USB-C charging law in the EU.

[tooki]

It’d certainly be trivial for the manufacturers to make an AC-powered dummy battery, akin to what’s common in cameras.

[wraper]

It’d certainly be trivial for the manufacturers to make an AC-powered dummy battery, akin to what’s common in cameras.

That PSU most likely will be more expensive than AC powered tool, and likely oversized quite a bit to have enough power. I doubt you want something like 0.5-1.5kW PSU attached to the tool. Somewhat reasonable only for low power tools.

[Siwastaja]

Yes, the problem with extra low voltage stuff is that power tools require high peak currents so power supplies need to be overdimensioned for the maximum monentary current. Power supply capacitors can supply peaks only for milliseconds, while li-ion batteries can easily supply 20-30A peak currents for seconds or even minutes. This makes corded/battery hybrid solutions infeasible, they would be even more expensive and generate even more e-waste.

With corded stuff that operates directly at mains voltage, this problem does not exist. 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. Material and manufacturing cost dominates, and it's the smallest with a small crappy mains universal brushed motor directly switched through simple power switch to a cord, barely dimensioned to handle the current without melting. Manufacturers are good at cost minimization of this kind of stuff.

The cost of a corded power tool for $20 and similar battery version for $40 reflects this difference.

[tom66]

It’d certainly be trivial for the manufacturers to make an AC-powered dummy battery, akin to what’s common in cameras.

That PSU most likely will be more expensive than AC powered tool, and likely oversized quite a bit to have enough power. I doubt you want something like 0.5-1.5kW PSU attached to the tool. Somewhat reasonable only for low power tools.

You almost want a small 'buffer' battery that can handle the peak load and a charger that can top it up at, say, 200W.  But I suspect that such a pack would still be quite heavy and probably need air cooling (if only for the battery cells) which creates lots of headaches in a high dust environment.  Just get the 4-5Ah equivalent pack if you need a long endurance, or use a wired tool for those odd jobs.  Trying to get one tool to do both is unlikely to work out that well.

[wraper]

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.

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.

[tom66]

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.

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.

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.

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.

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]

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.

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.

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.

"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]

"A bit more" and 4-10X are very different figures. Brushed motors are quite efficient actually, so 4x improvement in efficiency is physically impossible.

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]

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.

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.

[Siwastaja]

Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets.

120V 13A or ~1.6kW is plenty for all of these typical low-cost power tools we are discussing. Even in 230V 16A land, (where our crap sockets also melt at rated current, which has been mentioned to you), these power tools are usually in 500W-1500W range.

[Siwastaja]

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.

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.

It's not nonsensical. AC universal motors in power tools are designed to high winding resistance to artificially low efficiency, which serves two purposes, (1) inrush/stall current limitation in absence of any current sensing control circuitry (so that a cheap triac circuit won't blow up on switch overcurrent; or house fuses won't blow up), and (2) cost, weight reduction due to copper savings.

Remember, in non-current-controlled DC motor, the ratio between stall current and nominal operating current is proportional to efficiency. If you make an efficient motor, stall current is massively huge and you need to actively control it, which costs easily more than $1 in parts. Inefficient motor can be directly connected to a voltage source, or PWM'd without current sense.

Battery powered tools have incentive to use higher efficiency motors because otherwise the runtime would suffer so much (and cells would need to be rated to even higher discharge). Therefore they also have some kind of MOSFET-based switch which does some rudimentary Rds_on current sensing and limitation. So yeah, they are not more expensive only because they come with a battery and a charger (with isolated transformer), but also because the motor itself is more expensive.

As you point out, brushed vs. brushless is actually quite irrelevant, you can design efficient or inefficient motors both ways. Brushless enables a bit better power density by saving the volume occupied by the brushes (especially higher efficiency brushes would be larger). But there sure are brushed DC motors over 90% efficient, used in old forklifts, early EVs, industrial applications etc.

Look at the difference in vacuum cleaners producing roughly the same amount of flow and static pressure: from 1000W of 1980's/early 1990's, up to 2000W during the power bloat season starting late 1990's, finally back to even below 1000W after EU made that illegal.

If you don't believe me, observe it yourself: look how easily an electric drill rated to 500W or more stalls and compare it to even a cheap battery powered drill. The difference in power consumption isn't 10x I admit that but 4x difference is well possible. If one is 60% efficient then the other can be 15-20%. You can also see how much more air flow the cooling fans on these cheap-ass corded tools produce compared to battery variants.

Upper limit for motor efficiency is obviously 100%, but remember that lower limit is as low as 0%, and as long as you can get any cost savings operating at low tens of %, and it's not illegal to do so, it's not nonsensical at all. With easy availability of 1.5kW - 3 kW from a wall plug, there is little incentive to be efficient, but running with a battery totally changes the game.

[Siwastaja]

Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets.

At least in EU it's possible to draw 2-3kW without melting the plug, socket or wiring. To standardize on 230V and CEE 7/7 was a really smart decision.

Here's a fun fact to you: in the UK, the country of EVEN BETTER plugs than ours, there is a complete separate ecosystem of 120-volt power tools for really serious professional use at construction sites*, so clearly 120V isn't a problem. Let that fact sink in; OTOH, with a political anti-USA agenda, I'm quite sure you are not interested about such trivial things as facts.

*) the idea is to use a 240-V input, 120V output transformer with earthed center tap. This way, potential between either legs to true earth/PE/plumbing is 60VACrms, which is deemed pretty safe. One can see how great this idea was before the era of RCDs; UK electrical system is full of great ideas implemented well.

[vad]

Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets.

120V 13A or ~1.6kW is plenty for all of these typical low-cost power tools we are discussing. Even in 230V 16A land, (where our crap sockets also melt at rated current, which has been mentioned to you), these power tools are usually in 500W-1500W range.

There is no such thing as a 13A circuit on this side of the Atlantic. Standard outlets are rated at 15A and 20A. Loads must be derated to 80%, so the maximum constant drawn power is 1,440W and 1,920W, respectively.

[Siwastaja]

There is no such thing as a 13A circuit on this side of the Atlantic.

I first wrote 15A, but specifically lowered that to 13A since I was watching the video posted in this thread which showed an extension cord rated to 13A. Here, it is illegal to sell non-fused extension cords rated to anything lower than the sockets (16A).

On the other hand, I forgot the derating factor so numbers ended up quite close to that 15A value. The 20% derating rule is ridiculous IMHO, but oh well, maybe it's better than our situation where everything is 16A on paper except that it's strongly suggested that EV charging is derated by 50% to avoid fires, yet similar rule does not exist for anything else and there are swimming pool heaters which operate at 14A continuously.

[nctnico]

If you don't believe me, observe it yourself: look how easily an electric drill rated to 500W or more stalls and compare it to even a cheap battery powered drill.

I'm not sure this is a fair comparison as the power versus torque graphs for the motors may be different depending on the intended use. In the end the power rating says very little over what amount of torque a drill can develop at the chuck. You need to take the gear ratio into account. An electric drill designed to primarily drill holes will have a different gear ratio because it needs to rotate as higher speeds (like 3000 RPM) compared to a drill primarily designed to drive screws in (which rotates at ballpark 450 RPM). For example: the Makita corded screw driver 'drill' I have is made to provide torque at low speeds. As a consequence it is stronger (=more torque) compared to its battery powered counterparts.

[AVGresponding]

Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets.

At least in EU it's possible to draw 2-3kW without melting the plug, socket or wiring. To standardize on 230V and CEE 7/7 was a really smart decision.

Here's a fun fact to you: in the UK, the country of EVEN BETTER plugs than ours, there is a complete separate ecosystem of 120-volt power tools for really serious professional use at construction sites*, so clearly 120V isn't a problem. Let that fact sink in; OTOH, with a political anti-USA agenda, I'm quite sure you are not interested about such trivial things as facts.

*) the idea is to use a 240-V input, 120V output transformer with earthed center tap. This way, potential between either legs to true earth/PE/plumbing is 60VACrms, which is deemed pretty safe. One can see how great this idea was before the era of RCDs; UK electrical system is full of great ideas implemented well.

Nitpicking I know, but it's 110VAC with a CTE.

Bizarrely enough, for the higher power stuff (big core drills, concrete saws etc) we jump straight from 110VAC to 400VAC 3-ph...

[wraper]

If you don't believe me, observe it yourself: look how easily an electric drill rated to 500W or more stalls and compare it to even a cheap battery powered drill. The difference in power consumption isn't 10x I admit that but 4x difference is well possible. If one is 60% efficient then the other can be 15-20%. You can also see how much more air flow the cooling fans on these cheap-ass corded tools produce compared to battery variants.

Cordless drills usually are more like electric screwdrivers that can also drill. So RPM will be like a half of an average mains powered drill that has higher RPM and no torque adjustment, so not suitable for screws. And again, cordless tools, especially cheap usually have brushed motor. BLDC is usually used in better tools. Often basically the same model comes in both variants with some performance advantage in BLDC version.

[SiliconWizard]

Yep. And while efficiency per se is not that much different as you pointed out, a brushed motor will by design wear out much faster. When it does, either you feel like renovating the motor by changing the brushes yourself (as long as you can find the parts), or you throw it away as finding the motor itself as a spare part is even less likely. Brushless motors have much, much longer lifetime.

[wraper]

When it does, either you feel like renovating the motor by changing the brushes yourself (as long as you can find the parts), or you throw it away as finding the motor itself as a spare part is even less likely. Brushless motors have much, much longer lifetime.

If you replace brushes timely, brushed motor can last a very long time. In better tools, brushes usually have a wear protection, they electrically disconnect when become worn out to prevent motor damage. As of DIY use, they'll last forever. The downside of BLDC is that it can accumulate magnetic dust and shavings.

[coppice]

When it does, either you feel like renovating the motor by changing the brushes yourself (as long as you can find the parts), or you throw it away as finding the motor itself as a spare part is even less likely. Brushless motors have much, much longer lifetime.

If you replace brushes timely, brushed motor can last a very long time. In better tools, brushes usually have a wear protection, they electrically disconnect when become worn out to prevent motor damage. As of DIY use, they'll last forever. The downside of BLDC is that it can accumulate magnetic dust and shavings.

50 years ago a good brushed motor lasted a very long time. Now its not just the brushes that wear. In a lot of motors the commutator wears a lot, too. I think with all the higher end motors going brushless, brushed motors have been driven into a super low cost space where quality can't be maintained.

[nctnico]

Yep. And while efficiency per se is not that much different as you pointed out, a brushed motor will by design wear out much faster. When it does, either you feel like renovating the motor by changing the brushes yourself (as long as you can find the parts), or you throw it away as finding the motor itself as a spare part is even less likely. Brushless motors have much, much longer lifetime.

For as long as the electronics keep working... Brushes are just a mechanical part and likely you can source ones that will fit even if the original ones are no longer available. Then again, I have never had to replace brushes in any tool used around the house. I did buy brushes for a Makita reciprocating saw which was worn more than I initially hoped for. Turns out the brushes didn't need replacing. Only some bearings and a seal.

[Siwastaja]

Yep. And while efficiency per se is not that much different as you pointed out, a brushed motor will by design wear out much faster. When it does, either you feel like renovating the motor by changing the brushes yourself (as long as you can find the parts), or you throw it away as finding the motor itself as a spare part is even less likely. Brushless motors have much, much longer lifetime.

Not all brushed motors wear up quickly, it's again a design decision. Larger brush area not only increase efficiency by decreasing current density, but slows down the wear. High-quality brushed motor power tools easily lasted years of daily professional use while cheap ones fail in worst cases in just few hours. Similarly, some brushed EV traction motors were good for easily 150 000 kilometers before brush swaps.

[tooki]

It’d certainly be trivial for the manufacturers to make an AC-powered dummy battery, akin to what’s common in cameras.

That PSU most likely will be more expensive than AC powered tool, and likely oversized quite a bit to have enough power. I doubt you want something like 0.5-1.5kW PSU attached to the tool. Somewhat reasonable only for low power tools.

I suggested looking to the ones on cameras: the actual SMPS doesn’t fit into the battery compartment, so the power brick is connected via a cable so that the camera stays compact (= existing accessories will still fit).

[David Hess]

Cordless drills usually are more like electric screwdrivers that can also drill. So RPM will be like a half of an average mains powered drill that has higher RPM and no torque adjustment, so not suitable for screws. And again, cordless tools, especially cheap usually have brushed motor. BLDC is usually used in better tools. Often basically the same model comes in both variants with some performance advantage in BLDC version.

Many of Milwaukee's M12 tools come in brushed and brushless versions, with the later offering noticeably higher performance.  I started with their brushed M12 drill but found it to be underpowered in some applications, so picked up the brushless version.  I am not sure why this is the case since both use electronic control and rely on the same batteries, but I suspect one significant difference is simply the effective number of poles in the motor.  4-pole brushed motors are only common with starter motors, so 3-pole brushless motors will have a natural power advantage over common 2-pole brushed motors.