Request electrical schematic with solar/genny/batt/inverter

[Uglydog56]

I tried the search guys, I promise!

My recently purchased bus has a 5.5kw genny, and uses the starting batteries as the battery bank.  I want to put a few solar panels on the roof, use a MPPT controller/charger, and put in a dedicated house battery bank (planning on 4 golf cart batteries).  I want to move most of my 120v stuff to an inverter off the battery bank, except for the a/c units.  The a/c units I'm figuring on wiring the front one to run off the genny or shore power (so I can use it on the road) and the rear off shore power only.  Could someone draw up a schematic of how all this would tie together?  I have done wiring, both 120 and 12v, but nothing this complex.  I could really use some recommendations on how you switch between solar/genny/power pole.  I would prefer to hard wire everything and have abt's or switches somewhere, rather than move plugs around.  My bus is 12v, 30A shore.  Thanks for your help!

[Iceni John]

Does your Crown have a 160A alternator (like mine)?   How much power does your front AC need to start and to run it?   Is this within the ability of your alternator's output, assisted if needed by your battery bank during start-up, through a suitable inverter?   Just an idea.   I'm thinking of something along these lines when I eventually start building the interior of my bus  -  would this even work?   Obviously this would only be for when driving;  when parked the AC would need to be powered from generator or shore.

John (fellow Crownaholic)

[Uglydog56]

Mine does have the 160 amp alt.  My bus only has a 15k basement unit currently.  Even with 3" of blown in insulation, I can't see that being enough.  I am going to add a roof unit in the front.  So a looked up a couple and anything in the 13.5 to 15k range of cooling pulls like 14-16 amps.  That would be marginal for a 160 amp alt imho.  Run the wipers and the headlights and you are discharging your battery.  I am planning on running the genny down the road when a/c is needed and not incorporating the alt into the house battery charging - just letting the solar panels take care of it down the road.  I thought the engine alt didn't do a very good job of charging house batts?

[artvonne]

  That 14 -15 amps is likely starting load, not running load.

[gulfyankee]

I know for a fact that my Coleman Mach 3, 15,000 btu roof air pulls 15-16 amps while running steady. As a side note, when the outside find get dirty, it can pull over 20 amps.

[bobofthenorth]

I don't have a schematic for you but I'm going to throw this out there so other people can tell me why I'm a fool.

When we bought our boat it had one battery bank that served both the house and the engines.  It also has a generator with a separate battery to start the genset and obviously the genset can charge the house/engine bank.  Based on my bus experience with separate house/engine banks I thought that was a really stupid setup and assumed I would have to change it.  8 months later I don't think its such a bad setup and I'm actually considering changing the bus over to the same setup.

Here's my logic: the start or engine bank never really gets used on a bus conversion.  Its not like we are starting and stopping these things regularly.  Generally they get started, run all day and then sit for an extended period of time.  Its also not like we need the big surge starting capacity of a starting bank.  And if we do need a huge surge its available anyway because our house banks tend to be seriously over-sized relative to the starting load.

So where I'm heading with this is that the OP should at least consider having one larger bank of batteries that serves both the engine and the house.  As long as there is some redundant provision built in for the occasion when the house system is too discharged to start the engines I don't see what the problem is.  In our case that redundancy is provided by the charge capability of the genset.

Flame away.

[lostagain]

I agree with you Bob. My opinion on this subject doesn't weigh much however, because I don't know much about electricity, but I know that my start batts and house batts are "married" to each other most of the time, effectively making one batt bank. And yes if needed, a few minutes with the genset would be enough to start the bus.

JC

[technomadia]

We're smack dab in the middle of installing a similar set up, except with a 500 ah lithium ion phosphate battery bank and a 3000w pure sine inverter, with the ability to run an A/C for up to 3 hrs.    We spent about 3-4 doing extensive research, weeks planning it out our schematic (and bringing in some experts to advise), shopping for parts and doing the install. And I'd say we're only about 1/4 done with the project as of this morning   (But, we have the inverter & batteries speaking to each other, and an A/C starting an running off battery. Woohoo).

We do plan to add solar to the system (so have pre-planned that into our schematic), have all sorts of fancy generator switch over and running an A/C off the alternator while under way. 

I guess what I'm saying is.. these sorts of projects are pretty darn complex, especially when going into buses that have had years of mods & changes. We've run into all sorts of contingencies in our project, and lots of stuff to consider.

Best wishes.. and if you'd like to see what we're up to, we'll be going into extensive technical detail on our install in the coming weeks on our blog.

- Cherie

[luvrbus]

The amp draw thing goes around and around on the board I don't care what brand it is but here in the AZ heat the roof tops will draw close to 20 amps while running some 15,000 btu units will exceed 20 amps and will trip the 20 amp breaker

good luck

[Mex-Busnut]

Uglydog56 (Post a name!):

I just did some figuring along these lines. The formula is: Volts times Amps = Watts. When calculating your amperage required from the alternator, you will have to do like this:

Most 13.5 K/BTU A/C units will take around 2,900 watts to start, and 1,300 once running, so at 120 volts, let's say 24.17 amps for compressor start-up, and 10.8 amps for compressor running. But entire wattage must come from your 12 volt source. Say you add a conservative 25% to cover the losses inherent in your inverter, and we get/need 3,625 watts (302 amps) start-up and 1,625 watts (135.4 amps) running, being drawn from your 12-volt source.

Golf cart batteries are each usually 35 amps per hour for 20 hours.

Somebody correct me if I am wrong.

[thomasinnv]

Bro. Steve, I think you are a little conservative on your running amperage for a 13.5K unit. My experience on several different units has been right around 12A running, and close to 20 for startup. On the one 15K I had I don't remember the startup but the running amps was around 16.

[luvrbus]

My 13,500 Dometic Penquin say 14.6 in the book it is 115 here and went out as it's been ruining all day drawing a even 18 amps with the fan on high.
Steve  how are you figuring the 20 hr amp draw those are 6 or 8 volt 

good luck

[thomasinnv]

Clifford as you pointed out before, it really varies depending on the ambient temp and humidity. Also, lower voltage will pull higher amperage. Earlier today it was 97 ambient with 30%humidity and I was pulling 12.8A. Voltage was 112. Right now it is 89 ambient with 30% humidity and I just checked, I am pulling 12.3A. Voltage is steady at 113. When it's hotter, they do work harder.

[bobofthenorth]

Here's another data point - 13.5 Dometic in our last 5th wheel - ran fine on a 2800 Onan until we really needed it and then it would kill the Onan every time.  At about 75 degrees the Onan could handle it but when we got down into Mexico and the temps got up around 100 then forget about it.

[luvrbus]

No way can I get there with the 13,500 Penguins Derrick it is 14.6 at 80 degrees just like the book says maybe the 3 speed fan is the problem LOL.
Yea Bob some say 5000w will run 2  13,500 roof tops doesn't work for me I fight to get a 7.5 to run the 2 units


good luck