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Dyson v7 Trigger cordless vacuum - TEARDOWN of battery pack

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diebog:
hey guys, im new to the forum but have been on it for many years reading/researching but just finally joined.

So I have an SV10 off an V8 Dyson and unknowingly I removed the board before I knew to unsolder a wire from the switch, my goal was to balance the cells and put it back together as the cells were healthy and not even a year old, well as you might of guessed, it bricked the battery.  Went to put together and got 5 red 1 blue, so I tried doing the reset with a pickit3 knockoff and while it reads and writes fine and the red light went away but now i get a single blue blinking light that doesn't stop.   I wish I had the foresight to save the original hex file but I didn't.    And I did uncheck "program Memory" ahead of all this. The pic on this is an PIC16L1F1847.  Any suggestions?  Does anyone have a good hex file for this model?  Ive thought about buying a working used Dyson brand one off eaby and getting the hex off it to fix this one.  But thought Id ask first. 

davegsm82:
@tinfever I just wanted to come and drop a post on the board since this is a journey I've recently been on myself. I was given my mothers old handheld which would only work for a few seconds before cutting off, plugging and unplugging the charger would get it going again so I thought a balance might be in order.

Disassembled the battery pack to try and balance it, but found that oddly all the cells were still in good balance so disassembled further and after dis/reconnecting the PCB to the cells was greeted with the 32 blinks of death. Found the same thing as you guys, the PIC and it's EEPROM data but since it was bricked, meant it was fairly useless.

So I did what any self respecting particle accelerator engineer would do, bought a job lot of 'faulty' or more accurately in this case 'untested' batteries from ebay after the seller informed me that only 1 or 2 were completely knackered. Dumped the EEPROM data from a good one and uploaded it to my bricked one with the PICKIT3 clone and a little adapter plug that hits the pins on the PCB. That brought it back to life even though most of the EEPROM data was different, so I then bricked it again, read out the EEPROM and found the changed bytes. Changed them back and got it functional again.

So, my quick question to tinfever would be, does any of the EEPROM data look like configuration data for the BMS chip? I'm guessing some of it is likely to be info like battery parameters (min/max safe charge voltage/current etc) but does anything you (or anyone else?) has extracted, look like data that is dumped directly into the BMS chip's configuration registers? i'd be interested to find out if there's any information we could garner about remaining capacity, dis/charge cycles etc once the bulk of the EEPROM data has been ruled out.


--- Quote from: diebog on August 10, 2022, 10:34:23 pm ---hey guys, im new to the forum but have been on it for many years reading/researching but just finally joined.

So I have an SV10 off an V8 Dyson and unknowingly I removed the board before I knew to unsolder a wire from the switch, my goal was to balance the cells and put it back together as the cells were healthy and not even a year old, well as you might of guessed, it bricked the battery.  Went to put together and got 5 red 1 blue, so I tried doing the reset with a pickit3 knockoff and while it reads and writes fine and the red light went away but now i get a single blue blinking light that doesn't stop.   I wish I had the foresight to save the original hex file but I didn't.    And I did uncheck "program Memory" ahead of all this. The pic on this is an PIC16L1F1847.  Any suggestions?  Does anyone have a good hex file for this model?  Ive thought about buying a working used Dyson brand one off eaby and getting the hex off it to fix this one.  But thought Id ask first. 

--- End quote ---

@diebog - as far as I know, no one has yet found an un-protected PIC in one of these batteries, meaning the firmware can't (easily) be extracted. I've looked into having PIC protection defeated in the past and it's a minefield, there isn't one particular method which works for all chips and it's a very hit-and-miss process. One way that is used currently is to decap the chip and (somehow) manually disable the code protection bit, but that's very specialised and very expensive. Are you aware that tinfever has written an alternative firmware that you can use to unbrick your battery though?

diebog:

--- Quote from: davegsm82 on August 18, 2022, 03:31:32 pm ---
@diebog - as far as I know, no one has yet found an un-protected PIC in one of these batteries, meaning the firmware can't (easily) be extracted. I've looked into having PIC protection defeated in the past and it's a minefield, there isn't one particular method which works for all chips and it's a very hit-and-miss process. One way that is used currently is to decap the chip and (somehow) manually disable the code protection bit, but that's very specialised and very expensive. Are you aware that tinfever has written an alternative firmware that you can use to unbrick your battery though?

--- End quote ---

Hi, thanks for the reply.  After reading the forums I did find his firmware and on my Dyson V8 SV10 battery I can confirm his firmware works!  Thanks tinfever!  on the SV10 it changes the led pattern from how it used to display but no biggie, at least the pack is up and working again.  Only thing is I can only use it on the low suction setting which lasts for 20 mins or so.  But even with a fully charged battery when I try the high suction mode I get like 5 seconds and then it cuts the power and blinks the blue led 3 x, 3x, 3x, 3x then back to a solid blue led on and after that led turns off (I’m guessing it goes to sleep) only after the last led turns off can use the vacuum again, and once I can the led blinks 6 times indicating it’s still fully charged.  My thought was even though I balanced charged the cells before I put the pack back together, maybe I didn’t do it correctly and the cells are still out of balance so when the high output is used the BMS sees the unbalance and cuts off power?  I’m going to check cells again and and see if that could be the case.   Does anyone know of a sequence to properly balance the cells?  I’m using a Hyperion 6 cell charger (which I use for my Traxxas batteries) with the balance wires soldered on the leads of battery, I first used the balanced function which lowers all the rest to the lowest cell and once finished I use same charger to charge which is also balancing them as it charges.  Only thing I didn’t do is to let the battery sit after the first balance, perhaps the cells need to sit to settle down to their nominal voltage and then rebalance a second time before charging? 

Does anyone know of an aftermarket BMS for these batteries that will actually balance charge the cells?  I bought a battery off Amazon (First Power Brand) to try out and after I charged it and discharged it a few times I did a time test with out the carpet head and on low setting and the battery only lasted 10 min when they advertised 35-40 min. Either I got a bad battery or they are full of crap!  I’m leaning towards the latter.   But I opened that battery up to see if they were at least balance charging them and found the circuit board had all the populated slots to solder the tabs going to each cell, however they weren’t even being used as there was no tabs/leads coming from the other cells even though there were spots for them in the shell moldings.  And looking close the populated slots don’t have any traces going anywhere top or bottom of PCB. 

tinfever:

--- Quote from: davegsm82 on August 18, 2022, 03:31:32 pm ---
So, my quick question to tinfever would be, does any of the EEPROM data look like configuration data for the BMS chip? I'm guessing some of it is likely to be info like battery parameters (min/max safe charge voltage/current etc) but does anything you (or anyone else?) has extracted, look like data that is dumped directly into the BMS chip's configuration registers? i'd be interested to find out if there's any information we could garner about remaining capacity, dis/charge cycles etc once the bulk of the EEPROM data has been ruled out.


--- End quote ---

I honestly haven't analyzed the stock EEPROM data much. However, I would guess it is mostly logging data and also a record of tripped flags. For example, when you run the vacuum until the battery gets too low and cuts out, it remembers that it had a low battery cutout and even if the PIC loses power (like it does when the BMS board goes to sleep), it remembers that flag was set and only clears it when you connect the charger.

I'd guess the min max voltages and safe current settings are all hardcoded in the firmware. EEPROM would only make sense to use for data that changes over the use of the battery. For anything that is always the same, like the cell low voltage cutoff limit, I don't see why they'd use any of the precious 256 EEPROM bytes.

The BMS IC doesn't actually have much configuration loaded in it, other than the overcurrent and short circuit levels and time windows, and few other boring operational settings. Nearly all the smarts are in the MCU.

I'm glad it sounds like you had success in repairing your vacuum, or at least bringing someone else's battery back to life  :D

When you said that the cells were balanced but the vacuum was still cutting out very quickly, those may be cells that have legitimately aged and now have higher ESR (a normal age/use degradation thing I think). High ESR cells may measure fine with no load, but as soon as you apply a load to them, their voltage plummets. A good cell might have an ESR of 50mOhm, so 3A draw (normal vacuum power) might cause cell voltage to drop 150mV, like going from 4.20V to 4.05V while the load is applied. A high ESR cell with something like 350mOhm (random number I made up) would drop from 4.2V to 3.15V, which is very close to the 3V cutout. Thus, you get very little time until it cuts out but as soon as you remove the load, the cells measure OK.


--- Quote from: diebog on August 18, 2022, 07:24:48 pm ---Hi, thanks for the reply.  After reading the forums I did find his firmware and on my Dyson V8 SV10 battery I can confirm his firmware works!  Thanks tinfever! on the SV10 it changes the led pattern from how it used to display but no biggie, at least the pack is up and working again.
--- End quote ---

I'm glad it worked for you!  ;D



--- Quote --- Only thing is I can only use it on the low suction setting which lasts for 20 mins or so.  But even with a fully charged battery when I try the high suction mode I get like 5 seconds and then it cuts the power and blinks the blue led 3 x, 3x, 3x, 3x then back to a solid blue led on and after that led turns off (I’m guessing it goes to sleep) only after the last led turns off can use the vacuum again, and once I can the led blinks 6 times indicating it’s still fully charged. 
--- End quote ---

I'm curious, was the battery able to operate longer in high suction mode before installing my firmware? What it sounds like is happening is under the high suction mode (draws 17A vs 3A in low suction mode) any higher ESR of the battery cells is greatly exacerbated like I describe earlier in this post.


--- Quote --- My thought was even though I balanced charged the cells before I put the pack back together, maybe I didn’t do it correctly and the cells are still out of balance so when the high output is used the bms sees the unbalance and cuts off power?  I’m going to check cells again and and see if that could be the case.   Does anyone know of a sequence to properly balance the cells?  I’m using a Hyperion 6 cell charger (which I use for my Traxxas batteries) with the balance wires soldered on the leads of battery, I first used the balanced function which lowers all the rest to the lowest cell and once finished I use same charger to charge which is also balancing them as it charges.  Only thing I didn’t do is to let the battery sit after the first balance, perhaps the cells need to sit to settle down to their nominal voltage and then rebalance a second time before charging? 
--- End quote ---

My firmware doesn't lock you out if the cells are far out of balance. However, it will shutdown with those 3 blue blinks if any battery cell goes too low. Of course, it can only charge the battery pack until the highest cell hits 4.2V, and only discharge the pack until the lowest cell hits 3.0V, so if the pack it out of balance, you'll get diminished usable battery capacity.

I don't claim to be a Li-Ion battery expert, but I don't think there is a terribly wrong way to balance a pack. As long as the cell voltages are all close together after letting the pack sit for a few minutes, I'd consider it successfully balanced. The way I would recommend balancing it, at least with a bench PSU, is to charge the battery pack with the normal charger until full, then charge the cells individually with the bench PSU set to 4.2V and a current limit of maybe 500mA (all assuming no cell is terribly low like 2V). Once the cell being charged goes in to current  voltage mode, you'll see the current going in to the cell slowly drop. Once it drops to maybe 50mA, you can probably consider it done. Rinse and repeat for any cell below 4.2V. Once you are done going through all the cells, they should all be pretty close to 4.2V. They will drift a bit after you stop charging though.

At that point, you could call it done balancing. Or to be extra thorough, you could use the battery pack until low voltage cutout, charge it back up again with the normal charger, and then recheck the cells and rebalance any lower ones.

Using the cell charger that also balances like you described also sounds perfectly fine. As long as all the cells are close together and all near 4.2V when completely, I'd call it a success. Waiting a few minutes and rebalancing isn't going to hurt anything either though.


--- Quote ---Does anyone know of an aftermarket BMS for these batteries that will actually balance charge the cells?  I bought a battery off Amazon to try out and after I charged it and discharged it a few times I did a time test with out the carpet head and on low setting and the battery only lasted 10 min when they advertised 35-40 min. Either I got a bad battery or they are full of crap!  I’m leaning towards the latter.   But I opened that battery up to see if they were at least balance charging them and found the circut board had all the populated slots to solder the tabs going to each cell, however they weren’t even being used as there was no tabs/leads coming from the other cells even though there were spots for them in the shell moldings.  And looking close the populated slots don’t have any traces going anywhere top or bottom of PCB. 
--- End quote ---

That's disappointing to hear the battery off Amazon doesn't even monitor the voltages on each cell, let alone balance them. Unfortunately I haven't worked with any of the aftermarket BMS's or batteries so I can't help much there.  :)


diebog:

--- Quote from: tinfever on August 18, 2022, 09:53:00 pm ---

--- Quote ---When you said that the cells were balanced but the vacuum was still cutting out very quickly, those may be cells that have legitimately aged and now have higher ESR (a normal age/use degradation thing I think). High ESR cells may measure fine with no load, but as soon as you apply a load to them, their voltage plummets. A good cell might have an ESR of 50mOhm, so 3A draw (normal vacuum power) might cause cell voltage to drop 150mV, like going from 4.20V to 4.05V while the load is applied. A high ESR cell with something like 350mOhm (random number I made up) would drop from 4.2V to 3.15V, which is very close to the 3V cutout. Thus, you get very little time until it cuts out but as soon as you remove the load, the cells measure OK.
--- End quote ---

Can I use a standard DMM on the \$\Omega\$ setting and test a cell?  Or would I need an ESR capable meter?



--- Quote --- I'm curious, was the battery able to operate longer in high suction mode before installing my firmware? What it sounds like is happening is under the high suction mode (draws 17A vs 3A in low suction mode) any higher ESR of the battery cells is greatly exacerbated like I describe earlier in this post. 
--- End quote ---

So no the vacuum wasn't able to run longer in high suction mode, its the same.  Before I messed with the pack when it was fully charged it would only last a short time and the BMS would cut power.  But the battery was still charged.  So your probably right about one or more cells have high resistance.  I figured that sense this vacuum was only a year old or so that they were fine, just out of balance, so I stupidly (without researching first) removed the board to check stuff out which bricked it because I didn't know to remove the wire from the switch. |O


--- Quote ---
I don't claim to be a Li-Ion battery expert, but I don't think there is a terribly wrong way to balance a pack. As long as the cell voltages are all close together after letting the pack sit for a few minutes, I'd consider it successfully balanced. The way I would recommend balancing it, at least with a bench PSU, is to charge the battery pack with the normal charger until full, then charge the cells individually with the bench PSU set to 4.2V and a current limit of maybe 500mA (all assuming no cell is terribly low like 2V). Once the cell being charged goes in to current  voltage mode, you'll see the current going in to the cell slowly drop. Once it drops to maybe 50mA, you can probably consider it done. Rinse and repeat for any cell below 4.2V. Once you are done going through all the cells, they should all be pretty close to 4.2V. They will drift a bit after you stop charging though.
--- End quote ---

Thanks for that info, im very new to lipo hacking so other then use the Hyperion EOS0606i I haven't done much manual charging of cells.  Ill give that a try and see where it takes me.   :-+


--- Quote ---That's disappointing to hear the battery off Amazon doesn't even monitor the voltages on each cell, let alone balance them. Unfortunately I haven't worked with any of the aftermarket BMS's or batteries so I can't help much there  :) 
--- End quote ---

Ya I was very disappointed to find that out.  The brand "FirstPower" on Amazon had decent reviews and was one of the more costly brands but was odd that the battery did not have a manufacturer name on it, so I think there are just multiple sellers of the same battery coming out of a couple of factory's and they sell them however they want like allot of the rebranded items we see nowadays.  This one was listed as 5.0Ah which is impossible because these are in series so it goes off what 1 cell is which is more like 1.5Ah or something.  The battery I got wasn't anywhere near the stock 2.8Ah

 So I thought there would be a market out there for a good BMS for these that actually checks and balances the cells properly.  I would diffidently be interested in replacing mine if it made the cells last along longer and had the bonus of resetting/open source if you needed to replace the cells.  But I guess if one is willing to open the pack to replace the BMS they will most likely are to just use a bench top power supply and manually charge like you explained above.

--- End quote ---

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