On Mon, May 20, 2019 at 7:55 PM Erik Christiansen <dva...@internode.on.net> wrote:
> > Switching normal loads is back to less than 100 A for less than 5 kW, but > still hard on contacts. (The contacts on the starter solenoid for an old > Caterpillar D6 are blocks of copper with a mm of silver on the surface, > to take the several hundred amps at 24v. IIUC, silver oxide conducts.) > This is why no one builds 24 or 48 volt DC power system for solar or backup batteries. Not on electric cars either. Car batteries are usually 400+ volts. You need to be carful when working on even a Toyota Prius as there is 400 VDC present. You were talking abou the cost of a high amp switch. That si NOTHING compared to the cost of the inverter you would need. You would need racks of MOSFETs. No one does that. You all know the formula for power loss right? i^2R. That's "i squared R" because the current is squeared you REALLY want to make it small. not more than about 40 amps for a residence. Also no one is every going to dichage a batter at the 100 amp rate. you design the system so it cycles only one per day. Even with lead acid batteries you can place a 10 amp fuse oneach one of them. Then you KNOW the maximum current on the switch is 10 amps. If you wire 20 lead acid batteries in series you can have 1KW of power at only 4 amps. if the switch is rated at 10A you are good. > > It is not hard to find a good 60 or 80 amp switch. You can > > buy one on Amazon.com for $120. Switches that can handle high DC loads > are > > very common. Here is one examle > > amazon.com/Siemens-HNF362-600-volt-... > > < > https://www.amazon.com/Siemens-HNF362-600-volt-Non-Fused-Switches/dp/B005G953DE/ref=pd_day0_hl_60_1/140-9661733-2175833?_encoding=UTF8&pd_rd_i=B005G953DE&pd_rd_r=a160cb45-7b31-11e9-b1ee-5b598291dad5&pd_rd_w=8QFZM&pd_rd_wg=4YekC&pf_rd_p=ad07871c-e646-4161-82c7-5ed0d4c85b07&pf_rd_r=QQK03FTGP5PQVYKFENBP&psc=1&refRID=QQK03FTGP5PQVYKFENBP > > > > These DC disconnects are a code requirement and are installed by the > > million, literally. > > All the switches I've come across are stamped with their AC and DC > current breaking capacity. That must cover the potential fault current, > if there's no HRC fuse, or you're building a fire starter. (I.e. you > still need the fuse.) > > > No competent engineer will design a high power low voltage system because > > you can no longer us wire, you'd n=be into solid copper busses. > > The hundred amps only flows from battery to inverter - and yes, the > cables are about half an inch in diameter, much like starter motor > cables in a car. > > I'll be running low voltage DC for LED lighting, but that's at modest > current. > > Erik > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
