CR123 rather than 2xAA cells - UK Vintage Radio Repair and Restoration Discussion Forum

Neil Purling · 23rd Dec 2018, 10:23 pm

To use a CR123 instead of two AA cells would I need to have a diode to 'lose' the difference in voltage?
If so. Which one?

trh01uk · 23rd Dec 2018, 10:32 pm

The nominal voltage of a CR123A battery is 3 volts. Much like 2 x AA alkaline cells in series. Why do you need a diode at all?

Richard

Neil Purling · 23rd Dec 2018, 11:38 pm

I thought they were 3.7V or a different make-up of CR123 made the extra voltage when fresh.
It is purely a space consideration choosing this battery rather than a pair of AA's.
How many mAh is average vs the pair of AA for the same chemical make-up?

Nuvistor · 24th Dec 2018, 12:22 am

Primary CR123 Lithium batteries are 3 volt, rechargeable CR123 Li-ion are 3.6 volts.
Information from Wikipedia.

Neil Purling · 24th Dec 2018, 7:13 am

I was looking at the re-chargeable CR123.
I figured i'd need to lose 0.6V, assuming the voltage remained constant until the charge was exhausted.

Diabolical Artificer · 24th Dec 2018, 8:25 am

Almost all things powered by batteries I've come across are tolerant of over voltage. I've powered 9v radio's off car batteries for instance without harm. 0.6v in the scheme of things is nowt.

Andy.

trh01uk · 24th Dec 2018, 9:19 am

While pondering this query I came across this post about problems with this specific battery format, which you might want to consider:

https://www.knivesandtools.co.uk/en/...ry-rcr123a.htm

Neil Purling · 6th Jan 2019, 8:48 am

The little pocket radio kits I am making mean I am not drawing more than 10mA & the CR123 is for these. A re-chargeable CR123 would be OK here?
I know just how damn hot these cells can get if inadvertently shorted

Hunts smoothing bomb · 10th Jan 2019, 4:04 pm

Quote:

Originally Posted by Diabolical Artificer

0.6v in the scheme of things is nowt.

Andy.

I'm always happy to be proved wrong but 0.6v in relation to a supply voltage of 3v is 20%

The appliances in my house run on 230v but I don't think I'd be willing to test that theory by winding them up to 276v on the variac...

Cheers

Jolly 7 · 10th Jan 2019, 5:08 pm

If I am not mistaken, the voltage of a fully-charged CR123 lithium battery will be 4.2 V, similar to a 18650 battery. That's quite a bit over the 3V or more expected from a fresh pair of AA alkaline cells. Personally I would be reluctant to use this long-term but I don't think it would cause any immediate damage as most 3V radio components would have higher voltage ratings. Some unregulated radio and Walkman AC adaptors often provide an output well over their specified voltage e.g. 9V instead of the rated 6V.

If using a CR123 is a must, a 3 V zener diode circuit might be the best solution. AFAIK there are no ICs that would regulate down to 3V without requiring a much higher input voltage. I am not fan of IC based voltage regulators in radio circuits as they can cause RF noise.

One important point is to make sure to add a fuse to the power supply circuit if using a rechargeable battery.

G6Tanuki · 10th Jan 2019, 5:15 pm

Quote:

Originally Posted by Jolly 7

AFAIK there are no ICs that would regulate down to 3V without requiring a much higher input voltage.

Modern LDO regulators often only need a few hundred millivolts more supply than their regulated-output voltage.

Example - the TDA3663 which is used in laptops etc. to provide the 3.3V rail.

Jolly 7 · 10th Jan 2019, 5:20 pm

The TDA3663 is SMD only if I am not mistaken ?

G6Tanuki · 10th Jan 2019, 5:50 pm

Quote:

Originally Posted by Jolly 7

The TDA3663 is SMD only if I am not mistaken ?

SO-8, yes. I generally solder these sorts of chips to something like this:

http://www.hobbytronics.co.uk/soic-dip-breakout-8-ht

so I don't lose the SMD chips if I sneeze. ((my most-recent bit of 'gash' electronics involved a NE602/SA602 type SMD chip as a mixer)).

Jolly 7 · 10th Jan 2019, 6:23 pm

It's the flu season after all

In your experience have you found RF noise being generated from the TDA3663 ? I once tried to use a 78LO5 in a radio circuit but was forced to remove it because of the interference from it.

G6Tanuki · 10th Jan 2019, 6:41 pm

I've not had noise issues with the likes of the 3663 - or 78xx-series for that matter. I've used 78xx etc. to regulate the supply to VFOs/post-VFO buffer-amps and found the result to be a lot smoother than the classic resistor-Zener regulators.

But there again - anything with gain can oscillate if you tempt it correctly!

23rd Dec 2018, 10:23 pm	#1
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,085	CR123 rather than 2xAA cells To use a CR123 instead of two AA cells would I need to have a diode to 'lose' the difference in voltage? If so. Which one?

23rd Dec 2018, 10:32 pm	#2
trh01uk Octode Join Date: Nov 2010 Location: Ross-on-Wye, Herefordshire, UK. Posts: 1,652	Re: CR123 rather than 2xAA cells The nominal voltage of a CR123A battery is 3 volts. Much like 2 x AA alkaline cells in series. Why do you need a diode at all? Richard

23rd Dec 2018, 11:38 pm	#3
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,085	Re: CR123 rather than 2xAA cells I thought they were 3.7V or a different make-up of CR123 made the extra voltage when fresh. It is purely a space consideration choosing this battery rather than a pair of AA's. How many mAh is average vs the pair of AA for the same chemical make-up?

24th Dec 2018, 12:22 am	#4
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: CR123 rather than 2xAA cells Primary CR123 Lithium batteries are 3 volt, rechargeable CR123 Li-ion are 3.6 volts. Information from Wikipedia. __________________ Frank

24th Dec 2018, 7:13 am	#5
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,085	Re: CR123 rather than 2xAA cells I was looking at the re-chargeable CR123. I figured i'd need to lose 0.6V, assuming the voltage remained constant until the charge was exhausted.

24th Dec 2018, 8:25 am	#6
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,657	Re: CR123 rather than 2xAA cells Almost all things powered by batteries I've come across are tolerant of over voltage. I've powered 9v radio's off car batteries for instance without harm. 0.6v in the scheme of things is nowt. Andy. __________________ Curiosity hasn't killed this cat...so far.

24th Dec 2018, 9:19 am	#7
trh01uk Octode Join Date: Nov 2010 Location: Ross-on-Wye, Herefordshire, UK. Posts: 1,652	Re: CR123 rather than 2xAA cells While pondering this query I came across this post about problems with this specific battery format, which you might want to consider: https://www.knivesandtools.co.uk/en/...ry-rcr123a.htm

6th Jan 2019, 8:48 am	#8
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,085	Re: CR123 rather than 2xAA cells The little pocket radio kits I am making mean I am not drawing more than 10mA & the CR123 is for these. A re-chargeable CR123 would be OK here? I know just how damn hot these cells can get if inadvertently shorted

10th Jan 2019, 5:08 pm	#10
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: CR123 rather than 2xAA cells If I am not mistaken, the voltage of a fully-charged CR123 lithium battery will be 4.2 V, similar to a 18650 battery. That's quite a bit over the 3V or more expected from a fresh pair of AA alkaline cells. Personally I would be reluctant to use this long-term but I don't think it would cause any immediate damage as most 3V radio components would have higher voltage ratings. Some unregulated radio and Walkman AC adaptors often provide an output well over their specified voltage e.g. 9V instead of the rated 6V. If using a CR123 is a must, a 3 V zener diode circuit might be the best solution. AFAIK there are no ICs that would regulate down to 3V without requiring a much higher input voltage. I am not fan of IC based voltage regulators in radio circuits as they can cause RF noise. One important point is to make sure to add a fuse to the power supply circuit if using a rechargeable battery. Last edited by Jolly 7; 10th Jan 2019 at 5:17 pm.

10th Jan 2019, 5:20 pm	#12
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: CR123 rather than 2xAA cells The TDA3663 is SMD only if I am not mistaken ?

10th Jan 2019, 6:23 pm	#14
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: CR123 rather than 2xAA cells It's the flu season after all In your experience have you found RF noise being generated from the TDA3663 ? I once tried to use a 78LO5 in a radio circuit but was forced to remove it because of the interference from it.

10th Jan 2019, 6:41 pm	#15
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: CR123 rather than 2xAA cells I've not had noise issues with the likes of the 3663 - or 78xx-series for that matter. I've used 78xx etc. to regulate the supply to VFOs/post-VFO buffer-amps and found the result to be a lot smoother than the classic resistor-Zener regulators. But there again - anything with gain can oscillate if you tempt it correctly!