24v or 12v inverter?

[Stolaas]

I've got a question here..

I currently have a 6 batt 6v bank tied together for 12v and have a converter/charger.

I am installing an inverter for the 120v needs like the refrigerator, TV, DVD etc.

Since I have not got a inverter yet (well I do have one laying around but it's not a Pure Sine Wave) now is a good time to get what I need and not have to Upgrade later...

The main question is, do I opt for the 12V inverter which will be easy to install and the bank will be recharged by shore power or Gen,  and use all 6 batteries.

or go for the 24V and pull 4 of the 6V batteries out of the bank for a"second" bank.  This bank would be used strictly for the 120VAC while the other two 6V (series for 12V) will power the lighting and water pump etc.   The advantage I see is I could have the bus alternator charge the batteries over the road which would be nice for the fridge, and I can use smaller gauge wire to the inverter (which isn't that far a distance however)

What are your thoughts?

[robertglines1]

your limited on out put on 12v--around 3000 watts where 24 volt are much higher...use recommended wire size..other more elect savvy will chime in . Has been reviewed  in past here.try search function...again depends on use.... Bob

[bevans6]

I have just finally finished up the installation of my inverter.  My need was to be able to run my 15K btu rooftop AC on the road from the bus alternator, and to be able to use typical 120VAC items when I wanted.  I went with a simple straight PSW inverter, not  an inverter/charger, but I think in hindsight an inverter charger may be a good choice as well - downside is they are a lot more expensive.

I chose a Samlex America 24 volt 3000 watt pure sine wave inverter, connected to the bus batteries and alternator via a disconnect switch.  I chose a manual battery combining switch for now, I will probably install an automatic switch later.  I installed a house battery bank of four 235AH 6 volt batteries, and used my Vanner to equalize them so that I can draw all 12 volt needs from them, up to 60 amp limit of the Vanner although my 12 volt needs are actually quite small.  I use a stand-alone charger, currently a quite small 3 stage 24 volt charger, and I will upgrade to a larger charger when this one shows it can't keep up.  My 24 hour typical electricity needs are very small (as long as I'm not using the air conditioner, which I wouldn't run from batteries anyway), so I may not have to upgrade.

Advantages:  24 volts allow use of smaller DC wiring.  Bus alternator charges house bank and supplies the power for the air conditioner.  House batteries can be combined with bus start batteries for starting boost in cold weather.  Charger can maintain the start batteries and the house batteries when the bus is not being  used.  The Samlex inverter has a direct connect AC option, and has a simple remote control and monitor panel.  It starts my rooftop AC unit effortlessly.

I used cascaded auto-transfer switches so that the various AC feeds are prioritized and switched automatically.  I went with pedestal first, generator second, inverter third in the priority list.

Disadvantage - not having an inverter/charger means I can't use the  inverter to boost current level when starting multiple AC units.  Sean recently pointed out how he uses his inverters to allow him to run two rooftop AC units reliably on a single 30 amp pedestal.  His inverter synchronizes to the incoming AC feed, is normally charging the batteries, but when the starting surge for the second AC unit hits it seamlessly changes to supplying the excess current required so both AC units can run.  I have no idea if all inverter/chargers can do this, or if you need the really  sophisticated kind that he has, with additional programmability, but it struck me as a really neat trick.

I am very happy with my setup, it works perfectly for my needs.

Brian

[Tenor]

As bevans6 mentioned, Sean has the ideal setup.  Mine is quite similar.  Xantrex sw4024 inverter, with a vanner equalizer for your 12v lights and such.  I can run 2 roof airs while going down the road while pulling 24v from the buses alternator.  This model also has the automatic generator start/stop function that i love!  Batteries getting too low while you're not at the coach?  No problem!  Generator starts automatically.  Don't want it to run at night?  No problem.  It will wait until absolutely necessary.  This way you can use your whole bank and get the most bang for your buck.  Good luck!

Glenn

[Jriddle]

For me 24v is the only way to go. Now with that said you need to know what you want to happen with the inverter/electrical system. I have a setup similar to Sean's Gumpy's and others here. You will find the more watts, auto start and load sharing the inverters do, will cost you some good money. I had to build a transfer switch to allow the neutral to go back to the shore source. I had to buy a good equalizer to convert 24v back to 12v for lighting and such. These things all cost money but in my mind well worth the expense. I have to admit when I was  planning all  of this, I wasn't  aware or didn't make myself aware of the final cost of doing it right.

Good luck
John

[Stolaas]

I didn't think of using a Vanner to pull the 12V from the lager 6 bank instead of keeping 2 separate for a 12Vbank.  I have a Vanner now but I have it hooked to the coach batteries to run the toad lighting and ecc. items in the dash to keep the all the coach stuff separate from the house.

I do only have a 12V water pump and a fair amount of 12V lights so that would work.  Of course I already have a nice converter/charger from the PO that I hate to discard.

[bevans6]

I was keeping coach 12v separate from house 12v too, until I set things up so that the alternator could charge the house batteries.  Then, while the combiner switch is thrown, there really is no difference between coach and house systems since they are connected.  I only have a little dash radio, my brake controller, and my electric seat motors that run off the bus 12v system anyway.  So I ran two separate 30 amp fused circuits from the 12v tap on the house bank, one to the house and one to the bus (terminal 6 in the AC breaker panel in the bay).  I also have a nice, new 12 volt smart charger with a built in AC and DC distribution panel that I installed last year, I just pulled the 12 volt charger out and shed a small tear (about a $150 tear, to put a point on it), and carried on with life.  I'll  use it somewhere, for something.  It's a pretty nice smart 45 amp charger, has to be a use for it around here somewhere!

Brian

[Jriddle]

I didn't think of using a Vanner to pull the 12V from the lager 6 bank instead of keeping 2 separate for a 12Vbank.  I have a Vanner now but I have it hooked to the coach batteries to run the toad lighting and ecc. items in the dash to keep the all the coach stuff separate from the house.

I do only have a 12V water pump and a fair amount of 12V lights so that would work.  Of course I already have a nice converter/charger from the PO that I hate to discard.

I had to put one 12v battery after my Vanner. The Vanner kept shutting down. With this buffer battery between the Vanner and the 12v loads it seems to have solved all my problems.

John

[Stolaas]

What size of battery isolator have you all used to hook up your 24v bank to your alternator so it will charge both coach and house banks?

[Jriddle]

I have not hooked it up yet. I have a White-Rodgers type  586-114111-3 coil 24v DC cont. I have gotten some advice from Sean (Quote) Because of the nature of the Relay signal from the alternator, I recommend you use this only to drive a 12-v cube relay.  Then use that to switch a 24-volt circuit to operate the solenoid.  If you still have the blower circuit, you can just use that
I have been without work and have been working on getting a job so my time has been limited lately. But plan to hook this up soon.

John

[Stolaas]

Hey John, it looks like we have very similar buses Not sure what you mean by the solenoid.  I was planning on putting an isolator at the connection under the coach battery cut off, or near there and just run a wire from the +pole where the alternator wire and coach wire meet at the switch.  I may just have one wire coming from that pole connecting to the isolator and then continue to the 24V bank and leave the "coach side" of the isolator empty since the coach batteries will still be getting juice at the switch junction.   

Can an isolator be hooked to only one side?

[bevans6]

There are a couple of ways to go about the joining of the bus battery/charging system to the house battery system, presuming that they are both 24 volts.  There are some  automatic devices that you can get (I have not researched this at all) that can sense when the alternator is charging and connect without any manual control.  You can build a relatively simple system with a relay, or you can get a marine type battery combining switch.

If you go with a relay based system, you get one like this:  http://www.texasindustrialelectric.com/Relays_24824_01.asp which is a 225 amp continuous, 600 amp surge relay designed for this application.  You connect it to bridge the two battery banks, and control it with a switch or low current relay of some type.  Your alternator is set up, stock, so that it doesn't start to charge until air pressure builds up and there are a number of systems (like the stock AC heating and cooling fans) that only can be powered after the alternator has switched on.  You control the relay  from the same source so that it connects the two battery banks only when the alternator is charging.  You can also add the ability to connect them at any time with an over-ride switch, useful if you want to boost the bus start batteries with the house bank, for example.  Now you have an auto connect system that only bridges the two battery banks when the alternator is charging, with an over-ride capability.

I went with a simple battery combining switch from a marine store.  It has the ability to turn two battery banks on or off, and to combine them.  For some reason I wanted to be able to completely disconnect the inverter from the battery so I wanted the on/off switch, and it simplifies combining the start and house batteries, but obviously is manually switched and I have to be in the electrical bay to do that.  So far it is working perfectly.  I start the bus for the first time in the morning with the switch to not-combine, after the bus warms up and the alternator is running I switch to combine, and leave it there all day.  While it works fine, I think that the relay based automatic system is better and I will probably upgrade later.  I like to do things in stages and prove in the steps before adding more complexity.

Hope these ideas help a bit.

Brian

[Jriddle]

Brian said what I was trying to. Thanks Brian. The only time my house and Bus banks will be close to being connected is when the alternator is charging. If I need power from the house bank for starting I will use jumper cables. I do not want to ever forget that the manual switch was engaged and now have dead start batteries also. I also made my pickup tubes for my webasto and generator from my diesel tank shorter than the bus engine pick up. That way I should have fuel to get back to town. I have tried to make the house and bus systems separate with the bus engine getting priority

John

[Stolaas]

Thanks for all your help guys!

Here are two crude drawings I made to use my 6 6V batteries.  The 12V is what is currently being used.  But in order to have 24V out of 6 batteries I have to make one Series of two  and then two parallel series.  Would this work right and charge correctly or is it not a good idea to mix it up like that and just either parallel or series and not both. 

Trying to find a way to use all 6 instead of dropping two or adding two.

[Sean]

... in order to have 24V out of 6 batteries I have to make one Series of two  and then two parallel series.  Would this work right and charge correctly or is it not a good idea to mix it up like that and just either parallel or series and not both. 

Trying to find a way to use all 6 instead of dropping two or adding two.

Not advisable.  Use four or eight, not six.

-Sean
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