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 <mailto:[email protected]> NABCEP certified solar PV installer Positive Energy, Inc. 3225A Richards Lane Santa Fe NM 87507 505 424-1112
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