Beginning the journey. A 20' solar food trailer.

[Benjammann]

My wife and I are mostly finished converting an 8.5' x 20' enclosed trailer into a concessions trailer. Since the beginning we've been very interested in some sort of solar / battery powered system but resorted to a 12,000W generator due to not having the budget for a full solar system. As we get closer to launch I've been seeing you guys build with these inexpensive lithium batteries ordered overseas and it has made me realize we could possibly scratch something together sooner than later.

So right now we have a full 50A RV style system installed, although there is regrettably zero DC right now, aside from a 12V water pump run off a little transformer block plugged into 120V.

The idea right now is to not do solar yet, as we only have room for about 13-16 panels, and they would all have to be 400W to stand a chance of satisfying our power needs. What I'm thinking of starting with is building up a bank of lithium batteries that at first would just supplement the generator (likely with a victron multiplus II), allowing us to use a smaller quieter one, and then possibly replacing it all together. Current rough estimate of power consumption per day is around 20,000WH or around 6,000W max load.

This brings me to my first question for you guys. I'm trying to get a more accurate reading on power consumption since a lot of the equipment either cycles on and off by itself, such as fridge and freezer, hot water, etc. and some gets cycled manually like blenders, food processors, water pump, and then some cycled manually but likely have different levels of consumption than just what is listed (things like pressure cookers and expresso machines) So it's difficult to calculate. Thus, I'm looking to install one of these power meters on the AC panel so I can know without a doubt what we are looking at.

Wondering if anyone had experience with these on 50 amp systems. I think the deal is that the two 120V lines have been run into either side of the panel. I read something in a review for a similar product that in order to hook one of these up to a system with two 120V lines, you ignore the neutral, and you wire in the hot line from each side into the device. Does anyone have experience here with this?

Thanks for taking a look, and I hope to grow here to be able to help others in the future, as I am sure it's going to take a lot of help from others for me to get going.
Thanks again,
Ben

 

[snoobler]

Welcome to the forum.

I wouldn't spend a dime on anything until you get a handle on your power consumption. I'm hoping a 12kW generator is just massive overkill, or you likely have no hope of going solar.

You're on the right track with determining consumption. I have no experience with that unit, but the price seems right to me!

While that shows monitoring the neutral, I believe you would place one around each hot wire, L1 and L2, for split phase and ignore the neutral.

I would prefer to look for similar units with some legitimate ratings over that one.

 

[elpulpo]

That's a great start. I did my estimate with a Kill-O-Watt at each device, and it really helped me size my system. Sounds like you have a lot going on in your food trailer so getting better numbers on power consumption would be critical.

I used this sheet to figure out how many LiFePO4 banks I would need, I think for 20000 watt-hours you'll need at least 4 8-Cell, 24V banks. That won't give you more than a single day of autonomy though, so you'll have to expect to generate that much each day. You could do that with

Solar Plan

Watts ,Select Number of days of Autonomy,Select days to charge Consumption,1,Storage (Batteries),Production,1 Device,Wh/n-Days,Wh/Day,H/Day,W,Ah/Cell,V/Cell,Charging Range 60%,Sun H/Day,Panel Efficiency,Needed W per Hour LIGHTS,270,270,1,270,280,3.2,716.8,5,0.7,4546.8 FRIDGE,300,300,3,100,Cells...

docs.google.com

I made this sheet to help me figure out how much storage and production I wanted, helped me get my head around having enough power to sort my needs.

 

[Benjammann]

Welcome to the forum.

I wouldn't spend a dime on anything until you get a handle on your power consumption. I'm hoping a 12kW generator is just massive overkill, or you likely have no hope of going solar.

You're on the right track with determining consumption. I have no experience with that unit, but the price seems right to me!

While that shows monitoring the neutral, I believe you would place one around each hot wire, L1 and L2, for split phase and ignore the neutral.

I would prefer to look for similar units with some legitimate ratings over that one.

Thanks for the warm welcome! Receiving the AC panel test unit today and might try to get it installed tonight. I know that one had no reviews, and usually I would not go for that, but I liked the look of the display much better than anything else, also it showed time and temp. I figure for less than $20 it's not much risk as long as I install carefully. Yeah, I'm not sure why the pic shows the neutral going thru the clip. Also I'm confused about the wires they have tied into the lines and then having that wired into the device. From reading reviews on similar devices I see that people are using one wire from each hot line and connecting those to L1 and Neutral. Aside from that are you saying try to run both wires thru the clip? Would it be the same wires I am coming off the terminals with? or I go before that and try to get around the actual hot lines that are running into the box?

Thanks again!

 

[Benjammann]

That's a great start. I did my estimate with a Kill-O-Watt at each device, and it really helped me size my system. Sounds like you have a lot going on in your food trailer so getting better numbers on power consumption would be critical.

I used this sheet to figure out how many LiFePO4 banks I would need, I think for 20000 watt-hours you'll need at least 4 8-Cell, 24V banks. That won't give you more than a single day of autonomy though, so you'll have to expect to generate that much each day. You could do that with

Solar Plan

Watts ,Select Number of days of Autonomy,Select days to charge Consumption,1,Storage (Batteries),Production,1 Device,Wh/n-Days,Wh/Day,H/Day,W,Ah/Cell,V/Cell,Charging Range 60%,Sun H/Day,Panel Efficiency,Needed W per Hour LIGHTS,270,270,1,270,280,3.2,716.8,5,0.7,4546.8 FRIDGE,300,300,3,100,Cells...

docs.google.com

I made this sheet to help me figure out how much storage and production I wanted, helped me get my head around having enough power to sort my needs.

Hoping to get the device connected tonight to get some proper readings. I know it's a bit early on but I'm very interested in what everyone is doing for batteries. I see in your spreadsheet you have the 3.2V cells listed. Curious which ones they are. Also if you think it would be possible to charge the 4 8-cell 24V bank from shore power overnight? It's interesting you suggest the 24V config because that's what I was suspecting I should choose. Do you have any recommendation for an inverter? Also interested in an inverter that could let me use a generator as a suppliment to the batteries while I built up a bank, maybe buying half of the batteries at a time. Any clues as to what that might look like? 2 8 cell banks at a time or something?

Sorry for throwing all the questions at you. Lol.
Thanks!

 

[elpulpo]

Hoping to get the device connected tonight to get some proper readings. I know it's a bit early on but I'm very interested in what everyone is doing for batteries. I see in your spreadsheet you have the 3.2V cells listed. Curious which ones they are. Also if you think it would be possible to charge the 4 8-cell 24V bank from shore power overnight? It's interesting you suggest the 24V config because that's what I was suspecting I should choose. Do you have any recommendation for an inverter? Also interested in an inverter that could let me use a generator as a suppliment to the batteries while I built up a bank, maybe buying half of the batteries at a time. Any clues as to what that might look like? 2 8 cell banks at a time or something?

Sorry for throwing all the questions at you. Lol.
Thanks!

The ones in the sheet are the 280AH 3.2V Eve / Lishen cells that are popular. Most people seem to get them off Alibaba or Aliexpress, though they can be had on Amazon as well. Saw them first on https://www.mobile-solarpower.com/lithium-batteries.html. I bought mine but they haven't shipped yet. I'll be posting when I get them (Shipping right now is like 2 months). To size your batteries you'll need to figure out how many Watthours per day you need to use. You can copy my spreadsheet and put in your devices on the left hand side, and how many watts each devices uses. Then put in how many hours you think the device will run for and then up top put in how many days you would like to go without charging. If you are planning to charge from shore each night you can just leave that at 1. The middle column will update with how many cells and 4x12v banks you need. Just divide the number of 4x banks by 2 for the number of 8x banks.

Should be possible to charge onshore power, a lot of people have that worked into their designs. Many people charge from alternators or from a power supply. Mine is purely solar so I know less about that, but I think you basically just wire the power supply up to the BMS with the appropriate fuses and voltages. I'd poke around and see what people have done before.

I think the inverter is separate from the power supply in most systems, though I have seen some all in one solar chargers. To size your inverter you'll need to figure out your max AC load in Watts. They come from like little 200W car inverters up to 10000W+ beasts.

 

[snoobler]

Thanks for the warm welcome! Receiving the AC panel test unit today and might try to get it installed tonight. I know that one had no reviews, and usually I would not go for that, but I liked the look of the display much better than anything else, also it showed time and temp. I figure for less than $20 it's not much risk as long as I install carefully. Yeah, I'm not sure why the pic shows the neutral going thru the clip. Also I'm confused about the wires they have tied into the lines and then having that wired into the device.

Voltage sensing and power. See pic below. The hall effect sensor can only sense the magnetic field/current.

From reading reviews on similar devices I see that people are using one wire from each hot line and connecting those to L1 and Neutral. Aside from that are you saying try to run both wires thru the clip? Would it be the same wires I am coming off the terminals with? or I go before that and try to get around the actual hot lines that are running into the box?

You need two of those - one for each leg. If you pass both L1 and L2 through the same sensor, they are 180° out of phase and devices running on each leg will offset the other, e.g., 20A on L1 and 30A on L2, you will only see 10A net.

 

[Benjammann]

Voltage sensing and power. See pic below. The hall effect sensor can only sense the magnetic field/current.



You need two of those - one for each leg. If you pass both L1 and L2 through the same sensor, they are 180° out of phase and devices running on each leg will offset the other, e.g., 20A on L1 and 30A on L2, you will only see 10A net.

Thanks for the explanation! So I fairly easily managed to get this thing installed the other night. What I noticed when I did so is that 90 percent of the circuits for the food truck are on one line. (so I put it on that side until the second one arrives) I think they did this because they tried to separate it into left and right sides of the trailer, which 90 percent of the power needs are on the one side. So my question is, I've been seeing people talk about unbalanced loads, so is this going to adversely effect the generator or the potential future battery bank install? (We're using the 50A generator connection to supply the two 120V lines running into the panel.

 

[snoobler]

Thanks for the explanation! So I fairly easily managed to get this thing installed the other night. What I noticed when I did so is that 90 percent of the circuits for the food truck are on one line. (so I put it on that side until the second one arrives) I think they did this because they tried to separate it into left and right sides of the trailer, which 90 percent of the power needs are on the one side. So my question is, I've been seeing people talk about unbalanced loads, so is this going to adversely effect the generator or the potential future battery bank install? (We're using the 50A generator connection to supply the two 120V lines running into the panel.

Bummer. That's unfortunate. Yep. Imbalanced. Since the loads are mostly on one side, but you have a 120/240V split phase panel and presumably the same output on your generator, the heavily loaded side basically requires a generator that's 2X your actual power needs.

Do you have anything that requires 240VAC?

 

[Benjammann]

Bummer. That's unfortunate. Yep. Imbalanced. Since the loads are mostly on one side, but you have a 120/240V split phase panel and presumably the same output on your generator, the heavily loaded side basically requires a generator that's 2X your actual power needs.

Do you have anything that requires 240VAC?

I don't at the moment. I've been looking it up and seeing that some people are very concerned, and some not so much. But I'm sure it's much better to have it balanced. From what I understand each 120V leg can handle 50A draw. So I'm going to end up drawing like 35 from one side and 10 from the other right now. Are the implications of this enough to try and move circuits over to the other leg? We are using this generator.

 

[snoobler]

It's a concern because of the reason I state - you need 2X the power on the 240VAC input than you're actually using. It also forces the neutral line to carry more current. When the two legs are balanced, the neutral moves very little current. Not really a concern, just a thing.

Your case: 45A * 120VAC = 5400W... but since you're pulling 35A on one leg, but need to supply power to both, you need 35A * 240VAC = 8400W capable source.

Of course, the generator was likely sized purely on the 50A * 120V * 2 = 12000W, which is clearly overkill. You're running your generator at < 50%, and they use more gallons/Wh of energy at low power than they do high. You typically want to run a generator at 70-80% rated power for a good balance between economy and longevity.

Two options:

1) balance the load better.
2) Switch completely to 120VAC.

#2 entails reconfiguring the generator to output only 120VAC (it says it can do that, "Maximum power: with DuroMax MX2 technology, get the maximum power from each of the 120 volt receptacle. Choose between operating the generator at both 120 V and 240 V Simultaneously, or at 120 only with full power."). Depending how the generator outputs power in that configuration, you might not need to do anything to your panel.

With the generator reconfigured for 120VAC, if L1 to N is 120VAC, and L2 to N is 120VAC, but L1 to L2 is 0, then you're golden. Nothing else is needed. This means the L1 and L2 are bridged at the generator.

What I'm describing is identical to what happens when you plug a 50A RV into 30A shore power. The 30-50A dogbone adapter does this by bridging L1 to L2.

Advantages: Easy mode. Panel is instantly balanced. No other changes needed. A single power meter on the Neutral would capture all power use of the trailer.

Disadvantages: 1) No 240VAC power. 2) limited to 6000W total power as the N will be limited to 50A total as both legs now use the N.

 

[Benjammann]

It's a concern because of the reason I state - you need 2X the power on the 240VAC input than you're actually using. It also forces the neutral line to carry more current. When the two legs are balanced, the neutral moves very little current. Not really a concern, just a thing.

Your case: 45A * 120VAC = 5400W... but since you're pulling 35A on one leg, but need to supply power to both, you need 35A * 240VAC = 8400W capable source.

Of course, the generator was likely sized purely on the 50A * 120V * 2 = 12000W, which is clearly overkill. You're running your generator at < 50%, and they use more gallons/Wh of energy at low power than they do high. You typically want to run a generator at 70-80% rated power for a good balance between economy and longevity.

Two options:

1) balance the load better.
2) Switch completely to 120VAC.

#2 entails reconfiguring the generator to output only 120VAC (it says it can do that, "Maximum power: with DuroMax MX2 technology, get the maximum power from each of the 120 volt receptacle. Choose between operating the generator at both 120 V and 240 V Simultaneously, or at 120 only with full power."). Depending how the generator outputs power in that configuration, you might not need to do anything to your panel.

With the generator reconfigured for 120VAC, if L1 to N is 120VAC, and L2 to N is 120VAC, but L1 to L2 is 0, then you're golden. Nothing else is needed. This means the L1 and L2 are bridged at the generator.

What I'm describing is identical to what happens when you plug a 50A RV into 30A shore power. The 30-50A dogbone adapter does this by bridging L1 to L2.

Advantages: Easy mode. Panel is instantly balanced. No other changes needed. A single power meter on the Neutral would capture all power use of the trailer.

Disadvantages: 1) No 240VAC power. 2) limited to 6000W total power as the N will be limited to 50A total as both legs now use the N.

Wow! Thanks for taking the time to write this up so I can understand. Going to be taking a closer look at the panel tonight, as well as getting a more accurate reading on total power consumption on Saturday when the other power monitor arrives.

Likely will be attempting to move circuits to the other side to balance. What are the implications of the unbalanced load if and when we get a battery bank? Is it still pulling double the power?

Thanks again so much.

 

[snoobler]

Honestly, I'd disconnect the trailer, flip the MX2 switch to 120VAC, fire it up and then check the output of the 50A plug. If both legs show 120V to N, and 0V to each other, you're literally done. Your panel is instantly balanced, but the trailer is limited to 6000W @ 120VAC.

You're not actually using double power. The generator has to provide enough current on the highest demand leg. 35A * 120V * 2 = 8400W capable generator to supply a 4200W load. This means you're running a bigger generator at a lower power setting, which costs more $/kWh.

To state it another way, if you need 5000W of power, a 7000W generator will burn less fuel producing 5000W than a 12,000W generator producing only 5000W.

Your generator is based on rating, not need, i.e., your 50A 120/240VAC panel is capable of 12000W, thus a 12000W generator was used when you likely need less than half that. You're basically using a city bus to deliver for door dash when a sedan would be more efficient. A gross exaggeration, but hopefully, it illustrates the concept.

If you don't balance the panel OR convert to 120VAC only, you will need an INVERTER that's large enough to supply 35A on one leg, i.e., the 8400W again. Inverters consume power just by making 120/240VAC available. Bigger inverters consume more. Something of that size will likely eat 100W just by being powered on.

 

[Benjammann]

Honestly, I'd disconnect the trailer, flip the MX2 switch to 120VAC, fire it up and then check the output of the 50A plug. If both legs show 120V to N, and 0V to each other, you're literally done. Your panel is instantly balanced, but the trailer is limited to 6000W @ 120VAC.

Thing is.. I strongly suspect we are going over 6000W when everything is operational. Although another test this weekend with both power meters should confirm that. We are using two 1500W small tank hot water heaters that could be converted to 1 propane water heater if required. That would save 3000W when they are both kicked on. We went with electric due to needing reliable instant hot water to pass inspections, and my buddy said he has been having issues with his propane tankless heater. We did have an extra access point put in the propane lines when they got installed tho.

Another thing I was wondering, if we eventually started building up a battery bank, I noticed the Victron multiplus ii says it can supplement a generator with battery power if the load required it, although I was kind of thinking that it was the other way around and the battery bank would be the main source with the generator supporting it as needed, so that the generator was not overloaded. Anyway, I was wondering if it's possible to have the generator charging the batteries when power demand is low.

So the idea right now that I'm forming is to first get the load balance deal sorted, get a proper reading on power usage, start vending, then as we get the money start phasing in a battery bank, possibly buying something like 2 8 cell banks, and then the other two later. Also figuring out what inverter we need to support all this along the way.

I imagine it will be much more nailed down when I get the power reading and go from there with the rest of it.

Thanks so much!

 

[snoobler]

Thing is.. I strongly suspect we are going over 6000W when everything is operational. Although another test this weekend with both power meters should confirm that. We are using two 1500W small tank hot water heaters that could be converted to 1 propane water heater if required. That would save 3000W when they are both kicked on. We went with electric due to needing reliable instant hot water to pass inspections, and my buddy said he has been having issues with his propane tankless heater. We did have an extra access point put in the propane lines when they got installed tho.

I feared you have some pretty heavy loads. Hopefully the unit also reports a peak load.

Another thing I was wondering, if we eventually started building up a battery bank, I noticed the Victron multiplus ii says it can supplement a generator with battery power if the load required it, although I was kind of thinking that it was the other way around and the battery bank would be the main source with the generator supporting it as needed, so that the generator was not overloaded.

That's the power assist function, and it's to provide a boost to weak AC input, i.e., NOT your 12kW generator.

Anyway, I was wondering if it's possible to have the generator charging the batteries when power demand is low.

Yes.

So the idea right now that I'm forming is to first get the load balance deal sorted, get a proper reading on power usage, start vending, then as we get the money start phasing in a battery bank, possibly buying something like 2 8 cell banks, and then the other two later. Also figuring out what inverter we need to support all this along the way.

I imagine it will be much more nailed down when I get the power reading and go from there with the rest of it.

This.

When you actually get a handle on your energy requirements, I suspect the amount of solar, battery and inverters needed will be a pants-shitting moment on your part, and you will wonder how the off-grid power system can cost more than the trailer... At a SWAG, it will likely take you 7+ years to break-even in terms of fuel savings.