Electrical build to run roof AC units while driving

[DrewGerhan]

I've attached my schematic for my electric plan. The main goal is to be able to run at least one roof AC unit while driving.

I just installed a 320A Leece-Neville 40SI in the bus, so it should be able to keep up with the calculated demand of 142A for one AC unit. The calculation still works out, but both ACs might be pushing it for any serious length of time. My understanding is these big alternators have a much higher duty cycle than regular automotive ones, but I'm not sure it's 100% at max output.

I also want to isolate the starting batteries from the alternator. I assume a 150A battery isolator would work fine? The stock alternator was 150A, so that should be able to handle the remaining bus 12V loads (ECM, lights, blower fan, etc).

Basically everything 120v inside the bus is connected to the main panel and the input to that if fed from a 50A shore power outlet. I am able to pick which power source feeds the main breaker panel by which cord is plugged into the shore outlet. I have one 50A cord for when we are parked at a campsite, one 30A cord to connect to my 3500w generator and the inverter output is wired to a 30A plug. So when I'm driving, the inverter will be plugged into the shore outlet and power everything inside the bus.

I'm going with either four or six 6V golf cart batteries wired in series and parallel to make 12V and either 420Ah or 630Ah.

I do not plan to add solar at this moment.

Does anyone have any suggestions or critiques for this plan? My biggest question is with the battery isolator. Will a solenoid type be sufficient to keep the starting batteries charged while driving? It's a DT466E, so I can't be without power to them.

 

[Rucker]

Great start! And love the detail provided.

Those batteries will not be able to run the AC, but I'm guessing you already knew that;

I'm not clear on the physical equipment/devices/receptacles/cords and how they will connect, or how you will plug in one, unplug another. What I can't evaluate is whether there is a risk you could have two separate sources plugged in at the same time-either a)heating up wires and circuits from the other sources and the inherent risk of shock or b)grounding.

Regarding switching between sources, there are devices that do this automatically. Are you planning to use any of these?

And related to grounding, there are a lot of threads in this forum with discussions on that topic. Basically, the grounding in your bus (in the 'house' portion of your bus) should tie back to the source of the power, and NEVER bind to the neutral/common wire. This business is tricky, and not often enough discussed. Since you are working on multiple sources of power, you probably want to be extra careful about ground and the scenarios where you may see risks of shock (like 'hot skin' due to a short or reverse polarity of the power source).

 

[DrewGerhan]

Great start! And love the detail provided.

Those batteries will not be able to run the AC, but I'm guessing you already knew that;

I'm not clear on the physical equipment/devices/receptacles/cords and how they will connect, or how you will plug in one, unplug another. What I can't evaluate is whether there is a risk you could have two separate sources plugged in at the same time-either a)heating up wires and circuits from the other sources and the inherent risk of shock or b)grounding.

Regarding switching between sources, there are devices that do this automatically. Are you planning to use any of these?

And related to grounding, there are a lot of threads in this forum with discussions on that topic. Basically, the grounding in your bus (in the 'house' portion of your bus) should tie back to the source of the power, and NEVER bind to the neutral/common wire. This business is tricky, and not often enough discussed. Since you are working on multiple sources of power, you probably want to be extra careful about ground and the scenarios where you may see risks of shock (like 'hot skin' due to a short or reverse polarity of the power source).

Thanks for the feedback Rucker, why do you say the batteries won't run the AC unit? I won't have the AC on without the bus either driving down the road, plugged into shore power at a campsite or plugged into my generator.


The way I designed everything was each "power source" having its own plug and only one can be connected to the main shore outlet at a time. If I want to use my inverter, I have to plug it in to the shore outlet. When we get to a campsite, I unplug the inverter cord and plug in the shore cord. Same with the generator. My thought was that this guarantees only one power source can be used at a time and it's about as simple as can be. I thought about a rotary transfer switch or even an automatic one, but wanted to keep it simple.


I do understand about the ground concern and that's how I set everything up.

 

[Rucker]

Thanks for clarifying.
Sounds like you have no plan to run the AC off the batteries alone then-which is good, since those batteries will not go long. How are you planning on recharging the batteries?

On a related note, your isolator may get a surge of amps if the batteries are really low and you fire up the bus. 320 amps over the wires to a nearly dead battery may heat things up a bit.

I have a couple of autotransformers in series in my bus-they allow shore or genny inputs to feed the AC circuit, and switch to battery when those sources are not present. Works very well except for the diesel heater kicking out when I switch from battery to shore power for some reason. I just power it down between the swaps, otherwise everything else cuts over smoothly.

Might be worth building your initial setup such that if you choose to add autotransfer units in the future the work is relatively simple.

Again, nice to see the thought and detail in the planning phase. I tried to be deliberate like this for each system, and I think it paid off.

 

[DrewGerhan]

Thanks for clarifying.
Sounds like you have no plan to run the AC off the batteries alone then-which is good, since those batteries will not go long. How are you planning on recharging the batteries?

On a related note, your isolator may get a surge of amps if the batteries are really low and you fire up the bus. 320 amps over the wires to a nearly dead battery may heat things up a bit.

I have a couple of autotransformers in series in my bus-they allow shore or genny inputs to feed the AC circuit, and switch to battery when those sources are not present. Works very well except for the diesel heater kicking out when I switch from battery to shore power for some reason. I just power it down between the swaps, otherwise everything else cuts over smoothly.

Might be worth building your initial setup such that if you choose to add autotransfer units in the future the work is relatively simple.

Again, nice to see the thought and detail in the planning phase. I tried to be deliberate like this for each system, and I think it paid off.

Correct, no AC use off of batteries alone, the alternator will be utilized when driving.

When the bus is parked at the house and in "storage mode", I will have a dedicated 15A shore outlet that's connected to only a battery charger. With the isolator, both banks should be able to be maintained with just the one charger, right? The inverter will be plugged in and running to keep the fridge and lights on, if needed.

Sometimes we have guests stay in the bus when it's at our house, so in those cases, the inverter would be unplugged and the 50A shore cord would be plugged in to the main shore outlet so they can use AC if desired.

The main shore plug is located in the space where the third starting battery would be. I have two 31 series batteries for the bus 12V systems and the empty space where the third could go worked out perfectly to have each "power source" shore plug come right into the battery box. Everything is nice and out of the elements too since the box has the locking door. Maybe a picture would be worth more than all these words lol

 

[DrewGerhan]

The outlet is 50A and the short line green cord is a 50-->30 adapter. The orange plug comes from the inverter output and the yellow cord is for the generator. The adapter gets disconnected and a big 50A cord gets plugged into the outlet when we get to the campsite.

 

[Rucker]

Looks practical, and efficient!

 

[turf]

cool system! i use a different approach to running my ac on the road. i run my belly mounted generator while driving.

 

[Jono14]

I am unsure about the role of the isolator in your setup.
My understanding of isolators are those that have 3 positive posts: an input from a single alternator and two outputs to the two battery banks. Internally they work like two 1-way valves allowing current from the alternator input to charge both battery banks, but when the alternator is off, neither bank will feed back to the other (isolated).
Maybe your isolator is doing something else I am unfamiliar with - you have it drawn as grounded so maybe there is something I am missing.
I could see an isolator allowing a single battery charger charge both battery banks, so maybe there is a role there, but it also might be simpler to allow the engine alternator to keep the starting batteries topped up and only connect the charger to the house batteries.

There is also an inherent inefficiency with connecting shore power to a charger to charge the batteries which then feeds the inverter to power AC stuff - as each transition may only be 85% efficient. But it sounds like you might only use this setup with low power needs (like the fridge).
It might be cleaner to plug into shore even if only 15A and run both the fridge and the charger from internal plugs and leave the inverter off.

Make sure the alternator wires back to the battery and inverter are thick. 4/0 AWG is appropriate for a 3500W inverter and fuses would be 350-400A

 

[DrewGerhan]

cool system! i use a different approach to running my ac on the road. i run my belly mounted generator while driving.

That was my first version, but unfortunately the generator overheated and roasted the motor. It was a 6.5kw Onan with a dedicated fuel cell. I followed the installation manual and exceeded the air flow requirements and it still got too hot.

 

[cessna175]

good afternoon, there are certainly more than one way to skin a cat as the saying goes. I've been an a/c guy for many years, on multiple vehicles such as big boats, aircraft, as well as my busses, very expensive RV's, commercial/residential a/c's as well. What I've seen for a/c systems that are used during on the road travel almost always, use an engine belt driven compressor system, no mater what kind of evaporator and fan/blower used. The reason is simple enough. To pump refrigerant thru a large capacity systems requires lots or power. Generators that are used for on the road travel, especially to run an a/c system with an electric hermetic compressors, are typically large kw generators and are designed with air flow in mind for cooling while in use, or on the road. Some generators are even liquid cooled to solve the on the road over heat issue. Heat is resistance when using electric driven components. You have to go big to over come all the heat generated load of an a/c system. Large capacity belt driven compressors are available for busses and over the road Semi's. Large Motor coaches usually have a combination of both kinds of a/c's available for redundancy. I hope this helps with your decision moving forward.

 

[turf]

just being honest here. im running a liquid cooled 12kw genset.

 

[LargeMarge-TC]

Contrarian here.
.
a)
How many horsepower does your 320a alternator require?
At a significant/full load, how much pass-through air is required to keep it from melting (no exaggeration) or turning into a smoking belt-driven 'Check! Engine!' light?
.
What engine?
Occasionally, a light-duty engine -- under 300hp/1,000#ft/1,300nm -- might need all its get-along just keeping up with traffic.
With the alternator load, add a hill, add significant windage (kayaks strapped on the roof, the obligatory roof deck, etcetera Etcetera ETCETERA), and a small hp engine might decide on a 'time-out'.
.
.
[edited to add]
Off-Topic and probably irresponsibly irritating to the Add! More! Complexity! crowd:
b)
We travel with the weather.
Never much cared for anyplace hot enough to require a cooler.

 

[DrewGerhan]

Contrarian here.
.
a)
How many horsepower does your 320a alternator require?
At a significant/full load, how much pass-through air is required to keep it from melting (no exaggeration) or turning into a smoking belt-driven 'Check! Engine!' light?
.
What engine?
Occasionally, a light-duty engine -- under 300hp/1,000#ft/1,300nm -- might need all its get-along just keeping up with traffic.
With the alternator load, add a hill, add significant windage (kayaks strapped on the roof, the obligatory roof deck, etcetera Etcetera ETCETERA), and a small hp engine might decide on a 'time-out'.
.
.
[edited to add]
Off-Topic and probably irresponsibly irritating to the Add! More! Complexity! crowd:
b)
We travel with the weather.
Never much cared for anyplace hot enough to require a cooler.

320A at 14V is about 4500W. Convert that again and it works out to about 6hp, I think I can swing that.

I'm glad traveling with the weather works for you, we plan to use ours differently.

Thanks for your input.