How do RC LiPo's not need protection?

Batteries and Chargers Rechargeable Batteries
1

Not directly related, but this stems from the IMR 16500 that HKJ reviewed.

I struggled to understand what used this size as a 1 x 16500. I had proposed that 2x 16500 = 3 x CR123a. But HKJ seem against running these in series without protection.

For those threads:

And here is a quote from HKJ:

[QUOTE=HKJ;4588196]No LiIon chemistry is completely safe, they all needs protection. Generally IMR will be safer, but a reverse charge is always problematic and for a protected cell this cannot happen.

[/QUOTE]

I think based on the conversation that HKJ was saying (although I don’t have direct confirmation):

For series use:
-protected cells = yes
-non protected cells = no

However, as IMR’s generally (or almost exclusively) can’t be found protected. That would also mean:

For series use:

-IMR = no.

Now I may have gotten this wrong, if so I apologise to HKJ, but I would truly love to learn from all of this. And for the record I have huge respect for HKJ and I’m not questioning what they say, just seeking a “why” to it.

Part of my reasoning is, I was just thinking about RC batteries. As I understand it a LiPo uses pretty much the same chemical make-up as ICR’s do.

But RC LiPo’s are not protected and almost all of them are multi-cells in series.

Ok, most have a balance plug for charging. But during discharge there is nothing, just a single connector, which brings us back to the issue of reverse charging.

How come this isn’t really a problem in the RC world? 3, 4, 5 and even 6S is pretty common. And all with high discharge use. Many speed controllers will have low voltage warning, but that will be the entire packs voltage, not each individual cell.

If it isn’t a problem, fundamentally is there then any difference to an individual taking non protected ICR or IMR’s and “balance charging them”, i.e. making sure they are pretty similar voltage when charged and using matched pairs.

And then run them in series and just be mindful not to run them too low?

I suppose all in all the questions I’m asking is:

-Is the risk really any different between RC multi cell and flashlight multi cell? (I suppose physical proximity to the battery might be, as you hold a light, but not an RC plane/car).

-Is it really risky and inadvisable to run IMR’s in series?

2

Some RC Platforms can balance while discharging(keeping a balancer on there or by using a speedcontroller with balancing)

6S+ Packs are mostly used in planes where some of the capacity of the pack will usually left as safety. Capacity differences are most prominent at the far end of the curve.

Still RC stuff going up in flames happens quite often. At this point the RC is probably far away - the flashlight will be i your hand(or mouth).

personally i run IMRs in series. 4S 16350 on a XM-L2 triple - Balanced to voltage at every charge. Still ten fingers on my hands…

3

You got it correct.

With RC battery pack the cells are often delivered together from the factory, this means the factory has selected cell with equal capacity and age. You can also be fairly confident that the cell will have the same usage. Each charging will balance the cell, when using a hobby charger correctly.

This improves how well they track, but to be safe you need equipment that stops before the cells are drained, i.e. for a 3 pack the equipment must not drain the cell below 9 volt.

Low current LiPo batteries do have protection, even the battery in your phone has a protection board.

4

If your charging the cells in series then yes they need balancing but not if you are charging in parallel. Flashlight cells are usually loose cells whilst rc lipo’s are packed together (hence the balance tap, they cannot be charged in parallel).

Batteries in use -

Unless you’re one of the freaks on this forum that likes to push led’s and batteries to and beyond their limits then you have little to worry about. Even if a led pops then the circuit is broken.

RC’s on the other hand tend to push the limits of the battery, speed controller and motor. Generally speaking each should be quite warm equally. If one or more of the components is hot then something is wrong with the system (wrong gearing or propeller size). If one component fails it can cause a short and as a result damage the other parts of the system. The point is so much more can go wrong with RC so I guess it has earned a reputation as being hazardous.

5

cells in an RC pack are matched to have similar parameters ( especially their internal resitance and capacity) and ESC cut-off is set not to push the cells to their limits ( I personally use 3,4V/cell as a cut off voltage). Other than that I do not see any other difference. Correct me if I am wrong.

6

Good question. LiPo packs for RC usage can provide extremely high currents (hundreds of amps peak) and adding a over-current protection circuit would simple add resistance to that, as well as the fact that it’s normal for RC equipment to draw hundreds of amps, but not 18650 cells in flashlights, so the distinction (cutoff) for protection is clear.

As for low-voltage cutoff, RC hobbyists push their battery packs hard anyway (high currents, over-voltage charging, etc) so the longevity of the battery packs aren’t that critical. As mentioned above, the LiPo packs are impedance matched from the factory and usually have very similar capacities so they will have similar voltages while discharging in series. (Although I’m not sure about capacity matching, that might take too long of a time in the factory)

Another thing that I thought about was the consequence when a LiPo pack or a Li-ion battery vents. In RC cars, planes, or drones, the vehicle will “just” be engulfed in a fireball and shut off. However, in flashlights, the watertight nature of the light can create extreme pressure buildups as well as trigger neighboring cells in series to vent as well. I’m sure you’ve heard of the recent SolarForce flashlight explosion. The effect is much more detrimental.