capcitors for energy reserve

Yes, and 1200uF is a lot less than 7000uF

Cheers

Klaus

The capacitor formula: Q=EC or

Q=CV (or delta v in your case) Q=It Don't forget to allow for capacitance tolerance, capacitance decline over time, changing load current with voltage, load time tolerance and slight inefficiencies

NT

he was doing. Alkaline batteries aren't designed to be recharged, and don't seem to be guaranteed when used that way.

Even though you have a Phd, you do not know everything. The following is f rom Wiki.

A rechargeable alkaline battery (also known as alkaline rechargeable or rec hargeable alkaline manganese (RAM)) is a type of alkaline battery that is c apable of recharging for repeated use. The first-generation rechargeable al kaline technology was developed by Battery Technologies Inc in Canada and l icensed to Pure Energy, EnviroCell, Rayovac, and Grandcell. Subsequent pate nt and advancements in technology have been introduced. The formats include AAA, AA, C, D, and snap-on 9-volt batteries. Rechargeable alkaline batteri es are manufactured fully charged and have the ability to hold their charge for years, longer than NiCd and NiMH batteries, which self-discharge.[1] R echargeable alkaline batteries can have a high recharging efficiency and ha ve less environmental impact than disposable cells.

Most people do not need posts with every thing perfect. I try to cut posts down to a minimum , so people can read them quickly.

Dan

I think it's the CV product that tends to be nearly constant, so since energy is CV**2/2, you win by going to higher voltage.

Cheers

Phil Hobbs

t he was doing. Alkaline batteries aren't designed to be recharged, and don 't seem to be guaranteed when used that way.

from Wiki.

echargeable alkaline manganese (RAM)) is a type of alkaline battery that is capable of recharging for repeated use. The first-generation rechargeable alkaline technology was developed by Battery Technologies Inc in Canada and licensed to Pure Energy, EnviroCell, Rayovac, and Grandcell. Subsequent pa tent and advancements in technology have been introduced. The formats inclu de AAA, AA, C, D, and snap-on 9-volt batteries. Rechargeable alkaline batte ries are manufactured fully charged and have the ability to hold their char ge for years, longer than NiCd and NiMH batteries, which self-discharge.[1] Rechargeable alkaline batteries can have a high recharging efficiency and have less environmental impact than disposable cells.

Do any of the broad-line distributors stock them?

Could you post a link to an item in on-line catalogue?

Too many "advances in technology" turn out to be remarkably hard to get you r hands on. I tend not to take them seriously until a broad-line distributo r keeps them in stock.

Note that the Ph.D. is a remarkably specialised qualification - pretty much at the sharp end of knowing more and more about less and less until you kn ow almost everything about about practically nothing.

ts down to a minimum , so people can read them quickly.

Sure. But it's polite to mark your edits. And this time, you managed to inc lude my signature line, which did waste bandwidth.

The last time I looked (which, granted, was a while ago) it was C * V^2.

It wasn't by any authority -- it was primary research. I just pulled out a DigiKey or Mouser catalog, chose a package size, and looked at the highest C rating available in any particular V rating, and plotted a line.

For that matter I think I only actually checked electrolytic caps -- so I could be wrong about ceramics.

Or... replace or modify the offending circuit so the peak draw never exceeds 30mA.

Jes' a thought...

Frank McKenney

E = CV**2/2, just as (mechanical) E = MV**2/2

Did you plot cost, too? Volume?

HV ceramics get expensive in the larger sizes. 50V 1210s can get pricey.

Linear regs are inefficient, and waste valuable joules when the cap voltage is high. There must be a place to add an inductor to help things out. Whether that's practical, can't say yet.

Cartainly a 9-to-5 switcher would make better use of the energy in the cap, by roughly 3:1.

I'm well aware of that. And capacitor size seemed to go by * C * V^2. You can roll the 1/2 into the constant or not, your choice.

Volume went more or less by energy stored. Cost, except at the very high voltage end, pretty much went by volume.

It wouldn't be a bad thing to do over again, if someone out there has time on there hands.

That is a generalization that is not at all universal. Switchers have inefficiencies that are proportional to the power delivered (with a base power drain) while the efficiency of a linear is determined by the input and output voltages (typically the quiescent power waste is relatively small). I've seen use cases where a linear was *more* efficient across the current range required.

Which may or may not be useful. The comparison would be several extra parts of a switcher vs a linear and a slightly larger cap. I bet the larger cap wins out by most metrics: size, complexity, cost.

I believe that is what is being done here. Modifying the existing circuit to even out the power draw.

rechargeable alkaline manganese (RAM)) is a type of alkaline battery that is capable of recharging for repeated use. The first-generation rechargeabl e alkaline technology was developed by Battery Technologies Inc in Canada a nd licensed to Pure Energy, EnviroCell, Rayovac, and Grandcell. Subsequent patent and advancements in technology have been introduced. The formats inc lude AAA, AA, C, D, and snap-on 9-volt batteries. Rechargeable alkaline bat teries are manufactured fully charged and have the ability to hold their ch arge for years, longer than NiCd and NiMH batteries, which self-discharge.[

Do not knew, but there are vendors on both Amazon and Ebay that have them f or sale.

I have not looked for any since about 1974. They were available at that ti me. But you can recharge a regular alkaline if the cell voltage is about 1 .3 volts or higher. We used to do that at work where flash lights were use d a lot.

our hands on. I tend not to take them seriously until a broad-line distribu tor keeps them in stock.

ch at the sharp end of knowing more and more about less and less until you know almost everything about about practically nothing.

Prety much the reason I studied up on vacuum systems. A good vacuum is clo ser to practically nothing than anything.

osts down to a minimum , so people can read them quickly.

nclude my signature line, which did waste bandwidth.

OK, the /2 *is* a constant if you're talking about ratios. It made no sense to make a point of it unless you didn't know.

Yep. The energy is "stored" in the dielectric. Just asking if you'd looked at it that way.

I've found cost is a higher order function, at least above some point (depending on package).

I'm often a proponent of just doing the simple solution -- there's no reason to spend a month searching out the best epoxy to use to glue something to the ground if you can just set a rock on it.

But in this case, you could buy a lot of switching supply for the price difference between 1200uF and 7000, even before you factor in the real and opportunity cost of using up that much space in the system.

I have used the trick of running the cap at higher voltage to lower the physical size of the capacitor a couple of times. The CV product is pretty constant for the same package size

Cheers

Klaus

Really? How much do you suppose the "opportunity cost" is for the OP's system?

Several people make switcher blobs that are cheap drop-in replacements for a 7805. OP probably has a 5 volt regulator already.