Hello, I have a question: RC car has a lion battery. Why can't the ordinary 7.5

[david smth]

Hello, I have a question: RC car has a lion battery. Why can't the ordinary 7.5 volt charger charge it, but the adjustable adapter can?

[david smth]

I tried it today, I wanted to charge the lion battery, I wanted to charge it with the 7.5 volt charging adapter, but it definitely does not charge, but I can charge it with the adjustable adapter.

[IanB]

We don't have extrasensory perception. We don't have any magical ability to see what you have not told us. How can we possibly answer a question with a lack of relevant information provided?

Hint: What is the make/model of RC car? What is the "adjustable adapter" you speak of? What does it look like? What does it say on it? What brand is it?

[david smth]

I sent it above, sorry, this is my last question, I am not permanent in your form, I will not open a topic here again.

[jzx]

If the adjustable adapter is what is in the picture, these adapters are not regulated (almost sure, of course I have not seen the internals of yours, but I have seen many not regulated adapters with this appearence). Often they give more voltage than marked, specially if the load is low (easily 25% or more excess).
If the other adapter is regulated and gives exactly 7.5, this can be important, as some devices with a 7.4 volt battery (2 cells) can need some extra voltage to work (7.8 to 9V, thats depend on device), due to the circuitry in the car, (in your case). You have to check what is the nominal voltage needed by the car, an check also the output voltages of adapters, probably 7.5 volst is too near the limit.

Be very careful with these adjustable adapters, is very easy to give your device an overvoltage or inverse polarity. If I use them, I cover the switches with tape to block their position.

We need more details to find the problem.

[tooki]

I sent it above, sorry, this is my last question, I am not permanent in your form, I will not open a topic here again.

You can ask as many questions as you want, but to get answers, they need to be well-formed questions!

We cannot answer questions that don't contain anywhere near enough information. (I don't mean "can't" in the sense of "we could but choose not to", I mean "it is literally impossible for us to do so".)

You need to provide all the basic info like the model numbers of every part involved, what you tried, what you expected to happen, and what happened instead. List all troubleshooting steps you did.

[tooki]

If the adjustable adapter is what is in the picture, these adapters are not regulated (almost sure, of course I have not seen the internals of yours, but I have seen many not regulated adapters with this appearence). Often they give more voltage than marked, specially if the load is low (easily 25% or more excess).
If the other adapter is regulated and gives exactly 7.5, this can be important, as some devices with a 7.4 volt battery (2 cells) can need some extra voltage to work (7.8 to 9V, thats depend on device), due to the circuitry in the car, (in your case). You have to check what is the nominal voltage needed by the car, an check also the output voltages of adapters, probably 7.5 volst is too near the limit.

Be very careful with these adjustable adapters, is very easy to give your device an overvoltage or inverse polarity. If I use them, I cover the switches with tape to block their position.

We need more details to find the problem.

Plenty of those are regulated, especially newer ones that are SMPSs. I've definitely seen old transformer-based ones that weren't (both adjustable and fixed-voltage!).

[BeBuLamar]

A 2 cell Li-Ion battery pack would need 8.4V to charge and some form of current limiting.

[pcprogrammer]

To answer the question of the original post it depends on the type of lithium ion battery in the car.

If it is a two cell having a maximum voltage of 8.4V when fully charged it is clear that a 7.5V adapter won't be able to charge it.

But a big warning here: Do not charge a lithium ion battery with a basic adapter of any kind!

A proper charger for a lithium ion battery uses a constant current / constant voltage setup and when more then one cell is in play it needs taking care of balancing.

Lithium ion batteries are dangerous and can explode or burst into flames that are difficult to extinguish. Easily caused by overcharging with the wrong kind of charger.

For a single cell the nominal voltage is 3.7V. The max voltage is 4.2V. The minimum voltage is about 2.5V. If you drain a lithium ion battery below this you risk it to become dead. Charge current depends on the cell specifications. A proper charger also monitors the battery temperature to make sure it does not go over the rated values.

Hopefully this gives you enough information to be careful with what you try to charge the battery in the future.

For a better answer provide us with the make and model of the RC car, the battery used, how you connect the power supply to charge the battery, etc. Pictures say much more than many written word and we do like pictures, so post some to please us and get a better answer.

[pcprogrammer]

If the adjustable adapter is what is in the picture, these adapters are not regulated (almost sure, of course I have not seen the internals of yours, but I have seen many not regulated adapters with this appearence). Often they give more voltage than marked, specially if the load is low (easily 25% or more excess).
If the other adapter is regulated and gives exactly 7.5, this can be important, as some devices with a 7.4 volt battery (2 cells) can need some extra voltage to work (7.8 to 9V, thats depend on device), due to the circuitry in the car, (in your case). You have to check what is the nominal voltage needed by the car, an check also the output voltages of adapters, probably 7.5 volst is too near the limit.

Be very careful with these adjustable adapters, is very easy to give your device an overvoltage or inverse polarity. If I use them, I cover the switches with tape to block their position.

We need more details to find the problem.

Plenty of those are regulated, especially newer ones that are SMPSs. I've definitely seen old transformer-based ones that weren't (both adjustable and fixed-voltage!).

No doubt in my mind that the one in the picture is transformer based and not regulated. Just a bunch of taps on the transformer and a diode or bridge rectifier and a capacitor. I have a couple of these lying around.

[janoc]

No doubt in my mind that the one in the picture is transformer based and not regulated. Just a bunch of taps on the transformer and a diode or bridge rectifier and a capacitor. I have a couple of these lying around.

Maybe look better at the picture? It says 110/220V AC. That is extremely unlikely to be transformer based because it would need a tap on the primary + switch to change the voltage. 500mA linear supply would be also about twice the size of this (or the 500mA is wishful thinking). I have an old 1A linear adapter like this and the thing weighs over a kilogram because of the size of the trafo inside.

That's a cheap SMPS adapter. Says nothing about how well regulated it is - given the complete absence of any regulatory markings, it is most likely a piece of crap if not outright a deathtrap because of very poor insulation between the primary & secondary.

[david smth]

I disassembled the inside to help you, please examine it sir.

[david smth]

this scheme

[IanB]

Goodness heavens, no! That's not what we asked for.

We asked for the make and model of the car, and maybe a picture of it. We didn't ask you to take it apart.

We asked, for example, how the car is normally charged? Did it come with a power supply from the manufacturer? What did that power supply look like, and what is written on it? Does it plug into the car to charge it somehow?

Are you trying to replace the original charging supply with another one?

Can you please tell us the story?

[david smth]

Sir, I do not understand your language. My question is very clear. There is an RC car that works at 7.5 volts. What is important here is not how many volts the RC car is, but how many volts the battery is charged. It needs 7.5 volts, the battery itself, this question is a simple problem, there is no need to discuss it, after all, it charges the battery, I took the adapter back. This is the adapter itself in the same picture

[IanB]

Sir, I do not understand your language. My question is very clear. There is an RC car that works at 7.5 volts. What is important here is not how many volts the RC car is, but how many volts the battery is charged. It needs 7.5 volts, the battery itself, this question is a simple problem, there is no need to discuss it, after all, it charges the battery, I took the adapter back. This is the adapter itself in the same picture

And we are telling you this is not true.

You have an RC car with a battery inside it. Batteries have to be charged. Battery charging requires a special charging circuit. Perhaps the charger is built into the car. Perhaps it is not.

What the car looks like from the outside might help to answer that question. What is written on the car, what make and model it is might help to answer that question.

If you buy an RC car as a new product, it will probably come with a charger in the box. That charger might be special. It might not be an ordinary 7.5 V power adapter. Showing us the original charger (if you have it) might help to answer that question.

Since we are not helping you to understand these things, it will be very difficult to answer any of your questions.

[david smth]

If the adjustable adapter is what is in the picture, these adapters are not regulated (almost sure, of course I have not seen the internals of yours, but I have seen many not regulated adapters with this appearence). Often they give more voltage than marked, specially if the load is low (easily 25% or more excess).
If the other adapter is regulated and gives exactly 7.5, this can be important, as some devices with a 7.4 volt battery (2 cells) can need some extra voltage to work (7.8 to 9V, thats depend on device), due to the circuitry in the car, (in your case). You have to check what is the nominal voltage needed by the car, an check also the output voltages of adapters, probably 7.5 volst is too near the limit.

Be very careful with these adjustable adapters, is very easy to give your device an overvoltage or inverse polarity. If I use them, I cover the switches with tape to block their position.

We need more details to find the problem.

This explains everything, this is the answer

[david smth]

It works on DC current and definitely does not work on AC. These adapters have ac-dc switching.

[pcprogrammer]

No doubt in my mind that the one in the picture is transformer based and not regulated. Just a bunch of taps on the transformer and a diode or bridge rectifier and a capacitor. I have a couple of these lying around.

Maybe look better at the picture? It says 110/220V AC. That is extremely unlikely to be transformer based because it would need a tap on the primary + switch to change the voltage. 500mA linear supply would be also about twice the size of this (or the 500mA is wishful thinking). I have an old 1A linear adapter like this and the thing weighs over a kilogram because of the size of the trafo inside.

That's a cheap SMPS adapter. Says nothing about how well regulated it is - given the complete absence of any regulatory markings, it is most likely a piece of crap if not outright a deathtrap because of very poor insulation between the primary & secondary.

Well take a look at the pictures the OP provided and guess again. 

Edit: I did not notice the 110/220V statement on the supply, but this is not what usually is used on SMPS adapters. Most of them will specify a range of voltages it can work with.

[pcprogrammer]

I disassembled the inside to help you, please examine it sir.

Are you sure these are lithium ion batteries?

Looks like they have been hot quite a bit. Can't tell if there is any protection circuitry often found on lithium ion batteries.

If these are NiCad or NiMH batteries it will be a different story.

[dietert1]

The battery pack in the image seems to have 5 cells. Each lithium battery cell needs about 4 V from the charger, so 20 V in total. It cannot be charged by a 7.5 V supply. Maybe the adjustable supply can reach 20 V.
A 20 V lithium pack can work in the RC car, if that model includes a step-down convertor for 7.5 V.

If the nominal battery voltage were 7.5 V then the battery pack would be NiMH instead. Each NiMH cell needs about 1.5 V from the charger, so 7.5 V in total. Both chargers would work.

Regards, Dieter

[jzx]

A 2 cell Li-Ion battery pack would need 8.4V to charge and some form of current limiting.

Yes, I have done a mistake with the numbers, taking 3.7 V instead of 4.2, but I assumed that the car has some charging circuit, as the phones are charged with usb 5V, therefore you need a bit more voltage. But 7.5 V for 1 cell seems too much.

[jzx]

Do you connect the charger directly to the battery pack, or to the car with the battery into the car?

Have you tested if your 7.5 V fixed adapter is working? (with a dmm and a dummy load)

[tooki]

Sir, I do not understand your language. My question is very clear. There is an RC car that works at 7.5 volts. What is important here is not how many volts the RC car is, but how many volts the battery is charged. It needs 7.5 volts, the battery itself, this question is a simple problem, there is no need to discuss it, after all, it charges the battery, I took the adapter back. This is the adapter itself in the same picture

Your understanding of the topic is certainly not sufficient for you to be telling us what is and isn’t important!

And indeed, your refusal to give the information that actually matters is hindering us from helping. Your judgment on what is and is not important is poor. So give us what we ask for, not what you think we should have.

I also agree that those do not look like LiIon batteries..

[BeBuLamar]

Sir, I do not understand your language. My question is very clear. There is an RC car that works at 7.5 volts. What is important here is not how many volts the RC car is, but how many volts the battery is charged. It needs 7.5 volts, the battery itself, this question is a simple problem, there is no need to discuss it, after all, it charges the battery, I took the adapter back. This is the adapter itself in the same picture

I am quite sure that if you take a voltmeter and measure the voltage of your battery it's not 7.5V.