Converting Home's - RV's to DC

Was going to post in a current thread thought this maybe better in it's own.
From: Help converting an RV house battery to lithium

Well if you find any cool 12v appliances let me know. At one time decided a house would be best to convert the AC coming in to DC. After looking into it found not that many good DC appliances, most at different voltages. Had come down to running 24v with a DC to DC for each different item that I wanted to power. Was not going to do that.

That was 5-10yrs ago maybe time to revisit it.
The new TV's run on DC, they all have AC to DC converters in them. A person could pull that out and put a DC to DC in them.
I should stop here, think this warrants a new thread.

Better to state the type of appliance.

And do not expect everything to be the same as those designed for grid power.

And do not use solar / stored DC for priducing heat, or aircon.

The whole point is getting consumption down

a couple hundred Ah per day at 12V is a big system

but a tiny fraction of what a thirsty (stupidly criminally wasteful) USian house consumes.

Have learn about electric heating. Don't use it unless no other choice. The other lesson is use as little as possible.

We have Natural gas here it is the cheapest to heat with. Gas stoves, ovens, dryer and water heater. No pilots, electric ignition.
Years ago went Central HVAC was in stalled in the house they added electric heat with it and took out he gas heater. Once I move in put a gas heater back in. It's not hooked with the central unit. Have the central heat on but turned down to a low temperature where it does not come on.

The goal is it get the power requirements as low as possible. AC appliances were not designed to be energy efficient. Devices to lower power requirements have moved to DC with AC to DC inverters installed in them. My min split is the same with a variable speed compressor and DC fans. AC refrigerators need replaced with the DC versions and should be of the chest type.

The new TV's are DC and use less watts and don't make as much heat as well as the led lights. Don't have any plans on running any high energy devices. Only want to power the basics when the power is out. Cold milk, light to drink it by and some music...

Anything with a battery should be charged direct from DC, not using the AC power brick

Winter is almost here and if it's cold enough will not worry about the frig, just set it all out side in ice chest's and the non frozen items will need to be moved in for a time not to freeze.

Have only 3 old panels left think it's only 40w. 12v Solar charge arrived to charge the battery when put together. I know this is next to nothing but they would charge up my trike battery in less than a month. We have two or three power outages in the last 7 months that lasted for an hour or two. They would deal with that. Once I get started with a min setup then it will be upgrade's that will never end.

Kill-A-Watt meter arrived going to start getting an idea of the power that will be needed starting with the Frig.

There is the 5V USB standard that is starting to be used for Phone's and rechargeable lights. Makes me wonder what Voltage the rest is running on or would a 5V setup cover quit a few things.

Anyone check what DC voltage there smart TV's are running on. PC's are 12V and 5V or has that changed. My new PC Monitor has a Wall Wart powering it so that will be easy to figure out.

Like to hear your thoughts john61ct. I know this is rocket science. Things change, last time I took a look at it was just now worth it.

I agree that 12V system is a high amp system. Would like later to move up to 24V or the whatever voltage is best.

by john61ct » Nov 02 2021 5:23am

Anything with a battery should be charged direct from DC, not using the AC power brick

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CPS (City Public Service) has approached me twice in the last week. They want to pay for and in stall solar panels on our roof.
The we would then pay them back monthly for the equipment and not charge us a utility bill until payed for. Has anyone see a setup like this?

It used to be the company would mount their equipment on your rood and give you a discount on they bill. This sounds different. Not that i'm not trusting but can't help feel like there is something they are not telling me.

PowerFin Brings SolarHost, First-of-its-Kind, Rooftop Solar Program to San Antonio

ZeroEm said:

The new TV's run on DC, they all have AC to DC converters in them.

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There has been some work done for 400VDC for buildings and businesses. This came about because just about every computer, motor drive and TV out there first boosts to 370 volts DC then converts down to the voltages needed by the device.

Also Pika Energy had a 370 volt bus they called the REBus that was pretty ingenious; it connected solar to battery and to inverter and required much less copper to do it. You could also distribute the 370V to other devices. But since Generac purchased them, I haven't heard much about the REBus.

https://www.powerelectronics.com/technologies/power-electronics-systems/article/21861841/400-vdc-power-distribution-for-data-centers-emerges

https://www.revisionenergy.com/wp-content/uploads/2015/12/Pika-Energy-Island-Brochure.pdf

ZeroEm said:

The goal is it get the power requirements as low as possible. AC appliances were not designed to be energy efficient. Devices to lower power requirements have moved to DC with AC to DC inverters installed in them. My min split is the same with a variable speed compressor and DC fans. AC refrigerators need replaced with the DC versions and should be of the chest type.

The new TV's are DC and use less watts and don't make as much heat as well as the led lights.

Click to expand...

With inverter based appliances (starting to become more common) there really isn't any significant difference between AC and DC. Also modern fridges and TV's are starting to be more and more energy efficient to qualify for energy saving programs. Your mini-split, for example, likely uses 370 volt DC as the link voltage.

Thank you, remember reading about the server farms switching but it did not hit home. This has increased my understanding. Now i'm thinking, 5V for most things, appliances would run the 400V. 5V would be step down from 400V maybe or not.

The development for the Server Farms would trickle down to us. Mostly Cooling. Guess I need to look for an Fridge that has an inverter.

by JackFlorey » Nov 02 2021 10:43pm

The new TV's are DC and use less watts and don't make as much heat as well as the led lights.
With inverter based appliances (starting to become more common) there really isn't any significant difference between AC and DC. Also modern fridges and TV's are starting to be more and more energy efficient to qualify for energy saving programs. Your mini-split, for example, likely uses 370 volt DC as the link voltage.

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The issue is your storage bank voltage, which becomes your "backbone" supply.

Only go over 12/24V if you have a compelling reason, i.e. saving copper costs over long wire runs

5V is only useful for USB designed devices, as with high EV style voltages at appliance **internals**

The highest backbone I would go for DC in a living space is 48V.

Don't think I would run that much voltage in the walls. Would need to bypass all the inverters in the appliances.

Main reason for voltage higher than 12v is to avoid big copper for the amps. Will start out with 12v bank for back up don't want to cycle it all the time. thought about panels for charging the 5v during the day, have that now. Don't want the battery in the house. Don't want to use a long extension cord. Thinking about a robust case with inverter mounted that could be rolled in with a dolly or one of my bike trailers. Until the bank gets to big.

by john61ct » Nov 03 2021 2:04pm

The issue is your storage bank voltage, which becomes your "backbone" supply.

Only go over 12/24V if you have a compelling reason, i.e. saving copper costs over long wire runs

5V is only useful for USB designed devices, as with high EV style voltages at appliance **internals**

The highest backbone I would go for DC in a living space is 48V.

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How much does DC voltage dissipate over certain lengths?
Thicker the wire the less resistance, the thinner more..... so balance is key.
Shorter = less resistance, longer = more.
Do you go solid core wire as its not moving or flexing but its curving around corners and you got vibrations in a moving RV, so do you go stranded wire.
How much noise would be introduced into the DC line, maybe from a generator motor, or rv motor or some appliance.
Then do you need to isolate each appliance or you just wire it straight in, no protection. Got to think about if the appliance is damaged you dont want it to back flow and fry other components (dc converters, controllers or what have you) or appliances on the circuit. Could be the snow ball affect.

Its the biggest reason AC won, AC can go long distances. Less equipment and stations required. Split the power into phases for industrial vs comm/res. AC appliance more common, but solar is popular so lots to choose from.

An RV your talking 30' at best right, a 5th wheel trailer maybe 40', motorcoach 50' max.

Have read on this for years now. So I have a flimsy grasp of it. Not thinking of an RV for myself but as planning for this project will be considered off Grid or Backup only. Do not plan on tying it in with the current system it should all be valid for an RV.

We are looking at getting a Grid tie Solar System thru our city utilities (CPS = City Public Service). The current talks with CPS, we pay for the Solar System over 25yrs. Don't pay for electric or Natural gas used in this house during during the payment program. Will have a water bill that is thru a different service (SAWS = San Antonio Water System).

The largest CPS bill this year was close to $200 and the cheapest not sure, under a $100. Last time I did an daily average for a year was 24KW per day. The first look, rough guesses are $85 month for a 6.6Kw grid tie system. The payments would be less than our lowest CPS bill. Sounds to good to be true. So i'm looking for what is the catch?

The issue with grid tie, if there is a black out then your system is shutdown too. During the summer or hot weather need to keep the refrigerator running as not to spoil food. 24hrs is the longest outage but 1-2hrs is common.

This last winter was different 4 days without and a couple days of interment power in a week. Did not have a problem with the food it was cold outside 9 deg F. Phones, flashlights rand down. No radio or TV. Some power would be nice. Did charge up the phones in the EV but needed to leave it on for hours and worried about someone driving off. Next time will just tap into the 12V.

In the long run will want to mount the back up system in a Converted Garage/Game room not attached to the house. 15' from the house. This is when I will decide on wire runs. Making AC out there might be best or run thick copper for 24V into the house with a mounted inverter. In the mean time going to setup one Solar panel to charge 5V devices and get used to using it so if power goes out then it's not an issue.

by markz » Nov 04 2021 1:13am

How much does DC voltage dissipate over certain lengths?
Thicker the wire the less resistance, the thinner more..... so balance is key.
Shorter = less resistance, longer = more.
Do you go solid core wire as its not moving or flexing but its curving around corners and you got vibrations in a moving RV, so do you go stranded wire.
How much noise would be introduced into the DC line, maybe from a generator motor, or rv motor or some appliance.
Then do you need to isolate each appliance or you just wire it straight in, no protection. Got to think about if the appliance is damaged you dont want it to back flow and fry other components (dc converters, controllers or what have you) or appliances on the circuit. Could be the snow ball affect.

Its the biggest reason AC won, AC can go long distances. Less equipment and stations required. Split the power into phases for industrial vs comm/res. AC appliance more common, but solar is popular so lots to choose from.

An RV your talking 30' at best right, a 5th wheel trailer maybe 40', motorcoach 50' max.

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Having a grid tie solar system has worked out really well for me. It has paid for itself in about 6 years of use. We got a very generous installation rebate from both state and feds. It helped that we quit having to buy gas for the Volt along with not having a home electric bill. 14 panels was enough to cover ~90% of our use. When the power goes out we can get by with a 1.5K inverter powered off of the Volt's 12V battery that the Volt's ICE keeps charged. If needed, I don't think it would be too hard to jerry-rig a small battery/220V inverter/isolator switch that would engerize the solar system to power the house and car charger when the sun is shining.

You need to go over the grid tie agreement with a fine toothed comb to make sure that the power company can't change the terms on you down the road. Mine has a minimum 10 year term that is renewable. You might even think about paying a lawyer to have a look at it.

markz said:

How much does DC voltage dissipate over certain lengths?

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That's the big issue. 12V works great for small devices, up to maybe TV size. For any higher power, your losses are too high with small gauge wire, and large gauges are too expensive to run any distance.

An RV has the advantage that you can place loads very close to the battery bank so distances/losses are minimized.

ZeroEm said:

The issue with grid tie, if there is a black out then your system is shutdown too. During the summer or hot weather need to keep the refrigerator running as not to spoil food. 24hrs is the longest outage but 1-2hrs is common.

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You might consider a hybrid inverter that can do both grid tie and standalone. The Outback GVFX line can do this, as can the Outback Skybox and the StorEdge.

Blue Seas Circuit Wizard

is a great app to calculate the AWG to use

exposes all the variables, very educational

Use round trip wire distance, actually measure with a rope not as the bird flies.

And round everything up.

JackFlorey said:

You might consider a hybrid inverter that can do both grid tie and standalone. The Outback GVFX line can do this, as can the Outback Skybox and the StorEdge.

Click to expand...

I wish these would have been around (or I would have known about them) when I was planning my system. IMHO without the 40% gov subsidy, it's too pricey to do right now if the only benefit to me will be emergency power.

Have a 2013 Leaf, the battery is getting dated. Still have enough range but will need to replace the battery in a few years. Can use power from it but would need to leave the car on. would rather save it as last line of reserved power.

Thx for sharing. I can think of all kinds of angles but never think of everything. Not buying Gasoline and everything else with ICE was a big deal. Have only replaced the 12v and now need to replace the rear wiper blade and hatch struts. No other expenses in 3 years.
No more than we drive it's around $5 a month on our utilities.

Did some basic math. Nothing is on paper yet. First offer is a 6.5 KW system at $85/month. Guessing that is a 100% markup at 0%/interest + all the KW we don't use. We know they want to come out a head. Will 6.5KW be enough after say 10yrs.
Don't want to pay it off and it would be useless or need all new panels. I'm sure the Box will not last 20yrs or will it?

by nicobie » Nov 04 2021 3:27pm

Having a grid tie solar system has worked out really well for me. It has paid for itself in about 6 years of use. We got a very generous installation rebate from both state and feds. It helped that we quit having to buy gas for the Volt along with not having a home electric bill. 14 panels was enough to cover ~90% of our use. When the power goes out we can get by with a 1.5K inverter powered off of the Volt's 12V battery that the Volt's ICE keeps charged. If needed, I don't think it would be too hard to jerry-rig a small battery/220V inverter/isolator switch that would engerize the solar system to power the house and car charger when the sun is shining.

Click to expand...

That is a good information, before getting locked in.

You need to go over the grid tie agreement with a fine toothed comb to make sure that the power company can't change the terms on you down the road. Mine has a minimum 10 year term that is renewable. You might even think about paying a lawyer to have a look at it.

Click to expand...

At the moment trying to stay from long wiring runs. Don't even like typical extension cords always buy the heaver one's. What little I know, which is more than most that do not have a back ground in it. Bigger is always better with out going to extremes.
Thx for the Wizard tip.

Have been amazed that CPS runs smaller wires to the houses. I know, in the air they dissipate heat but they are losing watts to heating. I know it's not costing me but what a waste if you multiply that by 2 million connections.

Going to stay portable with my back up battery at the moment. I'm sure when I expand and bolt it down will do a run from the back building to the house and have one plugin. Will run 120V AND big enough not to heat up or have room to run more amps.

by john61ct » Nov 04 2021 4:09pm

Blue Seas Circuit Wizard

is a great app to calculate the AWG to use

exposes all the variables, very educational

Use round trip wire distance, actually measure with a rope not as the bird flies.

And round everything up.

Click to expand...

Thx, did not even think about asking if I can have options on the equipment. If not optional and there is a black out maybe switch the solar output to another system not tied or replace their box with something that would work for me. Outback seems to have some good equipment, been around for some years.

by JackFlorey » Nov 04 2021 4:07pm

You might consider a hybrid inverter that can do both grid tie and standalone. The Outback GVFX line can do this, as can the Outback Skybox and the StorEdge.

Click to expand...

Do have a question about charge controllers. Have always look at panels as 12, 24 or 36 for a single panel. Want to buy panels local, made here in the city. They are 40V and now looking at 24V charge controllers they can handle up to 100V. Is this the way it is done now. Run whatever voltage in the panels and if the charge controller is rated for that it is ok. Have some old 18V panels and think of them as 12V. If they were 36V and the 12V charge controller was rated for 40 or 50V then that is ok?

ZeroEm said:

Do have a question about charge controllers. Have always look at panels as 12, 24 or 36 for a single panel. Want to buy panels local, made here in the city. They are 40V and now looking at 24V charge controllers they can handle up to 100V. Is this the way it is done now. Run whatever voltage in the panels and if the charge controller is rated for that it is ok. Have some old 18V panels and think of them as 12V. If they were 36V and the 12V charge controller was rated for 40 or 50V then that is ok?

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The VOC rating of the panels should usually be higher than the battery/SC output voltage.

With MPPT as high as you like, 40VOC or higher is ideal for 12V or 24V output from Victron SmartSolar for example, very efficient conversion.

Flexible pricing based on output amps lets you optimise, get one SC well matched per panel, e.g. 75/15 model good for

250W rated at 12V output, a bit higher is OK (overpaneling) even 300W

(double for a 24V bank)

if you get a crazy good deal on panels rather than controllers.

48V bank, only the bigger Victrons, or might look at the few "boost controllers" out there.

Had a cheap boost controller, used to charged my eTrike. Connected three 18v panels in series to up the voltage and boosted to 80v to charge my 72v batteries. One day it quit charging.

Better to use a quality, well documented controller.

Last longer, Victron has a worldwide 5-year warranty that actually gets honored.

Much better conversion with MPPT, also give lots more input voltage flexibility.

And much safer.

I would use a nice big regular voltage House bank for the fridge, screens/PC charging, lights, pumps fans etc

And then DC-DC charging during peak solar for the high-voltage propulsion packs.

Maybe using a genset when needed, not enough panelage input compared to House power needs,

poor insolation conditions etc

Going to build 4s 64p LiFePO4 as a 12V system. Battery will be around 50lbs. going to make it fit my bike trailer or use a dolly to move it. Don't think I will use it but 3-4 times a year. Have everything but battery building materials. Have the cells.

Still would like a generator that ran on propane or Natural gas. I'm sure I can change jets between the two. Not sure if I have enough gas flow for a big generator. We have a gas heater in the house and gas clothes dryer.

Kill A Watt's reported: Refrigerator 76 hrs 4.1 kW = 54w/hr. That will be around 1.2 KW in 24hrs. The battery should do that, if I add a 300w solar panel that should give enough power in the summer. My inverter is a 12V 2000w/4000w. Figure #2awg wire and 150a fuse should do it for now.

For comparison, the portable 12V compressor fridges, Engel as a leading example

can sip 10-14 Ah per 24hrs in drinks-fridge mode, coolish weather

double that in super hot ambients

double again in rock-hard-ice-cream freezer mode