How Do I convert my daughters bubble gun into a rechargeable toy?

i have a Bubble gun that take 3 AA batteries How can i convert it into a rechargeable one

i have   lithium batteries  and i also have a portable charger i can use for the conversion .

Its for my daughter and im trying to show her how "creative" iam 


new to this forum so i dont know what other info is needed ..Help

Picture of How Do I convert my daughters bubble gun into a rechargeable toy?
-max-10 days ago

The easiest solution would be to fit it with decent quality NiMh rechargeable cells, and perhaps modify the case to fit a NiMh charging circuit inside with a barrel jack connector in it.

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If you prefer lithium batteries, you need to be aware the cell voltage about 3 times that of the original alkaline battery chemistry.Your device appears to connect all 4 cells in series, so I think it requires a voltage range of 4V to 7V. 2 lithium cells in series should match that operational voltage. 14500 lithium cells are conveniently the same size as AA batteries, so drop 2 of those in on the lower slots. The remaining space can then be used to fit in a lithium charging module. You need one that supports charging multiple (2) series cells, and connect it such that it can ballence the cells during charging and disconnect the cells from the device when a safety mechanism (such as over-charge, over-discharge, over-temperature, etc.) is reached. Since only 2 of the 4 battery slots are populated, you can have the charging /safety cut off module intercept the connection between the end of the battery (the last spring it connects to) and the other end of the battery holder. Of course you will also want to again install a USB or barrel jack connector somewhere on the device.

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The hard part is really going to be sourcing a suitable charger. The majority of them appear to be designed only for charging a single cell, whereas you need one that has appropriate balancing capabilities for multicell configurations and appropriate safety cutoffs to prevent nasty accidents.

I am guessing you have some kind of lithium-ion (Li-ion) battery, since you say it is rechargeable, (in contrast to actual lithium batteries which are not), and you say you have a charger for it.

https://en.wikipedia.org/wiki/Lithium-ion_battery

Usually Li-ion cells are used with a protection circuit that disconnects the cell (or cells) from being discharged too much. In the case of the the 18650, a popular, cylinder shaped, Li-ion cell, that protection circuit is this tiny circle shaped circuit board, that fits on one end of the cell. I think the Wikipedia article I linked to above has a picture of this.

Regarding what Bwrussel commented about the necessity of matching the nominal voltage of your new battery stack, to the voltage of the battery stack this toy was intended to run on, well, you might wonder at how close this match has to be?

Do you want to match it to the nearest volt? The nearest 0.1 volts?

I claim the match does not have to be close, and you could probably err by like 25%, higher or lower, and still have it work. Although it is little more dangerous to err in the higher voltage direction, since this will naturally make the motor move faster, make the electronics dissipate more heat ( I remember seeing one of these toys that had blinking LEDs on it.)

In constrast, erring in the direction of lower voltage will tend to just make the motor slow down, maybe to the point where it stalls the motor, and nothing moves, but this condition usually does not risk burning things out, the way a too high voltage condition does.

As a consequence of this thinking, I think this toy, originally wanting a stack of 3 AA cells (3*1.5V = 4.5 V, nominal) , would work well with a lot of 5.0 volt power supplies. In particular I think 5.0 volt chargers intended for mobile phones would work well, or USB. I am guessing that this toy does not want more than about 1 ampere (1 A) of current.

Before you say, "But I want it to be portable," consider that there are portable 5.0 volt phone charger gizmos. These are called, "power bank", "emergency phone charger", and other names. Actually those are essentially the same thing, a "boost" type DC-to-DC converter that uses either 2 AA (2*1.5=3.0V nominal) batteries, or a single Li-ion cell (3.7 V nominal), on its input side, and gives regulated 5 volts on its output side.

I am naively guessing these phone charger gizmos will have enough power for your bubble blowing gun, but that is because I am guessing the bubble gun does not want more than about 1 A of current.

Note that this toy might also work well, with just a single Li-ion cell
as its input. The actual voltage output from a single Li-ion cell is
like 4.2 V, when fully charged, to around 3.2 V, when the protection
circuit disconnects it.

bwrussell17 days ago

You could just get rechargeable AAs. As long as the voltage matches you'll be fine.

You could use a Nokia 3.7V lithium battery and salvage the rest from a cheap USB charger for these batteries.
If I am not mistaken they are BLc-5.
Only a few bucks for the battery but go for genuine or OEM over fake high capacity models.
The cheap charger is nothing more than a battery holder with the charging electronics matched for a 5V supply.
Assuming the toy already has a power switch you can take the charger apart,
solder the battery directly to the corresponding connection of the charger and place it all inside the toy so you can make a hole for the USB cable.
If in doubt convert the power connection to a headphone socket and plug to safe on space.
Connect the power cable from the toy (from where they were connected on the original battery terminals) and solder them to the corresponding connection on the battery or better on the charger.
If you can then try to use the battery holder from the charger so you can avoid soldering directly on the battery.
If that is no option due to a lack of space in the toy then be very quick with the soldering to prevent damage ond overheating.