Author Topic: Supercap - Something Interesting from Davis  (Read 22951 times)

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Offline jchen

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Supercap - Something Interesting from Davis
« on: June 24, 2009, 07:24:13 PM »
I posed the supercap question to Davis and got this informative response. The last paragraph is especially interesting.

QUOTE

We don't recommend  customers install supercaps themselve. We prefer to repair it. In theory it should be OK (but we can not guarantee it).  There are considerations.

Special care needs to be taken when working with these parts. Improper handling can lead to capacitor damage. When forming the 90 degree bend in the leads, special care needs to be taken to assure no stress travels through the rubber seal on the bottom of the part into the part, as this can damage the seal.  This is typically done by holding the part with narrow-tipped pliers near the rubber seal, and bending the leads against the pliers.  When installing, special care needs to be taken to (again) assure no mechanical stress travels into the part.  Similarly, solder time needs to be minimized to keep thermal stresses from the part.

The part also needs to be affixed to keep mechanical shock from producing stresses between the part and the leads that are soldered to the board.  This can be done with double-sided foam tape, silicone gel, or similar affixing.

Aside from this, one or two super-capacitors can be installed.  Also, several values can be installed.  The night run-time is proportional to capacitance.  The reason for our selection was need/cost.  The boards was designed to take 10F, 25F or 50F parts, up to two each.  They can be mixed/matched in any combination.


UNQUOTE

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Offline Bushman

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Re: Supercap - Something Interesting from Davis
« Reply #1 on: June 24, 2009, 07:28:35 PM »
Interesting.  I'd be real careful about using silicone gel on PC boards.  Since these things (SCs) are like porcelain dolls, one has to wonder why Davis did not use something else to hold a charge over the night time.
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Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #2 on: June 24, 2009, 07:51:50 PM »


 When forming the 90 degree bend in the leads, special care needs to be taken to assure no stress travels through the rubber seal on the bottom of the part into the part, as this can damage the seal.  This is typically done by holding the part with narrow-tipped pliers near the rubber seal, and bending the leads against the pliers.  When installing, special care needs to be taken to (again) assure no mechanical stress travels into the part.  Similarly, solder time needs to be minimized to keep thermal stresses from the part.

The part also needs to be affixed to keep mechanical shock from producing stresses between the part and the leads that are soldered to the board.  This can be done with double-sided foam tape, silicone gel, or similar affixing.
I agree totally that this repair should be done by experienced technicians and someone with soldering experience.
Notice in my photo how I held the leads with special lead bending pliers.  I used hot melt glue to hold the caps in place mechanically before soldering the leads.
I have 50 years soldering experience.  I've written a soldering book, "Exotic Soldering". 
Also RTV is OK to be used on circuit boards.  I've been using it since 1975.
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Offline Bushman

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Re: Supercap - Something Interesting from Davis
« Reply #3 on: June 24, 2009, 08:54:44 PM »
RTV is not the same as ROTM silicone (acid is the solute in that stuff that mucks up the boards)
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Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #4 on: June 24, 2009, 10:10:07 PM »
RTV is not the same as ROTM silicone (acid is the solute in that stuff that mucks up the boards)
Electronics grade RTV is safe for circuit boards.  Its made for bonding/sealing and is used in industry.  Most RTV releases acetic acid as it cures.  Most of the acid evaporates.  I've never seen or heard of any copper corrosion due to residual acetic acid from RTV.  A two part silicone rubber is also used and it does not release acetic acid.  I don't buy RTV from a hardware store or auto parts stores.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline Bushman

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Re: Supercap - Something Interesting from Davis
« Reply #5 on: June 24, 2009, 11:19:17 PM »
Exactly.  Electronics grade stuff is far diff. than what you get at Home Depot/Lowes etc.
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Offline Garth Bock

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Re: Supercap - Something Interesting from Davis
« Reply #6 on: June 25, 2009, 09:26:01 AM »
Quote
Aside from this, one or two super-capacitors can be installed.  Also, several values can be installed.  The night run-time is proportional to capacitance.  The reason for our selection was need/cost.  The boards was designed to take 10F, 25F or 50F parts, up to two each.  They can be mixed/matched in any combination.

So the mystery is solved.....there can be 2 supercaps on the board. So this would give a longer run time in darker or low sun areas....right ? As for the need/cost....from what I have read here the cost is not that much. As for need....guess their tests showed that in about 99% of the cases one supercap was more that adequate.

Offline ncpilot

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Re: Supercap - Something Interesting from Davis
« Reply #7 on: June 25, 2009, 10:10:24 AM »
Oh yeah baby!

Toolman for weather stations--MORE POWER!!!!!!!

 :grin:

But seriously, I guess the practical question is comparing the value/risk of soldering in a new larger value capacitor, and or installing a second one, versus the cost to replace a battery every few years...

I'd imagine this could be valuable to someone that has their ISS mounted in a difficult or remote location...
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Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #8 on: June 25, 2009, 10:23:37 AM »
There is also the question if the solar panel can charge the higher capacitance plus power the wx station.

What is the daytime temperature inside the SIM?
I found this info about ultra capacitors. 
Ultracapacitors have a longer lifetime than do secondary batteries, but their life is still limited.

Capacitor life is affected by operating temperature. In general, lowering ambient temperature by 50F will double the life of a capacitor. Use the capacitor at the lowest possible temperature. Operation above the maximum specified temperature not only shortens capacitor life, but can also cause serious damage such as electrolyte leakage.

1000 hours (41 days) under full charging conditions at temp 160F is equivalent to 7.3 years of room temp under normal use.

If an ultracapacitor is used at a voltage exceeding its rated voltage, not only is its lifetime shortened, but depending on the actual voltage, gas generated by electrochemical reactions inside the capacitor may cause it to leak or rupture.  Engineering has set the capacitor voltage at 2.56 volts (can't be changed).  At that voltage, life expectancy is 10 years @ 95F; 4 years @ 120 F.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline dalecoy

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Re: Supercap - Something Interesting from Davis
« Reply #9 on: June 25, 2009, 10:31:14 AM »

So the mystery is solved.....there can be 2 supercaps on the board. So this would give a longer run time in darker or low sun areas....right ?

Not exactly.  The supercap(s) can only store whatever energy is available.  So, if there's not enough sun exposure in a particular area to run the board through a long night with 1 supercap, there won't be enough to run the board with 2 supercaps.  No improvement at all.

However, if there's "excess" energy during sunny days, the second supercap will be able to store that to carry through more "very cloudy" days.  

Offline Garth Bock

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Re: Supercap - Something Interesting from Davis
« Reply #10 on: June 25, 2009, 12:33:56 PM »
Just thinking that should the station be in a place where it got enough sun to charge both, it might coast longer through a low sun period than if it only had 1 cap.

Offline dalecoy

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Re: Supercap - Something Interesting from Davis
« Reply #11 on: June 25, 2009, 03:05:22 PM »
Just thinking that should the station be in a place where it got enough sun to charge both, it might coast longer through a low sun period than if it only had 1 cap.

Yes.

Now, very roughly, insolation during very dark days tends to be about 1/2 of insolation during cloudless days......

Offline jchen

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Re: Supercap - Something Interesting from Davis
« Reply #12 on: June 25, 2009, 07:31:46 PM »
A question regarding RTV silicone sealants. Would one not recommend using the stuff from Home Depot or Lowes in this application?

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Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #13 on: June 25, 2009, 07:38:57 PM »
A question regarding RTV silicone sealants. Would one not recommend using the stuff from Home Depot or Lowes in this application?
There are many formulations of Room Temperature Vulcanizing silicone rubber (RTV).  Select the type most appropriate for your application.  RTV from a home supply store may be good for bonding/sealing home uses.  Get your electronics grade RTV from an electronics supplier.  You can smell the difference.  Be careful, some is very potent.
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CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #14 on: June 25, 2009, 08:20:16 PM »
Some trivia.
1  RTV releases acetic acid as it cures.  Smells like vinegar.
2  Vinegar and salt makes the best copper cleaner you can use.  After you clean your kitchen copper cookware, you have to neutralize the acid and protect the pink copper pans before they turn red then green. 

The acetic acid released by RTV will evaporate.  There won't be enough acid remaining to continue to corrode the traces.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline dalecoy

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Re: Supercap - Something Interesting from Davis
« Reply #15 on: June 25, 2009, 09:00:37 PM »
A question regarding RTV silicone sealants. Would one not recommend using the stuff from Home Depot or Lowes in this application?
There are many formulations of Room Temperature Vulcanizing silicone rubber (RTV).  Select the type most appropriate for your application.  RTV from a home supply store may be good for bonding/sealing home uses.  Get your electronics grade RTV from an electronics supplier.  You can smell the difference.  Be careful, some is very potent.

A reasonable alternative would be RTV (Silicone Sealer) from the local pet store - the kind designed to seal aquariums, without killing the fish.

Offline DanS

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Re: Supercap - Something Interesting from Davis
« Reply #16 on: June 27, 2009, 08:58:11 PM »
I believe using a small piece of 2-sided tape would be best. It sure will be a lot easier to remove if/when this replacement capacitor fails the same way.

Offline wxtech

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Re: Supercap - Something Interesting from Davis
« Reply #17 on: June 27, 2009, 10:18:40 PM »
I believe using a small piece of 2-sided tape would be best. It sure will be a lot easier to remove if/when this replacement capacitor fails the same way.
In the AF we (El Techs) used hot melt glue to anchor components and wires on circuit boards and inside chassis.  Every workbench had a soldering iron and a hot melt glue gun.  Eliminated the need for cable ties in some places.  Hot melt glue is easy to remove.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline Mark / Ohio

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Re: Supercap - Something Interesting from Davis
« Reply #18 on: June 27, 2009, 11:06:54 PM »
I would wager that odds are no matter how well or sloppily you install the cap (provided you do not damage the PCB in the process) the replacement will outlast the other circuitry.
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Offline johnd

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Re: Supercap - Something Interesting from Davis
« Reply #19 on: June 28, 2009, 02:30:04 AM »
I would wager that odds are no matter how well or sloppily you install the cap (provided you do not damage the PCB in the process) the replacement will outlast the other circuitry.

No that's simply not true! The key issue with supercap installation is avoiding initial damage to the supercap during installation - that's what caused the supercap problem in the 2005-6 vintage VP2 stations in the first place. If you don't take care great care to avoid bending the leads direct from the supercap body then there's a good chance that the supercap will fail again in 1-2 year's time. The anti-vibration glueing is a good extra touch but it's taking care with the leads that's the main concern.
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Offline Mark / Ohio

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Re: Supercap - Something Interesting from Davis
« Reply #20 on: June 28, 2009, 05:55:35 PM »
Oh I agree they should be installed in the manor noted in this thread.  I didn't mean to sound argumentative or skeptical.   :-)


It's just that I'm not totally convinced it was all a lead dress and lead stress issue that led to the failures.  A bad run of caps from the supplier during that time could also have played into it.  The computer makers had their share of problems for several years in particular with caps too.

http://en.wikipedia.org/wiki/Capacitor_plague

In 23 years doing field and bench consumer electronics service I've replaced more then I care to remember leaky caps both glued and unglued with straight leads into the PCB where no other voltage regulation or issues were found to be the cause of it's failure.  I don't ever recall having to replace one twice that failed on it's own with no external causes both times.  Customer probably junked the unit the second time it failed.   :mrgreen: ;-)   

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Offline DanS

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Re: Supercap - Something Interesting from Davis
« Reply #21 on: June 28, 2009, 06:19:20 PM »
Mark, I too have had a career in the electronics tech field and dealt with my share of electrolytics leaking, popping, etc. Never have seen where bending the leads the "right or wrong way" made any difference. I have not had an opportunity to see the relatively new "supercap" (or any in the farad range) and wonder if due to the higher farad specifications if the construction is different? Could it be the lead passages are designed for over pressure vents as well and bending the leads allows leakage?
Sorry if this sounds ignorant but knowing that you're still active in the field I thought I'd ask.

Dan

Offline Mark / Ohio

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Re: Supercap - Something Interesting from Davis
« Reply #22 on: June 29, 2009, 12:20:00 AM »
It's not a value I see either.  Only thing I recall remotely comparable was a cap used to briefly hold stored programs and clock time in the old RCA VCRs of years passed during a power interruption.  It looked similar to the caps the VP1's used.  About penny size diameter and maybe 1/8-1/4" thick.  I still have one of those lying about someplace.  I can't recall what the actual value of it was at the moment.  It's also rare I see a radial lead cap laid horizontal on the PCB. 

Maybe the TV guys already learned it's risky reliability wise during PCB assembly to do that?  ;)
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Offline DanS

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Re: Supercap - Something Interesting from Davis
« Reply #23 on: June 29, 2009, 01:09:14 AM »
I was figuring that they are laid flat on the board due to space restrictions and maybe these supercap high values in farads aren't produced in anything but radial lead design.  Axial lead would be a better fit but not made yet in farad values? I'm still impressed though to be able to get that kind of spec. in any package that small. 10,000uf would be the size of a big beer can "way back in my day" and now 10F in these supercap sizes.
« Last Edit: June 29, 2009, 01:11:28 AM by DanS »

Offline Mark / Ohio

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Re: Supercap - Something Interesting from Davis
« Reply #24 on: June 29, 2009, 09:38:29 PM »
... I'm still impressed though to be able to get that kind of spec. in any package that small. 10,000uf would be the size of a big beer can "way back in my day" and now 10F in these supercap sizes.

Same here.  I also remember the two or three caps inside the can with solder terminals.  That was the first place to look when a TV or radio said BRRRRRRRRRRRRRRRRR every time you turned it on.   :lol: 

Interesting Wiki article and links on the caps and shows how they are made in comparison to standard and electrolytic caps.  They are definitely different in construction even though they look the same on the outside.

http://en.wikipedia.org/wiki/Electric_double-layer_capacitor
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