Talking of batteries

[Brian Gaff (Sofa]

I have a number of Nickel metal hydride cells both AA and AAA, and though some seem to be still working after several years, others say they have charged and sit there saying good, they tend to lose voltage on load very quickly. These all have been charged in either the radios own charger, or in proper 'intelligent chargers, so on the face of it it seems there are some which just lose capacity and others which don't. Most were from Maplin of course. Is there any way to get these back or is it a junk the duff ones and buy new again? My initial feeling on what happens is that most things they are used in use at least two in series, so if one is bigger in capacity, surely it must at some point reverse charge the weaker one making it worse. Is this the reason? Brian

[whisky-dave]

It could be, all I know is that the modern lipo rechargable for drones charge and measure the cells seperatly or in small banks ensuring they are balanced.

[Brian Gaff (Sofa]

This issue have dogged rechargables of one sort or another for years. I had a Grundig radio cassette machine that contained a Dryfit battery. It lasted a couple of years then gradually died over just a few months. Suspect the cells in series issue again as it charged in situ and as far as I could see only had three wires to the pack. Same for the Nicad pack on a sony luggable cassette deck, Four batteries in a case with an extra electrode, which I think was dumb and only used to charge them in series. Then there was the Dustbuster vacuum, that had some sub C cells in series but although the charger was constant current, you ended up with a good cell and two duff ones.

Brian

[Dave Plowman (News]

Li-Ion with a decent charger is simply light years ahead of old technology.

[newshound]

+1. Apart from the capacity factor, I suspect that some of this is because Li-Ion requires far more "control and protection" stuff for basic safety.

That said, I'm still running a couple of Makitas on third party NiMH replacements for their original NiCads (using the original chargers).

[Dave Plowman (News]

I have a razor (used every day) where the batteries lasted far longer than expected. When they failed, took it apart expecting to see Li-Ion. But wasn't. Perhaps just a very good charger?

[Jacob Jones]

Yeah, found the same thing with my Panasonic cordless phones, brilliant charger.

[Brian]

Recovering / restoring cells is a waste of time in my experience.

If you have a set an one or two in the set have gone bad dump the lot - at least if they are old.

If they cells are built into a battery pack, you can usually get cells of the right size to build a copy. Salvage any protection devices ( over temp sensors etc) from the old pack. You can buy the nickel strip to connect the cells and spot weld them with a home made spot welder.

That said, if looked after, NiMH cells can have a long life. I rebuild some batteries for some of my amateur radios in about 2002. I give them a charge every month or so. They still seem good.

[Brian Gaff (Sofa]

On the other hand I've never had any luck with cordless phones. They nearly all trash the cells out of sequence making them die too soon.

Mine used to last a day if just on standby. once again its down to less than

2 hours and about ten minutes if used. It has three AAA cells in series.Its branded Cable and Wireless, but probably badge engineered in China. Brian

[newshound]

Found the battery on the Dyson cordless vac dead yesterday, Amazon replacement for £19 arrived today. This is my third "chinese" replacement on this vac, curiously the previous two both lasted 25 months. Genuine ones are guaranteed for two years, but cost £60 when I checked two years ago.

[Dave Plowman (News]

I vape, and the coil takes about 15w. Single cell 18650 about 2.5 amp/hr.

Obviously short bursts. But used all day every day until 'flat' - recharged overnight.

Battery life seems better than 5 years.

Perhaps Dyson are asking too much from an undersized battery?

[whisky-dave]

Probably due to supply and demand , we've replaced a D6 one seems to work OK. Could be other reasons too, such as child or slave labour, or unethical practices.

I remember ordering paper & ink from the channel islands worked out about 30% cheaper because they were shipped as printer parts. Then I'm guessing someone checked up and found that they weren't actually spare parts so did incur VAT which at the time was 25% which they weren't paying hence why they were cheaper. Maybe that's why they went out of business.

But we know sometimes amazon aren't the best employers and who knows what conditions and employment those cheaper battery makers use.

We can buy cheaper hormone injected meat too, battery hens and anything else that saves us money. We could bring back slavery to make sugar and tea cheaper amonst other things, don;t think I'd buy them if I knew.

[Martin Brown]

Until the day when it self immolates. Lots of great videos online of overcharged vapers going off like fireworks with a lovely violet flame.

The Chinese clone replacements come with a helpful warning to allow them to cool before recharging. The original Dyson unit has no such warning but dies relatively quickly (but >2 years) if charged when hot.

Dyson batteries get too hot to touch if the unit is used from fully charged to flat in a single session of 20-30 minutes.

[Brian Gaff (Sofa]

That does not seem very long. How many cycles is that, as this often seems to be the controlling factor. You need some way to tell just before they go too low and then again something to stop you overcharging them. I have a feeling that the new chargers for Apple phones shorten the lives of the batteries as they charge faster. One might have thought that the phone had the smarts. I know this is not the case as the newest chargers are actually small power supplies and can be used to power other things while they charge the phone as well. Brian

[Brian Gaff (Sofa]

A lot of small gear are now using mobile phone batteries, ie the old type with the tongue and connections and an indent on the other end. These do not get hot but they do bulge and strain the battery cover!

Brian

[Dave Plowman (News]

Which suggests Dyson are caning a too small battery - despite the very high price. Although not sure when I'd use a vaccum cleaner continuously for 30 minutes.

[Theo]

These are handheld units - a larger battery would make them heavier and more awkward to use. Running it at a lower power would mean less suction.

The 'high' power setting goes through the whole battery in about 6 minutes.

6S lithium ion (21.6v pack) with 2Ah cells suggests a current of 20A, that's 430W, plausible for a vacuum.

Not surprising that pulling 20A out of a pack with no cooling isn't good for it. I think the fault really is they should have better battery management that won't start charging until the pack has cooled down, maybe with an external fan like some Makita chargers. Or even some heatsinking/heat pipes on the battery case.

Also quite plausible that Chinese knockoff cells in the clone batteries aren't rated for 20A continuous current, and so they don't last so long. They probably don't have much thermal management either.

Theo

[Dave Plowman (News]

Or perhaps make it cut out if the battery temperature is dangerously high? When in use? But not in Dyson's interests - they seem to expect you to buy a new unit every few years.

True.

[Theo]

The BMS has a temperature cutoff, but I'm not sure what it's set to (it could be 'about to catch fire' rather than 'life-shorteningly warm'). The main thing is there is no active cooling and the batteries aren't ventilated, so the temperature rises and there's nowhere for the heat to go.

But you can't shut off too early, otherwise the thing won't be usable as a vacuum. Basically to make the thing work at all they're in a tight spot as regards capacity/weight/runtime/heat/longevity and they can't curtail one without compromising another.

I think the thing to do would be a heatpipe or something from the battery into the exhaust airflow, to provide some active cooling. But that is awkward from a mechanical design point of view.

(possibly the newer models are better, I have only used an old V6)

Theo

[Dave Plowman (News]

Eh? Is vacuuming a safety critical operation?

I have a fairly decent cordless tyre inflator. If you run that for too long, it shuts down until it cools. Not a problem in normal use when simply topping up tyres, but stops it breaking when say trying to inflate one from scratch.