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They say they have very low leakage, and stay charged for a long time. But I've never confirmed that experimentally.
Just a hunch, but I think you won't find any rechargeable cells that are really small because the labor or assembly costs for a small cell are not much cheaper than a large cell. And since you can buy throw- away button cells for next to nothing, it's just not economical to use rechargeable cells.
Has anyone noticed this? If you look at the prices of batteries, you see that they are cheapest in the AA and AAA sizes, and as they get smaller the price goes up, especially if you look at it from a cost per mAh. The justification for using the smaller cells is for use in small sized equipment, so they can sell them for more per mAh. Of course there is less demand for cells smaller than AA or AAA, so the economies of scale are less. In any case, it will probably be cheaper to use two or three rechargeable cells and a V boost circuit to get the voltage you need.
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That is definitely true. Distribution cost plays a role as well. Keeping all this stuff in stock may be more expensive that making it in the first place - as is demonstrated by the availability of packaging with
10 or so different watch batteries for 1 euro, where a single one will set you back more.
Also don't forget the gouge factor. "Oh, mr. Device wants to have his expensive gadget working again, that'll be 7,49 then!" - and the supply chain adjusts to that.
How does one build an ultralow power inverter? Circuit complexity and expense (within limits) isn't a big factor, but efficiency and light weight are. I can tollerate high ripple as long as the oscillation frequency is relatively stable and is >10 kHz.
I need 80 to 120 vdc variable and regulated (or stiff enough so that regulation is not necessary). Note that my load will draw 100 microamps (worst case) and will be as low as 100 nA (or less).
My idea was to use a small stack of batteries, which would not have inefficiencies at low load currents.
If you can give me a boost circuit that won't waste a lot of power when the load current is in the pA range, I'd be a happy camper.
Maxim has an ap note on this, although they only make 75 volts. Despite their low power expertise, they do not have anything that is anywhere near the efficiency I need. I am happy to send you the Maxim ap note outlining their best effort to make an efficient supply.
Hence, my inquiry about batteries:>: Batteries do not suffer low efficiency at low load currents.
Ok, that's an utterly reasonable, and totally impractical solution (in many cases) reliability will suck, as a hundred cells in series only needs one to fail.
Why do you want this? Some numbers on your proposed solution. Call it 90 1/2N cells. That's 10mm or so diameter by 14mm * 90, or about 10mm diameter by a meter. Call it 100cc, and I'll guess 800g, probably a kilo of battery pack, and it'll store maybe 10Wh. You say you want efficiancy down to picoamps, which is under a microwatt. The batteries will typically self-discharge by at least a percent a week, or 100mWh/week, or about .59mw, so around 5ua. There generally isn't much point in going below 2-3ua.
You need 100ua *150V, or say 15mw.
Not a really big number, you might concievably get it from one cell.
If weight is a big concern, I'd probably be looking hard at using a Li-ion cell (mobile phone battery) that are light, availble nearly free, and have very good self-discharge rates. They also have a reasonable voltage, whereas Ni* get a bit low on one cell at the low end.
I'd look at maxims low power chips that have low battery cutoff (li-ion hate being deep discharged) with a transformer on the output inductor. You probably want a very low frequency, perhaps 10Khz. Also perhaps an external FET rather than an internal one.
http://inquisitor.i.am/ | mailto:firstname.lastname@example.org | Ian Stirling.
Actually, that's YOUR proposed solution I think:>:
1/2 N cells are too large.
The supplies for the upper dynodes need less current still.
I'm not sure there are batteries appropriate for this, which is why I asked on usenet.
I heard that some battery fabrication using semiconductor processing techniques were just developed, but I can't find the source of them. They will certainly be small and cheap, since they don't need sealed metal packages.
Most photomultipliers I have seen use a 1.5 to 3 volt supply and step it up through a voltage multiplier. This is so simple to do that I am astounded that any piece of equipment would not do this. Now you have a single cell or a pair of cells and they can run the equipment for a very long period of time, and are very cheap and easy to replace. You may want to look into voltage multipliers.
Well, it was the one you implied by saying you wanted a simple battery, I was just doing the numbers.
Perhaps, but you won't get that much smaller. I have some 6mm dia *4mm NiMh cells (the maker no longer makes them) but even with those it's quite bulky.
While you probably could do this with really small rechargables, you almost certainly don't want to. It'll be expensive, and time consuming, especially when a cell fails, and you need to hunt through the pile.
Multiplying the voltage up using a small transformer and driver from a small battery/cell giving several volts is simply the right way to go. Do you really need rechargable? One Lithium AA cell could last a very long time. Even ordinary alkaline would.
http://inquisitor.i.am/ | mailto:email@example.com | Ian Stirling.
I have looked into multipliers. A multiplier is how I hope to get my
100 volts boosted up to 1000v (so I can run the PM tube).
Driving a multiplier is not trivial, it takes real power to charge and discharge those caps on each transition of the input signal.
I might be able to start with 20 volts (from 3 X 7.2 volt transistor batteries), and multiply that up to 100 volts though.
This would mean I'd have 2 cockcroft-walton voltage multipliers.
I tend to think that the efficiency of a transformer goes to heck fast at the higher turns ratios, maybe a dual cw multiplier chain is the answer.
Maxim has an ap note using a multiplier and one of it's low power chips. The single inductor method works poorly. The transformer step up method works better, but they end up with 30 percent efficiency at best (they only made 75 volts output, I need 125 volts). Even with Maxim's low power chips, the overhead of sensing the output (for regulation) and driving the switching transistors takes a big toll on battery power.
My hope was that a battery solution would be direct, quick, clean and more practical. I'm not necessarily looking for 1.2 volt cells either!! If someone made a 100 volt cell, I'd be happy as a clam with it.
OK, this is complicated and there is no simple answer.
It has to be the right combination of cost, weight, bulk and life spec. If it's cheap, it can be soemwhat heavier/bulky. If it's very small, I can live with some extra initial cost. If it's expensive, it needs to be reusable (battery power that can be recharged).
Above all, it has to be reasonably dependable as it will be backpacked to the hilltop and used outdoors, Radio Shack will be very distant:>:
If I could power all th edynodes directly from batteries, that would be awesome! For the upper stages where current is nanoamps and picoamps, a surface mount string of batteries would be great! That's surface mount as in the size of surface mount electronic components. Not sure if any battery technology is available for microminiature batteries.
For the lower dynodes, I'm guessing that a string of hearing aid sized batteries would do the job.
Are there any battery chemistry that produce higher voltage per cell than 1.2, 1.5 or 3.6????
I wish I could give a better definition of 'small', 'service life', 'cost' and 'volume'. But, they interact as specified above.
Is this hopeless??
The pm tube is a 3/4 inch head on tube, 3/4 inch diameter (not including shielding) and about 4 inches long.