5v mini solar charger

Hi I’m looking for a mini 5v solar panel to trickle charge a Cygnett 5V power bank (which in turn powers a mobile phone).
Would core electronics have anything suitable? Or any advice please?

Thanks
Michael

Hi Michael,

Welcome to the forum!

I’d recommend checking out this product. Should do exactly what you’re after :slight_smile:

Regards,
Oliver
Support | Core Electronics

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Thanks unfortunately the dimensions are a little too large. Would you have or recommend something like this:

I have the Panel linked by Oliver and can confirm it will do what you want even though it is too large for you. The built in voltage regulator ensures the output remains at 5V. Other panels I have tried vary with the amount of sunlight. Katmandu have panels you can use to charge a power bank, at a suitable size because they open out. But they are rather expensive.

Cheers
Jim

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Hey Michael,

Unfortunately, we don’t have much in that smaller size range that is regulated to a constant 5V like the one Oliver sent originally.

We do have smaller panels, like this one, but it is rated for a typical output of 5.5V and jumps all the way up to 8.2V at an open circuit voltage.

You could throw in some sort of buck converter, this would be a good and efficient way to regulate to a lower voltage. You should of course ensure that the converter can handle the maximum current that the solar panel can produce.

Having said that, there is a potential problem in matching the load that is fed by the converter to the available power from the panel. If you “suck” too much power, the voltage from the panel will be pulled down. So the load needs to be matched to the available power to optimise the power draw.

Sorry we can’t be of more immediate help with this one.

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Thanks Owen, that looks like a suitable panel size. Could you recommend a suitable buck converter? and/or would an inline blocking diode be required to prevent reverse current flow back into panel?
Thanks
Michael

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Like this?

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have a look here not an core product though the dimensions look correct 4 you…

Thanks Brian, panel looks like the correct dimensions but unfortunately previous reviewers mention no voltage control (hence would vary between 4-10 V) depending on sunlight. Similar to what Owen was saying about the Core mini panel…

FYI The Katmandu solar panels are 5W $100 & 7W $150. 20% discount at present.
The 7W one is the size you are after and opens out.

For a non regulated solar panel.
I have one of these that works very well and has heaps of options, not too expensive either.

Cheers
Jim

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Thanks Jim, the Katmandu panels are too large. As previously mentioned I need something very compact (to be inserted inside a small mobile phone sized waterproof case). These cases are typically around 15cm X 8cm.
I want to deploy unit in the field for 6 months (phone + power bank + solar panel) all together inside waterproof case. The case is transparent so panel will get some light (enough to trickle charge the power bank). The phone for what I’m using it for condumes uses about 450mAh a day. So as long as the panel can generate this much on average per day (into the power bank) it will be sufficient.

Hi Micael
If you find the best solar panel to fit into a 15cm x 8cm case has not enough grunt for your requirement and a panel with output equal your minimum requirement is too large then I don’t think there is much of a solution. All down to physical area exposed to whatever sunlight there is really. May be back to the drawing board or wait for the development of better solar panel material.
Cheers Bob

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Thanks Bob
I calculated the phone runs for about 7 days on it’s 3000mAh battery (standby mode which is all I need).
Therefore it’s using about 420mAh a day.
If a the solar panel can achieve 100mAh for in average 5 hours a day (and put this into my power bank) that should be adequate?

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A bit more head room would probably be nice. You are almost depending on nice bright sunlight every day with may be OK, depending on where you live and are to use this device. Can you find a suitable panel that fits this spec. At the end of the day whether you have to compromise on panel choice or bite the bullet and have to use a larger panel is going to be up to you. A redesign / rethink of the enclosure this lot is going into may be in order.
Cheers Bob

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Thanks Bob,
Agreed a bit of wriggle room would be nice.
I’ll order one each of the above core panels (Large 1A) and small (170mA) and run some tests.

I have a month to build prototype before deploying.

The site goes a couple metres under water each wet season so I was hoping to avoid anything external to the waterproof case…

Cheers
Michael

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Don’t know how well solar panels perform under water. If your project gets dunked you probably should include that scenario in your testing.
Good luc
Cheers Bob

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Thanks Bob, will do.
Fortunately the river comes up and goes back down within 24 hours so the panel only needs to be short term “dunkable”… But as you say I’m guessing that is not standard on any of the solar panels mentioned above (so it needs to go inside a waterproof case of some sort)…

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Just had a quick look at the link provided by James, looks interesting. I refer to the DFRobot unit DFR0559.Coupled with a 900ma/hr battery this unit seems to be a self contained power bank in its own right. Battery capable of being charged by USB (5V) or MPPT controlled Solar with a steady 5V output. The MPPT is a good thing as it maximises solar efficiency.
If heading down this path you would dispense with your existing power bank as you don’t want 2 power banks in series. This would reduce overall efficiency.
Interesting to scroll to the bottom of CoreE blurb and click on the “Wiki” link and have a read. The text in the Core description says that battery under voltage protection must be provided as part of the battery. The Wiki says that the latest 1.1 version has this on board and any battery can be used. Very useful.
A bit unrelated remark in that Wiki re usual power banks on the market. They apparently shut down when the current demand gets below a pre-set level. I have a couple like that. Absolutely useless for powering low demand projects. One requires about 300mA load to stay on. Keeps turning on and off. Pain in the you can guess. OK for charging phones etc but not much else.
Not sure how well your phone would work under water either.
Cheers Bob

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Thanks agreed that the solar controller linked by Jim looks a good option. Can optionally direct power to 3.7v battery, or can send via 5V usb directly to larger power bank (or phone).
Some power banks have “always on” function like the ones from Voltaic. The Cygnett one I have seems to be clever enough to turn itself back on when the phone comes off standby occasionally to take a photo (with time-lapse app).
My plan is to put the whole lot (phone+solar+power bank) inside one of the Whitworths submersible marine cases which have a transparent lid. For the camera lens I will drill out/Dremel a hole to glue in a $20 GoPro lens into the case.

I may not have read the description in full detail but my impression is this(I am probably wrong)
The 3.7V battery is charged via USP input or solar. The USB charger takes priority when connected. The 3.7V battery then provides the 5V output using booster/regulator electronics via headers or type A USB output. Thus a power bank with 2 charging options.
What I am getting at is you don’t want 2 power banks in series. As with anything in series the system as a whole is only as good as the weakest link. This will probably be the smaller solar charging system.
Example: Suppose a power bank of 1 Amp/hr 5V output. This feeds into power bank of 10 Amp/hr with say 80% efficiency. That is for every Watt/hr fed into this you can only extract 800mWatt/hr. and because both are in series the overall result is still the 1 Amp/hr capacity of the smallest supply less the 20% lost in the second power bank. A loss that most times is best avoided.
As you probably want to avoid any unnecessary losses my suggestion is find an efficient or suitable way to charge your existing power bank or go with the DFRobot unit or something similar and discard your existing power bank. Using both will only be a waste of available power.
Another alternative. Is this unit accessible when in situ. How much of a hassle would it be to change batteries or power bank. It may be feasible to change the power source every couple of weeks or so or any other suitable period.
Cheers Bob

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