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Question about battery fusing in Midnite wiring diagrams

jameshowison

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I've been looking at the Midnite solar wiring diagrams, such as this one:


The confusing thing is that they don't seem to include the equivalent of a Class T fuse on the battery positive. I see that in almost every other wiring diagram (e.g. explorist.life or Victron, which tend to show an ANL fuse for the batteries). Midnite show the battery positive coming to a stud on their big inverter breaker (which have high AIC ratings), so I thought that was being used as the equivalent, but the positive bus bar is wired directly off the the same stud, so the busbar is not "downstream" of the inverter breaker, in essence the busbar is wired directly to the batteries.

I think I'm missing something here? Is the assumption that the batteries are fused at the battery (or inside a Midnite battery combiner boxes), but they just don't show this in the diagrams? Is the difference something about fixed installations compared with mobile installations (but Will's fixed videos always show a Class T or equivalent, other than the new single server rack batteries where there is a circuit breaker built into the battery)

Thanks,
James
 
I've been looking at the Midnite solar wiring diagrams, such as this one:


The confusing thing is that they don't seem to include the equivalent of a Class T fuse on the battery positive. I see that in almost every other wiring diagram (e.g. explorist.life or Victron, which tend to show an ANL fuse for the batteries). Midnite show the battery positive coming to a stud on their big inverter breaker (which have high AIC ratings), so I thought that was being used as the equivalent, but the positive bus bar is wired directly off the the same stud, so the busbar is not "downstream" of the inverter breaker, in essence the busbar is wired directly to the batteries.

I think I'm missing something here? Is the assumption that the batteries are fused at the battery (or inside a Midnite battery combiner boxes), but they just don't show this in the diagrams? Is the difference something about fixed installations compared with mobile installations (but Will's fixed videos always show a Class T or equivalent, other than the new single server rack batteries where there is a circuit breaker built into the battery)

Thanks,
James
The following is pure speculation...... take it with a grain of skepticism.

Midnight has been around a *long* time. When they started, Lead-Acid was pretty much the only game in town. Furthermore, since cars did not have fuses between the battery and the starter, it was accepted practice.

Fast forward to today.... LiFePO4 has a tiny fraction of the internal resistance that Lead Acid does so a short can be far more disastrous so not only do we fuse the battery, but we pick a fuse with a huge AIC.

My speculation is that their diagrams are still stuck in the lead-acid days.
 
Your diagram, Item 15. They have a breaker.


That breaker has an AIC of 50,000A - notably higher than ANL fuse but lower than Class T.

Yeah, those breakers are substantial. But trace the red wires one more time, unless my eyes entirely fail me, the busbar is linked directly to the battery, it doesn't pass through that breaker.
 
Your eyes are failing you. 31 is the inverter. You may be confusing the charge controller, 27, for the inverter?

Battery positive (red) line runs to bottom of breaker, 15. But also off the bottom of the breaker a smaller red line runs horizontally to the bus bar (21). My read is that the busbar is not protected by the breaker.

On the other side of the breaker the thick red runs to 31, the inverter, so that wire is protected by the breaker. But I don't see anything between the battery and the bottom of the breaker, which means no protection between the battery and the busbar.

I think that's quite different than other diagrams which would have a Class T (or similar) "as close to the battery positive as possible."
 
Note that the only thing connected to that bus bar is the charge controller. It's not a primary bus bar in the way that you're thinking. From that bus bar it goes to another breaker for the charge controller.
 
Note that the only thing connected to that bus bar is the charge controller. It's not a primary bus bar in the way that you're thinking. From that bus bar it goes to another breaker for the charge controller.
Good point. And the charge controller wire is protected through the circuit breaker 16.

But they do say in the notes that this is where DC loads would connect, they just aren't shown in this diagram. See the note for 21: "Battery Positive Bus Bar. This is where we would wire the Battery positive side of the Classic, as well as where we would wire up DC loads. Do NOT wire the battery cable to this bus bar." So that's all DC loads other than the inverter. The loads would have their own breakers, but those breakers wouldn't have the high AIC that something like a Class T would provide. If the battery dumped with a short circuit, the wire to the busbar and to the load breakers, as well as the load breakers themselves, wouldn't be protected.

I'm not in a position to say that it is wrong, just that it is quite different from the recommendations in other places.
 
It’s a lead acid diagram.

Add a class t fuse directly after the battery if you are running lifepo, move on.
So breaker #15 would be replaced by a Class T fuse ?

1641350197185.png
 
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There is just too much to criticize about that diagram. That CB you refer seems to be directional based on the connectors labeled 'load' and 'line'. With LiPo a Class-T type fuse is needed as close to the battery positive as possible.
 
This is my "Logical" Diagram for my Midnite Setup with E-Panel.
I had a Class T Little Fuse on my Lead Battery Bank. (Bank is now decommissioned)
Each LFP Battery within the LFP Bank is individually Fused with an MRBF Fuse @ Common DC Busbar.
1641391119399.png

1641391500541.png

Breakers within E-Panel










ACTUAL Instalation:

1641391179772.png

Hope this helps a bit, there is more info in the links in my Signature, including Midnite Solar Stuff.
Steve
 
I also use the Midnight E-panel supplied by Midnight but on my system there is a Class T fuse at each battery bank. I have made a few other changes as well as I have Two Classic 150,s and at least 2 inverters. Each of the Classic’s hot wires go to the battery fuse, not to the inverter breaker as each inverter can run off either battery bank , as well as each controller can charge either battery bank.

The Magnasine Inverter is mounted on a midnight E-Panel much like the one Steve_S has posted but most DC breakers are in a Midnight Solar DC-15 DC breaker box which contains the charge controller breakers and other DC circuits.

Bit more complicated but these changes were made for 100% redundancy, If any component were to fail I can throw a few switches or breakers and swap out any critical component with just a throw of breakers or switches. In under 1 minute at any time. Rapid Shutdown of the entire system can happen remotely or locally by pushing a button. Also automatically in case of fire, etc.


The Magnasine inverter battery switches are special Midnight switches which were meant for a rapid shutdown system that was shelved. They are 4 gang Carlingswitch E series switches (not breakers) that were originally wired in series for a rating of 156 amps @600 volts but I have changed the wiring on these to parallel so that they are rated 624 amps at 150 volts. They also have remote trip capability. I can push a trip switch and shut these down remotely. (just in case hell breaks out)

The Exeltech inverter switches are Midnight MNDC breakers located in the MNDC-15 DC breaker box so either Exeltech inverter can be powered by either battery bank or both (never done)

Basic circuit to main inverter, Class T fuse right at battery——battery selector switch——MNDC250 breaker—Inverter
Basic circuit to auxillary inverter, Class T fuse at battery—MNDC Breaker in MNDC breaker box—-Inverter
each inverter can feed from either battery or both, controlled by MNDC breakers in MNDC-15 breaker box
Basic circuit to each SCC, Class T fuse—MNDC breaker in MNDC box—SCC

It is setup so that the breaker should trip first, the class T is there as a “hail mary” incase everything goes to hell in a handbasket. Will blow if a main cable shorts.

The whole point of this is 100% redundancy, ANYTHING can fail and be switched out in under 1 minute without disconnecting anything and have power 24/7/365 no fail....I do not need a huge amount of power but I do need it 24/7/365 (I will not discuss why here, not the approiate place)

I do have a very small utility feed 30 amps at 120 volts and two Onan generators, one at 30 amps 120 volts, the other 30 amps 120/240 volts split phase OR 60 amps 120 volts (hacked) formerly motorhome generators 1800 r.p.m. low noise

Battery banks FLA, 426 a.h. @ 24 volts 2 ea. (Separate, not in parallel)
Main Inverter Magnasine MS4024AE 4 kw. 120/240 split phase
Quiet inverter Exeltech XP-1100 1100 watts 120 volts
Quiet Inverter Exeltech XP-600 600 watts 120 volts
Main Charge controllers Midnight Classic 150 with Whizbang jr (2 each)
Auxillary charge controllers Midnight Kid (2 each)
Diversion controllers Trace C-40 (water heating)
 
Good point. And the charge controller wire is protected through the circuit breaker 16.

Your eyes glazed over following the lines. Wire to breaker #16 which connects PV and surge arrestor to SCC.
Wire from unprotected side of breaker #15 goes to breaker #17, for SCC connection to battery.

You can daisy chain a second breaker downstream of main breaker, may provide coordinated tripping, bigger breaker may provide greater short circuit protection (question is what happens to smaller breaker when both trip, due to "let through" current.)

But daisy chained means voltage drop from inverter surge through main breaker is seen by SCC on second breaker. Having SCC's breaker wired to battery might avoid some issues. Then it does for sure need sufficient AIC rating.

That CB you refer seems to be directional based on the connectors labeled 'load' and 'line'.

Which picture are you looking at with "load" and "line" labeled?

Some of their smaller breakers are polarized, and there is a game played for bidirectional usage (including SCC, where moderate normal currents flow one direction but extreme fault currents the other.)

However, I don't see line & load indications in the particular Midnight schematic I'm looking at.

That breaker has an AIC of 50,000A - notably higher than ANL fuse but lower than Class T.

Not for DC it ain't "lower". Typical Class T fuse is rated 20kA for DC (and 200 kA for AC)
There are some fuses rated 50kA for DC. Ferraz Shawmut has them.
 
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So breaker #15 would be replaced by a Class T fuse ?

View attachment 78389
No I would source a diagram for lifepo system or modify this one.

I would have 15 be a class T fuse and connect the load side of it to bus bar 21, then all load including SCC connected to that bus bar with their own overcurrent protection device.
 
No I would source a diagram for lifepo system or modify this one.
I've been looking for a detailed diagram for off-grid system with LiFeP04 batteries and generator backup.
Using two Midnite Classic 150's too, but I don't expect the diagram to be specific to them.
Anybody got one ? :)
 
I've been looking for a detailed diagram for off-grid system with LiFeP04 batteries and generator backup.
Using two Midnite Classic 150's too, but I don't expect the diagram to be specific to them.
Anybody got one ? :)

I say use the search within the forum. It is not great (I'm being polite here), try it though. Curious if you find it as frustrating as I do.
I mentioned this to someone yesterday. MidNite answers the phone and IS VERY helpful.
 
According to Midnight Solar the MNDC-250 is non polarized
Midinght sources this breaker from Carlingtech
According to Carlingtech the breaker is non- polarized

It is tradition the input terminal is marked “line” and the output terminal is labeled “load”

Sources of information:

Robin Gudgel @ Midnight Solar president and CEO of Midnight Solar and founder of Trace, Outback, Midnight Solar
boB Gudgel @ Midnight Solar head guru and founder of Trace, Outback, Midnight Solar
Carlingtech
 
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