Beginner. Question on how to make a power bank/solar work for me.

[dcook3333]

Hello all!
I've already started searching through some threads and will continue to do so... But I thought I'd post my question(s)
just in case anyone can help steer.

Basically, I've wanted to build a power bank/inverter for my RV for some time. The thing that has stopped me is that it's a lot of expense for a few weeks a year.
So it occurred to me, is there a way to put these batteries and devices to use year round at my home?

The first thought I have is could I place some solar panels and battery bank to help power my home? My best sun is my garage which has a steel roof that I don't have to worry about as much if I get a small leak or something from placing solar panels. It's a 100% steel building only used for parking. And it's near the main breaker of my house.

I think I get the basics about how the solar works and devices, but I'm not sure how the battery bank could work to my advantage.. Is there some way to make power from them each night to aid in powering my house? Is this just a bad idea?

I'm from PA so I don't really have any hope for 100% solar to power my home. But maybe 20%??? Just enough to make buying this stuff worth it. Appreciate hearing thoughts good or bad.

 

[Supervstech]

I have a few panels at my condo, on my suburban roof parked out front, as it's impractical to setup a full solar system there...
Anyway,I use it to exclusively power my internet, TV and mobile device charging.

 

[dcook3333]

I have a few panels at my condo, on my suburban roof parked out front, as it's impractical to setup a full solar system there...
Anyway,I use it to exclusively power my internet, TV and mobile device charging.

Interesting. I like the idea of having a seperate set of "things" that the solar is responsible for running. Like a separate subpanel which gets powered by solar but can be powered by grid power when needed. Same kind of idea as a backup gen switch.
Then that got me thinking about doing some heat/cool powered exclusively by solar. I have a 2nd floor that I finished and has it's own mini-split heat pump. It seems to keep up in summer, but needs some help in winter. It's all one big room and could benefit from an auxillary unit(s) that I could switch on when charge is 100% and then it could run until the batteries reach some level that I don't want to go below for battery health. Wait till 100% then repeat. Could do that manually or perhaps there's some automation to help.
Thanks for making those brain cells bump together.

 

[DIYrich]

Where do you park the rv? Yes, the batteries can be used for the home. At s minimum for backup power. The problem is moving the batteries. If you can plug the rv into the home, then you wouldn't have to move the batteries.

 

[Mattb4]

First you need to decide what it is you would like to power (load) and afterwards you can work towards designing your supply. Lets go with something simple to get the ball rolling.

You want to keep a night lite lit to allow you to see your entrance. The bulb is 14 watts at 120vAC. In order to have it on all night requires it to operate 14 hours. 14hX14w=196wh. (W=VA) How to supply it? If you are using a 12vDC battery feeding an inverter to get the 196wh at 120vAC it will need to have 196wh/12vDC=16.33ah plus conversion losses or about 20ah. So at minimum your would need a 20ah 12vDC battery that would need to be recharged 100% after every night. If you are using lead acid batteries they do not like being fully discharged (kills them pretty quickly) and the recommendation is to only 50% discharge them. Thus you would need a 40ah 12vDC battery.

So hopefully this gets you started on your planning.

 

[dcook3333]

Where do you park the rv? Yes, the batteries can be used for the home. At s minimum for backup power. The problem is moving the batteries. If you can plug the rv into the home, then you wouldn't have to move the batteries.

I'd make a rack out of aluminum or steel. The camper is a tow behind, so when I'd use the battery bank for RV power, the battery bank would sit in the back of the truck. The bed is 6.5' x 5'. When at home, I'd create a platform I could pull the battery bank on to. It could be in either heated or unheated space. From what I'm reading, it sounds like keeping the battery bank in a heated space would be most beneficial, yes? And thank you.

 

[dcook3333]

First you need to decide what it is you would like to power (load) and afterwards you can work towards designing your supply. Lets go with something simple to get the ball rolling.

You want to keep a night lite lit to allow you to see your entrance. The bulb is 14 watts at 120vAC. In order to have it on all night requires it to operate 14 hours. 14hX14w=196wh. (W=VA) How to supply it? If you are using a 12vDC battery feeding an inverter to get the 196wh at 120vAC it will need to have 196wh/12vDC=16.33ah plus conversion losses or about 20ah. So at minimum your would need a 20ah 12vDC battery that would need to be recharged 100% after every night. If you are using lead acid batteries they do not like being fully discharged (kills them pretty quickly) and the recommendation is to only 50% discharge them. Thus you would need a 40ah 12vDC battery.

So hopefully this gets you started on your planning.

That's very helpful. Though I've got a little more power than that in mind. I think the benchmark I'd use for power requirement is to run a 6000 btu Air conditioner for 8 hours. From what I'm reading and calculating, that should put me in the 300-400 ah. Right now, when we stop at a rest stop or boon dock, we just run 12v fans and sweat it out a little. We have a bedroom in the camper which can be closed. I installed a portable A/C and that is the reason for that BTU amount. Usually the hottest it is right when we decide to set up and the heat of the day has sunk into the interior of the camper. I have an 1100w inverter generator that is just enough to run that portable a/c but... I don't want to listen to a generator run all night. But I could use it for the first 30mins or so each evening to help "knock down" the temp before switching to the battery bank. I hope that makes sense. As far as charging the battery bank, I'd run a dc to dc charger while travelling. Also would consider a solar panel for on top of the RV. I do have a heavy 4awg wire on it's own 50 amp breaker running from the main battery junction back to the rear of the truck for running some accessories like a trailer winch. I could use that as a reliable source of 12v for the dc to dc charger. The truck is a duramax so I have 2 12v batteries up front and a good alternator with upgrade options.

And where my mind is right now for home use, Is that I'd hook it to the solar panels and a small 2-tube portable heat pump when at home. Then each time the battery bank reaches 100%, i'd flip on the heat pump and let it run down until the battery bank is 50%. Open to suggestions/changes.

 

[Mattb4]

That's very helpful. Though I've got a little more power than that in mind. I think the benchmark I'd use for power requirement is to run a 6000 btu Air conditioner for 8 hours. From what I'm reading and calculating, that should put me in the 300-400 ah. ...

AC can be a bit difficult to calculate since it is going to vary based on outdoor ambient temperature, room insulation and thermostat setting. It actually helps out a great deal to get a meter like a Kill-A-Watt and plug it in during a period you wish to run the AC for. That way you have a much more accurate idea of load.

 

[dcook3333]

AC can be a bit difficult to calculate since it is going to vary based on outdoor ambient temperature, room insulation and thermostat setting. It actually helps out a great deal to get a meter like a Kill-A-Watt and plug it in during a period you wish to run the AC for. That way you have a much more accurate idea of load.

I do have one that I've used in the past! I didn't even think about plugging in my portable to get an idea of actual usage. Will do. Thank you.

 

[dcook3333]

First you need to decide what it is you would like to power (load) and afterwards you can work towards designing your supply. Lets go with something simple to get the ball rolling.

You want to keep a night lite lit to allow you to see your entrance. The bulb is 14 watts at 120vAC. In order to have it on all night requires it to operate 14 hours. 14hX14w=196wh. (W=VA) How to supply it? If you are using a 12vDC battery feeding an inverter to get the 196wh at 120vAC it will need to have 196wh/12vDC=16.33ah plus conversion losses or about 20ah. So at minimum your would need a 20ah 12vDC battery that would need to be recharged 100% after every night. If you are using lead acid batteries they do not like being fully discharged (kills them pretty quickly) and the recommendation is to only 50% discharge them. Thus you would need a 40ah 12vDC battery.

So hopefully this gets you started on your planning.

So I plugged in the kill-a-watt. It said 850va and on another screen said 820 Watt. So if I use the equation above 820 watt * 8 hr = 6560wh / 12v = 547ah. Does this sound right? It's a number higher than I wanted... Especially at 50% discharge it would mean I'd need 1100ah of battery. Is that correct? I mean, there's batteries out there when connected in parallel would give that to me. How come the batteries say the most I can connect in parallel is 4 batteries?

 

[Supervstech]

So I plugged in the kill-a-watt. It said 850va and on another screen said 820 Watt. So if I use the equation above 820 watt * 8 hr = 6560wh / 12v = 547ah. Does this sound right? It's a number higher than I wanted... Especially at 50% discharge it would mean I'd need 1100ah of battery. Is that correct? I mean, there's batteries out there when connected in parallel would give that to me. How come the batteries say the most I can connect in parallel is 4 batteries?

Actually, you would go by the VA number...
So it's even worse.
But air conditioning loads are rarely constant, so the number likely will be half or so depending on duty cycle of the load...

 

[Mattb4]

So I plugged in the kill-a-watt. It said 850va and on another screen said 820 Watt. So if I use the equation above 820 watt * 8 hr = 6560wh / 12v = 547ah. Does this sound right? It's a number higher than I wanted... Especially at 50% discharge it would mean I'd need 1100ah of battery. Is that correct? I mean, there's batteries out there when connected in parallel would give that to me. How come the batteries say the most I can connect in parallel is 4 batteries?

Batteries have different chemistries so you first need to decide which type. For instance LiFePO4 can be discharged 80-90% without harm. You also should understand cyclic loads vs constant loads. Cyclic loads, like air conditioning, are loads that do not run all the time at full running current.

So taking your test wattage of 850w. Due to the thermostat setting, size of area to be cooled, outside ambient and the space's insulation value, your A/C might need to run full wattage for 45 minutes out of each hour. That is 3/4 of an hour. So your 8 hours X 3/4 = 6 hours. 6h X 850w = 5100wh

This is why I suggested you keep the Kill-A-Watt meter on it for several hours so that a base line could be worked with.

One other thing. 12v batteries are not the best voltage to work with once you step up in loads that require over 1500w.