Forums

capcitors for energy reserve

Started by Richard October 2, 2014
On Fri, 03 Oct 2014 14:51:48 -0400, rickman wrote:

> On 10/3/2014 2:35 PM, Tim Wescott wrote: >> On Fri, 03 Oct 2014 00:27:33 -0700, Klaus Kragelund wrote: >> >>> On Friday, October 3, 2014 5:46:51 AM UTC+2, Tim Wescott wrote: >>>> On Thu, 02 Oct 2014 14:53:44 -0700, Klaus Kragelund wrote: >>>> >>>> >>>> >>>>> On Thursday, October 2, 2014 11:47:08 PM UTC+2, Richard wrote: >>>> >>>>>> On Thursday, October 2, 2014 2:12:22 PM UTC-7, Tim Wescott wrote: >>>> >>>> >>>> >>>>>>> On Thu, 02 Oct 2014 15:44:19 -0500, Tim Wescott wrote: >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> On Thu, 02 Oct 2014 13:21:05 -0700, Richard wrote: >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>>> I have a circuit that draws 30mA except that there is a 150ms >>>>>>>>> long >>>> >>>>>>>>> draw >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> at 120mA. This occurs every 2s. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>>> >>>> >>>>>> >>>> >>>>>>>>> I I am limited to 40mA current draw. I would like to provide >>>> >>>>>>>>> reserve >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> energy from a large capacitor. I have built a circuit that >>>>>>>>> limits >>>> >>>>>>>>> the >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> input current to 40mA. This runs the circuit and charges the >>>>>>>>> cap. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>>> >>>> >>>>>> >>>> >>>>>>>>> I have run caps up to 3300uF, the cap voltage drops to far and >>>>>>>>> in >>>> >>>>>>>>> too >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> short a time. Is there any methodology for calculating required >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> capacitance? Any ideas on implementation beside my current >>>> >>>>>>>>> limiter >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>>> plus cap? >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> Hark back to your sophomore electronics engineering courses: >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> dV/dt = i / C >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> For a constant current draw, you can change that to >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> deltaV / deltaT = i / C >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> Do some algebra, and you get >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> C = i * deltaT / deltaV >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> You've got 40mA in, 120mA out, which means you need 80mA out of >>>>>>>> the >>>> >>>>>>>> cap. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> You know what voltage drop you can stand -- plug that figure into >>>> >>>>>>>> the >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> above equation along with the rest of your knowns, and you should >>>> >>>>>>>> get a >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> minimum capacitance. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> I must say, though, that if 3300uF isn't enough, then at those >>>> >>>>>>>> current >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> levels there's something else going on. If your calculations >>>>>>>> show >>>> >>>>>>>> that >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> 3300uF is way more than plenty, then your problem may be that >>>> >>>>>>>> you're >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> using aluminum electrolytics where you need to use something with >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> significantly lower ESR. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>>> I'm doing something similar to you right now, except that my >>>> >>>>>>>> current >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> draw is for a shorter period of time. I have my filter cap in my >>>> >>>>>>>> "raw" >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> power line, ahead of my local regulator. With 5V on the "raw" >>>>>>>> side >>>> >>>>>>>> and >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> 3.3V on the regulated side, I can accept a 1V drop during the >>>>>>>> 'on' >>>> >>>>>>>> time, >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>>> as long as the cap charges back for the next cycle. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> Note that I messed up my in-the-head math: 3300uF is, indeed, >>>>>>> pretty >>>> >>>>>>> small >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> for this unless you charge the cap with a boost circuit, regulate >>>> >>>>>>> after >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> the cap, and accept large voltage swings. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> -- >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> Tim Wescott >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> Wescott Design Services >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> http://www.wescottdesign.com >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>> Thanks guys for the ideas. I used 3300 because that is what I had. >>>>>> I >>>> >>>>>> am now using ~7000uF and I see better results, the voltage drops >>>>>> from >>>> >>>>>> 9V down to ~5V so I am too close to the 5V minimum. Charge time is >>>> >>>>>> ~1.7s. The input current is limited at 40mA. >>>> >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>> I think this will work with a larger cap but sure seem inelegant. >>>> >>>> >>>> >>>>> You have 10mA surplus during normal op, right? >>>> >>>> >>>> >>>>> Use that to charge a lower value capacitor with a boost converter >>>> >>>> >>>> >>>>> When you need the 180mA, draw that from a buck converter, so you can >>>> >>>>> draw all the energy out og the capacitor >>>> >>>> >>>> >>>>> Cheers >>>> >>>> >>>> >>>>> Klaus >>>> >>>> >>>> >>>> Assuming 100% efficient supplies: >>>> >>>> >>>> >>>> (120mA)(150ms)(5V) = 90mJ >>>> >>>> >>>> >>>> (30mA)(150ms)(9V) = 40.5mJ >>>> >>>> >>>> >>>> Leaving you with a 49.5mJ deficit. >>>> >>>> >>>> >>>> Energy in a capacitor: W = C * V^2 / 2. Let V = 9V (it could be >>>> anything >>>> >>>> if we're switching in and switching out), then >>>> >>>> >>>> >>>> C = 2 * (49.5mJ) / (9V)^2 = 1222uF >>>> >>>> >>>> >>>> That's the ABSOLUTE MINIMUM capacitance you can use if you only go up >>>> to >>>> >>>> 9V. >>>> >>>> >>>> >>> Yes, and 1200uF is a lot less than 7000uF >> >> 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. > > Really? How much do you suppose the "opportunity cost" is for the OP's > system?
I have no clue -- it's just something for him to consider. I do know that I generally end up spending more for a pretty case to put a board into than I spend for the bare board and its parts -- and bigger cases cost more. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On 10/3/2014 3:14 PM, John Larkin wrote:
> On Fri, 03 Oct 2014 13:35:09 -0500, Tim Wescott > <seemywebsite@myfooter.really> wrote: > >> On Fri, 03 Oct 2014 00:27:33 -0700, Klaus Kragelund wrote: >> >>> On Friday, October 3, 2014 5:46:51 AM UTC+2, Tim Wescott wrote: >>>> On Thu, 02 Oct 2014 14:53:44 -0700, Klaus Kragelund wrote: >>>> >>>> >>>> >>>>> On Thursday, October 2, 2014 11:47:08 PM UTC+2, Richard wrote: >>>> >>>>>> On Thursday, October 2, 2014 2:12:22 PM UTC-7, Tim Wescott wrote: >>>> >>>> >>>>>> >>>>>>> On Thu, 02 Oct 2014 15:44:19 -0500, Tim Wescott wrote: >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> On Thu, 02 Oct 2014 13:21:05 -0700, Richard wrote: >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> I have a circuit that draws 30mA except that there is a 150ms >>>>>>>>> long >>>> >>>>>>>>> draw >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> at 120mA. This occurs every 2s. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> I I am limited to 40mA current draw. I would like to provide >>>> >>>>>>>>> reserve >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> energy from a large capacitor. I have built a circuit that >>>>>>>>> limits >>>> >>>>>>>>> the >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> input current to 40mA. This runs the circuit and charges the >>>>>>>>> cap. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> I have run caps up to 3300uF, the cap voltage drops to far and >>>>>>>>> in >>>> >>>>>>>>> too >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> short a time. Is there any methodology for calculating >>>>>>>>> required >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> capacitance? Any ideas on implementation beside my current >>>> >>>>>>>>> limiter >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>>> plus cap? >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> Hark back to your sophomore electronics engineering courses: >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> dV/dt = i / C >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> For a constant current draw, you can change that to >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> deltaV / deltaT = i / C >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> Do some algebra, and you get >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> C = i * deltaT / deltaV >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> You've got 40mA in, 120mA out, which means you need 80mA out of >>>>>>>> the >>>> >>>>>>>> cap. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> You know what voltage drop you can stand -- plug that figure >>>>>>>> into >>>> >>>>>>>> the >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> above equation along with the rest of your knowns, and you >>>>>>>> should >>>> >>>>>>>> get a >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> minimum capacitance. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> I must say, though, that if 3300uF isn't enough, then at those >>>> >>>>>>>> current >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> levels there's something else going on. If your calculations >>>>>>>> show >>>> >>>>>>>> that >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> 3300uF is way more than plenty, then your problem may be that >>>> >>>>>>>> you're >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> using aluminum electrolytics where you need to use something >>>>>>>> with >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> significantly lower ESR. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> I'm doing something similar to you right now, except that my >>>> >>>>>>>> current >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> draw is for a shorter period of time. I have my filter cap in >>>>>>>> my >>>> >>>>>>>> "raw" >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> power line, ahead of my local regulator. With 5V on the "raw" >>>>>>>> side >>>> >>>>>>>> and >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> 3.3V on the regulated side, I can accept a 1V drop during the >>>>>>>> 'on' >>>> >>>>>>>> time, >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>>> as long as the cap charges back for the next cycle. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> Note that I messed up my in-the-head math: 3300uF is, indeed, >>>>>>> pretty >>>> >>>>>>> small >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> for this unless you charge the cap with a boost circuit, regulate >>>> >>>>>>> after >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> the cap, and accept large voltage swings. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> -- >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> Tim Wescott >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> Wescott Design Services >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>>> >>>>>>> http://www.wescottdesign.com >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>> >>>>>> Thanks guys for the ideas. I used 3300 because that is what I had. >>>>>> I >>>> >>>>>> am now using ~7000uF and I see better results, the voltage drops >>>>>> from >>>> >>>>>> 9V down to ~5V so I am too close to the 5V minimum. Charge time is >>>> >>>>>> ~1.7s. The input current is limited at 40mA. >>>> >>>> >>>>>> >>>> >>>>>> >>>> >>>>>> >>>>>> I think this will work with a larger cap but sure seem inelegant. >>>> >>>> >>>>>> >>>>> You have 10mA surplus during normal op, right? >>>> >>>> >>>>> >>>>> Use that to charge a lower value capacitor with a boost converter >>>> >>>> >>>>> >>>>> When you need the 180mA, draw that from a buck converter, so you can >>>> >>>>> draw all the energy out og the capacitor >>>> >>>> >>>>> >>>>> Cheers >>>> >>>> >>>>> >>>>> Klaus >>>> >>>> >>>> >>>> Assuming 100% efficient supplies: >>>> >>>> >>>> >>>> (120mA)(150ms)(5V) = 90mJ >>>> >>>> >>>> >>>> (30mA)(150ms)(9V) = 40.5mJ >>>> >>>> >>>> >>>> Leaving you with a 49.5mJ deficit. >>>> >>>> >>>> >>>> Energy in a capacitor: W = C * V^2 / 2. Let V = 9V (it could be >>>> anything >>>> >>>> if we're switching in and switching out), then >>>> >>>> >>>> >>>> C = 2 * (49.5mJ) / (9V)^2 = 1222uF >>>> >>>> >>>> >>>> That's the ABSOLUTE MINIMUM capacitance you can use if you only go up >>>> to >>>> >>>> 9V. >>>> >>>> >>>> >>> Yes, and 1200uF is a lot less than 7000uF >> >> 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. > > Several people make switcher blobs that are cheap drop-in replacements > for a 7805. OP probably has a 5 volt regulator already.
That's not accounting for the drop out voltage which on switchers, especially the cheap drop-in replacements, tend to be several volts. So if you limit your cap range to 9-7 vs 9-5 volts you probably need an even larger cap than the one you could get by with not using a regulator at all. lol -- Rick
On Saturday, 4 October 2014 04:19:24 UTC+10, dca...@krl.org  wrote:
> On Friday, October 3, 2014 10:54:50 AM UTC-4, Bill Sloman wrote: > =20 > > > A rechargeable alkaline battery (also known as alkaline rechargeable =
or rechargeable alkaline manganese (RAM)) is a type of alkaline battery tha= t is capable of recharging for repeated use. The first-generation rechargea= ble alkaline technology was developed by Battery Technologies Inc in Canada= and licensed to Pure Energy, EnviroCell, Rayovac, and Grandcell. Subsequen= t patent and advancements in technology have been introduced. The formats i= nclude AAA, AA, C, D, and snap-on 9-volt batteries. Rechargeable alkaline b= atteries are manufactured fully charged and have the ability to hold their = charge 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. =20
> >=20 > > Do any of the broad-line distributors stock them? >=20 > Do not knew, but there are vendors on both Amazon and Ebay that have them=
for sale. Sounds like some people thought that they could make them once, but the cru= cial ingredient stopped being available. I had the same experience with orienetation-insensitive mercury-wetted reed= relays. For a while there were a few manufacturers who claimed to be able = to make them, but you could never buy them when you wanted them. =20
> I have not looked for any since about 1974. They were available at that =
time. 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 u= sed a lot.=20 The manufacturers don't endorse the technique.
> > Too many "advances in technology" turn out to be remarkably hard to get=
your hands on. I tend not to take them seriously until a broad-line distri= butor keeps them in stock.=20
> >=20 > > 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 yo= u know almost everything about about practically nothing. =20
>=20 > Prety much the reason I studied up on vacuum systems. A good vacuum is c=
loser to practically nothing than anything. Inter-galactic space seems to do better. <snipped comments about snipping> --=20 Bill Sloman, Sydney
On Friday, October 3, 2014 10:57:00 PM UTC-4, Bill Sloman wrote:
>=20 >=20 > > Do not knew, but there are vendors on both Amazon and Ebay that have th=
em for sale.
>=20 >=20 >=20 > Sounds like some people thought that they could make them once, but the c=
rucial ingredient stopped being available.
>=20 >
Why do you think that? I have no interest in buying any so did not look f= or an industrial supplier. I may be mistaken , but do not think you are in= terested in getting any, or you would have searched for them your self. So= looking for an industrial supplier would just be wasted effort.
>=20 > I had the same experience with orienetation-insensitive mercury-wetted re=
ed relays. For a while there were a few manufacturers who claimed to be abl= e to make them, but you could never buy them when you wanted them.
>=20 > =20 >=20 > > I have not looked for any since about 1974. They were available at tha=
t time. But you can recharge a regular alkaline if the cell voltage is abo= ut 1.3 volts or higher. We used to do that at work where flash lights were= used a lot.=20
>=20 >=20 >=20 > The manufacturers don't endorse the technique. >=20 >
If I were a manufacturer I would not recommend anything that would decrease= sales. =20
>=20 > > > Too many "advances in technology" turn out to be remarkably hard to g=
et your hands on. I tend not to take them seriously until a broad-line dist= ributor keeps them in stock.=20
>=20 > > >=20
>=20 > > Prety much the reason I studied up on vacuum systems. A good vacuum is=
closer to practically nothing than anything.
>=20 >=20 >=20 > Inter-galactic space seems to do better. >=20
High vacuum in Inter-galactic space seemed to have little practical applica= tion. Dan
> --=20 >=20 > Bill Sloman, Sydney
On Saturday, 4 October 2014 22:39:53 UTC+10, dca...@krl.org  wrote:
> On Friday, October 3, 2014 10:57:00 PM UTC-4, Bill Sloman wrote:=20 > >=20 > > > Do not knew, but there are vendors on both Amazon and Ebay that have =
them for sale.=20
> > =20 > > Sounds like some people thought that they could make them once, but the=
crucial ingredient stopped being available.=20
> > =20 > Why do you think that? I have no interest in buying any so did not look=
for an industrial supplier. I may be mistaken , but do not think you are = interested in getting any, or you would have searched for them your self. = So looking for an industrial supplier would just be wasted effort. You implied that they were an off-the-shelf solution. They don't seem to be= .
> > I had the same experience with orienetation-insensitive mercury-wetted =
reed relays. For a while there were a few manufacturers who claimed to be a= ble to make them, but you could never buy them when you wanted them.
> >=20 > > > I have not looked for any since about 1974. They were available at t=
hat time. But you can recharge a regular alkaline if the cell voltage is a= bout 1.3 volts or higher. We used to do that at work where flash lights we= re used a lot. =20
> > =20 > > The manufacturers don't endorse the technique.=20 > >=20 > If I were a manufacturer I would not recommend anything that would decrea=
se sales.=20 Different markets. NiCd and NiMH rechargeable cells sell in respectable num= bers, and I can buy them in my local supermarket. If alkaline cells could c= ompete in that market - possibly with tarted up packaging, they would. they= don't. so the assumption is that they can't. =20
> > > > Too many "advances in technology" turn out to be remarkably hard to=
get your hands on. I tend not to take them seriously until a broad-line di= stributor keeps them in stock.=20 <snip>
> > > Pretty much the reason I studied up on vacuum systems. A good vacuum=
is closer to practically nothing than anything.=20
> > =20 > > Inter-galactic space seems to do better. > >=20 > High vacuum in inter-galactic space seemed to have little practical appli=
cation. Interplanetary space is more accessible than it used to be, though I've not= yet seen evidence that people are exploiting it as a manufacturing environ= ment. --=20 Bill Sloman, Sydney
On Saturday, October 4, 2014 10:52:29 AM UTC-4, Bill Sloman wrote:

> > > Sounds like some people thought that they could make them once, but t=
he crucial ingredient stopped being available.=20
>=20 > > > =20 >=20 > > Why do you think that? I have no interest in buying any so did not lo=
ok for an industrial supplier. I may be mistaken , but do not think you ar= e interested in getting any, or you would have searched for them your self.= So looking for an industrial supplier would just be wasted effort.
>=20 >=20 >=20 > You implied that they were an off-the-shelf solution. They don't seem to =
be.
>
What makes you say that they do not seem to be an off the shelf solution. = All I said is that I not looked to see the availability since I am not look= ing for any.=20
>=20
> > If I were a manufacturer I would not recommend anything that would decr=
ease sales.=20
>=20 >=20 >=20 > Different markets. NiCd and NiMH rechargeable cells sell in respectable n=
umbers, and I can buy them in my local supermarket. If alkaline cells could= compete in that market - possibly with tarted up packaging, they would. th= ey don't. so the assumption is that they can't.
>=20 >=20
Alkaline batteries also sell in respectable numbers and in the same markets= as Nicd and NIMH batteries. At least in the U.S. Maybe alkaline botterie= s are not available in Australia Dan
>=20 >=20 >=20 >=20
>=20 > Bill Sloman, Sydney
On Thu, 2 Oct 2014 13:21:05 -0700 (PDT), Richard
<rsoennichsen@gmail.com> wrote:

>I have a circuit that draws 30mA except that there is a 150ms long draw at 120mA. This occurs every 2s. > >I I am limited to 40mA current draw. I would like to provide reserve energy from a large capacitor. I have built a circuit that limits the input current to 40mA. This runs the circuit and charges the cap. > >I have run caps up to 3300uF, the cap voltage drops to far and in too short a time. Is there any methodology for calculating required capacitance? Any ideas on implementation beside my current limiter plus cap?
You have to specify the minimum voltage your load will accept at the end of the current peak. In any capacitor based storage system, the voltage starts linearly drop as charge is removed, thus the load should accept as much voltage variations as possible. This might require using some switching regulator between the capacitor and actual load, say 24 V fully charged and 8 V at the end of the discharge cycle. Depending on your life time and temperature requirement a secondary battery (such as NiCd) might be a better solution. Make sure that the charge current is only slightly above the _average_ load current. As long as your excess average charge current is well below C/10, the battery can dissipate that extra charge without overheating. Lead accumulators are available at 6, 12 and 24 V (nominal), so you can leave these on float charge for years on 6.9, 13.8 and 27.6 V.
On Saturday, October 4, 2014 4:31:35 PM UTC+1, upsid...@downunder.com wrote:
> On Thu, 2 Oct 2014 13:21:05 -0700 (PDT), Richard > <rsoennichsen> wrote:
> >I have a circuit that draws 30mA except that there is a 150ms long draw at 120mA. This occurs every 2s. > > > >I I am limited to 40mA current draw. I would like to provide reserve energy from a large capacitor. I have built a circuit that limits the input current to 40mA. This runs the circuit and charges the cap. > > > >I have run caps up to 3300uF, the cap voltage drops to far and in too short a time. Is there any methodology for calculating required capacitance? Any ideas on implementation beside my current limiter plus cap? > You have to specify the minimum voltage your load will accept at the > end of the current peak. > In any capacitor based storage system, the voltage starts linearly > drop as charge is removed, thus the load should accept as much voltage > variations as possible. This might require using some switching > regulator between the capacitor and actual load, say 24 V fully > charged and 8 V at the end of the discharge cycle. > Depending on your life time and temperature requirement a secondary > battery (such as NiCd) might be a better solution. Make sure that the > charge current is only slightly above the _average_ load current. As > long as your excess average charge current is well below C/10, the > battery can dissipate that extra charge without overheating. > Lead accumulators are available at 6, 12 and 24 V (nominal), so you > can leave these on float charge for years on 6.9, 13.8 and 27.6 V.
Though compared to a cap they're expensive, heavy, short lived and prone to spray acid about. NT
=20
> Depending on your life time and temperature requirement a secondary batte=
ry (such as NiCd) might be a better solution. Make sure that the charge cur= rent is only slightly above the _average_ load current. As long as your exc= ess average charge current is well below C/10, the battery can dissipate th= at extra charge without overheating. Normally, i would suggest battery as well. But in OP's case, he is running= a 2 seconds cycle, which is probably not good for a battery.
On Sat, 4 Oct 2014 07:52:24 -0700 (PDT), Bill Sloman
<bill.sloman@gmail.com> Gave us:

> >Interplanetary space
You mean the void between your ears? That is only about the size of a walnut, due to the thickness of your skull! You are a fucking BONEHEAD! You epitomize the term! How difficult is it to understand that YOU need a different interface to Usenet, and that YOU are fucking up entire threads? YOU goddamned inconsiderate, RETARDED BASTARD! COMPLY, MOTHERFUCKER!