Hello, I have a question: RC car has a lion battery. Why can't the ordinary 7.5  - Page 1
Forum section: electronics / beginners

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 04:53:33 pm
content: 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?

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 04:58:09 pm
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: September 04, 2024, 05:07:51 pm
content: 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?

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 05:28:29 pm
content: 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.

author: jzx
author_rank: Regular Contributor
timestamp: September 04, 2024, 06:10:48 pm
content: 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.

author: tooki
author_rank: Super Contributor
timestamp: September 04, 2024, 06:17:48 pm
content: Quote from: david smth on September 04, 2024, 05:28:29 pmYou 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.

author: tooki
author_rank: Super Contributor
timestamp: September 04, 2024, 06:19:30 pm
content: Quote from: jzx on September 04, 2024, 06:10:48 pmPlenty 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!).

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 04, 2024, 06:39:25 pm
content: A 2 cell Li-Ion battery pack would need 8.4V to charge and some form of current limiting.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 04, 2024, 06:39:51 pm
content: 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.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 04, 2024, 06:42:35 pm
content: Quote from: tooki on September 04, 2024, 06:19:30 pmNo 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.

author: janoc
author_rank: Super Contributor
timestamp: September 04, 2024, 06:55:09 pm
content: Quote from: pcprogrammer on September 04, 2024, 06:42:35 pmMaybe 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.

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 07:24:42 pm
content: I disassembled the inside to help you, please examine it sir.

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 07:25:35 pm
content: this scheme

author: IanB
author_rank: Super Contributor
timestamp: September 04, 2024, 07:39:57 pm
content: 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?

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 07:45:06 pm
content: 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

author: IanB
author_rank: Super Contributor
timestamp: September 04, 2024, 07:53:47 pm
content: Quote from: david smth on September 04, 2024, 07:45:06 pmAnd 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.

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 08:05:05 pm
content: Quote from: jzx on September 04, 2024, 06:10:48 pmThis explains everything, this is the answer

author: david smth
author_rank: Contributor
timestamp: September 04, 2024, 08:19:43 pm
content: It works on DC current and definitely does not work on AC. These adapters have ac-dc switching.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 05, 2024, 05:50:05 am
content: Quote from: janoc on September 04, 2024, 06:55:09 pmWell 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.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 05, 2024, 06:01:51 am
content: Quote from: david smth on September 04, 2024, 07:24:42 pmAre 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.

author: dietert1
author_rank: Super Contributor
timestamp: September 05, 2024, 06:18:21 am
content: 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

author: jzx
author_rank: Regular Contributor
timestamp: September 05, 2024, 11:42:25 am
content: Quote from: BeBuLamar on September 04, 2024, 06:39:25 pmYes, 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.

author: jzx
author_rank: Regular Contributor
timestamp: September 05, 2024, 11:50:36 am
content: 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)

author: tooki
author_rank: Super Contributor
timestamp: September 05, 2024, 12:30:55 pm
content: Quote from: david smth on September 04, 2024, 07:45:06 pmYour 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 thatactuallymatters 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..

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 05, 2024, 02:13:22 pm
content: Quote from: david smth on September 04, 2024, 07:45:06 pmI am quite sure that if you take a voltmeter and measure the voltage of your battery it's not 7.5V.

author: jzx
author_rank: Regular Contributor
timestamp: September 05, 2024, 02:43:31 pm
content: Quote from: david smth on September 04, 2024, 07:45:06 pmSome batteries can be charged with a fixed voltage (lead or lithium), others with a constant current (NiCd, Nimh), but always there is some "protocol of charge" (start chaging with x current or voltage, later continue in another mode, cut current when something occurs..) that charges better the battery (faster and with less probabilty of damage the battery). So normally no battery is charged connecting directly to a power supply, but through a special circuit, the charger. Many people call "charger" to any adapter, but they are not the same.There is no battery that can be charged with 7.5 V, if you use lead, you need 2.4 volt per cell, if you use liion, 4.2, so 7.5 V is not adecuate. Also, be very carefull with liion,they do not tolerate any overvoltage, the voltage has to be very precise. Other batteries normally fail without too much viloence, but liion explode easily.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 05, 2024, 06:05:24 pm
content: Good Morning David, I agree with others that your battery pack is not Lithium. It 'looks'like it is comprised of 6 cells. Nimh cells are 1.2 VDC, so that would give your pack a 'NOMINAL' voltage of 7.2 VDC. The word nominal is important in battery descriptions.

author: tooki
author_rank: Super Contributor
timestamp: September 05, 2024, 06:31:32 pm
content: Quote from: jzx on September 05, 2024, 02:43:31 pmLithium-ion batteries require CC/CV charging, with most of the charging done at constant current until the maximum voltage, then a constant voltage phase to finish charging.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 05, 2024, 06:40:21 pm
content: Quote from: jzx on September 05, 2024, 02:43:31 pmPlease don't tell porkies.A lithium ion battery can not be charged with a fixed voltage, there has to be current limiting. Why because the internal resistance of a very good lithium ion battery is ultra low and when empty the voltage is maybe 3.2V or less. When you then attach a fixed voltage of say 4.2V to the battery the current will go up to as much as the supply will give and the cables can handle. 1V / 0.05 Ohm means 20A, but the resistance can be much lower. At the moment I'm using Sony VTC4 batteries which have a Ri of ~12.5 milli Ohm. 1V / 0.0125 Ohm means 80A. The battery is rated for 1C charge current which in this case is only 2A.So you start with a constant current until the voltage reaches 4.2V. Then you switch over to constant voltage and stop charging when the current is less then 10% of the start of charging current. That is why you need a good charger for a lithium ion battery.Ah, tooki was faster with typing then me.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 05, 2024, 06:44:07 pm
content: Quote from: BILLPOD on September 05, 2024, 06:05:24 pmIf you count the buds of the batteries you will see only 5. So 6V is more likely. But I do not see a wire going to the bottom of the pack, so it is a bit of a guess on how the pack is made up.Edit: they are also a bit weird with the indents in the middle of the battery. As if they stitched two together some how.

author: david smth
author_rank: Contributor
timestamp: September 05, 2024, 07:11:16 pm
content: Sir, please allow me to explain, there are 10 cells in total and only two of them are connected.

author: david smth
author_rank: Contributor
timestamp: September 05, 2024, 07:29:38 pm
content: Quote from: BILLPOD on September 05, 2024, 06:05:24 pmThere is no writing on it. So far, I have charged it with an adjustable adapter. Even though it is 7.5 volts and 12 volts, it will definitely not harm the battery. I tried it at least a few times and it did not harm the battery.

author: david smth
author_rank: Contributor
timestamp: September 05, 2024, 08:25:32 pm
content: I'm as skeptical as the people here since this battery is not lithium, so I bought it from the store but they didn't say anything, it will require a special charger for the lithium battery. The page only says lithium, I have no knowledge, I don't want to waste people's time here, what are the good and bad aspects of lithium and Ni CD? Are these dangerous? Charges between 7.5, 9 and 12 volts, 12 volts charges quickly

author: david smth
author_rank: Contributor
timestamp: September 05, 2024, 08:27:52 pm
content: Interesting page says lithium, this seems like a scam

author: IanB
author_rank: Super Contributor
timestamp: September 05, 2024, 08:33:39 pm
content: It really would help if you could tell us more about the battery, what packaging it came with, how it was described by the seller, anything like that?Typically, a removable battery for an RC car or plane would have a special RC charger, it would not just be charged with a simple power adapter.

author: tunk
author_rank: Super Contributor
timestamp: September 05, 2024, 08:58:10 pm
content: What's the size of the battery pack and the individual cells?If the cells are 18x65mm (diameter x length), most likely they're Li-ion.If they're 14x50mm, then most likely NiMh (though they could be Li-ion).Edit: Even if they don't look like they're harmed, they could still be damaged.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 05, 2024, 09:46:09 pm
content: Quote from: david smth on September 05, 2024, 08:25:32 pmIf it's NiCad or NiMH it would be more difficult to charge than Li-Ion.

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 05:48:40 am
content: this charging adapter

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 05:51:18 am
content: It usually charges at 7.5 volts and 9 volts, the adjustable adapter charges faster than the original adapter.

author: Gyro
author_rank: Super Contributor
timestamp: September 06, 2024, 08:20:47 am
content: Quote from: david smth on September 06, 2024, 05:51:18 amHow are you deciding when the battery is fully charged? I don't see any indicators. This is a very important question if theyareLithium cells.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 06, 2024, 01:33:33 pm
content: The adjustable adapter is capable of 500mA and the fixed voltage adapter is capable of only 250mA. If the battery is Li-Ion it can be charge with higher current than those and the 500mA would charge faster.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 06, 2024, 01:44:53 pm
content: To get things more clear the question is if the OP has a multi meter to measure the voltages on the battery pack, but more importantly the voltages of the individual cells, at least for as far as possible.A better picture of the connections on the battery pack, preferably with the insulation removed, would help a lot in determining what is wise in this case.A picture of the inside of the original adapter would also provide a lot of information.Based on what I have seen so far, the original adapter connects to the battery pack directly with the same type of (Molex ?) connector. The connector looks a bit like what is used for PC mother board power supply, but with only two pins.

author: tooki
author_rank: Super Contributor
timestamp: September 06, 2024, 02:18:13 pm
content: Quote from: IanB on September 05, 2024, 08:33:39 pmIt’s clear that OP is intent on not answering any questions, since he’s already certain he knows better…

author: CaptDon
author_rank: Super Contributor
timestamp: September 06, 2024, 03:41:16 pm
content: Reading through the O.P. who is trying to educate the teachers.....His 7.5 adapter does seem to charge but slowly. Now look at the stupidity of his next statements, "It charges faster at 9 volts and even faster at 12 volts". Fortunately for him, that feeble piece of shit 'adjustable adapter' is only capable of a current limited by the core size of the transformer, otherwise he would have blown the battery pack apart by now. We can only guess how the pack is wired since we can't really see the cell to cell connections. Could be 7.2 nominal NiMH or 7.6 nominal Lithium Ion, doesn't really matter when you are improperly charging in the first place. Either of the battery styles I mentioned would charge from 9 volts or 12 volts provided by a craptastic P.O.S. variable supply. Either type of battery would also charge very poorly from 7.5 volts as the O.P. observed. Surely if he was stupid enough to set the charger on 12vdc and leave the battery charging for several days the absolute outcome would be a destroyed battery, possible fire/explosion or a burned out 'adjustable adapter'!!! Go ahead, try it and see!!! To the O.P., do you think anyone could even guess as to how the cells are wired when showing us a picture of a multi-cell battery that still has the shrink wrap surrounding the cells? IF it is lithium ion my guess from looks is 5 parallel pairs of cells needing a minimum of 8.4 volts to charge and also an EXTREME fire explosion hazard with that many parallel cells should any one cell short do to the ignorant un-certified way you are charging them. Ignorance is bliss!!!

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 04:09:58 pm
content: Is this stupid? The photo you sent has a high IQ. I will send you a video. It doesn't matter if it's 7, 12 or 9 volts. Buy any charger. These batteries will definitely not charge. If it happens, I'll give you 100,000 thousand dollars.I'm giving you this battery as a gift. Buy it and charge it. If it works, I'll admit I'm stupid.

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 04:13:25 pm
content: It only charges with a regulated adapter. I tried with many adapters but it didn't work. I don't train anyone, I'm not a teacher.

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 04:20:22 pm
content: I left it charging for 2 days but it didn't explode. What do you think about it? Well, I charge it every day. I will send it to you as a gift. You can try it with your friend in the picture. Please don't tell me the result.

author: valcher
author_rank: Contributor
timestamp: September 06, 2024, 04:55:40 pm
content: Judging by the photo provided, these are ten AAA NiMh (NiCd) batteries connected in parallel and series to form a 6.0 volt battery. I dare to assume that this is a Chinese car model, which should indeed be equipped with a 7.4 volt Lion battery. But for some reason, the manufacturer equipped them with a different type of battery, and did not display this in the description.Sorry for the English.

author: david smth
author_rank: Contributor
timestamp: September 06, 2024, 07:07:20 pm
content: How do you know these? Thank you for the correct answer.

author: tooki
author_rank: Super Contributor
timestamp: September 06, 2024, 07:36:43 pm
content: Quote from: david smth on September 06, 2024, 07:07:20 pmLike everyone else here he is guessing, since you stubbornly refuse to provide basic information that has been requested repeatedly.