LED voltage vs. battery voltage (a way higher?!)

[ArminVanBuuren]

Re: 1 LED @ 2A versus 3 LEDs @ 700mA

That's your 3^rd time "One last thing", I guess! ;-)

Sorry, I was still much hesitant about buying the 3x LED lamp, because of the enormous heat that ONLY ONE LED produces, I feared that this 3 LEDs would be even non-usable.

Now I think, the decision is clear.

OK I'm going for the 3x LED CREE lamp then. Still don't know if understand perfectly, but this booster circuit will definitely help reduce some heat. Moreover, the 3x 700 mA current will produce a bit more brightness than 1x 700 mA (single CREE), and also the case temperature will be by 10°C lower compared to the single CREE due to the booster circuit. (Yet, your calculations with no-wind conditions at 25°C is too rough, I think I will ride at highest temp. of 15°C and a bit windy, so I hope I will not reach Tmax of the junction.)

The 4 18650 accus delivered with the lamp were blue (sic!) packaged cells labelled UltraFire SX 18650 3200mAh 3.7V . My measurement with 700mA discharge current from 4.2 down to 2.5V resulted in about 2800mAh.

Not too bad, at least no fake. The charger actually stops charging at 4.15 .. 4.2V.

Well, on eBay, they always state much higher values than they really are. But actually, even 2800 mAh cell is really good compared to those that eg. on the YouTube link were.

Could you please advise the seller from who you bought your light? I would check his items, whether he sells those single batteries / battery packs. Even though it is not 3200 mAh as advertised, 2800 mAh is still a way better than those 66 mAh presented on the video :lol:

 

[erikl]

Re: light lamp & 18650 cells' sellers

Could you please advise the seller from who you bought your light? I would check his items, whether he sells those single batteries / battery packs. Even though it is not 3200 mAh as advertised, 2800 mAh is still a way better than those 66 mAh presented on the video :lol:

The headlamp **broken link removed** (with 2 18650 cells), the torchlight **broken link removed** (with 3 18650 cells), and extra 18650 cells **broken link removed** or **broken link removed** (which delivered - like the blue ones mentioned - 2800mAh @ 700mA load current, and **broken link removed**, which indeed had only a capacity of about 3500mAh.

 

[ArminVanBuuren]

Re: light lamp & 18650 cells' sellers

The headlamp **broken link removed** (with 2 18650 cells), the torchlight **broken link removed** (with 3 18650 cells), and extra 18650 cells **broken link removed** or **broken link removed** (which delivered - like the blue ones mentioned - 2800mAh @ 700mA load current, and **broken link removed**, which indeed had only a capacity of about 3500mAh.

So **broken link removed** is the set that you personally purchased & measured 2800 mAh? I'm quite confused from that many pieces, sorry

Concerning the (reportedly) 5000 mAh (actually 3500 mAh) ... is single cell meant by this? Or their overall capacity when 2 of them connected? Because I thought that the maximal capacity of a single LiIon 3.7V cell available was Panasonic 3400 mAh / cell...

Thanks

 

[erikl]

Re: 18650 cells

So **broken link removed** is the set that you personally purchased & measured 2800 mAh?

Yes, and several blue ones with the same imprint.

Concerning the (reportedly) 5000 mAh (actually 3500 mAh) ... is single cell meant by this?

yes

Or their overall capacity when 2 of them connected? Because I thought that the maximal capacity of a single LiIon 3.7V cell available was Panasonic 3400 mAh / cell...

There are a lot more available, between 3200 and 5000mAh. But you can't always trust the imprint - or may be the higher capacity ones have shorter life expectancy.

 

[ArminVanBuuren]

Re: 18650 cells

Yes, and several blue ones with the same imprint.

yes


There are a lot more available, between 3200 and 5000mAh. But you can't always trust the imprint - or may be the higher capacity ones have shorter life expectancy.

What would you personally recommend? Do you think 5x more expensive Panasonic are worth the price? Or **broken link removed** (eg bought 2x) would be a better idea?

 

[erikl]

Re: 18650 cells

What would you personally recommend? Do you think 5x more expensive Panasonic are worth the price? Or **broken link removed** (eg bought 2x) would be a better idea?

I really don't know. I'm content with all of them. But I haven't recharged them more often than about 20 times, which is nothing against the promised 1000 times. Until now, the measured capacity didn't noticeably change, at all of them.

 

[Audioguru]

There are probably fake Panasonic batteries also sold on e-bay. Buy directly from Panasonic or from a certified dealer.
Cheap no-name-brand stuff is usually junk.

 

[ArminVanBuuren]

There are probably fake Panasonic batteries also sold on e-bay. Buy directly from Panasonic or from a certified dealer.
Cheap no-name-brand stuff is usually junk.

I intend to take **broken link removed**, as the user "erikl" measured them & reports capacity of 2800 mAh, which is pretty decent. Do you think they can be different to those sent to him?

 

[Audioguru]

I intend to take ....., as the user "erikl" measured them & reports capacity of 2800 mAh, which is pretty decent. Do you think they can be different to those sent to him?

The link I posted showed fake Ultra Fire batteries. I do not buy cheap junk from e-bay so I do not know how many products are fakes.

 

[D.A.(Tony)Stewart]

Firstly step down from 8 to 3.5V will be more efficient than 4 to 3.5 with lower conduction losses.

Second, the 3 mode position is usually flash, Dim and bright, done by PWM on the driver to the LED.

Thirdly, you will never know how bad they are until you test a decent quantity over the lifetime of cells. Keep in mind when you put cells in series, when one fails they both fail, so get spare cells. If you value economy over quality, go for the cheap batteries.

But if you value Reliability, Capacity, Lifetime and Meeting specs which comes after lots of R&D and quality control, something that Panasonic excels in, get Panasonic batteries only.

Most cheap batteries are priced this way for a reason, due to internal shorts after so many uses ( less than you expected) from material or process quality escapes.

 

[ArminVanBuuren]

Firstly step down from 8 to 3.5V will be more efficient than 4 to 3.5 with lower conduction losses.

Second, the 3 mode position is usually flash, Dim and bright, done by PWM on the driver to the LED.

Thirdly, you will never know how bad they are until you test a decent quantity over the lifetime of cells. Keep in mind when you put cells in series, when one fails they both fail, so get spare cells. If you value economy over quality, go for the cheap batteries.

But if you value Reliability, Capacity, Lifetime and Meeting specs which comes after lots of R&D and quality control, something that Panasonic excels in, get Panasonic batteries only.

Most cheap batteries are priced this way for a reason, due to internal shorts after so many uses ( less than you expected) from material or process quality escapes.

After reading this, I have to say that I will not purchase the cheap quality ones, but rather HQ which will last longer.

However, as already mentioned, even some Panasonic batteries are fake. What about **broken link removed**? This is a local shop selling various batteries. They sell original batteries, but some are also labeled as "compatible". In this case, however, I would believe that it is a real Panasonic 3400 mAh battery. Would you trust them? The price, 289 Kč, is about 14.5 USD per accu, so it should correspond with the quality.

They also state that it is the latest Panasonic's model. It there any accu (of genuine brands) that offers more than this "breathtaking" capacity?

Thanks a lot

 

[erikl]

... I would believe that it is a real Panasonic 3400 mAh battery. Would you trust them?

Seems to be a good one. Still about 3200mAh @ 1A .

 

[ArminVanBuuren]

Seems to be a good one. Still about 3200mAh @ 1A .

And how much at 700 mA?

Btw where the 200 mAhs are lost? The driver consumes it? (To operate - transfer 8.4V into the voltage that the LED continually needs.)

 

[erikl]

Re: capacity vs. discharge current

And how much at 700 mA?

Now don't start to split hairs or count beans ;-). Check the table linked to above!

Btw where the 200 mAhs are lost? The driver consumes it?

They aren't lost, they are simply not available when discharging with higher currents.

By standards, the capacity of accu cells is given for a low discharge current, e.g. @ 0.05C, means 20h discharge @ 5% current of the given capacity, i.e. 170mA during 20h for this NCR18650B cell. It's normal that the extractable capacity is lower for higher discharge currents. Once more: s. the table!

 

[ArminVanBuuren]

I checked the table and want to ask concerning the Charging graph. At the end of charging, how come that capacity still rises when current supplied drops dramatically? Is there a webpage that describes this charging process? I would like to know more about voltage & current during charging, their values & how they influence the process (eg why it is not possible to charge with extreme current values to reduce time).

 

[Audioguru]

Batteries and especially Lithium rechargeable ones are detailed at www.batteryuniversity.com .

A Lithium battery voltage reaches its maximum allowed voltage of 4.20V per cell when it is only about 70% fully charged. Considerable extra time is needed to charge the remaining 30% of a charge because the current slowly drops. When the charging current drops to a low percentage of the normal charging current then the battery is fully charged and the charger should detect it and shut off.

Here is a Lithium-Polymer (Li-Po) battery used in electric radio controlled model airplanes and cars. Its capacity is 5000mAh and its maximum allowed continuous output current is 350A (!). Its maximum allowed charging current is 60A and it is fairly small and lightweight. This battery is from last year. This year there is a new series of them (80C) that are smaller, lighter and produce higher current.

 

[ArminVanBuuren]

Re: 1 LED @ 2A versus 3 LEDs @ 700mA

That's your 3^rd time "One last thing", I guess! ;-)



Ok; one more (last) estimation:

A single cool white XM-L-T6 CREE LED on its highest setting (2A) uses a voltage of about 3V (at 100..125°C junction temperature - yes, it will get so hot!), i.e. it uses 6W , resulting in a bike's case surface over temperature of 60K, i.e. 85°C @ 25°C ambient temperature at quiet air condition (no wind). Driver losses not yet implied. Under this condition, the luminous flux will be 692lm * 85% ≈ 590 lm (85% is the light yield at about 100°C LED junction temperature).

A single such CREE LED @ 700mA needs a voltage of ≈2.8V (@ ≈100°C junction temperature), i.e. an input power of 2W. Hence 3 of them need 6W, so we have similar thermal conditions as above, the single LED just getting 2W*2.5 K/W=5°C hotter than its inner case contact (instead of 15°C difference for the above single LED @ 2A condition). Also the outer case will be 10°C colder than in the above condition, 75°C at still air. Much higher life expectancy for the LEDs. Luminous flux (=brightness) for a single LED @ 700mA is 280 lm * 90% ≈ 250 lm, or 750 lm for all 3 of them.

Now I think, the decision is clear.


2A for all 3 of them, i.e. ≈700mA per LED.

I found this post extremely helpful, it clearly describes the differences between the currents dependent on temperature.

I still, however, do not understand one thing. To what extent can the temperature of the surrounding influence the current? Because the temperature range for the current limitation (you mentioned 100 ... 125 °C) in your prognostication were at 25°C of the air. If I ride at only 5°C (whole 20°C less), and strong windy condition, does it mean that the current limitation range is not going to be reached and the current stays at 2.8 A, producing 900 Lumen for the single CREE light diode?

I am asking because of this. Tonight I rode at 5°C, and **broken link removed** died after about an hour. One explanation can be that their actual capacity is very close to 66 mAh those in the YouTube 'fake batteries' video had. HOWEVER, it can also mean that the temperature of the LED was so low, that there was no reason for it to lower the amount of current. Therefore, it might could have been possible to run on its maximal current, producing maximal amount of light it can.

Concerning **broken link removed**, the vendor stays:

"Circuitry: 2800mA."

Which would make sense; one of the users has mentioned that he has purchased reportedly 3200 mAh batteries, which actually were only 2800 mAh. My light lasted for an hour, so at 2.8 A and the highest possible flux (900 Lumen), this makes complete sense.

What do you think?

 

[Audioguru]

Lithium batteries do not work well when cold. They are rated at a cosy +25 degrees C. But the battery heats itself a little when discharging making it work a little better than when cold.

 

[ArminVanBuuren]

Lithium batteries do not work well when cold. They are rated at a cosy +25 degrees C. But the battery heats itself a little when discharging making it work a little better than when cold.

This is even 3rd approach to the problem. I know this is quite advanced, but I rather wanted someone to confirm or deny whether the current may stay 2.8 A for the entire discharge if conditions (low temperature) do not require it to get down to 0.7 A.

Apparently, it would be smartest to pack the batteries in some lots of textile, so that they are not exposed to the low temperature. On the contrary, the diodes SHOULD face the wind so that they do not heat immediately.

By the way, how come that overheating here is so serious? How does it work at normal house bulbs, based on LED emitting? I saw a CREE bulb that was a way stronger, working on 230 V. And in no wind. How come this one does not overheat much more easily?

 

[Audioguru]

I rather wanted someone to confirm or deny whether the current may stay 2.8 A for the entire discharge if conditions (low temperature) do not require it to get down to 0.7 A.

I did not read the entire thread to see what circuit you are using to regulate the current at 2.8A.
If the current regulator works and the battery voltage does not drop too low then the current will stay at 2.8A until the capacity of the battery runs out.

Apparently, it would be smartest to pack the batteries in some lots of textile, so that they are not exposed to the low temperature.

Then in summer they will overheat which might cause a fire.

By the way, how come that overheating here is so serious? How does it work at normal house bulbs, based on LED emitting? I saw a CREE bulb that was a way stronger, working on 230 V. And in no wind. How come this one does not overheat much more easily?

LED light bulbs are new so maybe they overheat and will not last long. Many LED flashlights also fail soon. The streetlights and traffic lights in my city are all LEDs and you can see the failed ones.