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

[Muhendis]

3 hours ago, tjo o tjim said:

I wonder what they have in the way of a charge controller and low voltage cut-out for these things. No matter the brand, I feel lucky to get about full 100 cycles on the consumer units (and only ~300 with commercial units).  I have had little luck replacing batteries, even when it is possible— the charging circuits are not very forgiving for new batteries. 

Good question. The limited number of cycles (300) is not so unusual but 100 cycles tends to indicate poorly made batteries. Perhaps some chemical impurities have crept in somewhere along the line. Do you have any examples of the battery specs. for your new batteries?

[Crossy]

4 hours ago, tjo o tjim said:

I wonder what they have in the way of a charge controller and low voltage cut-out for these things.

 

I suspect that many of the cheaper lights rely on the internal protection that (some) cells incorporate. Also our lights go into "dim" mode after several hours, I'm assuming that's because of battery depletion.

 

I will have a look at one of my lights when I take it down to install a bigger pack, but are people really getting less than 12 months of decent operation out of these lights?

 

Reports from other members suggest they are still working just fine after 2+ years.

[Muhendis]

1 hour ago, Crossy said:

are people really getting less than 12 months of decent operation out of these lights?

 

Reports from other members suggest they are still working just fine after 2+ years.

I guess I'm getting a bit lazy. I should have included my justifications as follows:-

 Battery life expectancy is dependent on depth of discharge per cycle. 

Cycle life versus DoD curve for lithium-ion NMC battery

This graph is not the best but it gives a reasonable indication of the relationship of DoD/cycles.

The 300 cycle number is based on DoD of 80% per cycle and at 25 deg C. If the lights spend all night at reduced brightness then the batteries are most likely no where near 80% discharge/cycle and will undoubtedly keep going for years.

 

tjo o tjim raised the question of charge controller potentially not doing it's job. That could well be the case.

 

[Crossy]

1 hour ago, Muhendis said:

The 300 cycle number is based on DoD of 80% per cycle and at 25 deg C.

 

But even from the "not the best" graph (and assuming the Y axis is linear below 10,000), 80% DoD heads for about 2,000 cycles life.

 

[Muhendis]

18 minutes ago, Crossy said:

 

But even from the "not the best" graph (and assuming the Y axis is linear below 10,000), 80% DoD heads for about 2,000 cycles life.

 

 

At 80% DoD the actual number of cycles from the graph is more like 400 (NMC). LiPO4 does better at 900. I think I mentioned that the graph was only a reasonable indication. I guess my 300 can be taken with a pinch or two of salt but non-the-less those DoD figures don't take into account the charging voltage which is not known. It would be useful if the street light spec. included some sort of average battery life expectancy. 

Thanks to the battery university for the table below.

Depth of discharge	Discharge cycles		Table 2: Cycle life as a function of depth of discharge.*  A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life. Note: 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.
	NMC	LiPO4
100% DoD	~300	~600
80% DoD	~400	~900
60% DoD	~600	~1,500
40% DoD	~1,000	~3,000
20% DoD	~2,000	~9,000
10% DoD	~6,000	~15,000

 

[Crossy]

26 minutes ago, Muhendis said:

It would be useful if the street light spec. included some sort of average battery life expectancy. 

 

Yeah, the original floodlight in the OP says 2-3 years.

 

The streetlight says nothing about battery longevity but it does say it's a LiFePO battery and gives light for 12 hours (evidently not at full power from the ones we have).

 

Is there any way to verify the technology of a battery other than look at the label?

 

[Muhendis]

3 hours ago, Crossy said:

Is there any way to verify the technology of a battery other than look at the label?

The voltage of a LiFePO4 cell when fully charged should be 3.6v and the nominal voltage should be 3.3v. The nominal voltage will remain at that level during most of the discharge cycle.

The NMC cell when fully charged should be 4.2v and the nominal 3.7v.

The only trouble with these figures is that we don't know the charger configuration so in reality there is only the label to go by (which may be just a blank plastic shrink wrap) or the battery packaging information sheet written in mandarin of course. All this is somewhat academic since you already have the batteries in the light. Boosting the capacity with LiFePO4's carries a little risk because the charger circuit may be the bottleneck, but a few real life tests up the pole to confirm the charging voltage should give you the confidence.........???? ????

[Crossy]

7 minutes ago, Muhendis said:

up the pole

 

Round the bend more like. 

 

I will do some tests to see if there's a low voltage cut off in the light itself but I'm not measuring anything whilst up the pole

 

I've got some Tipsun 6Ah x 32700 LiFePO's on the way, once the real capacity has been checked I'll put a full 7 cell pack in one light and upgrade another by adding 2 cells to the existing 5 cell 20Ah pack. I can also verify the capacity of the 20Ah pack.

 

Then time for some empirical tests (watch what they do).

 

[maxpower]

19 hours ago, Crossy said:

I'll put a full 7 cell pack in one light and upgrade another by adding 2 cells to the existing 5 cell 20Ah pack.

 

I guess you have already found headroom in the solar panel from a full sun test as labels on brand-x panels can be wild. If you don't know the real panel output, adding additional cells might not work well. Most of these cheap solar lights have solar panel with basic 1S LiFePO4 packs working down to the bone.

 

But then there's not really much to lose. Throw them up and hope they will provide a $40 satisfaction period considering a professional dusk to dawn 30W solar street light can cost $250+.

 

I am surrounded by solar light manufacturers, everyone wants in on this green free energy sales pitch. Production methods and quality varies immensely.

 

For those wishing to build their own modular lights there are lots of reliable inexpensive Chinese solar street light controllers available like SRNE SOLAR. These devices  will smart charge LiFePO4 packs and PWM control the LED array based on settings. They are used in many of the more expensive street lights and custom built solar lights.

[Crossy]

2 hours ago, maxpower said:

I guess you have already found headroom in the solar panel from a full sun test as labels on brand-x panels can be wild.

 

Since I only intend going up the pole once to retrieve the light, task "A" will be to check the panel is providing something like the purported 30W. Size wise it's the right dimensions but like the "20Ah" battery who really knows until you test the beast.

 

If I can get it to go (almost) all night for the cost of a couple of 5/6Ah cells I'll be happy, if it doesn't the cells can go in my UPS.

 

 

 

[Crossy]

OK, been doing a bit of shopping.

• Eight x 6000mAh Tipsun 32700 cells https://www.lazada.co.th/products/i919830708-s5785878869.html
• A battery capacity tester https://www.lazada.co.th/products/i1654540670-s4601582727.html
• And a smart charger https://www.lazada.co.th/products/i1058460996-s2362918307.html

The cells test as 6000mAh so I can recommend that seller.

 

I made up a 7 cell pack for the light (5 in a pack + 2 separate), these squeeze nicely into the available space secured with 3M tape and a good splodge of silicon (this idiot forgot to take a photo).

 

I also looked at the light itself, sadly it's a miserable day so I've not been able to test the panel output.

The panel goes direct to the cells via a blocking diode which also serves to sense when the panel isn't active and turns on the light in "Auto" mode. There's no charge control.

The controller device is unmarked, so no indication what it is.

Testing the light on a variable power supply yielded the following (current measured with my clamp meter):-

• 3.3V - 3.8A = 12.54W
• 3.2V - 1.75A = 5.6W
• 3.1V - 1.4A = 4.3W
• 3.0V - 1.2A = 3.6W
• 2.9V - 0.9A = 2.6W
• 2.8V - 0.7A = 1.9W
• 2.6V - 0.2A = 0.5W

The light finally went off (and the current fell to zero or at least below what my meter can handle) at 2.3V

 

I checked the remaining charge in the 20Ah pack that came out of the light, it still had 50% of the rated capacity left (I'm checking the actual capacity as I write). 

 

With my fully charged 43Ah pack the current was 4.8A! Light was noticeably brighter.

 

We shall see how bright it is compared with the other lights after it's been on all night for a few days so it's only using energy from the panel and not gradually running down the pack from fully charged. 

 

 

 

 

[Muhendis]

Happy Christmas to you Cratchet Crossy and to all who might like to receive the seasons greetings.

I note you didn't mention the BMS in your list of bits. I would imagine it's lying unseen at the bottom of your stocking.

It looks something like this; https://shopee.co.th/(ของใหม่-พร้อมส่งจากไทย)-ตัวควบคุมการชาร์จ-แบตเตอรี่ลิเธียมฟอสเฟต-BMS-12V-4S-LiFePo4-3.2V-ขนาด-30A-i.98346870.2489134400

 

[Crossy]

1 minute ago, Muhendis said:

I note you didn't mention the BMS in your list of bits.

 

Cells in the packs are all in parallel, no BMS needed ????

 

Happy Christmas to you too, our family party (small this year) is on Sunday as everyone is working today.

 

 

[Muhendis]

A 3.3v system?

[Muhendis]

2 minutes ago, Crossy said:

everyone is working today.

Aah yes! I remember those days.

[Crossy]

9 minutes ago, Muhendis said:

A 3.3v system?

 

Yup.

[tjo o tjim]

16 hours ago, Crossy said:

The panel goes direct to the cells via a blocking diode which also serves to sense when the panel isn't active and turns on the light in "Auto" mode. There's no charge control.

From personal experience, I would recommend doing one complete charge-discharge cycle of the batteries externally to help condition them.  The lack of a charge controller really does a job on them especially when you have a new battery and a few cloudy days. 

[Crossy]

17 hours ago, Muhendis said:

I note you didn't mention the BMS in your list of bits.

 

You are of course correct. Lesson learned 1 set of LiFePO4 cells fried by over-charge.

 

The pack originally installed has a board like this inside 

https://www.lazada.co.th//products/i328498693-s629166183.html

a 1S protection board.

 

So my earlier note of no charge protection is incorrect, the pack has the protection.

 

More cells and a bag of BMSs on order.

 

Crossy Labs - Frying stuff, so you don't have to!

 

[maxpower]

1 hour ago, Crossy said:

 

You are of course correct. Lesson learned 1 set of LiFePO4 cells fried by over-charge.

 

The pack originally installed has a board like this inside 

https://www.lazada.co.th//products/i328498693-s629166183.html

a 1S protection board.

 

So my earlier note of no charge protection is incorrect, the pack has the protection.

 

More cells and a bag of BMSs on order.

 

Crossy Labs - Frying stuff, so you don't have to!

 

 

One problem with using battery voltage close to the LED array voltage is that battery voltage will sag under load and often trigger the BMS leaving unused capacity. The battery voltage will rise when the load is removed but might not be high enough satisfy the BMS recovery value. 

 

Many of these lights use PWM to control brightness levels. Be aware of this when measuring the LED array current in circuit.

 

Lights with higher voltage battery packs often use PWM to limit array current and control consumption as battery capacity reduces.

 

Test charge your cells or packs using bench power supply set to constant current and voltage.
 

[Muhendis]

1 hour ago, Crossy said:

Crossy Labs - Frying stuff, so you don't have to!

Nicely put and for which we are all eternally grateful. 

[Crossy]

1 minute ago, Muhendis said:

Nicely put and for which we are all eternally grateful. 

 

It's all part of the learning process, at least my failure only cost 700 Baht not 216 million US$ (Space-X Starship SN8 explosion).

 

Crossy and Space-X now know something they didn't know before ???? 

 

[Muhendis]

8 minutes ago, maxpower said:

Lights with higher voltage battery packs often use PWM to limit array current and control consumption as battery capacity reduces.

Absolutely right

https://shopee.co.th/3A-CC-CV-LM2596-DC-DC-Step-down-Adjustable-Power-Supply-Module-Converter-LED-บอร์ดชาร์จแบตเตอรี่-ควบคุมความสว่าง-LED-i.57748591.3748654871

[Muhendis]

2 minutes ago, Crossy said:

 

It's all part of the learning process, at least my failure only cost 700 Baht not 216 million US$ (Space-X Starship SN8 explosion).

 

Crossy and Space-X now know something they didn't know before ???? 

 

Crossy and Elon have much in common

[Muhendis]

3 minutes ago, Muhendis said:

Absolutely right

https://shopee.co.th/3A-CC-CV-LM2596-DC-DC-Step-down-Adjustable-Power-Supply-Module-Converter-LED-บอร์ดชาร์จแบตเตอรี่-ควบคุมความสว่าง-LED-i.57748591.3748654871

Ooops! Sorry that's not a switched output. Have a look at motor speed controllers. They are good for LED control.

[Crossy]

15 minutes ago, maxpower said:

One problem with using battery voltage close to the LED array voltage is that battery voltage will sag under load and often trigger the BMS leaving unused capacity. The battery voltage will rise when the load is removed but might not be high enough satisfy the BMS recovery value. 

 

I was quite surprised to find such a low-voltage pack and the decrease in brightness as the pack discharges is quite noticeable, this is the reason I want to try a bigger capacity pack to stay bright for longer.

 

At least with only 50-60% depth of discharge the pack should last a good while despite being cooked in the sunshine.

[Susco]

20 hours ago, Crossy said:

And a smart charger https://www.lazada.co.th/products/i1058460996-s2362918307.html

 

Just see this post Crossy. At that price it will most likely be a copy, as they are copied a lot.

 

But they have a very good counterfeit check.

 

https://www.skyrc.com/antifake/public/

 

Every charger can be checked only once, so next time you check it will notify it has been checked already.

[Crossy]

5 minutes ago, Susco said:

Just see this post Crossy. At that price it will most likely be a copy, as they are copied a lot.

 

Yeah, it makes no attempt to pretend to be the SkyRC unit.

It works well enough although the charge/discharge current is lower than that displayed.

[Susco]

1 hour ago, Crossy said:

The pack originally installed has a board like this inside 

https://www.lazada.co.th//products/i328498693-s629166183.html

a 1S protection board.

 

 see these for sale on Lazada

 

https://www.lazada.co.th/products/wenfengzhi-3a-2s-bms-18650-li-ion-lithium-battery-37v-charger-protection-circuit-pcm-board-i1601084217-s4363240736.html?

[Susco]

39 minutes ago, Susco said:

 

 see these for sale on Lazada

 

https://www.lazada.co.th/products/wenfengzhi-3a-2s-bms-18650-li-ion-lithium-battery-37v-charger-protection-circuit-pcm-board-i1601084217-s4363240736.html?

 

If I attach one of these to a battery, would that result in the solar light switching off when the battery reaches 3v?

[Crossy]

41 minutes ago, Susco said:

 

If I attach one of these to a battery, would that result in the solar light switching off when the battery reaches 3v?

 

Do you have two cells in series (2S)?

For some reason the pictures are not showing for me so I can't really comment ????

 

It doesn't say anything about low voltage cut-off.