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Wiring 4 Battle Born 12 volt batteries into 2 banks of 24 volts each

tucsonjwt

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Sep 29, 2019
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I am considering buying 4 Battle Born 12 volt 100 AH batteries and wiring them in 2 banks of 24 volts each, and connecting them to a Growatt SPF 3000TL LVM - 3kw 120Vac all in one inverter/charger.

I would like to wire the batteries in the most efficient way possible, and I want a disconnect between the batteries and the inverter/charger, along with overcurrent protection from the batteries.

Is there some sort of combiner box that would give me overcurrent protection as well as a disconnect between the inverter/charger and the battery bank?

I have been reading about Square D QO breakers being DC rated, but I don't know if this is the best way to get what I want. I guess I would need two breakers for 100 amps each at 24 volts.

I think the benefit of a DC breaker box is that I could have one large cable off the positive buss bar and one off the negative buss bar going straight to the inverter/charger. I like the idea of having the electrical connections inside of a metal breaker box.

Any thoughts?

 
For the combiner part, I'd almost check out some of the equipment they use in boating, as they often deal with multiple battery banks for house and engine batteries.

I had my eye on something like this for connecting my 2 banks together:

For the breakers, you could either do a DC breaker panel/DC breakers, or do standalone surface mount breakers.

Blue Sea Systems is a reputable brand for high quality parts, beware of cheap quality surface mount breakers...


I don't know best place to get a DC breaker panel. I just bought a MidNite Solar DC combiner box, but it is intended for PV solar run, with safety disconnect. I don't know if one could use a panel like that and just buy large breakers for it...

My gut says there are better DC panels made for larger boats or whatever like maybe from SquareD or other industrial level supply outfit which would be purposed specifically to house large DC breakers, equipped with larger bus bars and all...

EDIT:
Just found this from MidNite Solar which could work for DC breaker box:

Box:

Breaker:

You could also convert it into a combiner by making a bus bar built into it, if you didn't want the battery selector thing.
 
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Ideally, you would set 2 BB's in series for 24V then connect that to a common DC Bus, then to BlueSea 9000 Series switch, then to Main Breaker, then to SCC & Inverter. Each battery should have its own fuse, can be on the battery itself or on the common DC Busbar.
 
Thanks for the information.

Steve S. - are your saying that it is best to have 4 fuses (one on each battery)? I would think that combining two BBs in series creates (in effect) one 24 volt battery, with each 24 volt battery being fused or protected by a circuit breaker in a service panel. Do I have that correct?

I am planning on using a Midnite Solar MNPV6 for the combiner box for the solar panels, and I thought about using one of those as a disconnect/overcurrent protection for the batteries also - but I have not read about anyone doing that.

I do like the idea of a small conventional AC style service panel but those AC boxes are much larger than I need.
 
Thanks for the information.

Steve S. - are your saying that it is best to have 4 fuses (one on each battery)? I would think that combining two BBs in series creates (in effect) one 24 volt battery, with each 24 volt battery being fused or protected by a circuit breaker in a service panel. Do I have that correct?

I am planning on using a Midnite Solar MNPV6 for the combiner box for the solar panels, and I thought about using one of those as a disconnect/overcurrent protection for the batteries also - but I have not read about anyone doing that.

I do like the idea of a small conventional AC style service panel but those AC boxes are much larger than I need.
Yes, one fuse per battery. Breakers STILL Go on. The fuses are protection only.
I use a proper Midnite DC E-Panel (mine is 250A Main, 30A in from solar, 90A out from Midnite-C200
I also use Square-D AC Panels but ONLY for AC, do NOT use them or DC, people make that goof, don't.
See my "About my system" link in my signature. That is out of date I need to update it but the essentials are there. My system is what you see on that page PLUS 4 LFP Packs in their own bank for 910AH (2x24V/280 & 2x175AH) I'll be updating those pages next week,
 
I am new to this, so I must ask some dumb questions.

The breakers you link to are very expensive. I understand the need for good protection, but would a AN type automotive fuse provide the same protection? Would there need to be a fuse attached to each individual battery at its source - like directly attached to each battery terminal, so 4 fuses needed for my application? I don't understand why I would need both a fuse and a circuit breaker for each battery. Doesn't a breaker serve the purpose of a fuse?
 
I have this same setup, modular -with 2 battery banks in separate boxes. Each bank is a pair of 12v batteries wired in series, with a bolt-on Bussman fuse on the positive terminal (of each pair, not each individual battery). I currently use a 1/0 SB175 Anderson plug to connect each battery bank to the load side of my system.

On the load side (plywood with my inverter, SCC etc) - I have a BlueSea battery selector switch - that gives me the option of bank 1, bank 2, both, or off. I have a short Sb175 cable wired to the selector so I can plug in either battery bank, or both (depending on my needs/setup).

On the other side of the selector switch, a BlueSea circuit breaker (surface mount), and then into my inverter.

I'm about to rebuild this with 2/0 welding cable - using DINSE panel/socket mounts on the battery and load side, and have 2' jumper cables with DINSE to connect it all up. Will have some sort of protective cover on the battery-side sockets so no accidental shorts can happen. And then 3rd battery bank next.
 
I will be using a Midnite Solar MNPV6 combiner box for the solar panel PV input. Can I also use the same combiner box for the battery output? That would involve using 2 circuit breakers at 100 amps each (one for each 24 volt battery bank). The following text from the Midnite Solar instructions seems to indicate that I can do this. I like the idea of having all of the connections inside one metal box, rather than scattered along the wall. The separate positive and negative buss bars inside the box with large lugs on the end would allow for a larger cable going to the Growatt inverter/charger. Am I wrong?

IMPORTANT! Polarity of the din rail DC breakers. The DC breakers supplied by MidNite Solar are custom manufactured in Lesotho Africa by CBI. These breakers are polarity sensitive. This means that they need to be installed correctly in order to insure that they will be able to trip if called upon to do so. In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus. This hook up is not obvious. The + sign designates the highest potential should be connected there. This is an easy one to determine in a PV combiner. Follow the current path through the combiner, into the PV input of a charge controller and out of the controller to an output breaker and then into the battery plus. You would think that the end of the output breaker connected to the controller would be at a higher potential than the battery plus. In normal operation this is true. The main job of this output breaker is to trip when and if there is a catastrophic failure. (Any manufacturer of power electronics will tell you that power electronics can fail). If the output breaker fails to trip, you are at risk of fire from the output wires burning up. When a charge controller fails, they always short from positive output to negative output. Since these two terminals inside the charge controller are normally connected up to a very large battery bank, you have a direct short across the battery bank if the controller fails. During this condition, the controller is acting like a piece of wire. The battery positive terminal is the highest potential! Make sure that the plus (line) of the breaker is connected to the battery plus terminal. If the breaker is connected backwards, it can fuse in the closed position as it attempts to open.

What about two of these:


Inside one of these:


It seems like the screw type lugs at the ends of the buss bars can accept up to 2/0 cable.
 
I ordered a Midnite Solar MNPV6 with two 20 amp breakers.

I got 4 Trina 405 solar panels.

I am planning 2 panels in series, then the wires from those 2 strings will run separately to the MNPV6 combiner box to separate circuit breakers.
This setup will be inside the trailer and primarily serve as a convenient means of disconnecting the pv array from the rest of the system when necessary.

My plan is to use 4/0 cable to connect the batteries, then 4/0 to a 300 amp buss bar, then run 2 AWG wire to my Growatt 3000 watt /24 volt combination controller/inverter/charger. The Growatt terminals only accept 2 AWG wire max.


I bought the 200 amp circuit breaker which I will use on the positive line between the batteries and the Growatt. If possible, I will attach the 4/0 cable from the batteries to the circuit breaker and have a short piece of 4/0 from the other breaker terminal to the buss bar.


I ordered 4 batteries from Battle Born this past Monday but no word on shipment yet. I am working on getting all of the bits and pieces together.
It is taking me a long time and some considerable money since I am completely ignorant on the topic of solar. I do appreciate the help I am getting here.
 
On another topic, the issue of grounding the system is something I don't understand with regard to a solar installation in a vehicle. I am not going to drive ground rods in the dirt beside my trailer, so I won't have an earth ground. RVs use the vehicle chassis as a ground, but it seems to me that this is really connecting to the "Faraday Box" properties of the steel structure of the vehicle, not a true earth ground.

I see YouTube videos of DIY solar installers like me connecting an ac output ground wire to the equipment chassis (inverter) which I suppose gives you someplace to put the green wire in the extension cord cable, but I don't see how that gives you a true ground. That might allow you to use a GFCI receptacle without getting an immediate trip, but I don't know it this is a true ground.

Any thoughts?

Thanks.
 
On another topic, the issue of grounding the system is something I don't understand with regard to a solar installation in a vehicle. I am not going to drive ground rods in the dirt beside my trailer, so I won't have an earth ground. RVs use the vehicle chassis as a ground, but it seems to me that this is really connecting to the "Faraday Box" properties of the steel structure of the vehicle, not a true earth ground.

I see YouTube videos of DIY solar installers like me connecting an ac output ground wire to the equipment chassis (inverter) which I suppose gives you someplace to put the green wire in the extension cord cable, but I don't see how that gives you a true ground. That might allow you to use a GFCI receptacle without getting an immediate trip, but I don't know it this is a true ground.

Any thoughts?

Thanks.

Grounding is relative on a vehicle. It's more of an alternate return path for safety. If you are inside the RV, then the RV is your Earth... If an appliance shorts out (to the metal body of the appliance itself), it's good to have that 3rd wire ground go back to the inverter's chassis ground which would allow it to induce enough current flow to blow the AC breaker as it should. Just treat the vehicle chassis like your mini-Earth... Many inverters have common ground/neutrals as well... You can check it though. I would at least want the green wire of an appliance wired back to the ground of the inverter so there is a safety return path back to it, you can ground the inverter to the vehicle chassis too if you want...
 
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I follow your logic, but I do have one question. If an appliance has a direct short to its metal body, isn't that a direct short which will cause a circuit breaker to trip upstream? I am assuming ac loads in this case being protected by an ac circuit breaker.

As you can see, my knowledge of electrical theory is beyond inadequate.;)

I will take your advice and ground ac circuits to the inverter chassis and trailer frame.

On another topic, would you bother with lightning protection? I am thinking it would not be helpful, using that analogy of a metal vehicle being a big Farady box. In this case, a box with a nice big aluminum lightning collector on top.:)
 
I follow your logic, but I do have one question. If an appliance has a direct short to its metal body, isn't that a direct short which will cause a circuit breaker to trip upstream? I am assuming ac loads in this case being protected by an ac circuit breaker.

As you can see, my knowledge of electrical theory is beyond inadequate.;)

I will take your advice and ground ac circuits to the inverter chassis and trailer frame.

On another topic, would you bother with lightning protection? I am thinking it would not be helpful, using that analogy of a metal vehicle being a big Farady box. In this case, a box with a nice big aluminum lightning collector on top.:)

Yeah on the first point about 'If an appliance has a dead short to its metal body' thing, it goes back to what I said (but I'll articulate it a little different), if it is only a 2-wire appliance with no ground on the cord, and hot shorts to the chassis of the appliance, then there is no safety, that chassis is live because that circuit isn't ground so it will never induce enough current to trip the AC breaker protection. So even a week later, someone could walk up to it and touch it, and it is still silently alive.

Now on 3-wire, you have a safety ground (alternate current return path), grounded to the chassis of the appliance, so if that device's hot wire shorts to ground (which is effectively the same potential as neutral, but just on an alternate path), then it will become a short, inducing full load current, and tripping the AC breaker protection, killing the circuit. So it is no longer a danger. That's how it's intended to work.

On the next topic, well, lightning protection is considered a best practice, since the solar panels are outside, you can draw even inductive current from distant, non-direct lighting strikes which can damage equipment.

When I used to work for a wireless internet ISP, we had lightning strikes 1/2 mile away that could take out a radio on our tower. Any protection you can provide is a good idea. But if you rarely have lighting in your area, then that is another consideration, I mean it's up to you...
 
I won't have to worry about lightning because my house was already struck by lightning once and we all know lightning does not strike twice in the same place. ;)

Regarding lightning arrestors for solar equipment, are they actually effective. I have read discussions about the huge voltage in a lightning strike being so fast and powerful that the lightning arrestor in a solar system will not be able to divert a lightning strike.
 
I won't have to worry about lightning because my house was already struck by lightning once and we all know lightning does not strike twice in the same place. ;)

Regarding lightning arrestors for solar equipment, are they actually effective. I have read discussions about the huge voltage in a lightning strike being so fast and powerful that the lightning arrestor in a solar system will not be able to divert a lightning strike.

Also, solar parts are getting less and less expensive, so if you are lucky enough to get a lightning blast that blows out your stuff, maybe it was a sign from above that it's time to get some new equipment hehe...

I may not worry about putting lightning arrestors on, I guess I might, will have to price them out and see if they are worth it or if they have any cons. I might just put in a lightning rod on the other side of our ranch property to draw potential strikes over there...

I heard from a lady from Canada a long time ago she said they had a lightning rod on the other side of their property and the strikes would always hit over there so not to come near the house, because they were in the open plains...
 
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