Solar Charger Question

Why not just discuss it here or give a url to the information so that EVERYBODY that wants the info can have it rather than a one-on-one?

Thanks,

Jim

-- "If you think you can, or think you can't, you're right." --Henry Ford

Nothing wrong with the HD solar panel.

you will find the VOC and the ISC, as well as the R thevinin, changes dynamically with solar flux. If you are going to maj\\ke a commmercail device and want to optimize the power pumped out of this or any cell. PLease contact me as our group has optimize the solar cell to battery, (or any other load) interface.

best regards,

Marc Popek

Because you can't commercialise an answer that's already been distributed via usenet. :-)

I'd be wary of trying to 'optimise' this type of solar array, not that there's anything wrong with it, just that it's small. Unless your switcher is REALLY efficient and has virtually no overhead, you're going to lose more in the conversion rather than just pump and dump into your SLA battery and do very crude voltage limitation.

Something like a schottky diode to prevent current going back into the array at dark, and a zener for crude voltage limitation. Many implementations do away with the voltage limitation, as they find there is enough buffering within the battery to not overcharge anyway (on small arrays of course). Many small panels in fact do away with reverse current protection at all, and recommend you babysit the thing during daylight hours (which saves the drop over the diode to help charge an itsy bit faster.

The larger array controllers use either a FET as the switching mechanism, or a relay over the semiconductor switching mechanism to try to keep the impedance down, but there's overhead of the control electronics to cater for, and for a small system, it's really not worthwhile - losing even a little bit is too much compared with what you have to start with (very little).

In my opinion, "proper" regulation (of any type) doesn't become economically worthwhile until you're dealing with tens of watts.

What he's talking about is (most likely) a so-called "maximum power point tracking" charger. If you Google the acronym, MPPT, you'll have lots of hits. Essentially you purposely change your operating point between the solar cell and the load to see whether you're not getting more or less power -- this is usually done with a microcontroller, as when using discrete op-amps/logic/etc. it can be difficult to avoid building oscillators. :-)

Essentially an oscillator _is_ what you are building but one with limited excursions and riding around the peak. The kids call that dithering I guess. Dang, now I revealed that I am over the hill.

Perspective gentlemen. He has 38mA to play with. How much of that do you think is going towards the micro and support logic?

I agree with this post completely.

The only thing I would add is that you check the zener rating for conditions where the battery is NOT connected. (such as changing out the battery during full sunlight conditions and where the load is off, or drawing minimal current.) This could damage the zener. A small ohmic value series power resistor should fix it though. -mpm

Yeah, I thought of this, however, when you're looking at about a half watt total power of the array, you're not going to kill any zeners that way.

Exactly.

I've got a ~10W panel,and don't feel the need to bother with a charge controller. Aslong as the charge current is like C/10,or under,you don't even NEED a charge controller. The battery can take a constant trickle charge.

This,of course,assumes you have enough battery capacity to deal with the solar panels output,which shouldn't be an issue with a small panel,and a SLA of any reasonable size.

You might well be better off putting a pair of similar sized mirror plastic sheets either side to form a hexagonal solar flux concentrator around it - like a trough \\__/. Pointed at the sun it roughly doubles output. No fancy electronics can turn half a watt into anything worthwhile - but mechanical hardware improvements can get you 1W from the same photovoltaic array at little extra cost but some increase in windloading.

If you are prepared for slightly more exotic engineering solutions a pair of parabolic curves with axis perpendicular to the collecting surface and focus placed at the opposite edge is about as good as non- imaging flux concentrators get. A good one can manage about 10x but is big and ugly - arguably the law of deminishing returns sets in well before then unless you are struggling to detect very weak single photon signals in a big volume with small expensive detectors.

There isn't really enough power output to be worth the effort of regulating. Think of it more as a trickle charger and defend the battery against leakage current back through the solar cells at night with a low voltage drop diode, and a suitably rated zener to stop overvoltage.

I'd be surprised if 500mW applied for half a day every sunny day would ever inconvenience a decent sized lead acid battery. But my intuition could be wrong here. 10W and above would need a controller.

Regards, Martin Brown

You know, strictly as a convenience to anyone who may be looking for small wattage solar panels, in the US, there's a company called "PowerUp". I believe their URL is

They carry aluminum framed, glass covered solar panels with attached cord (and on some models, integral blocking diode), in sizes as low as

I do not own stock in this company nor do they pay me to mention them. I only mention it because on a recent project, I almost pulled my (remaining) hair out trying to find a vendor who could actually deliver small quantities of commercial grade, low-wattage panels.

We used them, and had no problems. Note, several manufacturers no longer make the small panels (evidently due to conversion of factories to supply the European demand that is being driven by some legal environment there?)

-mpm

Easily under 10%, and pobably

Often, a great controller can be realized with analog control loop! Not every thing requires a micorporcessor. and in the case of managing modest sized solar arrays and optimizing the power harvested,you DO NOT want the excess power of a micro, unless it is absolutely necessary!

current consumed by the power optimizer is less than 1 mA!

Marc

If you do that with CD4000 logic or maybe a MSP430 with a micro-power regulator it should be feasible. At least it would be a nice challenge from an engineering perspective. I have to deal with this kind of situation a lot. No power to speak of available but the client wants this, that and the other thing user programmable. And since the client is king I do my best.

It is not impossible to increase efficiency via MPPT even with a grand total of 38mA or less. Of course in the end it could cost more than buying $2 worth of more solar cells.

"Joel Koltner" skrev i en meddelelse news: snipped-for-privacy@corp.supernews.com...

Hereteic! A square wave oscillator is "pushing" the set point of the usual regulator up and down. Then a synchronous rectifier is used to move the regulator set point via an integrtator. the maximum power point is when the up/down steps reverses i.e. the controller end up "siting" on the peak of the power curve.

I.e.100% analogue should work just fine.

Should really slap a design on the web together with a design for a resonant power supply for the "i need EHT people". Maybe Later ;-)

This one I'd also do analog. For larger installations a uC can make sense because they also need time tracking, calendar, sun position and all that for the big motor controllers that steer the array heading.

Joerg & Fritz ...

Could you flesh out your thinking a bit? My control theory class was a LOOOOOng time ago, and I've never reduced it to practice.

Audio and RF on the other hand ...

Jim

The energy yield versus voltage increases, crests and then goes back down for higher voltages. For maximum energy yield you want to stay around the peak. Problem is, that peak also moves about depending on clouds rolling through and such. So, for example, you can sweep and then dither around that peak and the electronics can track it. Basically you'd be looking for the point where the gradient of the sweep is the least, meaning total power drops on either side and hence the peak must be in the middle. Now you steer your switch mode stage so that it pumps the maximum juice into the battery or grid while keeping the input at maximum power point. Unless your are located off grid and the batteries are full in which case solar panels are often shorted.

The last one I built was not for solar and I can't disclose anything but except for min-max setpoints this was all analog. It had to be fast and also was cheaper that way.

It's called maximum power point tracking or MPPT. With solar stuff there isn't all that much detail in their "How it works" section but at least a little can be found here:

Probably universities have more but I had been in a rush so I just went ahead and designed it ...

My favorites as well. However, sometimes we must eat pea soup ;-)

In RF speak MPPT could to some extent be compared to automatic antenna tuners. There, you have to find the point of least VSWR. But in RF we mostly have phase information so we (usually) don't have to dither. Except when the "load" isn't free air but some odd object in which case it all needs to become more nifty (but still not necessarily digital).

Yes, they have some huge incentives. I know people in Germany who installed panels and rake in grid backfeed kWh rates several times higher than what a kWh normally costs. Of course, that is a hidden tax. There is no free lunch and usually the other "normal" ratepayers must subsidize this. Or the taxpayer does. Or both.