LowPowerLab Forum
Hardware support => Low Power Techniques => Topic started by: Kilo95 on September 21, 2017, 02:13:18 PM
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Felix, I saw your post on your main page using a 7.5f supercap and solar panel to charge it. do you carry the solar panels in your shop or can you tell me which ones you used? How did you keep it from overcharging or over shooting the 4.25v that it charged up to? Is 4.25v all that the solar panel puts out? If this holds up good in the cold, I'd like to put one outside in an enclosure to keep it from getting wet and try it in the Wisconsin winter
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I just had a few of these very small solar cells in my junk box. I think they are 5V cells but there is no spec. They do not seem to charge more than about 4.3v at the very most. But I haven't yet put these out in clear sunlight, just behind that glass block which is not very bright even with a sun blast. So maybe it would go to 5V. This feeds into the supercap + stock Moteino VIN so it really won't matter if its more than 5V. The supercap is 5v, I don't think it will explode if it ever reaches 6V :), which i doubt it ever would.
I think these were from ebay or someone gave them to me, can't recall but a simple ebay search can reveal lots of options from china. Most are 5V or 6V for small 1W range cells.
I imagine these would work wonderfully in extreme cold and extreme hot weather.
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I was thinking it'd be fine if i got a solar panel that was only rated for up to 5v output. I think this will be my next project. Install it in the top of my daughter's playhouse out in the yard where she can't reach it. Do the regular Moteino 915mhz high output boards accept a SMA connector? I was thinking of making a 12 element 915mhz beam antenna for kicks and giggles and connect with a short piece of coax since I'll be 150-200 ft from my Gateway Moteino. It'd need to run at lower power that way
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Have at it, but I think even the monopole 0 cost antennas would work at that range.
A 1W-ish 5V panel sounds good with the 7.5F supercap. I haven't gone through a winter (short days with lots of overcast) yet, but i think outside a 1W panel should charge that cap even with not lots/great sunlight - maybe not snow/ice on it - although wouldnt that be kinda like my glass blocks? ::)
If your charging the supercap enough, full power should be good enough. If the cap can't handle it, add another in parallel.
You can put an SMA (with a little care) on the small regular Moteinos. In R6 I enlarged the ANT pad on both sides and added extra GND pads to help solder an SMA on it. There's even a dedicated u.FL pad on TOP. There's SMA pigtails on ebay, they're SMA case mount on one side, and plain coax on the other, so you can just solder the shielding to GND and feed wire to the ANT port, just trim the coax length to 1/4 wavelength multiples.
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i'll be buying another moteino for this project, so i can get one of the newer ones. i'll probably try a 1/2 wave or full wave monopole first. i've got a full wave monopole on my gateway moteino now.
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Great, post here as you have updates and make progress!
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Ok. Got it built. Diode in place just like on the lowpowerlab.com home page. It tops out charge at 5.5v per my DVM. Is that going to hurt the Moteino? Also, when it’s sitting in the sun, it reads maybe 15-20 deg F hotter. Place it in the shade?
https://imgur.com/gallery/u0WiN
The plastic electrical box has a watertight cover that goes on it
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I would think that is not exposed to ambient enough. What are your results in box vs. out?
Yes place it in shade, 3-4 ft, 1m, above grass with no metal or concrete or asphalt around it...
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Not sure without the lid on. I’ll put it in the shade. That’s probably sufficient.
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Ok. Got it built. Diode in place just like on the lowpowerlab.com home page. It tops out charge at 5.5v per my DVM. Is that going to hurt the Moteino?
https://imgur.com/gallery/u0WiN
The LDO on the Moteinos take up to 16v tops so you're safe.
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Great. Thanks. Eventually I’m going to try to add an anemometer to it. We’ll see how it survives the Wisconsin winter with the supercap
UPDATE: i've had my Weathershield +supercap(7.5F)+solar panel out all winter with numerous nights below 0 deg F. I've only had one night where it dropped below 5v. that was down to 4.98v. very pleased
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So what's your consumption anyway? I don't think you send once per hour, which would make consumption very small + you get through night each day. How much does it drop then? Could you go without any good light for few days?
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i don't know what the consumption is. it updates every 2 minutes. i haven't tried covering up the solar panel to see how long it lasts. it was serving the purpose i had. My voltage always shows 5.01v. I am using a 5v solar panel with the diode just as Felix did
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Do you monitor voltage? you should see some drop before sunrise
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i do. it has only dropped below 5.01v once that i have seen
I suspect my reading on the Gateway is maxed out and I'm i'm sitting a little above 5v all the time. there probably IS a drop but it doesn't drop low enough to go below 5.01v. where could i increase the max that it will show on the Gateway page for the voltage?
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I will soon give this a go, got my capacitors today. My question would be, I don't need to worry about same level of charge, do I?
I got two HB1625-2R5256-R
http://www.farnell.com/datasheets/1640984.pdf
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your HB1625-2R5256-R have the following specs :
Working Voltage 2.5V
Surge Voltage 3.0V
you have to use both in series to accept the max voltage and supply your moteino
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that is the plan, 12.5F @ 5v. But since they will be in series, does one really need to have balance circuit or not
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that is the plan, 12.5F @ 5v. But since they will be in series, does one really need to have balance circuit or not
I would say no, not as long as they charge uniformly.
BTW there are now some 400F caps at 2.7V, 1.8mOhm ESR, 68mm length! Two in series to make 5.4V at 200F is not bad huh!
Their size is also very acceptable.
https://www.avx.com/docs/techinfo/General/AVX-SuperCap-Comparison-Matrix.pdf
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one problem though, their price is about 20$ for one... I think at that point you would be better off with batteries unless you temperature is REALLY low. Also 1mA discharge current, that seems a bit much already? Anyway, there are some that have lower current. Also at what point are you wasting money, 200F seems a bit much, for low power device
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LukaQ,
It's $11 at mouser, I just got a few to experiment with: https://www.mouser.com/ProductDetail/581-SCCY68B407SSBLE
Where do you get the 1mA discharge? Isn't that directly proportional to the ESR, which at 1.8mOhm is the lowest I've seen in supercaps?
400F is not a lot in terms of mAh, there's a formula to calculate it, it comes to a few hundred mAh. There are many very important advantages to supercaps over even the most energy dense batteries. Here's what comes to mind:
- virtually unlimited charge cycles - compare to something like 1000x for a LiPo
- very consistent performance in very extreme temps - HOT and COLD - both where LiPos fail miserably
- can be charged and discharged at MUCH higher currents than a LiPo without any risk of catastrophic failure/explosion - LiPos can only take 1C reasonably safely
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Where do you get the 1mA discharge? Isn't that directly proportional to the ESR, which at 1.8mOhm is the lowest I've seen in supercaps?
It's the DCL spec in the datasheet, and a 400F does seem to have 1mA self discharge current. Self discharge is due to a finite large resistance between the pins, ESR is a small resistance in series with the pins, I'm not aware of any relationship between the two.
However, the DCL spec is scaled with capacitance value, it's like having multiple smaller capacitors in parallel (slightly better actually), so the rate voltage drops due to leakage is roughly the same for smaller caps as it is for larger ones. That's also why I think the ESR is low too.
Mark.
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LukaQ,
It's $11 at mouser, I just got a few to experiment with: https://www.mouser.com/ProductDetail/581-SCCY68B407SSBLE
Where do you get the 1mA discharge? Isn't that directly proportional to the ESR, which at 1.8mOhm is the lowest I've seen in supercaps?
200F is not a lot in terms of mAh, there's a formula to calculate it, it comes to a few hundred mAh.
Short answer:
With a 1 volt change in output voltage (for example if you charge it to 5 volts and your circuit works when the voltage drops to 4 volts), a 1 Farad capacitor will give 277 microamp-hours.
The relationship is linear. 10 Farads gets you 2.77 milliamp-hours, etc.
so, if I have 12.5F and I can have 1.7v drop from 5v to 3.3v, that gives me about 5.8mAh. Compared to 1000mAh of batterys...
Even yours "only" come to 94mAh.
Equation from datasheet is 0.5*C*v^2*1000/3600 = mWh
I guess question here is, what is your device consumption over time. With a lot of sleep, that goes down to or below 1mAh
And yes, here are differences in caps: my has 28uA leakage current, if I would scale that up to 400F, that would be below 450uA, less than half of one of yours. Dave Jones would say, you are pissing power away ;D
While true, you can charge supercaps faster, just about no one would give more than 1-2w solar cell on it, that is still low IMO
Without testing, I'm just not sure, how long would moteino/sensor run before power would need to be put in (charge supercap)
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Mark & Luka, I am learning something every day!
You are right, 1mA DCL, but compared and rated at capacity it is much lower than the 7.5F cap discussed in this thread (70uA DCL). The 7.5F is 55mOhm ESR, many times more also, and i'm sure it's actually made of two 15F capacitors in series, rated at 2.5-2.7V to get the 5v+ total rating.
Without testing, I'm just not sure, how long would moteino/sensor run before power would need to be put in (charge supercap)
We shall see won't we!
To me they are an exotic power source.
Everyone seems to be using the overpriced volatile no-name made-on-a-ship on planet zorg chinese crap Lipos which fail if you look at them wrong. I guess it's the New Products video mantras that make them ubiquitous.
Why doesn't everyone use safe chemistries like LiFePo4 instead? Or at least some brand name LiPos? Even end-of-life smartphone LiPos seem to be reliable and run a Moteino for years (https://lowpowerlab.com/2018/03/31/mailbox-notifier-2-year-service/#comment-3040).
Or like me and a few uPower fans - supercaps : they run 4evaaaa! 8)
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they run 4evaaaa!
well I don't know about that, they do have 500k charge cycle rating :D
Even don't think esr is super important as long as it is not too high. Max power draw could be <100mA at any time.
Did that test...
Moteino without flash + adt7420 eval board with continuous sampling, sending every 1min to gateway = 6.4xmA all the time consumption for exactly 60min.
Took the led off, everything else the same, it is sitting now at 0.25mA, this should be then running at least 25 times longer I think.
Tomorrow I'll even try to send sensor to sleep, that would bring consumption WAY down still.
I have some LiFePo4, nowhere near rated capacity, but if it can run led torch for hours, then yes, could be looking at years with moteino
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After 550min, voltage on cap is 3.508v, that could run for few hours still. So take away here is, either make low power or have big supercaps or both ::)
Should also mention, that SI1145 and tsl2561 were connected, but not used in code...
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they run 4evaaaa!
well I don't know about that, they do have 500k charge cycle rating :D
That's pretty much forever in technology terminology ;)