Friends of mine have a Sunsynk installation with a 12 x 550 W (Imax < 16 A, Voc < 700 V @ 0 degC) panel string.  The installation is working well, as per expectation, but the fuse holder is running hot (~40 degC).  The fuse holder is an Inge, rated at 1000 V, 32 A.  The fuse is a 20 A fuse protecting a 6 mm2 cable.  We've double, tripple, fourdouble-checked all the connections; there's no loose connection.

Anyone else with experience of fuse holders warmer than expected?  Most I've seen are running at 2-5 degC above ambient, which I expect due to the internal resistance of the fuse holder itself.  But the 40 degC we see here is close to 15-20 degC above ambient.  The temperature was measured at ~11:00 in the morning on a sunny day with 5 kW solar yield.

I think the problem with these type of fuse holders is the part inside the holder that cradles the metal fuse connection endcaps, I had one that melted pretty badly, with 75v and about 20 amps it was Onesto branded upon dismantling the melted remains of the fuse holder, I saw that the connection area is very small between the fuse and the cradle that is connected to the terminals of the fuse holder.

2 hours ago, Tacet said:

Friends of mine have a Sunsynk installation with a 12 x 550 W (Imax < 16 A, Voc < 700 V @ 0 degC) panel string.  The installation is working well, as per expectation, but the fuse holder is running hot (~40 degC).  The fuse holder is an Inge, rated at 1000 V, 32 A.  The fuse is a 20 A fuse protecting a 6 mm2 cable.  We've double, tripple, fourdouble-checked all the connections; there's no loose connection.

Anyone else with experience of fuse holders warmer than expected?  Most I've seen are running at 2-5 degC above ambient, which I expect due to the internal resistance of the fuse holder itself.  But the 40 degC we see here is close to 15-20 degC above ambient.  The temperature was measured at ~11:00 in the morning on a sunny day with 5 kW solar yield.

20 deg higher than ambient is quite normal. I have measured MCBs at 35 deg higher than ambient and normal and even on Hager MCBs. 

@Tacet,

"Friends of mine have a Sunsynk installation with a 12 x 550 W (Imax < 16 A, Voc < 700 V @ 0 degC) panel string"

Maybe ask you friend to check his string. I was under the impression that Sunsynk MPPT Vmax = 500V, and 450V is Vmax recommended for a string.

So he should rather watch the inverter than the fuses!

or maybe Sunsynk have new models, as I have read about HV (on the battery side) models other than the 50kW 3ph ones.

20 hours ago, Scorp007 said:

20 deg higher than ambient is quite normal. I have measured MCBs at 35 deg higher than ambient and normal and even on Hager MCBs. 

True - any switchgear has internal resistance, and putting current through that will always result in P=I^2 x R.  That power can't really be converted to anything else than heat.  I just haven't seen a fuseholder go this warm on any other installation - mine at home and the others I've measured are usually about 2-5 degC above ambient.  So I'm trying to figure out at what point I should start worrying. 

 

17 hours ago, Sidewinder said:

@Tacet,

Maybe ask you friend to check his string. I was under the impression that Sunsynk MPPT Vmax = 500V, and 450V is Vmax recommended for a string.

It is a 3-phase 12 kW.  But yeah, I was lazy - typed "< 700 V" rather than recalculate the actual Voc.  Voc @ 0 degC is 637 V. The PV input range is up to 800 V on those.  MPPT stops tracking at 650 V, but with a Voc designed for 637 V @ 0 degC the system is pretty well within spec.

Thanks for the clarification @Tacet, yes the 12kW 3ph does indeed have higher voltage mppt's. Hopefully your friend doesn't stay in Sutherland or Bethlehem, where 13V for grace would be too close for comfort for me.

Back to the topic, I would carefully inspect the Isolator's "fingers" that clamp the fuses, to see if they show any signs for deformation/arcing, as they may have become "stretched" and the clamping force when the fuse is inserted is not to spec anymore. Maybe a small adjustment to tighten them.

5 hours ago, Tacet said:

True - any switchgear has internal resistance, and putting current through that will always result in P=I^2 x R.  That power can't really be converted to anything else than heat.  I just haven't seen a fuseholder go this warm on any other installation - mine at home and the others I've measured are usually about 2-5 degC above ambient.  So I'm trying to figure out at what point I should start worrying. 

 

It is a 3-phase 12 kW.  But yeah, I was lazy - typed "< 700 V" rather than recalculate the actual Voc.  Voc @ 0 degC is 637 V. The PV input range is up to 800 V on those.  MPPT stops tracking at 650 V, but with a Voc designed for 637 V @ 0 degC the system is pretty well within spec.

My age old method is to find the point that the temp remains stable under as close to full load as is possible. I use a infra red thermometer. Don't need to be accurate to 0.01 deg. Up to 50 deg to me is still OK. 

We have seen many of these fuse holders melting and some pictures have been placed here. 

Inside temp does conduct to the terminal so real Quick to just measure the connection point. 

I belief the key point is to use good brands. 

Edited October 2, 20241 yr by Scorp007

I don't think you have a problem with fuse temp in the 40°C range. Fuses are heat sensitive devices meaning that it takes heat (via the overcurrent) in order to melt the fuse element inside the fuse. The more heat… the faster it takes to melt the fuse element… the less heat… the longer it takes to melt the fuse element. If the fuse is protecting 6mm² solar cable( rated 50~55A) then change the fuse rating to match the fuse holder rating of 32A. The lower the fuse rating the higher the resistance the more heat will be generated. In your case the 20A fuse will generate more heat that the 32A fuse and the higher the temp rise above 20°C( lab conditions to determine the rapture current of fuse element) the more heat is generated. 

'20°C above ambient sounds a bit high to me given it's probably running at 50-75% of its rated value. Did you also check if any ventilation slots in the fuse holder are open and clear? Depending on the design sometimes if a fuse holder is mounted horizontal it can result in reduced airflow through it therefore warmer running temps. Likewise if there's several fuseholders mounted hard against each other they'll run warmer than if there's space between them.

A thermal camera is a great tool for seeing exactly where heat is being generated if you can beg or borrow one for a day. Personally I'd start by trying another fuse from a recognised brand name of the same value and see if it's still a similar temperature. If it is I'd probably replace the fuse holder with a Hager out of an abundance of caution. I prefer not to take any chances with PV panel DC wiring, if anything looks even slightly suspect I'd just replace it rather than waiting to see if it gets worse.

Edited October 2, 20241 yr by Marv

On 2024/10/02 at 2:10 PM, Scorp007 said:

We have seen many of these fuse holders melting and some pictures have been placed here.

This is the part I'm worried about - the fuse holder is an Inge, which I'm not too familiar with.  I'd have preferred something like Schneider or ABB, but I didn't have control over the installation.

On 2024/10/02 at 2:52 PM, TaliaB said:

The lower the fuse rating the higher the resistance the more heat will be generated. In your case the 20A fuse will generate more heat that the 32A fuse and the higher the temp rise above 20°C( lab conditions to determine the rapture current of fuse element) the more heat is generated. 

Good point - I haven't considered the resistance of the fuse itself (was fixated on the fuse holder).

18 hours ago, Marv said:

Did you also check if any ventilation ... mounted horizontal ... several fuseholders mounted hard against each other they'll run warmer than if there's space between them.

A thermal camera is a great....

Ventilation slots are open and clear, the holders are mounted vertical, and the layout is fuseholder, SPD, fuseholder, SPD.

I'm not at liberty to post pictures, but the warmest part of the fuseholder is in the bottom half of the older.