Do I need a bus bar?

JanC

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Hi, I'm just building my off grid system and I've been learning everything from scratch during the past few months. Someone shared this diagram (the first picture I attached) and it all seemed very simple and convenient so I'm planning to copy it. The other reason I want to copy it is that I get confused once I see bus bars and connections between the SCC and the inverter and I don't want to copy something I don't fully understand. These are two examples of builds I don't fully understand (the second and the third picture I attached).

My system is supposed to power a tiny home and I already bought 2x 485w solar panels, 100ah/24v lithium battery from Elkersolutions and Xunzel 24v 2000w inverter. I'll be adding the fuse block sometime in future.

There was no problem until I got to the issue of wires and fuses. People recommend T-class fuse on the battery because of the AIC. But as you can see on the diagram, I will have 3 lugs on the battery terminals. So my question is- Do I need to buy 3x T-class fuse in this scenario? If that's the case, I would probably be better off taking the time to understand the connections on the second and third picture.

Second question - Do I need to use a fuse holder with a T-class fuse, or it can be put directly on the battery terminal?

Third question - in the Wiring Unlimited book it says slow blow fuses are better when powering motors, compressors etc. I want to power one fridge with that inverter. The inverter has 4000w peak, but it doesn't say for how long. So is there a slow blow T-class fuse that should fit my application?

Thank you

Jan
 

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Delphinus

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1 - Battery - Fuse - Cables for Charger, Inverter
2 - T-Class is very expensive there is no point in save money in holder and a fuse is something to be replaced fast.
3 - You need a fast fuse for the battery.

Unless you plan to buy good circuit breakers it will be safer to buy fuses for the charger and inverter.

I don't see earth, connect panels, inverter and charger case to it.
 

JanC

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1 - Battery - Fuse - Cables for Charger, Inverter
2 - T-Class is very expensive there is no point in save money in holder and a fuse is something to be replaced fast.
3 - You need a fast fuse for the battery.

Unless you plan to buy good circuit breakers it will be safer to buy fuses for the charger and inverter.

I don't see earth, connect panels, inverter and charger case to it.
But I should have three T-class fuses because I have 3 pairs of cables connected to battery right?
 

OzSolar

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There was no problem until I got to the issue of wires and fuses. People recommend T-class fuse on the battery because of the AIC. But as you can see on the diagram, I will have 3 lugs on the battery terminals. So my question is- Do I need to buy 3x T-class fuse in this scenario? If that's the case, I would probably be better off taking the time to understand the connections on the second and third picture.
You are wise to make sure you understand things rather than just copy something else.

IMHO your system will be safer, and your life will be easier if you install a DC buss that is protected by one Class T fuse. That DC buss would in turn have appropriate fuse protection for each load or charging sources hooked up to it and give you room to expand in the future.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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Below is a "Generic Component System" diagram which shows where fuses/breakers should go.
Because you are building 24V, you can easily use MRBF Fuses https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A without any issues. These are quite affordable and very reliable for such an application. I run 24V and all my packs are connected to MRBF fuses on the DC Busbar. Image below shows my setup using Pike Industries HD Busbars, To provide ample clearance the RED(+) busbar is mounted to a 3/4" piece of plywood. You can see the 4/0 cable attached to the MRBF Fuse head and there is plenty of clearance so you get no issues.

Class-T Fuses MUST BE IN A HOLDER !, they cannot handle any stress or strain and can break apart, they are designed to be in a Holder

NOTE: Avoid the Cheapo busbars which sucker a LOT of folks like these here
1674313799521.png

Thee are typically $30 for one or $59 for black & red (amazon pricing)
Very Thin and barely capable of handling 50A let alone 100A




Pike Industries 400A Pure Copper Busbars
BusBar-closeup.jpg

Generic "Component Based" system diagram
Parallel System-setup PNG.png
 

time2roll

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Second question - Do I need to use a fuse holder with a T-class fuse, or it can be put directly on the battery terminal?

Third question - in the Wiring Unlimited book it says slow blow fuses are better when powering motors, compressors etc. I want to power one fridge with that inverter. The inverter has 4000w peak, but it doesn't say for how long. So is there a slow blow T-class fuse that should fit my application?

Thank you

Jan
2). Use a holder to retain the fuse parts if it should open. Don't want that loose connected wire moving around during a fault.

3). Class-T will pass 2x rating for close to a minute for accommodating surge performance. Size the fuse for basic rating. Don't worry a real short will open very quickly.
 

RoadTurtle

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Below is a "Generic Component System" diagram which shows where fuses/breakers should go.
Because you are building 24V, you can easily use MRBF Fuses https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A without any issues. These are quite affordable and very reliable for such an application. I run 24V and all my packs are connected to MRBF fuses on the DC Busbar. Image below shows my setup using Pike Industries HD Busbars, To provide ample clearance the RED(+) busbar is mounted to a 3/4" piece of plywood. You can see the 4/0 cable attached to the MRBF Fuse head and there is plenty of clearance so you get no issues.

Class-T Fuses MUST BE IN A HOLDER !, they cannot handle any stress or strain and can break apart, they are designed to be in a Holder
Do they make switches that can handle 400a?
 

time2roll

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Do they make switches that can handle 400a?
Blue Sea HD series up to 600 amps. Although I don't think they are designed to switch frequently under max load.

I generally recommend skipping the switch. Seems convenient and yet mine are connected for years at a time without disconnecting. I lift a cable if needed for some odd service. Switch just adds more connections and resistance compared to a direct wire.
 

JanC

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Below is a "Generic Component System" diagram which shows where fuses/breakers should go.
Because you are building 24V, you can easily use MRBF Fuses https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A without any issues. These are quite affordable and very reliable for such an application. I run 24V and all my packs are connected to MRBF fuses on the DC Busbar. Image below shows my setup using Pike Industries HD Busbars, To provide ample clearance the RED(+) busbar is mounted to a 3/4" piece of plywood. You can see the 4/0 cable attached to the MRBF Fuse head and there is plenty of clearance so you get no issues.

Class-T Fuses MUST BE IN A HOLDER !, they cannot handle any stress or strain and can break apart, they are designed to be in a Holder

NOTE: Avoid the Cheapo busbars which sucker a LOT of folks like these here
View attachment 130789

Thee are typically $30 for one or $59 for black & red (amazon pricing)
Very Thin and barely capable of handling 50A let alone 100A




Pike Industries 400A Pure Copper Busbars
View attachment 130788

Generic "Component Based" system diagram
View attachment 130786
So you're saying the MRBF fuse has sufficient AIC rating for my 24v lithium battery?

Also I have a somewhat dumb questions about basic laws of electricity. These questions were the reason I didn't want to get into busbars at first. If we look at the busbars on the diagram you sent, we can say that the busbars are like an electricity crossroad. So let's say the electricity coming from the panels through an SCC to this busbar- how does it know which road to take when there are so many options on the busbar. I suspect that it knows the correct road because only the battery (from all the other devices connected to the busbar) asks for the current (when it's not fully charged). But for example if you're using the inverter at the same time, there are two devices asking for electricity, so how does the SCC know, which way to send the current. If there is sunshine and you're using an inverter, could the current flow from the SCC to the busbar and then straight to the inverter? Bypassing the battery completely and also saving battery life. And would this effect be lost if I didn't use busbars?

Also this system I attached here- There is a connection between positive cable from the inverter to the SCC. Does that mean that it works as I mentioned above, that the electricity flows from the SCC directly to the inverter, or it only means that the builder of this system used the positive terminal on the inverter as a "busbar" to reduce the number of cables.
 

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Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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MRBF's are okay up to 36V and no issues with 24V.
A SOlar Controller will output whatever is demanded / taken up to it's capacity limit. It does not care or need to know where it is actually going, it will just push the amps as needed.

Quick Example. You have a 100A Capable SCC and panelled properly to be able to deliver 100A Charge Amps. Your charge 2 batteries in a bank and you have 100A charge available so each takes 50A @ XX Volts. As they get to Absorb the Amps Taken starts to reduce as the IR (Internal Resistance) increases so the demand decreases and the SCC will reduce automatically. Now you start your Coffee Maker (a most important device IMO) and it draws 50A, the SCC will step up to supply Max Amps it can and if short the balance will be pulled from the batteries. The Coffee Maker then finishes and the batteries are down a little, the SCC will continue to push to top up the batteries again until the Amps reduce. Once the batteries reach EndAmps/TailCurrent (100AH X 0.05 = 5A EndAmps/TailCurrent) the SCC switches to FLOAT Mode providing a trickle charge to the batteries to full & top them but will continue to provide what amps it can to the Inverter as demanded. If there is enough solar power hitting the SCC so it can output the 100A or even 75A and all of a sudden you turn on the coffee maker again, the SCC will ramp up the Amps provided to service the Inverter Demand and immediately step back down once the demand is over.

The Common DC BUS enables this very simply because you are feeding that BUS whatever the demand is, be it charging batteries or inverter demand. Once the Solar Controller is off (night) nothing changes and the demand is fed by the batteries. The next morning the SCC will start charging again as soon as the sun is up and it's generating power and all of this is completely transparent.

If you are Charging Batteries and the Inverter is demanding X Amps, the SCC will output what it can to it's max capacity. Again if there is 100A from the SCC to teh system and the Inverter is using 20A to deliver load, then 80A goes to the batteries. This will float up & down as demands come & go with the inverter. This is the normal operation of the systems.

Clarity on BMS' !
The are PROTECTION DEVICES ! They do NOT control Voltages or Amperages for charging. They only protect the cells within the battery from Over/Under Charging. If cells exceed the Allowable Voltage of 3.650V per cell the BMS will cut off charging. If the cells go below the Allowable Range which is 2.500V per cell, it will again cutoff discharging. It only takes one cell in a pack to trigger such a disconnect. They can also limit the Max Amps for Charging & Discharging and will cutoff if the values set in the BMS are exceeded.

LFP has a very flat Working Voltage Range which delivers the Actual AH Rating as specified and that range is from 3.000-3.400 with nominal voltage being 3.200 / 50% SOC @ 25C/77F temp.

Hope it helps, Good Luck.
 

Delphinus

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Think of electricity as water, you open the faucet for the amount you need, if you open two faucets it goes to both by the path of least resistance.

For a small system like yours class T make no cense to me, check the price of it and if you use fuses you must have at least one spare, I don't use them, too expensive and hard to find here, I prefer a slower fuse rated for 1.25% the max current that inverter will push, the only problem is higher resistance of it that will increase heat, I have 120A ANL in my 280Ah battery and 100A CH22 ceramic in my protection box, the first ones are always cold the ceramic became warm at 80A.
 

JanC

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Nov 20, 2022
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Portugal
MRBF's are okay up to 36V and no issues with 24V.
A SOlar Controller will output whatever is demanded / taken up to it's capacity limit. It does not care or need to know where it is actually going, it will just push the amps as needed.

Quick Example. You have a 100A Capable SCC and panelled properly to be able to deliver 100A Charge Amps. Your charge 2 batteries in a bank and you have 100A charge available so each takes 50A @ XX Volts. As they get to Absorb the Amps Taken starts to reduce as the IR (Internal Resistance) increases so the demand decreases and the SCC will reduce automatically. Now you start your Coffee Maker (a most important device IMO) and it draws 50A, the SCC will step up to supply Max Amps it can and if short the balance will be pulled from the batteries. The Coffee Maker then finishes and the batteries are down a little, the SCC will continue to push to top up the batteries again until the Amps reduce. Once the batteries reach EndAmps/TailCurrent (100AH X 0.05 = 5A EndAmps/TailCurrent) the SCC switches to FLOAT Mode providing a trickle charge to the batteries to full & top them but will continue to provide what amps it can to the Inverter as demanded. If there is enough solar power hitting the SCC so it can output the 100A or even 75A and all of a sudden you turn on the coffee maker again, the SCC will ramp up the Amps provided to service the Inverter Demand and immediately step back down once the demand is over.

The Common DC BUS enables this very simply because you are feeding that BUS whatever the demand is, be it charging batteries or inverter demand. Once the Solar Controller is off (night) nothing changes and the demand is fed by the batteries. The next morning the SCC will start charging again as soon as the sun is up and it's generating power and all of this is completely transparent.

If you are Charging Batteries and the Inverter is demanding X Amps, the SCC will output what it can to it's max capacity. Again if there is 100A from the SCC to teh system and the Inverter is using 20A to deliver load, then 80A goes to the batteries. This will float up & down as demands come & go with the inverter. This is the normal operation of the systems.

Clarity on BMS' !
The are PROTECTION DEVICES ! They do NOT control Voltages or Amperages for charging. They only protect the cells within the battery from Over/Under Charging. If cells exceed the Allowable Voltage of 3.650V per cell the BMS will cut off charging. If the cells go below the Allowable Range which is 2.500V per cell, it will again cutoff discharging. It only takes one cell in a pack to trigger such a disconnect. They can also limit the Max Amps for Charging & Discharging and will cutoff if the values set in the BMS are exceeded.

LFP has a very flat Working Voltage Range which delivers the Actual AH Rating as specified and that range is from 3.000-3.400 with nominal voltage being 3.200 / 50% SOC @ 25C/77F temp.

Hope it helps, Good Luck.
Thanks for the explanation. It really helped.

So the system is configurated in a way that the power stored in the battery is only used when the SCC can't provide enough from the solar panels. Is this correct? But which device manages this? Let's say you start the coffee maker, so the inverter asks for electricity. And you have two possible suppliers that can provide electricity- the SCC and the battery. How is it decided which device of the two is going to supply the electricity? How does the battery know to step back and let the SCC take care of it? Which devices makes the decision about this?

I suspect it's the SCC, but I just need it clarified to be sure. Because up to this point, I thought the only job of the SCC is to regulate the voltage and the amperage for the battery charging.
 

JanC

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Think of electricity as water, you open the faucet for the amount you need, if you open two faucets it goes to both by the path of least resistance.

For a small system like yours class T make no cense to me, check the price of it and if you use fuses you must have at least one spare, I don't use them, too expensive and hard to find here, I prefer a slower fuse rated for 1.25% the max current that inverter will push, the only problem is higher resistance of it that will increase heat, I have 120A ANL in my 280Ah battery and 100A CH22 ceramic in my protection box, the first ones are always cold the ceramic became warm at 80A.
I'm thinking of going for the MRBF fuse. I found this one with the holder on amazon https://www.amazon.com/Bay-Marine-Single-Terminal-included/dp/B07LC6B7DR?th=1 . I probably need 300 A because I'm going to connect it to a busbar. Do you know of some shop that has MRBF fuses or busbars and delivers to Portugal?
 

Delphinus

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Messages
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Location
Portugal
I'm thinking of going for the MRBF fuse. I found this one with the holder on amazon https://www.amazon.com/Bay-Marine-Single-Terminal-included/dp/B07LC6B7DR?th=1 . I probably need 300 A because I'm going to connect it to a busbar. Do you know of some shop that has MRBF fuses or busbars and delivers to Portugal?
The fuse is to protect, my 5.5KW only uses 120A, check the A that your battery deliver and how much A the cables can handle in CC, no point in have a fuse if it doesn't protect. Look at the datasheet of the fuses and how long it takes to blow with 300A usually is over 1 minute.

Don't know never search try a marine shop.
 

LakeHouse

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Dec 1, 2022
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2
Thanks for the explanation. It really helped.

So the system is configurated in a way that the power stored in the battery is only used when the SCC can't provide enough from the solar panels. Is this correct? But which device manages this? Let's say you start the coffee maker, so the inverter asks for electricity. And you have two possible suppliers that can provide electricity- the SCC and the battery. How is it decided which device of the two is going to supply the electricity? How does the battery know to step back and let the SCC take care of it? Which devices makes the decision about this?

I suspect it's the SCC, but I just need it clarified to be sure. Because up to this point, I thought the only job of the SCC is to regulate the voltage and the amperage for the battery charging.
Neither the batteries nor the SCC really know ‘exactly’ what’s going on here (I.e., that there’s a sudden load from the coffee maker), and they don’t need to. They both just respond to the only piece of data that they have access to: the Voltage of the system. If your system was sitting there fully charged with no load it would be at some happy full-charge voltage, let’s say 26.8V. SCC isn’t charging because that’s our float voltage in this example and the battery is doing nothing because there’s no pod going out and no power coming in from the SCC.
Now we turn on the coffee maker and it starts drawing some power. Immediately the system voltage drops because we’re pulling some power from it. The battery responds by supplying some current, but that doesn’t increase the system voltage back to 26.8V, it stays a little below that. How much below depends on the load, but the magnitude isn’t that important. What is important is that the SCC ‘sees’ this voltage drop as well and responds to it by trying to increase the system voltage back to 26.8V. If there’s enough solar power available, it does exactly that and the system voltage increases back to 26.8V, with the SCC figuring out how much current it needs to provide to maintain that voltage. Meanwhile, the battery returns to its full-charge 26.8V happy place and sits there doing nothing (neither charging nor discharging), while current flows directly from the SCC to the load.
When you switch the coffee maker off again, the SCC quickly figured out that if it keeps providing current, the system voltage rises and so it throttles back the current to zero again and the system voltage remains at 26.8V.
Note that from the SCC’s point of view, it would have done the same thing if the battery needed charging, and for the same reason; it would have seen a drop in system voltage.
 

JanC

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Neither the batteries nor the SCC really know ‘exactly’ what’s going on here (I.e., that there’s a sudden load from the coffee maker), and they don’t need to. They both just respond to the only piece of data that they have access to: the Voltage of the system. If your system was sitting there fully charged with no load it would be at some happy full-charge voltage, let’s say 26.8V. SCC isn’t charging because that’s our float voltage in this example and the battery is doing nothing because there’s no pod going out and no power coming in from the SCC.
Now we turn on the coffee maker and it starts drawing some power. Immediately the system voltage drops because we’re pulling some power from it. The battery responds by supplying some current, but that doesn’t increase the system voltage back to 26.8V, it stays a little below that. How much below depends on the load, but the magnitude isn’t that important. What is important is that the SCC ‘sees’ this voltage drop as well and responds to it by trying to increase the system voltage back to 26.8V. If there’s enough solar power available, it does exactly that and the system voltage increases back to 26.8V, with the SCC figuring out how much current it needs to provide to maintain that voltage. Meanwhile, the battery returns to its full-charge 26.8V happy place and sits there doing nothing (neither charging nor discharging), while current flows directly from the SCC to the load.
When you switch the coffee maker off again, the SCC quickly figured out that if it keeps providing current, the system voltage rises and so it throttles back the current to zero again and the system voltage remains at 26.8V.
Note that from the SCC’s point of view, it would have done the same thing if the battery needed charging, and for the same reason; it would have seen a drop in system voltage.
I want to thank you for taking the time to explain this to me. Finally I think I understand what I was missing. So it doesn't matter if you're using a busbar or not. Everything is interconnected, creating a system and the SCC is the only device that can put the system voltage back to it's 100% or like you said the float voltage. And it does that anytime it senses voltage drop. Whether it be from a battery discharging or from a load.

And if there is load and battery discharging at the same time it, the electricity flows from the SCC by the path of the least resistance which is usually the load first and then after the load decreases, the electricity flows to the battery as well.


I think I understand it now. Thanks again
 
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