the midrange PSU price range. I've been keeping my eye out for a used one for a while and only once or twice have I seen a working unit sell for less then ~$2000.

author: Psi
author_rank: Super Contributor
timestamp: August 13, 2015, 01:20:34 am
content: Thanks guys.Min acceptable current is 1A sink 1A source.I don't really want to go 2nd hand.Something in the $400-800 mark is what i'm after.It's main use will be charging and discharging lipo cells to a set voltage. but i also need a 2nd psu so thought i'd kill two birds with one stone etc..

author: eas
author_rank: Frequent Contributor
timestamp: August 13, 2015, 01:50:07 am
content: If you find a new unit in that price range with those capabilities, I'd be interested to know about it.For battery use, search ebay for EBC-A05. They go for under $75. I've got two, one of which has run through hundreds of charge/discharge cycles and hasn't shown any signs of trouble.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 13, 2015, 02:56:35 am
content: To the OP,If you don't care about wasting a little power, you could achieve what you are looking for with a conventional power supply in parallel with a load resistor:The results show as the load is varied from 2A to -2A (Charging) the load on the bench supply is always positive.Otherwise, +1 for HP6632A or HP6632BRegards,Jay_Diddy_B