| General > General Technical Chat |
| Arc blast - is is something for “normal” people to worry about? |
| << < (5/7) > >> |
| T3sl4co1l:
--- Quote from: Psi on January 10, 2024, 12:32:00 pm --- --- Quote from: T3sl4co1l on January 10, 2024, 10:27:53 am ---but it can cause extended damage to circuitry -- burned traces, pads, damaged nearby components as the ball of plasma sinks current into anything conductive nearby. --- End quote --- You forgot "taking a sizable chunk of metal out of your side-cutters and turning them into wire strippers" :-DD --- End quote --- --- End quote --- |
| BrokenYugo:
--- Quote from: tom66 on January 10, 2024, 01:33:27 pm --- --- Quote from: NiHaoMike on January 10, 2024, 01:24:53 pm --- --- Quote from: Berni on January 10, 2024, 11:02:57 am ---Another scary thing for arc flash are the giant UPS units that supply entire buildings. Those have a room full of lead acid batteries that will happily produce many thousands of amps at a few 100 volts. Being DC the arc might take a while to extinguish too. --- End quote --- An EV battery is basically the same, just with much higher energy density. --- End quote --- Surprisingly the prospective short circuit current of a typical EV battery is less than that a 240V domestic mains supply. It is DC though, which does pose unique risks. It does surprise me how many precautions are taken around EV systems compared to domestic electricians. --- End quote --- If I had to guess, you probably want to overkill the new safety training on a high energy 400+V DC system to people (mechanics) used to playing with 12V DC, which is pretty hard to hurt yourself with, nevermind die instantly. Must compensate for the known complacency of the audience. Ever see a Fluke meter with low voltage automotive fuses hacked into it? I have. |
| David Hess:
--- Quote from: Psi on January 10, 2024, 12:32:00 pm ---You forgot "taking a sizable chunk of metal out of your side-cutters and turning them into wire strippers" :-DD --- End quote --- I ground off the melted end of my diagonal cutters, as shown below. Just last week I tried to find replacements for these cutters which I have had since I was like 6 years old, but Diamond tools is long gone. I think they ultimately became part of Swanstrom Tools but wow, Swanstrom are expensive. Inexpensive tools are $15, expensive ones are $30, and Swanstrom are 4 times that. My survey of respectable tool makers last week found Knipex (best), Tekton (most economical), Klein, and Williams. --- Quote from: Psi on January 10, 2024, 01:14:04 pm ---Everyone accidently cuts an actively powered mains cable once. If you're lucky you learn the lesson using your budget cutters and not on the lindstroms. --- End quote --- The second example below shows that some of us are slow learners. The pliers are not Lindstroms, but they are at least Swiss. The conversation went something like this: "Shouldn't you turn the power off at the circuit breaker?" *ZOT!* "I took care of it." |
| Siwastaja:
--- Quote from: Psi on January 10, 2024, 01:27:04 pm ---At least cars are Lion or LiFe and not LiPo. The amount of energy you can pull from a shorted LiPo is insane. --- End quote --- You realize the first of these words is an animal, the second one is something some of us have and others (maybe me included) not, and the third one doesn't exist - none of the three have anything to do with batteries. There is no such a thing as LiPo and as an imaginary device, it isn't any more insane than lithium ion batteries; high power density variants of which you are probably thinking about. |
| Siwastaja:
--- Quote from: tom66 on January 10, 2024, 01:33:27 pm ---It does surprise me how many precautions are taken around EV systems compared to domestic electricians. --- End quote --- On the other hand, it has to be - it would be super dangerous without. On the other hand, EVs are self-contained devices where all large loads are internally accurately current-controlled so there is no concept of "inrush", except in form of bus capacitance, which is dealt with a separate precharge circuit. In commercial AC, one can plug whatever random stuff in, so the distribution has to provide enough inrush capability for large motors etc., and on the other hand protect the wiring using user-replaceable fuses, which then need large enough short-circuit current (small enough impedance) so that the fuses actually blow quickly. There is no such a thing in EVs - the only occasion where the main pack fuse would blow is total destruction of the drive inverter caused by a design error, or an external destructive reason like a serious crash. Therefore the fuse can be of quick acting type and dimensioned carefully, quite close to the actual limits, without concerns of nuisance blowing because the current consumed can be exactly controlled - in all other cases except the one where the vehicle is lost cause anyway, and fuse needs to blow to prevent fire. (Well, quick charging is another case where large currents go through the fuse. That is why the DC chargers need to be designed seriously well, and why all the handshaking is going on in the cable. And sure enough, there are cases where a faulty DC charger has "destroyed" the poor little vehicle, basically by shorting out itself and blowing the pack fuse, and since this is not meant to be user replaced, you need an expensive repair. |
| Navigation |
| Message Index |
| Next page |
| Previous page |