Does this make sense for a battery bank?

[Biscuitsjam]

I appreciate the vote of confidence! You don't happen to have the POC to submit the AMR from Lawson to Ladd Army Airfield do you? Our Air Load Planners could get some good training out of a non-standard schoolbus load.

I'm aware of the documentation requirements. The trip isn't going to be until May when the weather is milder. I'd also rather not stray too far off topic.

Thanks to everyone for the advice so far. Any further suggestions to improve my electrical system would be appreciated.

[Robin97396]

My thought is how can you expect an up to code electrical system when everything else in the bus is temporary? That could be a priority item, but you'd be guessing about how you'd want it set up. If you've got everything grounded properly there's no reason you can't use a temporary electrical setup until things start getting more permanent in the bus.

I have two 15 amp lines coming into my bus using standard construction type single plug extension cords. Certainly not an ideal setup, but not exactly dangerous either. A powerstrip here and a powerstrip there and voila. This helps me to decide how I do want a permanent electrical system.

[Rusty]

Here is his parts list from links. is there an XLS spreadsheet?

[Biscuitsjam]

Originally Posted by Robin97396

My thought is how can you expect an up to code electrical system when everything else in the bus is temporary? That could be a priority item, but you'd be guessing about how you'd want it set up. If you've got everything grounded properly there's no reason you can't use a temporary electrical setup until things start getting more permanent in the bus.

I have two 15 amp lines coming into my bus using standard construction type single plug extension cords. Certainly not an ideal setup, but not exactly dangerous either. A powerstrip here and a powerstrip there and voila. This helps me to decide how I do want a permanent electrical system.

That's essentially what I'm going for - the big concern is making sure I do it safely.

[Twigg]

Originally Posted by Biscuitsjam

That's essentially what I'm going for - the big concern is making sure I do it safely.

Fasten everything down away from easy access by the kids. Should be fine.

[Biscuitsjam]

Originally Posted by Rusty

Here is his parts list from links. is there an XLS spreadsheet? :biggrin

I will neither confirm nor deny the existence of any spreadsheets.

[802trees]

Good stuff

[david.dgeorge07]

What wire are you planning?


Sent from my iPhone using Tapatalk

[Biscuitsjam]

I spent some time working with a voltage drop calculator and a lot of time reading and digesting all the responses here. If any of the more experienced folks see any mistakes in my reasoning, please let me know.

As I understand it, the general rule of thumb seems to be a loss of no more than 2% voltage over any one run and no more than 5% for the entire system, including branches. Different folks are more or less tolerant of voltage drops, depending on their goals.

Battery Charger - > Batteries - > Inverter
2/0 AWG Outdoor-Rated

Reasoning: Assuming the total length of all the wire segments (1-way) is 5 feet, the voltage drop would only be 2% for a 300A draw (equivalent to 3x 1000 BTU air conditioners or double the maximum sustainable inverter draw - enough power that the batteries would be drained in minutes). Since this is an unrealistic draw for the size of the battery bank, that means we're talking a sufficiently over-engineered system with 2/0 AWG. Dropping the wire size quickly gets the system into problem territory.

It's important to note that voltage drops quickly with distance - if these components are spread out, then it creates problems.

AC Wiring (Shore Power - > Charger and Inverter - > Interior Wiring)
8/3 AWG Outdoor-Rated

Reasoning: If I went with 10 AWG for the AC wiring, the whole system should come in within specs, but why cut things so close when it is cheap and easy to upgrade that wire? 8 AWG or 6 AWG are affordable upgrades.

2-wire for the AC wiring is not a good choice, because you lose the grounding from your shore power (or combine it with neutral, also not good). Either 4-wire or 3-wire (using one wire as ground) would be safer. (8/4 or 6/4 would reduce voltage drop further, but I don't think it's necessary - correct me if I'm wrong or if I'm missing another benefit).

DC Wiring (Battery Bank - > Interior Wiring)
8 AWG Outdoor-Rated

Reasoning: This one, I'm a little less certain of. Most recommendations I've read are for 12AWG or smaller wires, which makes sense for short distances and single DC devices (which usually draw very little power each). However the single feed coming off the batteries potentially carries the current draw from many different circuits, and a 36 foot bus means that a percentage of the runs are going to be pretty long. I'll already have 8/3 AWG wiring, so I'm thinking at least this main feed should be 8AWG (with the 3rd wire unused). When it branches off, I can use smaller wires going to LED lights, etc. Let me know if anyone thinks this is unreasonable

I found this interesting site talking about DC amperage draw for RV equipment:
How To Calculate Amp Usage in a RV - Trailer Traveler .

Other Notes:
- I still don't have a surge protector at the beginning of the system. I'm on the fence about that one right now. I'm also on the fence about swapping out my fuse with a circuit breaker or other disconnect as suggested earlier.
- I'm sold on a circuit breaker box but only in conjunction with my "final install." Until then, I'm planning to wire my inverter to a double AC outlet inside the bus and use a couple extension cords with power strips/surge protectors out of the way. I want everything to fully get up to code when I eventually finish this.
- I'm still not completely sold on the battery monitor I chose, but I think it would be pretty easy to swap out later if I want.
- I am a huge fan of labeling everything. Every wire will have a tag on it.

[JDOnTheGo]

EXCELLENT WORK!!!

My suggestions are:
1. Don't use x-3 cable for the AC wiring. x-2 is sufficient unless you plan on 3-way switches. Believe it or not, x-2 cable is three wire (white, black, ground) and x-3 is four wire. Makes sense right?!?? The deal is that they don't count the ground wire.

2. 8-2 AC wire from shore to breaker panel is good. 12-2 is probably sufficient for each circuit (breaker to outlet) as that is good for 20 amps (as are most outlets) and it is easier to work with.

3. A surge protector can be added later if you decide you want/need and you can also use an external one.

4. There is nothing wrong with using 12 AWG for DC circuits. However; it might be overkill for some (which is far better than underkill). In many cases, a thicker wire is ran from the battery to a fuse panel and then thinner wires for each individual circuit (depending on length and power requirements). A series of LED lights is an incredibly efficient thing and sometimes only need a couple of amps.

[Biscuitsjam]

Small updates - added ground wires and updated wire gauges.

Just to clarify -the inverter is grounded to the chassis? I've read a lot of conflicting things.

I'm not sure how important a grounding rod is since most people don't use one. It would be a pain to set up and easily forgotten - I'm guessing it becomes more important if you have an onboard generator? It would be easy though -just attach a copper spike to the chassis using a big wire then hammer it into the ground.

[Defjr333]

"grounding" inverters and gennys etc have been an on going topic. I am of the camp to use the GROUND LUGS only off the genny or inverter to ground. NOT the actual ground wires from each circuit. Some are of the other camp. My reasoning is based and found in airframe grounds I am trained on by USN. I am sure you will see replies to all 3 camps.....Ground everything, Ground Lugs only, no grounding at all. There are benifits and pitfalls to each
Doug

[Robin97396]

It used to be popular to hang a chain from the vehicle frame to allow a ground with the earth.

[BlackJohn]

Originally Posted by Defjr333

"grounding" inverters and gennys etc have been an on going topic. I am of the camp to use the GROUND LUGS only off the genny or inverter to ground. NOT the actual ground wires from each circuit. Some are of the other camp. My reasoning is based and found in airframe grounds I am trained on by USN. I am sure you will see replies to all 3 camps.....Ground everything, Ground Lugs only, no grounding at all. There are benifits and pitfalls to each
Doug

This is how I feel and do it too Doug. Just the ground lug on my genny with about a 6 foot piece of #4awg bare down to the ground rod, which is just a piece of 3/8" with reebar, which has its own lug, pounded into the ground. Haven't forgotten it yet in driving away but people can and do. That's part of the walkaround I do before moving for the day.

Ground wires for each circuit in ac voltage are already grounded in the incoming service cable so do not confuse and connect to other systems.
Dc grounding is actually the completing of a circuit from source to fuse to any wiring device and then to ground, a simple circle in other words no matter how many controlling devices be on any one circuit. If one is open then nothing gets grounded and no dc current flows.

John

John

[BlackJohn]

Originally Posted by Biscuitsjam

Small updates - added ground wires and updated wire gauges.

Just to clarify -the inverter is grounded to the chassis? I've read a lot of conflicting things.

I'm not sure how important a grounding rod is since most people don't use one. It would be a pain to set up and easily forgotten - I'm guessing it becomes more important if you have an onboard generator? It would be easy though -just attach a copper spike to the chassis using a big wire then hammer it into the ground.
Attachment 18573

Diagram looks better but I see a change I prefer if I may suggest.

The inverter cabinet itself should have a chassis ground.
The actual negative side I would run directly to one of the battery terminals, the shortest run you can make it.
Genny grounding is hardly ever mentioned but highly recommended for safety. I described this in a reply to Doug above.

John

[BlackJohn]

Originally Posted by JDOnTheGo

EXCELLENT WORK!!!

My suggestions are:
1. Don't use x-3 cable for the AC wiring. x-2 is sufficient unless you plan on 3-way switches. Believe it or not, x-2 cable is three wire (white, black, ground) and x-3 is four wire. Makes sense right?!?? The deal is that they don't count the ground wire.

2. 8-2 AC wire from shore to breaker panel is good. 12-2 is probably sufficient for each circuit (breaker to outlet) as that is good for 20 amps (as are most outlets) and it is easier to work with.

3. A surge protector can be added later if you decide you want/need and you can also use an external one.

4. There is nothing wrong with using 12 AWG for DC circuits. However; it might be overkill for some (which is far better than underkill). In many cases, a thicker wire is ran from the battery to a fuse panel and then thinner wires for each individual circuit (depending on length and power requirements). A series of LED lights is an incredibly efficient thing and sometimes only need a couple of amps.

Some additional thoughts to JD's post here:

1. I like the 3c12-14awg copper, never aluminum cable, from the ac panel out to a junction box as it gives me a spare for future at minimal cost. Because this is a home run, I increase the size for voltage drop also but because there is less resistance to flow the larger the wire size in any application, ac or dc. Length of the bus is hardly a factor in determining cable size unless a full 15 amp load is required, then size accordingly up to #10awg on a run such as that.
As mentioned the bare ground is never considered in the cable description.

2. 8-2 AC wire from shore to breaker panel is good. (for 30 amp service only)

#8awg won't cut it for a 50 amp service connection being rated for only 40amps, so one size larger, to #6 when you built for a 50 amp service. often campground voltages suffer also from voltage drops, brownouts etc, so with the bigger wire, you have less resistance and are able to extract maximum amperage from the supply source of the grid.
For this heavier connection, I do not like cheap rv cords. never seen one for 60 amp anywhere in my lifetime.
The solution is a 60 amp, 3 phase welding outlet on the bus with a cabtire of SO grade with a female welding outlet end and no choice but a rv plug rated for 50amp for park service connection.

12-2 is probably sufficient for each circuit (breaker to outlet) as that is good for 20 amps (as are most outlets) and it is easier to work with.

Completely agree due to voltage drop and less resistance. It is awkward connecting switches and receptacles though with this size wire, so pigtail to the wiring device with more suitable #14awg.

3. Surge protection at individual workstations is a good thing and portable to other areas when needed.

4. As to oversizing, do it wherever your budget allows. For safety and for adding on in future should the need arise, then the work is already done.
But, fuse only to the size of the load being used at present.

John

[BlackJohn]

I think this may help the others in regards to figuring out some electrical mysteries. Wanted to post it earlier but couldn't find it.

John

[Jolly Roger bus 223]

That looks helpful?
I have to go find my nerd/egghead/math wizard (wife) to even explain (do it for me correctly) but I will probably give her this to check my non mathematical calculation method. And see how far oversized I will be.
Thanks for posting.
Hope the OP gets it.

[Biscuitsjam]

Originally Posted by Jolly Roger bus 223

That looks helpful?
I have to go find my nerd/egghead/math wizard (wife) to even explain (do it for me correctly) but I will probably give her this to check my non mathematical calculation method. And see how far oversized I will be.
Thanks for posting.
Hope the OP gets it.

That graphic looks complicated, but it's not. It just shows the relationship between volts, amps, watts, and ohms. If you know any two, you can figure out the others - the chart shows the formulas.
Volts x amps = watts (V x I = P)
Watts / volts = amps (P / V = I)
Volts / amps = ohms (V / I = R)

The chart doesn't help size wires, but it can help understand the terms and their relationships.

[Biscuitsjam]

Originally Posted by BlackJohn

Diagram looks better but I see a change I prefer if I may suggest.

The inverter cabinet itself should have a chassis ground.
The actual negative side I would run directly to one of the battery terminals, the shortest run you can make it.
Genny grounding is hardly ever mentioned but highly recommended for safety. I described this in a reply to Doug above.

John

I don't understand - the negative already goes straight to the battery terminal with just the shunt for the battery monitor between. Are you suggesting the shunt should go elsewhere?

I'm also proposing running the ground terminal on the inverter to a chassis ground. I'm not sure what change you're proposing.

I do finally understand your point on using the 6AWG wires for A.C. input - it lets me size the system to be able to handle 50A shore power instead of 30A shore power.