On Fri, 17 May 2019 20:23:57 +1000 Erik Christiansen <dva...@internode.on.net> wrote:
> On 16.05.19 21:18, Nicklas Karlsson wrote: > > > ... > > > I'd put the battery bank in an outbuilding. If something shorts out and > > > the battery bank melts down, the little building may burn but my house > > > won't. > > > > There certainly is a lot of power from a byttery and it could be a > > little bit hard to turn off. You put a fuse at battery cable? > > If local regulations do not require a HRC (High Rupture Capacity) fuse > between the battery bank and any connection to it, then it's an > invitation to disaster. A dc arc is much more difficult to extinguish, > because there are no zero crossings, and molten metal can end up flowing > on the floor. I got the feeling DC arc is much hard to extinguish but found no good information about it. Then reading about how welding should be done and EDM I learned then air i ionized resistance get lower, in practice I know it is often hard to ignite the weld while it work for some distance then lit. I suspect and get the feeling then welding not the least from the ignition problem some distance could be kept then lit distance to keep air ionized depend on current, happen to anything about this? > Small HRC fuses are generally in ceramic tubes, and are sand-filled, to > quench the arc when the element fuses. The one I have on the desk beside > me is a 100 A with a 100 kA (100,000 A) arc rupture capacity, but it's > 27x44x49 mm, and is overkill. Just 10 times AH rating seems to be normal, > i.e. 2000 A rupture capacity for a 200 AH bank. (The fault current will > be limited by battery internal resistance.) > > > I also think DC relays have to be a little bit different than AC > > relays, used an ordinary AC relay for a few few days connected to a DC > > voltage and even though two switches is connected in series it > > sometimes make a buzzing sound then turned off. > > Most relays and switches are marked with both AC and DC current ratings. > The DC rating is always much lower, due to the difficulty of rupturing a > DC arc. Rather than bother with maintenance/replacement due to contact > deterioration after many switching cycles, I prefer to switch DC loads > with MOSFETs - they're easy to parallel, as the inherently share. Agree, as is evindent furher up in message. For safety I learned relays fail open circuit while MOSFETs fail short circuited, I also experienced MOSFET short circuit failure. Happen to know anything more about this? Regard Nicklas Karlsson _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
