# Sizing a Solar Panel



## YYCHM (Sep 20, 2021)

That Calgary 2020 hail storm took out the solar panel for one of our outdoor motion detecting security lights.  Nothing wrong with the light but the solar panel was trashed and as a result the light doesn't survive the winter with out some sort of charging.  I'm seeing relatively inexpensive solar panels on Amazon, so my question is...... what size solar panel does one need to charge 3 - 1.2V NiCad batteries wired in parallel.

Anyone?


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## YYCHM (Sep 20, 2021)

This is the exact one I need.  Why can't they publish specs for this stuff

Solar Panel Replacement for Motion Lights (temporarily out of stock) / – Sunforce Products Inc. (sunforce-products-inc.myshopify.com)


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## Tom O (Sep 20, 2021)

What does it say on the battery? Walmart has some solar panels online also.


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## YYCHM (Sep 21, 2021)

Tom O said:


> What does it say on the battery? Walmart has some solar panels online also.



3 AA Ni-MH 1200 mAh 1.2V rechargeable batteries


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## PeterT (Sep 21, 2021)

_what size solar panel does one need to charge 3 - 1.2V NiCad batteries wired in parallel._

Do you mean 3 cells or 3 packs? Each nimh cell is typically 1.2v nominal. So 3 cells in series = 3.6v/pack. 3 cells in parallel is same1.2v (but 3X the maH capacity).

I actually know little about solar charge/maintenance, you'll probably have to research. But a dedicated typical charger might output 1C for NiMH. So a 2500mah capacity cell would require 1C * 2500 / 1000 = 2.5Amps at something above the pack discharge voltage. A trickle or maintenance charge is probably much less, maybe 0.1C? Dedicated chargers have kind of a ramp up - ramp down algorithm, they pump as much as they can in when depleted & then taper off so you get a full charge in least time. But trickle is different, its just perpetually topping up. Different battery chemistries have different allowable C ratings.


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## YYCHM (Sep 21, 2021)

PeterT said:


> _what size solar panel does one need to charge 3 - 1.2V NiCad batteries wired in parallel._
> 
> Do you mean 3 cells or 3 packs? Each nimh cell is typically 1.2v nominal. So 3 cells in series = 3.6v/pack. 3 cells in parallel is same1.2v (but 3X the maH capacity).
> 
> I actually know little about solar charge/maintenance, you'll probably have to research. But a dedicated typical charger might output 1C for NiMH. So a 2500mah capacity cell would require 1C * 2500 / 1000 = 2.5Amps at something above the pack discharge voltage. A trickle or maintenance charge is probably much less, maybe 0.1C? Dedicated chargers have kind of a ramp up - ramp down algorithm, they pump as much as they can in when depleted & then taper off so you get a full charge in least time. But trickle is different, its just perpetually topping up. Different battery chemistries have different allowable C ratings.



3 AA sized cells wired in parallel (not 3 packs).  The light doesn't take a pack arrangement, just individual AA cells.


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## Tom O (Sep 21, 2021)

Maybe try talking to PMS Hobby about what you would need. Besides it’s always nice to walk through looking at all the parts available gears and such.


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## YYCHM (Sep 23, 2021)

Hmmm....  Do you think I could use this as a guide?  Says 2W solar panel.

Solar AA & AAA Rechargeable Batteries Charger for 1.2V AA AAA NiMH NiCD & 9V Battery with 2Watt Solar Panel Portable Backup for 1.2V Ni-MH Ni-CD of Solar Powered Lights and Household Battery : Amazon.ca: Electronics

And then there is this.....

https://makingcircuits.com/blog/simple-solar-ni-cd-charger-circuit/

Just a tad over my head when it comes to electronics.


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## YYCHM (Sep 25, 2021)

No one on here has dabbled with solar cells eh?  I'm surprised.

My internet searches has yielded everything from needing 2V to 5V and requiring a diode to prevent the solar cell from draining the batteries at night?

AliExpress lists 2220 items when you search for solar panel.  Mostly 6V, 12V and 18V.  All the lower voltage stuff doesn't look like something you could leave outside all year long nor are they as big as the original panel?

Budget is $20 max. LOL


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## PeterT (Sep 25, 2021)

One thing I would also verify is how many cells are 'required'. Showing 4 cells in the bay with no other description might be a sneaky way of saying the solar panel output is somewhat fixed and it needs all 4 in place. This one looks like it has the smarts to allow different cell counts, voltages & capacities. Suspect more than your budget.
http://www.eblmall.com/product/ebl-...port-type-c-input-fast-aa-aaa-battery-charger

I've done a lot of RC charging & there are scads of chargers for 1-X cells for every chemistry, capacity & pack under the sun. But they all require 12V nominal input. That might have originated from (dating myself) lifting the hood & hooking up to car battery which is frowned upon now. These days we all pack a dedicated 12v battery source for field charging. Some people are solar charging those, probably because there are lots more solar cells orientated around 12v because its so common in cars, RVs etc.

But the main point is charging is more than hooking up appropriate voltage & current. The charger has to have an idea of what its doing - how many cells, maH capacity/cell, chemistry type, depletion state (especially if some are highly depleted or dissimilarly depleted which requires balancing). Its basically a program that runs behind the scenes constantly sampling voltage states & adjusting current. NiCD was more tolerant of a constant trickle in maintenance mode as long as the cell was known to be in good health & voltage was closely regulated. But NiMH & other chemistries have different characteristics, thats why there is a different mode on almost any charger. And lithium's are different again.

As mentioned before I don't really know much about these solar units. I would guess (hope?) if they are dedicated to specific cells it might work. Maybe another strategy is just buy a cheapo wall wart charger & bring more fully charged cells as spares? NiMH quality varies all over the map. Eneloops are supposedly good. Personally I buy Amazon Basics old school alkaline & chuck em when done. Some testing Ive done on my own equipment showed them to be better maH than a lot of higher priced NiMH. 
https://www.amazon.ca/dp/B00TOVTZ7K...41-25ab-4377-aafd-2bcb61c818f0&pd_rd_wg=kQK7n


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## YYCHM (Sep 25, 2021)

PeterT said:


> One thing I would also verify is how many cells are 'required'. Showing 4 cells in the bay with no other description might be a sneaky way of saying the solar panel output is somewhat fixed and it needs all 4 in place. This one looks like it has the smarts to allow different cell counts, voltages & capacities. Suspect more than your budget.
> http://www.eblmall.com/product/ebl-...port-type-c-input-fast-aa-aaa-battery-charger
> 
> I've done a lot of RC charging & there are scads of chargers for 1-X cells for every chemistry, capacity & pack under the sun. But they all require 12V nominal input. That might have originated from (dating myself) lifting the hood & hooking up to car battery which is frowned upon now. These days we all pack a dedicated 12v battery source for field charging. Some people are solar charging those, probably because there are lots more solar cells orientated around 12v because its so common in cars, RVs etc.
> ...



Ya,  I hear you about the smarts in these things.  I measured my 6V trickle charger as it attempted to figure out my 6V RV battery and it was all over the map up to 9V?

But a solar panel?  I can't picture some one putting those kind of smarts in a solar panel?


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## PeterT (Sep 25, 2021)

No I'm saying all (good) charger modules have smarts in order to properly charge. Well, typically they also do much more; discharge, condition, cycle, storage state, float.... But they all generally operate with a defined, constant voltage source. The solar panel is basically just another form of power replacing a battery or bench PS. But my hunch is even that is probably simplistic. Solar output must vary by light intensity so I suspect there must be some kind of regulator circuitry between it & charging module if its an integrated unit like the Amazon units. Early RC chargers usually specified nominal 12v source voltage with +/- limits, modern ones can handle input voltage variation. They are evolving over time but I'm talking a 200$ charger, not a 20$ charger, solar panel included.


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## YYCHM (Oct 15, 2021)

In case someone else runs into this situation....

I ordered this OEM replacement for my trashed solar panel https://sunforce-products-inc.mysho...lar-panel-motion-lights?variant=7889851383855

Ends up it outputs 5.79 volts (6 volts maybe?) for the 3 - AA Ni-MH 1200 mAh 1.2 volt rechargeable batteries wired in parallel.   After 3 days of solar charging she is nice and bright again


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