Fried Combinor Box [RE-wrenches]

[Kent Sheldon]

I can't address the 'multitude of problems' comment, but the main advantage
is cost, construction simplification, and size reduction. The main problem
with multiple mechanical connections to fuse blocks and bus work, is loose
wires over time, which also causes fires.

Kent Sheldon
Product Manager - Photovoltaic Engineering Group
Xantrex/Trace Technologies Inc.
925 245 5463/925 245 1022 Fax
kentsheldon at tracetec.com  www.xantrex.com


-----Original Message-----
From: Drake Chamberlin - Electrical Energy
[mailto:solar at eagle-access.net]
Sent: Saturday, March 24, 2001 9:16 AM
To: RE-wrenches at topica.com
Subject: RE: Fried Combinor Box [RE-wrenches]


What is the advantage of the new combiner boxes with printed circuit board
and a multitude of problems, over the basic technology of fusing strings
and connecting them to a solid bus?

Drake

At 01:55 PM 03/23/2001 -0800, you wrote:
>Don:
>
>The problem may have been the undersized fuses or possibly high ambient
>temperature.
>When I ran the original UL tests on the PCB-10 (later changed to TCB-10 for
>Trace)  it got VERY hot when we pushed the fuses beyond 80% (divide by
>1.25)of their rating.
>At 100% of rated current we discontinued the test when the holder
>temperature got above 150 C and it was still rising fast.
>
>This is one of the reasons for the 1.25 derate is in the Code for
continuous
>duty.
>Just to be complete - The second 1.25 is for high irradiance (1.25*1.25 =
>1.56).
>You should always use a MINIMUM of the 1.56*Isc derate from STC when sizing
>fuses.
>The basic rule of thumb is use the biggest fuse you can get away with while
>meeting wire ampacity and UL series fuse requirements for the module.
>
>Fuses are thermal devices and, at the fundamental level, they work by
>getting a wire hot enough to melt.
>If you run above the 80% level then the whole box just sits there and
cooks.
>
>We ran the box with (10)10 Amp fuses at 8 amps per fuse until we reached
>thermal stability.
>This is where the 80 Amps continuous output rating comes from.
>We then ran the tests again with (6) 15 Amp fuses in every other holder at
>12 Amps (15/1.25).
>As I recall, the hot spot temperatures were about the same for each test.
>This should be outlined in the manual.
>
>This testing was with an ambient room temperature of circa 25 C.
>UL allows you to extrapolate the data from 25 C up to 40 C by simply adding
>15 degrees to the test data.
>As long as you are within the temperature rating of the materials in the
box
>after you add the 15 degrees you can use the 40 C ambient.
>If you want an ambient temperature rating above 40 C then you have to run
>the test at that temperature.
>This adds significantly to the cost for UL Listing and is why we have a 40
C
>rating.
>
>If you are going to use the PCB-10 in higher ambient temperature then you
>need to add additional derates.
>The fuse manufacturer (Bussman in this case)publsihes some guidelines for
>additional temperature derating for operation at higher temperatures.
>Then there is the whole issue of solar gain contributing additional
heating.
>UL doesn't even have a procedure to deal with this yet.
>
>While I know this doesn't help with the problem I hope it helps to
>understand why it might have occurred.
>If you want to discuss it some more please feel free to contact me
directly.
>
>Best regards,
>
>John Berdner
>
>SMA-America, Inc.
>20830 Red Dog Road
>Grass Valley, CA  95945
>Tel: 530.273.4895
>Fax: 530.274.7271
>
>
>
>
>
>
>
>
>
>
>
>
>-----Original Message-----
>From: Don Loweburg, Offline [mailto:i2p at aol.com]
>Sent: Friday, March 23, 2001 12:11 PM
>To: RE-wrenches at topica.com
>Subject: Re: Fried Combinor Box [RE-wrenches]
>
>
>In a message dated 03/23/2001 11:31:55 AM Pacific Standard Time,
>mmangelsdorf at hei.com writes:
>
>
>
>That installation had Solarex MSX120s, four to a string,
>using slightly undersized 10a. fuses when they should have been 15a.  Bill,
>chime on this one if you want.  Since the TCB10 is one of only a few
>
>
>Marco, I was using 4 kc120 in series with a 15 fuse (according to
>kyocera-slightly big-they want 11 a).  I feel like saving the box and
giving
>it to Bill for his collection of "things that suck".
>
>Don
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