Is there a way to auto switch to grid power?

bluewickedburner · June 2011

Target system is a motorhome. We're putting up solar, have a diesel genset.

The typical time is mostly spent in a permanent space with grid power available. Is there a way to use the solar to charge the batteries and have a way to auto switch to take supplemental power from the grid to jump start charging in the morning or even have this happen at night when there is no sun, the day's power use is nearly over?

I'm asking because initially we won't have enough solar to provide sufficient charging to meet all our needs (at least during the times when we use more power and not traveling).

Ideally this would be a timer type of affair and be set to accept grid power during the wee hours of the early morning so that we always start out with full batteries and switch the grid power off when the sun comes up.

Is such a thing possible, practical (within the scope of my explanation) and something that could be done without rewiring the entire coach?

Cariboocoot · June 2011

Re: Is there a way to auto switch to grid power?

There are several ways of doing it. The timer is probably the simplest.
From there it can get more complex with Voltage controlled switches, auto-switching inverters, gen start adaptations ...

But running a timer set to turn a battery charger on and off at appropriate times would be easiest.

bluewickedburner · June 2011

Re: Is there a way to auto switch to grid power?

That's great. Keeping it simple is my first choice. Then it would look like:

Pedestal for grid power (250 volt 50 amp)
Surge protector
Voltage booster
ATS

The ATS would turn off the inverter and charging to bring the battery bank up to full would start.

As I add more panels down the road I'd see the amount of grid power I'm paying for decrease.

Glad I found this forum and hopefully I won't be a PITA newbie as I get all this straight in my head.

techntrek · June 2011

Re: Is there a way to auto switch to grid power?

No need for a timer. Your motorhome already has an AC battery charger in the converter. If your battery charging requirements are within the specs of the converter, you are all set. When the converter gets AC power from the pedestal OR the genset it will charge the house battery as needed. You don't have to do a thing. You'll need to get the make/model of your converter and look it up on the net to see what its specs are. Up to 2 house batteries should be fine.

If your battery charging needs are beyond what the converter can do, you'll need to buy a separate AC battery charger. Like the converter when it gets AC from either outside or the genset it will charge the batteries.

Once you add solar, you'll also have a solar charge controller. Most of the time when you are on the grid it won't do much. However, if you are on a seasonal site where they meter your AC useage and your goal is to reduce that useage you can turn off the AC charge controller and let the solar system maintain the batteries. If you are using the built-in converter this isn't quite as easy, possibly impossible since your only option would be to disconnect the battery and remember to hook it back up overnight once a month. But you shouldn't disconnect the battery, your converter expects it to be there to act as a buffer for its output.

If your goal is to treat this an an off-grid system to reduce your metered use even more you can just turn the power off to the AC charger or converter and monitor your battery condition every day. If you get low after a few days of clouds, turn it back on for a few hours. I still wouldn't put it on a timer because you'll end up saving very little and you could even use more. You have battery charging losses plus inverter losses (assuming you will be using an inverter to run things like your microwave) so you would actually use less energy by using it directly from the pole 24/7 instead of drawing down your battery overnight and then bulk charging it every morning on the timer!

bluewickedburner · June 2011

Re: Is there a way to auto switch to grid power?

Got it. My concern is that if I remain plugged into the grid, the ATS will turn off the inverter automatically. When I have available battery power I couldn't use it because there is no way to turn the inverter on while plugged in. See where I am headed?

My ideal scenario is starting the say with fully charged batteries and before getting up, have the grid power disconnect (possible timer) and the inverter automatically comes on using battery power. With very little power use during the day (refer on propane, same for water heater) the solar will make up some of the charge being used from the batteries.

After we hit the sack our power use drops back to very low levels after watching some TV, using lights etc. It is then that the timer could turn on the grid power and the ATS turns off the inverter. The ATS was designed to work that way according to all the manuals.

Then during the time we are asleep, the inverter/charger can make up any deficit the solar couldn't provide. While that would mean we pay fro grid power to recover battery charge, it will still be less than the total would be without solar.

Then, as we add solar panels, the amount of deficit would go down (along with grid power costs) until we either couldn't reasonable put up more panels, the battery capacity couldn't cover use without going to a very high DOD or a combination of that.

I am completely new to all this so what might seen perfectly logical to me might not to others. I take all that as learning so I'm appreciative of the help.

2manytoyz · June 2011

Re: Is there a way to auto switch to grid power?

My system started small, but is slowly growing. I now have 3 charge controllers, which all play nicely together. The first one is a MorningStar Sunlight 10L model.

http://www.morningstarcorp.com/en/sun-light

Regulates up to 10 Amps (120 Watts). A 20A version is also available. A slick feature about this controller is that it has the ability to control lighting, or other devices. When the sun sets, it starts a 10 minute timer to verify the array hasn't been briefly shielded from the sun. The internal relay then supplies up to 10 Amps of 12VDC to external lights (or 20A depending on model). The amount of time they are on is adjustable by turning a small switch. I'm using this to turn on my LED garden lights, and a 400 Watt inverter (via a larger relay), which is connected to a couple of Compact Fluorescent (CF) bulbs.

In your scenario, I'd use this same charge controller, connected to another relay, to turn on the grid powered charger at night. You can even select how many hours you want it to run, or even have it run dusk to dawn.

Simple solution with minimal cost & hardware.

Edit: To add a solid state relay, here's an article I put together for another website: http://www.alpharubicon.com/warlord/altenergy/solidstaterelays2manytoyz.htm

The charge controller lighting circuit will supply the control voltage for the solid state relay.

mike95490 · June 2011

Re: Is there a way to auto switch to grid power?

bluewickedburner wrote: »

....

Then during the time we are asleep, the inverter/charger can make up any deficit the solar couldn't provide. While that would mean we pay fro grid power to recover battery charge, it will still be less than the total would be without solar.

Then, as we add solar panels, the amount of deficit would go down (along with grid power costs) until we either couldn't reasonable put up more panels, the battery capacity couldn't cover use without going to a very high DOD or a combination of that.....

You have made the price between a KWh of grid (40 cents) and a KWh of Solar PV ( $4.00) haven't you ? Because spending $4K for solar, will buy a lot of campsite grid and genset power. it's a 15 year "break even" before the solar pays back 80 cents a night.

The popular theory is to run the genset (or grid charger) for short time in the AM, to bulk charge the batteries, and then let the solar finish the absorb cycle.

If you are boondocking, then there is no grid, and it's all up to the solar (and genset)
But, you have to top the batteries up - or you fall into the trap of deficit charging and ruin the batteries.

bluewickedburner · June 2011

Re: Is there a way to auto switch to grid power?

There is far more to our choices than economics and one of those is lifestyle. We chose to live in a motorhome full time because we like it and it affords us a way to take home with us when traveling. That being said, there are tradeoffs which we are also willing to accept. If it is all about money, we could have bought a house for less, paid for only grid power and never even thought about solar and come out ahead moneywise. We're spending the money, can't take it with you.

The solar aspect of what we're doing is also about a hobby and learning something new. Its fun and even if it never saved us a dime, that doesn't matter too much. Its a challenge to play with the numbers, scenarios and see just how effective we can make it.

We'd prefer not to stay at campgrounds and pay for electric, not because of costs but because of where those campsites are located. We figured that once we went the commercial campground route, we might as well just haul around an all electric rig and plug in everywhere we go.

Solar for us allows extended stays away from grid power to enjoy what we like to do. That I will need to add some energy source other than solar such as the genset or when at our permanent space, some grid power doesn't bother me at all, it is part of the deal. The cost of any solar we put up is nothing compared to the price of diesel fuel we spend. Every time we head out I could stay put and buy another panel for the same price.

I'm all for using solar to do as much as it can and what it can't do, I'll use whatever is available.

Eric L · June 2011

Re: Is there a way to auto switch to grid power?

The solar aspect of what we're doing is also about a hobby and learning something new. Its fun and even if it never saved us a dime, that doesn't matter too much. Its a challenge to play with the numbers, scenarios and see just how effective we can make it.

That's a good expression of my attitude toward my solar system as well. I knew from the beginning that it wouldn't be cost effective, but I still think it's cool and I'm glad I did it.

bluewickedburner · June 2011

Re: Is there a way to auto switch to grid power?

Eric L wrote: »

That's a good expression of my attitude toward my solar system as well. I knew from the beginning that it wouldn't be cost effective, but I still think it's cool and I'm glad I did it.

Exactly! I'm having so much fun and that is worth more than a lot of things right now. We're making a game out of it to see how each change will affect what we experience. I appreciate how serious this can be from a safety point of view and that to many, this is their only way to generate power but for us, if it isn't fun, why bother?

We started with changing out halogen to LEDs and that took months as we tried different types of LEDs. During the winter we tried out various space heaters vs the furnace and stuff like that.

I bought some small solar panels to test out the theory of a tracker vs flat vs single axis tilt and was amazed at how much difference it could make, especially over time.

I'm just so lucky to have a wife that shares the interest and supports my delusions of grandeur from time to time

techntrek · June 2011

Re: Is there a way to auto switch to grid power?

Glad to hear you've tried out the radiant propane heaters, I forgot to mention that. How did that go? I've heard mixed reviews on them. Certainly running the furnace's blower fan is something you want to avoid.

Personally I'm not saying "don't use solar", I'm saying use it when you are away from the grid but just let it maintain a float charge on your batteries when you are on the grid. And I'm saying you don't need a timer.

Is there a way to auto switch to grid power?

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