Solar Novice Needs Direction

[2Macs]

I keep dreaming up possible modifications for my TT that are sometimes excellent and other times "crazy".

Now, the subject is solar.

I use two 12 volt deep cycle batteries wired in series to power the TT when electricity or generator is not available.

I am considering using solar panel(s)to charge them if dry camping.
My initial research indicates I need a minimum of a 12 volt panel to charge one battery. Do I need 24 volts or larger for two batteries to keep them up and also use power from them at the same time for lighting, water pump and heating, etc?

Now, here is the crazy part. I also have 600 watt and 500 watt power inverters to 110 AC. I can't tell you if they are "pure sine wave" or "modified sine wave" inverters. One is a Rally Model 7294 inverter.

Can I attach these inverters to the batteries in such a way to generate AC to handle a 22 inch LED TV, charge a shaver, a toaster occasionally, or a 900 watt microwave occasionally?

Can I even do this? If I can, what size solar panel(s) do I need?

I did a search in the forum on this subject and did not find any satisfactory answers.

Forum members expertise would be appreciated.

[time2roll]

MEXICOWANDERER wrote:
My little Hwang Ho 800 watt microwave's output (wattage consumed) drops like a stone when voltage sags. At 105 volts, it's output is barely 420 watts. I wonder if all microwave ovens are like this?

I understand the answer is yes because the megatron feeds off the top of the sine curve. Very common to run at lower power on MSW because the peak voltage is lower even if RMS is the same.

[MEXICOWANDERER]

My little Hwang Ho 800 watt microwave's output (wattage consumed) drops like a stone when voltage sags. At 105 volts, it's output is barely 420 watts. I wonder if all microwave ovens are like this?

[Ron3rd]

Just a comment; how important is using the microwave to you? It certainly can be done with the right size (large) inverter, but you'll really need to beef up your battery bank as the microwave will quickly drain two 12v batteries.

I have a 300w PSW Samlex inverter that powers all the outlets in my trailer, but I only use it for the TV's, DVD's, etc, ie, low wattage stuff and it's plenty.

Basically, I have my shore cord plugged into the inverter to power all the AC outlets.

[NinerBikes]

2oldman wrote:

2Macs wrote:
I use two 12 volt deep cycle batteries wired in series to power the TT when electricity or generator is not available.

Really?

You should start here: 12v side of life.

Then here:Solar basics

These too:
Don Rowe site Inverter FAQ
Inverters by Phred
MSW v. pure sine

Everything you need to know is right here...OP, so start reading.

[BoonHauler]

2Macs

Here's another link for you, all really good info RV Electrical

This is a must read as well HandyBob's Blog

Educate yourself, it's WAY worth the time and effort!

[ewarnerusa]

2Macs wrote:
...I understad from the posts that I can't use the two inverters together, so I will have to use the 600 watt one or get another one to handle up to 1200 watts.

Well...you can't stack them to provide 1100 watts of capacity to a single outlet. But you can certainly hook them both up and operate them independently but simultaneously. But with only 2 batteries, their charge isn't going to last long with 1100 watts of AC demand via inverters placed on them. Smaller loads would be fine.

I use my inverters a bit differently. I plug my shore power cable directly into an inverter outlet, switch my converter off, and power the whole TT via the inverter. That way all the AC outlets in the camper are live. I also switch off breakers for the air conditioner and microwave so they aren't accidentally turned on and trip the inverter breaker. The fridge and water heater are set on propane. Usually I just need enough AC power to run the TV and some battery chargers and fans, so I use the 300 watt inverter because it is more efficient for those smaller loads. But if I want to try and run a bigger load like a rice cooker or waffle maker, I have the option of the 1500 watt inverter.

[MrWizard]

the 3500w, should run your A/C
but a few conditions need to be meet first
#run it before you need the A/C..bring up the charge on your batteries so the converter is NOT pulling a heavy load

# make sure the fridge and water heater are set ON LP aka propane..NOT on automatic and using the generator

# if you need the MW, hair dryer, coffee pot, but the A/C on FAN ONLY

even if you get a bigger inverter, you don't have enough battery to use the inverter for heavy wattage items

microwaving supper could ruin your evening entertainment and or forced air furnace heat use

[2oldman]

2Macs wrote:
I originally used the term volts in my original post when I meant watts. Chalk it up to ignorance on the subject.

Can you please point out where you meant watts?

[ewarnerusa]

2Macs,
Two pages of posts and everyone has provided advice I agree with, but I like these types of threads so I'll try and contribute.


My initial research indicates I need a minimum of a 12 volt panel to charge one battery. Do I need 24 volts or larger for two batteries to keep them up and also use power from them at the same time for lighting, water pump and heating, etc?

-I think this has already been addressed well. Your battery system is 12V and unless you go outside the box it will be 12V regardless of the number of batteries in it. When people refer to "12V solar panels" they are really something like 17V. A component called a charge controller will make sure the batteries are receiving the appropriate charge voltage. Higher voltage panels require different and more expensive controller technology (Maximum Power Point Tracking, or MPPT). Solar panels provide current to your system that is available for whatever you want, with anything unused by immediate demand going into your batteries for charging. If an immediate demand is for more current than the panels can provide, your batteries simply make up for the difference. At night when there is no solar input happening, your batteries run everything. Many consider the solar component to be primarily used as a battery recharger, including me.

Can I attach these inverters to the batteries in such a way to generate AC to handle a 22 inch LED TV, charge a shaver, a toaster occasionally, or a 900 watt microwave occasionally?

-Yes, absolutely. We do the same. As already mentioned, the high draw items like toaster or microwave are not conducive to being run off a battery, nor are your inverters of sufficient capacity to operate those items. A TV or recharging small battery devices is well within your inverter capacities, MSW or PSW issues notwithstanding.

Can I even do this? If I can, what size solar panel(s) do I need?

-Can of worms... Without having real applicable usage data from an energy audit, it can't be answered. Generically, plan on needing about 1-2 watts of solar for every 1 amp-hour of battery capacity. With 2x12V batteries, I'm guessing you're referring to typical OEM dual purpose marine batteries, you've probably got about 150 Ah of capacity.

[2Macs]

Based upon the comments, I need to add some information.

I do have two generators. One is a 3500 watt inverter genset which will not handle the A/C and a 5700 watt contractor genset which will handle 220 volts 30 amps, but is wired for the RV to 110 volts 30 amps and will handle the A/C and all other electricity needs. The inverter genset is supposed to be quieter than the contractor genset, but to me they both seem to produce about the same decibel level under load.

I originally used the term volts in my original post when I meant watts. Chalk it up to ignorance on the subject.

I understad from the posts that I can't use the two inverters together, so I will have to use the 600 watt one or get another one to handle up to 1200 watts.

[jrnymn7]

How much solar one needs is dependent on power usage, which in turn is dependent on where and when you boondock.

[Sandia_Man]

Larger inverter needed for microwave and toaster but with just 2 batteries they will get depleted pretty quick attempting to power high amperage items even for a few minutes a day. Running tv and charging small devices can be done with existing inverters.

Good idea to have at least 100 watts of solar per battery so on a sunny day they recover most (and maybe all) of the consumed amphours depending on how much they have been depleted. Out west where we camp most often we tend to have good results with solar replenishing our battery bank.

We find having both solar and a generator is the best of both worlds and makes for worry-free camping as it pertains to enjoying all the comforts an RV provides. When camping in good weather and mostly clear skies our genny sits idle except for the few minutes each day where we require 1K+ watts.

[2Macs]

Sorry, Yes the batteries are in parallel. I keep getting the terms mixed up even though they are wired correctly to maintain 12 Volts.

[MrWizard]

Your RV systems are 12v
Your two 12v batteries are wired "PARALLEL" , positive to positive, neg to neg,
Series is inline together to make 24v

You could have ten batteries in parallel, it is still 12v
Any solar will be for charging 12v
You cannot attach 24v or 36v to a 12v battery
Solar panels come in many sizes and voltages
It's the job of the solar Controller, to create the proper voltage 13~14 to charge the 12v battery bank

Either of your inverters is big enough to power the tv and minor device chargers
But if your want to run the toaster, microwave you will be better off with a portable generator, which can also be used to power the converter and charge batteries, when the sun and weather won't comply to your needs