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Dyson v7 Trigger cordless vacuum - TEARDOWN of battery pack
tinfever:
--- Quote from: deuteron on May 29, 2023, 11:58:48 am ---Dear Alll,
first of all many many thanks to all, who have contributed to this extremely interesting thread ! The work of tinfever & co is absolutely marvelous ! I read the thread from the very beginning since I'm a 'proud' owner of a Dyson V8 (SV10). The device was sold with a working battery, but the preowner said it is running only about 20 min with the actual battery. After having learned so much about the interior of the dyson batteries, I was curious to examine mine in more detail too. I'm not planning to 'repair' the pack or to change the cells, it's just that I wanted to now what's wrong. So I drilled alltogether 12 holes in the two side walls of the casing to be able to measure the individual cell voltages. Against my suspicion the pack is balanced pretty well, showing voltage between 4.07 and 4.12 V with an average of 4.10 V in the completely charged state, i.e. the charger stopped charging, all LEDs off. After all investigations done by various people about this batteries this behaviour was unexpected, at least to me. My imagination was so far that the charger charges the cells until the highest of them reaches 4.2 V, the unsual maximum voltage of Li ion cells. Ok, it's not much of a capacity which is unused in my case (got 24.5 instead of 25.2 V max). Nevertheless it looks like the charger doesn't use the full cell capacities. What do you think, could this be a fault from factoty, some bad adjustment of the parameters or even a 'feature' to sell faster and more batteries ?
What's your opinion ? Did you see such an behaviour in your battery packs too ?
Best regards
Stefan
--- End quote ---
20 minutes might actually be a normal run time. I don't recall what the vacuum is rated for when new. Even if that is actually low, I think it is normal for battery cells to have reduced capacity as they have more charge/discharge cycles on them.
I wouldn't worry about your pack only charging to 4.1V. It's possible on the V8 vacuums they charge to a lower voltage to preserve battery life. The ISL94208 BMS IC has an analog out tolerance of -15 to +30mV anyways, so it could just be error stacking. Also, once the battery is removed from the charger, I think it isn't uncommon for the voltage to drift down slightly, especially since the Dyson charging doesn't do a full constant voltage then constant current charge cycle. If you haven't already, I would watch the voltage on the highest cell when you connect the charger and see what it does.
deuteron:
Hi, thanks fpr the reply,
next, what I'll do is measuring the capacity of the pack, then we'll see whether or not the cells are weared in some way. These 20 min are just a guess, the seller told me, that the battery decreased in running time since he owned it. That's all I know. Is it possible that the charging voltage is programmed to decrease with time ? Frankly, I wouldn't believe.
Another question, maybe somebody knows: I was somewhat inspired by the discussion here to learn more about power tool batteries and the way these are BMSed. It seems to be the case, that usually there is no active balancing in most cases either. Dyson doesn't seem by far not the only company saving the extra money for a balanced charging. Also that the battery is blocked by the BMS in the case of a too strong unbalance is apparently not an exclusion. I'm just wondering what the special problem of the Dyson batteries is that they give up allready after about one or two years. Ok, the non resettable blocking via eeprom is some particular feature of the Dyson batteries. To my knowledge, resetting of a blocked power tool battery seems usually more simple. But this can not be the reason for this particulatly short running time. What is it ? Perhaps the max charging voltage intentionally diminishes with time (see above) ? Or did I overlook something else ?
Greetings
Stefan
tinfever:
--- Quote from: deuteron on May 29, 2023, 06:31:06 pm ---Hi, thanks fpr the reply,
next, what I'll do is measuring the capacity of the pack, then we'll see whether or not the cells are weared in some way. These 20 min are just a guess, the seller told me, that the battery decreased in running time since he owned it. That's all I know. Is it possible that the charging voltage is programmed to decrease with time ? Frankly, I wouldn't believe.
Another question, maybe somebody knows: I was somewhat inspired by the discussion here to learn more about power tool batteries and the way these are BMSed. It seems to be the case, that usually there is no active balancing in most cases either. Dyson doesn't seem by far not the only company saving the extra money for a balanced charging. Also that the battery is blocked by the BMS in the case of a too strong unbalance is apparently not an exclusion. I'm just wondering what the special problem of the Dyson batteries is that they give up allready after about one or two years. Ok, the non resettable blocking via eeprom is some particular feature of the Dyson batteries. To my knowledge, resetting of a blocked power tool battery seems usually more simple. But this can not be the reason for this particulatly short running time. What is it ? Perhaps the max charging voltage intentionally diminishes with time (see above) ? Or did I overlook something else ?
Greetings
Stefan
--- End quote ---
I doubt they do anything outright malicious like having the cell charging voltage reduce over time. It's probably just aging of the cell from the charge and discharge cycles I'd guess. Maybe power tools have a different usage profile that means the cells last longer? It's possible that most people's Dyson sits on the charger all day long which means it spends most of it's life at 100% charge, whereas maybe a power tool is only charged once empty? Maybe they just picked a different cell type? Perhaps the thought isn't right to start with? Maybe power tool batteries degrade the same but people are worse at counting number of screws driven on a charge vs number of minutes vacuumed on a charge? You'd need lots of data before considering declaring a trend in power tool vs vacuum battery life spans.
deuteron:
Yes, Tinfever that's all true and yours are similar to my thoughts. The idea with the long time in a 100% state sounds reasonable. And it would be certainly true, if the charger wouldn't stop charging after reaching full state. But as you kow, it ceases charging after a couple of minutes. Nevertheless, beeing fully charged is not a good idea over long time storage. Concerning the cell inventory you should have much more experience than me, since you dismanteld lots of packs, right ? So far - at least for the price of a new pack - I'm believing, they are using first class (japanese) cells, but this might not be the truth. I personly wouldn't also think that they act maliciously in any way. Nevertheless, when you look throughl all the forums and the comments at Amazon, it's more or less purely the battery, about which people are complaning. My personally strongest concern is more the very thin strength of the plastik housing, which causes these vacuums to crack, and this mostly at the handles, where the strongest forces are applied while unsing them. It makes no sense to speculate any further. Yesterday I ordered ordered an electronic load at Amazon and we will see what the capacity will be.
BTW a good workaround seems to be the usage of a quality battery pack from a power tool. I'm using the uasual adapter from for the V8 with a fitting to the Bosch 18V cells. The 4Ah procore is working pretty well even it is only five instead of six cells.
I'll keep the forum informed, if somebody is interested,
sincerely,
Stefan
deuteron:
Hello All,
the electronic load, which I've ordered, arrived today. Tomorrow I'll do the first capacity measurement with the Dyson SV10 battery pack. Just one additional question, because I'll try not to brick the pack:
Is there any minimum output voltage, which may cause the BMS to lock when fallen below ? Otherwise I would try 15 V discharge minimum being 5 x 3V. Surely I will measure all the cell voltages individually through the discharge process, in order not to get too much of an unbalance. If somebody knows, please let me know
Stefan
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