Battery charging advice please?

[PaulRB]

A year ago I built a circuit to provide light in my chicken houses: http://www.picaxeforum.co.uk/showthread.php?19178-My-first-PICAXE-project-Chicken-lights-Greenhouse-watering&highlight=chicken

The 12V, 1.2 Amp-hour lead-acid battery is trickle-charged by a 2.4W solar panel. The 08M2 circuit senses light level using an LDR and switches on the lights (via a medium-power logic-level FET) for around an hour at dusk. The lights consist of a total of 4 x 3W LED strips, one each in 2 smaller houses and 2 in the larger house.

This works great most of the year, but in Winter, if there are more than a couple of dull or foggy days in a row, there is not enough charge left in the battery to keep the lights on for more than a few minutes.

So I need a little more charge from somewhere.

With a budget of, say £50, what would be forum suggest? More panels would be easy to add (£25 each from Maplin). A small wind turbine would be a more interesting project, but I have seen almost none in that price range. Could I construct one myself from parts? I have been Googling for parts, but they all seem to be designed for turbines that would be over-the-top for this purpose.

Thanks,

Paul

 

[Buzby]

A slightly different approach.

Could you PWM the LEDs to reduce the consumption a bit, thus giving you more hours per charge ?.

 

[fernando_g]

I assume you don't have mains power? To add a small mains powered DC supply, as a backup for those rainy days.
In that case and considering your limited budget, then buzby's recommendation makes the most sense.

 

[bfgstew]

I know this is for a 1000W and is rather large, but, you could always reduce the size by a 1/4 if not an 1/8 and still generate enough for your batteries?
Could also disguise it by having a little man with an axe pretending to chop wood up on the back of it..............lol.

 

[geoff07]

Do both - an extra panel and a reduction in consumption. Perhaps you could use the state of charge to determine the pwm ratio so you get full brightness when you have the juice.

Did you do this to get more eggs? If so, did it work? Any data?

 

[AllyCat]

Hi Paul,

Linked with the above suggestions (if practical), I'd add a a larger battery! Whatever the (renewable) energy source, I suspect that there will be periods of many consecutive days when there is insufficient power generated. A car battery (maybe from a breakers yard) could be around 40Ahrs and at this time of year (Winter) it can be charged before installation. Or use a couple of batteries and swap in a recharged one every month or two, when needed.

Certainly wind power can be considered complementary to PV (more wind in Winter) but I have a simple weather station at home and have been surprised/disappointed how low is the average wind speed, even above house-roof level. I believe the "usable" wind speed range is quite small; below about 8mph no useful power is generated and above say 30mph (gust) the system may have to be protected against damage. For something cheap to try, how about a car radiator cooling fan, again from a breakers? But don't forget that it needs to automatically face into the wind.

Cheers, Alan.

 

[Buzby]

Why do the chuckies need light anyway ?.

Do they all read books in bed ?

 

[bfgstew]

Have you not seen 'Chicken Run'?

Chickens go in, pies come out............................side splittingly good fun.

 

[Buzby]

Oh, I see !.

They need a light on when going to sleep so they don't get nightmares about the Pie-O-Matic machine !

 

[bfgstew]

......LMAO

 

[Phil bee]

Hi, how about ussing an old stepper motor and some home made blades cut from 4" pvc waste pipe. This works quite well and can charge a small battery.
A blade lenth of about 12" should do the trick.

 

[manuka]

12V, 1.2 Amp-hour lead-acid battery is trickle-charged by a 2.4W solar panel

Some PV types (mono X, polyX,CIGS,amorphous) are better that others under overcast skies-what sort do you have? Have you attended to seasonal orientation? PVs are increasingly cheap (having almost halved in price in the last year!) & larger panel prices approach £1 a Watt. You could probably get a 5 -10 Watter for £10-£20. I recently picked up a quality 20W monoX for ~£30, & locally note the likes of top brand 190W going for ~£200.

Update -prices fall even as I type- here's a 200W mono-X going for NZ$330 (~UK£170). It's getting to the stage where they're not far removed from the cost of similar sized glazing! Wired sunbeams anyone?

Your battery is also probably too small, & may well "cook" in summer! Hence grab a larger capacity one as well. 12 V 7Ah SLA are the global standard for stationary work & 2-3 year old ones can be picked up for -ah- "chicken feed" at the likes of security firms.

 

[Haku]

BTW, old car batteries are excellent for solar lighting setups, especially as they're usually free

Even if it's only holding around 1/3 of its original capacity you're still looking at over 10Ah.

 

[SAborn]

The best solution is to add more solar, you can mess around with wind generators but the return for the time spent is next to useless in small scale wind turbines, you could have a look here for a stepper motor mill.
http://www.thebackshed.com/windmill/assemblyMini1.asp

My advice is not to bother with it as it wont help very much in your system, I build and use wind turbines and to extract any amount of usable power from the wind is not easy, and a far bigger project than a mini stepper mill.

All lead acid batteries should be fully recharged within 24 hours of use, or sulphation will start to effect the battery, this means 100% recharge and not partial top ups of charge.

To use old car batteries is not a good solution either, and they die quickly if deep cycled, the important fact is to have a balanced system where the battery size to recharge ability can be achieved within a average 24 hour window. (or 6 hours of sunlight)
To use a car battery with a 2.4w solar panel is just not practial as the battery capacity is huge to the recharge ability, and all you will do is slowly drain the battery without the ability to recharge it fully in the time between its uses.

If you look at the 2.4w panel that will allow ... 2.4 / 12 = 0.2 amp per hour to the battery or 1.2 amps over 6 hours.
This would allow about 1 amp for 1 hour a day to be drawn from the battery, with the ability to fully recharge the battery the next day on average.

There is little point in having a big battery when all you have is 1.2 amps a day to recharge it, this is what i mean by a balanced system.

 

[ZOR]

Can't you make the chickens go through a treadmill to get to there food, bit like a mouse running round a wheel.

 

[PaulRB]

Thanks for all the great replies everyone!

Lots of ideas there, but sounds like most of your votes go to solar.

The PWM idea: as I can't increase the current (the strips run at 12V and I can't see any current-limiting resistors) this could only dim the light, which I don't really want to do if I can help it. They're just bright enough (when the battery is charged). An interesting question, though, would be what frequency to use to avoid noticeable flicker. I suspect bird's eyes can see flicker at significantly higher frequency than humans, and I doubt they would like it any more than we do!

The mounting of the existing panel is about 15 degrees, tilting roughly due south. Should I go for a slightly steeper angle, to optimize for the position of the winter sun rather than the summer sun? My goal here is not to maximize power generation over the whole year, and I suspect I am getting more than enough in high summer.

If I use a much larger battery (car size), will the internal leakage be higher, and just loose any extra charge accumulated on sunny days before its needed?

The point about having a balanced system makes sense to me. As it is now, I suspect its not badly balanced, with 2.4W charging the 1.2 Amp-hour battery fully in around 6 hours with 0.2A, theoretically, on a sunny day. Then the 4 x 3W lights drawing 1A would discharge the battery in around 1.2 hours. Problem is in the winter I probably get a fraction of that charge on some days.

So, should I increase the battery capacity, hoping to build up more charge than I need on sunny days and hope that charge does not leak away too soon, or increase the panel capacity and hope to get more charge into the battery on dull days. With the latter, do I need to worry about overcharging on sunny days?

 

[PaulRB]

Have you not seen 'Chicken Run'?

Chickens go in, pies come out............................side splittingly good fun.

We do "secret Santa" in my team at the office, every Christmas. I finished up with 3 copies and had to ban anyone from getting me that in future!

 

[Dippy]

I would have thought that , if you have 'more than enough' during summer, then , on the face of it, adjusting the angle to optimise for winter was an obvious first step to try.

Have you actually done any real measurements? (I'm never totally happy with 'balanced' charging , especially when simply guessing.
Have you experimented with panels to see the efficiency droop when light is lower or sun off-axis?
Have you minimised the circuit current when lighting not needed (circuit and code)?

Regular dead-flattening of the battery is not good for it.

To be honest it's a fairly weedy setup for your requirements.
You can't get something for nothing so your solution may be bigger panels+ bigger battery with a pukka charging circuit.
It isn't hugely difficult, but you may have to get a few dusty fivers out of your wallet.
... but the chickens are worth it surely

 

[PaulRB]

Alan, I think it all depends where you live! On the top of our moor at around 1000ft above sea-level, we are surrounded by commercial wind farms and several neighbours also have up to 50KW turbines on their land too. Would like to have a 10+KW myself one day, but will need to save pennies to buy a little more land than we have now.

 

[SAborn]

When you break down the situation its not that much different than yourself living off grid for power using alternative energy, in this case the chooks live off grid.

The first thing you need to do is workout what watthours are used, meaning what current (amps) at what nominal voltage (12v) for how many hours the power is consumed for. (LEDs on)

Then this can be worked backwards to design a system to suit.
At the end of the average day ...power in needs to exceed power out to have a balanced system, for a reliable long term operation, if you simply flog the battery it will die quickly.
You maintain the battery charge and you will get long use from it, abuse it and you might get 12 months before a replacement is needed.

You ask about over charging on sunny days, the answer is yes you need to limit over charging or charge voltage (a picaxe can easy monitor and control this), in a ideal situation the battery needs to reach overcharge every day to achieve 100% charge of the battery capacity, or the battery life is reduced, its a catch 22 situation, if you cant replace what was used, then the battery will suffer, the longer you draw the battery down, without a full recharge the greater the damage done to the battery. (it will never recover to 100% from long discharge periods)
As i quoted its a balance act, that involves the amount of stored energy required over a 24hr period, and the ability to replace it in a given time period with relation to consumption over time.

A 2.4w panel is what i would call a toy panel, but if you made a tracker for the panel you could expect a 25% greater return for the day, thats the same for a large panel array or a toy panel, you track the sun and can expect around 25% more power.
In this case its about a 0.05W gain, hardly worth doing.
Far better in cost wise to up grade to a 10w panel i would think given the options.

 

[AllyCat]

The mounting of the existing panel is about 15 degrees, tilting roughly due south. Should I go for a slightly steeper angle, to optimize for the position of the winter sun rather than the summer sun?

Hi,

Yes, but I would say much steeper, a recommendation I saw (for night-time lighting) was that the angle of the PV panel should be 15 degrees steeper than the latitude (~55 degrees for Yorkshire?). However, it may depend on the amount of useful energy received from the sky, rather than direct sun, which I believe varies with the PV technology.

Whilst SAborn clearly has considerable practical knowledge, I wonder if the "balanced" principle is more relevant to Australia than Northern England. On some winter days in England I doubt if a PV cell receives much more than 1% of its rated value, so you would need an enormous area to fully replenish the battery every day.

Cheers, Alan.

 

[SAborn]

I wonder if the "balanced" principle is more relevant to Australia than Northern England.

How can it not apply to every location, unless Northern England know something about over unity that the rest of the world dont.

Simply you cant get more out than you put in, if it aint being put into the battery how can you get extra out.
Its a balance of what goes in, to what is taken out of the battery, i would love to know how Northern England solves the problem of more out to less into the battery, more to the point it would solve the worlds energy problems.....please share.

Yes you can have some reserved stored energy to get you by a day or 2 of bad solar hours, but at some point the energy needs to be replaced, and the longer the battery sits around in a semi discharged state the greater the damage to the battery, and if all you have is 2.4watts of solar then it will never catch up, the problem just keeps getting worst.

 

[AllyCat]

Yes you can have some reserved stored energy to get you by a day or 2 of bad solar hours,

Hi,

Yes, that was my point. Except that we may be talking about a week (or two) of "snow" clouds, perhaps with snow covering the PV panels as well.

But certainly we do need larger panels here than in Austrailia. I've just looked at todays theoretical (max) solar radiation and even here in the "sunny south" of England (Lat. 51) it's less than 200 watts/m2 at noon and only above 100w/m2 for 4 hours today.

Cheers, Alan.

 

[AllyCat]

Hi again,

Reading back over the thread, I had assumed that SAborn was proposing to fully charge the battery every day, but he actually said "average day". But averaged over how many days? In Australia a few days may be sufficient, but within the (ant-)arctic circle (polar regions) surely only a yearly average is relevant? If my calculations are correct, Adelaide is almost exactly the same distance from the Equator (or Tropic of Capricorn) as Yorkshire is from the North Pole (or Arctic Circle). So an "average" over a month (or longer) may be more appropriate for the UK.

For those that don't know, PV panels are normally "specified" with 1,000 watts/square meter illumination, so the maximum (clear sky) 160 watts/m2 of noon sun (and only above 80w/m2 for 4 hours each day) in the English midwinter makes the actual power produced rather pathetic.

Cheers, Alan.

 

[Jamster]

What about sticking peltier generators under where they sit?

For added effect tape them down to it with thermal tape

 

[BeanieBots]

Lots of good advice already given but I'd go along with SAborn & Manuka.
In particular, get more solar panels and increase battery size. Look after your batteries by not over discharging AND not over charging.
Meanwhile, periodically give your batteries a nice long charge with a quality charger to significantly help their longevity. Batteries need to be thought of as living things. Excessive starvation or any other form of neglect will result in death which like any creature, is irreversible.

 

[papaof2]

Synopsis of the research I did on solar panels charging lead-acid batteries: I can't afford a big enough system to take this old house off-grid - too many big trees. Leave the trees and too much shade for solar panels. Take out the trees and double the summer heat load on the house.

However, the process is the same regardless of system size.

Less discharge = more battery charge/discharge cycles. Discharging only 20% (80% charge remaining) should give years of life from a sealed lead-acid battery. Discharging to 50% will cause a major reduction in number of charge/discharge cycles. Discharging to 20% or less will probably kill the battery in a years or less.

One good reference is Battery University:
http://batteryuniversity.com/learn/article/can_the_lead_acid_battery_compete_in_modern_times

 

[bluejets]

In my experience, lead acid batteries prefer to be "worked" through the full range rather than a piddle in and a piddle out.

 

[boriz]

+1 Larger battery. Larger panel. Steeper angle. Chicken pie.

That stepper based wind turbine looks fun. Use bigger blades if your wind speed is lower. Can't hurt to lash one up for fun. Could be the start of something big. I wonder if a BLDC motor would be better? (Less magnetic breaking effect)

 

[SAborn]

That stepper based wind turbine looks fun. Use bigger blades if your wind speed is lower. Can't hurt to lash one up for fun

It is really a fun project and teaches a lot about how hard it is to extract energy from the wind.
Bigger blades have 2 effects, larger blades result in slower rpm, which results in lower voltage out, but it gives more torque.

Then you must also remember low wind speed is not always the case, and you will have some days of high wind speed, and need to design to also handle these odd days throughout the year, or your mill will self destruct.

Cogging as we call it or magnetic breaking effect, is the problem with steppers and in light winds the blades will just sit there and not move until the wind is strong enough to break free of the cogging, often it takes a good wind to do this.

Its not a suitable project for a 12v battery, but ok for a couple of nicad cells and a few single leds for garden lights etc.
The thing with wind generators is, the higher the rpm the higher the volts out, so to get 12v out of a stepper motor it would need to be doing 1000-2000 rpm which is not practical with wind.
A couple of 100 rpm and 3v out to nicad cells is about its limit, and its supprising how long it will take to charge a couple of nicad cells.
It is a good project to learn its not just a matter of sticking a slap together device in the wind and it returns lots of free energy.

 

[boriz]

I like the idea of a VAWT with the motors (generators) at the top and bottom, doubling as the main bearings. Could be wired in series for low wind and switch to parallel in high wind?

The disadvantage is that VAWTs are less efficient than traditional types. But sometimes where you live is the constricting factor. EG: Nearby structures, turbulence, frequent storms etc..

 

[Haku]

I have a 'homemade' setup for LED lights in my bike shed, it consists of an old car battery, a cheap charge controller (the same as this one) and a 30 year old Kyocera 30watt solar panel which still gives 24watts in full summer sun. The lights are controlled with a 'garage door' remote setup which is permanently powered and controlled with a keyfob.
I also connected the battery to a long mains extension cable so I have a '12v' source in this room, quite nice for charging USB things

With a 50 quid budget you can easily get a 20 watt solar panel (such as this) and a solar charge controller, leaving you to source an old car battery (usually free) or see if you can get a couple of old SLA batteries (to run in parallel) from someone replacing theirs in a golf cart or mobility scooter.

edit: Looked more closely at the 20 watt solar panel listing, it says it includes a charge controller but I would ask about that if you intend to buy one in case they say it's just a blocking diode, as a diode setup is only for low wattage trickle charging.

 

[SAborn]

Boris,

You will get about 1/4 to 1/3 the power from a Vawt compared to Hawt for about the same build cost.
A lot of people build a Vawt for their first mill, only to find it generates next to nothing.

As i quoted earlier rpm in equal volts out, and as a Vawt is a slow turning design it makes almost nothing in low to mid wind speeds, the old argument of adding gearing comes up then, but as soon as you go away from a 1 to 1 ratio you loose even more quickly in efficiency.

Its all been done before and well tested and documented, unfortunately there is a lot of misleading information around to.
Im all for someone wanting to build a wind turbine and playing with wind energy, but think there is right way and wrong ways to go about it, and in many cases people need to find out for themselves as they wont except advice from those who have already been there before them.

If anyone asks me if solar or wind is better the answer is solar will give a far greater return for cost then wind will ever do, even on those bad English winter days, (we have bad winter days here to) My wind turbine contributes about 5% of my power and solar the other 95%, so $1000.00 spent on solar would have given a far greater return than wind.
The Neo magnets i have for my next mill build are worth about $2000.00 on today's market, and should produce around a 3kw mill, so its not cheap to extract reasonable power from the wind.

 

[PaulRB]

Thanks Haku, that 20W panel is certainly much better value for money than the 2.4W one I bought in Maplin (even considering I got it 1/2 price on offer). I will ask about the "controller", although not hopeful of getting a technically accurate answer from them. They also offer a 10W panel which they claim can be used to charge 12V batteries, even though it only generates 9V, using their charge controller. Would a charge controller be capable of stepping up the voltage?. But the 20W panel is cheaper overall if it has the controller built in.

 

[manuka]

That 10W will not step up the voltage ! Your 9V reading may well be a consequence of the inbuilt controller, some of which may be a tad too smart for themselves at times. Bypass to the raw feed for more realistic readings. IMHO go for the 12 Volt 20 Watter - it's probably akin to one I have.

 

[AllyCat]

Hi Paul,

It would be worthwhile posting a link to the panel(s) that you're considering. Some appear to be only amorphous silicon (which has generally inferior qualities) compared with the crystaline silicon panels shown by manuka.

Cheers, Alan.

 

[Haku]

That 10 watt panel is for charging a 6 volt battery as it only has 18 cells, 36 cell panels are for charging 12v batteries.

 

[PaulRB]

Hi Paul,

It would be worthwhile posting a link to the panel(s) that you're considering. Some appear to be only amorphous silicon (which has generally inferior qualities) compared with the crystaline silicon panels shown by manuka.

Cheers, Alan.

Hi Alan, Haku posted the link in post #32.

 

[PaulRB]

That 10 watt panel is for charging a 6 volt battery as it only has 18 cells, 36 cell panels are for charging 12v batteries.

Hi haku, yes, that's what i thought. But their 10W panel item description on eBay says:

"To ensure proper use, the solar panel must: Step 1. Connect to the controller (not included. You may find it in our store); Step 2. Connect the controller with 12V battery;"

Hence my scepticism over getting any reliable info from them about the controller on their 20W panel.

 

[manuka]

10W 12 V PVs can be bought off the shelf for near that EBay price. I half expect to soon see them turning up in coin shops.

Here is NZ most boating supply outlets (a branch of commerce of course well known for their heady markups too) have great displays of them for peanuts. Take along your DMM & a 12V SLA battery, step outdoors (into whatever passes for British sunlight this time of year), and-test-it-right-there!

Rule of thumb: In bright sun a postage stamp sized PV cell will deliver ~100mA short circuit current at ½V open circuit voltage. Simply count cells & scale up accordingly. Most 12V PVs have 36 cells, but you often have to carefully inspect them visually to see the differences between connections & insulating gaps.