Author Topic: Notify when batteries getting too low  (Read 3872 times)

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Offline fixit7Topic starter

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Notify when batteries getting too low
« on: June 15, 2019, 01:58:25 am »
I have 2 18650s powering my bike headlight.

The light fails pretty suddenly when the voltage gets to about 2.5 volts.

I was thinking of building a low current monitor the uses a momentary switch to check the voltage without having to take the batteries out of the holder.

Are there other options?

Thanks.

 

Offline Audioguru

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Re: Notify when batteries getting too low
« Reply #1 on: June 15, 2019, 02:05:00 am »
An 18650 battery cell is lithium. It is destroyed when its voltage is lower than 3V and yours are probably in series so if they produce only 2.5V then they have only 1.25V each.
 

Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #2 on: June 15, 2019, 02:33:34 am »
No, that was voltage of INDIVIDUAL cells.

You should not make a lot of assumptions.
 

Offline SparkyFX

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Re: Notify when batteries getting too low
« Reply #3 on: June 15, 2019, 04:29:58 am »
Search the net for "18650 discharge curve", you´ll find various examples for the capacity/voltage relationship. As these curves are rather flat and then go steep, lithium capacity sensing is either imprecise (given all other factors, like ambient temperature) or contains some form of computational model - probably too big of a deal for a bike lamp.
You can of course test by adding additional load and if the lamp still works, the battery holds sufficient charge.

Spare batteries or premature charging might be more practical in the end.
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Offline sleemanj

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Re: Notify when batteries getting too low
« Reply #4 on: June 15, 2019, 05:00:40 am »
A simple cell monitor device

https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20190614205829&SearchText=lipo+cell+monitor

cycles through each series cell and displays it's voltage, typically handle 2-8 cells
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Offline mariush

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Re: Notify when batteries getting too low
« Reply #5 on: June 15, 2019, 05:52:52 am »
A 6-8 pin microcontroller could measure voltage and optionally disable light when voltage  goes below some threshold.. could have a tiny led blink when low.

You could start with an Arduinno and learn some  stuff...
 

Offline Mr.B

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Re: Notify when batteries getting too low
« Reply #6 on: June 15, 2019, 06:01:37 am »
No, that was voltage of INDIVIDUAL cells.

You should not make a lot of assumptions.

Please don't be so rude.
He was only offering accurate information about 18650 batteries.
Even if you are talking about individual cells, 2.5v is to low for a LiPo battery.
Where are we going, and why are we in a handbasket?
 

Offline soldar

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Re: Notify when batteries getting too low
« Reply #7 on: June 15, 2019, 06:44:16 am »
The light fails pretty suddenly when the voltage gets to about 2.5 volts.

No, that was voltage of INDIVIDUAL cells.

You should not make a lot of assumptions.

No need to be rude to someone trying to help you. Not only that but there is no assumption that is wrong. It is your phrasing that leads to the misunderstanding. As you do not specify otherwise it is correctly interpreted as 2.5 volts to the light.

You should always show respect to those who are your superiors in age, authority and knowledge but especially when you are seeking their help.
« Last Edit: June 15, 2019, 06:54:19 am by soldar »
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Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #8 on: June 15, 2019, 01:29:09 pm »
I was not trying to be rude.

I try to give all relevant information that I can think of.

But I sometimes or maybe often do not give all the information.

I do the best I can.

 


Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #10 on: June 15, 2019, 01:41:10 pm »
A 6-8 pin microcontroller could measure voltage and optionally disable light when voltage  goes below some threshold.. could have a tiny led blink when low.

You could start with an Arduinno and learn some  stuff...

Thanks marjush.

I will look for an Arduinno and learn more.

Andy
 

Offline sleemanj

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Offline TK

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Re: Notify when batteries getting too low
« Reply #12 on: June 15, 2019, 02:03:09 pm »
There are ICs that monitor LiPo batteries like TI BQ2023:

BQ2023 (NRND) Single-Wire Advanced Battery Monitor IC for Cellular and PDA Applications
 

Offline fixit7Topic starter

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Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #14 on: June 15, 2019, 03:24:22 pm »
There are ICs that monitor LiPo batteries like TI BQ2023:

BQ2023 (NRND) Single-Wire Advanced Battery Monitor IC for Cellular and PDA Applications

Thanks TK.

Andy
 

Offline Zero999

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Re: Notify when batteries getting too low
« Reply #15 on: June 15, 2019, 03:47:37 pm »
No, that was voltage of INDIVIDUAL cells.

You should not make a lot of assumptions.
That shouldn't make any difference. If the voltage of one of the individual cells drops that low, it's likely it'll be damaged.

People will make assumptions, in the absence of enough information.
 

Offline Audioguru

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Re: Notify when batteries getting too low
« Reply #16 on: June 15, 2019, 05:46:59 pm »
Since you said 2.5V then I thought it is too low for a white LED so your two cells must be in series and are producing a total of 2.5V.

My radio controlled model airplanes use two Li-PO cells in series and the airplane warns me the voltage is low at 3.15V per cell by pulsing the main motor, then cutting that motor when the cells are 3.05V each.
With the cells at 3.05V then there is enough power to control the servos for me to steer a glided-in landing. The manufacturer says that running the cells down to 3.15V frequently damages them, use a timer instead.
At home I use the two-cells display thing that shows total voltage, then cell 1 voltage then cell 2 voltage. I use it when I discharge the cells down to 3.7V each (half a full charge) for winter storage.
 

Offline sleemanj

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Re: Notify when batteries getting too low
« Reply #17 on: June 15, 2019, 10:30:21 pm »

Most negative, next most negative, third most negative... most positive

I do not understand your post.

Andy





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Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #18 on: June 16, 2019, 01:11:15 am »
No, that was voltage of INDIVIDUAL cells.

You should not make a lot of assumptions.
That shouldn't make any difference. If the voltage of one of the individual cells drops that low, it's likely it'll be damaged.

People will make assumptions, in the absence of enough information.

Double the voltage makes a lot of difference.

The batteries charged up to full capacity.

Your last statement is very humorous. You made my day. :-)

Andy
 

Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #19 on: June 16, 2019, 01:12:48 am »

Most negative, next most negative, third most negative... most positive

I do not understand your post.

Andy





Thanks.

Your artwork is impressive. :-)
 

Offline Audioguru

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Re: Notify when batteries getting too low
« Reply #20 on: June 16, 2019, 02:46:48 am »
My 2-cells Li-PO batteries have 3 wires so that they can be balance-charged and so the voltage tester can show the voltage of each cell and their total.
 

Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #21 on: June 16, 2019, 03:14:15 am »
My 18650s are a different type as yours, right?

Safety
Main article: Lithium-ion battery § Safety
Apple iPhone 3GS's Lithium-ion battery, which has expanded due to a short circuit failure.

LiPo cells are affected by the same problems as other lithium-ion cells. This means that overcharge, over-discharge, over-temperature, short circuit, crush and nail penetration may all result in a catastrophic failure, including the pouch rupturing, the electrolyte leaking, and fire.[18]

All Li-ion cells expand at high levels of state of charge (SOC) or over-charge, due to slight vaporisation of the electrolyte. This may result in delamination, and thus bad contact of the internal layers of the cell, which in turn brings diminished reliability and overall cycle life of the cell.[7] This is very noticeable for LiPos, which can visibly inflate due to lack of a hard case to contain their expansion.

For a comparison with LFP cells on this subject, please see LiFe cell safety

Weren't those banned on planes at one time? A little research.

Q2. What kinds of batteries does the FAA allow in checked baggage (including gate-checked bags)?
A2 . Except for spare (uninstalled) lithium metal and lithium-ion batteries, all the batteries allowed in carry-on baggage are also
allowed in checked baggage. The batteries must be protected from damage and short circuit or installed in a device. Battery-powered
devices—particularly those with moving parts or those that could heat up—must be protected from accidental activation. Spare
lithium metal and lithium ion/polymer batteries are prohibited in checked baggage—this includes external battery packs. Electronic
cigarettes and vaporizers are also prohibited in checked baggage. “Checked baggage” includes bags checked at the gate or planeside.
« Last Edit: June 16, 2019, 03:17:35 am by fixit7 »
 

Offline sleemanj

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Re: Notify when batteries getting too low
« Reply #22 on: June 16, 2019, 05:53:41 am »
For all intents and purposes "LiPo" and "Lithium-Ion" are the same thing, an 18650 can be thought of as equivalent to a LiPo which was rolled up and stuck inside a metal can, or conversely a "LiPo" can be thought of as an 18650 which was unrolled and put in a soft pouch.

This is a simplification, but not much of one, from the user perspective, charging, discharging, protection, balancing, and electrical safety are the same if you are using a hard shell (18650...) or a soft shell (LiPo...) Lithium-Ion cell architecture.

LiFePO4 is different and must not be confused with Lithium-Ion, they have different characteristics.




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Offline fixit7Topic starter

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Re: Notify when batteries getting too low
« Reply #23 on: June 16, 2019, 01:23:57 pm »
For all intents and purposes "LiPo" and "Lithium-Ion" are the same thing, an 18650 can be thought of as equivalent to a LiPo which was rolled up and stuck inside a metal can, or conversely a "LiPo" can be thought of as an 18650 which was unrolled and put in a soft pouch.

This is a simplification, but not much of one, from the user perspective, charging, discharging, protection, balancing, and electrical safety are the same if you are using a hard shell (18650...) or a soft shell (LiPo...) Lithium-Ion cell architecture.

LiFePO4 is different and must not be confused with Lithium-Ion, they have different characteristics.

It comes down to what the user personal choice is.

LiPo Batteries
Pros

    Much lighter weight, and can be made in almost any size or shape.

    Much higher capacities, allowing them to hold much more power.

    Much higher discharge rates, meaning they pack more punch.

Cons

    Much shorter lifespan; LiPos average only 150–250 cycles.

    The sensitive chemistry can lead to fire if the battery gets punctured.

    Need special care for charging, discharging, and storage.
 

Offline Audioguru

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Re: Notify when batteries getting too low
« Reply #24 on: June 16, 2019, 01:47:26 pm »

Cons

    Much shorter lifespan; LiPos average only 150–250 cycles.

    The sensitive chemistry can lead to fire if the battery gets punctured.

    Need special care for charging, discharging, and storage.
No. Name-Brand Li-POs last for 500 cycles or more, the same as Lithium-Ion. Cheap Chinese ones last for 20 cycles or less.
They have the same chemistry as Lithium-Ion so they need the same special care.
 


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