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Is the so-called "smart battery" really safe enough?

Old 08-21-2019, 10:54 AM
  #1  
Bobbyra
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Default Is the so-called "smart battery" really safe enough?

We have read many news about fire caused by drone battery. Some of them are due to battery overcharing, when a LiPo battery is overcharged, the anode of the battery becomes plated with lithium metal and the cathode produces carbon dioxide. The pressure inside the battery rises as more gas is produced until the outer skin of the LiPo bursts and vents gas. LiPo venting is usually accompanied by flames which leads to the entire battery destroying itself. Overcharging can be prevented by charging LiPo batteries to a maximum of 4.2 volts per cell (or 4.35V for lithium high voltage packs) and charging at a safe current setting.

Some due to over discharging. When quickly discharged in situations such as a drone race, a LiPo battery will heat up. If excess current is drawn from the battery causing it to overheat, gasses will form inside the battery. Like overcharging, if enough gas forms and the LiPo bursts, it will commonly vent with flames. If a LiPo is discharged below its stated C-rating, there should not usually be a safety issue (unless, as happens occasionally, LiPo manufacturers lie about the C-rating of their batteries).

I found some smart battery claiming it can prevent over-charging and over-discharging automatically, so does this mean it is really safe enough that we don't have to take precautions?
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Old 08-21-2019, 12:04 PM
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solentlife
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Smart batterys ... you must be referring to the DJI and similar battery packs that have controller boards slapped on the front end.

They are there for various reasons :

1. To shut off the dumb brick power supplies they give as chargers once pack is fully charged.
2. To disconnect power when cells get down to extreme low level to reduce damage
3. To provide telemetry data to the return signal so pilot has battery info on screen
4. To provide at least a rudimentary balance to pack when charging (this actually is highly debatable and poor function on its part).
5. Prevent power out / charge in when battery condition / temperature is unsuitable.

There are other - but those are the main.

Do they make the LiPo's safer ? Yes BUT not to the extent that users can disregard general LiPo guidelines. Regardless of 'smart board' or not - LiPo's are LiPo's and if abused - they will react badly.

I'm a general RC user but also a Multi Rotor flyer with various including DJI Phantom. I treat ALL with same caution ...
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Old 08-21-2019, 06:29 PM
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Wildflyer
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I look at it this way;
A"smart" battery is just a battery with a charge control board inside, nothing new about that. I have torn apart nicad packs from old laptops and found control boards inside them, exact use unknown but it seemed the laptop must have some special code or something to "turn on" the battery pack, as I could not get power out unless I removed the board.
The battery in my DX8g2 must be a smart battery because it's charging is controlled internally.
Some cell phone batteries have a control board in them. I guess they are "smart" (well maybe not.)

Another thing to keep in mind is that as batteries are used and charged over and over, and age over time, their internal resistance (IR) slowly increases. At some point the actual C capability of the battery will be considerably below what is was when new, no matter what or how honest the C rating was to begin with. That is why I believe older batteries puff because we are inadvertently running them over their true C ability.

I read somewhere that the current limit for any individual Lipo battery is the amount of current drain that causes a 0.3 volt drop per cell from a full charge condition. Some day I am going to sit and charge up every Lipo I have (1 at a time) and then put a load on it until I reach 0.3 v drop per cell, then I will write that current level on that particular battery. Then drop then to storage level. I would like to have that nice battery analyzer but no money for that yet.
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Old 08-21-2019, 07:37 PM
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solentlife
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Wildflyer has touched on a widely misunderstood fact.

As he correctly says - Internal Resistance increases with pack age and use. This in turn reduces the capability of the pack to produce the high power demands.

There are many 'experts' on forums who still claim that capacity reduces with use and age .... which is total rubbish. Capacity only changes with physical / chemical damage.

What actually happens is that the pack has the full capacity but its ability to turn that into productive power is reduced by the force needed to overcome Internal Resistance. Internal Resistance causes voltage drop under load ... but because motor requires WATTS for desired speed - it ups the amps to compensate ...
The more IR - the more voltage drop - the greater the demand for amps ... temperature increases in the cells - IR increases as a result ... its a vicious circle that reaches a point of 'balance' ... and you observe a shorter flight time ... this then leads to the misconception of lack of capacity to fly full time ... but in reality what has happened - is the amps have eaten up your mAh quicker to compensate for the greater voltage drop.
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Old 08-22-2019, 01:38 AM
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quorneng
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Not sure I agree that batteries do not loos capacity with age.
My 6 year old 5000 mAh 2s is still usable in a low current application but when charged to full (4.2 v/cell) from .storage level (3.8 V) the charger can only get in 1200 mAh. Storage is normally judged to be about 40 % capacity. On this basis ithis 5000 mAh battery has reduced to about 2000 mAh.
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Old 08-22-2019, 03:16 AM
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Originally Posted by solentlife View Post
Smart batterys ... you must be referring to the DJI and similar battery packs that have controller boards slapped on the front end.

They are there for various reasons :

1. To shut off the dumb brick power supplies they give as chargers once pack is fully charged.
2. To disconnect power when cells get down to extreme low level to reduce damage
3. To provide telemetry data to the return signal so pilot has battery info on screen
4. To provide at least a rudimentary balance to pack when charging (this actually is highly debatable and poor function on its part).
5. Prevent power out / charge in when battery condition / temperature is unsuitable.

There are other - but those are the main.

Do they make the LiPo's safer ? Yes BUT not to the extent that users can disregard general LiPo guidelines. Regardless of 'smart board' or not - LiPo's are LiPo's and if abused - they will react badly.

I'm a general RC user but also a Multi Rotor flyer with various including DJI Phantom. I treat ALL with same caution ...
You got a point. What I think is a battery has one job that is to chagre.

The parts that help us care for them, minimize harmful abuse, or try to extend their lifetime cycles, are external to the battery.

For example, adjustable low-voltage alarms. Buil these stuff into them only prevent them from properly performing their job.
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Old 08-22-2019, 03:21 AM
  #7  
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Originally Posted by Wildflyer View Post
I look at it this way;
A"smart" battery is just a battery with a charge control board inside, nothing new about that. I have torn apart nicad packs from old laptops and found control boards inside them, exact use unknown but it seemed the laptop must have some special code or something to "turn on" the battery pack, as I could not get power out unless I removed the board.
The battery in my DX8g2 must be a smart battery because it's charging is controlled internally.
Some cell phone batteries have a control board in them. I guess they are "smart" (well maybe not.)

Another thing to keep in mind is that as batteries are used and charged over and over, and age over time, their internal resistance (IR) slowly increases. At some point the actual C capability of the battery will be considerably below what is was when new, no matter what or how honest the C rating was to begin with. That is why I believe older batteries puff because we are inadvertently running them over their true C ability.

I read somewhere that the current limit for any individual Lipo battery is the amount of current drain that causes a 0.3 volt drop per cell from a full charge condition. Some day I am going to sit and charge up every Lipo I have (1 at a time) and then put a load on it until I reach 0.3 v drop per cell, then I will write that current level on that particular battery. Then drop then to storage level. I would like to have that nice battery analyzer but no money for that yet.
The thing is that many smart battery has way too many external functions other than charge control that somehow limit its ability.
BTW, how do you know that we are inadvertently running older battery puff over their true C ability?
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Old 08-22-2019, 03:26 AM
  #8  
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Originally Posted by solentlife View Post
Wildflyer has touched on a widely misunderstood fact.

As he correctly says - Internal Resistance increases with pack age and use. This in turn reduces the capability of the pack to produce the high power demands.

There are many 'experts' on forums who still claim that capacity reduces with use and age .... which is total rubbish. Capacity only changes with physical / chemical damage.

What actually happens is that the pack has the full capacity but its ability to turn that into productive power is reduced by the force needed to overcome Internal Resistance. Internal Resistance causes voltage drop under load ... but because motor requires WATTS for desired speed - it ups the amps to compensate ...
The more IR - the more voltage drop - the greater the demand for amps ... temperature increases in the cells - IR increases as a result ... its a vicious circle that reaches a point of 'balance' ... and you observe a shorter flight time ... this then leads to the misconception of lack of capacity to fly full time ... but in reality what has happened - is the amps have eaten up your mAh quicker to compensate for the greater voltage drop.
So how can we prevent this voltage drop?
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Old 08-22-2019, 03:28 AM
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Originally Posted by quorneng View Post
Not sure I agree that batteries do not loos capacity with age.
My 6 year old 5000 mAh 2s is still usable in a low current application but when charged to full (4.2 v/cell) from .storage level (3.8 V) the charger can only get in 1200 mAh. Storage is normally judged to be about 40 % capacity. On this basis ithis 5000 mAh battery has reduced to about 2000 mAh.
EoL is when capacity has dropped by 25-30%
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Old 08-22-2019, 09:07 AM
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Originally Posted by quorneng View Post
Not sure I agree that batteries do not loos capacity with age.
My 6 year old 5000 mAh 2s is still usable in a low current application but when charged to full (4.2 v/cell) from .storage level (3.8 V) the charger can only get in 1200 mAh. Storage is normally judged to be about 40 % capacity. On this basis ithis 5000 mAh battery has reduced to about 2000 mAh.
The IR action not only affects discharge but also charge ...

As we all know - charge C rates are substantially lower than discharge C rates and this is because of the chemical action that needs to take place. If you have a high IR battery - the slower you charge - the better the charge. The charger is governed by the voltage it sees resisting charge. If you charge at a rate that causes greater resistance - the charger shuts off saying full - but in fact its not.

I have old packs that do this ... when I disconnect from charger - I see ~4.2v per cell ... but check later and that same battery then shows lower cell count ... 4.12 ... 4.15 etc.

I did say though that chemical damage will reduce capacity ... seriously aged / abused packs will suffer chemical damge and or physical damage to the anode / cathodes.
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Old 08-22-2019, 09:09 AM
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Originally Posted by Bobbyra View Post
So how can we prevent this voltage drop?
You cannot prevent it. You can only lessen it by using suitably rated C packs. If you use a 20C pack in a 40C application - that pack will soon tell you !!
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Old 08-22-2019, 09:10 AM
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Originally Posted by Bobbyra View Post
EoL is when capacity has dropped by 25-30%
That's APPARENT capacity ...
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Old 08-22-2019, 09:11 AM
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As I said - its a myth that is hard to counter.
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Old 08-23-2019, 02:58 AM
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Originally Posted by solentlife View Post
The IR action not only affects discharge but also charge ...

As we all know - charge C rates are substantially lower than discharge C rates and this is because of the chemical action that needs to take place. If you have a high IR battery - the slower you charge - the better the charge. The charger is governed by the voltage it sees resisting charge. If you charge at a rate that causes greater resistance - the charger shuts off saying full - but in fact its not.

I have old packs that do this ... when I disconnect from charger - I see ~4.2v per cell ... but check later and that same battery then shows lower cell count ... 4.12 ... 4.15 etc.

I did say though that chemical damage will reduce capacity ... seriously aged / abused packs will suffer chemical damge and or physical damage to the anode / cathodes.
So how can you slow a charge? A smart battery that can automatically tune its voltage like MMC TI22000 can do that?
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Old 08-23-2019, 10:09 AM
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Originally Posted by Bobbyra View Post
So how can you slow a charge? A smart battery that can automatically tune its voltage like MMC TI22000 can do that?
It depends on the charger you use.

For example - I have a DJi Phantom 3. It has 4S High Voltage LiPo packs with smart boards.

The DJI charger is a fixed regulated Power Brick that supplies 17.5V to a value of 100W. This means that when battery is at low level .. amps can be max at 5.7A .... as the battery charges up - the voltage remains constant but the amps reduce till board detects battery 17.4V and shuts of.

If I use any of my regular programmable LiPo chargers - I can set that to 4S Li High voltage mode ... and any ampage I like from a trickle mA to the max A charger can deliver.
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Old 08-26-2019, 02:50 AM
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Originally Posted by solentlife View Post
It depends on the charger you use.

For example - I have a DJi Phantom 3. It has 4S High Voltage LiPo packs with smart boards.

The DJI charger is a fixed regulated Power Brick that supplies 17.5V to a value of 100W. This means that when battery is at low level .. amps can be max at 5.7A .... as the battery charges up - the voltage remains constant but the amps reduce till board detects battery 17.4V and shuts of.

If I use any of my regular programmable LiPo chargers - I can set that to 4S Li High voltage mode ... and any ampage I like from a trickle mA to the max A charger can deliver.
Thanks man
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