400 Farad 2.7v capacitors
HollyMinkowski
Posts: 1,398
I just ordered two 400 Farad capacitors.
Going to see how long they can power a
small project I built that uses a Tiny85V running
at 1mhz...should be a long time.
Supposedly these can deliver 86Amps of current
if they need to..WoW! They can also be charged at
86Amps (who has an 86amp 2.7v supply) They can
hold their full charge for 87600 hours at 25c.
The absolute maximum power they can deliver is
93amps for 1 second.
Not sure exactly how they should be charged up?
Maybe slowly using a resistor hooked to my variable
10amp supply set at 2V, I need 1.8V
for the tiny.
These are part no 407DCN2R7 from Illinois Capacitor.
(NOT CHEAP!)
www.illinoiscapacitor.com/ic_search/_super_products.aspx?seriesID=198
Going to see how long they can power a
small project I built that uses a Tiny85V running
at 1mhz...should be a long time.
Supposedly these can deliver 86Amps of current
if they need to..WoW! They can also be charged at
86Amps (who has an 86amp 2.7v supply) They can
hold their full charge for 87600 hours at 25c.
The absolute maximum power they can deliver is
93amps for 1 second.
Not sure exactly how they should be charged up?
Maybe slowly using a resistor hooked to my variable
10amp supply set at 2V, I need 1.8V
for the tiny.
These are part no 407DCN2R7 from Illinois Capacitor.
(NOT CHEAP!)
www.illinoiscapacitor.com/ic_search/_super_products.aspx?seriesID=198
Comments
-Phil
But still large enough that I will have to
get a slightly bigger case for the project.
They are just too fat to fit into the existing
case.
And BTW why are plastic cases so danged
expensive anyway!? Often the case is the most
expensive part of some project I create :-(
A friend of mine used to put everything he built into suitable cardboard boxes.
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Leon Heller
Amateur radio callsign: G1HSM
I had a friend who made me some small wooden
project boxes. They looked really nice once they
were stained. They had slots cut into the front and rear
so you could slide in panels. I used photoshop to print
up a nice front panel design and put a thin piece of
plastic behind that and a clear piece in front of it. It
looked very nice, it was a bit to shiny though, I should
have roughed up the panel somehow, maybe with an
SOS pad or something.
·
How much did they cost ?
Bean
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
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If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
I thought that was outrageous but then I checked Mouser
and it's actually a good price.
BTW Mouser sells a 4000 Farad cap for 246.90 it looks very similar to the 400 Farad ones.
A bit larger though and has screw terminals. Only 10 left so time is running out
www.mouser.com/ProductDetail/Nichicon/JJD0E408MSEG/?qs=sGAEpiMZZMsCu9HefNWqpvZlKmtZr9KSvm0zABeQkcw%3d
They wanted a copy of your diploma from engineering school?
Maybe it's because these could be dangerous if accidentally discharged?
Imagine if you had say 10 of the 4000 Farad ones and accidentally shorted
the leads....we are talking serious smoke.
-Phil
The 86,000 hours you refer to is the life of the capacitor at its maximum ratings; NOT how long will it hold a charge. The hold time is determined by its leakage current (worse with higher temperature) at 1.2 mA. So, by taking the stored energy at .4 Watt-Hours, and converting that to the 1.2 mA leakage for a 1.35 volt drop, is about 250 hours.
Cheers,
Peter (pjv)
I totally misinterpreted that specification.
I'm going to hook them up in series so that
it will take longer for them to drop below the
1.8v minimum I need. The tiny85V can take 5.5v
and continue to work all the way down to 1.8v
if run at 1mhz. Mostly my program has all the
peripherals shut down and stays in sleep mode
as much as possible so the current draw is
amazingly tiny. When all powered up from sleep
mode the current used is maybe 50ma, but
just for a second or so. I tried to use a watch
xtal to run at a super low speed but it was too
slow for my code to do its job properly.
When you hook them in series, they will (obviously) charge with equal currents, and the resulting voltage on each as it charges will be a function of it's actual capacitance. This value can have a considerable variation from unit to unit, so it is possible to 'over-voltage' the smaller of the two capacitors. That might be a bad thing. So my recommendation would be to monitor the voltage across each cap a couple of times along it's charge cycle to confirm balanced performance. In real life one would normally put a passive (resistors) or active (current shunt) nework across each cap to curtail this problem. But that in itself consumes current; something you don't want. So just watch the voltages, and if they track, then the caps are of comparable values, and you should be OK.
Cheers,
Peter
I'd really hate to fry these things.
They would not hold a charge very long. For these high voltage caps, the discharge rate is not linear but is a function of the voltage.
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Searider
www.tecategroup.com/store/index.php?main_page=product_info&cPath=18_20_32&products_id=12
Short circuit current is quoted at 1500A. I have my doubts too about this but aren't about to measure!
For 2 in series you need to "balance" the midpoint. If you use something like an Atmega you can use a single pin to sample the midpoint voltage via a series resistor eg 10kohm. Then depending on which cap needs bleeding either drive the output low (to bleed the bottom cap) or high (too bleed the top cap). When its suitable balanced just leave the pin in the high Z floating state.
www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1801,P90849
Until you build up sufficient charge won't this cap appear to be a short to your power supply? In the end product, when discharged, won't this have an extermely long start up time? (dependent on the current of your power supply to charge the device).
When I've built stuff in the past with this kind of design I've used a lead acid battery topped up by the power supply via a resistor in series so it doesn't drop the power supply voltage too significantly when charging.
Meanwhile a really cool CAP! But you probably don't want to short it!
Dave
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It's all a function of time.
800F @ 2.7 V is only 3000 Joules.
2 AH @ 2.4 V is well over 8000 Joules.
I think you should power your Tiny with an old-fashioned Gravity Cell (a.k.a. Crow's Foot). You could make your own w/o a great deal of trouble.
They are elemental (no pun intended) and last a very long time in low-drain apps.
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The early bird gets the worm but the second mouse gets the cheese.
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·"If you build it, they will come."
would power a uC for ages if it was clocked at a slow rate
and did a lot of sleeping.
I have been very eager to experiment with large value
capacitors and thought I would splurge and get these.
Really it's for the learning experience...it was painful to
pay so much for them especially for a hard core bargain
hunter like me
of cash by getting 100 watch xtals for just 9.98 so I deserved
a new toy)
erco, do you really design toys??
If so that sounds like a super job!
What sort of toys? Need an assistant?
For a quick and dirty charge balancer you can place a voltage divider circuit in parallel with the caps but this will increase your discharg3e rate.
If you want to use as a battery backup place a resister between the cap and the power rail. this will limit charge current and stop the cap from being a short on your circuit while it is charging. Placing a shotkey diode in parallel and reverse with this resister will let you still get full current out of the cap if you need it.
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Lots of propeller based products in stock at affordable prices.
The specs for your 400F cap is 12 milliohms, ie 0.012 ohms.
That is not much more than the resistance of the leads. It is a real capacitor. Clearly you do now want to short those leads, and this also explains those high charge and discharge rates of 80-90 amps.
Hmm - yes, you might need to charge them via a resistor - 80 amps would blow most transformers. Or a constant current source.
The energy density calculations are intriguing. Getting close to NiMH. What next, Lithium batteries. If they go better than NiMH they could be useful in electric cars etc. (If the cost can come down).
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www.smarthome.viviti.com/propeller
Post Edited (Dr_Acula) : 6/13/2010 7:43:02 AM GMT
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Lots of propeller based products in stock at affordable prices.
Huh, this is different from what I've seen in data sheets so far. 10,000uF electrolytic with 50-100uA leakage while what little I've found for leakage specifications for super capacitors is showing 5-10uA leakage on 500mF to 1F super caps. (I haven't searched out low leakage electrolytic capacitors yet) I'm designing some small BEAM solar engine circuits I want to work on indoor light. It's important to draw the minimum micro amps of current while waiting for the storage capacitor to charge.
Lawson
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Lunch cures all problems! have you had lunch?