How much power do I need?

[Vderks]

I am building a Boutique Candle Pouring Skoolie Party Truck. Think Food Truck only I sell/make candles. I REALLY want this to be solar, self sufficient, if possible. We do not need the normal house type stuff but there are a few pieces of equipment that do pull some watts that we will use.

1. Our candle melter - think overgrown crock pot. It will keep our wax at 160 degrees full time when we are on site. Per specs it is 12amp 120v 1440 watt.

2. A heat gun. This is used for short bursts of time, 1-2 minutes at a time, 1-2 hrs in total for a full day. Per spec 1200 watts.

3. a glue gun. Rare use but 30min to 1 hr when needed. 80 watt.

In addition to those big pull items - LED lights, maybe music, POS Square (I-pad), and to charge our phones, laptops etc.

That is just what we will need to operate the BUSINESS part of the bus. I don't know of anything else that will be needing power but I'm sure there will probably be something.

How do I calculate the load required? Wit that information I "think" I can calculate the size solar array? Inverter? Battery Bank? I will need... Thanks in advance...
Vicki

[kazetsukai]

So...

Originally Posted by Vderks

1. Our candle melter - think overgrown crock pot. It will keep our wax at 160 degrees full time when we are on site. Per specs it is 12amp 120v 1440 watt.

This load in particular could be difficult. I think your specs aren't accurate representations of your load- it will taper off at the desired temperature once reached rather than pulling 1440W constantly if this is what I think it is.

So here's what I'd do. Get yourself a Kill-A-Watt meter (any brand really) to monitor how much energy this appliance uses, something like:
https://www.amazon.com/dp/B07Y1SLZ8W

Run it for 24h and see how many Watt-Hours (Wh) the device consumes. That will tell us how realistic it is to power it off of solar.

Originally Posted by Vderks

2. A heat gun. This is used for short bursts of time, 1-2 minutes at a time, 1-2 hrs in total for a full day. Per spec 1200 watts.

3. a glue gun. Rare use but 30min to 1 hr when needed. 80 watt.

In addition to those big pull items - LED lights, maybe music, POS Square (I-pad), and to charge our phones, laptops etc.

These loads are actually pretty easy. You need a decent inverter to support the instantaneous loads of the AC components of course, but overall energy requirements should actually be fairly modest.

I think for an inverter you'll want something advertised at around 4000W. The ratings you see online are not the continuous delivery ratings, usually they are surge or short period of time ratings. Further, as you are hoping to support potential loads of well over 2000W (the candle melter could kick on at the same time as your heat gun is going, and your laptops are plugged in/lights are on, etc), I would not advise going with a 12V system, but rather a 24V or 48V system- referring to your battery bank voltage. You can power 12V appliances with a different voltage battery bank.

Originally Posted by Vderks

How do I calculate the load required? Wit that information I "think" I can calculate the size solar array? Inverter? Battery Bank? I will need...

Battery capacity is somewhat subjective based on your desires. If you could run your big loads only when you have sun, you could go with a good sized solar array and a small battery bank, but few people fit this model. How many days do you want to be able to power your loads without the sun, days of overcast or rain where you will not be generating as much power?

You're already on the right track by thinking in terms of wattage and time, my current suggestion is to try measuring how much your biggest load (the candle melter) uses, and maybe some of your other loads. Also, it would help people here if they knew what kind of budget you were working with. Solar is multi-faceted- you have generation, storage, discharge, and conversion all in the same thing. Trying to tackle them all at once without a good understanding of each can be challenging.

If you would like, we can arrange to have a phone conversation to answer any of your specific questions in real time. PM me if interested.

Hope this was somewhat helpful.

[john61ct]

Better to avoid using solar generated electricity for heat production. Propane directly burned is much more practical.

With DC electrics, you can't really predict the Ah per day at 12V until you're actually using the setup and log usage with a coulomb-counting wattmeter.

Or get a small quiet genset, that way you can keep adding / spending on more and more battery storage and solar panels over time

to reduce the hours / day you need to run the genset.

Parking in shade, or cloudy days, or seasonal changes to the angle of the sun, even ambient temperatures

will all greatly vary your solar system's Ah per day contribution.

When you have enough storage + panels to produce 3x the average daily need on "perfect days", there will still be the 20-30% days when you need the genny for a couple hours.

[Vderks]

Thank you for that information I will order the meter today.... for MOST of the time, we will be using the bus as a RETAIL Boutique and the Melter and heat tools will not even be in use. But we want the option of taking her to weddings, parties and such and actually pouring candles. Most of the time, you’re talking 2-3 hour spans. BUT Dream of Dreams ... Someday we hope to take it to WACO Silobration and pour for 3 full days.

Once I collect the information I will get back. As for solar capacity, I’m in Kansas City. So, while not Arizona, a fair amount of sunshine 🌞

[rossvtaylor]

Kazetsukai (heck...I worked in Japan for several years...what does that mean? I must look it up sometime)...anyway, he nailed it. Having had some small experience with wax melters (only a little) I'm guessing it won't run at 1440 W all the time...but it will until it reaches temp. Say you're on a site for 4-5 hours and the wax melter is running at. 1440 W for 3 of those hours...then you've drawn 360 amp-hours from your batteries. That means you need at least a 700 ah battery bank, if they're standard FLA or AGM batteries.

I do get your plan, so you have the advantage of letting the vehicle's alternator power that while you're driving to the party location. That will cut your battery energy draw by some unknown amount. And that unknown, plus the uncertain energy consumption, makes it hard to design a system without more info. So, I second the Kill-A-Watt meter to measure precisely how many pixies you use.

[john61ct]

Make sure you measure the Ah at 12Vdc, so if you **are** converting to mains AC , you are capturing inverter overhead as well.

Using an AC coulomb counter will give wildly inaccurate results

Ignore watts, only amps and Ah will give useful accuracy.

When usage of high draw devices can vary a lot,

Ah per day draw should ideally be separated into actual "typical" usage vs "worst case" scenario

Do not try to extrapolate from just a few hours' usage unless you really are confident duty cycling is short-term, like a fridge may turn on and off between 4 and 15 cycles per hour depending on temperature delta ambient vs inner thermostat.

[Jaybz]

Something else to consider for the wax melter- if you do the kill-a-watt test find that the duration the heater is actually on is fairly low, you could potentially use a Variac to drop the input voltage. In theory this would lower the peak usage and operate the heater at lower power for a longer period of time. It would have little effect on the total power consumption, but might enable you to downsize the inverter. This assumes there’s no fancy electronics inside the wax melter, just a heating element and thermostat.

I’ve been toying around with this idea for other resistance heating applications as well, like a block heater.