Using 3 x CR2 in place of a 9V battery - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: January 04, 2016, 02:52:48 pm
content: Are there any restrictions/concerns with using 3 x CR2 batteries connected in series in place of a 9V battery (battery connectors aside)?I remember reading a post on the forum here where someone mentioned doing just that with a power hungry multimeter and I wonder if there are any gotchas with it.The reason I'm considering this is capacity: 3 x ~800 mAh (for the CR2) vs ~300 mAh (for the 9V).

author: Audioguru
author_rank: Super Contributor
timestamp: January 04, 2016, 04:20:08 pm
content: Of course three CR2 lithium batteries in series provide more current for a longer time than a 9v alkaline battery. The modern lithium battery is better and is much more expensive than the cheap old alkaline battery.

author: jitter
author_rank: Frequent Contributor
timestamp: January 04, 2016, 04:31:59 pm
content: Quote from: giosif on January 04, 2016, 02:52:48 pmAfter looking at some datasheets, I wonder if you are using carbon zinc rather than zinc manganese-dioxide (i.e. alkaline) batteries. The former have about400 mAh @ 5 mAwhile the latter have a much more generous600 mAh @ 25 mA(both to 4.8 V).If it's indeed the zinc carbon you are now using, then I'd definitely first try a 9 V alkaline battery before bodging three relatively expensive CR2s together in, or more likely, under the multimeter.

author: Audioguru
author_rank: Super Contributor
timestamp: January 04, 2016, 04:51:41 pm
content: Why not replace the cheap old 9V battery with a modern Energizer LA522 lithium 9V battery that is the same size and shape as the original but it can provide high current for a much longer time and does not cost as much as three CR2 batteries?

author: edavid
author_rank: Super Contributor
timestamp: January 04, 2016, 04:55:18 pm
content: Has anyone tried the cheap 9V Li-ion rechargeables?http://www.aliexpress.com/item/9V-800mah-USB-Lithium-Rechargeable-Battery/32445276153.html

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 12:00:55 am
content: Quote from: jitter on January 04, 2016, 04:31:59 pmAt this point in time I'm just looking for a higher capacity option (the meter is still to arrive).

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 12:07:22 am
content: Quote from: Audioguru on January 04, 2016, 04:51:41 pmHmm... For some reason, I didn't find known brand lithium 9V batteries like this one in my previous searches.This looks promising.And, if I'm not wrong with my understanding of battery capacity, the LA522 is close to the ~800 mAh of the CR2.

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 12:09:22 am
content: Quote from: blueskull on January 05, 2016, 12:06:52 amAlso, how much trust would you have in such a battery, especially if you want to use it with a more expensive multimeter?

author: Audioguru
author_rank: Super Contributor
timestamp: January 05, 2016, 12:49:56 am
content: I would not trust a cheap Chinese 9V Ni-MH battery that claims 800mAh when an Energizer Name-brand 9V Ni-MH battery capacity is less at only 175mAh. Mine says it is made in Germany.

author: Audioguru
author_rank: Super Contributor
timestamp: January 05, 2016, 01:50:26 am
content: Quote from: blueskull on January 05, 2016, 01:03:27 amBut a 9V battery uses 7 or 8 tiny AAAA cells. Because the cells are in series then the capacity is the same as only one tiny cell.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 05, 2016, 02:58:53 am
content: Quote from: giosif on January 04, 2016, 02:52:48 pmWhat meter above? Some Agilent OLED?

author: jitter
author_rank: Frequent Contributor
timestamp: January 05, 2016, 05:46:47 am
content: Quote from: Audioguru on January 05, 2016, 01:50:26 amSince a zinc carbon or alkaline battery cell has a nominal voltage of 1.5 V, that would be 6 cells in series.I thought these were tiny round cells, and I seem to remember from decades ago that that was the case when I dismantled one. But recently I took the metal case off a private label alkaline battery that was made in Malaysia. Visual clues lead to believe that this one was made most likely by or for Varta. I was surprised to find rectangular cells in clear plastic.I guess this is the max. they can squeeze into this form factor...

author: mikerj
author_rank: Super Contributor
timestamp: January 05, 2016, 09:57:01 am
content: Quote from: Audioguru on January 05, 2016, 12:49:56 amIt's not an Ni-Mh battery, that's the whole point, it's two lithium-ion cells in series within a 9v battery form factor. The thing that would concern me is whether it contains any protection against over/under discharge for both cells.Wouldn't surprise me if the capacity has been greatly exaggerated however.

author: tszaboo
author_rank: Super Contributor
timestamp: January 05, 2016, 10:37:12 am
content: Well I've calculated that you can fit 3x 14250 or half AA cell into the dimensions of the 9V. 3x LiFePO4 would give 9.6V, safe operation. BMS is neccessary. Otherwise it would be very compatible with 9V.On the other hand, 9V battery should die out already. We have 0.8V boost converters, not a 7805.

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 07:12:00 pm
content: Quote from: retiredcaps on January 05, 2016, 02:58:53 amAgilent U1253A

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 07:53:31 pm
content: Quote from: mikerj on January 05, 2016, 09:57:01 amI have similar concerns, plus the unknown with regards to build quality.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 05, 2016, 09:11:31 pm
content: Quote from: giosifI remember seeing Dave's review and the 8 hour battery life comments. 14 hours on a new 9V alkaline ($1.50 or more) battery.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 05, 2016, 09:12:25 pm
content: Quote from: blueskull on January 05, 2016, 09:04:38 pmAnother Dave video ...

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 11:49:50 pm
content: Quote from: blueskull on January 05, 2016, 09:02:48 pmHehe... Like a reversed competition...

author: giosif
author_rank: Frequent Contributor
timestamp: January 05, 2016, 11:54:03 pm
content: Quote from: retiredcaps on January 05, 2016, 09:11:31 pmI've watched that video a few times already.

author: jitter
author_rank: Frequent Contributor
timestamp: January 06, 2016, 06:48:28 am
content: Quote from: retiredcaps on January 05, 2016, 09:12:25 pmThanks for the link, I'll watch the vid later today.I've seen quite a few of Dave's videos, but this one had eluded me, until now...Edit: seen it. Pretty sure my "Aerocell" batteries are actually Vartas.One tiny mistake by Dave: as he's dismantling the Varta you can see "Made in Malaysia" but says later they're from Germany. Most Vartas are, but for some reason not the 9 V batteries.Maybe interesting to know is that the Aerocell (private label for Lidl) did very well in recent tests, despite their low price (compared to A-brand batteries). They also asked Varta if they were the manufacturer of Aerocell, but Varta declined to answer. Understandable, the Aerocells performed the same at a fraction of the cost of "real" Vartas. BTW, they performed even better than Duracell.I've suspected Varta as the manufacturer of several private labels for many years. There are some visual clues that will only be found on Vartas and Varta-made private labels. If I then also find "Made in Germany" on most sizes (AAA, AA, C and D), I'm pretty sure.Attachment: the clue is the production date/expiration date stamp (formerly only the experation date as on the Simplex), only Varta have them in this postion and font. Also (not visible) the contacts are all identical.

author: nukie
author_rank: Frequent Contributor
timestamp: January 07, 2016, 10:51:21 am
content: I worked on this project for years until I found affordable and correct size cells from a rc heli. I found the best I can do is two 650mAh lipo cells wired in series with a 7.2v battery protection circuit and there is little space left for the boost converter that steps up 7.2v to 9v.There is another cell that is rated 800mah but there wont be space for anything else. For safety reasons I have considered 3.2v LiFePO4 cells which makes a 9.6v battery but they have lower capacity and unavailable in the right dimension. To invest in tooling to make these lower capacity cells wouldnt be very wise for a small scale project.The problem I have is that the device wont be able to detect low battery, and it dies suddenly as the protection circuit would go open circuit as soon as the cell drop below safe operating voltage.I use this in my irrigation systems for quite sometime now. I am planning for a solar charger and limit the voltage to 3.85v per cell or about 70-80% capacity to extend battery life so the system does not require maintenance for the life of the battery.I figured a supercapacitor will be a good candidate for this application because it should last longer as li-ion cells dont like the heat from the sun but they probably need to be quite large size.I think out of all cells the 9v battery(6 cells in series,therefore battery) is the one that requires a proper rechargeable equivalent. Its quite popular in the test equipment field, stage mics, irrigation systems, smoke alarm,etc but no engineer or company care to invest in development and tooling for a Eneloop equivalent. I have seen one or two rechargeable lithium based 9v but they are actually 7.2v nothing with a true 9v.

author: jitter
author_rank: Frequent Contributor
timestamp: January 07, 2016, 04:25:06 pm
content: Quote from: nukie on January 07, 2016, 10:51:21 amWhat exactly do you mean by "Eneloop equivalent"?If you mean the ready to use NiMh type with minimal self discharge, then there are several around of 8.4 V nominal voltage. Typically these have150 mAhor200 mAh, but I've also seen300 mAh.

author: KL27x
author_rank: Super Contributor
timestamp: January 07, 2016, 06:45:21 pm
content: QuoteI bet it takes more than 2.6667 times longer to change out the 3 jerry-rigged CR2 batteries.Or would you make an external charger to recharge it?

author: jitter
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:22:04 pm
content: Quote from: KL27x on January 07, 2016, 06:45:21 pmThose aren't rechargeable, are they?

author: Audioguru
author_rank: Super Contributor
timestamp: January 07, 2016, 10:26:56 pm
content: Why are we talking about a power hungry portable multimeter? Multimeters have not used Nixie tubes for many years.My Fluke multimeter uses one Energizer 9V alkaline battery every 5 years because I do not leave it turned on all day every day, I use it only when I need it. I would never use a cheap Chinese battery in it and it does not need a rechargeable battery.I would use an expensive LA522 Lithium 9V battery only for something that draws a high current and is turned on all the time. No I wouldn't, instead I would use a wall adapter power supply with it.

author: giosif
author_rank: Frequent Contributor
timestamp: January 07, 2016, 11:17:14 pm
content: Quote from: KL27x on January 07, 2016, 06:45:21 pmYeah... It was my initial misunderstanding of the total capacity for the 3 x CR2's.And it was also my lack of knowledge on battery types in the 9V format.Quote from: jitter on January 07, 2016, 09:22:04 pmNope, they're not.Quote from: Audioguru on January 07, 2016, 10:26:56 pmWell... Nixie tubes or OLED displays, same thing.Wall adapter power supply is something I've considered (maybe still considering?), but then that would be yet another cable to fiddle around with on what is my already very crowded workbench, computer desk, storage area, etc.I need a bigger place...

author: grifftech
author_rank: Frequent Contributor
timestamp: January 08, 2016, 02:41:57 am
content: Quote from: Audioguru on January 05, 2016, 01:50:26 amactually 6