Connecting CC & Inverter to Battery Bank

[johngalt]

I have a 48V battery bank - 4 x 12v in series. Would this double Terminal fuse make for a good option to connect the inverter and cc to the battery bank?

Since I have an ungrounded system could I put one of these on both the positive and negative battery terminals to make the fused connections?

Or would the single terminal work better with the Inverter and CC leads stacked on top of each other?

http://bluesea.com/products/2151

http://bluesea.com/category/81/21/productline/overview/378

Thanks

[Sunking]

John good find on the terminals. I have been using then for a few years now. Fuses are expensive but a good system. Use dual terminal type. Be sure to use appropriate sized fuses. For example if the CC is 40, and the inverter is 1000 watts, then the CC fuse will be 50 amps, and inverter 100 amps. Also pay attention to appropriate sized wire.

[johngalt]

Use dual terminal type. Be sure to use appropriate sized fuses. For example if the CC is 40, and the inverter is 1000 watts, then the CC fuse will be 50 amps, and inverter 100 amps. Also pay attention to appropriate sized wire.

Cool - will do.

It seems I can find panels, batteries, charge controllers, and inverters just about anywhere I search on the Internet. Finding the right components to actually connect everything together for my sized system has been a real challenge.

Thanks

[Naptown]

You discovered the marine suppliers. They have lots of DC stuff.

[johngalt]

Be sure to use appropriate sized fuses.

My MPPT CC is rated to put out up to 60 amps. But with my array of only 1450 watts and my 48V battery it will be more like 30 amps.

The inverter is rated at 1100 watts continuous 2200 watts surge. The inverter will cut off if the input voltage get to 41.5 volts so if I divide 1100 watts continuous by 41.5 volts I get 26.5 amps. The rated current on the spec sheet says 27A. Close enough.

However the specs also has a "peak current" of 30.5 amps. If I divide the 2200 surge watts by the same minimum 41.5 volts I get 53 amps.

I'm not sure where the 30.5 amps is coming from nor the correct fuse size. If I take the 30.5 amp number and multiple by 1.25 I get 38 amps. If I round up to the next fuse size that would be a 40 amp fuse but the 53 amp number is eating at me.

The manual also says the inverter has a "clipping" feature where it will clip the top of the wave to keep the inverter from being overloaded. Maybe this is why they say 30.5 amps and not 53 or more? Maybe the internal circuits will never let the amperage get that high?

Thoughts?

[Sunking]

With low voltage you go by voltage drop, then do a sanity check with NEC tables to make sure the amperage does not exceed maximum safe rating for the wire. 2% is a tough expensive spec to meet at low voltage. That is why utilities use very high voltage.

[johngalt]

Thanks

[johngalt]

Well I received the dual terminals and a couple fuses.

The terminal specs states they are rated for 58 volts up to 300 amps. OK, I guess that is good for my 48 volt system.

The 50 amp fuse, however, reads 50 Amps then 5000A AIC @ 32V DC Max

Are these fuses going to work on a 48V battery or will they blow as soon as I install them? Not sure what "5000A AIC @ 32V DC Max" means.

Terminal Specs:



Fuse Specs:

[Sunking]

All is well. AIC = Amps Interrupting Capacity which means the fuse can safely handle up to 5000 amps without vaporizing and exploding into flames aka Arc Flash. The higher the better. You are good to go.

[johngalt]

Thanks! It won't be long now. I'm still waiting on a few more cables and the inverter, then I can start hooking it all together.

I'll let you guys know how it works out.

[inetdog]

Thanks! It won't be long now. I'm still waiting on a few more cables and the inverter, then I can start hooking it all together.

I'll let you guys know how it works out.

Just FYI, the full specifications are on the manufacturers website, but they chose to feature just one of the numbers on the package itself:

"Interrupt Rating 10000 AMP @ 14Vdc 5000 AMP @ 32Vdc 2000 AMP @ 58Vdc"

But this does mean that if your batteries and interconnect wiring are capable of supplying more than 2000 amps into a dead short circuit, then the fuse will not be operating within its ratings.

[Sunking]

But this does mean that if your batteries and interconnect wiring are capable of supplying more than 2000 amps into a dead short circuit, then the fuse will not be operating within its ratings.

Not many batteries are capable of 2000 amps. If more then a few feet of copper wire are involved, not likely an issue because the resistance will be more than .02 Ohms. Only place it gets to be a problem is a bolted fault on the battery terminal post. At that point the fuse vaporizing is the least of your worries.

[johngalt]

I will have about 18" of cable from the battery fuse to a breaker box. The breaker box will act as a disconnect for the CC and inverter from the battery bank and the primary point of failure as the breakers are 10 amps lower than the battery fuse. ie. 50 amp fuse on the battery and 40 amps at the breaker. From the breaker box I will have another 12 to 18 inches of cable going to the charge controller and to the inverter. The idea was to have the breaker trip first and the fuse only as a last resort. Both sides of the battery will be fused and paired with a breaker. ie 4 fuses and 4 breakers. The cables will be #4 AWG stranded which is rated higher than both the breaker and the fuse. The battery bank is only 153AH at 48VDC and the array is 1450 Watts with an MPPT controller. At max output I will only be able to get about 30 amps to the batteries and about the same from the batteries to the inverter.

[inetdog]

...The idea was to have the breaker trip first and the fuse only as a last resort.

Unfortunately, with the wide differences in time characteristics of different types of breakers and fuses as well as unit-to-unit variations, the difference between a 50 amp fuse and a 40 amp breaker is not enough to produce any assurance that the breaker would normally trip first for a load which passes through both.
Since the fuse is primarily protecting you against accidental short circuits in the connecting wiring, rather than small overloads, making the fuse much larger than the breaker would make more sense.
And for manual operation, after interrupting any current with the breaker you could remove the fuse as a positive disconnect. Since a battery post fuse is normally there to protect the batteries, you need to make sure that it can handle the full surge current needs of the inverter.

[johngalt]

Unfortunately, with the wide differences in time characteristics of different types of breakers and fuses as well as unit-to-unit variations, the difference between a 50 amp fuse and a 40 amp breaker is not enough to produce any assurance that the breaker would normally trip first for a load which passes through both.
Since the fuse is primarily protecting you against accidental short circuits in the connecting wiring, rather than small overloads, making the fuse much larger than the breaker would make more sense.
And for manual operation, after interrupting any current with the breaker you could remove the fuse as a positive disconnect. Since a battery post fuse is normally there to protect the batteries, you need to make sure that it can handle the full surge current needs of the inverter.

To the best of my ability I believe I have allowed for the full surge current needs of the inverter. If you go up a few posts you can see the specs for the inverter I intend to use. It has internal circuitry that clips the wave to insure that the inverter never has an in rush of current it cannot handle. (paraphrasing) The manual says no in line fusing/breaker is needed because their circuitry is faster than anything I can put in front of it. Nonetheless, I want the extra protection for the batteries, wire, inverter, and a disconnect between them. I based the size of the fuse, breaker, cable on the higher spec of 30.5 amps from the manual. I choose the 40 amp breaker because 80% of 40 is 32 amps. I don't anticipate overloading the inverter as its use will be very deliberate with known draws. If I do create a high surge current I would rather the breaker trip as a reminder to reconsider what I am doing. I don't know if I can return the fuses for larger ones, I may just go with what I have and if I blow one move up to a much larger size as you suggest. Another semi-expensive learning experience. On the charger side my math says I need a 30 amp charger based on the 1450 watt array size and 48v battery bank. Mine can go to 60 amps but I don't have the array size to put out that much current and the likelihood of me adding more panels now or in the future is slim to none. (Out of roof space, money for this project, and patience ) I have the ability to program the charger for a specific max current which I will probably set to 32 amps (80% of the 40 amp breaker) even though I may never exceed 30 amps. I am pretty much limiting the system to my expectations. Anything way outside of those parameters and I want it to stop until I know why. If I am correct I should never have more than 32 amps coming into the battery bank or more than 30.5 amps going to the inverter. If either goes above 40 amps I want the breaker to trip so I can figure out where I went wrong in my calculations.

Maybe I am being too conservative, but that's just me.