Cheap Charger - what could possibly go wrong?

[Bob_about]

Like it says in the title

Saw this on evilbay.

I seem to recall a post stating that modern batteries with a decent BMS would adjust themselves to the charger used (or did I imagine that?).

So is it worth a try, or would I be stupid risking my expensive batteries with a cheap charger?

What could possibly go wrong?

Bob_about

 

[Haku]

Slightly hijacking this thread (hope you don't mind); on the subject of charging lithium packs, when my charger died last year I took the cable from the adaptor & hooked it into a hefty bench power supply that could supply up to 50A, setting the correct 29.4v I saw the battery was taking up to 3.5A, but the original charger only put out about 2A so I limited the current to 2A.

Just wondering is it ok to charge them at the higher rate? I did get a proper charger a few days later, but now I have my own bench PSU that can deliver 3.1A at up to 30v.

 

[rog_london]

Like it says in the title

Saw this on evilbay.

I seem to recall a post stating that modern batteries with a decent BMS would adjust themselves to the charger used (or did I imagine that?).

So is it worth a try, or would I be stupid risking my expensive batteries with a cheap charger?

What could possibly go wrong?

Bob_about

That's a very nice price, and the rating would be very suitable for most 36 volt lithium ion batteries.

What could possibly go wrong? Well, if it's badly designed it could obviously fry and do the same to your battery, though there's no particular reason to suspect it would fail in that way, and the price does not necessarily indicate bad design.

What you could do if you were especially concerned would be to load it up on a suitable power resistor to draw 1.8 amps at 42 volts and place the charger and resistor out on your concrete patio (in dry weather!) and see whether it runs without distress or obvious overheating for a while before letting it loose on your battery. You'd need 42/1.8 or around 23.5 ohms, and the resistor would need to handle around 80 watts. To *really* give it a good test you really ought to drop the resistor a bit to say 15 ohms and make sure that the charger current-limits effectively.

Of course that's probably beyond the facilities most people have, and if I needed a charger I'd probably take a chance but keep an eye on it for temperature especially during the initial stage of charging a flat battery. These things generally fail safe if they fail at all - the wide input voltage indicates it's a switch mode job and if they fail they usually go 'pop' and blow their mains fuse - and that's that.

Rog.

 

[rog_london]

Slightly hijacking this thread (hope you don't mind); on the subject of charging lithium packs, when my charger died last year I took the cable from the adaptor & hooked it into a hefty bench power supply that could supply up to 50A, setting the correct 29.4v I saw the battery was taking up to 3.5A, but the original charger only put out about 2A so I limited the current to 2A.

Just wondering is it ok to charge them at the higher rate? I did get a proper charger a few days later, but now I have my own bench PSU that can deliver 3.1A at up to 30v.

Maybe - maybe not. It depends on the battery's BMS. You really can't be sure except you might find out the hard way. It might be that the BMS relies on the charger to current limit during the initial stages of charging. I'd play safe and stick to 2 amps.

Rog.

 

[eddieo]

"what could possibly go wrong?"

It could kill you or burn your house down.......Insurance would probably be invalid as well if proven you used a non complaint device.


There has been a few programs on the BBC this week regards counterfeit goods. A boy in East London was killed recently using a counterfeit Nintendo charger that his grandmother had bought. It looked kosher with hologram stamp etc. boy plugged it in and was killed or murdered whichever way you look at it.

I would ONLY buy electrical devices from trusted/bona fida suppliers

 

[flecc]

If the spec is as quoted it will be ok Bob, the BMS does indeed look after the charge cutoff. However, it isn't fan cooled like the recommended charger, so if you wish to be sure, test it as Rog advises.
.

 

[Alex728]

it doesn't look like that bad a company (based in Birmingham with a telephone number) but TBH given the cost of the batteries I'd spend a few quid extra and get the recommended charger for them.

The similarly rated Wisper battery uses a robust fan-cooled charger (which reminds me a bit of 1980s electronic design for kit used in the public services such as Burndept and Cleartone radios for the Emergency Services). This is rated for 3A DC output but I've no idea what the actual output is, although the charger seems "smart" and gradually reduces the mains input wattage as the battery charges.

the company does look OK for cheaper bikes and various contraptions to transport live animals in such as a dog trailer for bikes, and a pram which can also be used for cats and ferrets(!). Presumably this practice is common in Birmingham

 

[rog_london]

(quote) The similarly rated Wisper battery uses a robust fan-cooled charger (which reminds me a bit of 1980s electronic design for kit used in the public services such as Burndept and Cleartone radios for the Emergency Services). This is rated for 3A DC output but I've no idea what the actual output is, although the charger seems "smart" and gradually reduces the mains input wattage as the battery charges.



Actually that's not what it does - it current limits initially by reducing its output voltage but then as the battery charges the output voltage rises - as does the wattage consumed by the charger from the mains - until a maximum power is achieved just as the battery reaches 42 volts. From that point the charger is in 'constant voltage' mode and the battery current reduces as it approaches full charge, so the overall power consumption reduces too. Finally the BMS in the battery cuts off to a small trickle charge, and the charger detects this and changes its light from yellow to green, and stops the fan.

So, to sum up, you have a peak power consumption part way through the charge, but not in the initial stages. Sounds odd, doesn't it? It's a characteristic of most switch-mode current limiting chargers.

Rog.

 

[Alex728]

Actually that's not what it does - it current limits initially by reducing its output voltage but then as the battery charges the output voltage rises - as does the wattage consumed by the charger from the mains - until a maximum power is achieved just as the battery reaches 42 volts. From that point the charger is in 'constant voltage' mode and the battery current reduces as it approaches full charge, so the overall power consumption reduces too. Finally the BMS in the battery cuts off to a small trickle charge, and the charger detects this and changes its light from yellow to green, and stops the fan.

So, to sum up, you have a peak power consumption part way through the charge, but not in the initial stages. Sounds odd, doesn't it? It's a characteristic of most switch-mode current limiting chargers.

Rog.

Interesting - thanks for the clarification, I've been meaning to get back into proper hardware work but haven't got half as much test/workshop kit as I would like - I even gave my stock of XLR "bodge" leads to my old mates on the rave crew when I lived in Reading (long before I started e-biking)

TBH even when I worked more with hardware I was always encouraged to treat switch mode supplies as "black boxes"....

 

[rog_london]

(quote) TBH even when I worked more with hardware I was always encouraged to treat switch mode supplies as "black boxes"....

Very sensible, because for the most part they're cheap to buy and not worth fixing, as it's difficult to source the right components (some very odd transistors in there), they're hard to fault find as they usually won't do anything at all unless everything is perfect, and there are some nasty voltages which can hang around on the capacitors.

Rog.

 

[onmebike]

Slightly hijacking this thread (hope you don't mind); on the subject of charging lithium packs, when my charger died last year I took the cable from the adaptor & hooked it into a hefty bench power supply that could supply up to 50A, setting the correct 29.4v I saw the battery was taking up to 3.5A, but the original charger only put out about 2A so I limited the current to 2A.

Just wondering is it ok to charge them at the higher rate? I did get a proper charger a few days later, but now I have my own bench PSU that can deliver 3.1A at up to 30v.

Only problem I forsee is, the bench power suppy provide's constant voltage and constant current as set by you. The original equipment may provide varying levels of volts/amps as charging progresses. I'd stick with the proper charger if possible.

 

[lemmy]

It looked kosher with hologram stamp etc. boy plugged it in and was killed or murdered whichever way you look at it.

Whichever way you look at it he was killed but to be murdered you'd have to prove it was the manufacturer's intention to kill him.

Murdering your customers is a rather short term business plan unless you are an undertaker so my guess is that the company was irresponsible or foolhardy and would be liable to manslaughter rather than murder charges.

 

[eddieo]

Semantics, lets see how you would feel if you lost a child in similar circumstances. I like the American system with choices like "Depraved indifference" and "reckless endangerment"

Ironically in China they often hang or shoot company directors..........Leman Brothers? RBS? You can only wish cant you

 

[monster]

just check that the positive and negative are the right way round for your battery and that the float voltage of the charger is the same as the old one.

 

[Haku]

Only problem I forsee is, the bench power suppy provide's constant voltage and constant current as set by you. The original equipment may provide varying levels of volts/amps as charging progresses. I'd stick with the proper charger if possible.

As far as I'm aware in regards to charging lithium batteries, the source voltage is set to 4.2v per cell and the source ampage is usually set to a specific level as determined by the battery manufacturer, but unlimited source ampage the cell/pack will only take as much as it can.
Unlike NiMH the method of determining when the li cell/pack is charged is not by measuring voltage but how much ampage the cell/pack takes, when it drops to a certain level it's determined the cell/pack is fully charged.

I was watching some tech show about the winter olympics a couple of weeks back and one part that got my interest was a mobile phone battery charger some major manufacturer had setup for people to pay for their batteries to be charged in about 30 minutes, which leaves me scratching my head because my mobile phone battery takes much longer than 30 minutes to charge from flat so they must have developed some sort of safe fast charging for lithiums.

 

[onmebike]

As far as I'm aware in regards to charging lithium batteries, the source voltage is set to 4.2v per cell and the source ampage is usually set to a specific level as determined by the battery manufacturer, but unlimited source ampage the cell/pack will only take as much as it can.
Unlike NiMH the method of determining when the li cell/pack is charged is not by measuring voltage but how much ampage the cell/pack takes, when it drops to a certain level it's determined the cell/pack is fully charged.

I was watching some tech show about the winter olympics a couple of weeks back and one part that got my interest was a mobile phone battery charger some major manufacturer had setup for people to pay for their batteries to be charged in about 30 minutes, which leaves me scratching my head because my mobile phone battery takes much longer than 30 minutes to charge from flat so they must have developed some sort of safe fast charging for lithiums.

I can only suggest that you proceed with extreme caution. Your bench psu has no means of either indicating when the battery is charged to capacity or cut off when this point is reached. Unlike Nimh's and NiCd charger's, Lithium chargers do not normally reduce to a trickle when charging is complete, they cut off completely. This is because heat generated by continued charging can seriously damage lithium cells and may cause fire/explosion.

 

[lemmy]

Semantics, lets see how you would feel if you lost a child in similar circumstances. I like the American system with choices like "Depraved indifference" and "reckless endangerment"

Ironically in China they often hang or shoot company directors..........Leman Brothers? RBS? You can only wish cant you

Personally, I don't want to see people shot, no. I have worked in countries that handle their population in that kind of way and like most of their people, do not find life in such places attractive. Each to their own, though and it can certainly seem an easy answer.

And, as you note, depraved indifference and reckless endangerment are not murder.

It's a pity there isn't a <joke></joke> tag on forums

 

[Alex728]

Ironically in China they often hang or shoot company directors..........Leman Brothers? RBS? You can only wish cant you

They shoot them, using a technique to end life as quickly as possible whilst causing minimum damage to the body - human bodies contain a variety of useful spare parts which can be (and are) harvested. Everything is recycled in China

Hanging is more commonly used as a penalty in Oriental countries once part of the British Empire such as Malaysia and Singapore - a technique inherited from Blighty (they still use the 1950s HMP operational manuals to work out the rope length!)

Even there company directors usually just get sent to prison if they are caught making or selling poor quality products (however a Malaya prison is not exactly "Holiday Bay!") Hanging was most commonly used against drug users and dealers - but less so now as a combination of the British rave scene being exported there and Indian gangs flooding Malaysia with ketamine as a reprisal for getting tough on illegal immigration means loads of Malaysian youths are getting high.. now its a few whacks with the rotan (cane) and compulsory rehab - if the authorities hanged them all there'd be no youths left to eventually build the worlds' hard drives and MP3 players and routers!

China is however comparatively lenient on "party" drugs for an Asian nation and Shanghai has the reputation of being "the Amsterdam of Asia" - (I've been told its a good place to go clubbing!) I suspect this is a "Bread and circuses" tactic to stop youths complaining so much about long work hours and/or wider political issues like Tibet - but of course if they get too mashed at weekends and are tired/sketchy on mondays it will also impact the quality of the factory output, just as British businesses were affected by young staff slacking off in the 1990s rave days)

What may have confused eddieo is that a couple of years ago there was a spate of China-made toys in the US being found to have toxic lead paint and other safety issues - when this came to a head the workers in China went into work one day to find the boss hanging from a beam right in the middle of the factory!

it wasnt the cops or a lynch mob, he had methodically arranged for the factory to be closed down, all the back wages to be paid and then took his own life.

All the workers lined the streets for his funeral and he was treated more like a hero/martyr (given a parade similar to our troops killed in the middle east) than a villain - the "bad guys" to them were the Americans for forcing down the budgets and thus the product quality and making corner cutting necessary.

something to think about when you are trying to drive the most ruthless bargain for your new gadgets

 

[lemmy]

something to think about when you are trying to drive the most ruthless bargain for your new gadgets

Interesting post, Alex. Also brings to mind the saying 'be careful what you wish for. It might come true'.

 

[Oxygen Bicycles]

Go for tested equipment

For the cheap components i would say you have to be careful with them. You can still buy cheap but make sure it is CE approved an compliant.

Make sure it doesn't have just CE sticker on it but iw was in reality tested and checked by the reputable company such as Tuv or SGS.

As Eddie said he cheap untested charger can burn (I've seen few i my life) your house or the smoke from it can even kill you which I don't wish to anyone.

So chaps be careful when you go for cheap as chips.

best regards

Andrew