Laptop power supplies

My wife's Lenovo laptop has taken to suddenly shutting down without warning - straight from working to a black screen and no power-on light.

I think I've tracked it down to the charger (she always use it plugged in to to the mains). Looking at the output from the charger jack, it goes from 20.05V (expected) to 0.00mV with wiggling. I know next to nowt about electronics, but I do know that my multimeter only reads a solid 0.00 when it's looking at a short circuit. So presumably the charger jack plug is failing to short circuit from the computer's point of view.

My naive theory is that when the battery protection circuitry sees a short on the charging input it just shuts the battery down, and as there is no direct power either the computer stops. It's no doubt much more complicated than that as electronic things always are!

Questions:

• Is my theory plausible?
• Anything to look out for in sourcing a replacement charger? Prices range from £40 on the Lenovo site to £8.99 on eBay. I think the eBay ones are out because the mains plugs they show have partially sheathed earth pins, so dodgy, but there are others at around £20 which look better. Don't want to fry the wife, but neither do I want to pay double for a Lenovo badge.

Robin.

Sounds like what happens when the battery has lost power due to not charging. It is usually preceded by the memory being backed up to disk but if you don't notice this happening it will look like a sudden shut down. Since you know that the external power supply is dodgy this would be my first guess.

Martin C

If you are reading zero volts when wriggling the lead/plug I would suggest that the lead has an intermittent break rather than a short circuit.

Alan

I'd be tempted to dissect the wire - hopefully you can narrow down which couple of inches by judicious wiggling - and make a repair. Or shorten the wire and fit a new power connector if you can find a suitable one. Or have a look here for a complete replacement unit - they list Lenovo compatible units at various prices.

Rob

I have recently bought a new charger for a Lenovo laptop. £18 off the bay, needed when the new puppy chewed the old lead. Be sure to check power outputs and jack plug sizes as they differ between models.

The sudden shut down - if that is what it is - likely means the battery is dead as well as the connection being intermittent.

Like their counterparts in BEVs - laptop lithium batteries lose capacity if charged (or depleted) fully, continually. Also temperature affects the lifetime while discharging or even if charged well below freezing (obviously the latter is unlikely to be the problem at the moment!).

Look up re Nissan Leaf battery life/capacity, to find how temperature management, or otherwise, affects battery life.

It would appear that the battery back-up period has reduced to zero - likely down to one or more dead cells - and the laptop is actually operating like a mains-fed PC - where turning off the mains would effect an immediate shut-down.

Good luck, but I reckon it may cost rather more than a new or repaired connector, especially if the laptop is old-ish. My tablet actually stops charging when fully charged - whereas older offerings may simply just carry on charging, at that point, which does the battery no good at all as the charge current is simply converted to heat within the battery.

One needs, of course, to be aware that excessive battery charging can lead to conflagration, if cell voltages/temperatures are exceeded excessively - obviously a rare event but you might recall that some mobile phone model(s) were recalled (due to spontaneous combustion) a while back.

Some lithium battery chemistries are better than others in this respect, LIFePO4 being the better choice (but with lower power density).

Edited By not done it yet on 24/08/2020 08:47:53

The fault is an intermittent break - or breaks.

As common, if not more common as a break in the wire just before the plug is solder cracking or a dry joint on one or more pins of the computer socket.

One computer I looked at had a faulty lead such as you describe but even after repair would not then charge the battery. The changeover switch was within the socket and what had happened was that the connection to the battery to charge the machine was cracked while the one to the computer was OK so it would run on power but not charge the battery. A spot of solder and then sorted. But even if this is repaired a battery left uncharged for a long time may need replacing as has already been suggested.

I doubt there is any battery protection as you describe, ie on the input, within the computer itself - if the power in shorts there will be no input but there will need to be some kind of protection within the PSU. A short across the battery may be protected against, but still unlikely.

Finally the sheathed earth pin may not be such an issue as most chargers are double insulated, those with 2 pin (figure of 8 or Telefunken) plugs certainly are and even those with three pin (Mickey Mouse) mains leads often are so the earth pin may be doing nothing.

Edited By Nick Clarke 3 on 24/08/2020 09:15:50

Some laptop power leads (Dell for example, possibly Lenovo) are confusing because the supplies are not connected by the outer braid and the centre wire on the jack, but between two coaxial braids. At the jack there is an inner and outer sleeve, and the socket connectes separately to each. The centre pin and wire is used for signalling between the PSU and the machine so the latter "knows" what PSU is connected and can also turn off the charging.  One possibility is then that the centre wire isn't making contact somewhere (possibly at the jack) and the PSU isn't switching on properly.

Edited By John Haine on 24/08/2020 10:17:41

Wonder if now we're out of the common market, Leadless solders and non Cadmium Silver Solders will be banned and we can get back to the good stuff?

There must be millions of pounds worth of electronic equipment binned due to rubbish soldered joints. If the PSU works with a wiggle, it could be a poor joint on the PCB. Voltage regulator pins suffer from "Leadless" solders.

Regards Ian.

Depending which model Lenovo laptop but mine has a battery charge level icon at the bottom RHS and as I normally use the lappy with the mains/charger lead connected there is a "Best Battery Life" setting. I always go for this setting (Frugal - Tight Yorkshireman) which means charge is static at 49%. On the odd times I'm going to use it away from charger, I normally disconnect lead and let the lappy run down to safe bottom level and the replugging charger back in, I get 100% charge.

Edited By Circlip on 24/08/2020 11:24:48

Seem to be some very complicated scenarios being proposed here.

Surely the most likely is an intermittent open circuit on the lead from the PSU and a battery which is not holding it’s charge.

If the laptop is always used via the mains, a worn out battery may go undetected.

I suggest just buying a replacement PSU initially and see if this fixes the problem. Probably best to avoid the ultra cheap but a reasonably priced compatible one should be OK.

Stuart

If the battery is not capable of taking any charge would the charger unit sense this and not send any voltage to the output ?

Emgee

www.allpsu.co.uk is a good source for these power supply units. Usual disclaimer

Not in my experience with many laptops with dead batteries over some years, including 4 on or around the table as I type this.

Edited By Frances IoM on 24/08/2020 18:33:14

Robin, where are you based? I probably have three Lenovo (round barrel) chargers you could try if local.

Thanks for replies. Perhaps I could have put my question more clearly.

My reason for thinking that the charger jack plug is failing to short circuit looked at from the computer end is that when when in the 'wiggle position' which doesn't give 20.04V, my multimeter gives 0.00mV rock solid. I've seen that before only when the test leads are shorted - looking into an open circuit the MM will flicker by some mV's depending on how many itinerant electrons are about I suppose, but never is the readout solid.

The battery isn't completely knackered - by using an arrangement of toolmaker's clamps (wife - 'where on earth did get you those from?' She's in for a few surprises if she has to clear the cellar out after I'm gone!) I got charge into the battery, it took a couple of hours to charge but the computer said 100%. So all was working well with a charged battery and mains plugged in. But then the dog decided to sit next to me and disrupted the clamps - the computer shut down instantly. So I restarted the machine from the battery with the charger unplugged - that worked fine, and the computer said 91% battery charge. Then I plugged in the charger - the computer shut down instantly.

It was this sequence of events that made me wonder if the machine somehow sensed a short on the charger input.

I'll go for a mid range replacement charger.

Thanks for your generous offer AJAX, but it's a 'slim tip' rectangular plug I need.

Robin