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Rechargeable 9V batterries for DMM or Alkaline only?
Kleinstein:
--- Quote from: J-R on November 23, 2022, 08:23:15 pm ---It's not hard to provide a floating/isolated supply to the DMM.
--- End quote ---
Yes : the obvious solution is using a battery of some kind >:D
Getting a very well isolated DCDC converter to provide mains power is however tricky. The usual CAT 2 and even more CAT 3 safety rating call for withstanding quite high transient voltages. A 2nd problem is that the usual DCDC converters tend to inject quite some high frequency common mode signal that can cause EMI problems. There are circuits / custom designs for relatively good isolated DCDC converters, but this really hard stuff if it needs to fit inside the small battery compartment and the isolation is still inferior to a simple battery.
There is no need to build a voltage doubler for a Li.ion cell. There are ready made 2S li-ion batteries with protection in the 9 V block form factor. This gives a higher capacity rechargible option.
bdunham7:
--- Quote from: JenniferG on November 23, 2022, 10:45:31 am ---Yeah I'm doing data logging with UT61E. Perhaps I should get a better bench DMM? I'm currently sing the 8251A and I don't think you can data log with it, even though it has a serial port and usb. Are there any good bang for the buck bench DMM with data logging? Fairly accurate etc? This 8251A is 120K count.
--- End quote ---
I don't have the UT61E, but as long as its battery cutoff is <7.2V, the EBL two-cell Li-ion 9 volt batteries should be great. Most reasonably designed devices will have the cutoff below that 7.2V mark because that is 1.2V/cell and less than that with alkaline batteries is wasting a lot of their energy. According to this video, your UT61E will have a cutoff below 7.0V.
As far as a bench meter for logging, check this thread on user HKJ's Test Controller program.
https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/
Your GDM-8251 should support logging if you find the software to do so. GW's webpage has USB and LabView drivers for it, but I don't see the DMM-Viewer program for logging. I had a GDM-8251 for a bit but I don't recall setting it up for logging. I'm sure there's a way.
mariush:
Strictly in the case of UT61E ( which I own), I think the meter shows low battery voltage at around 5.4v and will still go and measure well down to around 3v.
But the serial output may stop working right before you hit 3v due to the optical isolation (forward voltage of led used)
I actually made a battery replacement thing using a 20F -ish (don't remember exact value) 2.5v supercapacitor and a LT1307 step-up regulator to 5.6v ... charge the capacitor at 2.4v for 1 minute, and then it would last for around 40 minutes or something like that.
You can check in the part 3 of this review at around 20 minutes in :
You could probably use a digital isolator IC like Adum5000 if you want to power the meter from an external supply, for example : https://www.analog.com/media/en/technical-documentation/data-sheets/adum5000.pdf
Such isolators are expensive and noisy and low efficiency, like 33% efficiency - but if powered from some wallwart i guess you wouldn't care that you waste 10mA or so to get isolated 2-3mA to the meter
AVGresponding:
I use Znter Li-ion, they give a steady 9.0-9.1V across the entire discharge until shutoff, as they have an internal boost regulator. The only downside is that you don't get a low battery warning from your DMM...
A Fluke 87V lasts at least 6 months on a charge.
james_s:
I've used rechargeable 9V NiMH batteries in my Fluke 87 since new, it works fine. I can't see any reason why it wouldn't be fine in any other meter. With very few exceptions I don't buy disposable batteries anymore and haven't in years.
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