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DC Circuit Breakers
#1
I need to order some circuit breakers for a 48v (15s) system. I also need breakers for the solar input as well.

Here is where I think I need them: 1. between the battery and everything 2. Between the panels and the mppt 3. between the inverter and the battery

Is there anything else that I should put a breaker on? I have a DC-DC converter that drops pack voltage down to 13.8v for automotive things that I might want to run. I don't want to spend an arm and a leg but I don't want to buy junk either. Cost effective quality is my goal.

I should add that I have din rail on hand to mount them if that is an option for something like this: https://www.automationdirect.com/adc/sho...-1pcc30-dc
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#2
Get some Schneider breakers. They can be found Up to 63a. And yes you need Them everywhere . No source or load should be unfused. So the DC DC need it to
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#3
Agree with @Daromer 100%.    In most jurisdictions, for DC solar power, you need quick-disconnect (usually done with breakers) at the panels.  Then in the solar control room I have:
- A set of breakers just as the PV power goes into the Charge Controllers - this is useful disconnect PV power when on things.
- A set of breakers between Charge Controllers and battery bank - this (combined with above) isolate the Charge Controllers to work on them
- Breaker / shunt-trip between the battery and any loads.  Some allow BMS to bypass this as its only a couple of watts and BMS is critical to keep running.
- Breakers between Battery and Inverter.   *This has saved me me at least twice from catastrophic / fire even as inverters can draw a lot of power and cheap ones can fail/short out.
- My Inveter has breakers on its output 
- Distribution box  (Inverter AC output -> distribution panel) has breakers out to each circuit.

I don't think I have too many breakers per standard recommendations - the only optional ones might be the 1st one as I could use quick disconnect instead of breakers right by the charge controllers - but that's a convenience. 

I didn't call out fuses in the battery bank to isolate 'batteries' hooked in parallel because that's part of the recommended 18650 battery design - but if you have a different type of battery bank, you might need some fusing (or circuit breakers) within the battery bank.
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#4
Time to look for some scheider breakers! The packs have cell level fusing and a fuse on the + lead before it exits the neatly boxed up area. How should I size the breakers? For example, inverter is 1500 w continuous (27 amps at nominal, 33 amps at minimum voltage) surge to 3000w (54 amps at nominal, 66 amps at minimum voltage). Would I want a 63amp or should I go smaller and more conservative?

Also, When i've done small 12v stuff I have just fused the positive side of the circuit. Should I do the same for this or do I need to put a breaker on plus and minus?

I'm looking at these right now. They are fairly local to me and seem like a reasonable price. https://www.solar-electric.com/mnepv.html
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#5
(03-29-2020, 11:04 PM)gpn Wrote: Time to look for some scheider breakers! The packs have cell level fusing and a fuse on the + lead before it exits the neatly boxed up area. How should I size the breakers? For example, inverter is 1500 w continuous (27 amps at nominal, 33 amps at minimum voltage)  surge to 3000w (54 amps at nominal, 66 amps at minimum voltage). Would I want a 63amp or should I go smaller and more conservative?

Also, When i've done small 12v stuff I have just fused the positive side of the circuit. Should I do the same for this or do I need to put a breaker on plus and minus?

I'm looking at these right now. They are fairly local to me and seem like a reasonable price. https://www.solar-electric.com/mnepv.html

The *main* purpose of a wire based circuit breaker is to protect the wire.   If your wire is 10awg then 30amp circuit breaker.  If your wire 6awg then 50amp circuit breaker and so on.

A battery bank circuit breaker is to protect the battery from pulling more the max design of the battery.

Device(s) pulling the load will have their own fuse/circuit breakers.  I bet your inverter has it's own.

Therefore - assuming your battery can deliver 80a......  and your inverter tops out at 3000w / 52v = 57.7a....  you could go a couple of ways:
1) 80a on 4AWG wire.  This protects the wire and the battery.    The inverter will protect itself - but you've left a 60a - 80a gap where the inverter *needs* to protect itself.
2) 50a on 6AWG wire.  This overprotects the battery but is right-sized for the wire.  This 50a circuit breaker will likely trip before the inverter fuse blows.
and various combinations.

In my own case, my battery can deliver over 500a BUT I use a 400a 'overall battery shunt-trip/circuit breaker' because this protects the battery and is adequate for my max pull AND because I couldn't find a 500a circuit breaker at a good price.

I use 250a breakers on the wire from battery to the inverter = 13,000watts.  Which is a bit under powered for the inverter because it can do 12,000 watt continuous and 36,000watts peak but there is no 'correctly operating scenario' where I need more than 13,000watts.   In fact I recently had occasion where an AC compressor motor locked and triped the 250a breaker but did not trip the inverter - so it worked to keep the wire safe.
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#6
IMHO, breaker/fuse sizing simplifies to the lowest value of:
- the cables ampacity (current carrying ability incl de-rating for ambient temperature, bundling & enclosing in conduits, etc)
or
- the max the load/device needs per manufacturer specs
Running off solar, DIY & electronics fan :-)
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#7
The inverter should have specifiwd type and size of fuse/breaker to use

Just make sure this is the weakest point
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#8
(03-30-2020, 06:10 AM)OffGridInTheCity Wrote:
(03-29-2020, 11:04 PM)gpn Wrote: Time to look for some scheider breakers! The packs have cell level fusing and a fuse on the + lead before it exits the neatly boxed up area. How should I size the breakers? For example, inverter is 1500 w continuous (27 amps at nominal, 33 amps at minimum voltage)  surge to 3000w (54 amps at nominal, 66 amps at minimum voltage). Would I want a 63amp or should I go smaller and more conservative?

Also, When i've done small 12v stuff I have just fused the positive side of the circuit. Should I do the same for this or do I need to put a breaker on plus and minus?

I'm looking at these right now. They are fairly local to me and seem like a reasonable price. https://www.solar-electric.com/mnepv.html

The *main* purpose of a wire based circuit breaker is to protect the wire.   If your wire is 10awg then 30amp circuit breaker.  If your wire 6awg then 50amp circuit breaker and so on.

A battery bank circuit breaker is to protect the battery from pulling more the max design of the battery.

Device(s) pulling the load will have their own fuse/circuit breakers.  I bet your inverter has it's own.

Therefore - assuming your battery can deliver 80a......  and your inverter tops out at 3000w / 52v = 57.7a....  you could go a couple of ways:
1) 80a on 4AWG wire.  This protects the wire and the battery.    The inverter will protect itself - but you've left a 60a - 80a gap where the inverter *needs* to protect itself.
2) 50a on 6AWG wire.  This overprotects the battery but is right-sized for the wire.  This 50a circuit breaker will likely trip before the inverter fuse blows.
and various combinations.

In my own case, my battery can deliver over 500a BUT I use a 400a 'overall battery shunt-trip/circuit breaker' because this protects the battery and is adequate for my max pull AND because I couldn't find a 500a circuit breaker at a good price.

I use 250a breakers on the wire from battery to the inverter = 13,000watts.  Which is a bit under powered for the inverter because it can do 12,000 watt continuous and 36,000watts peak but there is no 'correctly operating scenario' where I need more than 13,000watts.   In fact I recently had occasion where an AC compressor motor locked and triped the 250a breaker but did not trip the inverter - so it worked to keep the wire safe.

I don't disagree, but I think it's important to know how the breakers ratings apply to their applications because its not always about protecting the wire. (Assuming we are actually buying listed brand name breakers)

UL 489 listed breakers are used for branch circuit protection. Meaning the wire, the outlet, the receptacle.

UL 1077 breakers are for supplementary protection.  This type of breaker could be sized for the load, to protect the equipment, not just the wire.  For example on a motor controller to control overload conditions.

On top of that, you should also be aware of your trip curve, and making sure that is appropriate for the application. 

Eaton has a really good product application guide that is worth looking at.
https://www.carltonbates.com/static/catalog/products/images/PDF/EATON_pg01101007e.pdf

Another final note is that I don't consider breakers a replacement for a fuse, especially on the battery mains.  Where a breaker might fail a fuse would not.  Make sure you understand what type types of interrupt currents you might be dealing with with a dead short.  

Someone from our community recently put out this video.
https://www.youtube.com/watch?v=SjzbQlsiiuk
Korishan and OffGridInTheCity like this post
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#9
So with regards to MCB and fuses, I have all but got or know what I am going to do, my only confusion is the main DC breaker.

So I have a 100A inverter with 30A charge,
I will be installing 3 x 7s80p 18650 banks.

At each bank I will be installing a NH-00 40A Fuse, on positive terminal u
and all these will feed to a 100A 2P DC MCB with shunt trip, my only confusion here is what curve DC breaker ? B,C,D,Z ? or does it really matter.
Are we installing the shunt trip just to control the current to and from the battrery bank ?, doers this need to be a 100A MCB or can it just be an isolator with a shunt trip ? ?



TRIP CURVE CLASS B
The MCB with class B trip characteristics trips instantaneously when the current flowing through it reaches between 3 to 5 times rated current. These MCBs are suitable for cable protection.
TRIP CURVE CLASS C
MCB with class C trip characteristics trips instantaneously when the current flowing through it reaches between 5 to 10 times the rated current. Suitable Domestic and residential applications and electromagnetic starting loads with medium starting currents.
TRIP CURVE CLASS D
MCB with class D trip characteristics trips instantaneously when the current flowing through it reaches between Above 10(excluding 10) to 20 times the rated current. Suitable for inductive and motor loads with high starting currents.
TRIP CURVE CLASS K
MCB with class K trip characteristics trips instantaneously when the current flowing through it reaches between 8 to 12 times the rated current. Suitable for inductive and motor loads with high inrush currents.
TRIP CURVE CLASS Z
MCB with class Z trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. These type of MCBs are highly sensitive to short circuit and are used for the protection of highly sensitive devices such as semiconductor devices.
TRIP CURVE CLASS A
MCB with class A trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. As like Class Z MCBs, these are also highly sensitive to short circuit and are used for the protection of semiconductor devices.
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#10
If by main DC breaker you mean the breaker that is serving as the master for the battery bank, I would be looking at a shunt trip.

Even if you didn’t need the shunt trip itself, those larger breakers like the ABB models you see around generally have a much higher interrupt rating that the smaller ones showed in this thread. That is probably the main reason why I gravitate towards those.

In terms of trip curve, its really more about the application... Most of my loads are pretty stable with little to no surge. I would gravitate towards a more sensitive trip curve. If this was a motor, it would be a different story.
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