Solar panel charging two Lead Acid batteries

[Noam Sain]

Hi everyone,
I am working on a project which will be in my yard and built around a Raspberry Pi Zero. My power - for round the clock operation - is two 6v 7ah lead-acid batteries in parallel. The 14ah capacity of the pair should provide just a bit shy of four days operation without adding charge to the batteries.

I also have a nice 10w solar panel which puts out 12v. In order to use this panel, I need to charge the batteries in series when the sun is shining, and draw power from them, continuously, in parallel. Not sure how to do this.

Would someone here point me in the right direction?

Thanks!

- n -

 

[rjenkinsgb]

You need a step-down voltage converter (buck regulator) at some point.
The most logical place is after the batteries, with those series connected. That can then give you a stable voltage for the other electronics.
The voltage across a "6V" lead acid battery can range from about 5.5V as it gets near dead flat, to 7.4V on charge and full.

Also note that unless the solar panel has a built-in regulator, you will need a charge controller or voltage limiter of some sort to prevent the batteries being damaged by overvoltage, once they reach full charge.

In cyclic use, the voltage should never exceed 14.8V across a 12V pack.

 

[Pommie]

Alternatively, keep the batteries in parallel and use a charge controller that can take 12V in. However, i suspect you'll need some kind of regulator to power your Pi.

Mike.

 

[Noam Sain]

Thanks for the input, guys. My panel appears to have a regulator built into it; there is a small box on the back and in full sun, it puts out 14.5v.

Further research and taking some measurements, led me to keep the entire system running on batteries in series for simplicity.

I have a 12v to 5v converter I can use, and found that the current draw at the converter's 12v input, with the Pi connected, is just 50ma which would deplete the 7ah battery between 5 and 6 days. We never go that long without significant sunshine here, so this should work.

Right now, I have the panel in the yard and Volt/Amp monitor on my desk for observation. The panel was buried by the snowstorm on Monday and is still under a foot-plus of snow; it got up to 6.5v output today. I am letting snow melt naturally around it to see what performance I get, and at what point it starts charging.

If there is interest, I'll update over the weekend when the snow should be mostly gone.

- a -

 

[EmmaSim]

Spam removed.

 

[MacIntoshCZ]

I want to know... if I put 4 12v lithium in parallel in my Prius. As I daily drive this car will it power my house with a 12v split phase inverter? Grid-tie of course but feed that power thru the night and gain credibility as it discharges...

In general, it depends on the charging part of the car. Anyway, I think it's at the expense of the battery life of the car. I'm not sure if the charging plug of every electric car allows a two-way flow of energy or some modification will be needed. If so, it is possible ...

BTW you should create new thread...

 

[rjenkinsgb]

Note that the Prius main battery, that has high current recharge and runs the electric drive part, is high voltage.
200V or more.

The 12V system is not intended for high load.
Also connecting lithium batteries to a vehicle 12V system,, unless they have their own internal voltage control, may overvoltage them as a lead-acid system will run at up to 15V.

 

[Nigel Goodwin]

Note that the Prius main battery, that has high current recharge and runs the electric drive part, is high voltage.
200V or more.

I've not seen a Prius, but I've worked on Lexux hybrids, and as I recall they were 340V or so?

I read about an island somewhere the other year, and they were using the EV's that were on charge to feed back to the grid at busy times - essentially like a big reservoir capacitor.

 

[JimB]

I read about an island somewhere the other year, and they were using the EV's that were on charge to feed back to the grid at busy times

An interesting idea, but how would you feel if you were to get into your car and find that someone had siphoned half the petrol out of the tank?

JimB

 

[Nigel Goodwin]

An interesting idea, but how would you feel if you were to get into your car and find that someone had siphoned half the petrol out of the tank?

It was part of the deal of running an EV on the island - 'presumably' what was taken was put back for free?.

 

[JimB]

t was part of the deal of running an EV on the island - 'presumably' what was taken was put back for free?.

Yes I realise that, but if you need more electric juice than is left in the battery and you need it NOW, then the whole thing can be quite annoying.

To continue the petrol analogy, it would be like finding the tank nearly empty and someone had left a £20 note under the wiper blade as recompense. But it is the middle of the night and there are no petrol stations open within range of the petrol remaining in the tank.

JimB

 

[Nigel Goodwin]

Yes I realise that, but if you need more electric juice than is left in the battery and you need it NOW, then the whole thing can be quite annoying.

To continue the petrol analogy, it would be like finding the tank nearly empty and someone had left a £20 note under the wiper blade as recompense. But it is the middle of the night and there are no petrol stations open within range of the petrol remaining in the tank.

My next door neighbour but one, a nice lady called Jane, leased a Nissan Leaf for a couple of years - while she's nice' she's a bit 'social worker', so not very 'real world'. Needless to say, she ran out of power on quite a few occasions.

 

[Pommie]

I live in a high rise, about 100 apartments. If everyone went electric they'd have to install a new feed cable to handle the extra load. If all the towers around here went electric then the main feed cable into the area would need upgrading. It's a huge problem that nobody seems to appreciate. And, end of the day, you just move where the pollution is generated.

Mike.

 

[Nigel Goodwin]

I live in a high rise, about 100 apartments. If everyone went electric they'd have to install a new feed cable to handle the extra load. If all the towers around here went electric then the main feed cable into the area would need upgrading. It's a huge problem that nobody seems to appreciate. And, end of the day, you just move where the pollution is generated.

Mike.

Exactly, no one seems to consider where the electric is going to come from.

 

[Pommie]

Exactly, no one seems to consider where the electric is going to come from.

It'll be green though. /sarcasm

Mike.

 

[MacIntoshCZ]

main feed cable into the area would need upgrading.

 

[Pommie]

Is that a fusion reactor? Or something from a comic?

Mike.

 

[MacIntoshCZ]

Is that a fusion reactor? Or something from a comic?

Mike.

Wardenclyffe Tower - Wikipedia

en.wikipedia.org

 

[Pommie]

What is this " Insulting another forum member due language barrier count: 2 " about? Are you saying I insulted you somehow and if so, how?

Mike.

 

[MacIntoshCZ]

What is this " Insulting another forum member due language barrier count: 2 " about? Are you saying I insulted you somehow and if so, how?
Mike.

Thats my points. When i insulted someone due misunderstanding of the vertebrae.
First time i though another member is bot. And second it was some job project i think and i though he wants from us to route pcb for free. I replied that no one will do so. Then word shootout began. He said that i am donut or something like that =D.