Hi John.using an inverter and a step down transformer you have two areas for losses of power in the circuitry .I would invest in a 24v-12v converter to run your low power 12v  appliances and perhaps change the exhaust fan for a 12v unit.When using batteries any savings are a plus, are you using LED lighting,as there is a great saving there?     Cheers Peter.

-- Edited by 2foot6 on Sunday 9th of February 2014 10:52:57 AM

-- Edited by 2foot6 on Sunday 9th of February 2014 10:53:17 AM

You cant transform DC. 24 to 12 needs some fancy electronics called a DC to DC converter, just not worth the effort

You will need a very large inverter to run an aircon, I have some 8 inch 12V DC fans in my van they are OK on "most" hot nights. Running an aircon on an inverter will drain any battery bank fast, you may need 4 110AH batteries to get close to a full night, especially if the inverter cuts out at 10 odd volts.

My suggestion is to get at least a 2KVA generator (3KVA to be sure) that will run your aircon.

Safe travels.

BTW I would run all 12VDC gear direct from the battery, the solar stuff should be only charging the battery bank. FYI inverters draw a lot out of a battery bank even at low loads, we have a 3000W inverter and only run low end stuff at night. Im an advocate for the generator, sorry folks they work much better than inverters even though they have one on board, the trick is they will not flatten your battery bank.

-- Edited by Phil C on Sunday 9th of February 2014 11:54:47 AM

John
You have a 24V vehicle and rightly have a 24V house bank to allow charge while driving but you mainly run 12 volt so the best way to get maximum efficiency would be to use a BB241230 Battery charger from your cranking battery to your house bank which you convert to 2x batteries in parallel for 12V then configure your solar into 12V.
The BB241230 uses the same algorithms as a mains charger and can take your batteries to a higher state of charge than a standard alternator increasing your useable battery capacity.
You will still need to look to a generator to run your air con due to the type of unit it is but with Inverter air cons there are instances where they can run off batteries due to the greatly reduced power demand.
DC/DC Chargers are currently successfully driving DC air con systems in trucks but this is in a cabin area not a motorhome.
Ian

Thanks powerstream, I just looks these up on the net. I have 24v solar panels, 2 X 210 amp batteries in series, and 24v inverter. Will that charger still work?

John

At the moment my alternator is not hooked up to the house batteries. I relocated the house batteries and inverter, and need to run  about 3 metres of cable to the smart charger.

 The 240v -12v transformer has been in about 1 year.

Batteries are usually topped up by midday, unless overcast. If day is overcast I run out of battery.

I go by the reading on the P40 controller

oldbobsbus

Bob you cannot use a TRANSFORMER to change a DC voltage/current but you can use a CONVERTER to achieve that. If you look at the items in the link you posted you will see they are labelled as a CONVERTER.

Maybe I am being a bit pedantic but using the correct terms may avoid confusion.

learmo wrote:

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Hi, I use a 240v to 12v transformer to run my 12v lights, water pump, toilet, winegaurd  etc. My question is, is this okay or should I use a step down fro m 24v to 12v.

My coach has 4 X 175 panels (24v), 2 X 12v - 210 amp AGM's and 1000W inverter. The only 240v appliances we run are TV, microwave, domestic fridge, extractor fan in bathroom, CPAP machine.

My system will not run my air cons. Would a bigger inverter help this, or more batteries.

John

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G'day John, we've had a few 24v buses over the years and found the best set up for us is a follows.

 

We have 710w of solar,(1000w coming up soon), 250w is 24v and they all run through a 30amp MPPT into a 200AH lifepo4 bank. Our start batteries are connected via a redarc to 60amp AGM 24v bank and from their through a 60amp 24v-12v DC converter and into our lifepo4.

 

This means we can charge our transfer batteries and house batteries whilst travelling, then switch the 250w 24v panel to keep the start and transfer batteries charged when stopped, or keep them on the house system. All this operates on 3 way switches.

 

The only appliances we use on 240v is a big TV, everything else is 12v and LED lighting, changed all the bus lights to LED, except headlights and we never run out of power, even after 4-5 days of no sun we are fine.

 

We have HE and 12v hot water, backed up with solar, this reduces the need for power and the hot water can also be heated with 240v if we have mains power. We only use a 1000w inverter and always carry at least 2 spares of everything electrical.

 

If you're going to update your system go for the simplest and most versatile one you can come up with, the more options for charging and reduction of power lose you can come up with, makes life on the road so much easier and safer.

 

Make sure you have the right cabling size, ran across many people with 12v fridges who are having troubles with them. Most times it turns out they have to small cabling for providing the kick start fridges need. Cabling is another expense you can reduce by using the right size for individual appliance connections, our bus has different cabling for different things, which reduces lose and provides the needed power for what it drives.