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chrish avatar image
chrish asked

Smartsolar MPPT trips its Noark battery breaker often

I have a customer using a Victron MPPT 250/60 with 3.6kW of PV (and 190Ah 48V Marathon MF/T)
It is exporting from the batteries, so the controller runs at full power for a few hours in the middle of the day in sunny weather.
The controller is isolated from the batteries by a Noark Ex9BP (DC) 63A breaker, but it has tripped a couple of times in the middle of the day. I wouldn't have thought a Victron 60A unit could hold 63A or more for the time needed to trip the breaker?

Aren't they limited to 60A continuous?
From the breakers trip curve, worst case, I get something like:
2.8 hours @ 63A
10s @ 130A
5ms @ 6kA
ex9bp-curves.jpg

Is it possible the MPPT circuit control could be switching on and off too quick when doing a retracking under full power, and creating a very high current spike of 6kA for 5ms?
Eg, mosfets have inadequate snubbing? or poor snubbing algorithm in firmware? (if it can respond that fast!) - I'm guessing - any ideas please?

MPPT SmartSolar
ex9bp-curves.jpg (96.6 KiB)
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5 Answers
chrish avatar image
chrish answered ·

It took a couple of visits as the fault became intermittent. It turned out to be that the MPPT was connected to some older, and now undersized wiring. The days of almost perfect insolation meant that the undersize wiring would heat up, and transfer the heat to the breaker, thus tripping it thermally.
Also, this same high current was busy heating up an (old) oxidised bolt terminal on the battery fuse switch making it more corroded and resistive - this would intermittently send the detected battery voltage wavering up and down. :o(
A thorough check and clean of all old connections revealed all this, and cabling and terminals were replaced, with relevant cabling all upsized.
Now it is completely stable with no discernible cable heating.
It was an 'oops' that I did not check the old cabling sufficiently when replacing the old PWM regulator with an MPPT.
I am happy that in this instance there was not, nor is there now, any problem with the Noark breaker!
Thanks.

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Alexandra avatar image
Alexandra answered ·
@chrish

I have found the noarks do this. (Also had one catch on fire - so no longer a fan)

It seems to be a thermal trip not an amp based one.

Swapped it out for a chint and the chint did better, same rating I may add.

Are the loads also running through the breaker?

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chrish avatar image
chrish answered ·

Ok, sounds interesting - I've never had a Noark play up, but then I've never had one run near flat out its current rating either, now that I think of it. We have had exceptional sun with cold weather (I noticed my 2nd hand 6 x 250W clunker polys were putting out a steady 1575W!)
No loads through it - just a dedicated isolator for controller to battery.
I'll find a substitute and swap it! Thanks ;o)

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Alexandra avatar image Alexandra ♦ commented ·
@chrish

On the battery side it is better to use fusing anyway. And maybe because you are running so close to its rated output, it is working harder than it can cope with?

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chrish avatar image
chrish answered ·

In AU, we need to have a 2-pole isolator for each piece of gear connected to the battery. Overcurrent protection is separate to that, so it is attractive to have both isolation and overcurrent in one device. A fuse-switch is possible but it must have a 'disconnect under load' capability.
So it was either a 63A breaker, or jump to a 100A chassis-breaker (space is also an issue on this one).
I have now swapped the Noark for an ABB DC-rated breaker, so heres hoping.
Thanks for your suggestion - I'll post an update after a few sunny days!

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Mike Dorsett avatar image
Mike Dorsett answered ·

I think your 63A breaker is undersized for the 3.6kW array. Regulations require array fusing to be 1.25 times the nominal current, this gives 93A for the breaker.So you should be using a 100A unit, not 63. Long term warm / hot running of a 63A breaker will permanently shift its trip point towards a lower current.

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