Blew a fuse... why?

[Sammeh]

Over the weekend I built an 800 Watt solar array (8x100 watt panels, 60 amp Renogy MPPT, w/ a 2000 Watt Inverter, 200 AH 12v FLA Batteries.). I'm using this for a residential setup to suppliment / partial power 1 - 15AMP Circuit in the house.

Between the Batteries -> Inverter I have a 200 AMP ANL fuse. On the AC output of the Breaker I have a small breaker box with a 15amp residential breaker then feeding the circuit (I was just testing, but intended on taking an existing circuit that powered a section of house + some lights and move to this sub panel).

To "Test" I installed a simple outlet next to the breaker panel and plugged in a few loads (Circular saw, leaf blower, other random garage equipment) and they all worked ok (uniquely). I figured "Let me plug in my 30 AMP RV and turn on the air conditioner, it always resets my 15amp circuit breaker, and just see what happens.

I plug in the RV (30 amp -> 15 amp dongle) and near instantly hear a pop and my 200 amp fuse had blown. What I'm confused about is the 15 AMP AC breaker has a max wattage of 1800 watts? (15 x 120) - which would equal 150 AMPS (1800 / 12v). How come that didn't trip before the breaker blew? The Inverter can surge - so I recognize it could go higher than anticipated but I was hoping to prevent that via the breaker panel / 15 amp breaker - do normal residential breakers also surge, again it popped near instantly.

Unfortunately - I didn't have another fuse - so my weekend fun was somewhat over while I wait on Amazon to deliver another one on Monday. I'm hoping to prevent this in the future.

Any input would be appreciated.

 

[gnubie]

The AC breaker has two trip mechanisms, a bimetalic thermal strip for lower overloads and a electomagnet for gross overloads. The thermal strip has a time rating indicated by a letter on the breaker to prevent false tripping in the event of a short term overload such as motor starting current.

The time that it took the AC breaker to react may have been long enough for the DC side current to go well beyond the fuse rating.

This is all just a guess since there's nothing mentioned about the specs of the RV aircon.

 

[Sammeh]

The AC breaker has two trip mechanisms, a bimetalic thermal strip for lower overloads and a electomagnet for gross overloads. The thermal strip has a time rating indicated by a letter on the breaker to prevent false tripping in the event of a short term overload such as motor starting current.

The time that it took the AC breaker to react may have been long enough for the DC side current to go well beyond the fuse rating.

This is all just a guess since there's nothing mentioned about the specs of the RV aircon.

This is great information. Any idea how to identify the "time rating indicated by a letter on the breaker?" This was the breaker I bought:

https://www.lowes.com/pd/Square-D-Homeline-15-Amp-1-Pole-Standard-Trip-Circuit-Breaker/1111791

 

[gnubie]

I couldn't find any information about the trip performance of those with a quick google search only a glossy catalogue style blurb with tables of current ratings. Someone else might be able to turn up a proper datasheet for them.

 

[PHoganDive]

https://download.schneider-electric.com/files?p_enDocType=Data+Bulletin&p_File_Name=0600DB0105.pdf&p_Doc_Ref=0600DB0105

 

[robaroni]

Over the weekend I built an 800 Watt solar array (8x100 watt panels, 60 amp Renogy MPPT, w/ a 2000 Watt Inverter, 200 AH 12v FLA Batteries.). I'm using this for a residential setup to suppliment / partial power 1 - 15AMP Circuit in the house.

Between the Batteries -> Inverter I have a 200 AMP ANL fuse. On the AC output of the Breaker I have a small breaker box with a 15amp residential breaker then feeding the circuit (I was just testing, but intended on taking an existing circuit that powered a section of house + some lights and move to this sub panel).

To "Test" I installed a simple outlet next to the breaker panel and plugged in a few loads (Circular saw, leaf blower, other random garage equipment) and they all worked ok (uniquely). I figured "Let me plug in my 30 AMP RV and turn on the air conditioner, it always resets my 15amp circuit breaker, and just see what happens.

I plug in the RV (30 amp -> 15 amp dongle) and near instantly hear a pop and my 200 amp fuse had blown. What I'm confused about is the 15 AMP AC breaker has a max wattage of 1800 watts? (15 x 120) - which would equal 150 AMPS (1800 / 12v). How come that didn't trip before the breaker blew? The Inverter can surge - so I recognize it could go higher than anticipated but I was hoping to prevent that via the breaker panel / 15 amp breaker - do normal residential breakers also surge, again it popped near instantly.

Unfortunately - I didn't have another fuse - so my weekend fun was somewhat over while I wait on Amazon to deliver another one on Monday. I'm hoping to prevent this in the future.

Any input would be appreciated.

Check your inverter data and how long and large a surge it can take. I suspect it's at least double for several seconds. At 4kw you're drawing over 300 amps at 12v. The inverter also very likely doesn't double its power instantly, it's like a delay line. The 200A fuse will see the load before the slower acting 15AAC breaker does.
Rob

 

[efficientPV]

I have a 100W fridge and it draws 120A @12V when it starts. For sure you were much higher than that,