Cordless vacuum cleaners battery life

[woodchips]

Sorry about this rather basic and homely thread, but want yet another cordless vacuum cleaner, which one?

There are many on the UK market, presumably worldwide as well. They all seem to offer 40 minutes run time, some say they have a performance equal to the best corded cleaners.

We have a couple of dogs, and live in the country, so carpets often need a clean. The Henry is wonderful but just get fed up with the cable and sheer size. Have bought several cordless cleaners but they don't last, Dyson, Gtech, Vax etc. Typically you fully charge them, light goes green, then start to use it. After about a minute or two the cleaner cuts out. But you can continue to keep switching it on for ages, 20 minutes or so, provided all your cleaning can be done in 10 second chunks. Why does it do this?

The question is, how do you get equivalent performance to a corded cleaner, taking 600-800W, from a battery which is from 22V to 40V? The weight is around 2.2kg so battery weight can't be more than, what, 30% of that? The Lithium batteries used are, presumably, AA size since other battery powered things that have failed seem to use that size cell. Just how much current can you take from an AA cell? For how long? How many recharge cycles will it do?

Whilst the cleaners have guarantees, the batteries seem to be hedged by exclusions.

The bottom line is, are they worth buying, again? What is others experience please?

[wilfred]

The cutting out is probably due to overheating and tripping some thermal cutout.  Since you say you use them for pet hair this is my guess. A mass of pet hair in the cooling inlet grills could easily do this.

[madires]

Typical Li-Ion batteries are 18650s and there are high current types delivering 20A or even more. My sister has a large hairy dog and is quite happy with an AEG and a Dyson, both cordless and meant for pet owners. They have floor nozzles with rotating brushes.

[Marco]

Maybe buy a Makita? At least you'll have swappable battery packs if one does go into thermal overload.

[klunkerbus]

We have two Dysons that will run non-stop until the vacuums start to show low battery.  Both are the pet variety, since we have two cats and a dog. 

Both, however, are a bit sensitive to the type of carpet.  On very smooth rugs, the vacuums apparently can't pull in enough air and that will cause them to (momentarily) shut down and restart.  Disabling turbo mode helps with those rugs.

One of them had some sort of intermittent in the electrical connection from the main head to the motor at the rotating brush, and that vacuum would randomly shut down.  Bypassing the extension tube connections with wire fixed that.

Edit: IIRC, one Dyson is around 8 yrs old and the other is about 5.  Both are on the original battery. I haven't noticed any battery degradation.   

[Siwastaja]

Typically you fully charge them, light goes green, then start to use it. After about a minute or two the cleaner cuts out. But you can continue to keep switching it on for ages, 20 minutes or so, provided all your cleaning can be done in 10 second chunks. Why does it do this?

Broken-by-design, by one way or another. Likely some kind of protection feature, which has been tuned wrong. I wouldn't even rule out planned obsolescense. Older battery technologies were even more crappy, so people are mentally still accepting that "batteries just die".

If the battery is old and reaching its end-of-life (years of use), its DC resistance has increased, which the thing would detect as an excessive voltage drop. But if you really can go on with this for 20 minutes, it seems it's a badly mistuned protection. If the battery actually was that bad, you wouldn't be able to go on for that long.

The question is, how do you get equivalent performance to a corded cleaner, taking 600-800W, from a battery which is from 22V to 40V?

First, the voltage doesn't matter, naturally; it's the power. In principle, the same power can be delivered at 20V, 200V, or 2000V. (Of course, extreme ends are impractical.)

But, they also do have much lower power consumption (< 300W) than the corded cleaners (ranging typically from 800 to 1600 W).

Their absolute trick #1 are the rotating thingies at the nozzle! Using little motor power, these physically remove the dirt (embedded into textiles, for example), and once it is up in the air flying, the vacuum can pick it up way more easily.

All the rest, such as using BLDC motors and making a big deal about it, is small optimization.

The weight is around 2.2kg so battery weight can't be more than, what, 30% of that?

Assuming the battery would be 1kg, and using modern power tool cells, this would equate to around 200Wh capacity, approx. $50 raw cell BOM cost. For the 40 minute runtime specified, the power would be around 300W.

The Lithium batteries used are, presumably, AA size since other battery powered things that have failed seem to use that size cell. Just how much current can you take from an AA cell? For how long? How many recharge cycles will it do?

They use 18650 cells (18mm diameter, 65mm length), which is much bigger than AA.

A typical "power tool" type of 18650 cell easily supplies (at acceptable efficiency) continuous current of 4-5 times it's capacity, meaning it can be fully discharged in about 15 minutes, if necessary. For a typical 2.5Ah power tool cell, this means over 10A. Cells can be paralleled to increase the max current, and put in series to increase the voltage. (The best ones are specified to 30A discharge, but this is only possible given brand new cells with no aging-induced increase in DCR, and still tends to mean case temperature of 80-90 degC at the end of discharge, definitely not recommended.)

Typical 18650 li-ion cells do about 500 to 2000 cycles depending on how hard they are pushed, how deep the cycles are, etc. 500 cycles is about right for fairly hard, yet non-abusive full cycles. End-of-life tends to be defined as a drop of capacity by 30%, or increase of the resistance by 100%, whichever comes first.

Note that the doubled resistance already makes most power tools quite crappy if there was no proper "extra power" available initially. This is actually what can make a huge deal in actual battery life. Say, your vacuum or drill needs 200W to be usable. Now, design a battery pack to provide 300W max when new, and it's total crap after a year when the resistance has only risen by some 30-40%. But, design a slightly bigger pack which can supply 500W, and is charged at a slightly lower C rate (although the actual charge power is still the same), and it may be usable for over 5 years just fine!

Whilst the cleaners have guarantees, the batteries seem to be hedged by exclusions.

This sucks. Li-ion systems can be designed to last fairly well, but such exclusions do not motivate the designers to do good job.

[MosherIV]

How many recharge cycles will it do?

I agree with Siwastaja.
Most lithium based cells around typically have 500 cycle life.

That is IF you put them through FULL charge/discharge cycles.
 
If you never run them down, you can extend their life somewhat.
The company I work for are delivering packs for automotive and the company is guarenteing 6 year life regardless of use.
To achive this, the packs actually artifically limit the discharge limit, ie they are not allowd to discharge down to empty.

From a practicle point of view, NEVER let your phone, tablet or vacuum run down to empty and you will find that your battery last longer.
I still have a phone (Sony Ericson T610 from the 90s) working with it's original LiIon battery working.
I typically never let my tablet or phone below 40% battery.

[NiHaoMike]

Also don't full charge to 100% regularly - stop at about 75-80%. Or tweak the charger to stop at 4-4.1V/cell, if that's possible.

I have an old Dyson where the battery started to wear out so I added two additional sets of 18650s in parallel with the existing ones. It works nicely now, just have to 3D print an extension for the collection can to let it sit flat and give it some extra capacity. (Of which, didn't Dave also have one of those Dysons? It must have needed a battery replacement or rebuild by now, right?)