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18650 Under voltage protection

Al Slitter

Nov 4, 2016
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Hello All;
I have a small project that I am going to build and want to run it by the members here.
I live in South East Asia and power availability can be a major issue during the monsoon season. What I want is a light that is portable for movement around our home when the AC is out
I decided to go with a 10 Watt SMD running at 12 volts and 900mA.

The circuit is simple starting off with a TP4056 to charge a used 800mA cell phone battery.
(Please note after charging the USB cable is removed).
The + lead from the battery then runs to a XL6009 boost converter which powers the 10 Watt LED which has a heat sink and fan attached.
On the negative side of the batteries output cable it runs to a basic single pole switch to turn the unit on and off, then connects to the XL6009.

The problem comes if I find that the cell phone batteries do not last long enough, if that is the case I will swap out the cell phone battery for a Li-ion 18650 battery. However this being a standard battery unlike the cell phone battery it does not have under-volt protection available . I want this feature so obtaining a small board that acts this way is a minimum.

Living hear in Asia does not give me ready access to components so I end up dealing through E-Bay and Bangood etc.

Thoughts please.
 

Bluejets

Oct 5, 2014
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Al Slitter

Nov 4, 2016
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Thank you for the quick reply.

I want to use one of the many 18650's that I have versus buying a new one. These cells will not working in the standard battery cases that I have and finally the item you liked to is not available to me in Thailand.
However thanks so much for taking the time to reply!
 

dave9

Mar 5, 2017
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You can get "battery protection board" shipped world-wide on eBay (usually coming from China). Will they not ship to you?

A few other thoughts about this project...

Some major brand 10W LEDs are fairly good quality, but many of the generics that look like the following picture, have very poor quality manufacturing and a large % of them are defective in having excessive leakage, essentially being very inefficient and creating excessive waste heat, to the point where they cannot be run at ratings or else that will cause cascade failure from one die at a time.

I simply would not use that type of LED for any battery powered project, especially in this case which leads up to my next suggestion which is that whether it is a cell phone battery or an 18650, this seems quite undersized for something meant to withstand the duration of a power outage.

Consider that you're starting with 3.6V (nominal) and boosting to around 12V, and suppose it's about 90% efficient. The result would be that even from a 3000mAh 18650 cell, it won't even run for an hour.

Then there is the other problem. Although the LED is spec'd as 900mA at 12V, this is just a generalization. It should still have current regulation rather than the voltage regulation. It should be limited to 900mA, then whatever voltage it takes to achieve that, not 12V then whatever the current is to achieve that.

Really not even that if it is as mentioned above, that it's a generic Chinese LED. In that case I would only drive it at half power for both LED lifespan and increased efficiency BUT as I also mentioned, I just wouldn't use a generic Chinese LED at all. You might literally get the same amount of light with less than 2/3rds the current using a major brand LED.

With experimentation you could get the XL6009 to work for this single prototype by monitoring the current then once the LED heats up to max temperature, adjust the voltage down to where it needs to be to have 900mA, but if you do not have the XL6009 yet, then I would just abandon the idea of using it and get a 10W (or as already mentioned a 5W might be more suitable with the other parameters) current regulated driver. These too should be available on eBay with worldwide shipping for $2-3 USD.

If I were building something like this for the described purpose, I would more likely pick 2 x 18650 cells in series as the battery, powering 2 x 3W LEDs in series, after a buck current regulating driver. Many such drivers will continue to power the LED at progressively lower current until you get most of the rated capacity out the cells while a single 18650 boosted to 12V, not so much.

Edit: Almost forgot the pic of the generic 10W LEDs I'd avoid, which use a 3x3 array of dies in them:
 

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Al Slitter

Nov 4, 2016
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Thank you for all of your input.
Regarding the E-Bay dealer not shipping to Thailand it is just a sellers choice maybe due to shipping theft here. I buy lots pf components to have on hand due to long delivery times.
At present I have about 10 of the 10W SMD's and yes they are your dreaded 3x3 12 volt configuration.
In addition I have 20W to 100W SMD's along with an assortment of drivers for them.
This is a project for me but more importantly it is a learning exercise.
I intend on lowing the voltage on the first unit to a level that gives me the brightness I need as well as battery life.
If I have to up the battery count so be it, the question will then be to run them in Parallel or Series mode.

Thank again.
 

Externet

Aug 24, 2009
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What I do with undervoltage Lithium cells (usually salvaged) that the charger refuses to accept because their voltage is under the minimum acceptable to enable the charging process, is apply 3 to 4 Volts to raise the minimum.
Then, the charger accepts them for a normal charging process.
Cheap single 18650 cells chargers are about $1. This will work in a place with difficulty in obtaining parts.
The cheap chargers look like
----> https://www.aliexpress.com/wholesale?SearchText=18650+charger&opensearch=true

Another way I recharge lithium cells is by applying regulated 4.100 Volts directly. It recharges them just fine and never presented safety problems nor heating. Perhaps this helps.
 

Audioguru

Sep 24, 2016
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Many videos on YouTube show fake 18650 lithium cells with FIRE in their name sold on Chinese websites.
 

BobK

Jan 5, 2010
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I love the teardown video where the guy opens one up and pours out a bunch of rice and a tiny battery.

(Oh, we meant 2000uA hours, it’s a typo)

Bob
 

Al Slitter

Nov 4, 2016
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You bring up a very good point.
Yes I have been stung on one or two occasions with small purchases, so what I do now is follow several rules to try and find a 18650 battery that is close to the advertised rating.

1. I ignore any adds that states the AH rating above 3200.
2. I check the weight given for the item must be in the 42 grams to 49 gram range.
3, I look for cells that are from major manufactures or companies that may have been relabeled such as Sanyo, NCR, Samsung, LG etc.

So far good results.
 

Bluejets

Oct 5, 2014
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dave9

Mar 5, 2017
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Umm...

3, I look for cells that are from major manufactures or companies that may have been relabeled such as Sanyo, NCR, Samsung, LG etc.

... Last night I ordered 5 more 18650 for a project and inventory;

https://www.aliexpress.com/item/Lii...325.html?spm=a2g0s.9042311.0.0.6ab34c4dvoooZi

AliExpress Shopper review said:
One cell exploded in my hands when I inserted into the powerbank :) Now I have not 5, but 4. But I am very pleased

:rolleyes:

I wonder if the reviewer meant batteries or fingers?
 

Al Slitter

Nov 4, 2016
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I saw the feedback prior to ordering and it just reminded me that Russian Vodka and Polarity just don't mix. HaHaha !
 
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