Wiring electirical service

[bevans6]

The answer is it depends.  What is most important is the current that you will draw from the batteries to the inverter.  That depends on the voltage and the wattage of the inverter.  Pretty much if you are 12 volts and over 1,000 watts, the distance is too long if it's over three to five feet.  You can get around that by up-sizing the cable, but at some point you really need to have the inverter close to the batteries.  24 volts cuts the amperage in half, of course, and really reduces the voltage drop that you get between the batteries and the inverter, and increasing the wattage drawn from the inverter adds to the current and increases the voltage drop.  Cable size capacity is measured in amps of current, called "ampacity", so you need to do the math to figure out what your loads are and what your draw will be.  Then you can measure your distance, consult a voltage drop table on-line, and have your answer for your situation.

Brian

[Brett G]

Comments for Brett - I would put a switch in the ground connection to the Vanner, so you can turn it off.  I would probably not use fuses in the cable to the start batteries, so that if you need to use the house bank to start the bus the inrush current to the starter motor doesn't risk blowing the fuse.  My battery switch is a combiner, so that I can turn power to the inverter completely off if I want to.  I have off, house bank, or house plus starter bank.  I also love the bus pictures!

Brian

Thanks Brian, my switch is the same.  In my setup, will the Vanner back feed and equalize the starter batteries?  Is that the influx you are talking about?

[bevans6]

Hi Brett.  No, as drawn the Vanner will only equalize the house bank - in other words supply +12V current to equalize anything drawn by 12 volt loads - but if the combine switch is thrown it will draw +24V power from both the house bank and the start bank to supply that +12 current to the load.  Which is fine, in my opinion.  The in-rush current I referred to is the high current spike that any motor has when it first gets switched on and before it starts to spin (and create its CEMF for the electron geeks).  This is the reason that there is never a fuse or breaker in the main cable from the batteries to a starter motor on about any vehicle I can think of.  If you have the switch set to "combine" and the master battery switch off (it's gonna happen, it happened to me by accident) then if you start the bus it will start from the house bank alone.  Depending on things, that stands a good chance of blowing those fuses.  You don't need two fuses in series anyway, adds nothing but lack of cash in your wallet to the equation.  You show a fuse before the switch and a second fuse after the switch.  One would do, and I have none in that location in my setup.

The switch in the Vanner ground is to turn the Vanner off.  If it's connected it always draws some power, and if a battery starts to fail it can kill the whole bank trying to keep a dying battery equalized.  Again, happened to me.

Brian

[mike802]

Brett:  Thanks for the pictures and the diagram, this will really help me alot.  I enjoyed the bus picts, I have twin sisters just about the age of the young lady in your pictures and look forward to the day we can take them busing!  One of them tried really hard to make an appearance in one of my bus videos!  Your system looks like you feed 24 volt to the inverter? My inverter is only rated for 12 volt input.  Maybe I'm missing something, but I don't understand how you are isolating the 12 and 24 volt, or is that the Vanners job?

Brian: Appreciate the details and your input on Brett's system, I'm starting to take notes and print off pictures to help me put this all together.  Can you guys tell me what a Vanner is?  I Googled it and Wikipedia thinks its a guy who builds vans LOL.  How is your generator working for you?  I Goggled it and I really like the price, if it is working out for you and is as quiet as they say, I would really consider something similar, if not the same thing.

[bevans6]

http://www.vannerinverter.com/battery-equalizers/

Something I wrote a few years ago;

http://busnut.com/forum/index.php?topic=1586.0

Brian

[mike802]

Thanks Brian:  It looks like I am going to have to figure out how to rewire Brett's system to work with my 12 volt input inverter.

[bevans6]

Mike, you pretty much can't do what Brett and I did with a 12 volt inverter in a 24 volt bus like an MCI.  The reason is that our system is built around using the bus to power the inverter and charge the batteries at 24 volts and run the roof top air conditioner on the road.  That is the heart of the design.  With a 12 volt inverter you need to build your house bank at 12 volts and figure a way to charge it, and you can't reasonably run the inverter at 12 volts from the 24 volt bus alternator.  If you can, I would move to a 24 volt inverter as the heart of your system if you plan to run the MCI bus alternator as the charging system and power source for your setup.

Most people who run 12 volt inverters in an MCI (or other 24 volt bus with the big alternator) keep the battery banks separate and run a separate 12 volt alternator, don't bother using the engine to charge the house batteries at all, or you can connect a Vanner in the battery charging mode I outlined in my article.  Given that it takes around 165 amps of continuous 12v current to even consider running a roof top AC unit (my killer app, my personal reason for building the system that I built) you can see that you would need a huge 12 volt alternator to do that, and a typical Vanner is around 60 amps max, and not continuous at that level.

Brian

[mike802]

Thanks Brian:  Yea, I was starting to get that sinking feeling looking over Brett's diagram.  I was looking forward to using a roof mount AC while going down the road, an also running the fridge.  I could move up to a 24 volt inverter, but it means this project will have to be put on hold for now while I come up with the funds to due so.  I can still go ahead with all the breaker panels and circuit wiring, I have a 30 amp converter I could use to test my circuits, but I guess the system will have to be incomplete until I can upgrade my inverter.  I would like to thank you and everyone who had offered their advice, I have decided to install the inverter in the basement and now I have a good plan in place for where I want to put everything and why.

Anybody have any advice on just what inverter would be a good choice, and where is a good place to purchase one?

[eagle19952]

Magnum or Xantrex.

[LuckyChow]

Magnum or Xantrex.

What he said. 

[Iceni John]

The solar folk on the Northern Arizona Wind & Sun forum generally prefer Magnum these days over Xantrex, if only because of customer-service issues.   Magnum always scores high marks for good helpful customer service, but Xantrex has not done so well since being taken over by Schneider . . .

For a lot less money than new, one can buy factory-refurbished Magnums from Wholesale Solar.   I got my MS2000 this way, and it cost less overall than buying a separate Cotek inverter and charger.   I would rather have a refurbed US-made repairable unit than a new Taiwan-made unit that may or may not be repairable.

John

[digesterman]

You can always put a 12 volt alternator on to charge your house batteries, a lot of Prevosts are this way

[mike802]

You can always put a 12 volt alternator on to charge your house batteries, a lot of Prevosts are this way

My son and I were discussing this very possibility.  I dont think it would be that difficult, but I was wondering if I would be able to run the air conditioner and the fridge?  I could go without the AC if I had to decide between the two, but would like to have the option of running both if I could.  What do the Prevosts guys run for an alternator?

[eagle19952]

My son and I were discussing this very possibility.  I dont think it would be that difficult, but I was wondering if I would be able to run the air conditioner and the fridge?  I could go without the AC if I had to decide between the two, but would like to have the option of running both if I could.  What do the Prevosts guys run for an alternator?

130 to 170 amp alternator should be able to maintain 2-3 8d batteries under load..

so if that amount of batteries will run your needs for an hour or two static...then my guess, it will run them under way.

if i want AC i just run my generator...uses .75 gallons per hour...about 11-12$ a day while driving.

the numbers don't make sense to me to dedicate batteries inverters and build time to go any other way.

[bevans6]

You need to plan on 165 amps of DC power to run an air conditioner at nominal 12 volts.  Add 15 to 20 amps when the refrigerator is on.  The thing with alternators is they aren't all designed to run at continuously at full rated power.  A typical car or truck alternator will start to overheat if you run it continuously at over 50% of rated output, so you need to look for heavy duty continuous power ratings.  They do exist, obviously.  What you want to do in your design is make sure that the alternator is large enough to run all of you loads with some headroom.  If you draw from the batteries at idle, when the alternator output is low, that's fine -  but you definitely don't want to be drawing from the batteries with the alternator at full output.  Unless the alternator is designed to run at 100% output continuously it will fail, perhaps spectacularly.

Brian