Solar lighting - What do the specs really mean, how much light can I actually expect to get and for how long?

[Susco]

1 hour ago, Muhendis said:

Batteries of all types will have a shorter life if they are charged and discharged too quickly. There are more stresses involved. By using a BMS for both directions the amount of stress is minimised and the batteries last longer. 

Soldering is not the preferred method of connection. The batteries are spot welded to the interconnecting strips. Once again it is less stressful in terms of the amount of heat against the length of time to make the connection. 

 

But spot welding is not something the average tv technician can do, I assume, or can I solder to the battery holder connectors?

[Susco]

3 minutes ago, Muhendis said:

In addition to my earlier comments (I just checked the specs.) I noticed this:-

Main function: over charging protection, over discharge protection, short circuit protection, over current protection function. So that's a job the BMS does not appear to do now. I do have a concern however that not all cells will charge and discharge at the same rate and eventually there will come a time when one cell is significantly different from the others and will make the whole pack under-perform. Normally a BMS would monitor each cell and balance the whole pack ensuring higher charge rate in some cells which need it and also ensuring that all cells discharge at the same rate. This is essential for higher voltage series connected strings. Parallel connected packs are similarly affected but it would be difficult to know which cell is poorly without monitoring all of them. With parallel packs the good cells would ensure that the poor cell is kept upto date so to speak but the whole pack would still be affected because of this self maintenance effect. Charge from the better cells would be shuttled into the poorer cell.

 

In my case they will be used on single cells, to prevent that they discharge too low.

 

Are they suitable for that?

[Muhendis]

1 minute ago, Susco said:

Are they suitable for that?

Yes they are. But you still need the main BMS to ensure that all cells are balanced otherwise your pack may become seemingly shorter lived than you might otherwise expect.

[Susco]

4 hours ago, Crossy said:

 

The "tails" or the large rectangular pads at the end of the board (marked B+ & B-) go to the relevant terminal of the battery.

 

The smaller square pads towards the centre of the board (marked P+ & P-) go to your load EDIT and charger.

 

The controlling FET on the other side of the board is between P- and B-.

 

EDIT Here's a better picture showing the connections, battery on the end pads, load on the centre pads.

 

 

 

 

So if I understand this correct. I could solder B+ and B- to the battery holder connectors, so that if I replace the battery, the BMS doesn't need replacement.

 

Then remove the wires that are now connected at each end of the battery holder, and solder those to P+ and P-?

[Susco]

2 minutes ago, Muhendis said:

Yes they are. But you still need the main BMS to ensure that all cells are balanced otherwise your pack may become seemingly shorter lived than you might otherwise expect.

 

Don't know if something is lost in translation, but my lamps have only a single battery

[Muhendis]

9 minutes ago, Susco said:

But spot welding is not something the average tv technician can do, I assume, or can I solder to the battery holder connectors?

You'd be surprised how easy it is. Do a You Tube search on it. The down side would be how to change a bad individual cell.

[Muhendis]

2 minutes ago, Susco said:

 

Don't know if something is lost in translation, but my lamps have only a single battery

In that case you have no string of cells to balance so you have no need for a BMS. Those protection strips would be useful especially if the charger is dodgy.

[Muhendis]

6 minutes ago, Susco said:

Don't know if something is lost in translation, but my lamps have only a single battery

That'll

 

18 minutes ago, Susco said:

can I solder to the battery holder connectors?

teach me to read more carefully.....

[Muhendis]

Just now, Muhendis said:

can I solder to the battery holder connectors?

Yes

[Susco]

21 minutes ago, Muhendis said:

In that case you have no string of cells to balance so you have no need for a BMS. Those protection strips would be useful especially if the charger is dodgy.

 

The purpose for me would be to switch the lights off before the battery get completely depleted.

 

That seems not to happen now. The lights dim and dim more until there is no power left.

 

At one point I have removed a light in the middle of the night when it was very dim, and measured 2.3V on the battery. I guess if I didn't take it off at that point, it would discharge further

[Susco]

13 minutes ago, Susco said:

38 minutes ago, Muhendis said:

In that case you have no string of cells to balance so you have no need for a BMS. Those protection strips would be useful especially if the charger is dodgy.

 

The purpose for me would be to switch the lights off before the battery get completely depleted.

 

So will the BMS do the job for that purpose?

[Muhendis]

2 hours ago, Muhendis said:

Main function: over charging protection, over discharge protection, short circuit protection, over current protection function

Those battery strips which are referred to as BMS are supposed to protect against over discharge. Lithium ion cells are not supposed to go below 2.5v. I think it would be useful to run a test on the strips to see if they are doing their job properly. Your measurement of 2.3v on the cell is running close to the life expectancy of the cell.

[Muhendis]

6 minutes ago, Muhendis said:

Those battery strips which are referred to as BMS are supposed to protect against over discharge. Lithium ion cells are not supposed to go below 2.5v. I think it would be useful to run a test on the strips to see if they are doing their job properly. Your measurement of 2.3v on the cell is running close to the life expectancy of the cell.

If it help at all, I copied this from an advert here: https://www.rkbbattery.com/product/18650-4v-3-5a-for-lithium-li-ion-battery-protection-board-bms/

Features (Specifications):

Overcharge Voltage Range: 4.2V ± 0.05V

Over-Discharge Voltage Range: 2.9V ± 0.05V

Charging Voltage: 4.2V

Upper Limit Working Current: 4A

Upper Limit Instantaneous Current: 6A

Protection: Overcharge Protection, Over Discharge Protection, Short Circuit Protection, Over Current Protection

 

Note the over discharge range.

[Susco]

1 hour ago, Muhendis said:

If it help at all, I copied this from an advert here: https://www.rkbbattery.com/product/18650-4v-3-5a-for-lithium-li-ion-battery-protection-board-bms/

Features (Specifications):

Overcharge Voltage Range: 4.2V ± 0.05V

Over-Discharge Voltage Range: 2.9V ± 0.05V

Charging Voltage: 4.2V

Upper Limit Working Current: 4A

Upper Limit Instantaneous Current: 6A

Protection: Overcharge Protection, Over Discharge Protection, Short Circuit Protection, Over Current Protection

 

Note the over discharge range.

 

 

Thanks, these are the ones that I had in mind. They show an over discharge of 2.5V and an over discharge recovery of 2.9V

 

You think the 2.9V in your product could actually also be the discharge recovery rate, and they both have the same spec?

 

https://www.lazada.co.th//products/i1763224647-s5113978004.html?

 

Over discharge testing range: 2.50±0.1V
Over discharge recovery voltage: 2.90±0.1V

 

 

Edit : Is 1 MOS or 2 MOS important?

[Muhendis]

1 hour ago, Susco said:

 

 

Thanks, these are the ones that I had in mind. They show an over discharge of 2.5V and an over discharge recovery of 2.9V

 

You think the 2.9V in your product could actually also be the discharge recovery rate, and they both have the same spec?

 

https://www.lazada.co.th//products/i1763224647-s5113978004.html?

 

Over discharge testing range: 2.50±0.1V
Over discharge recovery voltage: 2.90±0.1V

 

 

Edit : Is 1 MOS or 2 MOS important?

Last question first. Yes. Two MOSFETs are important. One controls charge and the other controls discharge. Be aware they could both be in one package. Also they each have an extremely useful substrate diode which will allow current to flow the wrong way through MOS 1 when MOS 2 is turned on and vice versa. See the data sheet link and particularly page 14.

The device DW01-P is a dedicated battery cell control ic. 

https://ic-fortune.com/upload/Download/DW01x-DS-17_EN.pdf

I think the answers to your other queries are buried in the information on page 14. At a guess I would say that if the battery voltage dropped to 2.5v±0.1v it would be disconnected from the discharge circuit until it has been charged to 2.9v±0.1v before you can use it again. Likewise the overcharge condition.

[Susco]

4 minutes ago, Muhendis said:

Last question first. Yes. Two MOSFETs are important. One controls charge and the other controls discharge. Be aware they could both be in one package. Also they each have an extremely useful substrate diode which will allow current to flow the wrong way through MOS 1 when MOS 2 is turned on and vice versa. See the data sheet link and particularly page 14.

The device DW01-P is a dedicated battery cell control ic. 

https://ic-fortune.com/upload/Download/DW01x-DS-17_EN.pdf

I think the answers to your other queries are buried in the information on page 14. At a guess I would say that if the battery voltage dropped to 2.5v±0.1v it would be disconnected from the discharge circuit until it has been charged to 2.9v±0.1v before you can use it again. Likewise the overcharge condition.

 

Thanks I found this, but my head is tolling with so many other things at the moment, that I'm unable to comprehend it

 

https://electronics.stackexchange.com/questions/277248/lithium-battery-protection-circuit-why-are-there-two-mosfets-in-series-revers

 

The main question for me is, since for me only the discharge function is of importance, since the panel does not produce enough power to overcharge the battery, will a BMS with 1 Mosfet be sufficient for my purpose, or should I select 2 mosfets anyway?

 

The one I selected are 1 mosfet only, are significantly cheaper, and have the soldering strips attached.

 

So cheaper is preferred, but if 2 mosfets has an advantage even for my purpose, I will buy those of course

[Muhendis]

12 minutes ago, Susco said:

 

Thanks I found this, but my head is tolling with so many other things at the moment, that I'm unable to comprehend it

 

https://electronics.stackexchange.com/questions/277248/lithium-battery-protection-circuit-why-are-there-two-mosfets-in-series-revers

 

The main question for me is, since for me only the discharge function is of importance, since the panel does not produce enough power to overcharge the battery, will a BMS with 1 Mosfet be sufficient for my purpose, or should I select 2 mosfets anyway?

 

The one I selected are 1 mosfet only, are significantly cheaper, and have the soldering strips attached.

 

So cheaper is preferred, but if 2 mosfets has an advantage even for my purpose, I will buy those of course

From your previous comments (2.3v after lamp has faded out) I would say you have problems with your discharge circuit so logically this is the MOSFET which is not included with your single MOSFET BMS board if that is what you are using. Getting a board with both MOSFETs on board will give you the security and the satisfaction of knowing you've done the right thing.

[Susco]

28 minutes ago, Muhendis said:

From your previous comments (2.3v after lamp has faded out) I would say you have problems with your discharge circuit so logically this is the MOSFET which is not included with your single MOSFET BMS board if that is what you are using. Getting a board with both MOSFETs on board will give you the security and the satisfaction of knowing you've done the right thing.

 

Currently there is no BMS attached yet, hence my post, to find out which one to use, but if you say that I should order the 2 MOS version, then that is what I will do.

 

The solar light was still on when the battery had only 2.3V, but very dimmed, I switched it off

 

I'm not knowledgable on this subject, as you must have figured already, but I think the mosfet is what does all the work.

 

So that brings me to the next question

 

Do those things exist in different versions, for example a mosfet that stops discharging at a 3V , and would it be possible to build a simple PCB with just a mosfet and a few resistors that does the job?

 

 

[Crossy]

23 minutes ago, Susco said:

Do those things exist in different versions, for example a mosfet that stops discharging at a 3V , and would it be possible to build a simple PCB with just a mosfet and a few resistors that does the job?

 

Yes, for different cell chemistries.

 

No, there's a controller chip on there for a reason.

 

The spread in parameters of semiconductors is massive, often a factor of >100% over a production run (even on the same wafer). You could probably make one that worked, but another using the same device type and resistors that worked at the same levels would be an impossibility.

As an example the venerable 2N2926 (an NPN BJT not a MOSFET, but I happen to remember the numbers) has an h_FE that ranges between 35 and 470, you either select devices or design a circuit that works with the whole range.

 

Even if it was possible, you couldn't do it for the price these things go for.

 

[maxpower]

2 hours ago, Susco said:

The solar light was still on when the battery had only 2.3V, but very dimmed, I switched it off

 

Common over discharge protection voltage for 18650 cells is 2.4V-2.6V.

 

This is the death safety voltage that should only be reached if other control fails or a device is left without charge for long periods.

If a solar light is constantly falling to the safety discharge voltage is is either badly designed or faulty.

 

Your circuit has a protection chip as shown below. Its likely got a very low cut off voltage and the light has no control over discharge in its operation software. Running to the death is a common feature of these budget lights especially if they don't keep some battery capacity for rainy days.

 

 

 

[Susco]

7 minutes ago, maxpower said:

If a solar light is constantly falling to the safety discharge voltage is is either badly designed or faulty.

 

Your circuit has a protection chip as shown below. Its likely got a very low cut off voltage and the light has no control over discharge in its operation software. Running to the death is a common feature of these budget lights especially if they don't keep some battery capacity for rainy days.

 

 

I have 15 lights with 4 of them having the issue, but I have moved them around already, and it are always the lights in the same location that have the problem, because they have shade from a tree during certain times of the day.

 

I can monitor till around 2am, as I also have to sometimes sleep, so I don't know what happens with the other lights after I went to bed. By the time I wake up they had some hours of sunlight already, so no point in measuring the battery voltage then.

 

I'm not sure if adding a higher capacity battery, and charge it manually before inserting, will sort the problem, so they have enough backup for the shade or cloudy days.

 

I think for 145 Baht including shipping you can't expect high quality., but you think the BMS would be a solution?

 

[maxpower]

1 hour ago, Susco said:

I have 15 lights with 4 of them having the issue, but I have moved them around already, and it are always the lights in the same location that have the problem, because they have shade from a tree during certain times of the day.

 

For lights in areas that don't get good sun, you could tune the overall power consumption of your light by changing its current limit resistor. 

 

Replacing the existing 1Ω with a 1.2Ω 5W or even 1.5Ω will lower consumption with some reduction in light level.

 

[Susco]

1 minute ago, maxpower said:

 

For lights in areas that don't get good sun, you could tune the overall power consumption of your light by changing its current limit resistor. 

 

Replacing the existing 1Ω with a 1.2Ω 5W or even 1.5Ω will lower consumption with some reduction in light level.

 

 

 

Thanks for the suggestion, but the lights are already in "ambient" mode in that setting, so reducing that would probably result in not enough light.

 

Better would be if i could add some easy solution timer, as the lights don't need to be active after midnight.

 

They are inside the perimeter, only to provide some ambient light to the surroundings

[Trujillo]

Sort of off topic but on....

 

Does anyone know where to buy locally a 1500mAh 4/5 AA Ni-MH 1.2V Rechargeable Battery?

 

It's for a solar light. 

[Crossy]

8 hours ago, Trujillo said:

Sort of off topic but on....

Does anyone know where to buy locally a 1500mAh 4/5 AA Ni-MH 1.2V Rechargeable Battery?

It's for a solar light. 

 

Try Amorn, anything on Lazada or Shoppee?

 

These sub-sizes can get difficult, will a full AA shoehorn in with some adjustment to the light?

[Susco]

Anyone know a trustable source to purchase 1s BMS? Shopee or Lazada definitely are not

 

I've been looking at this one, which is all over named sites, and it shows a 8205A MOSFET, which is a dual channel one.

 

 

But when I look at the pictures in the reviews, there is no MOSFET at all, much less a dual channel one. Yet this one is claimed to have sold 287 pcs x 10, and get a rating of 4.7/5. Am I wrong or am I wrong?

 

 

[Crossy]

The MOSFET on the unit you show is one of the 6 legged chaps which could easily be a dual (3 legs per side). That said, it's not going to be particularly ampy, the 8205 is a 5A beastie.

 

 

[Susco]

On 1/16/2021 at 3:58 PM, Crossy said:

The MOSFET on the unit you show is one of the 6 legged chaps which could easily be a dual (3 legs per side). That said, it's not going to be particularly ampy, the 8205 is a 5A beastie.

 

 

 

 

The 8205 is normally 8 leg, as shown in the top picture, The lower pictures are from customer reviews, and show 2 thingies with each 6 legs, so it is clearly not a 8205A MOSFET on there.

 

 

In the meantime I have found and ordered some with the customer review pictures showing the same 8 leg MOSFET, and a 6 leg DW01. as in the listing. The listing says 3A BMS. Why it says 3A, and why the spec of the MOSFET give so many currents for the same thing, from 5A to 3A?

 

https://www.maritex.com.pl/product/attachment/91261/8205A.pdf

 

 

In the spec is also defined that it is a 8205 MOSFET. What means Ampy, is 5A a positive or negative in my case? I'm gonna use 3400 mAh batteries anyway

 

 

 

I have also found these batteries, which seem a good deal, with protection and seller get great reviews

 

https://www.lazada.co.th/products/18650-3400-mah-37-panasonic-ncr18650b-mate-in-japan-18650-i454910693-s839304493.html?

 

I'm afraid though the battery gonna be a few mm to long for my holder. If so is it possible to remove the protection, and use the BMS which I ordered already?

 

 

[Crossy]

7 hours ago, Susco said:

and show 2 thingies with each 6 legs, so it is clearly not a 8205A MOSFET on there.

 

There are other MOSFETs than the 8205 in many different packages, a dual unit configured in the same way could use as few as 4 legs. The little 6 leg chap on your other picture will likely have the required performance, without knowing the device type we can't tell. The SQ1922AEEH from Vishay Silconix is a device in that package which would probably do the job in that smaller BMS.

 

7 hours ago, Susco said:

The listing says 3A BMS. Why it says 3A, and why the spec of the MOSFET give so many currents for the same thing, from 5A to 3A?

 

The BMS is designed to limit at 3A, the device is rated at 5A continuous so it's well within its ratings. A competent design would never run a device at or near the Absolute Maximum Rating as it's just that "absolute maximum" (exceed and it goes "pop" and lets out the Magic Smoke).

 

7 hours ago, Susco said:

I'm afraid though the battery gonna be a few mm to long for my holder. If so is it possible to remove the protection, and use the BMS which I ordered already?

 

If the battery already has protection why remove it (and risk all the nasties associated with opening a lithium battery)? Far better to modify the holder or get a holder that fits the cell.

 

I must admit I've lost track of what you're actually trying to achive here. The limiting factors will be the size of the panel (how much energy it can generate) and the size of the battery (can it store all the energy the panel makes). What are the actual numbers from your light (measure the size of the panel and the battery capacity)? 

 

[Susco]

3 hours ago, Crossy said:

I must admit I've lost track of what you're actually trying to achive here. The limiting factors will be the size of the panel (how much energy it can generate) and the size of the battery (can it store all the energy the panel makes). What are the actual numbers from your light (measure the size of the panel and the battery capacity)? 

 

These are my lights.

- Power: 5.5V, 2.5W
- Battery capacity: 2000mAH

 

For now the lights stay on all night. The other day I tested one that was fully charged, and after 16 hours constant on, the battery still had 2.78V. But on a cloudy day, or the lights that have a little shadow from a tree during part of the day, may not get fully charged on those days.

The reason I want to add a bigger battery, is to build some reserves for those days.

 

3 hours ago, Crossy said:

If the battery already has protection why remove it (and risk all the nasties associated with opening a lithium battery)? Far better to modify the holder or get a holder that fits the cell.

 

From what I can see from the pictures, and read in a few of the customer comments, the protection is added to the battery, so it probably will not be internal. The question is of course if those BMS PCB are soldered on the battery, or just held in place by the battery casing. Adding or modifying the holder is not easy, because it is integrated in the back panel.

 

3 hours ago, Crossy said:

The BMS is designed to limit at 3A, the device is rated at 5A continuous so it's well within its ratings. A competent design would never run a device at or near the Absolute Maximum Rating as it's just that "absolute maximum" (exceed and it goes "pop" and lets out the Magic Smoke).

 

Thanks for that explanation, but I still don't understand if the 5A MOSFET is a good or a bad thing in my case.

My point with the other BMS was, that if the listing shows a 8205A MOSFET, but the delivered item clearly has something else on the PCB, then I don't trust it anymore.