Fw: Trace Charge Controller Ratings [RE-wrenches]

Allan Sindelar allan at positiveenergysolar.com
Tue Apr 23 12:49:03 PDT 2002


Wrenches,
Here's a pretty well thought-out opinion from Mister Wiles on the C40/C60
amperage question. Now it's time, I think, for a confirmation or
clarification of the "somewhat confusing" aspects from the engineering
department at Xantrex.
Allan at PozEnergy

----- Original Message -----
From: "John Wiles" <jwiles at nmsu.edu>

Allan:
Please post this on the wrenches web site when you have time.  Take credit
for it if you feel it is OK.

Trace sales literature, product markings, and engineering literature are
somewhat confusing.  Here is what I "think" based on
UL testing and the NEC requirements.

The Trace controllers are rated by UL at 60 amps or 40 amps based on a
maximum heat sink temperature at some ambient temperature (probably 25°C).
I note that the C-60 has a "HOT" warning label which may indicate that its
heat sink is allowed (by UL) to operate at a higher temp.

This continuous rating would be similar to the 100 % duty rating that
Heinemann and AirPax magnetic-hydraulic circuit breakers have. Neither the
charge controllers nor the breakers have to undergo the 80% derating that
normally all other overcurrent devices and conductors must undergo.

However, in PV source circuits, we do have the 1.25 imposed on these 100%
duty devices because the irradiance can and frequently does go above 1000
watts per square meter for several hours around solar noon.  In terms of
Isc, that would make the C60 rated at 48 amps Isc and the C40 rated at 32
amps Isc.  This would be the code and UL-required starting point for a
design.  Of course, then the arguments can start about how much current a
given array will put out under various conditions of temperature,
irradiance, wind, etc, etc.

If the batteries are low and the days are cold, windy, and bright and sunny
and you don't live in Southern California or an other area where there is
less-than-clear-air, the array current can exceed the rated Isc.  This is
the reason for the 1.25 in the first place.

Given that the charge controller may be operating in ambient temperatures
higher than 25°C (who knows what the FET and heat sink temperatures are),
driving it close to or above the rated continuous current may pose longevity
problems.

In current production, both units seem to have the same maximum (peak)
current limit of 80+ amps. The early C-40s had a current limit at 63 amps.
The controller may actually indicate a fault if currents hit those levels.
With a higher heat sink temperature, the C-60 will normally be operating
closer to its maximum temperature and current limit than will the C-40 under
similar conditions.  This may be why we see more problems in pushing the
C-60 than the C-40 over their ratings.  In one system, I have seen a C-60
hitting 60-62 amps this winter in a cold garage.  There may have problems as
the garage temperature goes to 40-45°C this summer and the irradiance gets
greater.

Because these charge controllers are rated at 100% duty and the commonly
available breakers from Heinemann and Airpax (the "E Frame" breakers) are
also rated at 100% duty (when installed in an enclosure that is listed with
the breaker for 100% operation, the breaker rating should match the charge
controller.  This means use a 60-amp breaker with a C-60 and a 40 amp
breaker with a C-40.  Other breakers without the 100% duty cycle will have
to have a higher rating to meet the 80% derate.

In these particular installations (100% controllers and 100% breakers), the
conductors should have an ampacity after temperature deratings equal to or
greater than the breaker rating.
--

If I can provide further information, please do not hesitate to call,
e-mail or fax me.

John

John C. Wiles,  Program Manager
Southwest Technology Development Institute, New Mexico State University
505-646-6105      505-646-3841 (FAX)   http://www.NMSU.Edu/~tdi/pv.htm
SWTDI/NMSU
1505 Payne Street-Campus
Box 30001/MSC 3 SOLAR
Las Cruces, NM 88003

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