Solar Power for Dataloggers ? - Few Commercial Choices

OK ... this has been driving me crazy for awhile now.

Solar battery-charger products generally assume you need hundreds of watts - enough to light a house or RV or something. Dataloggers need maybe 20 mA, perhaps a brief surge to 250 mA when peripherial devices switch on for the measurements.

Dataloggers also need tightly regulated voltage OUT of the batteries - WHILE they are being charged. Ards generally want 5.05v, Pi's I think are 3.3v ... not any old thing between 3 and 7 but dead-on perfectly regulated high-conversion-efficiency voltage.

Now for the Ards, two products sold by Seeed - the "Li-Po Rider Pro" and a similar shield-incorporated setup do in fact handle both functions pretty well, for Li-ion cells anyway. Your solar can provide most anything between 3.0 - 6.5 volts and it'll charge the battery pack, and a seperate output provides rock steady 5.05v whether the sun is bright or not or you're on pure battery power.

AdaSoft also sells their version ... but it's NOT very well regulated at all - indeed it could likely roast an Arduino if the sun got really bright. They've got a good cheap outdoor solar PV panel that's decent however.

Note that said panel (1-watt, allegedly 6v), coupled with the Li-Po Rider could be a problem. In very bright sun the panel surges up to a little over 7v, and the Li-Po Rider's specs say 6.5v max. As the PV panel produces so little power, I just bridged a 6v/3w zener across the outputs to nail down any voltage peaks without wasting power during off-peak output (could probably have gone to a 6.25v, but I already had those others in the parts drawer).

Li-ion batteries do have their attractions ... but they're also nefarious for having a rather short shelf-life (three, maybe four years) and then they just die. You likely won't know when the one YOU bought was actually manufactured. If it's cheap, it's likely near its EOL.

Alternatives are, of course, Ni-Cad (charge memory effect and sudden death if crystals bridge the plates), NiMH (DC package from Recom Power (digikey 945-1690-1-nd) that can deliver a steady 5.05v up to 500 mA from a source anywhere between

9v (a tad less actually) and 36v at (claimed) 87% efficiency.

The whole regulator fits onto a roughly 1/2" square tiny board with the contacts at the corners. I just put another protoboard under it and pushed some pins through at the corners so they could be easily soldered to the regulator ... instant pluggable power module. These things cost about $4 ... buy half a dozen on a tape just to have 'em around. There exist higher-output DC-->DC's in case you have really large transient loads.

Using this, I can port directly to an Arduinos +5v IN pin and bypass the wasteful onboard 5v regulator (still need the little 3.3v reg alas ... dammit !)

Now it's a pity that I can't find any commercial source for what's essentially both kinds of chips integrated into a single off-the-shelf style device. If you KNOW of one ... I'd really like to hear about it because the Powers That Be are fond of off-the-shelf solutions because they SEEM cheaper, come in a pretty box and, of course, you can blame failures on someone else.

Reply to
Mr. B1ack
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Much less of a problem in the real world than the vendors of all other chemistries would have you believe. There will now be 500 follow-up posts arguing this point to death.

Powerstream sells a couple that might do what you want. They have this board

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that they say they will program how you want; they have off-the-shelf versions for PbA
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and NiMH/ NiCD
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for $80 qty 1. They also have a smaller one, but it's designed for

48 V telecom stuff
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, for $38 qty 1. I don't know if these chargers suck or not; I just know that they exist.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

On Tue, 7 Jan 2014 21:34:07 +0000 (UTC), snipped-for-privacy@att.net Gave us:

Battery tech is getting better all the time.

Look at how those "tree cams" work. They are solar maintained, and a form of data logger as well. Would seem not too difficult to actually use on that has been hacked (literally).

Reply to
DecadentLinuxUserNumeroUno

Tell that to the three dead expensive cordless drills I have in the toolshed ... all NiCad powered. They died WAY before I'd gotten good mileage out of them and the battery packs are so expensive it's better to just buy a whole new drill/battery set.

I'll NEVER use NiCads again !

You've counted ? Betcha it's really under 100 cycles. I have a bunch of semi-dead ones that got that way in less than 100 cycles ... lost half their capacity or more, and I had decent chargers too.

NiMH batteries are also a pain to charge since you can't really use voltage as an indicator of reaching a full charge but instead have to measure the temperature ... they start to get hot once fully charged.

True, I've seen odd-voltage cells/batteries ... but with "odd" comes *expensive*. As usual, the rules of mass-manufacturing and mass-consumption are at work here ; "popular" batteries cost a lot less. Usually those are 12v gels and wets.

That's my dilemma ... the devices are gonna be WAY off-grid, some with cellular data links due to accessibility issues. I'm looking for "affordable" solar/battery setups that'll keep working for a minimum of two, preferably five, years. "Affordable" does not have to mean "dirt cheap", but it can't be near what the commercial datalogger people charge for their setups. For $50-$75 I can combine an adequate Pb, or maybe Li-Ion, battery and a one or two watt panel plus electronics to charge 'em and efficiently siphon off tightly regulated voltage.

I'd *rather* have an "affordable" off-the-shelf solution - mostly because of the way bosses think - but I just can't find one anywhere. This seems odd, given the increase in the use of remote sensing.

I looked ... and they ain't bad. Still a "board" of course, no nice artistic plastic box with a logo and plugs.

Their output-voltage range offering is quite broad (but only some testing would show how stable it is). Some of the lithium/solar chargers I looked at claimed "5-volt" output but actually varied quite widely when the charging voltage changed. I guess they meant a "nominal 5-volts" or "average 5-volts" :-)

Seeed's LiPo Rider Pro is less than half the price ... though it only charges at about 800ma max instead of the claimed 1800ma for the above device. For MY purposes, even 500ma is more than enough. Those using PI's or other boards that suck more juice might lean towards Powerstreams product. We using small Ard/ARM/Propeller/PIC-based boards can get by for less.

The homebrew combo I mentioned - the TI battery manager plus the little DC/DC converter - works beautifully, is cheap and really easy to wire up. It kind of boils down to whether I trust lithiums or Pb to last longer in the field given my power production/consumption profile. Guess I'll have to make a couple of each and actually put 'em out there in the untempered environment.

Reply to
Mr. B1ack

So's the science of horseshoe-making ....

Face it ... ALL the current battery technologies are still pretty sucky, each for various reasons. Better-lousy still doesn't equal "good". We need a whole new tech.

Hey ... didn't Walter Cronkite promise us atomic power-packs for everything back in the 60s ? So, where ARE they ? I want my flying car too !

Reply to
Mr. B1ack

Have you looked into what is available in the Marine Market. Plenty of boats these days have solar chargers for their instrumentation and lighting batteries. Might cost a bit more than doing your own bespoke unit but would meet the "off the shelf" requirement.

Many of the road-side signs in the UK have solar panels on them, presumably with battery also, that flash up warnings as you approach. So, that would be another area to delve into to see what they use.

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Reply to
Paul E Bennett

Excellent suggestions ... I'll add "marine" and maybe "DOT" to my searches. I suspect "marine" will be pretty expensive though ... people with boats are presumed to be rather *rich* people. On the positive side, any units would be extremely weather-resistant. On the downside, I doubt they'd be well regulated ... mostly aimed at producing "12 volts" for radios, GPSs and lights.

The DOT type stuff though ... large market but not a *fancy* market ... some potential there.

Reply to
Mr. B1ack

I've had good and bad luck with NiCDs, but it's often hard to tell whether a short-lived battery pack is a result of the battery technology or the charger. When you buy a package, like a drill with a charger, it can be difficult to determine which is the case.

Case in point: The $20-on-sale HF drill set I bought a few years back had a removable 18V presumed-NiCD power pack and a charger. As far as I could tell, the "charger" was a simple wall-wart; this feeling was reinforced by the note in the instructions telling me to remove the pack from the charger when it got warm and never to leave it charging overnight.

As you might guess, the battery pack lasted less than a year with moderate-to-infrequent use and several occasions when I plugged the pack into the charger and left it there overnight (several overnights, on at least one occasion).

What I've read about chargers, and NiCD and NiMH chargers in particular, leads me to believe that _with_ a well-designed charger those hundreds of recharges might be achieved, but without one, the NiXX cell's life is, as Hobbes put it, "nasty, brutish, and short."

The problem, of course, is that the chargers generally don't come labelled as E, M, or C (Excellent, Mediocre, or Cr***y). Sigh.

Frank McKenney

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Reply to
Frnak McKenney

I'm sure that's a big part of the problem. Google-up a major battery-makers specs for achieving a full charge without roasting the cells - they're VERY detailed, all sorts of voltage/current/time/temperature charts. In short it's HARD to make a good charger for NiCads or NiMH, so nobody but NASA bothers.

Lead-Acids are fairly tough and tolerant. Much easier to make a good - or "OK" - charger. You'd THINK they would put one in those UPS's ... but they don't, and usually manage to roast the batteries in a couple of years.

There's an obscure kind of battery called NiFe, nickel-iron, that I'd like to experiment with. They don't pack as many amp-hours/pound as NiCads or even Pb ... but they have a rep for being tough as nails and VERY long-lasting. I think Edison invented 'em ... but now the only source is China. Solar Home freaks covet the things.

Nope ... they don't. There's no "National Battery-Chargers Institute" to test 'em all. At best you get word-o-mouth. The manufacturers ... well ... they want you to buy new cells - often.

NiMH cells are particularly frustrating because, I think I mentioned it somewhere, you can't even use voltage or even a change in the voltage curve to detect when the things are at full capacity. THE telltale sign is that the cells start to get warm, then hot.

A spec sheet I found suggested that you ignore voltage or current monitoring and instead find a way to slap a thermistor up against each cell and wait for x-percent temperature increase over y-minutes. This means thermistors on spring-loaded bars (good luck determining whether you made good contact or not) and a microprocessor to do the math. In theory you could do it analog with some sort of "leaky" integrator that'd only respond to a "fast" rise, but that sounds like trouble.

Reply to
Mr. B1ack

You are allowed to dis NiCads all you wish, just remember that they have been used successfully in space for periods over 20 years. It isn't the particular battery technology, but the application as well. Of course huge budgets for system design helps.

that

PbA batteries have lasted over 20 years in telecom battery backup systems, again more application (and maintenance) than battery technology.

?-)

Reply to
josephkk

If I may suggest, why not use a sealed lead acid cell. They are cheap, rugged, can be charged with a simple shunt type charge controller and immune to over- charging. A Li-ion battery, on the other hand has to be charged very carefully. There is some excellent documentation at the Battery University regarding the the charging cycle of the Li-ion battery, and how overcharging must be strictly avoided.

Reply to
dakupoto

Actually I'm leaning towards "old tech" Pb-A because it's just plain tougher. Yep, Li-ion and NiMH and NiCads are a royal PAIN to charge properly. I've seen some of those "how to do it perfectly" documents and I can see why no commercial outfit bothers to even try very hard at doing it right.

Pb-A can be killed too by poor charging practices ... but it's more tolerant. Most UPS devices seem to slay the battery in about two years, likely they just charge it at x-milliamps constantly. DOES encourage people to just buy a new UPS every couple of years though, doesn't it ? :-)

Li-ion seems to just die of its own accord, even if you just have the things in a drawer. Three years, maybe four. You'll have a hard time buying such cells too because you won't know when it was actually made until you can put your eyes on it and read the data stamped on the battery pack.

So ... I think my TI battery manager chip (which is intended for Pb-A, ought to guarentee a very long life for my battteries - and my tiny little DC/DC converters do a great job creating tightly regulated output for my devices.

I'd like to get my hands on some NiFe, nickel-iron, batteries sometime just to check 'em out. They do not have as much power density as any of the more modern designs, but they're supposed to be tough as nails and hold up almost forever ... most commonly used in disaster/military equipment in the past and now they've become popular with the off-gridders in their solar houses.

Reply to
Mr. B1ack

I bought the $100 DeWalt drill-driver kit, and a spare 12 V NiCd for it, at Home Depot in 2007. In 2007-2008 I used them at work; after that it was just homeowner-type occasional use. By 2012 both batteries were pretty tired, but I could still get some work done by juggling them on the charger. One thing that I think helped is that I kept the charger and batteries in my kitchen, and approximately whenever I thought about it (which probably means once every 1 or 2 months), I would top off both batteries on the charger.

By 2013 the batteries were pretty much gone. In mid-2013 I got both of them rebuilt with new NiCd cells at Batteries Plus for about $35 each, out the door. I figure 5 to 6 years of use for $35 is not a bad deal. Also, they at least say they recycle the batteries in some acceptable manner.

There seems to be a constant (intentional?) churn of voltages and connectors on cordless tool battery packs. New 12 V NiCds to fit my drill were 1) hard to find and 2) a significant part of the price of a new set, as you noted. The rebuilds were priced right for me; I may or may not get them rebuilt a second time - depends on how well the drill is doing in 5 years.

That low internal resistance is great for getting drill bits moving, though.

I still have some working NiMHs from the first batch I bought with my first digital camera in 2000. I've used them with that camera, the other pointy-shoot cameras that have replaced it, and some other portable equipment. I guarantee I have more than 100 cycles on them. The capacity is not what they were when new, but it's not ridiculously low, either.

Some of the NiMH cells from that first batch *have* expired.

In 2011 I bought a set of Sanyo Eneloop NiMHs and they seem to do a pretty nice job for "consumer" equipment. The low-self-discharge thing seems to be true; they stay charged better than the previous NiMH cells I have used.

I just buy a charger with a 120 V plug on one end and battery holders on the other. I realize this is different than *designing* equipment to use and charge them.

I understand about the boss thing. Maybe you should design such an off-the-shelf solution and sell it to other people! :)

For 12 V PbA "gel cell" batteries from about 4 to 10 Ah nominal ratings, in UPS-type indoor service, I have found Panasonic and PowerSonic brand batteries to work the best - to go for the most cycles. PowerSonics used to be made in Mexico, but some recent ones I got were made in China, so I'm not sure if they are still as good. I put a set of Chinese PowerSonics in my computer UPS a few months ago; check back with me in a couple of years. :)

If your gadgets also have to get serviced in the field, and they are deployed in the US, one thing to recommend 6 or 12 V PbA is that every Home Depot has a couple of sizes of these batteries on the shelf, for use in emergency lights, EXIT lights, and similar. In extreme cases of field service, it's not too hard to make a harness to plug your gadget into a car (RV, boat, etc) battery.

One kink particular to the PbA 12 V 7 Ah nominal size: they exist in the world with both 3/16" (0.1875", 4.76 mm) and 1/4" (0.25", 6.35 mm) male push-on terminals. PowerSonic sells adapters that will make a battery with 1/4" push-on male terminals fit a wire with 3/16" push-on female terminals.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

I don't know where you're getting $35 replacement NiCad packs. Typical off-the-shelf price is more like $75 ... which is like half of more the price of the original tool + batteries.

Yep ... it IS nice - however the fix is to just use higher voltage Li-Ion packs instead. If you can't get enough amps, use volts :-)

Um .............. what kind of Frankensteinian device are you trying to describe here ........???

"Design" is very important when it comes to battery chargers. Google-up the detailed charging specs the major battery manufacturers have and see ... to really get best performance AND long life you can't just blast 'em with amps for an hour or so.

Even my simple homebrew charger centers around an actual programmed charge-manager chip that will carefully profile the rate and amps. Alas most of what you'll find at Wal-Mart are vastly stupider devices ... you're lucky if they'll even stop charging before yer cells are smokin'.

Hmmm ... maybe I could send off the "perfect" design to a manufacturer, have 'em put it into a nice looking plastic case contained within a nice looking box with snazzy graphics ... and then I could buy 'em back as "off the shelf" solutions :-)

As I said somewhere ... certain sizes of Pb-A batteries are just plain "common" and found in all sorts of devices. Those are both availiable and relatively cheap due to the usual market factors. They ARE much bulkier than Lithiums, but if properly charged and not abused they can last for a LONG time - and replacements are as close as yer local Home Depot store.

The devices I'm looking to power ... some of them are going WAY out "in the field" ... nasty places it could take a couple of difficult hours to get to. These both warrant radio/cell data connections AND need to be very robust so nobody will have to actually go replace things very often.

So, while I'll experiment with Lithiums ... I've now decided that Pb-A will be the preferred storage medium.

Reply to
Mr. B1ack

He told you. The had them rebuilt by Batteries Plus. I've had both VOltman and PrimeCell rebuild NiCd tool batteries. PrimeCell was significantly cheaper last time I looked. Both did good work. $35 is about right. The last one I had rebuilt was for a tool that the cordless versions are no longer sold and batteries are unobtanium.

Reply to
krw

The standard charging method for LiPo doesn't work with solar because it requires uninterrupted power. The good news is that, despite what's said, you really can trickle charge LiPo batteries. The catch is that you can never reach 100% charge. Drop the voltage limit by 100mV and you'll hit about 80% capacity in a reasonable amount of time but never reach 100%. For low power solar applications, simply put a shunt across each cell to get automatic regulation and balancing. Something cheap like the LTC4070 works great and has temperature compensation.

LiFe doesn't store as much but it's fine with trickle charging and it has a very long life. You'll need some kind of regulator still.

Reply to
Kevin McMurtrie

Batteries Plus is a chain of stores that sells batteries. And cells.

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I took my worn-out DeWalt NiCd packs to the local Batteries Plus store, and then left.

The guy at the store disassembled the packs.

He looked at how the existing cells were arranged.

He spot-welded new cells together in the same physical layout.

He transferred over the insulators and terminals from my old pack (I think... he may have brand new ones he used).

He put the new cell assembly back in the original housing.

He gave the rebuilt pack a charge and discharge test.

He called me on the phone.

I went back there and gave him money.

He gave me my rebuilt packs back.

Simple.

Yes, I found prices north of $50 when I was looking for *brand new* NiCd packs to fit my drill. That helped make the decision toward

*rebuilding* for me.

Um... a battery charger?

What I was trying to say, and apparently failing to say, was that I haven't been in a position to *design charging circuitry into a product*.

Most of my charging needs can be met by commercial chargers; I don't have to design a charger, I just go buy one.

Most of my NiMH charging has been done by a Rayovac PS-12 charger. It does have a "smart" controller chip in it - if I put in a lightly- discharged cell, it finishes charging much faster than if I put in a heavily-discharged cell. It refuses to charge at all if the cells or the charger is too hot.

More recenly, I got a Maha/Powerex MH-C9000. It does all kinds of tricks, like charging, discharging, repeated charge/discharge cycles, etc. It tells you how many mAh it put in or took out.

Both the Rayovac and the Maha have a wall plug on one end, and holders for AA and AAA cells on the other.

For my flooded PbA batteries, I use a Schumacher Battery Companion (6 or

12 V at about 1.5 A and "smart"), a Deltran Battery Tender (6 V, 1.25 A, "smart"), and an ancient Western Auto (probably rebranded Schumacher) charger (6 or 12 V at 6 A, very dumb).

The PbA chargers have a wall plug on one end, and big alligator clips on the other.

For my sealed PbA batteries, if I need to charge them outside of the equipment they live in, I use a regulated, adjustable benchtop DC power supply.

Oh, I also have a very fancy NiMH charger (273.6 V nominal, dozens of amps, very very "smart") that runs on unleaded gasoline. It has a few other features as well. :)

Matt Roberds

Reply to
mroberds

I wonder how old the cells are that they're using to do the rebuilds ...

I took one of my useless cordless drills, removed the batteries and put in a plug cord with spring clamps. I connect it to a live 12vdc battery. Not as handy as the original, but OK around the shop.

In any case, NiCads are especially prone to the thing where conductive crystal "fingers" creep across the plates and short out the cell. Yes, they're better than they used to be, but "better" doesn't always add-up to "good". Frankly I've just come to hate NiCads.

Pb-A are clearly not suited for portable power tools, but to power an environmental datalogger forr five years at a stretch isn't anything to be sneezed at. An 18v solar panel, a UPS battery, a charging-management chip and gettting that five years becomes attainable.

Hey ... I distinctly remember Walter Cronkite promising us atomic batterues for *everything* when he served as the voice for Union Carbides "The 21st Century". I want my damned atomic batteries ! The flying car would be cool as well :-)

He also promised us "home computers" that'd only be the size of a writing desk .............

Some years later, I came across an IBM computer in a science museum which actually was just the size of a desk (not counting the external memory - a few K of magnetic-core RAM inside a meter-square box. Looked neat-o and I wanted one.

Probably had 1/10th the computing power of your iPhone.

Reply to
Mr. B1ack

last time I had a pack rebuilt I watched the guy spot-welding the strip to brand new cells.

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Reply to
Jasen Betts

Oh, good grief. They're new cells. They do a *lot* of business.

What a kludge. Just spend the $35 or buy a corded drill.

They have their place. The "primary" tools are all LiIon, now but the NiCds have their place and I still use the other-than-drill components.

No Surprise. Water Crankcase was about as dumb as they come. *WAY* overrated, even for his time.

Since I wouldn't have an iPhone... ;-)

Reply to
krw

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