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cookinwitdiesel avatar image
cookinwitdiesel asked

Lynx Shunt 1000a Fire Hazard

My dad's system at his ranch has now had dangerous high heat and smoke when running only about 700a across the ANL 750a Blue Sea Systems fuse in the shunt. The fuse did not blow but essentially otherwise cooked due to heat. All connections were snug and tight.

The first time, the plastic holding the busbars actually melted. We replaced the shunt and this 2nd time the fuse cooked (and again, did not blow, per VRM max current was right at 700a).

What is the best/recommended fuse for this setup that will not create a dangerous thermal bottleneck?

We are currently using this:
https://www.bluesea.com/products/5163/ANL_Fuse_-_750_Amp

Pictures of the first failure after which we replaced the shunt and then the 2nd incident with the new shunt. In both incidents, the fuse did not blow. VRM screenshot is the 2nd incident and the last 2 pictures.

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fuseslynx shuntfire
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janieronen avatar image janieronen commented ·

That's serious overheating. Looks like that fuse is not only what have been overheated. How is load side busbar also heat damaged? What were environment temperature and is there sufficient amount of cooling airflow?


With 24V 700A is very strict about contacts. I have changed system voltage from 24V to 48V after noticing that cable and connection losses went absurd high with over 10kW power. As first unit were already overheated I suggest that in future fit few temp sensors to the bus bars to give alarm when rising close to cable heat limits. First test cycles heat camera is best tool but with probes you can be sure that there is no fire hazard.


Can you plot DC-power and AC-power to same to get picture how much energy were lost? I would be also interested did your AC-load increased after 19:00 or did cabling/busbars overheated and load increased because of higher temperature. Co-efficiency factor drops when overheating dramatically what causes even more resistance.

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cookinwitdiesel avatar image cookinwitdiesel janieronen commented ·

He does have temperature monitoring and probes now, added after the first incident. Seen temperatures as high as 250f multiple times. The bus bars got so hot they melted the plastic posts they are supported by the first time. This prompted a full replacement as we could not trust any of the physical connections on that unit after that.1687367885727.png

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janieronen avatar image janieronen cookinwitdiesel commented ·
Ouch. Cables normally have something like 150F/70C maximum temperature so system should automatically been shutdown at that point to prevent short circuit. My experience I would not use Lynx for over 400A continuous currents as limited heat dissipation often creates issues if not force cooled environment.
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cookinwitdiesel avatar image cookinwitdiesel janieronen commented ·

There was a good amount of loss, but that is not all heat in the conductors. There are 6 24/3000 MPs and 14x 250/100 MPPTs all powered on as well. Clearly a lot of heat was still generated though! My dad went down and bypassed the inverters and powered down the system when the smoke alarm went off, that is why the data stops. Smoke was from the fuse cooking.

1687370643809.pngWe would love to have done a 48v system but the UL listed inverters were only 12 and 24v at the time.

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janieronen avatar image janieronen cookinwitdiesel commented ·
That is way too much current for a lynx if 1400A total from MPPTs is possible to push power to Multis and battery.

If remember correctly in the Lynx manual it's said that all connected load/generation fuses cannot exceed 1000A in total.

You should definitely to go with custom massive bus bars and physically larger fuses which can dissipate more heat. That's my own suggestion even love VE-products.
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cookinwitdiesel avatar image cookinwitdiesel janieronen commented ·
I do not push anywhere near that much current - honestly could have done 250/70s in this design. Only 23kw of solar panels (56x 415w) and max charging is set to 700a with DVCC as well as max inverter power set to 14400w with ESS.
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3 Answers
natebert avatar image
natebert answered ·

It looks like the fuse is the source of heat. Maybe you've got a couple from the same bad batch?

Or maybe, could the use of Bussman/Eaton's 800a ANN model offer additional surface area as the tabs on the ANN model of fuse appear to be thicker?


ANN:
https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/bussmann-series-supplemental-fuses/supplemental-fuses-limiters/bus-ele-ds-2023-ann.pdf

vs
ANL:
https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/bussmann-series-supplemental-fuses/supplemental-fuses-limiters/bus-ele-ds-2024-anl.pdf

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cookinwitdiesel avatar image cookinwitdiesel commented ·
I agree, the negative bus bar which handles the same current shows zero signs of high heat. Only around the fuse on the positive side.
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pwfarnell avatar image
pwfarnell answered ·

Is the fuse being run too close to its rating. I can not find the tech specs for an ANL 750A fuse, but I have seen fuses are typically 100mV voltage drop at rated current. As a thought experiment, lets say that dV is 93mV at 700A, this means that the fuse would be generating 65W of heat which is a fair load to dissipate. Sure when a fuse blows it creates a very high heat load but that is short lived so there is limited time to heat the rest of the system. Running the fuse close to rated will generate the heat continuously, which will then soak into the system. Perhaps a 1000A fuse would be better, with a lower resistance and lower heat production for continuous running at 700A. There are various reference stating that the max continuous load is ideally 75% of the fuse rating or the fuse is rated for 125% of the maximum continuous load.

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cookinwitdiesel avatar image cookinwitdiesel commented ·
I would love a larger fuse with lower Vdrop but it seems that 750/800 is the highest rating you can find on reputable sourced fuses for ANN/ANL form factor.
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Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

@cookinwitdiesel it has been discussed already as I see, but would like to add I do agree with most here that the fuse is used too close to its rating which causes heat generation when used on high power for longer periods. getting a higher rating would tackle this I feel. we have tested the system on 1000A , with large cabling 9which also divert heat) and 1000A fuse which did of course get warm , but did not had a burnt/deformed enclosure as result.


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cookinwitdiesel avatar image cookinwitdiesel commented ·
Thank you for the input Johannes, can you share what fuse you used that fits and is rated at 1000a? I have not been able to locate anything on my own so far. Nothing else in the system is getting hot, just the fuse and attached bus bars so I am very confident that the fuse is the main source of heat here.
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cookinwitdiesel avatar image cookinwitdiesel cookinwitdiesel commented ·
@Johannes Boonstra (Victron Energy Staff) Can you share what fuse was used for this testing that fit in the Lynx Shunt? Thanks!
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Alexandra avatar image Alexandra ♦ cookinwitdiesel commented ·

@cookinwitdiesel

It is designed for the CNN fuse. Bigger ones come from littelfuse that can go up to 2500A.

In the manual.

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cookinwitdiesel avatar image cookinwitdiesel Alexandra ♦ commented ·
@Alexandra where are you seeing this larger sized fuses? I could only find mention of up to 800a
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Alexandra avatar image Alexandra ♦ cookinwitdiesel commented ·

I got (rather stupidly) messed up by the up to 2500A interrupting speel.... you are right they only go up to 800A. I apologise for not reading more thoroughly and leading you to wasting your time looking for one.

screenshot-20230703-192021.jpg

The CNN is a much slower blow fuse than the ANL which tends to blow right on its rating.

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Alexandra avatar image Alexandra ♦ Alexandra ♦ commented ·

@cookinwitdiesel Further thought on your system, 1000A is alot to go wrong (as you know)

I would bridge the fuse with a nice fat bus bar of appropriate size; interrupt the Lynx system with NH fuse holder and 1000A NH fuses.

(Head not in the clouds this time) The NH is what we normally use on bigger amp systems, sinply for arc quenching and heat is not a thing to deal with.

Class T fuses and holders are a bit more elegant

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Alexandra avatar image Alexandra ♦ Alexandra ♦ commented ·
If all your batteries and mppts are individually fused to the bus bar, you could also just bridge it with a piece of bus bar and still be safe.
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cookinwitdiesel avatar image cookinwitdiesel Alexandra ♦ commented ·
EVERYTHING attached to the busbars is fused. The fuse at the Lynx Shunt should be to protect the busbar itself as a conductor I would imagine since collectively, this system can produce over 1000a (but never should as configured/programmed) it is appropriate to have an overcurrent protection on that conductor (the busbar itself).
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Lynx Shunt VE Can online manual


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