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A primary D cell is producing 1.3V when 20% depleted, and a rechargable (nickel-something) D cell less than 1.3V even when fully charged.

You forgot to post the part number.

Maxim are infamous for discontinuing parts.

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Jasen Betts
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look at the graphs bottom of page 4

5V out only with 1.5V or more in and at 1.5V only about 250mA at poor efficiency.
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Jasen Betts

At the bottom of page 15 is a circuit that puts out 5V at 1A, of course that is with a Lithium-Ion battery which are 3.3V, I think.

Bill Garber

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Bill Garber

Sorry, no. I just scanned their catalog to see what they have that can provide 5v off 1.5v in at more than a few milliamps. Only one chip cam e up that can do the job and, as I said, it will keep running down to 0.7v in and can source up to 4 amps. IIRC the OP was asking for a PSU capable of providing up to 2A @ 5v from a single D cell, so as I'd asked if a Maxim chip would be suitable, I just looked at the catalogue and said in effect "there is one that can meet your requirements".

IIRC the OP wanted 2A but didn't specify why he needed such a high current.

Indeed. I'm well aware of the quality (or lack of it) in cheap battery holders contacts.

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martin@   | Martin Gregorie 
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Martin Gregorie

MAX 1709 - and its in their online catalogue.

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martin@   | Martin Gregorie 
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Martin Gregorie

The power required to charge and discharge gate capacitance at the high frequencies which might in some applications be needed to reduce inductor size and weight (assuming a switching supply) would probably be fairly high. What sort of efficiencies do high current charge pumps deliver? Intuitively I'd think there would be high resistive losses in such devices (but intuition can be wrong).

It should be easy to do that with standard parts so good for a quick homebrew approach. And if you wished to go above 50/60 Hz to reduce weight, there might be some fairly inexpensive 400Hz transformers (or the losses resulting from driving a small 50Hz transformer at 400Hz might be acceptable). There must be some 3000Hz transformers around, but probably expensive since that's mostly aerospace stuff. I think.

Could maybe manage a small inductor if I couldn't find ready-made. I've rewound small transformers etc. in my day, and despite the final appearance they mostly worked. But craftsman I am not!

The LED torch I have solves that problem neatly and inexpensively by making the screw-on bottom of the torch also act as the switch. So the contact area regularly gets a gentle scraping. Maybe they also arranged things so that the whole cell rotates slightly at the end of the tightening process, cleaning the contact area at the nipple end. At least there doesn't appear to be a problem with that, AFAIK.

Does a D cell fit in an old 35mm film canister?

There seems to be a wide range of tabbed D cells available on line. And I fixed my electric toothbrush by soldering the tags pried from the old AA cell to a standard replacement, using a 150 watt iron with a heavy bit to very quickly tin the new cell (Baker's soldering fluid is/was still being made as of some years ago), allowing it to cool, and carefully cleaning off the corrosive flux before attaching the tabs with rosin core solder. A year later, the cell appears to have survived the heating. Wouldn't have done all this, but I was insulted by the price of a replacement and acted on impulse.

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Windmill

I suspect it wouldn't particularly high but, like yourself, that's only an assumption. You could always try an internet search to gather some data on this issue.

Intuition can be wrong or right, it depends on the quality of your experience in these matters. If in doubt, try an internet search.

There are several sources of inductor data and ferrite core design tables available via the internet. A search for these can be quite revealing. There's no need to consider 'expensive' ready made high frequency transformers based on space industry technology.

Winding such high frequency inductors and transformers isn't too difficult due to the thicker wire and the reduced turns count.

You've been quite lucky then.

A quick look at the wiki page on batteries (and, if necessary, the wiki page on film formats) should answer that question.

I know where you're coming from. However, you're talking about cells that can't be bought off the shelf in Pound shops. Whilst a proper, soldered in, rechargable "battery pack" neatly solves this contacts resistance issue, it, in general, doesn't apply in the case of the user replaceable classical cylindrical cell.

What does seem to obviate contact resistance issues is the use of gold plated spring loaded connections, e.g. expensive laptop batteries and lithium based camera batteries. I don't think we'll be seeing AA, C and D primary cells endowed with gold plated contacts anytime soon.

However, 'Premium' versions of NiMh cells in those sizes might be offered at an outrageously premium price most likely appearing in the D and C cell sizes before trickling down to the humble AA cell.

If such cells ever did become available, the battery compartment contacts would also need to be gold plated to properly address the contact resistance issue. This has all the hallmarks of a "Catch 22" situation and, as such, seems unlikely to be resolved.

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Johny B Good

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