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| USB-C charging law in the EU. |
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| Siwastaja:
--- Quote from: PapierzToaletowy on November 15, 2023, 09:46:29 am ---Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets. --- End quote --- 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:
--- 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 --- 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:
--- Quote from: PapierzToaletowy on November 15, 2023, 09:46:29 am ---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. --- End quote --- 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:
--- Quote from: Siwastaja on November 15, 2023, 03:50:36 pm --- --- Quote from: PapierzToaletowy on November 15, 2023, 09:46:29 am ---Using mains powered tools is probably unlikely in US given how they still cling onto 120V and low-amperage sockets. --- End quote --- 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. --- End quote --- 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:
--- Quote from: vad on November 15, 2023, 04:49:45 pm ---There is no such thing as a 13A circuit on this side of the Atlantic. --- End quote --- 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. |
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