Breakers AC, DC & AC/DC - Solar Safety Part 2 - 12v Solar Shed

In a follow up to part one ( ) I'm looking at breakers. I talk briefly about how they work and then I take look inside an AC breaker, a AC & DC Breaker and a DC only breaker. It turns out they have some similarities as well as some differences.

Remember, please use the correctly designed breaker for your circuit. Do not use AC breakers on DC circuits (or vice versa).

The above video is only presented for interest - please complete your own research - nothing contained within comes with any guarantee.

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[DocMicha]

Super tear down. there is another very important difference. I was told by an old fellow of a well known German relay manufacturer: Its the chemistry of the contacts. While AC contact do not have this arc so much, DC contacts have to withstand a longer duration arc, so the contacts of an AC would not last and even worse they could weld together if switching a high load, where they are supposed to separate. So never do use AC breakers for DC, otherwise they could catch fire!

[josepeixoto]

Nice to see them open, i learned about that only a year ago or so;
I could not find DC ones so been using 2 AC breakers, 25 Amp each, for a year now on my 60 VDC solar system, up to 32 Amps; i switch them off manually, only, sometimes several times a day ; it's impossible for the current to go over 32 amps, that is the MAX, so it's not expected that they trip on their own, ever, that is not why they are there; they are there because i need to manually disconect them ( solar panels from the MPPT/batteries ) when i need to adjust the MPPT voltages; this seldom happens;
i expected them to not last, but they still work perfectly; cost me 2 or 3 euros each;
i use 2 of them, 25A each, in parallel; amazingly they never burned and still worl fine;
they are in a place that if they start smoking, or on fire, it does not matter, nothing to burn nearby; i would not do it, otherwise.

[willfoley]

Great info! Safety, safety, safety. People need to understand this!

[MrOpenGL]

You can use AC breakers perfectly safely on DC, but you need to make sure that:

1. The voltage is not exceeding 50V for a 230/400V breaker
2. The breaking capacity (Icu) is at least 4500A (4, 5 kA), this means it has a large enough arc extinguishing chamber.
3. If the breaker is *directly* connected to a large battery bank (more than 200 Ah) use a breaker with Icu=6000A (6kA)
4. If the breaker is *directly* connected to a very large battery bank (more than 500 Ah) use a breaker with Icu=10000A (10kA)
5. If the breaker is connected to another breaker whose Icu is 6000A, you can use an Icu=4500A breaker or a Icu=6000A breaker.
6. If the breaker is connected to another breaker whose Icu is 10000A, you can use an Icu=6000A breaker, an Icu=10000A breaker *but not an Icu=4500A breaker*

This is because larger batteries can supply higher short circuit currents because the internal resistance is lower.

On many US-made DC/AC breakers you can see they are rated for AC at 250V and DC at 50V, which is why this works.
DC arcs are a problem only above 50V. Most welders have an open circuit voltage of 85V, for that reason.

*Also I highly advise AGAINST using breakers with only a magnetic trip (unless you are using them for the intended application that is powering MOTOR ONLY loads), as it is possible that they won't trip on medium overloads that are not enough to trigger the magnetic trip. This can cause damage to wiring.*

[Kuro-Velfire]

Thanks Mr Weich, your observations helped me make my mind. Really appreciate it

[tanishqbhaiji]

If you read the datasheet, most AC breakers are rated for 48-60V DC nominally systems with 72V DC peak voltage.

[its.r.r]

Thank you for a very descriptive and detailed video on the differences between the types of breakers. It was just what I needed.

That said and much as I am convinced, I am not going to replace the AC breakers currently fitted between my solar panels and charge controller as they have worked well for over a year now.

[KDCAC]

Adam, you could use an automotive load tester to test breakers & fuses .
Two main types, resistance wire [ I would not use this one, less control ] and carbon pile - this one you can dial in the load amount .
John

[jorarofu]

Hello Adam! First, thank you so for your very informative videos.
Just FYI, I have installed an inline 30A fuse/breaker(just like your 80A) from my 400W panel array to my charge controller. I can assure you it works nicely, as it opens the circuit at 32A coming down from the panels.
Actually I'm in the process of connecting the panels in series to increase voltage and decrease current and replace my PWM with a EPEVER 40A, for which I appreciate so much you review.
Greetings from the Caribbean!

[mikenewman]

The permanent magnet is why the Midnight Solar is listed as polarised and has the positive signs printed. The South African breaker can handle AC and DC because it doesn't have the magnet. The permanent magnet seemed like a good idea at the time but is prone to installation error and is the reason they catch fire (and why they are no longer recommended).

I have looked up the Clipsal AC MCB (4CB150/6) specifications and found them rated for up to 48 VDC, for how much longer I don't know. Definitely not usable on PV strings.

Merlin Gerin and Clipsal are both Schneider brands.

I have just looked up the details for the Merlin Gerin C60H breakers. The standard AC breakers do not list a DC usage, they are a high rated (10KA) AC breaker. There is a C60H DC range rated at 250 VDC per series pole which means for PV strings buy the appropriate 2, 3, 4 pole breaker dependent on the string open circuit voltage at its coldest temperature and connect the correct number of poles in series. The diagram show connection details.

The two items that aren't Merlin Gerin are called magnetic circuit breakers and the cylinder inside the coil which contains oil is called the dash pot. Magnetic breakers tend to be over sensitive to inrush current.

Your attempt to explain more positive in a circuit is a good idea but needs editing for accuracy.

[affordablesolarguy]

wow, , I have tested my AC breakers on my solar system and they worked flawlessly. Never thought to rip them open and look for differences though. You rock. Still though, the only thing I can think of that could ark that way is lightning strike. And I don't think the magnet will save anything. ;) Like high voltage DC is much more likely to arc than any 12 volt system could ever dream of arcing.

[artist]

The use of circuit breakers in alternating current (AC) and direct current (DC) circuits has some differences, and typically requires specialized designs to cater to specific power types.

In AC circuits, the design of circuit breakers is generally standardized and can be widely applied across different power systems. They have the ability to adapt to a wide range of voltages and frequencies, allowing them to function properly under varying AC power conditions.

However, in DC circuits, the design of circuit breakers is more specialized. The characteristic of DC circuits is that the current does not undergo periodic variations. Therefore, in order to interrupt the circuit, circuit breakers in DC circuits cannot rely on the natural zero-crossing of AC current. DC circuit breakers need to be specifically designed to handle the requirements of interrupting DC current.

DC circuit breakers typically have a more robust structure and special interruption mechanisms to ensure reliable current interruption in DC circuits. They require larger contact gaps and powerful interruption mechanisms to accommodate the continuous DC current.

Therefore, to ensure safety and proper circuit protection, it is important to use circuit breakers that are suitable for the specific power type (AC or DC). Using the wrong type of circuit breaker may result in failure to properly interrupt the circuit or damage to the circuit breaker itself.

In summary, the use of circuit breakers differs between AC and DC circuits and typically requires specialized designs to adapt to the specific power type, ensuring the safety and reliable operation of the circuit.

[tanner]

It is NOT a convention for AC breakers to open at zero voltage OR zero current.
The reason why AC breakers and switches can operate with relatively simple and conservative means is because of the inherent plasma/arc quenching which occurs at relatively low frequency (60Hz), low voltage and low current. Crossing 0V and 0A 120x per second causes quenching/extinguishing of plasma repeatedly, which minimizes the heat and conductivity of the gas/plasma and prevents a self-sustaining continuity/conductivity across the gas/plasma.
DC, on the other hand does not self-quench, and requires either a much faster movement and larger gap during opening, or it requires a sufficient 'opposing' magnetic field (per the right hand rule), which deflects and 'spreads' the electron flow, which effectively cools/dilutes the plasma and also increases the linear distance/gap the charge must flow. The opposite magnetic polarity would pinch/squeeze the charge together, sustaining the plasma/arc.
It's surprisingly complex for a switch, but basically, in order to sustain a plasma, you either want RF power or DC... low frequency AC does not inherently support plasma. Think welders... (as mentioned in the video).

[SoheiThoth]

Nice video!! I use AC breakers on my solar system and for 6 years without a single problem. Just a tip.
Regards....

[rogerrabbit]

Some good stuff on your channel bud though re the Chinese cct bkr don't you think most of the branded expensive ones are also made there?

[Mechone]

You should be using a double pole dc breaker breaking the positive and negitive simutaneously as per code on solar panels

[truthexposed]

The reason for that sticker, is because Midnite Solar has taken that particular circuit breaker from the South African company CBI, and they have had them "certified" to 150VDC. CBI has a new breaker currently being certified at 300 volts, so the 150VDC breakers from Midnite may soon no longer be available.

[howardsway]

Thanks Adam, good video - keep 'em coming!

[SVAdAstra]

The AC breaker is thermally actuated, the other two are magnetically actuated. The advantage of magnetic breakers is they have lower series resistance. Thermal breakers depend on heat to trip, and therefore need series electrical resistance to generate that heat. Both thermal breakers and fuses consume some power from the system because of their dependence on thermal operation. The magnetic arc interrupter on DC breakers is POLARIZED. It is critical to safely interrupting the arc that the polarity not be reversed, which is why they are labelled with polarity markings. Otherwise, the arc may be sustained and cause catastrophic failure (fire). This problem makes those breakers unsuitable in applications where current could be traveling in either direction, such as at a battery terminal where either charging or discharging current is present.

[ZerHour]

Great video, the points on most potential still confuses many of my electrically minded friends, argument being if a charger outputs say 60 amps going to a leisure battery they say that is a lot of potential so why wire the positive on the polarity sensitive breaker to the battery if the charging current is flowing from a charger ?