Whilst searching online for a replacement for a Dyson vacuum battery, I noticed that several of the sites suggested that when recharging, it is best to let the battery cool first.
I haven't come across this before, should I have?
Chris
Some chargers will not charge hot batteries whilst some will stop charging if the battery temperature rises above a threshold, that is the case for my grandsons Vex IQ robotics kit.
Richard
Batteryuniversity usually has the details.
"LiIon: No charge permitted below freezing. Good charge/discharge performance at higher temperature but shorter life [lifetime charge cycles]."
On the Dyson, with machine sitting in household, the low temp issue is unlikely to occur. Only when the item ships to you in a box, should you let the equipment equilibrate before doing anything with it.
If the machine has been a-vacuuming, the batteries might well have been discharging at 20A, and they are pissed. They're hot as blazes, and typically, there is no ventilation for quick cooling. In such a case, you might wait a couple-whiles, until the batteries are a bit cooler. And then you might get 200 charges instead of 175 charges, something silly like that. I'm sure there will be a graph around somewhere, that tells you what the penalty is at 50C or 60C charge temps.
Things you can do:
1) Leave some charge on it. Don't discharge to 0%, place in broom closet, go on vacation for 3 months. A residual charge should be left on it (50-70% is good).2) Only charge to 100%, just before usage. This means the cells spend less time at 4.2V. Charge to 100%, vacuum for ten minutes, put unit away.
3) If vacuuming for 30 seconds, it is unlikely to need a charge. You would not charge to 100% and use for 30 seconds, because the cells are now 4.15V and still a bit on the high side. If the pack was 50% full, it might be able to vacuum for 30 seconds without needing a charge.BEV cars, you can program the charge control to fill the battery to any desired level. Filling and running from 50% down to 0%, is preferred to running from
100% to 50%, as the time spent at 100% is not good for the pack life. On a BEV then, there is normally some means (via console), to avoid the 100% condition except when you really need it. If you're driving cross country for 200 miles, then filling it to 100% just before you leave, is great. (The regenerative braking doesn't work when it is 100% full, but will eventually come back when there is room in the pack for regenerative charge. The friction brakes work during this interval.)Paul
Dysons often suffer from battery death, and my theory is they're being charged when hot. The charger is just a dumb wall-wart, with a BMS inside the battery, so there's no temperature monitoring or cooling outside the pack. The pack is plastic and unventilated. While the BMS could in theory back off the charge current or suspend charging until the battery has cooled down, there's no evidence that it does this.
This is why I let mine cool down before plugging it into the charger. I also don't leave it on the charger constantly.
Lack of decent battery cooling is why Nissan Leafs have such worse battery lifetime over other EVs, so it's a real issue.
Theo
Slightly OT but I have put a couple of "eBay" replacements in my cordless Dyson. Half the price of Dysons, which come with 2 year guarantee. My first replacement lasted 25 months (putting it straight back on charge when hot, and using "boost" most of the time although Dyson say for best battery life use it on standard).
YMMV
I thought that Dyson put great emphasis on design, and, goodness knows, there's no sparing of the customer's money. Surely, a decent BMS that maximises life of the battery is important? Or does design just mean fancy looks, but poor functionality?
I recently had a modern battery pack apart. Full of pretty sophisticated electronics. Which suggested to me they'd moved everything to within the battery - allowing a simple PS to be used as the charger.
Yes. In general as a rule of thumb, it's better to not charge a hot battery.
However the better LiIon chargers include forced air cooling and intelligent thermal management, so in those cases, it is actually
*better* to put them on "charge" when they are hot, since the charger will recognise the situation, and rapid cool the battery before it actually starts the charging cycle.
Yes. It is bad for their lifetime if they are recharged when potentially too hot to the touch after heavy use of a vacuum cleaner. I find it interesting that the cheaper aftermarket clone replacement batteries mention this fact but the OEM part fails to do so (or at least did).
Ours is going strong again on its slightly higher capacity clone battery that was bought for under half the price of an official OEM part.
It makes me wonder about super fast charging of electric cars...
As it turns out, super fast charging IS bad for electric cars.
And the car computer knows it.
What happens is, you fast charge certain brands of cars a handful of times, the car computer does the math, and denies further attempts to fast charge at 250KW or whatever.
What is going on, is the car computer looks at the warranty period (7 years say), and it has a table of info to refer to. To last for 7 years, you cannot super fast charge the car every day for seven years. The rate of super fast charging allowed, is closer to being "only enough for one holiday jolly per year".
The cars are equipped with heating and cooling loops, using the cabin environment equipment for dual purposes. But even with controlled cooling of the battery, apparently the 250KW rate is not good for them, as attested to by the car computer. If the car computer allowed unlimited charging that way, then that would be the proof that the manufacturer was "not afraid of fast charging".
This doesn't seem to be addressed in articles like this. The state of charge of the car, affects the max power that can be applied. And some cars have a "more rectangular" power curve than others during charging. On the road, you would never use a roadside charger to charge your car from 80% to 100%, because the chargers charge by the minute, and it takes a lot of minutes at a low power rate, to "top up". The pricing scheme at the charger, affects how people plan road trips, and what the "useful" battery fill range is (it isn't 0% to 100%). If the charger charged by the kilowatt hour, then you would charge to anywhere within the 0% to 100% range, as a function of how anxious you were to get back on the road. But they don't bill that way, because "time is money" and you can squeeze more customers in, if you distort their needs.
This is quite strange considering that the Taycan had been promoted as a car that could routinely charge at 350 kW. Porsche, for its part, explained that the update is designed to preserve battery life and performance.
The sports car maker also noted that the maximum charging speed reduction had been requested by some Porsche customers. <=== kooky??? This was explained by Robert Meier, Taycan vehicle line director, in a statement to the media on Monday. "The charging process might take 5 to 10 minutes longer, but it gives some battery saving for customers who want to take care of the battery." "
for some value of "we don't believe you" :-)
I think I'd want to read their warranty more carefully.
People believe what you promised them - if the car had only charged at
200KW in the original adverts for the car, then this would be all-OK from a deceptive trade practices perspective.That's also a problem with over-the-air software updates. Your car is about as stable as Windows 10 (Paul thanks Microsoft for breaking his webcam).
Paul
If you can afford one, you are unlikely to keep it more than a year or two, and not care much about resale value.
It's worth also mentioning that the plastic casing means there's a lag between the cells getting hot and that getting conducted through to the casing.
If I've been using the vac on max mode for its 6 minutes runtime, the battery casing is only lightly warm when it's flat. But over the next 10 mins or so it warms up - the cells are hot, but it hasn't conducted through to the casing during the runtime.
This is why it's not enough to feel the case after running it - in any instance you should leave it for a while before charging it.
Theo
Depends on how hot it got I'd imagine. I thought these batteries contained management circuits to avoid the reverse charging you used to get in other devices when one cell was low and went flat.
Brian
The Dyson BMS is, um, "flavorful"
If buying a new third-party pack for replacement, you want a product with its own, factory-fresh, BMS. Then you don't have to worry about flaws in your re-celling procedure, if someone else is building the pack for you.
The BMS has undervoltage cutoff for the whole pack, which enforces the reverse bias rule without needing to monitor each cell voltage individually. As soon as just one undervoltage event happens, it won't allow charging ever again. That's why the people in that thread were asking about "BMS reset", which you would think would be necessary for the factory to build a pack. (Assemble, BMS reset, ship.)
Paul
I think it depends somewhat on model.
Our Chinese friends will sell a replacement BMS:
You can also get a DIY kit to supply your own 18650s or 2170s:
These aftermarket BMSes do appear to monitor individual cell voltages (at least they have balance wires for them).
Theo
It's like BMS roulette in there.
Some of the other listings have a diagram. It has a string of cells: B- CL1 4V CL2 8V CL3 12V CL4 16V CL5 20V B+
(6 cell pack = 21.6v at 3.6v/cell)
P+ / P- : power springs to the motor body SW1 / SW2 : the trigger switch CHG+ / CHG- : the charger socket DIP1 : probably the programming port for the microcontroller
Looks like every cell has balancing bleed transistors, there's a thermistor on the back, and there is current sensing and cutoff capability. These vacuums appear to use the cutoff transistors in the battery for motor switching, since the trigger mechanism presses a switch in the battery, not in the motor body.
Which all looks fine, although I'm somewhat dubious of the current carrying capacity of that PCB. It looks like it's set up to have extra busbars soldered on top but they didn't bother.
Theo
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