Fried Combinor Box [RE-wrenches]

Sat Mar 24 09:16:24 PST 2001

<x-flowed>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
>
>
>
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>
>
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>
>
>-----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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To unsubscribe send a message to: 
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To check out the other RE-Wrench participants:
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Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

____________________________________________________________
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Newsletters, Tips and Discussions on Topics You Choose.
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