D size battery converter for 3V

[rogerzilla]

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.

[aidan.f]

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

[grams]

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.

[aidan.f]

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]

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.

[rogerzilla]

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!

[Wobbly John]

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. 

I had just come on this thread to suggest using one (or two) for this application...

[rogerzilla]

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.

[andrew_s]

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.

[Diver300]

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.

[Kim]

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.

[aidan.f]

One D lithium thionyl would run a Red led (20mA) for 900 hours. Probably the lowest hassle solution.