Victron 100/20 MPPT almost caused fire. battery terminal gave 80v , same as PV side

DIY
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I had 2x Victron 100/20 MPPT on my setup. 1x 300A shunt, RPI4 Venus. They were working without a problem over 2 months. One of them almost caused fire. I am glad I was close by. I heard an unusual sound. I got close and I smelled it right away. And I then I saw the smoke. I immediately turned off the battery and PV lines. My system is 24V

It burned my 24v to 12v converter and my 24v inverter.

I checked voltages one charger at a time. I immediately saw battery terminal voltage was at 80v when the MPPT2 charge controller was on. Basically it was giving the same pv voltage to the battery side. That’s why it burned my inverter and dc converter. Over voltage. Back of the dc converter melted to the wall. Smokes came out of the inverter. MPPT1 was normal. But unfortunately MPPT 2 damaged MPPT1 as well. MPPT1 looked normal but it turned off. Basically stopped charging. No way to enable it back on again.

Because , it was not an over current issue, all fuses were normal. None of the fuses were burned.

I check youtube. I guess there are several videos on this issue. Battery terminals , output side, burn for some reason. Victron should come up with better and more reliable terminals. Possibly they should separate them little away from each other ,

i am glad it happened when I was there. If I was not there, it was a guaranteed fire.

I tried to call their customer service but they are in Netherland, I couldn’t find a local number in California or USA.

Be very careful. I will try to find out why it happened. I cannot think of any reason for now, other than just bad luck.

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I will take a wild guess and say that your battery terminals wasnt properly torqued down, heated up and melted into the pv terminals.

a picture or two will help the assessment.

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This same thing happened to me on the 100|50 MPPT. Output voltage to the battery was the same as the PV voltage - 44V on a 12V system. It caught my stove lights on fire and burt up several of the overhead 12V lights in my camper. Luckily I was in the camper when the stove lights started burning and pulled the fuse or it could have been catastrophic. I couldn’t believe it when I saw 44.3V on the system. Traced it back to the charge controller. No corroded wires or loose terminals. I haven’t pulled it out yet (just disconnected it), I have a replacement on the way. The system is only 3 years old and professionally installed at the dealership (if that even means anythng other than it’s not a DIY system).

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My understanding is the larger sccs like a 250/100 have a monitoring circuit and relay that will trip if the pv shorts to battery, to avoid cooking the battery and other equipment.

Perhaps that doesnt exist on the smaller sccs?

And then the rs450s are galvanically isolated so such a failure mode isn’t possible at all.

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These charge controllers are non-isolated, which means that any internal fault could expose the battery side to high voltage from the PV source. It is essential to include a battery protect between the chargers and the battery. The 12-24V battery protect is typically rated up to 65V and will disconnect if the voltage coming out of the MPPT charger exceeds 16.5V. By designing the system with these parameters in mind, you can prevent such failures. There are many examples online where people have included them in their schematics.

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Hello Ara, Thats very sad to hear and should not happen of course. it seems in your case it was not a matter of a bad connection but something internal. I would like to get in touch with you by mail to discuss further and see what we can do for you. (sales@victronenergy.com)

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Stefan, battery terminals were torqued properly.

AJGD2022 , exactly. It’s a big safety issue.

Brucey , they should all be safe to use. Even the smallest unit.

Owen, You probably meant 65A. They have multiple versions, 65A, 100A and 200A. I looked into Battery Protect. It might help but still… I wish the battery protect maximum voltage was adjustable through the settings. Just like the charge controllers, battery protect may fail too, but it is better to have it. Technically, MPPT charge controller has voltage regulator already.

Johannes, that would be great. I might have some ideas or suggestions. Thank God I was there. It could have been a disaster. I will email you.

To summarize.. Connections were tight, PV voltage NEVER exceeded 82V. PV current was low. None of the fuses burned. I checked

This is what ChatGPT said..

”Wow… that absolutely makes sense now — and explains the exact behavior you’re seeing.

A Victron SmartSolar should NEVER output 80V to the battery side, so what happened was a catastrophic internal MOSFET short inside the MPPT.
When that fails, the PV input can pass straight through to the battery output.

This is extremely rare, but when it happens:

:fire: PV voltage (80–100V) gets dumped directly into the 24V battery bus.

That will instantly destroy:

  • Inverters

  • DC-DC converters

  • Other MPPTs connected to the same battery

  • Any fuses not fast-blow

  • Wiring that isn’t protected

You were lucky to stop it in time.”

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I will mention as an aside, please don’t trust ChatGPT -or any other LLM- with anything at all. It’s not usually entirely incorrect, but since it doesn’t know anything at all, it’s rarely entirely correct. As an example, voltage won’t destroy your wires, nor will voltage trip your fuses - that’s not how things work - and if you went back to the same prompt and told it “wait no, that’s not how things work”, it would say “oh, you’re right, actually it’s this…” because it doesn’t know things, and is programmed to be agreeable above all else.
That said, it is correct that you were fortunate to be able to shut things down in time, as indeed damage could have been done to other components (largely the capacitors in those components, which are what would pop under high voltage), and I’m very glad you’re safe!

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Hi Johannes and Justin,

I agree with you on the voltage and the fuses but it burned my Inverters, DC-DC converters, and Other MPPTs connected to the same battery. However, some fuses have maximum voltage rating as well to be safe.

I still have them. They have 5 year warranties.
Are you willing to replace them ?
Are you in USA or Netherland ?

I think you need to find out the exact reason to prevent it in the future.

I had to replace my inverter and DC converters myself.

Thanks
Ara

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The maximum voltage rating on fuses is related to their arc-quenching capability (or lack thereof), but they won’t blow due to over-voltage - that’s not how fuses work.

With regard to replacements, I don’t work for Victron; get in touch with Victron via email at the email address given above by Johannes!

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I was going off memory. Looks like the 12/24V models can handle up to 35V and the 48V will go to 70V. So if you design the PV input below the max values the battery protect will be able to disconnect if there is an internal fault. Here is the manual there is an example where the charger is used on page 8 to disconnect when the voltage is too high.

114439-Smart_BatteryProtect-pdf-en.pdf (1.1 MB)

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Hi @Ara
In the end, how was this solved?
Thanks for the info!

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@Justin I understand what you are saying (I didn’t know that), do you know if DC breakers work in the same way?

The reason I’m asking is that I have a couple of MCCBs with a massive voltage rating at 1000V (!) and a current rating of 120A. I wanted to use these between my 450/100 chargers and my 48V batteries but I wasn’t sure their voltage would be appropriate. I looked for a rating of 80V DC but I couldn’t find those (only MCBs) on the local market (I’m in a fairly remote area).

Of course, it would help if you could give me a good reference link, but this is not crucial.

F.

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@Fideri
Yes. They break on amperage. And voltage rating matters because of arc quenching. Particularly if using lithium. So higher is technically better but somit the arc rating.

Over voltage protection is done with SPDs.

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@lxonline You are right. Everything I have read agrees with you. I had forgotten about SPDs because I didn’t intend to put them in those lines. I have since reconsidered that. The new problem I’m facing is that I can’t find anything lower than 100v DC or anything with big terminals (For this, I’m thinking about using some distribution blocks to reduce wire size). I will also look online much as that is not ideal for me.

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@alexpescaru Hi Alex. Victron Customer Service ( @JohannesBoonstra ) was great. I am sending back the defective MPPT controler. BV=PV. We hope they can find out what happened. The weakest and the most dangerous part of these controllers are over voltage imho. Because over current is protected by a 25A fuse. Over Voltage is not. Panel side over voltage may destroy the charger and possibly the panels. But battery side over voltage can destroy everything. It may even cause a fire.

I am researching DC Surge Protective Devices (DC SPD) . I like to put one between the panel circuit breaker and the MPPT Panel Input. 90V-92V limit protection for a 100V MPPT. I also like to put another one between MPPT Battery output and the battery and all other devices connected to it. For a 24V battery setup, probably around 30V limit. They should work bidirectional. I guess Hybrid MOV + gas discharge tube SPDs last longer than MOV-only units. I don’t know much about them but I am learning.

I think about this all the time. It bothers me. That’s why I am trying to find a very safe solution. I am trying to learn as much as I can. i will post here again when I have more update.

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Hi @Ara , reading this post with interest and understand the MPPT device possibly failed at the DC/DC stage with the main power MOSFETs going short and allowing PV level voltages through to the battery side. Not good. I run a 150|70 Tr CAN charge controller and am seriously thinking to replace this with the newer RS models that do have built in isolation and so this issues can then not be possible.

But, what I wanted to mention from your last post is that SPD are surge protection devices and being primarily designed for surge or transient conditions. The fault you experienced would not be a surge or transient, where the battery volts went up to PV volts for a short period of time, but would have stayed there. A SPD will not really handle this condition. Maybe if the SPD caused a fuse or breaker to trip, then it may function, but you need to look carefully at the design of this as the time for this to activate and trip a breaker might already be too late to prevent destruction of your inverter and other devices connected on the battery side.

It would be good if Victron could present some suggestions around such designs to provide reliable protection. Maybe there already is a white paper on this, I have not checked.

I think your idea of SPD on the PV side would seem worthwhile, to clamp the PV side from any transient conditions, such as might be caused by lightning.

I think it is good that Victron have taken an interest in your situation too. Hope you get a safe system going.

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Very bad news

I also have 2 mppt 100/50 with 2x435w pv panels in series. 24V setup. They get really hot in summer, even the peak current is only about 28A. Now I’m developing a paranoia about such event, catching fire or breaking down all my system due to overvoltage. Cannot afford to buy another toys fire proof or fail safe…

What’s the recommended solution from Victron point of view. Please johannes boonstra take care of this issue…

I also suggest Victron engineers should simulate on a benchmark test the short between PV+ and Batt+ with two panels 2s. Mine cs6r435T have a 13A shortcircuit current, about 70-80V at mppt point. Well , an internal shortcircuit on mppt charger, will inject in batteries maximum 13A from panels. So, the voltage on batteries will not surge instantly to 60-70-80V, if the SOC is bellow 80%, the batteries absorb the current slowly , as everything is normal. The problem became dangerous after the batteries should entry in absorbtion phase, constant voltage, current decrease almost to zero. The voltage continues to rise, and this can be very fast, but not instantly, seconds or minutes… Lifepo4 bms will disconnect, Pb will boil…

Please Victron deploy such as experiment and think what countermeasures can be taken…

My first thought is a BMV using internal relay to drive a coil of a larger DC relay, in case of overvoltage, which NC contact will interrupt the mppt from busbar. Every mppt charger needs it’s own relay, to avoid the defective charger kills another , beeing in parallel

I feel no safe anymore with almost 800W running through the relatively small charger, very hot, in full sun… waiting for disaster. Mine is at home, wooden structure above, sufficient airflow, but I don’t imagine what could be in a boat or RV, confined space, in case of smoke or fire

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You can install a Smart Battery Protect on the output of the MPPT(s). Configure the voltage thresholds to not allow current to pass over a certain voltage. I do think Victron should deal with this internal to the MPPTs, but then it would raise the cost of the MPPTs and people would complain about that, too. So either way, to do this properly will cost a few more dollars/euros/pesos/shekels/etc.

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Battery Protect is not very helpful. The 12/24V has max. voltage 35V and the 48V only 65V. The BP will disconnect busbar from mppt at 32V treshold (DC voltage exceeds 16V respectively 32V). After disconnection, the input of BP will rise to the voltage of PV panel (80V in my case) so the internal mosfet of BP will be exposed at high voltage, with unknown consequences. So , definitely NO for BP solution, maybe usable if panels are in parallel (bad idea, waste of cables, Y splitter) . And definitely not for 150 and 250 mppt series…

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