24 Volt Inverter with a 12 Volt RV System

BFL13 wrote:
I like 24v for the "house" because 24-24 solar is better than 24-12.

I would love a 24v inverter to go with that. The solar can already do 24v so all that leaves is how to do the Rv's 12v stuff. One way is to use the inverter to run the existing 12v converter to run the Rv's house 12v.

Seems inefficient but so is solar 24-12. Anyway, that does not solve the OP question about charging the house batts while going down the road. Unless you have solar on the roof and it is daytime and sunny.

If the rig has a built-in generator that would run while driving down the road, that would power a 24v charger instead of the alternator on the "house"

All seems a bother when the inverter was free (it is not free when you have to spend money to use the darn thing), so I agree with the others, just take the free batts and get your own 12v inverter :)

Typically on most UPS units the batteries are GELL type (some newer more expensive UPS units might feature AGM) and unless it is an industrial UPS (2KW+) the batteries will be pretty darn wimpy 12Ahr size (UPS units are typically designed to provide full load power for only 10 minutes, basically long enough to counter typical power company short outages or give enough time for a proper shut down) .

Typically when a place replaces the UPS units it IS because the batteries HAVE "expired" and are no longer any good. Some places replace units every couple of years as routine maintenance, those will have very little life left..

Rather than goofing around with this unit, perhaps post it on craigslist for $50 if it is working.. Then put the $50 towards a inverter and do the job correctly the first time.

Exactly what inverter model and what do you expect to run?

Most likely purchasing a 12 volt inverter will be easier and lower cost than up fitting your system to make the 24v usable.

I like 24v for the "house" because 24-24 solar is better than 24-12.

I would love a 24v inverter to go with that. The solar can already do 24v so all that leaves is how to do the Rv's 12v stuff. One way is to use the inverter to run the existing 12v converter to run the Rv's house 12v.

Seems inefficient but so is solar 24-12. Anyway, that does not solve the OP question about charging the house batts while going down the road. Unless you have solar on the roof and it is daytime and sunny.

If the rig has a built-in generator that would run while driving down the road, that would power a 24v charger instead of the alternator on the "house"

All seems a bother when the inverter was free (it is not free when you have to spend money to use the darn thing), so I agree with the others, just take the free batts and get your own 12v inverter :)

chiz33 wrote:
Hi everyone

I recently acquired a 24v inverter along with 2 12v batteries for free. They are from a computer backup system (UPS) consisting of the 24v input inverter along with 2x12v batteries in series (24v). I know this isn't the best option for an RV with a 12v system (alternator, fridge, lights, radio, etc.) My question is, is there any way to wire this inverter to my RV so that when I'm driving, the alternator charges the batteries and the batteries power the 12v appliances AND the inverter?

Thanks

Quick answer, no.

Long answer, not in the present form you have.

The 2 12V UPS batteries would need reconfigured to parallel for 12V.

Then the 12V from the vehicle could charge them.

Then to get 24V DC for the inverter you will need to 12 to 24V DC-DC BOOSTER (a switching power supply which takes 12V in and outputs 24V DC).

To get one large enough to run the UPS inverter is going to cost you much more than simply buying a 12V inverter. Typically UPS units of 600W and larger operate at 24V DC so your UPS must be at least 600W..

UPS inverters are also not known for being energy efficient and adding a additional DC to DC power supply into the chain will waste a lot more energy. This is going to add a lot of needless load to your vehicles charging system..

Then to add insult to injury, many UPS units will not "cold start", in other words they NEED 120V AC in order to turn them on.. This is done so they can sync to the AC line.

Some APC units can indeed be started without 120V AC but only on select models.

Wasted money and time.

My suggestion is use it as a UPS when on shore power and when not on shore power use a plain old inverter..

Hi,

Isolate the house bank from all loads and charging sources.

wire it to be 24 volts.

connect the ups battery cables to the 24 volt bank

plug the RV shore power cord into the UPS output

plug the UPS into 120 volt shore power or when traveling into a 500 watt msw inverter powered by the engine battery (engine running first, please)

run the 12 volt part of the "house" by the built in converter.

You can't have the batteries connected in series and parallel simultaneously. Laws of physics/topology and all that.

Some cleverness in switching could allow them to be either 12V or 24V; but in 24V mode you would not be able to power 12V stuff or charge them from a 12V alternator, and in 12V mode you couldn't run the inverter. This would require some rather hefty switches or relays, and you'd still need some additional 12V battery for the other 12V systems in the RV. Mex is absolutely right; there's no real easy and inexpensive solution.

If the batteries are in good condition etc., I would suggest keeping them and exchanging the inverter with a 12V inverter.

I suppose a DC-DC "inverter" could do it, but getting enough amps will likely be expensive.

2oldman this is difficult to resolve easily. Fitting a small case 24V alternator is possible if here is room and using a longer serpentine belt with tension pulley

I guess it would be possible to charge each battery separately with a 12v source. Can't come up with anything better than that right now.

OR purchase a 400-watt Meanwell 24-volt power supply. It cost the US Air Force four thousand four hundred dollars for me to configure a single alternator 12/24 volt simultaneous charge system for a black-projects service truck in 1992.