3
\$\begingroup\$

As generally known Li-ion batteries (whether pouch or cylindrical) may catch fire but depending on the application I see completely different attitudes of the users:

Consider as one group RC car drivers. That's where I see much respect for the Li-ion batteries. Many use lipo bags etc. and are aware of the possible dangers with the use of Li-ion batteries.

On the other side consider for example electric tools like a cordless saw. In that case most users don't seem to be even aware that there might be risks associated with their Li-ion batteries. Almost nobody stores batteries in special containment. People don't use a tool or a Li-ion battery for month or maybe a year without looking for the battery voltage and recharging etc. and nothing happens.

What I want to understand by asking this question is this: What makes the lithium-ion batteries of electric tools so much safer than in the case of RC cars?

In the beginning, the answer would be "the battery management system" (that was missing in RC cars,) but today there are smart battery management systems for RC car Li-ion batteries like offered by Spektrum, Battgo or Traxxas id:

  1. The charger automatically uses optimal charging parameters for the battery.
  2. The charger detects bad batteries (for example by measuring internal resistance) and refuses charging.
  3. Using a proper ESC you have a low voltage cut off, i.e. the car stops before the battery becomes overdischarged.

Are there any features or security layers that electric tools have more or better?

Instead of electric tools I might have chosen other applications like smartphones or laptops as well, but in this case one might say that the currents are not so high, so I have chosen electric tools as an example, because it seems a high current application.

Note that also in the case of electric tools chargers are used which use charging currents to 16 ampere.

\$\endgroup\$

1 Answer 1

3
\$\begingroup\$

What makes the lithium-ion batteries of electric tools so much safer than in the case of rc cars?

The application, not the Li-ion cells and not the BMS.

RC models and drones are known for abusing the battery (excessively fast charge, insanely fast and too deep discharge). Some drones don't even have any BMS on board. Because that's what that market demands. An abused Li-ion battery becomes dangerous and has a short life.

Conversely, power tool manufacturers use the battery wisely and always have a BMS. Because that's what that market demands. So the battery remains safe for a long life.

using a proper ESC you have a low voltage cut off,

That's a perfect example why the RC model industry abuses Li-ion batteries. Stopping discharge when the battery voltage is too low is unsafe because, by then, a cell voltage may be reversed. Instead, a power tool stops discharge when any one cell voltage is too low.

\$\endgroup\$
5
  • 3
    \$\begingroup\$ In case it's not obvious to the OP: An important reason power tool manufacturers use the battery wisely is because they are making a complete commercial or industrial product and need to obtain third-party safety approvals (e.g. UL listings). \$\endgroup\$
    – Theodore
    Sep 13, 2023 at 16:16
  • \$\begingroup\$ Thanks, I think one essential point I have overseen is that the current used in power tools is much lower than in rc vehicles. Power tools use 5 to 15 ampere as far as I know whereas rc vehicles at a beginner level draw maybe 20 ampere in an intermediate level over 100 ampere and on a racing level several hundred ampere. Is there any other consumer product which draws such high amps and is powered with lithium batteries? \$\endgroup\$
    – martin
    Sep 13, 2023 at 19:43
  • \$\begingroup\$ Your comment about the "per cell" vs "total voltage" lvc is a good point. However if I set the LVC (for the battery voltage) a bit higher than needed and if the charger balances cells each time, shouldn't this aspect be pretty safe? Additionally, if the charger detects one individual cell that is over discharged, it refuses to charge. \$\endgroup\$
    – martin
    Sep 13, 2023 at 19:50
  • \$\begingroup\$ "shouldn't this aspect be pretty safe? " Absolutely not! There is No WAY to estimate the voltage of an individual cell from the total string voltage. Even it the battery is perfectly balanced at the end of charge, the voltage of a cell with low capacity and/or high resistance will drop relatively fast even though the total string voltage still looks fine. \$\endgroup\$ Sep 13, 2023 at 20:09
  • \$\begingroup\$ But it would be safe if the charger detects the over discharged cell and refuses to charge and you don't use this battery again after this event? Btw. there are also lipowatches which you could add to the balancer input to measure each cell individually during driving (and which gives an alarm if one cell voltage is below a threshold). \$\endgroup\$
    – martin
    Sep 15, 2023 at 17:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.