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Safely using MCB (mini circuit breakers) for PV & Bi-Directional Battery Protection

I am in a similar pickle, I have two batteries, and purchased some ebay DC 100A MCB with plans to use them to turn on or off each pack, as well as protect against excess current flow between batteries in case of a battery short / failure within the pack, the MCBs will be isolating each battery from the main bus bar. Between the bus and the inverter I have 160A ceramic fuses.
I think I have magnetic MCB (still in the post), so I guess they will only protect in one direction - but since each battery has one, then the combination of two should still protect from a battery short in either pack (ie one would be in the correct direction). I think I will swap for non-polarised regardless.
I was also curious if anyone knows of any reverse arc tests at low voltage with a magnetic MCB (ie 48V), all the videos I have seen are at 250+ DCV!
 
There are a lot of the DIN rail breakers that have both an AC and DC spec, with only the AC spec printed on the breaker case. You have to find the spec sheet for the breaker in question for the answer. I couldn't find a spec sheet for the CHNT CB-125A on line, so that makes it kind of difficult.
 
LifeWAT said:
1. TAIXI DC12V 24V 48V 250A Moulded Case Circuit Breaker Battery 100A 200A 300A 400A 600A MCCB Car Charging Pile Protector
I got the 2 Pole, 200A version

2. TOMZN 2P DC 600V DC Solar Molded Case Circuit Breaker MCCB Overload Protection Switch Protector for Solar Photovoltaic PV
Click to expand...
Thank you for posting the links, I too was looking at these two breakers on ebay.
Where I have already paid too much for Tomzn breakers and other kit.

Do you recommend having a breaker between two Sunsynk BYD 5.12kw 100Ah batteries, as well as another 150amp (going by the manual) breaker before the inverter?
If so do you recommend the same 150amp breaker?

Oh, before I go, what is a T fuse? I was thinking of using a 150a nv/nh 00 gL/gG or preferably a HRC type bolt down tab fuse. What do you think?
 
Fingers said:
Thank you for posting the links, I too was looking at these two breakers on ebay.
Where I have already paid too much for Tomzn breakers and other kit.

Do you recommend having a breaker between two Sunsynk BYD 5.12kw 100Ah batteries, as well as another 150amp (going by the manual) breaker before the inverter?
If so do you recommend the same 150amp breaker?

Oh, before I go, what is a T fuse? I was thinking of using a 150a nv/nh 00 gL/gG or preferably a HRC type bolt down tab fuse. What do you think?
Click to expand...
Yes, having a breaker for each battery is more convenient maintenance wise.
Say if one battery needs to serviced or is faulty, you will be able to disconnect it safely with its own breaker.
That is unless the battery already come with its own breaker.

Having a main disconnect breaker is also wise:
The main breaker should be rated according to the inverter's spec (150A as you mentioned). The battery breakers should be rated by the battery's maximum allowed continuous discharge.
This way, you are still protecting the inverter, but can use one battery to its maximum spec.

A class T fuse is a fast blowing fuse that can handled the higher voltages of 48v systems and safely extinguish the DC arc when it blows.
Those tab style fuses you mentioned are usually NOT rated for 48v system (which can go up to around 58v when battery is fully charged). They are usually suitable for 12v/24v systems where the DC arc is fairly small. These could melt or even burn if you try to use them in a 48v system.
 
Fingers said:
Thank you for posting the links, I too was looking at these two breakers on ebay.
Click to expand...

The Taixi breakers are not bi-directional, they are only designed to work in one direction - see my post here for a different option.

I actually went with 160A for each battery, and 250A for the entire rack, even though my system could peak at 400A. My reasoning is that the maximum continuos draw would be around 160A, once I have two batteries that would be 80A per battery. These breakers do not trip instantly, they have a trip curve and that shows how long they take to trip at a given current, so even with a brief peak of 400A they should not trip.

I have a 250A T class fuse on each battery, and 400A on the whole rack.
 
Ron-ski said:
The Taixi breakers are not bi-directional, they are only designed to work in one direction - see my post here for a different option.
Click to expand...
Can you share the proof of how the following TAIXI breaker is not bi-directional? The manufacturers of both below say that they are.

1. TAIXI DC12V 24V 48V 250A Moulded Case Circuit Breaker Battery 100A 200A 300A 400A 600A MCCB Car Charging Pile Protector
2. TOMZN 2P DC 600V DC Solar Molded Case Circuit Breaker MCCB Overload Protection Switch Protector for Solar Photovoltaic PV

I am asking this only from a safety standpoint, and want to ensure correct information is here for other users. My original question for this thread is still unanswered. If anyone knows how to physically test these breakers to confirm bi-directional protection, please share.
 

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I just received mine, and initial impressions are that both are very heavy duty, but the Tomzn is slightly better in build quality. The Tomzn is also slightly heavier at 3 lb. 1.9 oz vs the TAIXI at 2 lb. 12.2 oz. The Tomzn has a slightly more satisfying clunk, while the TAIXI is slightly more of a twang. Both are solid and require a good bit of force to trip. I do not yet have thermal equipment to test temperatures under load.

I would purchase the Tomzn over the TAIXI next time, but I believe both will work for my needs.
 

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LifeWAT said:
Can you share the proof of how the following TAIXI breaker is not bi-directional?
Click to expand...

Look at the attached picture, it clearly shows the + and- with load connected the other side, the Tomzn one you've pictured I'm not sure about. I originally bought the smaller Tomz MCB's, and Taixi 160A and 250A breakers the same as yours, then discovered the potential issue if they are not bi-directional, I did the same as you, and got the same reply back. Question is would I trust a salesman in China who probably doesn't have a clue, especially when the diagram on the breaker shows otherwise, my answer was no.

The Z Beny breakers I purchased specifically states on the website and in the documentation that they are no polarity or non polarised.

Here's an interesting video I just found, at higher voltage than we are using.


Here's another as well, but is at PV voltage. Note the rotatery isolator he is using is Z Beny

Incidently, my 32A Tomzn MCB breakers were marked the same as the breaker in the following video.

 

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Interesting. Thank you for sharing. Love that first video. I have pressed the Tomzn contact on Alibaba (not aliexpress) for engineer specifications for the breaker. Alibaba representatives seem to be more professional in my experience. It seems it may be difficult to conclusively prove the bi-directional functionality.
 
Just for reference, here is how the TAIXI 160A MCCB looks inside:
20220925_104024.jpg20220925_104022.jpg20220925_104006.jpg

I also bought 2 x 125A (for batteries) and one 160A as a main switch from busbars to 24v inverter.

I was in the same situation as you guys: Couldn't be 100% sure that these are bidirectional (or at least non-polarized) . So I ended up getting 2 x 125A ZJBENY and one 160A Suntree (from Renogy store), as both mention specifically that they are non-polarized. The illustration on the ZJBENY is confusing though...

Anyways, as for the TAIXI: I didn't find any magnets inside, which would be a good sign for non-polarized. Polarized MCBs usually have a magnet to pull the arc into the arc chute. But they are only useful for current flowing in a specific direction. I guess if the current is flowing in the opposite direction intended, the magnet does the opposite: it pushes the arc into the internal components if the MCB , which will probably destroy it or cause a fire.
I have read that manufacturers suggest/require that the "line" (supply) be on the non-moving side of the MCB. As you can see on the TAIXI, the non-moving contacts are connected to top terminals.

I'm not really sure why that requirement exists really...
As far as I could tell (without doing a complete teardown of the TAIXI), both sides look pretty much identical to me.
Except for the fact that the switch is on the left, but it open both sides.

One important thing to note:
It seems that if you press the "test" button it sometimes opens just one side. You should fully turn off and on to get things synced again. I've read this somewhere else too...

Just another thing: Although the 160A is bigger than the 125A, and looks massive, the 160A Suntree/Renogy MCCB is simply huge! I was expecting it to be around the same size as the TAIXI 160A, but it's even bigger!

I don't have a picture of it on hand, but I'll take a photo of mine for you to see the difference. Kinda gives you more confidence in the (expensive) product (also made in China...).
 
All my breakers are going to be Midnite. Seen too many burned examples to do otherwise.
 
Ron-ski said:
Incidently, my 32A Tomzn MCB breakers were marked the same as the breaker in the following video.
Click to expand...
So these are polarized, and single directional, and are good for solar panels? Just so we can put that to bed.
tomzn-breakers.JPG
Now that guy in the video has got me questioning myself.
I thought live from the panel top left, and neutral from the panel top right.

But, if current flows from top to bottom on these breakers, then the switch neutral being a return current should be top right so it flows down, and panel neutral should be bottom right. Or is it time for nursey to give me my medicine?
 
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DC does not have neutral. It is positive or negative. Follow the wiring diagram for the breaker. If it lists (+) than wire the positive to it. If it shows (-) than wire the negative to it. Follow through from top terminal (supply) to bottom (load). Breaker should be mounted upright.
 
Fingers said:
So these are polarized, and single directional, and are good for solar panels? Just so we can put that to bed.
Click to expand...
If wired up correctly they should be fine for solar panels, as the current always flows in the same direction with panels. The guy in the video was saying they were often wired up back to front.
 
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