General > General Technical Chat
USB-C charging law in the EU.
tom66:
--- Quote from: wraper on November 15, 2023, 10:25:08 am ---
--- Quote from: Siwastaja on November 15, 2023, 09:25:01 am ---Sure, it might take 2kW peak and 500W average to achieve the same you get from a battery with 500W peak and 50W average, but it's insignificant in energy bill if you use it for a few minutes a year.
--- End quote ---
Many if not most battery powered tools still use brushed motors. And they are not that much worse than BLDC variants of the same tool. Saying that if powered from AC, the same tool suddenly becomes 4-10x less efficient is nonsensical.
--- End quote ---
I think unless you are doing a complete home renovation, the electricity bill for either tool type is essentially negligible, and even then almost every other cost will outweigh it. It is true that BLDC motors tend to be a bit more efficient and produce more output power for a given input power, important on a battery powered tool but less so on mains powered equipment where a bigger fan is usually sufficient to deal with that problem.
NiHaoMike:
For the latest 80V mowers, the voltage is high enough for a buck converter to make sense and isolation will not be required as the voltage is well above the 60V or so low voltage threshold.
--- Quote from: tom66 on November 15, 2023, 11:21:36 am ---It is true that BLDC motors tend to be a bit more efficient and produce more output power for a given input power, important on a battery powered tool but less so on mains powered equipment where a bigger fan is usually sufficient to deal with that problem.
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The latest pressure washers in the US use BLDC motors to get every bit of power available from a 120V outlet. Aside from precision control over current draw, they also have the advantage of providing more flow at lower pressure settings.
wraper:
--- Quote from: tom66 on November 15, 2023, 11:21:36 am ---
--- Quote from: wraper on November 15, 2023, 10:25:08 am ---
--- Quote from: Siwastaja on November 15, 2023, 09:25:01 am ---Sure, it might take 2kW peak and 500W average to achieve the same you get from a battery with 500W peak and 50W average, but it's insignificant in energy bill if you use it for a few minutes a year.
--- End quote ---
Many if not most battery powered tools still use brushed motors. And they are not that much worse than BLDC variants of the same tool. Saying that if powered from AC, the same tool suddenly becomes 4-10x less efficient is nonsensical.
--- End quote ---
I think unless you are doing a complete home renovation, the electricity bill for either tool type is essentially negligible, and even then almost every other cost will outweigh it. It is true that BLDC motors tend to be a bit more efficient and produce more output power for a given input power, important on a battery powered tool but less so on mains powered equipment where a bigger fan is usually sufficient to deal with that problem.
--- End quote ---
"A bit more" and 4-10X are very different figures. Brushed motors are quite efficient actually, so 4x improvement in efficiency is physically impossible.
tom66:
--- Quote from: wraper on November 15, 2023, 12:42:03 pm ---"A bit more" and 4-10X are very different figures. Brushed motors are quite efficient actually, so 4x improvement in efficiency is physically impossible.
--- End quote ---
I didn't say I agreed with the 4-10x efficiency claim. However it is true in some areas high power appliances are considerably less efficient. For instance the EU vacuum cleaners law: 2000W mains powered vacuums were found to have only slightly better efficiency than well-designed 150W brushless motor battery powered stick vacuums. They may well have had a wall power that is high, but whether that power is needed or used appropriately is another matter.
I was surprised by how efficient my electrician-friend's battery powered SDS was. Whilst it wasn't quite as quick at going through the brick as my 1500W rated mains powered SDS, it was close. It definitely was not pulling 1500W from the battery pack. I'd be surprised if it was pulling more than 400W given it was running off a 4Ah pack. So I could see a factor of 2-3x being reasonable for some tools. Sometimes the problem is not power, but torque, and BLDC can produce far more torque for a given size of motor, and the motor controller can optimise for torque or speed, a brushed motor is at the mercy of the field/triac or switched winding control for speed.
PlainName:
--- Quote ---I was surprised by how efficient my electrician-friend's battery powered SDS was. Whilst it wasn't quite as quick at going through the brick as my 1500W rated mains powered SDS, it was close.
--- End quote ---
Might it be technique (of the technology kind)? I have a BFO mains impact driver, needed to get the reverse-threaded nut of the bottom of the mower spindle. It's an unwieldy thing but you can feel the massive bangs it's handing out. Then I got a Lidl battery impact driver which does the job much more easily, and is smaller and lighter, but it vibrates rather than bangs. I wouldn't be surprised to learn the impacts go in a different direction too, though I can't see how that would work with forward and reverse modes. But it shows that apparently tools with apparently similar functions can be very different.
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