using 3x CR2032 to power a fluke 77 series meter - Page 1
Forum section: electronics / testgear

author: robert.rozee
author_rank: Frequent Contributor
timestamp: October 19, 2023, 12:44:56 pm
content: i was thinking... how practical would it be to power a fluke 77 (or similar) from a stack of 3x CR2032 cells?1. a stack of 3 would easily fit within the volume of a PP3 battery. indeed, two stacks of 3 would fit along with a couple of schottky diodes and terminal clips;2. the capacity of a CR2032 is around250mA/h250mA.h, versus something like500mA/h500mA.h for a PP3;3. the battery housing could be 3d printed, or made out of a stack of PCB material, or consist of a single PCB with metal holder clips (2 on top, 1 underneath);4. CR2032 cells arereallycheap.i just did a quick test, with a stack of 3x CR2032 cells totalling 9.3 volts and having no trouble supplying the 500uA or so needed.an interesting idea?cheers,rob :-)

author: wasedadoc
author_rank: Super Contributor
timestamp: October 19, 2023, 12:55:18 pm
content: Quote from: robert.rozee on October 19, 2023, 12:44:56 pmMinor correction. Capacity is current multiplied by time. Hence you should be writing mAh, not mA/h

author: Fungus
author_rank: Super Contributor
timestamp: October 19, 2023, 01:07:52 pm
content: I'm sure it'll work but what would be the point?

author: Ian.M
author_rank: Super Contributor
timestamp: October 19, 2023, 01:13:21 pm
content: The Energiser datasheets I have seen differ from your numbers. Their Alkaline PP3 is about 600 mAH capacity but their CR2032 'falls off the cliff' with rapidly rising internal resistance around 200mAH. I doubt no-name or off-brand CR2032's will be any better.For the same life you'd need 9 cells, and there's only room for 6 so you'll be changing them more frequently. The only benefit is the reduced risk of leakage, which is pretty low anyway for a branded alkaline PP3, and can mitigated by wrapping the battery in clingfilm after fitting the clip, reducing the potential damage to the fairly simple to replace clip.TLDR: branded CR2032 cells would need to be more than ten times cheaper than the PP3 alkaline batteries before its even worth considering, if you were given the adapter for free. Figure in time and materials for the adapter amortized over lets say ten years and I think its not worth it even if the cells are free!

author: robert.rozee
author_rank: Frequent Contributor
timestamp: October 19, 2023, 01:14:23 pm
content: Quote from: wasedadoc on October 19, 2023, 12:55:18 pmgood point - i have corrected the error of my waysQuote from: Fungus on October 19, 2023, 01:07:52 pmto avoid a leaking battery destroying your favourite multimeter, or course. the meter i used for testing (above) had itself suffered a battery leak that wrecked it - it no longer zeros.cheers,rob :-)

author: Fungus
author_rank: Super Contributor
timestamp: October 19, 2023, 01:21:52 pm
content: Quote from: robert.rozee on October 19, 2023, 01:14:23 pmUse rechargeable 9V NiMH instead, like I do.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 19, 2023, 01:23:20 pm
content: The internal resistance of 2032s is rather high - it would likely die if you turned the backlight on.3x2450, maybe, but why?

author: robert.rozee
author_rank: Frequent Contributor
timestamp: October 19, 2023, 01:28:04 pm
content: Quote from: Ian.M on October 19, 2023, 01:13:21 pmthe numbers i used came from the element14 website. they had packs of branded 5x CR2032 rated at 265mA.h for around $10. non-alkaline PP3 batteries ranged from 400mA.h up. the difference between 1/2 or 1/3 the lifespan doesn't really matter when the battery lasts a number of years. i generally don't worry about amortizing when it comes to my precious flukes.Quote from: Fungus on October 19, 2023, 01:21:52 pmself-discharge precludes use in anything not used on a daily/weekly basis. for instance, would you want to use NiMH cells to power an emergency torch that sits in the glovebox of your car for years at a time?Quote from: mikeselectricstuff on October 19, 2023, 01:23:20 pmbacklight?fluke 70 series don't have backlight. these are devices that runs on the smell of an oily rag.cheers,rob :-)

author: bdunham7
author_rank: Super Contributor
timestamp: October 19, 2023, 01:51:07 pm
content: Just use an EBL 6F22 lithium battery, rechargeable or primary. Coin cells don't sound very efficient, although it's true that type of meter doesn't exactly draw much current.https://www.eblofficial.com/products/9v-batteries-with-battery-charger

author: AVGresponding
author_rank: Super Contributor
timestamp: October 19, 2023, 04:44:14 pm
content: Quote from: bdunham7 on October 19, 2023, 01:51:07 pm^ thisEBL, Znter, am currently trying the brand "PUJIMAX" in one of my DMMs, seems fine. Only issue you get with these is they give a constant voltage until the internal cell is empty then just stop, so you don't get a low battery warning.These are quite a bit less than a tenner these days, I see no good reason to use anything alse (in most use cases, YMMV).

author: Kleinstein
author_rank: Super Contributor
timestamp: October 19, 2023, 06:12:07 pm
content: There are 9 V Li primary cells, often intended for smoke detectors (to get a 10 year lifespan) and similar.Rechargeable only makes sense if empty every few weeks and not for a few years.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 20, 2023, 05:14:36 am
content: I get a few months out of the Znter in my 87V, my work meter, remains to be seen about the runtime of the PUJIMAX, it's in a TekDMM912, and is my current daily at home.

author: bastl_r
author_rank: Regular Contributor
timestamp: October 20, 2023, 05:58:49 am
content: HelloI get a lot of 1/2AA Li batteries which have served as backup batteries for 3 years. These are regularly like new and have about 1000mAh. Three of these fit exactly into a Fluke 9V battery slot and last what feels like forever even with frequent use....With button cells, I am concerned if they can supply the current for the resistance measurement and the continuity beeper.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: October 20, 2023, 11:53:30 am
content: Quote from: Kleinstein on October 19, 2023, 06:12:07 pmLi-Ion and similar make great sense if they are cheap enough and their self-discharge is so low they can hold up for several years. as an example, i've seen e-cigarettes containing a Li-Ion cell but with no means of accessing or recharging it. while rechargeable, it was cost-effective for the manufacturer use it in place of a primary cell.also to take into account is the cumulative damage to the plastic screw bosses every time a fluke 70 series is opened up.i still like the two stacks of 3x CR2032 idea, despite what others have said; the CR2032 has become so ubiquitous that the price of six has dropped below that of a single 9v lithium primary.cheers,rob :-)

author: Kleinstein
author_rank: Super Contributor
timestamp: October 20, 2023, 04:36:50 pm
content: The 9 V Li blocks are some 1.2 mAh, while Cr2032 is around 200-260 mAh. So it takes 3 in series and some 5 or 6 in parallel to replace one of the 9 V ones.

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 21, 2023, 02:55:48 pm
content: The 77 is rated for 2000 hrs of battery life. So whether using 9V Lithium or 9V NiMH for the reason to prevent alkaline leakage is fine. But the cost of battery is nothing. I wouldn't bother to build a pack out of 3 CR2032's.

author: edavid
author_rank: Super Contributor
timestamp: October 21, 2023, 03:12:50 pm
content: Quote from: AVGresponding on October 19, 2023, 04:44:14 pmIt sounds like you are talking about the USB chargeable kind with a built in DC-DC converter. That is the wrong choice for a DMM. The EBL batteries that were linked are a 2S Li-ion package. The voltage drops gradually and the low battery warning works. The downside is that you need the special charger.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 21, 2023, 03:15:02 pm
content: If you're worried about leakage, wrap the battery in cling film

author: AVGresponding
author_rank: Super Contributor
timestamp: October 21, 2023, 03:44:32 pm
content: Quote from: edavid on October 21, 2023, 03:12:50 pmWrong how?

author: wasedadoc
author_rank: Super Contributor
timestamp: October 21, 2023, 04:02:26 pm
content: Quote from: Kleinstein on October 20, 2023, 04:36:50 pmNope. Much more than that.

author: Fungus
author_rank: Super Contributor
timestamp: October 21, 2023, 04:42:13 pm
content: Quote from: mikeselectricstuff on October 21, 2023, 03:15:02 pmBrilliant!

author: edavid
author_rank: Super Contributor
timestamp: October 21, 2023, 05:53:00 pm
content: Quote from: AVGresponding on October 21, 2023, 03:44:32 pmAs you mentioned, the low battery warning doesn't work. Also they have lower capacity since there is only room for 1 cell, and shorter shelf life due to the self discharge caused by the DC-DC converter. So they are inferior unless you need the higher output voltage, which you don't for most DMMs.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 21, 2023, 06:48:15 pm
content: Quote from: edavid on October 21, 2023, 05:53:00 pmA 2S Li-ion is going to have a fair bit of its capacity unused, since the BMS will let the cells go to 2.5v before cutting them off. Pretty sure the DMM will have shut offlongbefore then.I've had no problems with these 1S w/dc-dc convertor; as I've said I get months between charges on my 87V and I don't let it run out, I give it a charge when I remember, which is usually 2-3 months.

author: bdunham7
author_rank: Super Contributor
timestamp: October 21, 2023, 07:43:44 pm
content: Quote from: AVGresponding on October 21, 2023, 06:48:15 pmMost DMMs turn on the low battery warning at about 7.0V, which means 3.5V/cell and the energy left at that pointat a low discharge rateis fairly low. That's not a bad point to make a mental note to charge the battery when you are done with the meter. I'm not saying the version you use is wrong--unless you don't like surprise shutoffs--but I find the 2S versions to be just about perfect. Their low internal resistance also helps prevent issues caused by ranges that draw more power (continuity, etc) when the battery is at or below the warning threshold. Even if the battery warning comes on while you are out at the beginning of your workday, the meter will work fine for the entire day or more. Other than initial testing, I haven't yet had a meter that actually used up even one charge with the EBL 2S 6F22 600mAh.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 22, 2023, 12:21:23 pm
content: I only had that happen the once, and it was after such a long time I'd completely forgotten about the battery, probably 6 months or so.Ultimately the best battery is the one that suits your own use case best.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: October 23, 2023, 05:11:55 am
content: i did a bit more experimenting today and found the maximum current draw of a fluke 77, in diode check mode with the probes shorted together and the beeper sounding, was 2mA. this was being supplied with no trouble by a stack of 3x CR2032 cells.there also seems to be a CR2450 lithium cell available, with a supposed capacity of 600mA.h. a stack of three of these would fit within the footprint of a PP3 battery while having the same capacity. i can get Panasonic branded CR2450 cells locally in a pack of 5 for a little under us$6 (for the 5). i will pick up a pack tomorrow, along with 20x off-brand CR2032 for the same price.cheers,rob :-)

author: dardosordi
author_rank: Regular Contributor
timestamp: October 03, 2025, 08:22:33 pm
content: Sorry to necropost, but seems like its doable so I'll be trying too. This guy designed the holder:https://www.thingiverse.com/thing:5424400