Meter to record quick current spikes - Page 1
Forum section: electronics / general

author: Veketti
author_rank: Regular Contributor
timestamp: January 23, 2024, 09:22:10 pm
content: Dear All,Is there a meter which can record sudden current spikes in milliampere range in DC? For example I want to measure the peak current some component draws when it powers on. Or would it work by having known resistor in series and using scope two channels to measure voltage drop?What about calculating battery life from a gadget you design and which is in sleep most of the time so current consumption varies dramatically. You have current peaks etc. How would you measure how many mAh, it draw in eg. one hour or something which you could use to calculate how long the batteries last?Thank you in advance

author: bastler59
author_rank: Contributor
timestamp: January 23, 2024, 09:47:02 pm
content: Power Profiler Kit II from Nordic maybe can do this job. You can get it from Digikey, Mouser etc. for about 100 € (if it's not sold out). But max. voltage is 5 V!

author: delvo
author_rank: Contributor
timestamp: January 24, 2024, 01:45:30 am
content: Sounds like the job for an oscilloscope with a current sense resistor

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2024, 01:47:09 am
content: https://www.joulescope.com/

author: lugaw
author_rank: Regular Contributor
timestamp: January 24, 2024, 02:34:33 am
content: HP 66311B Mobile Communication DC Source

author: faststoff
author_rank: Contributor
timestamp: January 24, 2024, 08:45:26 am
content: +1 on the Joulescope! You will never regret buying one of these if transient currents are a thing you are interested in. The SW is amazing and the auto-ranging resistors ensures you can fully capture <uA sleep currents to 100's of mA active currents with us resolution!

author: selcuk
author_rank: Frequent Contributor
timestamp: January 24, 2024, 08:45:49 am
content: You can measure the current to calculate maximum and minimum powers. But I can recommend other methods to estimate the battery life of a low power device. These devices may consume below 1uA while sleeping and goes up to 10s of mA while reading sensors or transmitting signals. More than 10000 of dynamic range. So it is difficult to measure current, time and pulse shapes accurately.1. Use a super capacitor to measure and calculate the average consumption.I assume your circuit voltage is 3.3V. Make sure you have a 5V capacitor so you can use it on a 3.3V circuit with a safety margin. You need to charge the capacitor with a 3.3V power supply about 2-3 hours. Be careful about the polarity. Plug (+) to 3.3V, (-) to GND. It will charge up to 3.3V immediately when you plug it but due to its internal resistance it won't be close to 100% charge. So after leaving the capacitor connected to the power supply for 2 hours, measure the voltage to be sure it is 3.3V. But don't leave the multimeter connected. It will drain it quickly.Then connect the capacitor to the circuit. Run the circuit with the typical scenario. Then leave it for a few hours. I recommend testing at least 24 hours, but I don't know whether it lasts that long, at this moment. After running i.e. 3 hours, measure the voltage on the capacitor. To calculate the estimated years for a given battery:(battery_capacity/((initial_voltage−last_voltage)*capacitor_capacity/3.6/test_hours))/(24*365)For example, assume 1000mAh battery, 3V to 2.5V voltage drop in 14 hours and the test capacitor has a capacity of 5 Farads:(1000/((3−2.5)*5/3.6/14))/(24*365) = about 2.3 yearsThere is also a leakage from the capacitor. You can repeat the same test without connecting your circuit to the capacitor. This will show the capacitor leakage. You can optionally skip this and use it as a safety margin about the battery capacity.2. If you have more time, use a smaller capacity battery having the same chemistry. If you are using CR2032, you can test the circuit with a CR1216. There is a 10 times capacity difference. If it runs more than a month, you can estimate about a year with the original battery.

author: Berni
author_rank: Super Contributor
timestamp: January 24, 2024, 10:22:03 am
content: I also recommend the Power Profiler Kit IIhttps://www.nordicsemi.com/Products/Development-hardware/Power-Profiler-Kit-2It gives you similar functionality than the Joulescope of being able to measure from nanoamps to miliamps with tight time resolution and a live graph, accumulates consumed charge etc... However it costs less than 1/10th the price of the Joulescope. Sure the Joulescope is an even better piece of kit, but not to the point where it is worth paying 10x the price, especially for a fairly specialized tool like this that you are not going to be using all the time.The running it from a known size capacitor method is also a good poor mans way of doing it. The low power devices can run quite a while from a capacitor, so you just measure a cap voltage at the start and at the end to find out how much charge was consumed. The thing to watch out for is the dielectric absorption of electrolitics or supercaps, due to this their voltage will sink a bit after charging and climb back up a bit after discharging, so you have to make sure you measure over a large enough voltage range to not have these effects cause too much error in your results.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: January 25, 2024, 09:15:36 am
content: DMM6500, DMM7510 are able to digitize current at a high sampling rate. Since they have little memory, they are able to record units of seconds....

author: Veketti
author_rank: Regular Contributor
timestamp: January 26, 2024, 06:13:02 pm
content: Power Profiler Kit II seems like perfect choice for me. Thanks everyone.

author: thephil
author_rank: Regular Contributor
timestamp: January 26, 2024, 08:40:14 pm
content: Quote from: MegaVolt on January 25, 2024, 09:15:36 amAnd if the spike in question does not occur within the time span the DMM6500 can record, you can probably use its trigger system to capture what you need. It's really a high-precision, low bandwidth oscilloscope in many ways.Here's a pointer that may help:https://www.calplus.de/fileuploader/download/download/?d=0&file=custom%2Fupload%2Fkeithley-dmm6500-datalogging-appnote-1kw-61357-0.pdf