Newby Girl from Wisconsin-HELP!!!

Huber1026 · 10-02-2019, 08:13 PM

I bought a school bus I'm converting to a tiny home... I'm stuck and my brain is frazzled at to what I need for my electrical system, i.e. how many batteries, what sz inverter, etc...
I tried computing total amp hours but confused as hell.
I will have an electric tankless water heater (50amp), an ac/heater combo (6amp cooling-15amp heating), fridge 1.5amp), freezer (1.2amp), tv, microwave (1000w)...
Eventually, I will have 400watt solar panel kit installed...
Looking for recommendations as to how and what is all needed for this set-up. TIA
Stephanie

Unpluggedone · 10-02-2019, 08:24 PM

Welcome to Skoolies. First thing are you planning on running on grid or on RV style with a generator? Either way, you’re on the right path by listing all your loads with the max current draws so you can wire appropriately. Now if you’re going off grid solar battery you will want to reconsider a few things, although the load sizing is similar just calculating hours of running for the battery sizing is next, 400 watts doesn’t get you much capacity maybe a couple lights. A spreadsheet is the best approach

o1marc · 10-03-2019, 12:22 AM

Does the tankless water heater run off the electric system, or off os D cell batteries inside it?

bus-bro · 10-03-2019, 04:22 AM

Your 400 watts of solar power won't even begin to deal with your tankless water heater and your space heater loads.

WIbluebird · 10-03-2019, 05:42 AM

Where are you at? I'm in Madison.

Ronnie · 10-03-2019, 06:21 AM

The electric water heater is a real problem if you ever want to be off grid. Propane would be a better choice.

Here is what we have that is propane fueled,
stove
instant on hot water heater
heat

Electric is 400 watts solar, with a 1000 watt inverter This runs,
lights
fridge
water pump
fans and roof vents fans
computer, phone charger, other small stuff

A/c is run by the generator or by plugging into shore power. The generator also serves as a backup in case we get too many cloudy days. So far have not used it for anything but a/c though

kazetsukai · 10-03-2019, 07:30 AM

Quote:

Originally Posted by Huber1026

I tried computing total amp hours but confused as hell.

So first, to help you with the math:

-Get all of your units into Watts (W), or units of power. Take the voltage they run at, and multiply it by their Amperage ratings. V*A = W. In some cases they'll already have a Wattage rating, like your microwave.

-Now that you have Wattage, calculate Watt-hours (Wh) that each appliance will run in a day. So for your microwave- it may pull 1000W, but you might only use it for 3 minutes four times a day. That's 12 Watt-minutes, and 12 minutes/60 minutes in an hour = 0.2 hours, or 0.2 Wh. Your fridge on the other hand may pull 40W, and be running for 8 hours a day. 40W * 8h = 320Wh.

-If you only use an appliance once every three days (laundry for instance), calculate its Wh for the day you use it and divide that by 3, that will give you its "average consumption" per day.

-Add all your Wh per day up. That's how much energy you will need in a day. If you divide this number by 2, I'd say that's a decent start at how much you'll want in panels- I have 700W of panels, that generate an average 2500Wh a day in good sun. So if all your appliances add up to 1000Wh (1kWh), a 500W solar array can typically keep up with your load and recharge the batteries if you have sun.

-Battery capacity: Take the Wh total and multiply it by 2, then again by the number of days you want to be able to run everything without sun (rainy days, etc). This is roughly the capacity you'll need. To figure out how many batteries that would be: A 12V 100Ah battery is 1200Wh (12V*100Ah), so divide your figure by the Wh rating of the battery/type you want to use.

The panel and battery figures are estimates. You'll have to play with the numbers a bit to find what fits your budget.

To echo what others have suggested here, even the smallest electric tankless water heaters pull between 3000w-5000w, many pull 8-15kw. To support that you'll need way more money in batteries and an inverter than a really, really nice propane tankless heater that will outperform whatever you hope to do in electric.

bigskypc50 · 10-03-2019, 08:26 AM

You won't be able to run a electric tankless and an AC and heater off of an inverter and solar system. Unless you just won the lottery and the system would be too big for an RV.

First you need to figure you if you will be spending most of your time plugged up or off grid. Then I would suggest you start dividing up your systems and using something besides electric.

The pretty standard setup in the sticks and staples RV world is the Fridge and or Freezer Lights Furnace Water Heater will all work off the 12V system and/or propane. Then you have to plug in, or start up the generator to use the microwave AC and electric heaters.

Thats how I have mine setup, for about 12-14 hours I can run my fridge, TV, lights, water pump, furnace (12v/Propane) , and water heater (propane) and rear heater (Wave 3 Propane). I have no solar panels yet, just 400Ah of batteries, and a 1000W Inverter Have to start up the gen set every morning or plug in

Depends on your budget, what appliances you have already and etc.

Quote:

Originally Posted by Huber1026

I bought a school bus I'm converting to a tiny home... I'm stuck and my brain is frazzled at to what I need for my electrical system, i.e. how many batteries, what sz inverter, etc...
I tried computing total amp hours but confused as hell.
I will have an electric tankless water heater (50amp), an ac/heater combo (6amp cooling-15amp heating), fridge 1.5amp), freezer (1.2amp), tv, microwave (1000w)...
Eventually, I will have 400watt solar panel kit installed...
Looking for recommendations as to how and what is all needed for this set-up. TIA
Stephanie

Huber1026 · 10-03-2019, 09:25 AM

Quote:

Originally Posted by WIbluebird

Where are you at? I'm in Madison.

I'm in Watertown

Huber1026 · 10-03-2019, 09:31 AM

Hi. Thank you for responding. To start out, mostly plugged in/generator and eventually solar panels. Good info.

Huber1026 · 10-03-2019, 09:39 AM

Awesome info. Thank you so much. Definitely considering propane tankless water heater now. For now, I will likely run off of plug or generator. I appreciate the feedback.

Huber1026 · 10-03-2019, 10:01 AM

Thankfully I didn't buy an electric tankless water heater sounds like propane it is.

Huber1026 · 10-03-2019, 10:09 AM

I just realized you have to click quote to respond to specific messages... I clicked reply and went to the bottom of replys. Thank you [AQUOTE=Unpluggedone;351899]Welcome to Skoolies. First thing are you planning on running on grid or on RV style with a generator? Either way, you’re on the right path by listing all your loads with the max current draws so you can wire appropriately. Now if you’re going off grid solar battery you will want to reconsider a few things, although the load sizing is similar just calculating hours of running for the battery sizing is next, 400 watts doesn’t get you much capacity maybe a couple lights. A spreadsheet is the best approach[/QUOTE]

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