12 volt verses 24 volt inverter.

Rocdiver

New member
Sorry in advance for the lengthy text. Trying to anticipate questions in advance so there is not a lot of back and forth. So here’s my dilemma. I have a small camper and currently have a 1000 watt modified sine wave inverter (Dewalt). It has run my medium size residential type fridge and 46 inch smart TV just fine for well over a year when I’m not on shore power. I sometimes live in it for extended periods, a month or 2 here and there.

Recently added 500 watts of solar to my battery bank of 700 amp hrs of Duracell group 31 deep cycle batteries so I rarely plug in to shore power anymore. I have room for a little bit more solar and a couple more batteries if I need them.

Problem is, my little 1000 watt inverter (modified sine wave) won’t run my microwave, induction cooktop, or the Keurig coffee machine. I have to be on shore power to run those.

Simple solution is to have Bezos deliver me a 12 volt 3000-3500 watt pure sine wave inverter and be done, right? About $350-400 for one with a remote switch and digital readout.

OK, now for the dilemma. I hear the mantra often “double the volts, half the amps”. (You know who you are ;)). Obviously, I have enough batteries in the house bank to series 3 sets of 2 for 24 volts. (and still have one left over, I could add another so I would have an even number). A dear friend has offered me a Magna Sine 24 volt pure sine wave 4000 watt inverter/charger for free. Presumably just needs a circuit board which I hear are easily replaceable. This thing goes for about 1700 bucks new and presumably is built to last a lifetime of continuous use.

Problem is, everything on my vehicle is set up for 12 volts, including the starting battery bank (2 12 volt group 31 starting batteries). So, is it worth it to use a step down transformer for all of my 12 volt needs just to get the efficiency of a 24 volt system? The solar system will be fine with charging a 24 volt system by the way. Also, wire runs are pretty short so not much loss there.

Another thing is, I have a Blue Sea ACR (automatic charging relay) which links the 2 battery banks when either one of them hits 13.6 volts to charge the other one. This is handy when driving as the alternator puts out a great deal of current. Also handy when parked as the overflow solar power keeps the starting bank topped off she is sitting for a while. Seems like I would lose this neat advantage if I switched the house bank to 24 volts. Obviously, losing the ability to electronically connect the 2 banks via a cab mounted switch would be disappointing should the need arise for mucho amperes, like a boost or maybe a winch down the line.

Was thinking this beast (The Magna) might be big enough someday to power an air conditioner if the ACs and solar become a little more efficient. But that’s a subject for a whole other thread.

I know there are some cool folks here that are way better at this stuff than me so I thought I would throw this out to the forum for some feedback. I really appreciate any advice and ideas. Should I go the simple route and stick with a 12 volt inverter or make the modifications to up the input voltage to 24? Would it really be that much more efficient?
Thanks in advance!
ROCKY
Excuse the messy wiring. Still cleaning it up after adding the solar array.

exp2.jpgexp3.jpgexp4.jpgexp1.jpg
 
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dreadlocks

Well-known member
Is this a truck camper or a trailer camper or what? Need this info, but I'm also curious what monster is carrying all these batteries and solar panels..

Personally I'd do seperate 24v house system, keep vehicle 12v and switch fully to Solar or Generator charging.. there is a reason why all the big inverters are 24v or higher..

How big is this DC-DC charger? for a 700Ah bank I doubt a single DC-DC charger is all that serious of charging amps.. the biggest ones I know of could only provide about half the needed current to charge back up in an 8h drive.. so that means your looking at like a full day of engine running for engine charging.. I'd rather be running a smaller, cheaper genset engine and then your interest in Air Conditioning would also be fulfilled.

Stepping down to 12v for minor loads should be extremely efficient.
 

john61ct

Adventurer
Do not make a major systemic decision based on a minor factor.

Stick to 12V unless you have a **very** strong reason to go to 24V, and you will still need to down-convert for some devices, adds cost & complexity.

Best is to actually **design** a solid foundation system, and stick to that.

Yes it is expensive if you insist on using inefficient high current AC powered mod cons while living off grid.

Nature of the beast, gotta pay to play.
 

Rocdiver

New member
Is this a truck camper or a trailer camper or what? Need this info, but I'm also curious what monster is carrying all these batteries and solar panels..

Personally I'd do seperate 24v house system, keep vehicle 12v and switch fully to Solar or Generator charging.. there is a reason why all the big inverters are 24v or higher..

How big is this DC-DC charger? for a 700Ah bank I doubt a single DC-DC charger is all that serious of charging amps.. the biggest ones I know of could only provide about half the needed current to charge back up in an 8h drive.. so that means your looking at like a full day of engine running for engine charging.. I'd rather be running a smaller, cheaper genset engine and then your interest in Air Conditioning would also be fulfilled.

Stepping down to 12v for minor loads should be extremely efficient.
Hey Dreads. Was hoping to hear from you. It's this:
exp7.jpg
Charging while driving was never something I planned on, just convenient. 6 mpg is not so efficient at charging :) Might go with a small gen to top off if needed if sun is not plentiful and I'm making too much coffee.

Thanks for your input!
 

luthj

Engineer In Residence
I would not change to 24V unless your vehicle already has a 24V alternator system.

Stick with what you have currently, and just upgrade the inverter. A bit of extra cable to handle any additional loads will not be very expensive. 12V inverters can be just as efficient as higher voltage units.
 

Grenadiers

Adventurer
We have a 24v system, 640 watts of solar, four Lifeline 4D batteries in series/parallel, 420ah total. Run microwave a couple times a day, coffee in the morning, c-pap for me, and for the wife, a small fan at night, charging iphones on USB/110v outlets, plus a Dometic CFX-65DZ fridge hanging off the back of the truck. Originally, the truck came with a Victron 24-230v 1600 watt inverter to run the Euro stuff. I added a 2000w 24-110v inverter to run additional stuff. I also added an Iota 24v charger hard-wired to the batteries that is used with either shore power or the generator (4000w loud beast brand!). We're on our first extended stay in the truck, three months and counting in Baja (currently in Loreto RV Park, just met Frenchie and the ROFs yesterday!). I have found out that we're good to go with all that crap for 8 days on a beach without using the generator. However, I don't have the correct battery monitor to keep an eye on battery 'levels'. My fear is running the very expensive batteries below 50% too often. On my charge controller, a Steca PR3030, the SOC graph is inaccurate due to items, like the Waeco fridge, connected directly to the battery. Have to add a shunt to the battery and a AH meter of some sort in the future. Also, I think I need to add more solar to my array and do have the room, and can extend that 8 days to infinity and beyond~!

So, to not answer your question, keep all of the above in mind when deciding on how long your boondocking trips will be, adding up your amp-hours of usage, and the availabilty of solar charging hours and strength when designing your system.
 

dreadlocks

Well-known member
nice rig, does it have a dual alt setup? you could swap one of the alts out for 24v and let it dumb charge while driving.. with that big of a bank you dont really need to have a DC-DC charger IMO.. its going to be mostly bulking it up and rarely floating it I'd suspect.. so a nice multistage dc charger would just choke out the bulk charge and make it less likely to ever need the later stages more than it helped anything.

If you want high AC load outputs 24v is worth it IMO.. due to the peukert exponent w/lead chemistry the higher the amps you pull the less capacity you have.. so halving the amp load will increase your runtime significantly enough to be worthwhile if you run these loads for any extended times.. Microwave and Coffee maker not so much, but induction stove could burn for half an hour or more, multiple times a day, of course depending on your cooking style.

However also consider replacing your appliances, I have a 1200VA 12V Victron Inverter.. it runs a 600W Dorm Microwave Oven just fine, and a 800W Travel K-Cup Coffee Maker just fine, Ive found induction stoves that fit within my inverter ceiling.. both were very cheap too.. however if I had any bigger needs I'd go straight to 24v, but large influence on that is cost of LFP and their considerably lower peak amp output.. If I had a dual battery setup I'd rather be pulling 50A outta each battery instead of 100A (the limit for these batteries).. with a Lead setup as large as yours you can really go either way, but that cheap inverter upgrade is pushing heavily to just rewiring it to 24v and reaping the benefits.
 

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