Tomzn DC Circuit Breakers (Yellow vs Blue)

Korishan said:

For one, an AC breaker doesn't make much of a difference. The disconnect arc well self quench due to the alternating current
With DC, this is not the case. These breakers can be designed directional. Some of the circuitry in them may be directional. If there is a +/- (meaning Line/Load) or a diode symbol (denoting direction of flow) you need to wire them in that direction. Otherwise, it is possible the breaker will not trigger when it is supposed to (either too late, or too early)

With DC breakers, some of them have a current sense coil. If the coil is energized in the wrong direction, then it will not trigger the overcurrent protection and in fact keep it from working at all.

Not all DC breakers use a bi-metallic current trip strip. This is because DC creates a nasty current arc during heavy load disconnect and the contact pads need to be moved away from each other by distance and speed to quench the arc.

Another term these are called are "Polarized" breakers.

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Thanks for the great explanation Korishan!

I am using that DC breaker in my system. Only polarity is marked, but no mention of direction...

The DC types are directional due to the internal magnetic polarity which deflects the arc in one design direction. DC breakers have a small magnet in which has the sole purpose of deflecting the plasma arc, which has/creates a directional magnetic field due to the current and is then effectively pushed and extended to the point of being extinguished during a fault. Every current creates a magnetinc field.

If you want to wire a breaker up in the "opposite direction" then you have to put it on the -ve side of the circuit so that the current flow is still in the same direction. The other option is just to put the breaker upside down because internally there are no real components that use gravity in any way for the device to work. This is an option if you want to use a copper busbar for connecting a few together, however the whole element of fault current direction with breakers creates some interesting thoughts as to how and what is really protected in various fault conditions.

AC breakers do not seem to have any magnets or need for a magnet due to the voltage always crossing zero every few mS, which self extinguishes the arc. High voltage breakers can also have arc ladders internally to extend the arc length.

The tripping mechanism is just effectively an electromagnet against a bit of metal, so can be AC or DC triggered.

The only other worry I have discovered is that some of the internal magnets might be around the wrong way, if the internal design is critical for one way current faults. I found this out when I had a bunch of the breakers next to each other an the majority pushed or pulled (cant remember which) each other appart from one of them.

Think of a scenario :
Solar 5 x 10A arrays ->> 50A breaker -->> charge controller -->> 60A breaker -->> cable to battery -->> 60A busbar -->> battery

How muuch fault current can occur on the "cable to the battery" and which way is the fault current actually flowing compared to the breaker polarity and intended protection direction. What rating should the "cable to battery" really be..... this is the thought process of a design you need to go through to try and make sure what you think is sufficiently protected really is protected.

completelycharged said:

The DC types are directional due to the internal magnetic polarity which deflects the arc in one design direction. DC breakers have a small magnet in which has the sole purpose of deflecting the plasma arc, which has/creates a directional magnetic field due to the current and is then effectively pushed and extended to the point of being extinguished during a fault. Every current creates a magnetinc field.

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Yes, this is what I was trying to think of. I forgot it had an actual magnet in there.

House wiring is way more simple as the fault currents only happen in one direcdtion, unlike a battery system with multiple charge sources where the current sources from multiple locations can add up in locations to very high levels.

High capacity DC battery systems are inherently dangerous in some areas of the system because the short term aggregate fault currents can be greater than the energy required to "burn" the fault clear by vapourising some copper or aluminium away while still being not enough to trip any circuit breakers within the circuit.

One of the most strange cable faults I saw was a large 3 phase SWA service cable on site which had 2 fuses of a 3 phase supply side blown, but what happened to the actual cable was that two of the cores welded together so that the end supply only saw one phase out and two phases together...

RolandW said:

Are you guys sure a breaker is one-directional? I never cared about that at an AC nor DC breaker. After all, they are just simple mechanical devices, with a bi-metal trigger. The trigger will heat up same regardless of direction of current flow. Its all about Amps. Voltage rating is all important about breaking the arc with DC. Dump any DC breaker which is light as a piece of paper as they lack thermal mass to help extinguishing the internal arc (there are several chinese brands which lack any mass. For example CS brand). Tomzn are definitly the best chinese ones. If you go for DIN rail, can look for ABB or Siemens too. Price will be 3 - 5x higher tho...

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My system is a very small one, my inverter has a pwm charge controller integrated and it has a maximun imput of 50volts DC and 50Amps.
I just 4 panels in parallel with a maximun DC 37.3V and 35.4Amps, (8.85A each) I have on each panel positive wire a 12amp fuse connected before I join them together in a connection box.
I am trying to get reviews or recommendations about 50A DC TOMZN or the 63A 450 VDC FEEO available on aliexpress.
Also will like to add a
Surge protector device than can protect my inverter with such a low input voltage I was looking a CN DUN with nominal voltage of 24vdc and maximum continuous voltage of 48vdc
Or a SHNAI with the same spec.

Please help me with your experience I don't know anything about those brands or if I'm making a mistake with the specifications of what I will assemble

RolandW said:

Are you guys sure a breaker is one-directional? I never cared about that at an AC nor DC breaker. After all, they are just simple mechanical devices, with a bi-metal trigger. The trigger will heat up same regardless of direction of current flow. Its all about Amps. Voltage rating is all important about breaking the arc with DC. Dump any DC breaker which is light as a piece of paper as they lack thermal mass to help extinguishing the internal arc (there are several chinese brands which lack any mass. For example CS brand). Tomzn are definitly the best chinese ones. If you go for DIN rail, can look for ABB or Siemens too. Price will be 3 - 5x higher tho...

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JCM said:

Also will like to add a
Surge protector device than can protect my inverter with such a low input voltage I was looking a CN DUN with nominal voltage of 24vdc and maximum continuous voltage of 48vdc
Or a SHNAI with the same spec.

Click to expand...

The clamping Voltage Uc of the surge protector must be well above your system voltage, otherwise it will start leak current during normal operation.

Electrical device typically do have a bit resilience against voltage spikes, if your system voltage is up to 48V, I would go for the protector which is starting to clamp at 60V. But you can go higher too, as a lightning strike is far higher voltage then what your device is running at.

I once had a lightning strike into my off grid AC side. The only thing what survived without damage was the PIP inverter. The devices connected to it had been fried.

So do not forget to put SPDs on DC and AC side!

RolandW said:

The clamping Voltage Uc of the surge protector must be well above your system voltage, otherwise it will start leak current during normal operation.

Electrical device typically do have a bit resilience against voltage spikes, if your system voltage is up to 48V, I would go for the protector which is starting to clamp at 60V. But you can go higher too, as a lightning strike is far higher voltage then what your device is running at.

I once had a lightning strike into my off grid AC side. The only thing what survived without damage was the PIP inverter. The devices connected to it had been fried.

So do not forget to put SPDs on DC and AC side!

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This is true, mostly. I would say for 48V system, you want at least 65-80V, as 4.2V * 14S = 58.8V. And if you only want to go to 4.0V and run 15s, then 4 * 15 = 60V.
The clamping voltage shouldn't be near the operating voltage for as you get close to the clamping voltage, it starts to heat up and gets ready to trigger the breaker. The same reason why you don't put a 15A breaker on a load that will consistently run at or around 15A. it weakens the device and when it is "needed" to trigger, it could fail to do so.
Generally if you are protecting against lightning, you need another device installed that quickly shunts to ground. I would not rely on any kind of breaker to protect against this type of attack. Lightning is basically DC voltage, and it's super high voltage (gigavolts). So any breaker would not be able to quench the spark fast enough to save the equipment.

So basically for the fuses 15 amps instead of 12Amps DC (my pannel produces each 9.85 on short circuit and 8.35 Adc nominal)

For the SPD go from 48-60 or 60-110vdc instead of 24-70 ( I need to avoid the peaks of voltage to damage my inverter /pwm controller wich has a rated imput of 50VDC and 40amps DC)


And for the breakers instead of 50Amps go to 63 amps DC. Just another question. I found them on 250v, 550v or 800.
my sister only produces in parallel 37volts...do I have to be concern about the big gap.


IS that OK?? Thank you all for sharing your knowledge

JCM said:

So basically for the fuses 15 amps instead of 12Amps DC (my pannel produces each 9.85 on short circuit and 8.35 Adc nominal)

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Yes, 15A fuses and the DC surge protector at the array and inverter (yes, 2x), if the cable length from panel to inverter is greater then 8m. If cable length is short, DC surge protector near the inverter only is OK. AC surge protector at inverter output.

JCM said:

For the SPD go from 48-60 or 60-110vdc instead of 24-70 ( I need to avoid the peaks of voltage to damage my inverter /pwm controller wich has a rated imput of 50VDC and 40amps DC)

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Yes, correct. 60-110V version. Don't worry about an over voltage other then surge from lightning. There can not be a over voltage coming from panels by generating it, if you did connect your panel string correctly. Its just physically not possible for a panel to produce a higher voltage then the idle voltage Voc.
And surges from outside ( due to a direct or nearby lightning) come in the kV range! That's what SPDs are for.

JCM said:

And for the breakers instead of 50Amps go to 63 amps DC. Just another question. I found them on 250v, 550v or 800.
my sister only produces in parallel 37volts...do I have to be concern about the big gap.


IS that OK?? Thank you all for sharing your knowledge

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The voltage rating of a breaker means the max. V until which a successful disconnect (without blowing up that thing) is guaranteed.
Higher rating is better in general. Any of those 63A breakers will be good for your system voltage!