Author Topic: D size battery converter for 3V  (Read 638 times)

D size battery converter for 3V
« on: January 24, 2021, 08:36:16 pm »
Supposedly these exist - to take 2 x AA cells in series, raising the voltage of an old single-cell bike light to take an LED that wants 3V.  Any idea where?  Obviously most AA to D converters put the AAs in parallel, to give 1.5V.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: D size battery converter for 3V
« Reply #1 on: January 24, 2021, 10:35:55 pm »
A boost Voltage converter circuit will happily drive your red led(s) it would be something like this circuit :https://www.electronics-lab.com/1-5v-battery-powers-white-led-driver/
I will have a hunt about for something ready made. Btw if you would like a few really bright red LEDs posted to you  pm me

Re: D size battery converter for 3V
« Reply #2 on: January 24, 2021, 10:42:31 pm »
You can buy these cheap tiny boost circuits:

https://www.ebay.co.uk/itm/MT3608-DC-DC-Voltage-Step-Up-Adjustable-Boost-Converter-Module-2A-UK/193424475011

They're constant voltage rather than constant current but would surely work with careful twiddling of the pot and appropriate tongue angle.

Re: D size battery converter for 3V
« Reply #3 on: January 24, 2021, 10:48:22 pm »
I am guilty of not addressing the problem directly.
There are dual AA holders that may fit in the D cell space. I have some and will measure up.

fuaran

  • rothair gasta
Re: D size battery converter for 3V
« Reply #4 on: January 24, 2021, 10:50:31 pm »
Or use an lithium ion battery instead? Would give about 3.7V to 4.2V fully charged, if your LED driver can cope with that.

An 18650 battery would be slightly longer than a D cell, could squeeze that in.
Or a 14500 lithium ion battery is the same size as AA. So you could use it in a regular AA to D converter.

Re: D size battery converter for 3V
« Reply #5 on: January 26, 2021, 10:44:30 am »
Or use an lithium ion battery instead? Would give about 3.7V to 4.2V fully charged, if your LED driver can cope with that.

An 18650 battery would be slightly longer than a D cell, could squeeze that in.
Or a 14500 lithium ion battery is the same size as AA. So you could use it in a regular AuA to D converter.
The 14500 cells sound like the best option.  The Nicelite LED bulb replacements can run on up to 9V.  They are actually too bright...a 1W red LED is a bit like an afterburner!
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: D size battery converter for 3V
« Reply #6 on: January 26, 2021, 11:24:55 am »
Or use an lithium ion battery instead? Would give about 3.7V to 4.2V fully charged, if your LED driver can cope with that.

An 18650 battery would be slightly longer than a D cell, could squeeze that in.
Or a 14500 lithium ion battery is the same size as AA. So you could use it in a regular AA to D converter.

I found one of those in one of our garden solar lights, that I had taken apart to repair (moisture/corrosion in the switch)...

...after I had put it in a 'dumb' NiMH cell charger.  :facepalm:

I had just come on this thread to suggest using one (or two) for this application...
If it ain't broke, fix it 'til it is...

Re: D size battery converter for 3V
« Reply #7 on: January 29, 2021, 04:12:42 pm »
Hmmm.  It turns out to be quite reasonably bright on 1.5V.  3V turns it into a right retina ripper, so maybe I'll leave it as it is!  It's an old Drydex "bullet" lamp with the Nicelite red LED.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: D size battery converter for 3V
« Reply #8 on: January 30, 2021, 04:37:42 pm »
You can get lithium rechargable D-cells that charge via a USB port. They are regulated down to 1.5V, and give that until they run out (at which point they turn off, with no warning). Regular alkaline D-cells may be 1.5V when fresh, but the voltage drops relatively soon, so a lot of the time they would be on 1.2 to 1.3 V.

You can also get D-sized Lithium Thionyl Chloride cells that are 3.6V. Very high capacity, but disposable.

Neither are cheap.

Re: D size battery converter for 3V
« Reply #9 on: January 30, 2021, 06:32:35 pm »
You can also get D-sized Lithium Thionyl Chloride cells that are 3.6V. Very high capacity, but disposable.
Lithium Thionyl Chloride have quite a high internal resistance. They aren't so good for high current loads.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Kim

  • Timelord
Re: D size battery converter for 3V
« Reply #10 on: January 30, 2021, 07:15:28 pm »
You can also get D-sized Lithium Thionyl Chloride cells that are 3.6V. Very high capacity, but disposable.
Lithium Thionyl Chloride have quite a high internal resistance. They aren't so good for high current loads.

They're also brilliant at low temperatures, and just a little bit explodey.
Careful, Kim. Your sarcasm's showing...

Re: D size battery converter for 3V
« Reply #11 on: January 31, 2021, 05:33:43 am »
One D lithium thionyl would run a Red led (20mA) for 900 hours. Probably the lowest hassle solution.