# HELP REQUEST: adjustable output current/voltage from solar panel

#### Khruangbin

Joined Jan 2, 2021
10
Thank you all for reading this. (If this is posted in the wrong section of the forum, I trust the admin to move it accordingly).

I need some help with the following:

To use a solar panel (currently gravitating towards the "big blue 28W" model linked below) to power a DC 12V 1A input device (batter charger also linked below), the output voltage of the panel needs to be increased. The manufacturer says that two of the three USB ports provide 5V with a current that ranges between 0 and 2,4A (depending on conditions), while the third USB port provides 5V and zero to 1A of power output.

http://www.ibigblue.com/product/detail/?id=17
https://charger.nitecore.com/product/d2

1st question: I am almost sure that monocrystaline solar panels operate between 6 and 6,2 Volts (perhaps more variations exist depending on the source of the panels). Therefore, the manufacturer has already included some sort of step-down circuitry [or some other trick that allows him to power the USB ports with nominal 5V]. Can anyone guestimate how he may have gone about this, so that it can be taken into account in the rest of my questions?

2nd question: Can the output of the two - or even better all three - USB ports be combined to distribute the current requirement of 1A. If "yes" how can this be done?

3rd question: Since the whole solution is going to be [manually] portable, minimising weight while maximising reliability and longevity would be very welcome. So, if you believe that a battery or batteries are required between the solar panel and the battery charger, please try to adhere to the following "rules":
3.1 Keep weight to a minimum and prefer li-ion over other types of batteries (hopefully 18650 format for the sake of commonality).
3.2 I would prefer some redundancy (e.g. 3 "lipstick" power banks over one single power bank and/or a power bank with replaceable cells over one whose cells cannot be replaced).

4th question: Finally, how do I ensure that the battery charger [or any device for that matter] I intend to power off the solar panel is fed with no more and no less than 12V 1A DC (no need to fry it with over-current or over-voltage)?

5th question: Could the output of the combined two or three USB ports be available to me in an adjustable manner [selectable range of output voltage / current, as in some buck/boost converters I have seen] to power other devices? How do these converters manage fluctuations in their input current (e.g. from cloud coverage)?

6th question: Finally, heat dissipation, ruggedness and resistance to humidity will be of some concern. What can I do for my setup in this regard?

Thank you all for reading through this!

#### anniel747

Joined Oct 18, 2020
1,025
Why not simply use a 12V solar panel?

#### Audioguru again

Joined Oct 21, 2019
3,172
He wants a huge 12V solar panel that he can unfold then wear it.
I have never seen anybody wearing a huge solar panel like that blue one.

#### Khruangbin

Joined Jan 2, 2021
10
No intention on wearing anything (even though, I too, have seen the advertisment videos with people doing that - yet fail to understand to be honest [*1])

[*1] Unless you always have the sun on your back - and I can't even begin to imagine plotting a course that would be something like: "head due west in the morning, lay face down or head North at noon (for the northern hemisphere), and head back east in the afternoon" I don't see how that works.

That said, it will all be carried in a backpack, and that means that if I can either minimise the weight of a battery, or ditch it all-together, it will be far easier to carry.

Thank you both (anniel747, audioguru again) for reading through this! Here is some music for your coffee!

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#### wayneh

Joined Sep 9, 2010
17,152
1st question: ...Can anyone guestimate how he may have gone about this, so that it can be taken into account in the rest of my questions?
It could be as simple as a DC-DC buck converter to regulate the output at 5V whenever the panel output is high enough above that. But I suspect in a nice product like this, they use a buck-boost converter to squeeze out 5V even if the panel voltage is drawn below that. This nicety buys only a few percentage points more power in fading light, so it's often not worth the trouble. Adding another cell would be the more efficient choice.

2nd question: Can the output of the two - or even better all three - USB ports be combined to distribute the current requirement of 1A. If "yes" how can this be done?
I suspect no, just a hunch, that the full panel power is already available at any one of the USB ports. Nothing to gain by using them in parallel. The details should be in the specifications, which I have not read in detail.

3rd question: Since the whole solution is going to be [manually] portable, minimising weight while maximising reliability and longevity would be very welcome. So, if you believe that a battery or batteries are required between the solar panel and the battery charger,
Do you mean a battery to provide charging power when the panel cannot? That depends on your specific needs and what you expect from your rig. Using one battery to charge another is usually something to avoid, but I do have an external pack for my iPhone that is enormously helpful. (This one, available for $35 on sale. https://www.amazon.com/gp/product/B01JIWQPMW I'd probably just put that in my backpack and be done with it.) 4th question: Finally, how do I ensure that the battery charger [or any device for that matter] I intend to power off the solar panel is fed with no more and no less than 12V 1A DC (no need to fry it with over-current or over-voltage)? If the voltage is regulated to the voltage range specified by the load, you're done. The load will not draw more current just because the capacity is available. Your car's dome light does not 400A because it's available from the battery. You give it 12V and it takes what it's designed for. 5th question: Could the output of the combined two or three USB ports be available to me in an adjustable manner [selectable range of output voltage / current, as in some buck/boost converters I have seen] to power other devices? How do these converters manage fluctuations in their input current (e.g. from cloud coverage)? Yes, although you might be better off bypassing the 5V regulator entirely and go straight from panel to converter if you want some other output. Every time you convert the power, you lose percentage points of efficiency. In theory you could convert to just about anything you want, even 120V AC. 6th question: Finally, heat dissipation, ruggedness and resistance to humidity will be of some concern. What can I do for my setup in this regard? You'll probably need some sort of enclosure. I'd put off worrying about this aspect until you've nailed down the plan. #### anniel747 Joined Oct 18, 2020 1,025 It could be as simple as a DC-DC buck converter to regulate the output at 5V whenever the panel output is high enough above that. But I suspect in a nice product like this, they use a buck-boost converter to squeeze out 5V even if the panel voltage is drawn below that. This nicety buys only a few percentage points more power in fading light, so it's often not worth the trouble. Adding another cell would be the more efficient choice. This is advertised as a 5V charger, he needs 12V. I suspect no, just a hunch, that the full panel power is already available at any one of the USB ports. Nothing to gain by using them in parallel. The details should be in the specifications, which I have not read in detail. No each output has a current limit. Paralleling may or may not work as this is a charger with 3 independent outputs. If the voltage is regulated to the voltage range specified by the load, you're done. The load will not draw more current just because the capacity is available. Your car's dome light does not 400A because it's available from the battery. You give it 12V and it takes what it's designed for. Solar cells have no voltage regulation. Yes, although you might be better off bypassing the 5V regulator entirely and go straight from panel to converter if you want some other output. Every time you convert the power, you lose percentage points of efficiency. In theory you could convert to just about anything you want, even 120V AC. Yes, he needs 12V and an accumulator for the device he wants to plug in. You'll probably need some sort of enclosure. I'd put off worrying about this aspect until you've nailed down the plan. Good conformal coating does a great job. Thread Starter #### Khruangbin Joined Jan 2, 2021 10 It could be as simple as a DC-DC buck converter to regulate the output at 5V whenever the panel output is high enough above that. But I suspect in a nice product like this, they use a buck-boost converter to squeeze out 5V even if the panel voltage is drawn below that. This nicety buys only a few percentage points more power in fading light, so it's often not worth the trouble. Adding another cell would be the more efficient choice. If you can have a look at this one... (http://www.ibigblue.com/product/detail/?id=41) in the 2nd, 3rd and 4th photos from the end of the photo gallery, it has some information about the circuitry they are using in the more expensive model. Given that the cheaper model has nothing like that, and that its losing somewhere 4 to 8 Watts of advertised power, I am guessing that they are simply burning off excess power. I wouldn't mind hearing your opinion on this for cross-reference. I suspect no, just a hunch, that the full panel power is already available at any one of the USB ports. Nothing to gain by using them in parallel. The details should be in the specifications, which I have not read in detail. The company advertises it as " BigBlue 3 USB Ports 28W Solar Charger(5V/4.8A Max)", which means that one of the USB ports is sharing power with the 1A 5V USB port. Not the 1st time a manufacturer has stretched the truth... They have a more expensive model (http://www.ibigblue.com/product/detail/?id=41) with built in Ampere meter, the exact same size and number of panels, and advertise it as 5V 4A (third picture in the picture gallery... you have to read the white letters on the polyester canvas). What I don't understand, is how they "do their math". If its 5*4 = 20W why advertise it as 28W??? And if the cheaper model I am speaking about is 2*2.4*5 = 24W it not only skews the wattage, but also - most likely - either states the rating of the ports or lies about their output current. Do you mean a battery to provide charging power when the panel cannot? That depends on your specific needs and what you expect from your rig. Using one battery to charge another is usually something to avoid, but I do have an external pack for my iPhone that is enormously helpful. (This one, available for$35 on sale.
https://www.amazon.com/gp/product/B01JIWQPMW
I'd probably just put that in my backpack and be done with it.)
I was meaning a small battery between the solar panel and the battery charger I intend on using. The reason being, that it would provide steady energy, acting like a shock absorber, for minor variations in output of the solar panel (e.g. a few seconds of cloud coverage). I agree about using a battery to charge another battery... In that case just bring along more batteries. But I am trying to cut down as much as possible on batteries without sacrificing quality of power output. It goes without saying that such a battery I am after, apart from being small, should be able to provide an output of 1A 12V DC while charging from the solar panel.

The power bank you are suggesting looks great but is useless to me because it doesnt have a 12V output. Furthermore, its cells are not replaceable. It seams the only "reasonable" power bank that had that feature was the sherpa 50 from goal zero, but being a good product (for me... it has USB AND 12V DC) its been discontinued and replaced with one that doesnt have a 12V output.

If the voltage is regulated to the voltage range specified by the load, you're done. The load will not draw more current just because the capacity is available. Your car's dome light does not 400A because it's available from the battery. You give it 12V and it takes what it's designed for.
Are you suggesting that the battery charger is "set" not to draw more than 1A 12V DC and I only need to worry about not giving it enough in terms of amps and volts? I would appreciate a more detailed explanation of this if possible.

Yes, although you might be better off bypassing the 5V regulator entirely and go straight from panel to converter if you want some other output. Every time you convert the power, you lose percentage points of efficiency. In theory you could convert to just about anything you want, even 120V AC.
I agree with you 100%. The thing is "do I feel comfortable ripping apart their product on arrival to bypass whatever circuitry they have in place to down-regulate to 5Vs to the USB ports"? I have been looking for barebones panels just for that purpose, but can't seem to find any in the EU. Especially the ETFE laminated ones that are better protected against water humidity. Those would be perfect for that kind of experimentation.

You'll probably need some sort of enclosure. I'd put off worrying about this aspect until you've nailed down the plan.
You are right, but it will still have to be addressed eventually

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#### anniel747

Joined Oct 18, 2020
1,025
So, why are you looking at a 5V charger when what you need is 12V panels?

#### wayneh

Joined Sep 9, 2010
17,152
I wouldn't mind hearing your opinion on this for cross-reference.
I'm not sure what you're asking. My hunch is that they are advertising the panels power rating, 7W per "page". They know their competitors are doing that, so they do it too. The rated power actually available at 5V is obviously going to be less, and indeed they specify 5V at 4.8A, or 23W. Efficiency = 24/28 = 86%, which is believable.
The company advertises it as " BigBlue 3 USB Ports 28W Solar Charger(5V/4.8A Max)", which means that one of the USB ports is sharing power with the 1A 5V USB port. Not the 1st time a manufacturer has stretched the truth... They have a more expensive model (http://www.ibigblue.com/product/detail/?id=41) with built in Ampere meter, the exact same size and number of panels, and advertise it as 5V 4A (third picture in the picture gallery... you have to read the white letters on the polyester canvas). What I don't understand, is how they "do their math". If its 5*4 = 20W why advertise it as 28W??? And if the cheaper model I am speaking about is 2*2.4*5 = 24W it not only skews the wattage, but also - most likely - either states the rating of the ports or lies about their output current.
Yup, hard to know what's really going on. But it's all moot when a cloud goes over anyway.
I was meaning a small battery between the solar panel and the battery charger I intend on using. The reason being, that it would provide steady energy, acting like a shock absorber, for minor variations in output of the solar panel (e.g. a few seconds of cloud coverage).
You don't need such a battery. The regulator will do a fine job as long as there's enough sun. If not, there's no real advantage to the extra battery beyond the power it carries.
The power bank you are suggesting looks great but is useless to me because it doesnt have a 12V output.
Well fine, but neither does the fancy solar panel. I know which one I'd rather carry around.
Are you suggesting that the battery charger is "set" not to draw more than 1A 12V DC and I only need to worry about not giving it enough in terms of amps and volts? I would appreciate a more detailed explanation of this if possible.
That's right. Link to the charger and we'll confirm, but any device designed to run on 12V should not blow up when supplied 12V. If it's meant for an automotive system, it needs to handle up to 16V even if the nominal rating is 12V.

You may ask the solar panel folks if you can get a naked panel without the electronics.

I agree with you 100%. The thing is "do I feel comfortable ripping apart their product on arrival to bypass whatever circuitry they have in place to down-regulate to 5Vs to the USB ports"? I have been looking for barebones panels just for that purpose, but can't seem to find any in the EU. Especially the ETFE laminated ones that are better protected against water humidity. Those would be perfect for that kind of experimentation.

You are right, but it will still have to be addressed eventually.

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#### Khruangbin

Joined Jan 2, 2021
10
There are two problems with what you are suggesting anniel:

1. Solar panels - depending on type / technology - give a voltage, depending on the type that can be 6,2V for monocrystallines, or 15,4V for thin film. Don't hold me to those numbers as they vary depending on several factors, the main being material quality in production. However, to my knowledge, no panel produces EXACTLY 12V to start with. Before you start protesting, please read the next point.

2. Of those panels that are produced for backpacking purposes (foldable / portable) the vast majority is at 5V because the industry believes [and they are right] that is far more attractive as a selling point to be able to plug in your USB-whatever, ignoring my own needs [yes, I know I represent a market slither... not slice]. Those panels produced at 12V - as far as I have seen - are not intended to be backpacked with (RV camping etc). However, if you have any suggestions of 12V monocrystallines, I will gladly look at them.

The problem with thin film panels is their longevity... they don't live as long as mono's and their performance degrades much faster, meaning you have to factor in their product life which makes things next to impossible in solving. Mono's on the other hand, have a predictable behavior and their degradation penalty is a much more gentle curve.

So, why are you looking at a 5V charger when what you need is 12V panels?

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#### andrewmm

Joined Feb 25, 2011
1,461
Solar panels,
As a basis the "power" they give out is variable depending on the sun ! Who would have thought !!
OK, but also, the optimum current / voltage point to run the panels at is variable. depending on the sun,

On bigger systems, the "invertors" have a track facility, such that the load they present to the panels keeps the current /' voltage coming out of the panels "optimal"

Now, the reason for saying this,
is these all cost money,
my bet is that the unit you have is not high cost.
so it will not have a power tracker.

My bet is it has a simple DCDC if your lucky, a LDO if your unlucky.

You will be able to tell by looking at the output voltage into a low current load,
If its a DCDC as the sun power varies the voltage out will be either there or off.
if its a LDO, it will always have a voltage , that increase to 5V

The type of regulator you have determines IMHO the way forward.

#### Khruangbin

Joined Jan 2, 2021
10
Solar panels,
As a basis the "power" they give out is variable depending on the sun ! Who would have thought !!
OK, but also, the optimum current / voltage point to run the panels at is variable. depending on the sun,

On bigger systems, the "invertors" have a track facility, such that the load they present to the panels keeps the current /' voltage coming out of the panels "optimal"

Now, the reason for saying this,
is these all cost money,
my bet is that the unit you have is not high cost.
so it will not have a power tracker.

My bet is it has a simple DCDC if your lucky, a LDO if your unlucky.

You will be able to tell by looking at the output voltage into a low current load,
If its a DCDC as the sun power varies the voltage out will be either there or off.
if its a LDO, it will always have a voltage , that increase to 5V

The type of regulator you have determines IMHO the way forward.
Thanks for participating andrewmm.

The whole setup is primarily and foremost intended for manual portability (backpacking). Everything else is a secondary requirement to A) keeping the weight low and B) being packable / foldable.

When set-up, there wont be any tracking capability unless I am willing to constantly re-orientate the setup (which I am not).

Therefore, I am forced to "aim higher" in terms of output power, to ensure an unattended charge. This - along with the fact I want to power a non-stadard device (12V 1A DC) is what poses lmitations on the output current/voltage, voltage regulation requirements etc.

I have provided the links to both the panel and the battery charger I want to operate in the 1st post. You can have a look at their specs if you want, and maybe make more pointed / accurate suggestions.

However, I agree that there is alot of speculation concerning how they buck the voltage from 6.2V down to 5. I personally lean towards believing that they are simply burning off power, simply because its the more affordable approach that maximises their profits. 95% of the buyers dont care about the "HOW"... they just want to plug in their USB gizmo and play.

Thanks for reading through all this though! Its appreciated!

Mod: All Off Topic Video's Deleted.

Mod: Please do not post Off Topic Video's.E

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#### anniel747

Joined Oct 18, 2020
1,025
There are two problems with what you are suggesting anniel:

1. Solar panels - depending on type / technology - give a voltage, depending on the type that can be 6,2V for monocrystallines, or 15,4V for thin film. Don't hold me to those numbers as they vary depending on several factors, the main being material quality in production. However, to my knowledge, no panel produces EXACTLY 12V to start with. Before you start protesting, please read the next point.

2. Of those panels that are produced for backpacking purposes (foldable / portable) the vast majority is at 5V because the industry believes [and they are right] that is far more attractive as a selling point to be able to plug in your USB-whatever, ignoring my own needs [yes, I know I represent a market slither... not slice]. Those panels produced at 12V - as far as I have seen - are not intended to be backpacked with (RV camping etc). However, if you have any suggestions of 12V monocrystallines, I will gladly look at them.

The problem with thin film panels is their longevity... they don't live as long as mono's and their performance degrades much faster, meaning you have to factor in their product life which makes things next to impossible in solving. Mono's on the other hand, have a predictable behavior and their degradation penalty is a much more gentle curve.
Exactly my point, you are looking at 5V CHARGERS. Panel technology or form factor has nothing to do with your problem. Choose witch ever you like and make series/parallel strings to achieve V/A you need. In fact if you can get 15.4V that would be excellent for the charger you want to use. Use raw solar PANELS, not solar CHARGERS.

Thanks for participating andrewmm.

The whole setup is primarily and foremost intended for manual portability (backpacking). Everything else is a secondary requirement to A) keeping the weight low and B) being packable / foldable.

When set-up, there wont be any tracking capability unless I am willing to constantly re-orientate the setup (which I am not).

Therefore, I am forced to "aim higher" in terms of output power, to ensure an unattended charge. This - along with the fact I want to power a non-stadard device (12V 1A DC) is what poses lmitations on the output current/voltage, voltage regulation requirements etc.

I have provided the links to both the panel and the battery charger I want to operate in the 1st post. You can have a look at their specs if you want, and maybe make more pointed / accurate suggestions.

However, I agree that there is alot of speculation concerning how they buck the voltage from 6.2V down to 5. I personally lean towards believing that they are simply burning off power, simply because its the more affordable approach that maximises their profits. 95% of the buyers dont care about the "HOW"... they just want to plug in their USB gizmo and play.

Thanks for reading through all this though! Its appreciated!

Mod: All Off Topic Video's Deleted.

Mod: Please do not post Off Topic Video's.E
If you absolutely want to use those panels you will need to rip the 5V electronics out and probably rewire the cells differently.

Of those panels that are produced for backpacking purposes (foldable / portable) the vast majority is at 5V because the industry believes [and they are right] that is far more attractive as a selling point to be able to plug in your USB-whatever, ignoring my own needs [yes, I know I represent a market slither... not slice]. Those panels produced at 12V - as far as I have seen - are not intended to be backpacked with (RV camping etc). However, if you have any suggestions of 12V monocrystallines, I will gladly look at them.
I see a lot of monocrystalline ETFE backpacking panels in the 60W range that all have direct outputs. If you don't find those in the EU, it's probably restricted.

#### Khruangbin

Joined Jan 2, 2021
10
Exactly my point, you are looking at 5V CHARGERS. Panel technology or form factor has nothing to do with your problem. Choose witch ever you like and make series/parallel strings to achieve V/A you need. In fact if you can get 15.4V that would be excellent for the charger you want to use. Use raw solar PANELS, not solar CHARGERS.
Unfortunately I can't find any LIGHTWEIGHT panels that would lend themselves to mix-and-match well enough for experimentation on your suggestion (which is absolutely valid - I agree with you on this). Mind you there is no shortage of various monocrystalline panels for RV and car-camping etc that fulfill the above requirement minus being lightweight.

So my next option is modifying (moderately "gutting") a solar charger, and either alter its output, or - as already suggested - bypass the buck/boost circuitry it already has, to install my own regulator. This option sounds far more appealing and sensible towards what I am trying to achieve.

I would welcome your (or anyones) suggestions for a regulator or buck AND boost converter that would allow for selectable (or stepless adjustability within reason) output between, say, 3V 0,5A DC up to 12V 1~2A DC. I have very little experience with this segment of electronics and I would like suggestions from people who actually own them and know a thing or two about the following:
1. Quality of design and manufacturing (including parts used)
2. Stated vs actual specs concerning what the circuitry can achieve (an honest manufacturer is hard to come by).
3. Durability of design (think reliability).

Since direct links to music have been erased, I will post no more (I am sure there is reason for this), but I suggest people look up

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#### Khruangbin

Joined Jan 2, 2021
10
I see a lot of monocrystalline ETFE backpacking panels in the 60W range that all have direct outputs. If you don't find those in the EU, it's probably restricted.
Anniel, do you mind posting some links so I can have a look? 60W its double my target range, but I would like to see whats out there. Perhaps I missed out on something because of my [strict?] specifications.

I am laying down the "rule" for my replies... one song suggestion per reply. Share music! Its good for the soul!

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#### anniel747

Joined Oct 18, 2020
1,025
Anniel, do you mind posting some links so I can have a look? 60W its double my target range, but I would like to see whats out there. Perhaps I missed out on something because of my [strict?] specifications.

I am laying down the "rule" for my replies... one song suggestion per reply. Share music! Its good for the soul!

If you must use pre-made panels have a look at Jackery SolarSaga, TP-Solar, Sunkingdom and Powerwerx, amongst others. They all make light and small units, some more than others. You would be way better off using raw solar cells to achieve your exact goal.

#### anniel747

Joined Oct 18, 2020
1,025
That looks a lot like what you want.

#### andrewmm

Joined Feb 25, 2011
1,461
Just to clarify
the tracking I mentioned was not the panels moving to follow the sun , which is what I think is what your implying I meant,
its power tracking,
where to maximise the power out of the panel, you need to control the amount of current you take , depending upon the voltage, its not linear .

#### bassbindevil

Joined Jan 23, 2014
158
Most "12V" panels put out something like at least 20V no-load, but they have a relatively high internal resistance, so terminal voltage drops once you put a load on them. If your goal is to charge lithium cells, the best approach might be to choose a charger which will operate directly from the solar panel output. I've successfully charged a 3S 18650 pack using an SY6912 charging module (1 to 3S set by solder pads, 2A set by shunt resistors). Except last time I plugged it into the battery pack, smoke came out of the SY6912 chip; maybe just bad luck, or some defective component on the board.
Another option could be a MAX745 module, which costs about twice as much, but does up to 4S packs (set by dipswitch), and has pots to adjust charging current and tweak the cell voltage (so you could choose to terminate at a lower voltage to extend cell life). Switching is done with big external MOSFETs, so if smoke comes out, it could be repaired.
And there's boards based on the BQ24650 chip for even more money, that don't look as easy to use or repair as the MAX745, but are probably more sophisticated.
And some using the CN3722; not sure if those will do 1S.

#### anniel747

Joined Oct 18, 2020
1,025
Most "12V" panels put out something like at least 20V no-load, but they have a relatively high internal resistance, so terminal voltage drops once you put a load on them. If your goal is to charge lithium cells, the best approach might be to choose a charger which will operate directly from the solar panel output. I've successfully charged a 3S 18650 pack using an SY6912 charging module (1 to 3S set by solder pads, 2A set by shunt resistors). Except last time I plugged it into the battery pack, smoke came out of the SY6912 chip; maybe just bad luck, or some defective component on the board.
Another option could be a MAX745 module, which costs about twice as much, but does up to 4S packs (set by dipswitch), and has pots to adjust charging current and tweak the cell voltage (so you could choose to terminate at a lower voltage to extend cell life). Switching is done with big external MOSFETs, so if smoke comes out, it could be repaired.
And there's boards based on the BQ24650 chip for even more money, that don't look as easy to use or repair as the MAX745, but are probably more sophisticated.