Bryan Anderson 1

@Mike T. I am sorry you have not enjoyed Christmas but I must protest. As the originator of this thread, I feel that I did not make a "blase dismissal of series charging" nor did I or anyone else, I think, call it "crap". I am sure that neither of us would ever misuse or misapply anything but I am not so sure about others with inferior abilities. Hence my warnings. Is not education the essence of safety? The fact that a 6S battery can be short circuited by simply plugging in two identical-looking connectors the wrong way, in the wrong socket,  when using a commercially-available dual 3S to 6S converter is surely worthy of a warning. This is not the time of year to be uncharitable but you might care to take a look at your writing and ask yourself who is being blase. Hint: count how many qualifications you make after dismissing the dismissal. Edited By Bryan Anderson 1 on 27/12/2016 18:21:16

Correction: If the black lead shown at the bottom of the picture, not the right-hand side.

Yes, Martin, that is a good example of one that can cause problems. You are right, the connectors are polarised to prevent them being plugged in the wrong way round but there is nothing to stop them from being plugged into the wrong battery of the serially-connected string. Red and black wires are connected to a common pin at the middle of the 6S connector. If the black lead shown at the right-hand side of the picture is connected to the balance plug of the most negative battery then all is well. But connect it to the balance plug of the most positive battery and those balance wires connected to each other short circuit the entire 6S pack. Not good. A mantra of safety is that, if it can be done, it will be done. So better not to allow the possibility.

The most likely danger is from dual 3S to 6S balance converters. There are 4 wires from each 3S connector but only 7 wires on a 6S connector. If you google for "3S to 6S balance converters" you will find examples where they connect a pair of these wires together - red wire to black wire. Use one of these and the danger I described is very evident. Cross over the balance connectors and you short the batteries. Don't try this at home.

This article glosses over the danger and problem with serial charging. The warnings at the end, where they might be missed by readers who skim read, seem to be aimed at parallel charging cases. 1. There is a possibility of shorting out one of the batteries in Figure 2 if the balance leads are crossed over. It depends on exactly how things are wired internally in the charger and whether any of the balance wires are connected to the negative terminal. 2. Rather than speed up charging it can slow it down. If the batteries are of different capacities or charge states then the higher capacity or more deeply discharged one ends up being charged slowly once any one of the lower capacity cells is charged. Ideally, one would want all cells being charged to be in identical batteries and in the same state of charge. Serial charging is bad advice and a safety hazard. Cell manufacturers specifically warn against serial charging. Battery manufacturers take care to match the cells in batteries to try to minimise these problems.

Second attempt. Aircraft wheels are not driven except by contact with the ground. When an aircraft lands, the tyres smoke until the wheels rotational speed increases enough for the speed of the tyre at the contact point to exactly match the speed of the ground, i.e. zero. The hub and the plane are of course moving at the ground velocity. The top of the wheel is travelling at twice the velocity of the plane and the average forward velocity of all parts of the wheel is that of the plane. No surprise there then. It sounds surprising but a point on the circumference of the wheel is stopped momentarily in the frame of an observer on the ground as it passes through contact with the ground After the smoking stops there is no slippage. There is an exact match as specified in the question. This is the normal mode of operation of wheels on flat surfaces. The conveyor belt is a red herring to throw the thought processes off course. If the planes engines are running normally it will take off, otherwise not.   Edited By Bryan Anderson 1 on 14/10/2016 16:50:04

Posted by WolstonFlyer on 12/10/2016 21:06:43: This simple little question has caused a lot of healthy discussion on Facebook today. Edited By WolstonFlyer on 12/10/2016 21:07:49 This is extremely badly phrased. "Exactly match the speed of the wheels". What is the speed of a rotating wheel? A wheel typically has two speeds: one translational and the other rotational. I think it means there is no slip between the tyre contact patch and the belt. Short answer: the plane will take off if the engines provide normal take-off thrust. Long answer. Start with no motion and no engine thrust. The situation is stable and nothing will move, ever. There is no problem. If, somehow, the initial conditions are such that the wheels are spinning and the belt moving such that the plane as a whole is stationary, then. in the absence of friction, that state will persist for ever. With friction, what happens depends on the inertia in the wheels /plane and the conveyor belt systems. Unless matched magically, I would expect some movement. Now begin again and start the engines. If there is no friction between the contact area of the tyres and the belt, the wheels will not rotate and just slide contradicting the conditions implied in the question. The plane will accelerate and take off. With friction, there will be a force in the backwards direction trying to rotate the wheel. This force must be supplied by the belt. As the plane accelerates, the wheel rotational speed has to increase so a force must persist. The belt system has to supply rotational energy to the wheel. Normally, the Earth does that. Now consider a very large wheel. If large enough, the contact area becomes almost indistinguishable from a caterpillar track in contact with the ground and with no relative motions. (Alternatively, zoom in on this area). The backwards velocity of the tyre at the contact patch relative to the hub exactly matches the forward velocity of the wheel hub, the plane velocity, So there is no problem. The belt does not need to move at all though it must be constrained. The Earth doesn't when a plane takes off (at least to an observer with poor sensors standing on the Earth).