1 V DC 2 Amp possible circuit ? for low resistance testing  - Page 1
Forum section: electronics / general

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 08:03:15 am
content: HelloSome micro ohmmeter deliver low voltage and high current as Valhalla 4300 which propose 200 mV 1 Amp and 20mv 10 Amp voltage to limit power in the resistorQuestion : Does some one have already built a low voltage as 1 V or lower voltage with 2 Amp current or some thing similar base on 5 V or 12 V DC imput ?RegardsOS

author: kripton2035
author_rank: Super Contributor
timestamp: October 16, 2025, 08:51:03 am
content: do you need microohm detection or milliohm is enough even sub milliohmif so you can build yourself a shorty-with-display, link in my signaturea really handy device to detect short circuits, can detect one in a millimeter range to 0.1mΩ and around.oh and the device outputs half a volt and 40mA to measure the device.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 09:32:09 am
content: HelloThankI search a way to reduce the power in my measuring resistor , right no I use a 5 V DC PSU , by using a 1V or even 2.5V I can save on dissipated energy in the resistorRegardsOS

author: Hedrix
author_rank: Contributor
timestamp: October 16, 2025, 09:45:33 am
content: What about using short current pulses to limit Power/Self-Heating - switching a current is a lot easier than trying to build a specialized source.? This way, you can measure the resistance before any thermal effects kick in. No need for specialized sources. And if you measure with the direction of the DUT beeing reversed between measurements, you'll also get cancellation of errors due to thermal EMFs. Could also use two synchronized, resonably fast ADCs (AD717x for example) with a well-known Shunt to measure both current through, and voltage over the DUT -> current source can be even simpler.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 11:42:25 am
content: Quote from: Hedrix on October 16, 2025, 09:45:33 amHelloYes regarding the pulse current as I already use it butCalibration lab use very low voltage in the aim to match the allowed maximum power of the standard resistor as 1 Ohms for exemple , even if a shunt are used with higher currentValhalla use very low voltage too .That could be interesting to know how , which schematic ?? I suppose that pure discrete circuit .RegardsOS

author: Jeroen3
author_rank: Super Contributor
timestamp: October 16, 2025, 12:30:14 pm
content: The GW Instek GOM-805 has PWM drive mode to reduce self-heating of the resistor you are measuring.But it cannot go up to 2A, only 1A for < 50 mOhm. It;s open circuit is 6V iirc.The trick is that your question is a bit odd. As most will configure a current range an then see what voltage appears.Not "have a low voltage".You can easily do this with any meter by choosing a larger range (lower current).

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 12:44:22 pm
content: Quote from: Jeroen3 on October 16, 2025, 12:30:14 pmHelloMy question is linked to these tables as the maximum power of the resistor is linked to the voltage and the current , that sound logical to use a lower voltage level to keep the power low ? in most case calibration power is 10 mW .RegardsOS

author: zlymex
author_rank: Frequent Contributor
timestamp: October 16, 2025, 04:00:29 pm
content: There is no need to explicitly limit the voltage if a proper current source is used for a given standard resistor.A DIY current source or a normal PSU won't fit the job because of the lack of current reversal.Valhalla 4300C is not suitable for measuring resistance standards either.For hi-precision test, use resistance meters such as RM3545.For ultra-precision test, use a DCC bridge, or with a current extender for low ohmetic resistors.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 06:22:07 pm
content: Quote from: zlymex on October 16, 2025, 04:00:29 pmHello , ZylmexI agree regarding the equipment requested for std resistor , NIST or other labs doc describe these equipements which are $$$$$ , but that don not solve the power ( Watt ) which need to be controled and low as possible to avois thermal problema very basic calculationif I use 5V DC in a 1 Ohm resistor I generate 5 W under 1 Ampif I use 1 V DC in a 1 Ohm resistor I generate 1 W under 1 AmpI don t measure electronic components I measure materials , less I have energy less thermal problems I have .RegardsOS

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 16, 2025, 06:54:39 pm
content: QuoteIt’s simple to build a reasonably precise current source or sink, using a mosfet and an adjustable voltage reference.(Simplest can be 4041+PMOS source, or 432+NMOS sink)That drops 1.25v across the sense resistor, you can add a low offset opamp to reduce that.For for measurements the average power is not high, so a moderate heat sink is fine at 5V.You can switch for say 50mA 100mA 500mA 1A 2A

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 07:18:08 pm
content: Quote from: PCB.Wiz on October 16, 2025, 06:54:39 pmHelloI have a current source quite descent , my concern is to locate a low voltage DC 1 V ? 2V PSU ? able to deliver 2 amp to feed the mosfet , the mosfet is driven by an Op Amp and a voltage ref as in any voltage to current converter r, right now I use a 5 v DC source .I have searched on google there is a batch of voltage PSU over 3V but underRegardsOS

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 16, 2025, 09:19:55 pm
content: Quote from: Overspeed on October 16, 2025, 07:18:08 pmif you can find 3.3V, use those.You may be able to adjust that down with a simple PCB mod, but your current levels are not high here and 6.6W at 3.3V is not a lot of heat to spread out.

author: mikerj
author_rank: Super Contributor
timestamp: October 16, 2025, 09:25:11 pm
content: Quote from: kripton2035 on October 16, 2025, 08:51:03 amVery neat little unit. I have a question about the transistor Q1 that powers the R1 to R3 resistor chain; it appears to get enabled during initialisation and never turned off. Was the plan to only enable it during ADC conversion to minimise the current draw on the battery?