Hi Allan I have had this problem. I can name a few installations where it happens. I think that it is the high ripple current if you have and average of 35 amps but it comes in a current that is 50% ripple, you have a thermal response of X^2 /2 or about twice the heating. So a thermal breaker will trip. A magnetic breaker has magnetic force equal to current, and a 50% duty cycle should average only the same force, but the magnetic buzz seems to trip them also. The peak force seems to be double, and after a little time ?? So I have had both magnetic and thermal breakers trip below average current when working on a low duty cycle.
--- On Wed, 12/17/08, jay peltz <[email protected]> wrote: > From: jay peltz <[email protected]> > Subject: Re: [RE-wrenches] Breaker tripping question > To: [email protected], "RE-wrenches" > <[email protected]> > Date: Wednesday, December 17, 2008, 11:57 PM > Hi Allan, > > I seem to remember that if you hook the breakers up > backward they will trip more easily. > > Be curious to try hooking them up the other way and see if > that matters. > > jay > > peltz power > > > > > > > On Dec 17, 2008, at 11:55 AM, Allan Sindelar wrote: > > > Wrenches, > > I am doing a series of corrective equalizations and > load tests on a set of Surrette S460 batteries. I'm > using an old Trace DR1524 mod-square inverter as a charging > source from in-shop grid AC power. I am also using the > inverter to power mostly-resistive AC loads: an electric > space heater on low with fan, an incandescent bulb and a CF > bulb - the combination being used to achieve a C/20 > discharge rate for load testing. DC metering is handled by a > Tri-Metric meter with 100A (low) shunt; AC by a Kill-a-Watt > AC monitor. The inverter is rated to charge DC at 35A > maximum, and consistently charges at around 32A measured. > 35A is a C/20 rate (5A per 100A of rated capacity for > corrective equalization) for these 350 ahr batteries in two > parallel strings. > > > > When I set up this station I used a CBI > (Outback-Midnite) DC panel-mount 50A breaker on the battery > cables. The cables are 2/0 or 4/0, being what was around the > shop. The problem is that the breaker tripped while > charging. Thinking it might be a defective breaker, I > replaced it with a 60A; same. It's not a surge load, as > it doesn't trip on startup, but 10-30 minutes later. I > understand that these are magnetic-hydraulic breakers, not > thermal, so I don't understand why they are tripping. My > hunch is there's a DC ripple that's messing with the > breaker's response curve. Since inverters are generally > installed with heavy cables and matching big breakers or > fuses, this never shows up in normal operation. But in this > application there's no surge capacity to accommodate, so > I just sized the breaker to the load plus reserve: 35A > max/50 or 60A breaker. And the OBDC/CBI breakers are rated > for 100% duty cycle. > > > > Any ideas? > > > > Thanks, > > Allan > > > > Allan Sindelar > > allan_(at)_positiveenergysolar.com > > NABCEP certified solar PV installer > > Positive Energy, Inc. > > 3225A Richards Lane > > Santa Fe NM 87507 > > 505 424-1112 > > > > _______________________________________________ > > 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 > > > > _______________________________________________ > 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 _______________________________________________ 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
