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At around £40 for two of these "5Ah" Ryobi compatible batteries I was expecting them to be fairly low capacity. In reality they're pretty close to the claimed capacity (80%) but the circuitry they use for monitoring the cell voltage is unusual, and doesn't give me confidence in leaving them charging unattended.
In the video I mentioned the potential for the 100 ohm balancing resistors to have a higher voltage across them at full charge current. Theoretically the current would need to drop to around 40mA for the resistors to safely pass the current without the risk of the cell being charged above 4.2V.
Although the cell balancing seems like a good feature, I'd have been a lot more comfortable with these batteries if they had used the simpler single chip unbalanced management chip as used in the cheaper tools. It would decisively detect any cell reaching full capacity and cut the charging current off.
The way the circuitry senses the voltage across the pack gave me doubts about its ability to detect a single cell going into the bypass mode. Maybe I'm just being pessimistic, but there is a lot of weird circuitry involved. All the divider resistors are critical values and even the tiniest manufacturing defect of a missing or incorrect resistor value could have significant consequences.
I spent a HUGE amount of time trying to get my head around the way the circuitry worked. To properly reverse engineer the circuit would require large images, removal of components and lots of time.
On a plus note they seem to have a decent cluster of 18650 cells. The temptation is to reconfigure them as a large parallel group as a chunky 20,00mAh power bank.
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Uh ryobi style battery, i say ryobi style, it's not actually a ryobi, it's a clone yeah. This one goes onto the name, bizway 18 volt and it claims to be five amp hour. I can already tell you it's four ampere, because i've opened one already and whipped all the bits out of it and uh done some tests. So let me show you how this opens.

You've got four screws around the case here and then one screw in the end. Technically speaking, depending on what you want to do, if you just want to explore it, you don't need to take the screw the end out, but i'd kind of recommend it as you'll see and i've analyzed the circuitry in this and uh. I've analyzed it for something. Like five hours and it's it's not really inspiring with confidence, it's made me wonder: is this thing actually safe to leave plugged in it's charge? Balancing well i'll, show you the circuitry in a moment so uh.

Now i've done that uh, you kind of have to get a spudger and slip it in here. So you have to take the screws out far enough and then kind of pop it like that and also slide it and pop it like that, and it should hopefully come out noting that uh as you take it out, just be careful, maybe take the screws. All the way out would help as well. Oh no see that's! That's me.

Rushing too much there just be careful as you take it out, because it's quite a beefy battery pack inside it's worth actually getting off the batteries. Perhaps, and this floppy thing on top right. Let me just lift this out to show you the batteries it has fairly classic for these type products. It's got two amp power cells, not all of those two amp power cells, but this one does and initially i was expecting this to be minimalist circuitry.

But it's not it's very complicated circuitry and there's this little chip here and the number has been. Let me just zoom down this. The number has been abraded off, not just scrubbed off, but they've actually machined the number off it. It has repetitive circuitry all the way around.

It will tell you what i can show you in this one. It does make more sense. It has a thermistor in the back that goes down onto the cells with a little bit of a silicone shmoo, and the circuit board is covered in these little six-pin chips are actually for balancing the cell. I thought they were going to be used for sensing when it was charged as well, but they're not there's some very odd circuitry.

Each cell has a little balancing circuit with a 100 ohm resistor, and then it's got a couple of extra transistors that do some really weird stuff. Now there are three connections on the top turret here and if i tilt this up well, you can. I can just leave it tilted down. I can shoot it, you'll be able to see the leds.

If i click the button, the leds light, you can see them if i also just happen to get a resistor of a value of approximately 10k uh and if you i'll clip it on here to the middle contact and i'll just shield, the leds that that didn't Work i'll shield, the leds - this is not working, because it's very very springy. I shall show the leds now. She'll dab this here and you'll see the leds wake and it goes into sort of charging mode because it thinks it's charging, and this is probably because in the early days the ryobi packs used to charge via the middle contact, the nikon ones. And there was a thermal switch so when it got to temperature, it would basically cut off on that and break the circuit and it wouldn't take any more charge.

In this case, i don't think they're putting charge. I think this is purely used as a signal down to the circuit board and then this extra contact and that sticks out the case here is actually being used as a signal back from the microcontroller here to the actual charger to tell it possibly the charge status And how much current it should be charging with, i think it may switch down to trichomona. I hope it does given some of the circuitry here. That is about it.

Oh, actually, it's not two mosfets two identical mosfets, quite beefy ones, specifically intended for power tools like this strong ir fat. Well, assuming it is international rectifier, uh super low on state resistance of just 1.5 to 2 milliohms and uh rated for the silicon rated for 250 amps or 195 amp in the package. So quite beefy things. There are two of them as i'll show you in the circuitry.

It's a this ability to charge and the ability to discharge, because the charge does appear to come from the two hours outer contacts. Now anything else worth mentioning. There's the shmoo for thermistor right, tell you what let's go straight into the drawing? Actually, i'm going to have to grab the drawing one moment. Please, and here is the drawing the back of the circuit board and the front of the circuit board.

Uh, i could say: do you want to try reverse engineering it because uh, it's not going to be easy because the the tracks literally they're just popping backwards and forwards all the time in this. It's one of those designs, so i'll actually zoom up in this bit. The main thing in the back is the we've got fairly heavy sort of bus bars. If you will, but the actual the connections.

The battery connections just go straight to the end of the batteries. They don't rely on the circuit board too much. So let me just uh zoom up on the bottom bit here, nudge back a little tiny bit. What we have is the scrubbed off microcontroller.

We have a power supply for the microcontroller, which is based on the positive supply from the battery uh, coming via a little twin diode package via a resistor, for i suppose of filtering, and also to take the stress of the regulator. Little five volt regulator. There's a capacitor here for the uh, this of 18 volt side, and then it provides five volts, this little smoothing capacitor to the circuitry. Here these little six pin chips.

Let me see if i can grab the data sheet. They are haikon technology hy2213 and you basically each one of these chips sits across the cell. So all the cells are in series in this and these chips are direct mount across them, they're, actually just three connections and they control it all mosfet and when the voltage they monitor the voltage with some filtering components and when it reaches the desired voltage. It turns on a transistor which adds a resistor in parallel, so that the it basically bypasses current past the cell.

The downside is, these are 100 ohm resistors and, if you think of it, if it kept charging at 500 milliamps, if it didn't cut off and those things came on, then v equals i times r. So that's voltage across the resistor and therefore the cell equals 0.5 uh, say that's the half an amp charging times the 100 ohms there's about 50 volts across those resistors you'd get yeah, so it must drop down to a lower trickle current. They just equalize it to degree, i'm not really sure it seems odd. It's not what i was expecting.

There's little contact and uh. The microcontroller can receive a signal from that middle pin the wire goes onto here and it goes via some level shifter circuitry. So it just gives a nice logic level signal and likewise it can send a voltage back and actually pull this pin down to the zero volt rail. That's of negative, that the common to the common battery - and it does so via two resistors 5.1 k and 20k.

So it can actually indicate various things back to the battery and i suppose it might also indicate just by that resistance that it is the correct type of battery or there might be some former communication, i'm not sure. Maybe some pulsing, i'm not sure about that. But across each cell, we've got that uh little voltage center chip for the balancing that lets the current bypass cells, so that others can keep charging until they're full as well, but there's also this very odd little double transistor arrangement with resistive dividers. So if i show you what i've doodled down so far, i shall zoom back out so this can fit in because i did it long ways just because that was the best way to do it.

I've abbreviated it to just two cells instead of the five. What we have here is the positive battery connection and the negative going out to the tool and they've got the back emf diodes across them. That's those two diodes i'll just show them in the circuit board. That's these two diodes here they're in parallel and all they do is there's any.

If there's any nasty spikes voltage, spikes it'll actually clamp them uh to actually protect the mosfets. There are the uh over charge. Well, not the overcharge. There's the balancing circuits that, if there's a small current going through when it reaches about 4.2 volts at these little hy2213 devices, they measure the voltage across each cell via 100 ohm resistor and 100 nanofarad capacitor, that's just to provide a basic filter.

So they get a nice steady voltage level when it reaches the designated about 4.2 volts. They turn on the little external mosfet. The mosfet puts that resistor across which then helps. If the current is at a below the level at which that can handle uh it can it, then i will bypass it via that resistor and it will let the other cells just gradually come up, but i'd expect only about 10 or 20 milliamps or so at That point the double mosfet at the end, it's interesting that they've got a little bus bar across the tabs and the middle pins are not connected.

So those are the drains that are coming together. That's normal operation, they're using two mosfets in series. The reason they're doing that is that one most feature in one way: one is around the other and it's to avoid it, so they can actually control. They can shut off charge and discharge, but because most fets have that accidental diode as part just the way they're built, there's effectively a diode in parallel with the source and drain.

Because of that, if they just had one mosfet, it would only be able to block current in one direction, so they have to put two in a different direction, and it just so happens that you know a mosfet. It doesn't seem to matter when you supply it with a the sort of gate voltage. It doesn't seem to matter which way around it is. It will still conduct that's purely to allow for those two diodes so that, when it's say powering the tool, it can turn both the mosfets on, and it will actually basically act as a super low series resistance to allow the tool to be powered.

And likewise, if the battery runs low, theoretic control, circuit's going to turn them off to actually protect the tools suddenly cut off or if it detects the battery pack overheating. It may also cut that off, and i would guess it's probably sent is that as well? There is a connection. The little bus bar has a tab going down into the circuit board that is feeding back via some voltage level adjustment, uh transistors. This thing is covered in transistors and resistors.

It's got a lot on it. However. There is that other bizarre bit of circuitry. Let me show you that this is a total mind.

Bender this bit of circuitry. I could not get my head around initially, because it was just all over the place across each cell is a mosfet resistor, and i was thinking. What is that, for? I thought is that to basically turn it on and discharge a resistor or put a slight load across it, while it's testing. But what happens when the microcontroller wants to test the voltage across the cells? It sends a signal to all these little n-channel mosfets and they then put a voltage divider in line with a tap going back to the microcontroller, with a little smoothing capacitor.

So it can actually remove any rifle or glitches, but it also turns on this p-channel mosfet that puts a random value of resistor in series. But it's like 3.3 k, 4.4 k, 13.3 k, it's all different, and likewise these are all different, because i guess it's basically trying to derive whatever voltage. This cell is above the zero volt rail because it's like a stack of cells above the zero volt rail, which is what the microcontroller's reference to uh so i'll, just put that down as the zero volt rail whatever it is. This compensates so it gets a specific level, and that seems to be how it's looking for that voltage.

I thought they might have done something like detect. You know tap off here and have some level shifter so that, when this turned on it would actually somehow trick. Uh the so it could feed back to the microcontroller. So if any of these ended the sort of started going into the bypass mode, it would send a signal back to the mic, control and say one of the cells is charged time to cut down to the lower current.

It's very strange. It doesn't really inspire a lot of confidence that they're measuring in that way it's very component dependent - and it's actually made me think that i have no confidence in that battery pack at all. I'm more tempted, maybe just to take the cells out of this, but i'm just maybe being over pessimistic here. It seems nicely made.

It just seems super complicated if anything, the little battery pack, i got with the cordless chainsaw, the generic chinese clone. It didn't have the balancing, which i thought was a bit of a shame really, but a lot of the cheap tools do it with the balancing uh, technically speaking over the life of two, the battery shouldn't go that much out of balance. This one does have the balancing, but i've ended up wishing it didn't, because it over complicates the circuitry so much that it actually makes me it it's. I lose confidence in it just because it seems like it's using very improvised ways for this chip here to actually measure those measure those voltages.

Maybe this is a dedicated battery pack chip. I don't really know they've ground amber off. I would expect - maybe it's just a little microcontroller, but you never know um, but it's strange, i yeah it's a nicely complex circuit board and all nicely complex. That's i'm not sure it is nicely complex and over complex circuit board might be better.

That might be down to the fact that their lb, maybe is quite fussy. It needs specific signals back to charge the battery, and i know that ryobi themselves had a withdrawal. They had to do a recall because they had their. You could store your batteries in a charger rack and it would keep them topped up and one of the early ones in the early days.

Uh did cause batteries to melt down. It might have been something similar to this, i'm not really sure, but there we go. It's a chunky, robust battery to test it. Incidentally, i soldered a power bank uh module.

I just sorted it across a couple of cells and then uh did the fuel charge discharge on them just at as a sort of like a pair as a single 3.6 volt cell, and that's where i got the 4am power market. It just seemed to have that capacity, so it's close to the 5am power, it's actually more than i was expecting, but it's not the full thing, but there we go a clone. Ryobi pack, you you couldn't imagine how much time i've spent working the circuit board and how i've been banging my head against a brick wall because really tracing these out and all the different component values. And the strange configuration made this a very, very complex circuit to trace out, but that is it um, maybe better sticking to the real ryobi packs.

You probably get something that isn't going to explode in flames in your workshop.

8 thoughts on “Ryobi clone battery with odd circuitry”
  1. Avataaar/Circle Created with python_avatars The Huguenot says:

    Sometimes if you need new battery packs, theres just no other choice but go chinese. I needed a pack for an old Dell latitude. All I could find was a pack from china and ebay. The sticker said 11 volts, 58 watt hours, in bad english. I was getting about an hour of charge max. So I took it apart and found 6 lithium batteries. Each battery putting out 4 volts, but 7 watt hours. There were 3 banks, each bank in series, then parallel. So I guess that puts out 42 watts, not 58. It's like the chinese just dont care, no morals whatsoever. If they can lie and cheat, they will.

  2. Avataaar/Circle Created with python_avatars Jon Oldroyd says:

    I run 1 6Ahh equivaent Ryobi clone to power Ryobi lawn mower & Ryobi drill. All decent & battery holds up very well; A full lawn cut drops Vbatt to around 18v. I trickle charge the pack from the spike at 100 to 200mA with a Vmax cutoff of 21.0V. 21.0V cutoff also seems to coincide with battery refusing more input current at 21.0V, is this the BMS kicking in? Solar panels provide green power to charge. I haven't reversed engineered the BMS but after 12 months of this Heath Robinson charge the battery's still fine & tickety-boo. Just need to understand better if I should do something else instead. p.s Awesome teardowns as ever by BigClive, much appreciated.

  3. Avataaar/Circle Created with python_avatars David Malcman says:

    Probably not going to be too difficult to narrow down what the microcontroller is with a bit of detective work. We already know the footprint, finding VCC and GND pins wouldn't be hard, also Avss and Avdd pins, maybe even MCLR/reset as well. Analog input pins and digital may be difficult to map if they are programmable IO. But it probably wont get you anywhere even if you did dedicate the time to that tedious task. If they ground down the markings then they would have code protected it.

  4. Avataaar/Circle Created with python_avatars Siana Gearz says:

    This might just be a genuine Ryobi PCB inside this off brand battery. It could be a faithful clone, but then if someone were to manufacture something new, wouldn't they just throw some sort of junk together, much simpler? I imagine this could be a salvage operation, where they get e-waste Ryobi batteries and get the PCBs and the still-good cells out of them, freshen everything up a bit, new outer casing, new shrinkwrap and spotwelds.

    This could have been a lot jankier.

  5. Avataaar/Circle Created with python_avatars Chris Delancey says:

    Hello Clive, This video came out with perfect timing. I have been looking for a good, reasonably priced supply of 2ah 18650 cells. (I need 20). I have been looking all over ebay and can`t seem to find any at the right price, other than the 9ah chinesium ones. I think I will invest in two of these packs and dismantle for the cells. Was the seller p*w*r-store-date by any chance? I would not want to buy a faked fake pack Ha! Great videos as usual Clive, complements Chris. UK.

  6. Avataaar/Circle Created with python_avatars Teardown Dan says:

    The charge balance doesn't really get much simpler than having one dedicated chip, transistor and resistor per cell short of having a single chip that integrates multiple cell channels and the transistors in one package to reduce total component count and board space. Nothing weird about the back-to-back FETs either, standard over-charge/discharge disconnect setup. The only "weirdness" is the cell voltage monitoring by the "BMS" chip or whatever it might be but then again, a voltage divider to bring each cell's voltage relative to pack ground within the ADC's dynamic range would need to have different values for each cell. If you don't want voltage dividers, then you need to transfer cell voltage to a floating sampling capacitor and then bring that capacitor down to ADC ground for conversion, which would be even more funky-looking when done using discrete components.

  7. Avataaar/Circle Created with python_avatars R Usack says:

    We purchased a deep tissue massage gun awhile back. After only a few uses it no longer would charge or display battery charge level. It was replaced under its warranty but they didn't want its return. Now left with two such guns and only so mush tissue to deeply massage I decided to crack open the faulty device. In its handle were 6-18650 cells, in series. Measuring pack voltage at the output plug I only saw a little over 10 volts. Wrapped up alongside the cells was a similar charge/discharge board as the one in this video, including the thermistor. Part of its connection were metal taps from groups of cells running to the board, I concluded for balancing. Ultimately wanting to check all cells I found two completely dead, the rest OK. Not sure exactly where the fault(s) lay I took the pack apart to use the cells in other projects. I was only able to find a like pack from Alibaba where I sent a bid in for one. Never heard back but was able to find the exact individual cells sold through a lithium-ion retailer and at a good price. Soldered 6 of them together, using the original connector. With no protection or balancing circuitry I charge it cautiously, watching charge current taper to hundredths of an amp. Perhaps a bit extra work to get it up and running but better than throwing it in the bin. Fun project.

  8. Avataaar/Circle Created with python_avatars bucky king says:

    The circuit is very similar to a VAX battery i have taken apart, the centre pin is marked as a SDL (presume serial Data Link) Ive tried to read the serial data which looks like 9600 baud UART protocol (universal asynchronous receiver-transmitter), with a 0x7E start bit (this is as far as i got with it!). If anyone want to try and read the serial data… Also I presume this battery will not work (i.e deliver current) unless it has the correct serial data command? or charge the batteries without the correct serial data command?

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