question about batteries

tim1970 wrote:

So, what happens to the DC only things when I am plugged in to shore power? Do they continue to run off of battery, and then the shore power keeps the battery charged? Or is there a converter that will convert AC to DC when I am plugged in? If it is the former, then that tells me I always need a battery, whether I am plugged in or not. Correct?

If I am understanding everything correctly, I could bring a small generator (2000W) and be able to charge my batteries and be able to run my TV, built in stereo, or even the coffee maker or microwave (just not at the same time) Pretty much everything except the AC?

When connected to AC power, the converter supplies 12V power to the 12V system. On modern RVs, this is just connected in parallel with the battery and everything else, so the power from the converter can either operate 12V systems or charge the battery or do both at the same time.

I'd say it's generally a requirement to have a battery all the time, even when plugged into power. Some converters do not produce very clean 12V power and rely on the battery to act as a filter. Sometimes you may need or want to (temporarily) use more 12V power than the converter puts out, and the battery supplies the excess for the surge. On a trailer, you generally need to have a battery installed whenever towing because it operates the emergency breakaway braking system, which is required by law in many areas and is a very good idea everywhere.

Some really old converters had separate battery charge outputs and accessory use outputs, and included some built-in switching arrangement (either manual or automatic via a relay) to select battery power when not plugged in. That's ancient history now, and if you happen to get a unit with such a converter, would be very very well served to replace it with a more modern unit.

A single battery will run your furnace, just not for very long, without charge from 120V source. Most folks report one single night of furnace use per battery.

You have a good understanding, as to generator use, and the capability of a 2,000 watt model.

Jerry

tim1970 wrote:

So, what happens to the DC only things when I am plugged in to shore power? Do they continue to run off of battery, and then the shore power keeps the battery charged? Or is there a converter that will convert AC to DC when I am plugged in?

Yes. Both.

Whenever "real" AC is present, either from the grid or from your generator the 12 V appliances still run on 12 V and the batteries are charged at the same time.

I think you are MUCH better off to get entertainment system parts that run directly from 12 V. I've done that and typically only have to run the gen twice a day for a few hours (unless it's really HOT out) which allows me to run the microwave and charges the batteries.

The more people you have involved the trickier the usage of 12 V power is to manage. With only me involved it's pretty easy.

bikendan wrote:


Since you don't have it listed in your sig line, if you told us what kind of RV you have, it would help with suggestions.

I don't have an RV yet. :)

I am just trying to do all the research I can before I get one.


That is nice to find out that my furnace blower can be run off of 12V DC. One of the salesmen I talked to told me that it DEFINITELY would not run it.

So, what happens to the DC only things when I am plugged in to shore power? Do they continue to run off of battery, and then the shore power keeps the battery charged? Or is there a converter that will convert AC to DC when I am plugged in? If it is the former, then that tells me I always need a battery, whether I am plugged in or not. Correct?

If I am understanding everything correctly, I could bring a small generator (2000W) and be able to charge my batteries and be able to run my TV, built in stereo, or even the coffee maker or microwave (just not at the same time) Pretty much everything except the AC?

Thanks

Tim

Tim,

Most motorhomes have 12 volt DC, a generator, a inverter to convert DC to AC. Even my 1975 motorhome had all three of these. What you can run depends on the size of the batteries, inverter, and generator. My 1975 had one large deep cycle battery an old simple inverter and a 6 kw (6000 watt) gas generator. The refrigerator was a three way so I ran it off of propane when not plugged in. And she had enough inverter power to run a TV or radio or computer. That was about it. Anything more and the genny had to be turned on.

Our current rig is 14 years old and is all electric. We have 6 8D (big big) batteries, 2 inverters of 3,000 watts each) and a 12,500 watt diesel genny. You can run pretty much anything except the air conditioners with the inverters. Although if the volts are lower the generator will sometimes kick on if you run the microwave.

The watts needed to power the device you want to run will determine how you have to power it.

tim1970 wrote:
Help me understand what can and can't be run off of battery power. Obviously I realize the A/C can't be run, but what else? I see where people are talking about upgrading their battery or getting a 2nd battery, but I am not sure why.
those of us who dry camp or boondock, want the ability to run the 12v stuff the others listed, for longer periods without needing shore power or a generator to recharge the batteries.

What else can be run besides overhead lights and the slides? Will it run the blower for the gas furnace?
the others have already provided a good list.

Do most RV's have built in inverters to allow me to plug small stuff into the outlets?
NO! only some motorhomes and even fewer 5th wheels, come with factory inverters.
many, like myself, add a stand-alone inverter to run the tv, dvd and electronic devices. if you want to power the outlets, it's much more complicated and will require a bigger battery bank.

Since you don't have it listed in your sig line, if you told us what kind of RV you have, it would help with suggestions.

This is the basics for a 30A setup...



Roy Ken

Boon Docker wrote:
The 12v system operates lights, furnace, fridge (on propane), water heater (on propane), entertainment system, some TV's, CO and Propane detector, water pump, stove exhaust vent, slides, vent fans.

If you boon dock a lot then 2 batteries will double the amp hours available, which allows you to boon dock longer. If you spent some of the time at sites with hook ups then 2 batteries are not necessary.

good summary. and with an inverter and appropriate battery bank you can also power things like the microwave, 120V TV, and other low draw 120V appliances. AC is likely the one thing you won't run. and it makes absolutely NO sense to try to run the fridge on 120V, when you are not hooked to shore power. 12V and propane is much much much more appropriate.

And the inverter (if equipped with) would take 12v DC from batteries and make 120v AC to run small items like tv, dvds, can opener and other small items from your house. BTW it takes a lot of batteries and a large expensive inverter to run a roof ac or washer dryer.