[cycle61]

Clean drawing. I like the ability to use CCP2 as a backup source for your 12v loads (assuming that's what is indicated by "12v fuses". Couple of questions/thoughts:

1) What are the hall effect sensors on your + battery connections for?
2) are you planning any disconnecting means or fuse protection on the individual batteries?
3) why two series 75a breakers in series on the solar input? I'm unfamiliar with the Midnight solar charge controller
4) are you planning on grounding the -DC bus to the vehicle chassis? You'll probably need to if your loads are counting on it as a reference, specifically if you're powering them from CCP2
5) assuming no battery fuses (see #2) make sure that 150a breaker between your + DC bus and the 120a DCDC can interrupt a maximum fault current from the batteries.
6) consider an ELCI on the shore power inlet.

 

[gregoryx]

Looks sound - with plenty of assumptions of what you're doing and why.

• Assuming the two halls are for measuring each battery individually? Not sure I see the relevance of that.
• Assuming the redundant 75A breakers on the solar are intentional for some reason? Both ends of the wire? Or just a typo?
• I'm hoping / assuming there are individual fuses and switches on those batteries; if not, I'd add them.
• Make sure that double-leg breaker for the solar meets the voltage expectations. (And make sure the mounting is 6-point not just 4-point on those large panels.)

I'd be going 24V with a 2.8kVA inverter-charger and 800W solar - and then I'd go DC-AC-DC charging; but that's just me. Of course, DC-AC-DC wouldn't increase your charging - still 125A limit with the MS2812 - but I like the simplicity and control of it running through the same charging unit.

Other details not important-ish:

• yeah, ELCI and/or GFCI on the other end;
• adequate wiring;
• presumably using the Magnum shunt and their controller unit;
• consider one 12VDC fuse box on each side of the rig;
• consider a switched fuse box as well as the non-switched.

 

[Sams stock van]

Your t fuse seems to be too far down steam for basic battery protection. I'd have it before your bus.

 

[kenryan]

Clean drawing. I like the ability to use CCP2 as a backup source for your 12v loads (assuming that's what is indicated by "12v fuses". Couple of questions/thoughts:

1) What are the hall effect sensors on your + battery connections for?
2) are you planning any disconnecting means or fuse protection on the individual batteries?
3) why two series 75a breakers in series on the solar input? I'm unfamiliar with the Midnight solar charge controller
4) are you planning on grounding the -DC bus to the vehicle chassis? You'll probably need to if your loads are counting on it as a reference, specifically if you're powering them from CCP2
5) assuming no battery fuses (see #2) make sure that 150a breaker between your + DC bus and the 120a DCDC can interrupt a maximum fault current from the batteries.
6) consider an ELCI on the shore power inlet.

Thanks @cycle61

1) In the hopefully unlikely event that one battery's BMS shut it down, it seems like it could be difficult to even know that it had even happened.
2) No. The cables to the bus bar will be very short. The batteries have built in short circuit protection. Not sure what I would gain with additional fuses and connections. Disconnection can be accomplished with a wrench.
3) As that wire can be energized from each end, protection on each end seemed appropriate.
4) Yes, chassis ground to negative battery bus. I will add that to the diagram.
5) Can you elaborate on this concern? How is it any different from the 50 amp breaker between the positive bus and the 3 way switch, or the 75 amp breaker between the positive bus and the solar charge control?
6) What advantage would an ELCI give me over Blue Sea PN 8077? I don't know much about AC.

 

[kenryan]

Thanks @gregoryx

Assuming the two halls are for measuring each battery individually? Not sure I see the relevance of that.
Assuming the redundant 75A breakers on the solar are intentional for some reason? Both ends of the wire?
I'm hoping / assuming there are individual fuses and switches on those batteries.

All addressed above.

Make sure that double-leg breaker for the solar meets the voltage expectations.

Rated 125 volts.

presumably using the Magnum shunt and their controller unit;
consider one 12VDC fuse box on each side of the rig;

Yes on Magnum battery monitoring.
Already have two DC fuse boxes, see "12v fuses" on diagram.
No interest in 24 volt system. If I had a specific DC load that could benefit from the higher voltage I would have considered it. I do not.

 

[kenryan]

Your t fuse seems to be too far down steam for basic battery protection. I'd have it before your bus.

Does the T fuse protect the battery, or does it protect the wiring? I believe it protects the wiring, not the battery.

 

[harryn]

You will be a lot happier if you have an individual breaker for each battery vs wiring them together and relying on a T fuse + switch combo.

Similar to how your chargers attach to the (+ ) bus bar.

This will allow you to have an easy way to re-set the battery BMS in case one of them trips vs dealing with disconnecting batteries.

Might have an extra breaker in the solar charger wire more than is needed.

The midnight solar controller might be able to do the battery monitoring for you with just adding one of their shunts.

I understand why you are trying to stay with 12 volts but obviously would not do it that way myself.

 

[kenryan]

Thanks @harryn

You will be a lot happier if you have an individual breaker for each battery vs wiring them together and relying on a T fuse + switch combo.

This will allow you to have an easy way to re-set the battery BMS in case one of them trips vs dealing with disconnecting batteries.

I considered breakers for each battery. I cannot justify it. The added circuit protection is insignificant in my opinion. And in the hopefully rare instance of a BMS shutdown, I do not have a problem with temporarily removing a cable to reset. If it turns out that the batteries are not easily accessible, then I would consider adding the additional parts and connections, but my current plan is to have the batteries easily accessible.

Might have an extra breaker in the solar charger wire more than is needed.

You are the third person now to note the "extra" breaker. The cable is energized from both ends. Which breaker would be the "extra" one? If I can keep the cable very short, then I can see just one breaker, more for maintenance than for over current protection. But if the cable is not kept very short, then it seems like it should be protected on both ends.

The midnight solar controller might be able to do the battery monitoring for you with just adding one of their shunts.

I am familiar with the Magnum battery monitors, and I like them a lot.

 

[njvagabond]

Still learning about circuit protection but here is my $0.02 anyway.

Does the T fuse protect the battery, or does it protect the wiring? I believe it protects the wiring, not the battery.

My understanding it that the main reason for t-class is the very high 30K amperage interrupt capacity (AIC) it provides in the case of a dead short in the lifpo which could possibly create an arc in a breaker or lesser fuse such that it will weld **** and fail to provide overcurrent protection. In the current position if a breaker on one of the circuits connected to the bus bar it would then be possibly overloaded. Right now only the inverter is protected from that situation. So, I agree with @Sams stock van that it should be between the batteries and the positive bus as close to the batteries as possible). Instead of using an additional bus I would think you could connect both batteries to the terminal on the t-class fuse holder.

Dunno about your DC loads, but it looks like you have 50A capacity shared by the two fuse boxes. The fuse blocks are rates much higher than that so a bigger breaker and wire would get you more capacity there if needed.

You are the third person now to note the "extra" breaker. The cable is energized from both ends. Which breaker would be the "extra" one? If I can keep the cable very short, then I can see just one breaker, more for maintenance than for over current protection. But if the cable is not kept very short, then it seems like it should be protected on both ends.

I've wondered about that some situation with the inverter charger when charging the batteries and was thinking that an ANL fuse right at the inverter might be prudent.

1) What are the hall effect sensors on your + battery connections for?

1) In the hopefully unlikely event that one battery's BMS shut it down, it seems like it could be difficult to even know that it had even happened.

Here is my take on the possible benefit.
If one of the batteries was to malfunction and then the other would then be getting charged and discharged at 2X the expected rate. Depending on the charge/discharge capacity of the BMS on the functioning battery, and the loads on it, that may not cause the other one to disconnect. I suppose the monitor could help you notice the situation if the loads are below that threshold, say you notice your SOC declining more rapidly than expected. They might also make diagnosis easier if the still functioning battery was to also now shut down due to overload. Remove all loads, do any BMS reset procedure, add small load, watch the sensor outputs.

 

[natecostello]

Agree with the others. I doubt you’ll find breakers w/ sufficient AIC. On our first build we had 300 amp blue sea breakers off the battery but still had an upstream class t. As it stands, you have breakers that could weld shut and no manual ability to disconnect the batteries. I wouldn’t consider that safe. It also violates abyc (not that it is required, but if you are deviating, it’s a good practice to justify why). If you are relying on the batteries internal short circuit protection, that may be ok, but I’d really need to understand their method/implementation if it was me.

 

[natecostello]

I've wondered about that some situation with the inverter charger when charging the batteries and was thinking that an ANL fuse right at the inverter might be prudent.

it’s been a minute but I think ABYC allows you to rely on short circuit/fold back protection for things like inverter/charging sources. Essentially if the source can’t exceed the ampacity (unlike a battery) an additional fuse isn’t required. I’ll look it up and confirm.

 

[cycle61]

What's the short circuit output from the solar charger? Is it internally limited or protected?

With regards to the question about why I'm specifically concerned about the 150a breaker having inadequate AIC but not the others, I'm assuming that wiring is significantly larger to carry the high amperage a long distance, and could therefore support higher fault amps than the other connections.

 

[Sams stock van]

Does the T fuse protect the battery, or does it protect the wiring? I believe it protects the wiring, not the battery.

Yes, it protects the wiring from the batteries in a major short event. It should be between your batteries and the bus. In it's current position (pun intended) there is no protection for anything on the bus. My two batteries are individually fused and both cables land on the T fuse before the main switch, then the bus. I used MRBF fuses on each battery before I read posts by @harryn discussing use of switchable breakers.

 

[kenryan]

Thanks @njvagabond

...the main reason for t-class is the very high 30K amperage interrupt capacity (AIC) it provides ... right now only the inverter is protected from that situation. Instead of using an additional bus I would think you could connect both batteries to the terminal on the t-class fuse holder.

Okay, now it is making sense. (Sorry @Sams stock van I misinterpreted your post.)

And, I like your idea of connecting both batteries to the class T fuse holder. Does anybody out there know what ABYC has to say about stacking two fat wires (4/0) on one terminal?

I have seen people (including Will Powers, I think) bolt the class T fuse directly to the battery. That looks like a recipe for disaster to me.

Dunno about your DC loads, but it looks like you have 50A capacity shared by the two fuse boxes. The fuse blocks are rates much higher than that so a bigger breaker and wire would get you more capacity there if needed.

Correct. Each of my two fuse blocks is rated for 100 amps. Each slot is rated for up to 30 amps. When I add up my DC loads (water pump, refrigerator, lights, charging, fans, furnace, and possible tank heater) I come up with about 35 amps total. That's everything, including the 13 amp water pump which will only run for a minute or two at a time. So, I'm confident that the 50 amp will meet my needs. But yeah, this wasted capacity bothered me a little bit, too. When I am actually doing the installation I will consider upsizing a bit.

I've wondered about that some situation with the inverter charger when charging the batteries and was thinking that an ANL fuse right at the inverter might be prudent.
/QUOTE]

Agree. I think that's why Magnum specifies the Class T where I put it.

If one of the batteries was to malfunction and then the other would then be getting charged and discharged at 2X the expected rate. Depending on the charge/discharge capacity of the BMS on the functioning battery, and the loads on it, that may not cause the other one to disconnect. I suppose the monitor could help you notice the situation if the loads are below that threshold, say you notice your SOC declining more rapidly than expected. They might also make diagnosis easier if the still functioning battery was to also now shut down due to overload. Remove all loads, do any BMS reset procedure, add small load, watch the sensor outputs.

My previous systems have all been completely trouble free. Never had a component fail and never even blew a fuse. I just set my Magnum battery monitor to display the battery state of charge and don't worry about anything else. Occasionally I'll check in to see what my charge rate is, but that has been just for entertainment. I'm not interested at all in the fancy monitoring that is available now, down to the individual cell level. I just want my electrical system to work.

Having two high capacity batteries in parallel, each of which has a BMS that can shut it down, complicates the monitoring because if one battery were for some reason removed from the system, the system would continue to function on the one battery. Even the inverter could put out full power on just one battery.

I might not notice this situation by simply monitoring battery state of charge because my system is purposely oversized for normal operations. It is sized to act as emergency back up power at the house in the event of a prolonged power outage, and for moderate use of an air conditioner. In normal conditions I will only be using a small fraction of the batteries' capacity and so it would not necessarily be easily detectable. With the hall effect monitors' readouts next to the Magnum state of charge readout, a quick glance should tell me all I need to know.

 

[kenryan]

It also violates abyc (not that it is required, but if you are deviating, it’s a good practice to justify why). If you are relying on the batteries internal short circuit protection, that may be ok, but I’d really need to understand their method/implementation if it was me.

Hard to argue with any of that. But yes, my system design has relied on the batteries' internal short circuit protection. I am going to talk to Battleborn. I think the bottom line is that if the batteries' internal short circuit protection can be relied on, my design is good. On the other hand, if the batteries' internal protection is more of a "last resort" if everything else fails, then my design needs to be changed.

 

[kenryan]

it’s been a minute but I think ABYC allows you to rely on short circuit/fold back protection for things like inverter/charging sources. Essentially if the source can’t exceed the ampacity (unlike a battery) an additional fuse isn’t required. I’ll look it up and confirm.

Interesting. Makes sense.

 

[kenryan]

What's the short circuit output from the solar charger? Is it internally limited or protected?

Not sure. Midnite Solar controllers have long been regarded as good quality. Here's what I could find from the manufacturer:

• 150, 200 & 250 operating voltages
• Classic SL-150 max current out: 96 amps
• Classic SL-200 max current out: 79 amps
• Classic SL-250 max current out: 63 amps
• ETL listed to UL1741 and CSA
• Type 1 environmental rating
• Terminals are rated for 75 C
• Exclusive HyperVOC extends VOC limits
• 12-72V battery
• Built in Ground Fault protection
• SOLAR ONLY

"The Classic SL-150 MPPT Charge Controller is a simplified SOLAR ONLY version of the Classic 150 with streamlined menus. The Classic SL-150 has a graphics panel and ground fault but no arc fault or Ethernet capabilities. The Classic SL-150 has a maximum output current of 96 amps, an operating voltage of 150 volts and works with 12 to 72 volt battery systems. As with the whole Classic line, the Classic 150-SL has MidNite’s exclusive HyperVOC which extends VOC limits when needed."

With regards to the question about why I'm specifically concerned about the 150a breaker having inadequate AIC but not the others, I'm assuming that wiring is significantly larger to carry the high amperage a long distance, and could therefore support higher fault amps than the other connections.

Got it.

 

[kenryan]

...discussing use of switchable breakers.

I would not be comfortable relying on a switchable breaker for AIC protection.

 

[Sams stock van]

I recall seeing a recommendation not to exceed two ring terminals on one post. Also, keep in mind that when connecting cables for individual batteries direct to the fuse you can properly size and use smaller gauge wire going to the t-fuse for each battery. After the T-fuse you'll be sizing wire on total system load from the t fuse to the master off switch and then the switch to bus. Good luck.