[RE-wrenches] Breaker tripping question

[Darryl Thayer]

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 <jay at asis.com> wrote:

> From: jay peltz <jay at asis.com>
> Subject: Re: [RE-wrenches] Breaker tripping question
> To: allan at positiveenergysolar.com, "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> 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
> > 
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