Cart of Death, or Cart of Life - Full Breakdown - Pre-Build Advice

[CodeJP3]

I’m about to build a hand-cart variation of the typical tiny house/jobsite trailer power stations. Looking for input from some of you seasoned pros first. #1 priority is fire and electrocution safety.


PURPOSE:
I live in Florida, and we have lost power for days or weeks at a time due to weather such as hurricanes and tornadoes. I’m basically aiming for the output and capabilities of a permanent house setup, for my large APARTMENT, where nothing can be permanent. Every option I’ve seen that could work is tens of thousands more than I want to spend. So, one day, I put a little too much sugar in my coffee, and next thing I know, there’s a few thousand dollars worth of stuff showing up at my door with the grand idea that I would MAKE what I needed, on a budget.

That’s where we are. I have the bulk of the stuff, but want your input on wiring and some of the components before I put it all together and apply power for the first time.

We need to be able to power 2 mid-size refrigerators, an standalone single-room A/C unit, box fans, lights, and the occasional cooking appliance (even a 1000W microwave). Ideally all at one time, without having to juggle plugged-in devices to manage the load. Est 300W low, 500-1000W avg, peaks upwards of 2500W or more. ...and we want some overhead to be able to grow and use more than that if needed. It’s an emergency power station to be able to live very comfortably for the days or weeks we don’t have power. It’s not just comfort. It’s also for health reasons such as powering healthcare devices, having a climate-controlled room, and keeping medicine cold. It’s also intended to be portable so that basically everything is self-contained, and we wheel it out when it’s needed and roll it out of the way when not needed. It’s closer to what many of you are doing with mobile job-site trailers and off-grid tiny houses than the other 2 or 3 much smaller cart projects I’ve seen on here.


BASIC DESIGN:
Back in the late 90’s and early 2000’s, I installed mobile electronics in vehicles as a profession. I’m going to treat this thing like it was custom RV panels being made using MDF and carpet, just like I would have back then. All components will be mounted to the MDF boards, and the boards will be mounted into/onto the service cart.

The cart will not only house the heavy batteries and all of the electronic components, but also have protective storage built-in for the solar panels when they’re not being used, and have storage for all the wires/adapters/accessories for this mobile emergency power station.

Generators will be stored separately outside, but other than that, it’s intended to be EVERYTHING, all-in-one, safe, with secure hard-mounted components, and portable, so there’s very little down-time and zero fuss pulling it out and setting it up when those emergencies arise.


MAIN COMPONENTS:
1.) PowMr (generic) All-in-one Charger/Inverter 120VAC In/Out, 80A MPPT Charger, 3500W Inverter, 48VDC
https://www.amazon.com/gp/product/B08HYHSD8G

2.) x4 Weize 12V 100Ah Deep Cycle AGM SLA VRLA Batteries (in series, 48V)
https://www.amazon.com/gp/product/B07SW353M8

3.) x4 Newpowa 120W 24V Solar Panels (Pmax: 120W, Vmp: 34.0V, Imp: 3.52A)
https://www.amazon.com/gp/product/B07H4HS7QM

4.) x2 Predator 2000 Generators (1600W continuous) with parallel kit (3200W continuous)
https://www.harborfreight.com/2000-watt-super-quiet-inverter-generator-62523.html

5.) Harbor Freight 450 lb capacity 24”x36” Service Cart
https://www.harborfreight.com/24-in-x-36-in-two-shelf-steel-service-cart-62587.html


It will be so much easier and clearer if I just share my tentative diagrams...and even easier if I break it down per-system. So here we go (many more posts coming).

 

[CodeJP3]

1. 48V DC IN/OUT

First a comment on the mounting of the batteries. I didn’t draw it up, but I will be making a battery tray from the same ½” MDF and carpeted. A single tray with 1” spacer between each battery (for breathing). Each individual battery area is 14.5”x7.5” (to accommodate larger batteries later) and individually lined with acid-safe mat material. The total size is 31”x17”. That leaves room for wiring and small storage in the bottom of the 36”x24” cart. Batteries will be individually strapped and bolted through the tray to the cart (in the event of tip-over).

Questions here deal with wire gauge, the optional extra display/alarm, and a capacitor.

a.) Is roughly 5-6 ft of 2/0 AWG acceptable (#4 in the diagram)? Doing the initial calculations, I figured 4 AWG would be OK, 2 AWG would be ideal for handling medium/full loads for extended periods of time, so, of course I goofed and ordered 2/0 AWG instead of 2 AWG. Besides the unnecessary slight added resistance and voltage drop, are there significant issues with 2/0 AWG? Am I OK with it or should I just return it and get 2 AWG?

b.) Is the extra display/alarm worth purchasing? The PowMr AIO controller has (visual) alarm for over-charge, but nothing listed for low-voltage (hitting that 20% capacity threshold that kills batteries), and certainly nothing at all for temperature. Since the batteries are the most common wearable item, I kinda want to maximize their life any way possible. Knowing low-voltage and over-temp conditions seems like critical pieces of information to have, and having audio/visual warnings is a major bonus. It’s also safety-related since the batteries are indoors, in living-spaces. Agree or disagree? Is this little display unit worth the $10-12 that I think it is? Or am I wasting money on it (budget build)?
https://www.amazon.com/gp/product/B08FDVSDJW

c.) I’ve had good luck using capacitors before, in line with the battery (typical hi-amp amplifier install in a car). I’m considering adding a single capacitor in-between the batteries (#5 in diagram) and the cutoff switch (#3 in diagram). These deep cycle batteries do great with steady loads for long periods, but they hate the quick bursts and spikes that a lot of AC equipment does at initial power-on. The cap would simply “smooth it out” by taking the brunt of those spikes (which they do very well). We’re trying to save battery life wherever possible, and this is one method I know of. Is it worth the cost of a supercap, or is it a waste of money (budget build)?

 

[CodeJP3]

2. PV DC IN

First a comment that the panels will not be grounded. They will only be setup in emergency situations, manually laid-out and picked back up when done being used, and will never see inclement weather.

Questions here deal with protection for over-voltage, and the optional display.

a.) Is there a safety measure I can take against over-voltage? The unit lists “over-voltage” protection, but it’s really ambiguous and unclear if it’s for batteries, AC IN/OUT, PV IN, all of the above, or only some of the above, or who really knows?!?!? I’m specifically concerned with the “Horrible Sun” setup in the diagram above. In the event that the sun pops out instantly and at optimum conditions, we could accidentally send more voltage to the controller than its’ listed max range. Will the unit protect itself, or am I on the right track of looking for a separate way to prevent over-voltage on the PV side?

b.) Is the optional display unit worth purchasing? Since the setup will vary based on each use, each time, it makes sense to me to have a large voltage display to see quickly the current PV voltage. The #1 complaint about the unit is the tiny single built-in display used for everything. This is a nicer way to track that important charge voltage. Especially if a.) above requires manually keeping an eye on voltage to prevent over-voltage conditions, and for trying to pick the right setup for that day to stay within MPPT range. Agree or disagree? Is this unit worth the $15-20 it costs like I think it is, or is it a waste of money (budget build)?
https://www.amazon.com/gp/product/B07W7XXKVF

 

[CodeJP3]

3. 120V AC INa.) Only real question I have is about better protecting this side of the system. I’ve been quite surprised at how many wall outlets, power strips, and extension cords I’ve found that tested as incorrectly wired, but still worked fine for most devices. As a good practice, this unit should not be plugged in to any outlet that hasn’t been tested with one of those 3-light plug-in testers. But….things happen (especially in emergencies), and not everyone is gonna know to do that. The controller unit lists “360 deg all-round protection with a number of protection functions, including short circuit protection, over-voltage and under-voltage protection, overload protection, reverse protection, etc.”, but what exactly does that translate to in actual use? Will this thing protect itself no matter what bad outlets/conditions I plug it into for AC input side?

 

[CodeJP3]

4. 120V AC OUT

Questions here deal with the circuit layouts and the optional Watt / kiloWatthour displays.

a.) Either option looks pretty standard. Is one better than the other for performance/safety reasons?

b.) Also unsure about the GFCI/AFCI outlets in the first option. This is for emergency uses, which may involve plugging in power tools like drills, saws, and other brush-motor devices. For that reason I’m thinking 1 GFCI & 1 GFCI/AFCI combo unit. I’m also wondering if the extra $20 for a GFCI/AFCI combo unit is worth it in the first place (budget build)?

c.) Is the optional Watt / kiloWattHour display worth it? The PowMr controller has a max output of 3500W split to 2 ~2400W circuits. We can use a total of 3500W, but only up to ~2400W per circuit. Being able to instantly see the current Watt usage per circuit seems like essential information to me. Otherwise it’s playing a guessing game based on specs and estimates without actually knowing. Agree or disagree? Are these displays worth the $30-40 total it will cost for 2 of them like I think it will be? Or are they a waste of money (budget build)?
https://www.amazon.com/gp/product/B01MRZAFAF

 

[CodeJP3]

5. Grounding


Posting the questions from the picture here for search/SEO reasons:

a.) Unit has “Grounding Screw Hole”. My understanding is that the unit is internally grounded and does not need this for my specific setup and use-case. Correct me if I am wrong, but this would be used if I wanted to tie grounds (generator/panels) to a single point. Since generators are grounded separately, panels are not grounded at all, and nothing else needs grounding, it would NOT be used. Correct?

b.) Since I don’t really have any way to ground the batteries to the cart, and the cart to ground, I’m skipping grounding the batteries altogether. If I could figure out a good method to route cables from outside to inside my apartment, I could use a new ground rod and ground the negative that way. Otherwise, they’ll be perfectly fine un-grounded. Correct?

 

[CodeJP3]

6. Solar Panel Storage

My original idea was to mount the panels to the sides of the cart, 2 per side. But when all the items started arriving and I could see it all in person, it became clear that we really don’t want to go much (if any) wider than the cart’s 24”. That way it still fits through all the doorways and hallway perfectly fine.

That made me get creative with other ideas to build UP instead of OUT.

a.) For those who have broken panels or stored panels for long periods - is one approach better than the other? What’s best for the panels to prevent damage and maximize life on a rolling cart storage system like this?

 

[CodeJP3]

I think that about does it. We want a “cart of life” from all of this, not a “cart of death”. Your input is Needed and Valued, specifically for my questions, but really about ANY aspect of this build.

...and if it wasn’t clear, this isn’t a general concept topic - I’m ready to start building!

 

[macheung]

The concept would work but needs to be scaled up to do what you want.

The batteries you have would be sufficient to power the inverter but would not last nearly long enough over the night until the sun shines again. AGM lead acid batteries should only be discharged to no lower than 50% if you want them to last, so you really have only 2kwh of batteries. If you are running 500-1000w average, then you will need enough panels to generate 3x of that and battery to store the charge overnight for 16hr until the sun shines brightly. I estimate maybe around 8kWh of LiFePO4 battery with around 1800W of panels would be required for average 500W load.

 

[CodeJP3]

The concept would work but needs to be scaled up to do what you want.

The batteries you have would be sufficient to power the inverter but would not last nearly long enough over the night until the sun shines again. AGM lead acid batteries should only be discharged to no longer than 50% if you want them to last, so you really have only 2kwh of batteries. If you are running 500-1000w average, then you will need enough panels to generate 2-3x of that and battery to store the charge overnight for 16hr until the sun shines brightly. I estimate maybe around 8kWh of LiFePO4 battery with around 1800W of panels would be required for average 500W load.

Generator(s) are the primary power source. The solar panels are only to help cut down on the overall total generator use. Whatever the panels charge each day is great, however small it may be. Generators will take care of the rest. kWh usage at night will be far less than during the day so I'm not worried about draining the batteries. The cost of just the batteries you mentioned is far more than the cost of this entire build, so maybe one day....but not now. Also, increasing the panel size and quantity to produce 1800W from the current 120W/240W is not practical or realistic for cost and storage reasons of something that will very rarely be used.

Thanks for the input!

 

[macheung]

Got it, if you are using gen set primarily then it would work. Though note that in the eve of a hurricane and such, gasoline may be hard to come by if the power is also out as stations cannot pump. In any case, consider LiFePO4 batteries instead as the can be drained to almost 0% and you will need less of them. I would consider using some larger solar panels, potentially 2 x full sized 300-350W units.

 

[CodeJP3]

gasoline may be hard to come by if the power is also out as stations cannot pump.

I have enough gas cans to run 1 generator 24/7 for a week and a half. I may get more as well. They're always full and every few months I use it in the car and refill them fresh again.

In any case, consider LiFePO4 batteries instead as the can be drained to almost 0% and you will need less of them. I would consider using some larger solar panels, potentially 2 x full sized

LiFePO4 batteries are on my wishlist for when this first set dies has to be replaced. It was just too much for a budget build all at once.

We have very limited options for placing solar panels at my apartment, and everything has to be temporarily setup and tore down for each use. I would love to bump up the solar charging, but that may have to wait until we move from here to a place with better panel placement options.

Both important points, and noted as future upgrades.

 

[labeeman]

I also live in a Hurricane area and I had to use my generator last year it had not been used for 20+ years Your batteries have to be kept charged ALL the time as they will sulfate and go bad not a good choice even if it was too save money.

 

[CodeJP3]

I also live in a Hurricane area and I had to use my generator last year it had not been used for 20+ years

Our area has poor grid power. There's typically brief outages most heavy rains or winds. In the past 5 years alone, I could think of a handful of times I wished we had this system together and functional, or at least a generator.

As a former mechanic, I can't stress enough the importance on maintaining the fluids in your generator, especially prior to first startup after it's been in storage for 20+ years. Good ones will outlive you if you take care of the basics.

Your batteries have to be kept charged ALL the time as they will sulfate and go bad not a good choice even if it was too save money.

I was unsure if I wanted to use the All-In-One unit to maintain the batteries, or get a separate "battery tender" for that one and only task. I settled on using the built-in features of the unit. It will be plugged into a wall outlet and maintaining batteries 24/7. I actually plan to have a small load on it as well (maybe both fridges with an estimated combined 36Ah usage within a 24hr period [1.5Ah/180Wh avg per hour]). The unit should have zero issues supplying that power and taking care of the batteries too.

 

[CodeJP3]

Thanks everyone for the input so far! Here's a recap of the current unanswered questions I have before I start building. I left out the opinion pieces regarding the optional displays and extra items:

48V DC In/Out:
a.) Is roughly 5-6 ft of 2/0 AWG acceptable (#4 in the diagram)? Doing the initial calculations, I figured 4 AWG would be OK, 2 AWG would be ideal for handling medium/full loads for extended periods of time, so, of course I goofed and ordered 2/0 AWG instead of 2 AWG. Besides the unnecessary slight added resistance and voltage drop, are there significant issues with 2/0 AWG? Am I OK with it or should I just return it and get 2 AWG?

PV DC In:
a.) Is there a safety measure I can take against over-voltage? The unit lists “over-voltage” protection, but it’s really ambiguous and unclear if it’s for batteries, AC IN/OUT, PV IN, all of the above, or only some of the above, or who really knows?!?!? I’m specifically concerned with the “Horrible Sun” setup in the diagram above. In the event that the sun pops out instantly and at optimum conditions, we could accidentally send more voltage to the controller than its’ listed max range. Will the unit protect itself, or am I on the right track of looking for a separate way to prevent over-voltage on the PV side?

120V AC In:
a.) Only real question I have is about better protecting this side of the system. I’ve been quite surprised at how many wall outlets, power strips, and extension cords I’ve found that tested as incorrectly wired, but still worked fine for most devices. As a good practice, this unit should not be plugged in to any outlet that hasn’t been tested with one of those 3-light plug-in testers. But….things happen (especially in emergencies), and not everyone is gonna know to do that. The controller unit lists “360 deg all-round protection with a number of protection functions, including short circuit protection, over-voltage and under-voltage protection, overload protection, reverse protection, etc.”, but what exactly does that translate to in actual use? Will this thing protect itself no matter what bad outlets/conditions I plug it into for AC input side?

120V AC Out:
a.) Either option looks pretty standard. Is one better than the other for performance/safety reasons?

Grounding:
a.) Unit has “Grounding Screw Hole”. My understanding is that the unit is internally grounded and does not need this for my specific setup and use-case. Correct me if I am wrong, but this would be used if I wanted to tie grounds (generator/panels) to a single point. Since generators are grounded separately, panels are not grounded at all, and nothing else needs grounding, it would NOT be used. Correct?

b.) Since I don’t really have any way to ground the batteries to the cart, and the cart to ground, I’m skipping grounding the batteries altogether. If I could figure out a good method to route cables from outside to inside my apartment, I could use a new ground rod and ground the negative that way. Otherwise, they’ll be perfectly fine un-grounded. Correct?

Panel Storage:
a.) For those who have broken panels or stored panels for long periods - is one approach better than the other? What’s best for the panels to prevent damage and maximize life on a rolling cart storage system like this?

General:
Besides my specific questions, do youse anything blantantly wrong with my wiring (besides the 25A server cable to 30A breaker on a 40A circuit)?

 

[Diysolar123]

as an FYI I use harbor freight three shelf carts to make my powerwalls with.
The bottom two shelves each hold a 24vx280Ah battery pack made from eight cells in a compression frame; I set the JBD bms units to 250Ah capacity each so thats 500Ah in total available.
The "equipment wall" is 3/4plywood mounted on the side of the cart (I thought about cement board but decided against it). Its simple, does not take up much space, can be wheeled around, and is easy to teardown and work on parts if needed.
Here is a pict of the powerwall (most of the shielding off), the battery, BMS units, and active balancers are attached to battery pack on the lower shelves.
The top shelf is where a raspbery pi sits which handles chatting with the smart shunt, JBD BMS units and mpp solar ( i use serial for everything no bluetooth) and upload all the data to an mqtt server. I have the mppsolar set to charge at 27.2V, with the active balancer cell variance is always under 10mv.

 

[Boondock Saint]

Every time I see the title of this thread it reminds me of the Lone Wolf and Cub Baby Cart movie series.


.

 

[CodeJP3]

as an FYI I use harbor freight three shelf carts to make my powerwalls with.

With the 48V SLA AGM storage and plans to integrate solar panel storage into the cart, I needed the larger size and they only had 2-shelf. Believe me, I looked at those too and wish I had a third shelf, but they are slightly smaller length/width and just wouldn't work for my purposes. Sounds perfect for yours!

The top shelf is where a raspbery pi sits which handles chatting with the smart shunt, JBD BMS units and mpp solar and upload all the data to an mqtt server.

I've been hoping to do something like this as well. Data port communication seems to be unclear/undocumented for this particular unit, so that'll be down the road. A "maybe one day" fantasy I have is to get a basic LCD display and program it to display what I specifically care about, and audio alarm for unfavorable conditions. Basically replacing every optional display from my diagrams and making a custom all-in-one display specifically for this cart.

Every time I see the title of this thread it reminds me of the Lone Wolf and Cub Baby Cart movie series.

Well now, THAT image will forever be stuck in my head now! Perhaps we just found a theme for this thing

 

[CodeJP3]

So the cart will use these power sources, in this priority order:

Power Working
1.) Grid main power: handles battery float & small inverter load at all times

Power NOT Working
2.) Solar as priority to get what whatever small amount we can with our panels
3.) Generator as priority for heavy loads, and to take care of what solar falls short on
4.) 2000W inverter hooked up to a car battery while car is running as an absolute last-case backup

That makes 3/4 options involve pluging into a traditional 3-prong female outlet.
Q?: Who else is doing something similar, and what are you using to accomplish this?

I know this is really a solar-first kinda community, but this is really my first big solar endeavor and has to be done within the limitations of apartment life, making it impossible to use solar-first as my main charge. Gotta start somewhere

 

[Millicurie]

Hey man, nice set up! I am relatively new to solar although I set up a smaller system for my off grid cottage to power CPAP, small fridge and lights. It works great so far but I am impressed with what you got here.

But I am curious how this all turned out over the past year?

I recently purchased an SRNE all in one charger/mppt/inverter and want to power an AC with it (Midea windows AC pulls a max 311 watts and averages 180 watts over 5 hours). Long term, I would beef up the system once we build a separate cottage on the property.

But I am struggling how to safely install plugs on the AC out. I found a couple of videos including Will’s power cart which was super helpful. I think Will just directly wired a female plug into his AC out. But I have seen other videos that point out a breaker or GFCI outlet should be used for additional safety. It sounds like having a small AC breaker (like 15 AMP) then into a 3 prong female plug would work and offer protection.

However, the SRNE unit has protection built into the AC out, so I am not even sure a breaker is needed. By the way, SRNE is the original company but many others rebrand them (e.g. Renogy, RIch Solar, DIY Midnight Solar line for example).

So if you have any relevant experience from that point of view, it would be great. i am also curious how you made out!

Too bad you didn’t get many comments on this thread last year. Pretty interesting and valuable set up for folks who need emergency power or have unreliable sources.