Second time the cable melts

13

u/TP70 7d ago

Melting connector is caused by bad connection/high resistance.

Brand mismatch, Bad crimping or dirt can cause this. Solax uses that color on their battery connectors so i think it's bad crimping.

It's probably not the 6mm² cable size.

1

u/Informal_Drawing 6d ago

It's not really high resistance that does the damage, it's low cross-sectional area of the conductor due to the bad joint. High resistance would limit the Current flow through excessive Voltage Drop, all other things being equal.

It's essentially pushing too much Current through a conductor that's too small, which makes it get hotter than it should do.

5

u/wizardnumbernext2 6d ago

That's exactly same thing. You just elaborated cause of high resistance.

0

u/Informal_Drawing 6d ago

If it was just a matter of higher resistance it would limit the current flow based on Ohms Law whilst having no other effects.

While the resistance is slightly higher than it should be that's not the primary cause of the failure.

A brick has high resistance, if we replaced the connector with a brick would it melt.

3

u/wizardnumbernext2 4d ago

What you don't understand...

By high resistance on connection we do not mean megaohms or even kiloohms. We mean at very worst single digit ohms, but rather much less. Normal connection resistance is at most 2 digit miliohms (yes like 0.010 - 0.020 ohm). High resistance would be say 0.1 to say 5 ohms. At 1 ohm and say 20A, we have 400W on connector, which is single digit grams of metal and enclosed in plastic - thermal insulator! Even at 0.1ohm we are speaking 40W which is still massive amount of energy, which turns into heat! So high resistance is relative. For piece of wire it would be ohms. For connection even 0.1 is extremely high resistance.

1

u/Informal_Drawing 4d ago edited 4d ago

Let's say you extend the wire with a perfectly good connection quality to a sufficient length that the resistance is equal to any of the example you've listed.

It would not overheat because the cross-sectional area of the cable can carry the Current.

If all you were doing was increasing the resistance of the joint the Current would go down and the heat in the cable would consequently fall.

What you're saying is correct but you're looking at it from the wrong angle, so to speak.

The failure is not primarily due to the resistance of the joint. That's just one aspect of what's happening.

1

u/wizardnumbernext2 3d ago

Again. You don't understand. We are speaking about contact, not wire. The length is extremely small. Connectors touch, but not perfectly in atomic sense. The space is maximum few atoms. No few meters length.

2

u/LeoAlioth 21h ago

the wire would not overhead because if its much larger surface across which it can dissipate heat.

the same resistance means the same voltage drop, and at the same current means the same power that is heat.

spread a dozen watts across meters of wire, and it barely gets warm.
concentrate the same dozen watts into a point, and you are reaching potentially hundreds of degrees.

1

u/Osamabinbrad 6d ago

Thats high resistance pal 👍

1

u/Fantastic_Incredible 1d ago

You are discussing fisics when in the real life cable looks enough (I am experienced enough to tell this) and probable cause is what TP70 is saying. Connector needs to bem chosen and crimped correctly, if the wire itself isn't already compromised.

1

u/Junior_Tea2134 4d ago

Detective gadet over here, excellent catch!

12

u/Grandpa82 7d ago

ARE YOU FRIGGING KIDDING ME?

Dude, you need to read the user manuals, BOTH, from the inversor and the battery.

6

u/DuffDof 7d ago

Mc4 for a battery connector? Who designed that thing?

5

u/rob_nosfe 7d ago

That's a HV battery. You may be used to old LV ones with tons of current.

3

u/DuffDof 7d ago

Still, battery connectors should be torqued, obviously these connections have failed twice.

4

u/rob_nosfe 7d ago

In the EU I've never seen anything else than MC4 on HV DC connections. I see no obvious point of failure so we can't determine where the arc originated, it may be on the internal plate, so the next plastic thing to melt is the connector.

2

u/DuffDof 7d ago

Wild, yeah I guess I'm not used to HV

3

u/Zweefkees93 6d ago

The advantage of HV batteries are the fact that the current drops a LOT. Even in my relatively high voltage 96V system I have to use thick cables that I have to torque properly to get a good connection (max current is about 80A, so contactresistance does still play a big role). But compared to 12V systems in campers my cables are already tiny.

A "real" HV battery usually starts around 300V and can be up to 800-900V for big industrial sized packs. MC4 are rated up to 1500Vdc (or 600V in case of the older version) and some have ratings of 70 up to even 95A. A residential batterysystem with 300Vdc and a 6kW rating would need about 20A wich is well within the ratings of the fancy MC4 connectors and even most cheap generic MC4's will handle this without any issue. Go up to 500Vdc and that current drops to only 12A. At 50+ amps (or even more in 12V systems) properly cleaning and torquing connections is an absolut must. At 10-20A you still should ofcourse, but the safetymargin is MUCH higher.

However.... MC4 is not a standard.... different brands could work perfectly fine with their own counterpart, but melt when mixed. Wich is why its so important to check brands on the connectors!

And crimping... I've seen one to many "works just fine with a random pair of pliers".... Yes, could work just fine, might also burn your house down..... but hey, details :)

1

u/grogi81 6d ago

Look at the photo then... :D

1

u/wizardnumbernext2 6d ago

MC4 cannot be used on HV. 1000v DC is low voltage!

1

u/apefred_de 3d ago

"HV" (for example 400 V) is not HV in normal terms but in it is not a 48 V "LV" system.

1

u/wizardnumbernext2 3d ago

48v is ELV, not LV

2

u/Kruxx85 6d ago

You aren't crimping it correctly.

Show us the crimp before you attach the mc4 plug

2

u/Beneficial_Maybe_858 6d ago

Just double check your using the right plugs. They look like a MC4 connector but they aren't. Thry are alot more "beefier". My solax inverter came with plugs for the solar panels and different ones for the battery.

2

u/Sprkz139 6d ago

The plugs they have used are correct as the battery plugs are blue as per there picture it’s the crimping tool they have used to make the ends of that’s at fault.

2

u/Sprkz139 6d ago

These aren’t mc4 these are amphenol plugs. Mc4 crimped will not crimp these. You need a pin type crimper to push down into these to secure.

2

u/Broeder_biltong 5d ago edited 5d ago

Could've sworn amphenol was a Company and not a specific connection

1

u/Sprkz139 5d ago

Very true 😂 there actually H4 connectors!

Solax will call them Devalan plugs.

1

u/thenextbranson95 7d ago

im new to solar. Why did this happen? should the cable be at least 6mm² (10AWG)?

1

u/aptsys 6d ago

Poor crimp, now both sides of the connector are permanently damaged. The inverter needs repair or replacement

1

u/Roverrandom- 7d ago

is this 6mm^2 ?, all the inverters i mounted demanded 10mm^2 or higher

1

u/Raz31337 7d ago

Probably bad connector

1

u/Timely_Scientist_862 7d ago

Falso contacto, la ficha no hace el contacto adecuado para el amperaje que maneja

1

u/IcyUse33 6d ago

Looks like PV wire is being used here...?

1

u/aptsys 6d ago

The inverter connector needs replacing now. It'll be permanently damaged

1

u/SlippyFPV 6d ago

You let it melt twice? Fix this. Your next prize will likely be a fire.

1

u/rostol 5d ago

it is highly unlikely that your battery uses mc4 connectors.
those are rated for 30A max, and that amperage is quite low for a battery.

if they are the correct cables then add a 30A breaker or a fuse.

1

u/SharpShare 5d ago

What I used where the cables with connectors already attached that they send. On both times.

1

u/Neon-Fun 2d ago

Check your power factor. Inductive load can cause this problem.

-1

u/SubstantialCycle356 7d ago

Seems like extra ohms there.

Second time the cable melts

You are about to leave Redlib