5A or 10A DC Current Source - Page 1
Forum section: electronics / testgear

author: denbigh1974
author_rank: Newbie
timestamp: August 10, 2015, 10:16:47 am
content: I have to test some 100ADCHall Effect Current sensors which have a window of 1 inch diameter through which to pass the primary cable.All I want to do is check that the sensor output changes when a current passes through the window. I don't need to check the calibration.I can get 10 turns of a 12AWG (4mm^2) cable through the window, so if I can pass a current of about 10A through this cable then I should be able to get close to full scale deflection on the output. (Alternatively, I could use a thinner cable and pass 20 turns through at 5A).Please can anyone suggest a suitable constant current source with a short circuit output of up to 5A/10A? It doesn't have to be regulated.I'm based in the UK and normally buy from RS Components or Farnell. Budget is GBP 200 (USD 300). I am considering a Elektro-Automatik EA-PS 2016-100http://uk.farnell.com/ea-elektro-automatik/ea-ps-2016-100/power-supply-1ch-16v-10a-adjustable/dp/1437540?ost=EA-PS+2016-100This is an expensive solution but I would prefer to buy something off-the-shelf rather than make something.

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 10:20:44 am
content: How about one of these?http://www.banggood.com/CPS-3205-0-32V-0-5A-Portable-Adjustable-DC-Power-Supply-110V220V-p-934530.html

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 10, 2015, 10:30:36 am
content: Quote from: denbigh1974 on August 10, 2015, 10:16:47 amIf all you need to do is make sure their output changes in the right direction by roughly the right amount then how about a bench PSU or a 6V or 12V gel-cell battery and a suitable power resistor (e.g. - 0.5 to 1 ohm, 100 to 200 watts) mounted on a heatsink?

author: denbigh1974
author_rank: Newbie
timestamp: August 10, 2015, 11:31:32 am
content: Quote from: MagicSmoker on August 10, 2015, 10:30:36 amThanks. Unfortunately, I don't have a PSU with a high current output capability. I thought about the battery but then the cost of a lead acid battery plus 10A switch plus the time to assemble a resistor on heatsink plus the requirement to recharge the battery made me lean towards buying a 5A or 10A PSU. I've done the battery method before for higher currents and it works well but doesn't have a great shelf life without a charger. Thank you for the suggestion.

author: VK5RC
author_rank: Unknown
timestamp: August 10, 2015, 11:34:34 am
content: Do you have access to a car, a starter motor often pulls 60-80A?

author: denbigh1974
author_rank: Newbie
timestamp: August 10, 2015, 12:25:40 pm
content: Quote from: BillW50 on August 10, 2015, 10:20:44 amThat looks a good option, Bill, thank you. They are inexpensive. I wonder if you can run two in parallel (through diodes) to get 10A?I will scout around for a 10A unit and go back to your suggestion as a back-up solution.

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 10, 2015, 12:33:07 pm
content: Be aware that many of those cheap Chinese PSU's rated for more than 5A and which claim to do CC require a minimum resistance to work. That is to say, they don't work all the way down to a direct short (going into foldback current limiting instead and/or releasing the magic smoke), so you are back to needing a big honking power resistor on a heatsink anyway.

author: denbigh1974
author_rank: Newbie
timestamp: August 10, 2015, 12:48:16 pm
content: Quote from: MagicSmoker on August 10, 2015, 12:33:07 pmYes, thanks for raising that, it's a worry. I've been searching for product reviews/teardowns to find out about this.I don't know if it applies to the Gopher CPS 3205C (recommended by BillW50) because the reviews I've seen don't put a direct short across the constant current output.

author: KJDS
author_rank: Super Contributor
timestamp: August 10, 2015, 01:17:30 pm
content: I've got a couple of HP6632B about. Old but good for an accurate 5A

author: Fungus
author_rank: Super Contributor
timestamp: August 10, 2015, 01:52:05 pm
content: Quote from: denbigh1974 on August 10, 2015, 12:48:16 pmI've got one of those PSUs, they're pretty good for the money.As noted: Even though it's only a 5A PSU you can pass multiple turns of wire through your probe to get a ballpark figure.If you want to feed the PSU into something then order up a couple of these:http://www.ebay.com/itm/310579716276Put them in parallel, that gives 2 Ohms at 50W. a 5A PSU only needs 10V to do that.PS: They'll get hot - either use a big heatsink or only power it on for as long as it takes to get a reading.Same goes for the PSU; It's passively cooled and not a heavy duty item! Don't expect it to put out maximum power for hours on end (it'll be fine for quick tests though).

author: denbigh1974
author_rank: Newbie
timestamp: August 10, 2015, 02:41:51 pm
content: Quote from: KJDS on August 10, 2015, 01:17:30 pmThanks for suggestion. Will the HP6632B unit need a resistive load like the others or can it output 5A current into a short-circuit?

author: SkyMaster
author_rank: Frequent Contributor
timestamp: August 10, 2015, 02:46:38 pm
content: Quote from: denbigh1974 on August 10, 2015, 12:48:16 pmI have a Gopher CPS-3205 (no "C") and it works correctly with a short on its output; the power supply goes into Constant Current mode, and the current is then as it is set on the current limiter. I tried this by connecting an ammeter directly to the CPS-3205 output.The CPS-3205 is a switching power supply.

author: KJDS
author_rank: Super Contributor
timestamp: August 10, 2015, 03:00:53 pm
content: Quote from: denbigh1974 on August 10, 2015, 02:41:51 pmI've just done a test and it seems quite happy running 5A through a 100mm length of wire.

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 03:32:57 pm
content: Quote from: denbigh1974 on August 10, 2015, 12:25:40 pmYes you can run them in parallel or even serial. Since the outputs are isolated.

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 08:42:21 pm
content: You know another idea, I don't know the resistance you are looking at? But with electronic cigarettes (aka vaping) we use mainly 18650 high drain lithium batteries which cost like 6 bucks each (Tesla electric car uses them too). And we can pull 20A to 25A each safely from them (Samsung 18650 25r are the most popular). And with a 0.15 ohm load one battery will pull 20A @ 3.0v (60 watts). It is a 3.7v battery, but because of battery sag it is about 3.0v. If you are interested to know more about this, just let me know.

author: johansen
author_rank: Super Contributor
timestamp: August 11, 2015, 12:55:33 am
content: 10 amps isn't much for 12 awg cable, why not just use 20+ turns of 14 awg wire?

author: denbigh1974
author_rank: Newbie
timestamp: August 13, 2015, 05:22:42 pm
content: Quote from: denbigh1974 on August 10, 2015, 11:31:32 amThanks to everyone for your ideas.In the end, as suggested by MagicSmoker, I borrowed an old lead acid 2V battery and soldered twelve 4.7 ohm 6W resistors in parallel as my shunt. Managed to get about 50 ampere-turns which was enough to see a deflection on my sensor output.The hardest thing was continually connecting and disconnecting the leads to the battery. I would have incorporated a high current switch if I had time. It's important to keep the contact resistance as low as possible.It's not a long term solution so I am grateful for the power supply recommendations. I will invest in one of these now that I have the luxury of some time to choose.Thanks again.

author: Macbeth
author_rank: Super Contributor
timestamp: August 13, 2015, 06:49:00 pm
content: Quote from: KJDS on August 10, 2015, 03:00:53 pmHeh, I'd just recently fitted my nice new binding posts to the front panel of mine (thanks Kev!) and decided a really clever experiment would be to chuck some fine guage wire to the output and switch it on to 20V @ 5A and watch it glow. Haha. it certainly worked. The hot wire burned a nice little ridge into the red plastic trim on the + output and melted itself inside before expiring in a crinkled death of burned copper wire.So yeah. No problem chucking 5 amps into a load. I would use a 4 ohm load next time. One with a decent heatsink.