"Pulse" gel-cell charge strategy?
larwe
randomly-spaced bursts of intense power (think 20V at 300A or more,
for 25ms every minute or two), that I'd like to store in a gel-cell to
power my device. The average power available from the source is way
way more than the continuous load requirements of my device, but the
design of a charger circuit to exploit this energy source is not
something often encountered. Simply putting a linear regulator on the
source and letting it deliver a couple of amps (safe charging current)
into my battery won't cut it; I need to capture more of the energy in
each burst and trickle it out to the battery, basically extending the
duty cycle at lower current.
Searching for circuits that allow the use of intermittent energy
sources (solar, wave, etc) finds me a lot of things like peak power
trackers, circuits to prevent reverse voltage into unilluminated PV
cells, etc. Not really what I'm looking for.
I'm thinking vaguely of a bank of low-leakage supercaps charged from
the environmental input, with some kind of clamping to prevent them
from being overcharged, powering a switch-mode charger to deliver an
amp or two into the [fully discharged] battery, more or less
continuously.
This is in the nature of a back-of-the-envelope thought process
though. Has anyone encountered a similar situation? Am I missing a
really obvious solution?
-jg
> This is in the nature of a back-of-the-envelope thought process
> though. Has anyone encountered a similar situation? Am I missing a
> really obvious solution?
Farad level caps are probably your best bet.
I found they have got quite a bit cheaper/more available,
and with tens of milli ohm impedance.
-jg
Jim Stewart
> I've got an application where the environment provides infrequent,
> randomly-spaced bursts of intense power (think 20V at 300A or more,
> for 25ms every minute or two), that I'd like to store in a gel-cell to
> power my device. The average power available from the source is way
> way more than the continuous load requirements of my device, but the
> design of a charger circuit to exploit this energy source is not
> something often encountered. Simply putting a linear regulator on the
> source and letting it deliver a couple of amps (safe charging current)
> into my battery won't cut it; I need to capture more of the energy in
> each burst and trickle it out to the battery, basically extending the
> duty cycle at lower current.
>
> Searching for circuits that allow the use of intermittent energy
> sources (solar, wave, etc) finds me a lot of things like peak power
> trackers, circuits to prevent reverse voltage into unilluminated PV
> cells, etc. Not really what I'm looking for.
>
> I'm thinking vaguely of a bank of low-leakage supercaps charged from
> the environmental input, with some kind of clamping to prevent them
> from being overcharged, powering a switch-mode charger to deliver an
> amp or two into the [fully discharged] battery, more or less
> continuously.
Makes sense. What's the rise time of your pulses?
If it is fast you might want to add a big hulking
inductor to treat the caps nice and reduce IR losses
and/or wire size. I'd sure like to know what your
power source is.
larwe
> Makes sense. What's the rise time of your pulses?
> If it is fast you might want to add a big hulking
> inductor to treat the caps nice and reduce IR losses
> and/or wire size. I'd sure like to know what your
> power source is.
It's a sort of internal combustion engine powered by a slow seepage of
gas. The gas, while mainly methane and oxygen with a little hydrogen,
is severely impure and not suitable for feeding to a fuel cell. A gas
bubble forms slowly; when it's big enough (minutes), my controller
fires an igniter that burns the gas and fires a rare earth magnet down
(or rather, up) a coil that provides my electrical supply voltage. The
magnet has a groove around its lower rim that provides turbulent
obturation during the expansion phase. The controller has other
responsibilities too, but that's basically it for the power system.
Walter Banks
larwe wrote:
What kind of rare earth magnet doesn't lose its magnetic
properties over time with mechanical and heat shocks?
Great idea though.
An open end at the top of the coil would produce nice
smoke rings
w..
larwe
> What kind of rare earth magnet doesn't lose its magnetic
> properties over time with mechanical and heat shocks?
That would be a "not my problem" problem :) I don't do thermodynamics
and mechanical engineering; all I know is I get somewhere between
400-600W @ roughly 20VDC for a few tens of milliseconds every couple
of minutes or so. Having said that, I'm not sure how vigorous the
expansion phase is, nor how warm the magnet actually becomes.
Jon Kirwan
wrote:
>On Nov 26, 12:54�pm, Walter Banks <wal...@bytecraft.com> wrote:
>
>> What kind of rare earth magnet doesn't lose its magnetic
>> properties over time with mechanical and heat shocks?
>
>That would be a "not my problem" problem :) I don't do thermodynamics
>and mechanical engineering; all I know is I get somewhere between
>400-600W @ roughly 20VDC for a few tens of milliseconds every couple
>of minutes or so.
I prefer this expressed more like, "about 10 Joules every few
minutes." Do you have a figure on the Joules yielded and an estimate
on the methane volume (I assume at atmospheric pressure?) Just out of
curiousity...
Jon
larwe
> I prefer this expressed more like, "about 10 Joules every few
> minutes." Do you have a figure on the Joules yielded and an estimate
"10J every few minutes" implies to my mind slow and steady delivery -
which would be a different problem to be solved, I think.
Each stroke burns enough fuel to release maybe 350J of energy. It's
quite variable though because the concentrations of the reagents
fluctuate. There is a lot of argument in the pistons-and-PV-diagrams
camp right now about the design of the hardware; I'm not sufficiently
erudite to follow it. I've been assured that the electrical
characteristics won't change much if at all.
-jg
> all I know is I get somewhere between
> 400-600W @ roughly 20VDC for a few tens of milliseconds every couple
> of minutes or so.
Earlier this was 300A - did you mean 30A ?
The 10J mentioned is not large in the scheme of things,
I get around 3.2F at 2.5V and 32mF at 25V
(assume full dV) - at such short times,
the series R of the 'SuperCaps' becomes an issue,
so you might do either a combination, or
just look at a FAT 25V Elco ?
ie a 100mF 25V cap, changing 11.25 Joules moves
from 20V to 25V
-jg
larwe
> On Nov 27, 10:51 am, larwe <zwsdot...@gmail.com> wrote:
>
> > all I know is I get somewhere between
> > 400-600W @ roughly 20VDC for a few tens of milliseconds every couple
> > of minutes or so.
>
> Earlier this was 300A - did you mean 30A ?
No, I meant 300A, I was tinkering in the simulation spreadsheet and
accidentally deleted a zero :) I blame the fact that I am currently
about 150lb heavier than normal due to being stuffed with Thanksgiving
food.
-jg
>
> No, I meant 300A,
Wow - So that's 6000W (?!) of peak power, or 150W over 1 second, or
~1W over 150 seconds
How big is that magnet ? ;)
How much of this 6000W do you actually need to capture ?
How many milli-ohms is the 'generator loop' ?
-jg
larwe
> Wow - So that's 6000W (?!) of peak power, or 150W over 1 second, or
> ~1W over 150 seconds
It's roughly roughly 6kW for a few tens of ms; on average, somewhere
around 25ms, once every couple of minutes (that couple of minutes
figure is extremely loose, but it will never be LESS than a couple of
minutes - it could stretch to four or five, though).
>
> How big is that magnet ? ;)
Big enough that you have to plan a route exactly when transporting it,
you may not allow more than one in the same room, and you should not
bring it within spitting distance of any CRT monitors. But it's more
the "propelled at speed through coil" aspect that makes it
electrically frisky.
> How much of this 6000W do you actually need to capture ?
Very little. My circuit VERY RARELY dissipates about 25W; however most
of the time it's cruising in the region of 200mW. The more I could
harvest, the better though - all sorts of interesting things could be
done with the excess. The other thing is that the fuel source is very
erratic. Sometimes the gas mix that's harvested won't contain enough
available energy to actually drive the cycle, in which case it gets
"burped" and collection resumes.
> How many milli-ohms is the 'generator loop' ?
It's about 52mohm; and, I might add, a scrap metal thief's dream come
true. Which is a bit of a problem, but again not mine :)
Jim Stewart
Very cool project. Thanks for sharing more about
it. Pictures would be greatly appreciated if ever
possible.
Walter Banks
larwe wrote:
I get the impression of a free piston engine and when enough
methane and air accumulate then bang. The piston races up
through a cylinder wrapped in wire. You capture the transient.
The piston returns maybe even with gravity and the electronics
lies in wait for the necessary gas to accumulate before sending
the piston again for a ride of a life time.
Mr. Goldberg would have been proud.
Nice project. With global warming I can just see great opportunities
for such a device in the Canadian arctic. The permafrost is melting
the amount of constable gases being released is huge.
Regards,
Walter..
__
Walter Banks
Byte Craft Limited
http://www.bytecraft.com
larwe
> I get the impression of a free piston engine and when enough
> methane and air accumulate then bang. The piston races up
That's it.
> The piston returns maybe even with gravity and the electronics
That is exactly why the "piston" uses turbulent obturation. The
compression/exhaust stroke works by slowly venting the exhaust gases
around the edges of the magnet and simultaneously condensing the steam
that formed during the expansion phase. If the piston was close-fit to
the cylinder, it would be necessary to have all manner of valves and
such. Yes, we lose some energy to leakage, but we get it paid back in
reliability. Mortars often use the same principle - you drop the shell
down the barrel, and it moves relatively slowly so there's plenty of
gas leakage around the edges. Once it hits bottom, the propellant
fires and the huge pressure differential creates rapid flow, lots of
turbulence around the obturating ring and your shell gets pushed off
towards the enemy...
Mark Borgerson
says...
Sounds like a neat idea for dairy farms and landfills. Lots of
methane generated in manure digesters and in the land fill. Our
local landfill runs a gnerator with some of their gas---but the
gas requires a lot cleaning lest H2S corrode the generator.
I wonder if it might be simpler to have the coil be open circuit
on the upward movement of the magnet, then capture the engergy
on the downward fall of the magnet. You could arrange the coil
impedance and gas venting rate so that the down stroke might
be 10x slower than the upward.
Another off-the wall idea: Use the main piston as a pump
to push the air above the piston into a reservoir with a
simple flap valve at the entry. You can then bleed the pressurized
air through a turbine to capture energy.
This sounds like enough fun that I may have to go out and buy
some PVC pipe and indulge my inner Rube Goldberg.
Mark Borgerson
larwe
> Sounds like a neat idea for dairy farms and landfills. Lots of
> methane generated in manure digesters and in the land fill. Our
> local landfill runs a gnerator with some of their gas---but the
> gas requires a lot cleaning lest H2S corrode the generator.
Yes, this project has similar problems to solve. Hence the desire for
no unnecessary moving parts.
> This sounds like enough fun that I may have to go out and buy
> some PVC pipe and indulge my inner Rube Goldberg.
Don't forget to add 1100ft of AWG 0000 copper wire to your shopping
list. You may wish to rent a truck... and an armed guard ;) Of course
you could make a scaled-down version with magnet wire, but that simply
wouldn't be fun.
I should point out that in my case the bottom (harvester) end of this
gadget is underwater; gases are evolved by reactions at the bottom,
and fill the combustion chamber. Atmospheric air is also bubbled in.
The "breech" seal, as it were, is simply a column of water. This is
also a safety valve - overpressure in the "barrel" is impossible.
There are a lot of mechanical engineering subtleties in the design,
most of which I don't know (and likely would not understand unless
they were explained to me patiently).
-jg
>
> Don't forget to add 1100ft of AWG 0000 copper wire to your shopping
> list. You may wish to rent a truck... and an armed guard ;)
So this project has no dollars per watt metric, that
it needs to meet ? ;)
Surely the power generation is _not_ the primary goal here ?
We have Bird Scarers here, that use similar 'sporadic explosion' basis
- called 'Bird cannon'
-jg
larwe
> > Don't forget to add 1100ft of AWG 0000 copper wire to your shopping
> > list. You may wish to rent a truck... and an armed guard ;)
>
> So this project has no dollars per watt metric, that
> it needs to meet ? ;)
It all depends where you put your break-even point; a thousand-year
payoff? :)
> Surely the power generation is _not_ the primary goal here ?
No, this is waste energy in fact.
> We have Bird Scarers here, that use similar 'sporadic explosion' basis
> - called 'Bird cannon'
They're propane though, aren't they?
Mark Borgerson
abda01...@d10g2000yqh.googlegroups.com>, zwsd...@gmail.com says...
> On Nov 27, 2:12 pm, Mark Borgerson <mborger...@comcast.net> wrote:
>
> > Sounds like a neat idea for dairy farms and landfills. Lots of
> > methane generated in manure digesters and in the land fill. Our
> > local landfill runs a gnerator with some of their gas---but the
> > gas requires a lot cleaning lest H2S corrode the generator.
>
> Yes, this project has similar problems to solve. Hence the desire for
> no unnecessary moving parts.
>
> > This sounds like enough fun that I may have to go out and buy
> > some PVC pipe and indulge my inner Rube Goldberg.
>
> Don't forget to add 1100ft of AWG 0000 copper wire to your shopping
> list. You may wish to rent a truck... and an armed guard ;) Of course
> you could make a scaled-down version with magnet wire, but that simply
> wouldn't be fun.
I was considering my alternative plan to (in smaller scale) use the
methane combustion to compress air---then vent the compressed air
through a turbine. That lets me spread the power out over a
much longer time and avoid the requirement for all that copper
wire.
>
> I should point out that in my case the bottom (harvester) end of this
> gadget is underwater; gases are evolved by reactions at the bottom,
> and fill the combustion chamber. Atmospheric air is also bubbled in.
> The "breech" seal, as it were, is simply a column of water. This is
> also a safety valve - overpressure in the "barrel" is impossible.
>
> There are a lot of mechanical engineering subtleties in the design,
> most of which I don't know (and likely would not understand unless
> they were explained to me patiently).
>
Mark Borgerson
larwe
> I was considering my alternative plan to (in smaller scale) use the
> methane combustion to compress air---then vent the compressed air
> through a turbine. That lets me spread the power out over a
There's nothing wrong with that plan, except that it involves many
more moving parts
lowcost
> There's nothing wrong with that plan, except that it involves many
> more moving parts
why not a peltier cell, heated by a small single flame burner ?
regards
--
lowcost
larwe
> larwe ha scritto:
>
> > There's nothing wrong with that plan, except that it involves many
> > more moving parts
>
> why not a peltier cell, heated by a small single flame burner ?
Because the burner requires fairly precise gas flow control and has a
strong potential of becoming clogged and corroded. The explosive
method is little more than a funnel turned upside-down, with a spark
plug at the narrow end of the cone.
Mark Borgerson
@j4g2000yqe.googlegroups.com>, zwsd...@gmail.com says...
the cost of the copper in a system that has to collect the
energy in a few milliseconds.
Mark Borgerson
Mark Borgerson
60653e...@j19g2000yqk.googlegroups.com>, zwsd...@gmail.com says...
Is the range of combustible mixtures wide enough to guarantee
ignition, or do you have to monitor the fuel/air mixture?
Mark Borgerson
larwe
> Is the range of combustible mixtures wide enough to guarantee
> ignition, or do you have to monitor the fuel/air mixture?
I think I said above someplace - no it is certainly not guaranteed. If
it fails, we try again.
Meindert Sprang
I just came across some interesting supercaps from Wima available up to
400F/2.5V. They store 1250J and the pulse current may be 600A. They can be
connected in series. Datasheet here:
http://www.farnell.com/datasheets/4736.pdf
Meindert
invalid
news:4b17caf3$0$22942$e4fe...@news.xs4all.nl...
What was known in the trade as an FGC.
GC = Great Capacitor.
F = unprintable
Paul Carpenter
says...
Aka a BMF capacitor
BM = Big Mother
F = ....
--
Paul Carpenter | pa...@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
<http://www.badweb.org.uk/> For those web sites you hate
larwe
wrote:
> Aka a BMF capacitor
>
> BM = Big Mother
> F = ....
And here is a real BMF complete with Ms.
<http://blog.modernmechanix.com/2006/09/05/giant-capacitor/>