ac powerbank keeps cutting out

[Galla153]

hi, so recently i got myself an xtorm AL480N to charge my laptop. It has all the good stuff like quick charge 3.0 and usb c PD(only 18W @20V) but it also has an ac outlet (up to 80w @220v) which is the reason i bought it. This way i can charge my laptop(lenovo L380) at school but it doesnt seem to work like intended. The power keeps cutting out so the laptop charging led is basically flashing every 2 seconds or so and windows is not liking it, it keeps spamming me with the ''low battery'' warning every 2 seconds or so. Anyway my question is this the charger's, the powerbank's or the laptop's fault? i assume it's the charger since the powerbank is charging my personal laptop perfectly fine and my school laptop is charging fine on ac(not with powerbank) with the same charger. also would getting a better and higher quality charger work(and if so , which one)?

 

i tried:

rebooting laptop

''rebooting'' powerbank

laptop has 2 usb c charging ports, i tried both

confirming the powerbank is outputting 220V (didn't test frequentie beceause i got no meter to do so) 

charging another laptop with a different charger (that works)

and a couple other things (but i'm writing this in class so i aint got all day)

 

what i think is wrong: the powerbank is not outputting a proper sine wave when a load is connected which this cheap charger doesn't like. this would explane why the cutting out is in regular intervals (of about 2secs) 

 

anyway, got to go.

any help appreciated      thanks already

 

(sorry for potentially broken english)   

[WereCatf]

15 minutes ago, Galla153 said:

lenovo L380

You don't mention the charger's specs. If it's close to 80W or more, then that'd be the reason your Xtorm is cutting out.

[emosun]

12 minutes ago, WereCatf said:

You don't mention the charger's specs. If it's close to 80W or more, then that'd be the reason your Xtorm is cutting out.

even if it was like 60w I've never seen an inverter actually reach it's wattage limit , they're kinda weird like that

[WereCatf]

14 minutes ago, emosun said:

even if it was like 60w I've never seen an inverter actually reach it's wattage limit , they're kinda weird like that

Well, it mostly comes down to apparent power vs. real power as far as I understand -- see https://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/true-reactive-and-apparent-power/ if you want an explanation on that. Plus obviously the quality of the inverter matters and whether they report the peak wattage or what it can actually sustain in long-term.

[mariushm]

The charger for the laptop is also not 100% efficient, it's maybe 90-95% efficient with pure sine wave AC input and good AC voltage and so on. So if your laptop takes in 65w from the charger, that is probably 90% or less of the actual power taken from the AC input... so 65w / 90 * 100 = 72 watts.

 

With AC input that's not pure sine wave, the efficiency can decrease, and the charger can work in a mode that's less optimal... imagine it wants to suck a lot of energy for a few milliseconds, filling its "buffers" with energy and outputting smooth output for a bit, but then the AC input is worse than it expected so the internal reserves discharge faster than expected so as soon as there's good AC input again the charger sucks a lot of energy again trying to fill up its internal reserves. So think of it like instead of continuously taking 70-75w to output 65w, the charger may ask for 80-90w for 800 ms and 20-30w for 200 ms and repeat.

 

Your power bank may not be able to actually give the charger more than 80w, which could make the charger deplete its internal energy reserves, so the charger turns off for a bit until its internal reserves fill up again, and everything keeps looping.

[Galla153]

hi me again, 

 

thanks for the quick responses. after some intense googling i found out that its most likely a 100-120w inverter that is designed te opperate at 80watts "max"  so i dont thing thats really the problem but opperating a such "high" power doe indeed distort the sine wave, which is what i thought. my new question is do these laptop chargers work on DC? so maybe i can just make/buy a bridge rectifier and some other rectifier components and get rid of the sine wave completely. I guess this would also reduce the load on the powerbank and reduce noice (as it has a whiny little fan).

 

regards mathias

[mariushm]

The power supplies have a bridge rectifier inside and often a boost circuit (for power factor correction) which steps up the converted AC voltage to some higher voltage, like 400-420v.

So your 110v AC gets converted to around 170v DC (peak) and then step-up to 400v -ish (if adapter has active PFC, not always required for low wattage adapters) 

No, buying/making a bridge rectifier and feeding dc voltage won't help.  The adapter probably won't mind as the bridge rectifier inside the adapter will just pass dc voltage through, but you'll have an extra 1-2w of losses by rectifying twice.

 

[Kilrah]

Adding a rectifier on the output makes little sense, it's if you tapped into the inverter's DC bus before the output switching that you'd gain.

 

I have an Omnicharge power bank with built in inverter that's switchable between AC and DC, and it's really great. 95% of what you'd want to run on it runs great on DC, and avoids the humming and awful harmonics of the square output.

[Scheer]

Both your powerbank and laptop have USB C, so just use a USB C to C cable.

 

Its always better to stay on the same power type for efficiency reasons, otherwise you are going DC to AC to DC, and ~20% of your power is just turning to heat being wasted.