Combining 18650 Cells (3.6-4.2V) & KR-SC 1200 1.2V Screwdriver Cell for 9.6V RC Car Battery

Hello. I would like to connect the 18650 cells in series with the cells from the KR-SC 1200 1.2V screwdriver.
I want to make a battery for a RC car that would have 9.6V, I am going to connect in series two 18650 cells (3.6-4.2V) and one cell
kr-sc (1.2V) and here I wonder if during landing the voltage will be distributed evenly to all cells or to each other? I'm going to land this charger
12V 500mA with a connected Voltmeter so that I can disconnect the battery when it reaches 9 - 9.6V (I know that the cells do not reach max 4.2V anymore).
Will it work?


ps. NEW QUESTION - would a parallel connection of two cells with a voltage regulator be a good solution instead of playing with creating a 9.6V battery? I have an input voltage regulator from 3V output to 30V, max 3A, I could set the output voltage with a potentiometer to 9.6V but will it be any difference than the usual direct connection from the battery?
it seems simple enough to work properly.

It will not work, and in addition it creates a very high risk of explosion + fire, especially in the case of Li-Ion, which require a balancer or protection in series connection. On the other hand, potentially the first 1.2V cell would break due to the charging voltage being exceeded significantly.

From your post I can also see a misunderstanding of the topic of charging - you want to charge the cells to a voltage of 9.6V, which I understand as charging Li-ion cells to a voltage of 4.2V (fully charged), and cr-sc to a voltage of 1.2 (i.e. not charged).

You can probably charge Li-ion to 4.1V, NiCd to 1.4V, in total it will be 9.6V - just be careful that no cell is charged to a higher voltage than it should.

When connected in series, the voltage does not "break down", the voltage results from the charge level of the cells (or discharge - you should also be careful not to discharge any too deeply).

so you can combine them and land as one package or not?
ps. I'm going to use 18650 cells with a capacity of around 1500mAh and a NI-Cd with a capacity of 1200mAh
I know that when the cells are charged, they reach the right voltage, and what if the one is charged faster?

We only connect cells of the same type. In the case of non-compliance, or colloquially speaking - the parameters differ due to wear, production errors, etc. - the consequences are different. Depends on the power received from the battery. I have already cleaned up the remains of the starter batteries after the explosion several times. It was enough that individual cells from a lead battery had a different capacity. In what you describe, you want to use cells from different suppliers - and thus different parameters. A balancer alone is not enough - it is only a voltage maintenance regime while charging. The same current flows during consumption and charging, which may not have a negative impact on the entire set of cells, but may also accelerate the wear of one of them or lead to heating up and, consequently, to a fire. If you want to experiment, I suggest you take apart everything about the cell and charge and unload it for a test. If all the cells have the same parameters, you can connect them into one battery.

Ture11 wrote:

It will not work, and in addition it creates a very high risk of explosion + fire, especially in the case of Li-Ion, which require a balancer or protection in series connection. On the other hand, potentially the first 1.2V cell would break due to the charging voltage being exceeded significantly.

From your post I can also see a misunderstanding of the topic of charging - you want to charge the cells to a voltage of 9.6V, which I understand as charging Li-ion cells to a voltage of 4.2V (fully charged), and cr-sc to a voltage of 1.2 (i.e. not charged).

As for the topic of charging, I know that my cells are not as efficient as new and they do not charge to 4.2V only up to about 4.1V, and as for the cell
ni-cd, I only know that it has a voltage of 1.2V, but I do not know if it is a constant voltage, or it changes when discharging or charging (in the battery from the screwdriver I had 9 such and gave 18V when it was charged)
Added after 11 [minutes]:

Nominal voltages: NiCd 1.2V (more precisely, 1.25V), Li-ion 3.7V; NiCd charges to 1.46V, 4.1V-4.2V Li-ion; 18V from 9 NiCd cells does not come out in any way.

_jta_ wrote:

Nominal voltages: NiCd 1.2V (more precisely, 1.25V), Li-ion 3.7V; NiCd charges to 1.46V, 4.1V-4.2V Li-ion; 18V from 9 NiCd cells does not come out in any way.

sorry, i got something wrong, there were 15 of them, not 9.


What if I used a step up converter and did 9.6V with 3.7V, will it work properly?
if someone had time to explain to me which solution is better, serial connection of cells or use of an inverter, what are the pros and cons of both solutions?

If you connect Li-ion and NiCd in series, you will have a problem with the difference in charge efficiency (Li-ion have a larger one) and the difference in self-discharge rate (NiCd discharge faster) - so you would have to recharge NiCd additionally.

There are no such problems with the inverter, but of course the amount of stored energy is less. And you have to make this converter. Besides, there is a dilemma: should it be constantly on (and use energy), or should it be turned on when it is needed?

_jta_ wrote:

If you connect Li-ion and NiCd in series, you will have a problem with the difference in charge efficiency (Li-ion have a larger one) and the difference in self-discharge rate (NiCd discharge faster) - so you would have to recharge NiCd additionally.

There are no such problems with the inverter, but of course the amount of stored energy is less. And you have to make this converter. Besides, there is a dilemma: should it be constantly on (and use energy), or should it be turned on when it is needed?

in total, the amount of energy would increase because I would connect identical 18650 cells in parallel and connect them to the converter, I guess I think wrong? I have voltage converters: nap. input from 3-28V voltage out from 4-30V max 3A.
I think it would be most sensible to connect it behind the switch so that the voltage comes when I turn on the car.
Tomorrow a courier will come to me with a car, I will check how much A is taking in the maximum and if it does not exceed 3A, I will install the system with the converter.

Since it popped up in the search engine, I will add 3 cents:
I would not be so attached to the tension of the original package. Electronics rather has its own voltage regulator, and the motor does not care how much voltage it gets, as long as it is able to give off heat, anyway, the transistors will not let go of any current. In the car originally powered by a 4.8V package (4 x NiMh 1.2V) I threw two 18650 cells in series and it runs, of course, clearly faster than on one (well, some plastic gears ate ).
If the 9.6V package was made of 8 NiMh cells, it means that the electronics must be resistant to 8x1.46V, i.e. almost 12V must withstand, and 3xLiXX is max 3x4.2, i.e. 12.6V.

I will give the author the basics:
1. Batteries, just like disposable cells, have some kind of voltage that drops when discharged. For nickel-cadmium batteries and dry cells (primary, disposable), the minimum voltage is 0.9V with a 20-hour discharge. When discharging with a higher current, the voltage is approx. 1V. A fully charged battery is usually 1.45V and a new primary cell is even 1.6V.
Lithium-ion batteries have a voltage range of 4.2V (fully charged) to 3V (discharged).
2. When connecting cells into batteries in series, the capacity of the cells and, possibly, the internal resistance are important. The current flowing through such a battery is the same for each battery and if a colleague puts in a less capacious one, it will discharge quickly, its voltage will drop below the minimum and if the discharge is not interrupted, the battery may change its polarity (the plus pole will change to the minus pole) ).
3. If the batteries are connected in parallel, their capacity is added up. You can connect two batteries in parallel and connect several such batteries in series, as it is (or was) in laptop batteries.
Following the last entry - the most convenient way for my colleague will be to use the same batteries to build the battery and accept a slightly different voltage. The converter will only introduce unnecessary losses, which will contribute to the colleague's excessive emission of carbon dioxide (we still have electricity from hard coal-fired power plants, not gas or lignite). You should also save every watt (or new watt) of power and not warm the climate with a hot converter and carbon dioxide from the Bełchatów or Ostrołęka heat and power plants.