DMM for off-line DC voltage logging - Page 1
Forum section: electronics / testgear

author: rlyoung
author_rank: Newbie
timestamp: December 14, 2016, 05:10:23 pm
content: I want to monitor the voltages on my car battery as it is charged and then 'maintained' by a smart battery float charger. I can use a pen type Lascar usb DC voltage logger which stores its readings then transfers them to a pc very handily for review with the included software. I can just leave it connect under the hood for a day or so and then collect it up and see what the charger has done.However, although I need another multimeter like I need a hole in the head, I have been looking at those ones that say they log data. Disregarding the variably quality issue of cheap meters, which is what my budget will allow, is there one that will long voltage as a stand-alone unit, store it, then upload it via a USB (only) cable to a pc. Don't want RS232 or Bluetooth if I can avoid it. The Hylec/Peakmeter PM8236 looks close, but one reviewer said it does not store data, it only streams it to a pc. I've done a lot of research but it hasn't come together in a sub-$100 meter.I've even toyed with the idea of a DSO Nano v3 pocket scope. I 'think' it can do this. (Hmm, not sure if I can slow down the sampling rate so as not to fill the memory)Thanks.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 14, 2016, 06:01:08 pm
content: At that price point, the UNI-T UT-71B is the only one to fit the bill, except perhaps for a few hard to obtain CEM meters .A maximum of 100 samples allow for a 10 hour logging session.The more expensive UNI-T UT-71D (130$) can log 10,000 samples at the same rate, or faster.http://www.ebay.com/itm/UNI-T-UT71B-Intelligent-Digital-Multimeter-Tester-USB-to-PC-True-RMS-LCR-AC-DC-/351229689257?hash=item51c6ebbda9:g:DeMAAOSwQJhUbExv

author: rlyoung
author_rank: Newbie
timestamp: December 14, 2016, 06:31:59 pm
content: Thank you very much. I suppose I could back off my cable restrictions if a common adapter would convert a RS232 cable to a PC USB input. In which case there would just remain the need for a meter to store its data for later analysis on the PC. The UNI-T UT-71D looks good, but I wouldn't mind something less expensive.

author: Fungus
author_rank: Super Contributor
timestamp: December 14, 2016, 06:57:11 pm
content: For car battery voltage an Arduino's analog input is probably good enough.If you're handy with an Arduino that would be really easy/cheap.Google "arduino voltage logger". There'll be something.

author: IanB
author_rank: Super Contributor
timestamp: December 14, 2016, 07:08:50 pm
content: I second the Arduino idea. I'm sure I've seen projects that let an Arduino log data to an SD card for later analysis. The example I saw was for logging temperature, but I'm sure logging voltage would be an easy change.One thing to note: if you use any kind of device without protected inputs, starting the car while logging could generate spikes that might damage the logger. So watch out for that.

author: Fungus
author_rank: Super Contributor
timestamp: December 14, 2016, 07:23:48 pm
content: Quote from: IanB on December 14, 2016, 07:08:50 pmYou have to divide the voltage from 12V to 5V so just use large value resistors (eg. 50k) in the divider and the Arduino clamping diodes will do the rest.

author: rlyoung
author_rank: Newbie
timestamp: December 14, 2016, 08:55:41 pm
content: Thanks. I've never played with Arduino components, and my time (and interest) isn't what it used to be for breadboarding and kits. It does look interesting though. The Lascar EL-USB-3 should do me with minimal effort, and I've hankered for one for a while. But it is worth my time just to see what meters might do the equivalent, and give me a bit more functionality.