From: [email protected]
Solar Ray writes: >> These are grid tie with battery backup systems. All inspected. >> >> Personally, I think that we should have OCP on each series string, but >> that's a whole nother can o' worms. >> Most sealed batteries (and golf cart batteries) are fairly current limited. >> You need at least 2 parallel strings >> to even get close to meeting the inverters surge requirements. (especially >> in 24 v systems) > >This is true for 24 volt systems with small banks of small batteries. >It is absolutely not true for 48 >volt systems where Vdrop is 1/4th what it is for a 24 volt system, and >1/16th what it is for a 12 volt system. >T-105s and similar sizes are pretty small, but there are sealed >batteries with the capacity and plate >surface area to deliver substantially more current. > >It's also a matter of where the battery is operating at the time you try >testing Psurge. All batteries have a >problem with "coup de fouet" / "the crack of the whip" (the sharp drop >after an abrupt increase in load from >a low or no-load condition), but most will recover significantly as the >battery adjusts to the load. Based on >that, the worst-case scenario is a steadily increasing load as the >voltage will fall much more slowly than >with a single large load applied at once. I've achieved C/1 in >discharge on AGMs during tests, and if I'd had >larger shunts, I would have tried higher rates of discharge. This was >for far longer than the 5 seconds you >mentioned elsewhere. > >I have a test coming up for a client where I'm going to try and get a >pair of GVFX3648's to sell 7.2KW. >I'll try to remember to capture some voltage plots and post them >somewhere. The reduction in voltage drop >is significant as the load is increased, compared to all at once. I had >those inverters at 2/3rds capacity >and still above 46 volts. I was able, just now, to run both at 100% >(and then the chargers turned on due to >low voltage, because I'd not turned them off ...) and keep the voltage >above 46.4V -- here's the plot: > >http://www.greenhousepc.com/GVFX-Sell-All.gif > >Here's the numerical meter info -- > >STATUS/FX/METERS-P01 >inverter 0.0 aac >current 31.0 max >DOWN UP TOP PORT > >STATUS/FX/METERS-P02 >inverter 0.0 aac >current 30.0 max >DOWN UP TOP PORT > >STATUS/DC/BATT---P04 >battery min today > 46.6 vdc >DOWN UP RESET TOP > >This is compared to clients' systems were they've had more transient >loads (in the range of 4.5KW for a >pair of VFX3648) and reached lower voltages (in the 44's and 45's) with >larger battery banks. > >> Main cables and breaker are sized as always, (4/0 with a 250 A breaker) but >> parallel string jumpers are >> reduced to 2/0 as they are carrying 1/2 to 1/3 of main current. > >Having seen all but one string of batteries fail in a multi-string >system, this is not a safe assumption. >You cannot assume all of the strings are working properly, or even that >only one string fails. >-- >Julie Haugh >Senior Design Engineer >greenHouse Computers, LLC // jfh at greenhousepc.com // greenHousePC on >Skype _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
