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RVing message boards => Boondocking => Topic started by: velcrostrip on April 11, 2017, 08:25:22 PM

Title: Converting 12 volt to 24 volt
Post by: velcrostrip on April 11, 2017, 08:25:22 PM
I would like to go to a 24 volt system as I want more stand by power and bigger /cheaper solar panels.
I want to run a 110 volt fridge on the inverter 24/7  and be able to run a 12 volt swamp cooler.
I want to shoot for 1000 watts with 4- 6 volt batteries.
What I'm not sure how of at this point:
1- Do I need a new converter that will charge 24 volts? [probably]
2- How do you convert 24 volts to 12 for all the factory appliances?
Any help is appreciated.
Title: Re: Converting 12 volt to 24 volt
Post by: BobNSam on April 11, 2017, 09:06:01 PM
Going to 24VDC will not help with anything on your list.
The 24/7 operating desire is possible with sufficient total battery power/storage and an efficient inverter and refrigerator. Note that total battery power provided must be more than (operating hours) X (power consumed by device) i.e. 24x300=7200 watts for an efficient small refrigerator. The only advantage to higher operating voltage is lower current for a given power (P=IE & P=I×IxR). This allows building smaller motors for given HP.
There are 24VDC Converter/chargers available to replace your current 12VDC unit. Converters for 24VDC to 12VDC are also available but might be pricey for current load to power your devices...and there will be conversion losses chewing up battery power.
Good luck
Title: Re: Converting 12 volt to 24 volt
Post by: Back2PA on April 11, 2017, 10:57:27 PM
X2. As BobNSam said, converting to 24V won't accomplish any of your goals, including saving money. Every 12V bulb, circuit board and motor will have to be converted or you'll have to use step-down converters. Four 6 volts batteries in series will provide the exact same number of watts (minus any step-down losses) as they would wired in a series-parallel 12V setup. If you simply want higher voltage panels there are solar controllers which accept higher voltage from the panels but feed a 12V system.

Re powering your residential fridge, while 1000W of solar is good you'll probably want 6 batteries for more storage, even then you're looking at running the genset the first cloudy day. This is especially true if you're running a couple amp swamp cooler blower many hours per day.

It sounds like you're planning on boondocking - have you considered the water usage by the swamp cooler?
Title: Re: Converting 12 volt to 24 volt
Post by: John From Detroit on April 12, 2017, 09:38:38 AM
The advantage of 24 volt systems is Not MORE POWER.. it is smaller DC wires.. Since in a DC circuit watts = Volts times Amps.. and I find it really helps if you figure 10 volts as this "Adjusts" for serveral things (losses) a 100 watt load will draw about 10 amps off the batteries at 12 volt

At 24 volt it draws 5
So, logically someone might thing "Well the battery will last 2x as long at 1/2 the amprage) and ..  The flaw is ... You now have two 12 volt batteries in SERIES, where as if you stuck with 12 volts you'd have those same two batteries in PARALLEL. (And thus double the amp hours) so the battery life is.. Identical.

But you will save a couple of dollars on the DC cables... ONCE,,,

All your lights, water pump, Radio, Everything else will either need to be changed to 24 volt or you will need a "Buck/Boost" converter to buck it down to 12 so they work normally.. There goes your savings on the wire..

As others said. Stick with what you got and upgrade the wire.

OH, solar panels... NO savings there either.   Just so you know. 100 watts of panel is 100 watts be it a 12 volt configuration or a 24 or a 48, it's still the same price.
Title: Re: Converting 12 volt to 24 volt
Post by: Gary RV_Wizard on April 12, 2017, 10:03:14 AM
Well, the higher voltage solar panels are probably slightly more efficient, but that seems to be of only minor value vs the cost of adding a 24v charger and converting or down-stepping for everything else. You can't eliminate the existing 12v converter because that is what provides 12v power when shore power or a genset is in use. Unless you always plan to run the house off the battery bank and just let the 24v charger keep it up when connccted to external power.

The batteries are no different - watts are watts regardless of voltage. And the RV wiring is already in place as well and will continue to operate at 12v, so no benefit there.
Title: Re: Converting 12 volt to 24 volt
Post by: 8Muddypaws on April 12, 2017, 11:06:36 AM
That's a losing proposition.  Every conversion, every buck converter, and indeed even the smaller wire will introduce losses, heat, complexity, and a failure point.

There are many thousands of RVs out there with residential refers doing this already.  For the most part they have 6 6v batteries. 

Absolutely no reason why a 24v panel can't charge a 12v system.  Just an issue of finding the right charge controller.
Title: Re: Converting 12 volt to 24 volt
Post by: velcrostrip on April 12, 2017, 04:29:10 PM
Gee.. thanks for all the help. :)
Title: Re: Converting 12 volt to 24 volt
Post by: Back2PA on April 12, 2017, 05:09:38 PM
Gee.. thanks for all the help. :)

"Help" here doesn't just come in the form of "here's how to do whatever it is you want to do", it also, in the nicest and most well meaning way, comes from those with a variety of experience trying to advise if your plan either isn't going to work and/or isn't going to accomplish what you thought it might. It's still "help", even if it wasn't exactly the "help" you were looking for.

In this case, can it be done? No doubt there are several ways that it can. Will it give you more standby power and allow you to go to bigger, cheaper solar panels? No.

To accomplish your goal of lots of standby power and 1KW of solar, while running a residential fridge and swamp cooler, you'll want:
1) The least expensive panels that also have the density to provide 1KW in the roof area you have available. With my available roof area for example (38' coach) I could only get 800W up there without going to the residential, higher power panels which cost a lot more money and are not warranted for mobile use (vibration, etc). I could have probably gotten 1100+ watts up there but it certainly wouldn't have been cheaper.
2) You'll want your panels on tilt mounts to make the best use of the spring and fall sun
3) You'll want six 6V batteries
4) MPPT solar controller that make the best use of your panels
5) You'll be using a lot of battery power with your fridge so you'll really need to know how much battery you have left to use before you need to fire up the genset and throw some more juice in there. The Trimetric TM-2030-RV ( is highly regarded
6) You'll probably need a full sine wave inverter for the fridge although you could go with a properly sized standalone FSW dedicated for fridge use only
7) Don't scrimp on wire size. It makes no sense to put in a cool, high power system with undersized wire that loses 5-10% of your expensive solar power. If there's any doubt, go to the next larger size wire.
Title: Re: Converting 12 volt to 24 volt
Post by: jmorrison on August 09, 2017, 01:28:06 PM
Most solar charge controllers already work with 24 V systems. With a PWM controller and a 24-40V panel it will definitely improve your efficiency because the PWM controller won't be wasting 50% of the power. With an MPPT controller which does DC-DC I wouldn't expect as much improvement unless your panels are in series at a higher voltage. Power losses (I2R) from your wiring will go down by a factor of 4 by doubling the voltage.

Finding a 24V inverter may be more difficult and expensive. But two 12 V inverters in series to two 12 V batteries in series would work but would give you separate 120V circuits unless your inverters have a synch/paralleling option to tie the outputs together. Watch out for chassis grounding if you are trying this!

You can power the 12V by tapping into one of the batteries connected in series - but this will put all the 12 V load on one battery.
24V-12V DC-DC buck converters are pretty cheap at small wattages - $50 from China for 360W
Title: Re: Converting 12 volt to 24 volt
Post by: boatbuilder on August 09, 2017, 01:39:27 PM
24V Inverters are definitely available.  Have used them on boats for quite a while.  Most 24V boats use a 50A DC-DC converter to power the 12V circuits.  This way you just have a 24V system for charging and a step down for the 12V items.  Makes the system much simpler.  The biggest reason that boats use 24V is for the bigger starters and thrusters and windlasses that are much more efficient at 24V as well as saving on copper on the cables.