Question about power adapters and supply

Hello just had a question on power adapters and capacities. What happens if a laptop consumer more energy (watts) than the ac adapter that is given. For example a laptop that I was looking at had a 1050ti with a 7700hq, but the 120watt ac adapter is not enough as laptops with same specs consume or peak a lot higher than 120. So my question is what happens if my laptop peaks or continues to draw more than 120watt for extended periods. Does it matter how big my battery is itself meaning would a bigger battery have a bigger threshold? Will my laptop throttle, is it dangerous etc. Thanks for any help or advice .

 

Usually the battery starts discharging under load.

 

Assuming it is a true overload of the adapter then yes there can be some issues.

1.) the brick usually is designed to supply so many watts cleanly meaning with out amperage or voltage variances. Once you overload these levels can vary causing instability issues.
2.) an overloaded brick may during operation overheat and eventually self destruct.
3.) stress on the battery will cause premature degradation.
4.) Dirty power levels going in can cause electronic geradation of the internal rail part of the laptop (internal capacitors and the like).

Etc., Etc., Etc..

 

Dell uses a centre pin on the DC plug to report the PSU power rating to the BIOS which will then manage the power drain to avoid overloading the PSU. This may involve reducing any battery charging, throttling the CPU / dGPU or taking power from the battery. Maybe some other notebook manufacturers do the same.

However, if the notebook doesn't know the PSU rating then there's the risk of overload with the consequences noted above. If you have a mains outlet power meter then you can check the power drain under a range of operating conditions and make a calculated decision about the appropriate PSU rating (the PSU won't be more than 90% efficient so using the mains socket power leaves a factor of safety). I've used this approach to determine that my Dell Precision 5510, which is shipped with a 130W PSU, will work happily with a 90W PSU and will even work with a 65W PSU provided I avoid loading the dGPU. But if you are going to be fully loading CPU + dGPU then make sure the PSU has enough output. If the system isn't clever enough to manage the power demand (throttling and/or using the battery) then don't be surprised of something trips over or breaks.

John

 

Out of curiosity, how much is a lot and were those numbers taken at the wall rather than at the laptop. A reading at the wall of 140 W, assuming 85% power supply efficiency, which is relatively high, would lead to 120W being drawn by the laptop.

Unless the laptop designers were being stupid (which sometimes happen), the power supply that comes with it should be capable of supplying enough power to the laptop in any circumstance.

 

The numbers that I were looking at were from notebookcheck where the power consumption level was, for example max or under really large loads under 141.1watt but the ac adapter is only 120 and states that the power supply is not enough

 

Usually Notebook check is looking at power draw from the wall. This goes to the above numbers where a 120 watt brick draws about 140 watts from the wall.

 

Notebookcheck's test criteria say that they use one of these multimeters which measures Watts. I would have expected them to be monitoring the DC power between the PSU and the notebook in order to correctly measure the power drain and exclude the PSU efficiency (which should be usefully measured and reported separately). However, the picture in the test criteria description shows the meter connected to an AC socket adapter so perhaps all their reports are misleading in terms of peak power drain as the PSU ratings are for the DC output.

John

 

I would want to see the power draw always from the wall. This gives the best idea of what to expect from an entire system should you need an inverter, solar charger etc..

 

Oh wow thanks for the information, so should I be taking the notebook check result as accurate? They also said they test peaks and high extended loads under tests i think individually of prime95 and furmark, I heard these were unrealistic tests, could anyone clarify or explain if this is true or not. Much appreciated.

 

Also real quick in this review under power consumption it talks about how the it draws so much power that its should be proceeded with caution and all that, could anyone tell me what they mean by that or what potential hazard are they talking about. Also should we be worried by these numbers as it overdraws by about 8 watts on prolonged use. Appreciate any feedback thank you

 

The idea of testing under those two programs is they unrealistically overload the processors. This creates both power draws and heat a typical system will not see during normal use. As far as peaks it is mainly to be sure that when those occur the system does not fold and cause issues.

Edit; They themselves do not seem to realize the 128w from the wall is within tolerance. It is however close to the maximum. The problem with all electronics is they degrade over time. The closer you are to the max the worse this can be. So over time it may come to the point the brick has trouble keeping up with the laptop. So do keep an eye on it, if you start to hear hissing or arking in the brick get a new one ASAP.

The other issue is overclocking. This will draw more power and may require a new power supply right away.

 

You can take notebook's check numbers as accurate, but here's the important part: they are accurate in respect to their testing methodology. So for example, where was the power draw measures and what were they testing with. Furmark + Prime 95 is unrealistic in that no actual real world scenario would put that much strain on a computer. I have seen cases where either the CPU or the GPU were solicited to levels similar to those two programs, but never both at the same time.

Gaming usually involves peaks in GPU usage, but rarely 100% load 100% of the time and normally, the CPU is never solicited like Prime95 would cause it to be.

Scientific computations are usually either CPU or GPU and there are always pauses in the load where data is sent to or retrieved from memory. The same can be said of most professional workloads whether they run on the CPU, GPU or both.

It's an easy mistake to make, even I sometimes forget that numbers at the wall are not indicative of actual power draw.

As an aside, the 85% figure I quoted is arbitrary as in that I took something similar to a decent desktop power supply. Actual figures may be higher or lower. Also, it is technically possible for the power supply to go a little bit above spec for a short period and be fine. A good engineer would still select a power supply that has some headroom though.

 

A question that I have is then why does a laptop with 7700hq with the gtx1050ti 4gb and the same laptop but different configuration has a 7700hq but has a 1050 with 2gb of ram both have the same amount 120 watt ac adapter when the first one clearly has a much larger tdp and more cram with the better graphis card that requires more watts to run and function also

 

LoL, it is funny though as the number worked pretty much spot on. Just goes to show sometimes rules of thumb are pretty good but it is true sometime they are pure crap.

 

Do you know why those to laptops have the same ac adapter of 120 watt

 

Because it's simpler for the OEM to use the same power supply and not track stocks of additional items.


Sent from my iPhone using Tapatalk

 

Basically this, it is overall easier to have a finite amount of power supplies and use the closest adequate power supply for multiple series of laptops. That is why you usually see 45W, 65W, 90W, 120W 180W and 240W laptop adapters with not much in between. I'm sure there are others, but those are the ones you see most often for laptops. Also, those power supplies are usually made by another OEM than the laptop manufacturer. You'll see a lot of laptop power supplies made by LiteON and Delta (there are others).

 

Thanks guys so if a notebook had a 7700hq with a gtx 1050 2gb 250nit screen and a hdd would a 120 ac adapter in realistic world scenarios not just based on tdp specifications