volts is pressure

[georgeodjungle]

what i'd like to know is could you have an light sensor on pvs?

so on normal days i'd have 21v coming from the panels "12v bank is what i run" and then on dark days or with moon light switch over to say 24v or 36v"got 6) 50w pvs"

multi switch?id love to do kind of the same for the gennys.

cuz i checked the volts at night with moon a most full and it was 8 volts !

is there some kind of auto switching thingy that would not eat up my juice?

another reason i think i could do it is that gennys run at a much higher volts like battery chargers.that's what were doing any ways?

would i toast-em "the pvs"if i just run 24v?

it works with my and every one eleses gennys, would it work with the pvs?

parts list with schematic for home brew would be great!  if i could with out roasting my panels.

bring the hot dogs and stuff for smores!

[TomW]

George;

Well, this might work but my feeling is that you would not get many Watts and while voltage is indeed the pressure without some amps to go with the volts to get watts you wont get much power. In case you don't know this already watts is equal to volts times amps.

Just how it works.

T

[Bruce S]

george

I haven't tried this yet , but I think you could use one of the dusk/dawn photocells in reverse.

The ones I have came with the solar lights, so they'll be sensitive enough to detect light/dark modes.

I may be wrong but it should work.

Cheers!

[richhagen]

The voltage of my panels falls off to basically nothing at night, it may be due to imperfections in the silicon cells, as you would think intitially that the available current would simply be reduced by decreasing light levels.  The levels of power you would receive would not make this worth the effort in my opinion.  The only time you would be able to make use of this type of switching for your size of array would be for a few minutes at dusk and dawn as the voltage of the panels rises past 4V through 13V or so, and for my panels, this doesn't represent much time, or much current under those conditions.







The top right chart shows voltage and current for a 24V 165watt sharp panel as a function of irradiance.

For my panels, although I havn't quantitatively measured it, it appears to me that the open circuit voltage (Voc)drops much more with decreasing irradiation than for the Sharp panel.  My panels are mainly old Siemens, Arco and Photowatt panels though.  Rich Hagen

[electronbaby]

if you have 6 panels, why not wire them in series to get a higher voltage and use a MPPT controller to charge a 12v bank with the higher voltage.  ??

RoyR

[RobD]

It's funny you guys should mention this.

I just did testing on an Astro panel thinking that I would build a high efficiency SMPS (switch mode power supply) that would boost the voltage when it dropped below the needed charging voltage.

When I tested my panel I found that the voltage stayed pretty constant (17 volts) in open circuit down to  a 100ma. or so, when it did finally drop below the needed charging voltage the current was so low that it was not useful even with the high efficient supply (<93%).

I'm working on a MPPT that will attach to a panel and keep the voltage at a point above the battery voltage to draw the maximum amps out of the panel.

Example:

Panel=17v@4.4 amps

The 4.4 amps is the maximum current the panel will supply REGARDLESS of the voltage. That means if the voltage falls to 15 volts you will only get 4.4 amps out of the panel. So you have effectively LOST 8.8 watts (17x4.4= 74.8 watts, 15x4.4=66 watts, 74.8-66=8.8 watts). It gets worse the lower your batteries are. So if your batteries are at 11.5 volts you still only get 4.4 amps charging power or 50.6 watts.

Now let's say we SMPS the 17 volt supply to a point just above the 11.5 volts that uses the maximum attainable power from the panel and let's say that voltage is 12.0 volts. 74.8 watts/12.0 volts = 6.233 amps! Even if we have 90% efficiency from the SMPS = 6.233 x.90= 5.61 amps. That means the 4.4amps x 12 volts = 52.8 watts, and our power = 5.61 x 12= 67.32 watts = 67.32/52.8 = 27.5% more efficient.

That's why MPPT is so great. I just don't think it should cost all it does and the new SMPS chips coming out will change that.

[RobD]

One more thing. Since the panel is no longer subject to frying when the sun goes down you can toss the diode in your charger. Let's say the diode is a schottky and it has a Vf of .5 volts ,which means it drops .5 volts from what we call insertion loss.  ( being placed in the circuit.) That's another 2.8 watts you pick up. (5.61 amps x .5 volts = 2.805 watts).

Why doesn't MPPT work on windmills? I think it's because the mills don't exhibit the same characteristics a panel does. That is if you load a mill the current will increase as the voltage drops to keep the same power.

You can, however, set up a boost configuration SMPS to boost the low voltage, say 8 volts to a usable voltage to run your charger, say 14.7 volts. The current will drop to keep the power the same but you will still get usable power that would have been lost. The thing to remember is to not load the mill down so much that it doesn't start which is the problem with using a mill for strictly heating. The element has to 'kick in' AFTER the mill is running a bit or you create problems.

[georgeodjungle]

yep: your right,kind of?

it's not realy worth it,it's kind of like pumping up the old cb radios and now cell and cordless phones.i get 4 miles out of my cheepy cordless and talk around the world with the old cb & the cell has more bars than any one!it's shure nice when you get out and the stock"legal ones" don't!we squeze every lil thing we can.changing out the old blocking diodes to schottkys does makes a bit more juice, and by passing makes a lil more.but bad juju can happen with it all.

i just thought we could squeeze a lil bit more on say a full moon or them stormy dark days.it might not be worth it to some,but others?

of course you don't get some thing for nothing.like motors, horse power goes up dependibilty and longegivity goes down.

right now? i think a tracker would be the best PUMP-UP "for you on c road"

[georgeodjungle]

p.s.

your meter must be a digtal,not the old needle type.

[RobD]

Worse then that!

It's a HP34401A with 6-1/2 digit readout to nanovolts and 4 wire ohms that can measure the resistance of relay contacts in milliohms.

Believe it or not I use every inch of it when I design a circuit and am looking to save every microwatt of power.

Jerry who? My 13" TV only gets a couple of stations. I think it still works.

HP34401A

[georgeodjungle]

sweeet meter!

so do ya think it can be done,

where can i get the sams and part list for home brew.

how much juice do you think it would take to run? or start with 24 and switch "on"

with light?

home brew tracker would be good to.i found one that i'd like to make for the solar cookers.this is not for me any ways but i'd like to help.SQUEZZZZZz N pump-em up.

  and jerry is just a personal goal i have to be on his show.i'm on the old antenna to.some people have to pay for tv, could you beleve that!

[boB]

>>> I just don't think it should cost all it does and the new SMPS chips coming out will change that.

Which chip(s) ya got in mind ??

boB

K7IQ

Everett, WA

[RobD]

Well first off one of the problems I see with charging SLA batteries from solar panels is that several designs use three terminal regulators to control current. This is very consumptive. I believe the UC3906 is better but it still doesn't have the efficiency of the SMPS(Switch mode power supply).

Now we're getting regulators out that are complete SMPS in a regulator like the National LM2678S that will handle over 5 amps. and the LM2674 (96% efficiency) that can make a very good NiCad or small SLA charger with very high efficiency.

National has a chip now (LM3490) to run the high power Luxeon Star LEDs that is current regulating and fits in a small package.

I don't know how many of you have seen a flashlight out of these but I've made several and the light is much better then any standard flashlight around, first off it's white and not yellow and the current is about 350 ma. not an amp.

I expect to see LEDs being the main lighting in houses and cars. They are already in street lights. Remember LEDs are current devices and the only way to truly run them is with current regulation which, until recently, has been a pain to do easily. I'm seeing a lot of chips to run series strings of LEDs in current mode which keeps the LED from being over driven. Ideally if we ran each LED in parallel it would need its own current regulator. We can run 4 or 5 in series and regulate them to say, 20ma with one supply which makes a nice flashlight with white LEDs.

Some of the Micrel chips are very good too, the  MIC2182 for instance.

I think we're way behind in electronics for alternate energy. I see a lot of new chips coming out for cell phones, Blue Tooth and low power battery efficiency but very few for wind and solar.

It's time for 'Smart' solar panels regulated by SMPS and controlled by uC's(microcontrollers) and that's what I'm working on.

I hope this will change now as fuel prices hit the roof. The Europeans are stocking up and building Wind and solar systems at a much faster rate then us while we're still stuck on oil and SUV's.

Hey the Bush's are in oil what did you expect them to tell you to wash your face so you would look better then them?

[richhagen]

I converted an old streamlight recargable to LED's, since the pack was 3.6V, I ran it directly.  I used a Luxeon Star-O for a light I built, but used an inefficient resistor to limit the current from the battery.  I like the Idea of the chips you are describing, and if I get the chance I will give them a try.  Rich Hagen