lowredrt avatar image
lowredrt asked

SmartSolar MPPT 150/45-Tr keeps tripping 50a DC breaker

I have a SmartSolar MPPT 150/45-Tr on my RV. It is connected to four 6v batteries hooked up in series parallel (12v) and six 100 watt panels in two paralleled sets of three panels in series. Between the MPPT and the batteries is #4 AWG (25mm2 ) copper with a 50a 12-24v DC breaker. It has worked flawlessly for the past couple weeks charging my batteries when they get drained and topping them off when they're not in use.

The last couple days I've found my DC breaker tripped open. I'm not sure if the 50a is just too sensitive for my setup or if there is something bigger going on.

I think the low minimum voltage listed for the battery is due to the breaker tripping because I've never seen the battery voltage dip below 11.22v on my Victron Smart Battery Sense through the VictronConnect app. And that was under heavy load during the nighttime with no solar. As soon as the load was done the battery bounced back to over 12v. As for the "#2 Battery high voltage" error, I have no clue.

As for the settings, the battery manufacturer states to add 0.005 volt per cell for every 1°C below 25°C and subtract 0.005 volt per cell for every 1°C above 25°C. So I have my MPPT set to -30mV for every 1°C. It hasn't been freezing where we are at and the Smart Battery Sense has been reading an average of 8-15°C.

I just ordered a 60a breaker to replace my 50a that may be just a touch too sensitive and I'll replace it when it comes in tomorrow.

So what do you think?

MPPT Controllersbattery system voltage
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4 Answers
JohnC avatar image
JohnC answered ·

Yeh, the high V error will be what the mppt detects internally when the breaker tripped. It can't react quite fast enough to prevent it.

Providing your wires aren't too long, they should be fine with a 60A breaker, even more. Especially if it's one of those little button'n'lever things. I find they get hot and cause spurious trips if not well oversized. You should be fine..

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lowredrt avatar image lowredrt commented ·

It is one of those "little button'n'lever" breakers. The thing that has me concerned is that it tripped yesterday night after the sun had set. I remember checking on it right around sunset and seeing it at 10 watts. Then I checked it again an hour later and I couldn't see it because it was tripped. I'm not sure why it would trip with very limited current and at very cool temperatures. I realize it could be a faulty breaker, but I think a faulty breaker would have been much more likely to trip during the higher currents and warmer temperatures that it had seen earlier in the day. But I am going to change out the breaker as soon as it comes in the mail today.

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JohnC avatar image JohnC ♦ lowredrt commented ·

I can't disagree with Boekel's din rail units, but I wouldn't get too excited either. Try what you have on the way. If it fails, chalk it up to experience. It should 'fail safe' in any case,

Congratulations too on your neat work, well done. Just one little thing I spotted with your batt wiring, which with such big wires shouldn't be an issue, but:

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boekel avatar image boekel ♦ JohnC ♦ commented ·

Well I rate the ones shown in the picture 'fire hazards' as there are a lot of cheap / bad versions on the market, and none are good for continuous current (they heat-up and melt).

If you want cheap and reliable: use a fuse, Littlefuse makes great fuses for max 32V and 58V

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JohnC avatar image JohnC ♦ boekel ♦ commented ·

Again I don't disagree with you. The ones I've seen are rated just 50V, there's cheap varieties of them, the terminals are often too small to fit the lugs you want to use, & they seem to dissipate their internal heat into the wires. Yeh, the question then arises - why do they get hot?

But there's plenty out there, and the good quality ones are way better than the junk. I did have a couple which became redundant when I upgraded my own system, and were repurposed as isolators for much lower capacity 12V sub-circuits. Fuses added to protect them from themselves.. :)

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lowredrt avatar image lowredrt JohnC ♦ commented ·

Thank you very much for the compliment on the wiring. I had read that article after I had finished the entire setup and I was considering running the batteries that way but I didn’t feel like getting everything back out again. Everything was pressed with a 6-ton hydraulic press and then soldiered. I plan on doing it if I have another project in the near future that requires the same setup.

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boekel avatar image
boekel answered ·

Do you have a picture of the breaker + wiring?

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lowredrt avatar image lowredrt commented ·

You see #4 coming out of the MPPT to the DC bus bar and then 4/0 welding wire going to the batteries below. The 4/0 is no more than 3' long.

This isn't the best picture, its just one that I already had. I can take another picture when I get home. I realize that it looks like the positive and negative look like they are touching but I assure you they are not.

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boekel avatar image
boekel answered ·

I would never use these breakers, I advice to use proper (dc-rated) din-rail mountable breakers.

The one you use is not good for continuous current, and because it has tripped a couple of times, contacts become damaged, leading to a high resistance and therefore more heat - early tripping.

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Bill avatar image
Bill answered ·

Those are junk, had seen a picture of someone using them so I bought them but on my first boondocking adventure at the Balloon Fiesta last fall they kept nuisance tripping. I replaced them with these. Bussman Surface Mount 60 Amp No trips since! Now if only they made ones that can handle the higher voltage of the panel side of the connections, these top out at 48v and I need 90v as I run my panels with a few seriel. -Bill

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Mark avatar image Mark ♦♦ commented ·

I agree that the cheap DC breakers are junk - I used some once & the switching mechanism jammed up after a few days (never switched under load so this is not the cause).

For the PV/Solar DC breakers I use Noark DC MCB's (Ex9BP-N series) - they come in ratings upto 63A & are rated @ 500V DC.

For the MPPT DC Out & Inverter DC In/Out I use Noark DC MCCB's (Ex9MD series) - the 2P versions come in ratings upto 250A (3P & 4P go much higher) & the 2P versions are rated @ 500V DC. They also have an adjustable trip curve.

They are not cheap & can be a bit hard to source but work nicely.

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Bill avatar image Bill Mark ♦♦ commented ·

Mark, are those surface mount? I read the pdf but it doesn't say and I cannot tell from the picture. The pic looks like they might be surface mount. I really need a 20 amp 90+ volt DC breaker for the panel side of my CC. Right now I am still using the OP was using on his Battery side of the controller. -Bill

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JohnC avatar image JohnC ♦ Bill commented ·

Yeh Bill. The Noarks are standard din mount and you can get matching enclosures to suit. Ckeck this link from my own Victron supplier and a brief explanation why double-pole:

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Mark avatar image Mark ♦♦ Bill commented ·

No, as John stated they mount to a regular MCB din rail. So you could simply buy a short din rail section (which you can screw down) OR just buy any regular MCB AC enclosure from any electrical retailer or even a hardware store. These come in all sizes 2/4/6/8/12/24/... pole.

I have 5 of the DC MCB's side by side all in the single MCB enclosure (4 for 4 x PV strings & 1 as the master)

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