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

[Crossy]

32 minutes ago, Susco said:

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.

 

The 8205 is available in a 6 pin package DSA00244866.pdf so it's quite possible it's not "something else". That said, it's naughty of the seller not to include photos of the actual item on sale and would be grounds to return said item.

 

With the peak current the panel can give being about 0.6A any BMS rated over about 1-1.5A will do the job just fine. A bigger unit won't hurt, but it won't give an advantage either.

 

[Susco]

53 minutes ago, Susco said:

- 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.

 

Would this be a viable idea, or a waste of money, and would I be better with only the BMS on the existing batteries?

 

To be honest, there is no real need for the lights to stay on after i went to bed, but it may be an added security

 

At the same day I tested the light for 16 hours, I tested another one, which I kept on for 22 hours.

 

The light was still glowing, so it hadn't switched off yet, and the battery measured 2.47V.

 

As you probably will recall from previous conversations, once the lights go in the completely dimmed mode, they use so little current that is not measurable any more.

[Crossy]

Adding a BMS to the existing battery (or using a protected battery) certainly won't hurt and should extend the battery life somewhat.

 

That said, 18650 cells are so cheap that simply replacing the battery when it fails may actually be the most viable option. 

[Susco]

Trying to understand those battery test in the reviews. Does this show the capacity of a single battery, or from the 2 combined?

 

Edited January 18, 2021 by Susco

[Crossy]

6 minutes ago, Susco said:

Trying to understand those battery test in the reviews. Does this show the capacity of a single battery, or from the 2 combined?

 

I assume it shows the parameter for the battery in the position with the little triangle on the screen (rightmost in your image). Not sure how you change the display or if it's automatic.

 

[Susco]

6 minutes ago, Crossy said:

 

I assume it shows the parameter for the battery in the position with the little triangle on the screen (rightmost in your image). Not sure how you change the display or if it's automatic.

 

 

Thanks, start to get a headache of this now.

 

Currently exploring a listing which has 400+reviews, with at least 30 or more reviews with pictures of the test.

 

Guess about 70% of them show capacity around between 3000 and 3500 mAh, while the others show half of that capacity, and that is all for the same battery.

 

You think this is possible, or should we assume that those which show low capacity have actually no idea how to properly test a battery?

[Crossy]

1 minute ago, Susco said:

You think this is possible, or should we assume that those which show low capacity have actually no idea how to properly test a battery?

 

This is a distinct possibility. Of course it's also possible that there are duff ones mixed in the batch.

 

I just got 40 x 32650 5,000mAh LiFePO4's from Power Idea, sample test puts them at between 4,950 and 5,060 which I'm happy with.

[Susco]

8 minutes ago, Crossy said:

I just got 40 x 32650 5,000mAh LiFePO4's from Power Idea

 

Is that a store available on Lazada or Shopee? If so, do you have a link to the store?

 

Edit : Found them on shopee, but seems they have only LifePo

Edited January 18, 2021 by Susco

[Crossy]

He's on Lazada too, but limited choice and no 18650's.

[maxpower]

3 hours ago, Susco said:

Thanks, start to get a headache of this now.

 

18650 cells are cheap, I would not stress too much.

 

Anyway if its really important ...

 

Genuine LiitoKala 18650 unprotected cells

https://www.lazada.co.th/products/18650-panasonic-liitokala-3400-mah-liitokala-1-p-i1103988743-s2514868108.html?spm=a2o4m.seller.list.5.5a985f83WFPlZo&mp=1

 

No need to worry about what flavor mosfet is used on the BMS as long as the board is set to pass enough current for your need.

[Susco]

 

 

I have a battery holder same as below, and an Imax B6 charger

 

 

Is it save to put just 2 or 3 batteries in there or is that tricky?  Google shows me many results that say the batteries need to have an identical charge to start with, otherwise they will not load correctly.

 

So can I use this holder with an Imax B6 charger, and safely charge multiple batteries at the same time, or should I better order a charger like the Liitokala for that purpose?

 

 

Edited January 21, 2021 by Susco

[Crossy]

Does that holder put the cells in series or parallel?

 

If they are in parallel you can charge as many or as few as you want with the Imax. The cells should be about the same charge level otherwise the lower ones will suck charge from the higher ones as they balance themselves (some pretty big currents can flow).

 

Don't charge (or discharge) a series string of cells without a BMS or cell protection (or you could use the balance function of the Imax if you have the leads).

[Muhendis]

https://www.west-l.ru/uploads/tdpdf/imax_b6_eng_man.pdf

Page 2 explains 

[Susco]

3 hours ago, Crossy said:

Does that holder put the cells in series or parallel?

 

If they are in parallel you can charge as many or as few as you want with the Imax. The cells should be about the same charge level otherwise the lower ones will suck charge from the higher ones as they balance themselves (some pretty big currents can flow).

 

Don't charge (or discharge) a series string of cells without a BMS or cell protection (or you could use the balance function of the Imax if you have the leads).

 

The holder pictured in my post is parallel, I have one in series as well.

 

No separate balance strings get included with the Imax, because they are fitted on a battery pack that is in series.

 

3 hours ago, Crossy said:

The cells should be about the same charge level otherwise the lower ones will suck charge from the higher ones as they balance themselves (some pretty big currents can flow).

 

But do they all get fully charged, if one of them is lower charge level at the start? With pretty big currents, you think they can reach dangerous levels.

 

Does the Liitokala charger work in the same way, or doesn't it matter there if one battery is significant lower charge level than the other?

[Crossy]

Just now, Susco said:

But do they all get fully charged, if one of them is lower charge level at the start? With pretty big currents, you think they can reach dangerous levels.

 

Does the Liitokala charger work in the same way, or doesn't it matter there if one battery is significant lower charge level than the other?

 

They all end up at the same voltage so they will be at the same charge level (they must all be the same chemistry of course).

 

The Liitokala is clever in that it monitors each cell individually so you can put any state in each position.

 

I'll check to see what magnitude of current will flow between a charged and discharged cell. "Significant" does not necessarily mean "hazardous" except maybe to the holder itself if the wiring is a bit small.

 

[Crossy]

3 hours ago, Crossy said:

I'll check to see what magnitude of current will flow between a charged and discharged cell. "Significant" does not necessarily mean "hazardous" except maybe to the holder itself if the wiring is a bit small.

 

Just tried a couple of cheap 4Ah 32650 LiFePO4 cells, one fully charged one fully discharged.

 

Putting them in parallel with a short length of 2.5mm² resulted in a circulating current of 15A, enough to make things in a battery holder get somewhat warm!

 

[Muhendis]

21 hours ago, Crossy said:

 

Just tried a couple of cheap 4Ah 32650 LiFePO4 cells, one fully charged one fully discharged.

 

Putting them in parallel with a short length of 2.5mm² resulted in a circulating current of 15A, enough to make things in a battery holder get somewhat warm!

 

A 4Ah liFePO4 cell should be discharged at no greater than 1C and charged at max 0.5C otherwise they get stressed and have a shortened life span. 15C is a very bad idea. It would be interesting to see how long those two cells last in more normal charge/discharge conditions.

[Muhendis]

Just for your information the following is from a manufacturer and is probably biased a bit but the figures seem about right to me. You will note the effect of the C rate on the life expectancy.

If you have a 500ah 48v battery and you regularly, on a daily basis, discharge it to 75% of it's capacity (25% DoD) at the rate of 500 Amps (1C), it will still have some life left after 100,000 cycles which is 274 years. I'm personally not too comfortable with that idea. I would imagine other factors would cause the battery to deteriorate over that sort of time span.

 

Below chart shows the estimated number of cycles for our new generation of Lithium LiFePO4 cells, according to the discharge power and DOD figures. The test conditions are those of a laboratory (constant temperature of 25°C, constant charge and discharge power).

We can read from the chart the below figures :

3 000 cycles at 100% DoD @ 1C

4 500 cycles at 80% DoD @ 1C

10 000 cycles at 60% DoD @ 1C

etc.

It should be noted that following the number of completed cycles, the cell still have a nominal capacity > 80% of the original capacity.