Cheap solar battery charging

[jansman]

I just picked up another solar panel . Cheapo battery chargers too. My panels can charge my AA and AAA for zero cost. They can charge a power bank too. It might take a couple of days at worst,but my Anker jobbies can charge seven devices,or power USB emergency lighting . Those seven devices don’t have to be plugged into the grid. Win win!

Any inefficiency in the solar charging system is down to the laws of physics. Which is why the ‘Green’ ‘Renewables’ are not the Nirvana that our leaders tell us it will be,after oil.

[jennyjj01]

Any inefficiency in the solar charging system is down to the laws of physics. Which is why the ‘Green’ ‘Renewables’ are not the Nirvana that our leaders tell us it will be,after oil.

I hear you.

But I somewhat disagree with your first sentence.

Some inefficiencies we can't fix. Some we can and should.

There are inefficiencies we cannot do anything about, such as the heating of batteries as they charge or the low solar efficiency of a panel. But there are some dreadful inefficiencies in my system by design, which a few pounds, or a bit of thought and a bit of redesign can completely put right. Those USB - AA chargers didn't need to throw away 73% of the electricity put into them as heat from the circuit board. It was a design choice to save a few pennies. Same with my own PWM vs MPPT controller option. Deliberately waste >40% of available energy to save £££ on components. Deliberately fix my panels rather than motorise sun tracking. Etc. Design choices. some of them bad.

A bit like deciding how long to put up with a dripping tap or a leaking cross country oil pipeline that we don't bother to fix because it's not deemed cost effective.

If I'm building my system now, I choose not to fit the 'dripping tap.'

The more precious the energy, the more we invest in not wasting it.

Now... It currently costs a few tens of pennies to charge 4 AA batteries from the mains, even with the most rubbish charger. But take away the mains and i want to squeeze the pips out of my charger. Right now it doesn't matter that it takes two days to charge batteries that will power a lamp for one day. But we don't prep for right now conditions.

Of course, I could just invest in bigger panels, now But I'm too tight.

With my latest Plan C... If it works, I'll not only give myself the ability to charge more AA cells per day, but I'll also save ~£100 on components. Win-Win

I agree that the renewables nirvana is a pipedream. And the fossil fuel Nirvana always was. But that's a different thing.

[jansman]

Any inefficiency in the solar charging system is down to the laws of physics. Which is why the ‘Green’ ‘Renewables’ are not the Nirvana that our leaders tell us it will be,after oil.

I hear you.

But I somewhat disagree with your first sentence.

Some inefficiencies we can't fix. Some we can and should.

There are inefficiencies we cannot do anything about, such as the heating of batteries as they charge or the low solar efficiency of a panel. But there are some dreadful inefficiencies in my system by design, which a few pounds, or a bit of thought and a bit of redesign can completely put right. Those USB - AA chargers didn't need to throw away 73% of the electricity put into them as heat from the circuit board. It was a design choice to save a few pennies. Same with my own PWM vs MPPT controller option. Deliberately waste >40% of available energy to save £££ on components. Deliberately fix my panels rather than motorise sun tracking. Etc. Design choices. some of them bad.

A bit like deciding how long to put up with a dripping tap or a leaking cross country oil pipeline that we don't bother to fix because it's not deemed cost effective.

If I'm building my system now, I choose not to fit the 'dripping tap.'

The more precious the energy, the more we invest in not wasting it.

Now... It currently costs a few tens of pennies to charge 4 AA batteries from the mains, even with the most rubbish charger. But take away the mains and i want to squeeze the pips out of my charger. Right now it doesn't matter that it takes two days to charge batteries that will power a lamp for one day. But we don't prep for right now conditions.

Of course, I could just invest in bigger panels, now But I'm too tight.

With my latest Plan C... If it works, I'll not only give myself the ability to charge more AA cells per day, but I'll also save ~£100 on components. Win-Win

I agree that the renewables nirvana is a pipedream. And the fossil fuel Nirvana always was. But that's a different thing.

If you have the time and energy to sort that, then fair play. I won’t disagree.I work in an industry that is labour intensive. That has its inefficiencies,but time is used as well as it can be,by those experienced enough .However,some may say there are better ways to do the job.Fine,you find that way.One thing I have learnt though; and that is how NOT to work, or worry about stuff I can’t change ,or plain old can’t be bothered.

We burn solid fuel for our primary heat.Coal we buy in. Wood we get for nothing. Except my sweat! It’s not a bad workout,and I don’t go to the gym like my middle aged peers who live sedentary lives Now my wood acquisition and processing MIGHT be more efficient. But it works as efficiently as I can make it,and I am not cursing it as “ bl** dy hard work”.When I deal with it,it is done close to where it’s stacked.As it’s cut,it falls into a wheelbarrow to save handling.You get it. Right now,the wood store outside the back door needs filling.I have a huge pile of logs on the top yard that needs stacking. I won’t make a job of it. Every time I walk past,I fill a bucket,and bring it down.I am going that way anyway.

That’ll be a bit like my solar charging. It may not be Uber Efficient, but it works. It happens. I plug it in ,and I can charge batteries and power packs for nothing. I am not having to do paid work to pay the electricity bill. That’ll do for me.Something is working for me,whilst I do something else.All I know is,is that it works. If it doesn’t charge as many batteries in a day,then what I shall have to do,is to use LESS batteries! Energy conservation.Use less,do less work.

This prepping/ self sufficient/ survivalist lifestyle can be a lot of work. If you make it that way. In our much discussed SHTF world, there will be a lot of physical work. That’s where the laws of thermodynamics kicks in.: don’t put in more energy than you are getting back.That’s why lions don’t chase mice.

[jennyjj01]

But I somewhat disagree with your first sentence.

Some inefficiencies we can't fix. Some we can and should.

This prepping/ self sufficient/ survivalist lifestyle can be a lot of work. If you make it that way. In our much discussed SHTF world, there will be a lot of physical work. That’s where the laws of thermodynamics kicks in.: don’t put in more energy than you are getting back.That’s why lions don’t chase mice.

I can spend hours researching how to save minutes. And then arguing about it. Don't get drawn in. In a SHTF world, I'd be the one trying to use a spreadsheet for the work roster.

Let's agree that taking those first steps, whether it's storing food, growing food, installing solar, harvesting firewood. We need to JFDI

Everything else is just detail.

[diamond lil]

I think just doing it sorts it out, you learn as you go along. Practical hands-on stuff. I used to be bad for overthinking.

[jennyjj01]

I think just doing it sorts it out, you learn as you go along. Practical hands-on stuff. I used to be bad for overthinking.

Yes. JFDI..... Make some mistakes.... Learn... Iterate
I do overthink it.
Speaking of JFDI...
https://www.youtube.com/watch?v=WroY8lQXqAs

[ukpreppergrrl]

My little 25W solar panel can generate about 18V at about 500mA in good sun. Estimating that if I pushed that STRAIGHT into AA cells in series, (12x 1.5V ?) with no other components at all, it would charge them in about eight hours of good sun. Call it one or two days.

That's best case scenario. Or to put it another way. Charge 6 - 12 AA cells per day. Pretty pathetic! That's without any waste.
(Does that sound right?)

Plan A: Solar panel -> PWM Charge controller -> Car Battery -> 2 x USB - AA chargers plugged into the crappy charge controller,
Plan B: Solar panel -> PWM Charge controller -> Car Battery ->12v - multi USB adaptor - > Multiple USB AA chargers

Flaw with Plan A. Massive energy waste at charge controller: Cost of car battery: Rubbish charging current. energy waste at AA chargers.
Flaw with Plan B. Massive energy waste at charge controller: Cost of car battery: Cost of adaptors and USB multi-way: Massive energy waste at AA chargers.

I'm now onto plan C

Rationale: The solar panel might struggle to recharge the car battery quickly enough, if I were trying to charge lots of AA batteries.

I know. I KNOW. It's free energy, but if we can eliminate some waste, there won't need to be as many panels or I can charge more AA cells faster.

Now. There's a thing on ebay called a DC-DC 'Buck' converter, on sale for about £3. These multi purpose things are built into all sorts of chargers. As I understand it, it steps down voltage and steps up current with very little waste. It gives a steady output voltage that can be limited and the current that can be limited too.
E.g from the solar panel, giving ~18V at ~500mA, it could give me 9V at (almost) up to 1A.

Here's Plan C:

Solar panel -> Buck converter -> Six AA cells in a simple battery box. Nothing else except a plastic box to put it in!

When the batteries are flat, they would be charging at up to one Amp, I.e quickly. When they are full, they trickle charge until I swap the AA cells out for the next depleted set. I'd have to experiment with the settings.

Can you say BOOOOOOM!? Well....FFFFFT!! at the very least? Smoke. Maybe sparks. Some smouldering. Definitely something smelly. Definitely something nasty and not just in the woodshed.

The assertion that "when they are full, they trickle charge" is incorrect. They don't. They will just continue to take from the solar panel the full amps available to them. Until they overcharge, overheat, swell up, start to get sweaty and not in a nice way. Then they do the FFFFFFT thing and start to smell bad, leak electrolyte and maybe even catch fire. To trickle charge requires a controller of some sort in between the power source and the battery being charged. It's the controller that does the trickling not the battery or the solar panel. Clue's in the name. With a really small panel (like 10 watts or less) you can probably trickle charge a 12v battery without needing a charge controller (because the output of the panel is low and the self-discharge of the battery is high so you don't get overcharging happening) but I really advise against trying to push power from a solar panel directly into AA batteries without any sort of controller in between. They WILL overcharge and bad things will happen.

Plan B is sort of what I do. Personally I have a 21ah* 12v , deep cycle sealed AGM golf cart battery (and by God it's heavy!) that is permanently fed by a few** 20watt panels in parallel via a cheap PWM controller. To the 12v battery I attach a 12v charger (i.e. it's powered by 12v) not a usb charger, which can charge all my small batteries: 18650, AA, AAA, 9v, and can do so safely. They also get charged in a matter of a few hours, not days. Yes there is energy loss, but loss is part of life. And it's considerably less loss than everything going up in smoke would be. This setup is not only safe, it also allows me to charge batteries overnight, and on overcast days and means I can utilise the power of sunny days even if I don't actually have to charge a battery that day. By having the intermediary 12v battery you are smoothing out your power usage and getting the best use out of your 25watt solar panel. The 12v battery doesn't need to be fully charged to power the little battery charger for a few hours.

My 12v battery charger is off Amazon. It can also be powered from the mains (which is undoubtedly how most people will be using it) but if you check the description on a lot of these chargers you'll see that quite a few of them can also be powered from 12v DC. Look at the pictures of the back of the device, they usually have a 2 pin AC socket and a round 12v socket. Buy one of those. EDIT: This is the one I bought which charges the 18650 batteries, it's gone up in price since I bought it. I have a different one which will charge C and D cells and 9 volt batteries. They both charge AA and AAA. https://www.amazon.co.uk/gp/product/B07239TM65/

Plan B also allows that 12v battery to be used for other things if required: e.g. power a CB/HAM radio, charge USB devices (you can use your buck converter here to go from 12v to 5v), power 12v lights etc.. Versatility is always good. I do use a buck converter to run the usb fan in my greenhouse directly off a small 20w solar panel. But the difference is the fan is never "full". It just turns and turns and turns until the sun goes down and the solar panel can no longer provide the buck converter with the amps required by the fan.

I am a woman of a certain age and an 18650 powered fan is a lifeline on the daily commute. The 18650 batteries (I carry spares!) are all charged using the Plan B setup outlined above. I get a kick out of the fact that the hot sun that is making my life all sweaty, is ameliorated by a fan whose batteries were charged using the power from the self-same sun! They are charged overnight because I need them to power the fan during the day.

* Smaller batteries are available. Something in the 7-12ah range would be sufficient. These are fairly cheap. They're used in UPS's and you can often get them second hand but still fine - big data companies will be replacing the batteries in their UPS's every year or so "just in case". Usually these batteries haven't even been cycled more than a couple of times, and the UPS will have been keeping them trickle charged all the while. Unlike a car battery (but like the golf cart battery) they are designed to be deep cycled and so will work better in this setup.

** Like you I discovered that a single 20w panel is often not sufficient in winter to counteract the power lost by the PWM controller and the battery's natural discharge. I found that in winter the battery, even if I never used it, lost power. Oddly a single 20w panel with the same PWM controller IS sufficient to keep by car battery trickle charged over winter. Probably to do with the fact that the golf cart battery's panels are hung vertically in the south facing windows and are therefore rather suboptimally positioned. Either way I now have three 20watt panels in parallel in the south facing windows and that is more than sufficient to keep the golf cart battery charged whilst charging my 1850 and other batteries, even in winter.

[GillyBee]

Personally I have a 21ah* 12v , deep cycle sealed AGM golf cart battery (and by God it's heavy!) that is permanently fed by a few** 20watt panels in parallel via a cheap PWM controller. To the 12v battery I attach a 12v charger (i.e. it's powered by 12v) not a usb charger, which can charge all my small batteries: 18650, AA, AAA, 9v, and can do so safely.

Thanks for pointing out a gap in my preps. We plan to use a 100w solar panel on the shed with a controller to charge multiple smaller lead acid batteries like these. https://cpc.farnell.com/pro-elec/pel014 ... 7-00001003
The size means that we can cary them easily from shed ustairs to the flat which is a consideration when arthritis kicks in. (Which is why the panel is still waiting to be mounted on the roof). The kit will also charge our big car booster/tyre pump/light/USB power gadget which takes mains and 12V inpt.
My AA/AAA battery charer is mains and I was thinking I would need to add an inverter to charge. I am now off to research more flexible 12v battery chargers like your one.

[jennyjj01]

Don't invert up to mains just to run an àà charger. Lots of options to go from 12v to usb for about £3 and usb to 4xàà for another 3

[jennyjj01]

My little 25W solar panel can generate about 18V at about 500mA in good sun. Estimating that if I pushed that STRAIGHT into AA cells in series, (12x 1.5V ?) with no other components at all, it would charge them in about eight hours of good sun. Call it one or two days.

That's best case scenario. Or to put it another way. Charge 6 - 12 AA cells per day. Pretty pathetic! That's without any waste.
(Does that sound right?)

Plan A: Solar panel -> PWM Charge controller -> Car Battery -> 2 x USB - AA chargers plugged into the crappy charge controller,
Plan B: Solar panel -> PWM Charge controller -> Car Battery ->12v - multi USB adaptor - > Multiple USB AA chargers

Flaw with Plan A. Massive energy waste at charge controller: Cost of car battery: Rubbish charging current. energy waste at AA chargers.
Flaw with Plan B. Massive energy waste at charge controller: Cost of car battery: Cost of adaptors and USB multi-way: Massive energy waste at AA chargers.

I'm now onto plan C

Rationale: The solar panel might struggle to recharge the car battery quickly enough, if I were trying to charge lots of AA batteries.

I know. I KNOW. It's free energy, but if we can eliminate some waste, there won't need to be as many panels or I can charge more AA cells faster.

Now. There's a thing on ebay called a DC-DC 'Buck' converter, on sale for about £3. These multi purpose things are built into all sorts of chargers. As I understand it, it steps down voltage and steps up current with very little waste. It gives a steady output voltage that can be limited and the current that can be limited too.
E.g from the solar panel, giving ~18V at ~500mA, it could give me 9V at (almost) up to 1A.

Here's Plan C:

Solar panel -> Buck converter -> Six AA cells in a simple battery box. Nothing else except a plastic box to put it in!

When the batteries are flat, they would be charging at up to one Amp, I.e quickly. When they are full, they trickle charge until I swap the AA cells out for the next depleted set. I'd have to experiment with the settings.

Can you say BOOOOOOM!? Well....FFFFFT!! at the very least? Smoke. Maybe sparks. Some smouldering. Definitely something smelly. Definitely something nasty and not just in the woodshed.

The assertion that "when they are full, they trickle charge" is incorrect. They don't. They will just continue to take from the solar panel the full amps available to them.

thanks for the thorough answer. I did do away with the pwm, but no risk of it going boom.
I put the solar panel into the buck converter and set the output voltage at 9V. Then I set a current limit of 50mA which my envelope batteries can take as long trickle. I feed 6 envelope in series at the same time. My charger is actually built in a 8cell battery box with the buck converter squeezed into the space where two batteries would have been.
The missing link was to use the current limiter of the buck converter. Constant 50mA