Off-grid tool shed in California

[Walkir]

I am designing an off-grid solar system for my tool shed.
I have a few power tools:

• https://www.homedepot.com/p/DEWALT-...le-Saw-with-Rolling-Stand-DWE7491RS/204512007
• https://www.homedepot.com/p/TR-Industrial-13-Amp-35-lbs-Demolition-Jack-Hammer-TR89305/305929405
• https://www.homedepot.com/p/DEWALT-...de-Wrench-and-Material-Clamp-DWS779/321488482
• https://www.homedepot.com/p/RIDGID-...Locking-Hose-and-Accessories-HD1800/304795088
• https://www.harborfreight.com/air-t...-hand-carry-jobsite-air-compressor-56829.html

+ Makita battery charger
+ LED lights

I never use more than two tools at the same time, but the compressor might be running for a few hours while I'm working on other things. Usually, I work a few hours every other day.

So far I decided to buy:

2*200Ah 12V batteries from Renogy:
https://www.renogy.com/deep-cycle-agm-battery-12-volt-200ah/
400W 12V off-grid solar kit from Renogy with 2*200W panels:
https://www.renogy.com/renogy-400w-12v-general-off-grid-solar-kit/
XYZ INVT 4000 Watt Pure Sine Wave Inverter:
https://www.amazon.com/XYZ-INVT-Inverter-Converter-System/
EQ 125 Amp 4-Space 8-Circuit Load Center
https://www.homedepot.com/p/Siemens-EQ-125-Amp-4-Space-8-Circuit-Main-Lug-Surface-Mount-Indoor-Load-Center

2*30A + 1*10A Siemens circuit breakers + GFCI receptacles, LAD lights, 10 AWG wire for receptacles, 14 AWG wire for the lights, 8 AWG wire between the Load Center and the inverter, grounding rod, cerrowire

I have 0 AWG wire to connect the inverter and batteries and 2 AWG to connect the batteries with each other.

I have doubts about the inverter, from my math, it looks like to run 2*15A tools at the same time I need 3600W, but how is it in practice, maybe I will be fine with 3000W Pure sine grom Renogy?
Also, it is very hard to find an inverter with GFCI or one that allows L and G bounding. Since I am using GFCI receptacles I am not so worried about it but it is always nice to have an additional layer of protection.

Unfortunately, price is the issue so I cannot afford a full-blown LFP system at the time, and already everything above costs me more than the materials for building the tool shed itself.

Any advice, suggestions, or criticism is highly appreciated.

 

[sunshine_eggo]

Your inverters need to handle the surge of any electric motors, which can easily be 5X the run current. Saws are particularly brutal. Most lightweight inverters can't handle the surge.

I would not expect that unit to handle surge reliably - maybe one tool at a time, but with one running and the surge of a second... probably not.

While this might be overkill:

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120/240V split phase 6kW with 18kW surge. It's also very inexpensive.

A big downside is it gulps juice just being on... about 120W.

 

[Walkir]

So I put everything together and started testing the system, it looks like my tools are hitting hard the battery with high current, so I am considering stepping up with the voltage to 24v

 

[hwy17]

What is happening? If it's shutting off it's probably the inverter not the batteries.

 

[Walkir]

The voltage both on the battery and the inverter is going down rapidly and then it shuts off.

 

[Partimewages]

Do you know what state of charge your batteries are?

 

[Hedges]

Does it start and run the motor, then shut off?
Or voltage drops without motor starting?
Those AGM batteries (if charged) should really deliver surge. like 5kW, 10kW or so. According to listing, 2000A (probably at 8V), so two of them 32kW for 5 seconds (but below low-voltage cutout.) Probably 18kW at 10V or 11V.

Do you know what state of charge your batteries are?

This must be the problem, if battery voltage drops too low (dropping from no-load voltage is expected.)

 

[Walkir]

Batteries were at 88% when I started testing the system with the sun already being low and only 1A charging current.

 

[Walkir]

And yes, motor started for few seconds and then inverter shut off everything

 

[Partimewages]

Batteries were at 88% when I started testing the system with the sun already being low and only 1A charging current.

How is the 88% measured?

 

[Hedges]

If 88% SoC, should be able to deliver multiple kW from the 2x 200Ah batteries, for maybe 1.2 kWh.

AGM, no BMS to get in the way. Possibilities are battery voltage dropped low, inverter quit due to heating/load, or large voltage drop across wires (check that with a meter while operating.)

You've got either 12V 400 Ah, or 24V 200 Ah, I'm not sure which.
I've got 48V 400 Ah, can run 5kW or 10kW space heater for a while. Start and run central A/C, etc.

Try charging batteries fully, to appropriate voltage plus absorption time.

 

[Walkir]

How is the 88% measured?

This is what my charge controllers shows

 

[Partimewages]

This is what my charge controllers shows

Probably going to need to figure out how this is being figured. If it's by voltage it's likely very inaccurate.

 

[Hedges]

Read the battery manual, see what no-load voltage is 100% SoC.
If charger is configurable, set its voltages and times according to manual.
Disconnect all loads, let battery charge until full. Disconnect charger, wait about 8 hours, then check voltage.

Check cable size, and connections.

Repeat load test after confirming you've got a fully charged battery.

 

[Walkir]

Read the battery manual, see what no-load voltage is 100% SoC.
If charger is configurable, set its voltages and times according to manual.
Disconnect all loads, let battery charge until full. Disconnect charger, wait about 8 hours, then check voltage.

Check cable size, and connections.

Repeat load test after confirming you've got a fully charged battery.

ok I will try that, thank you

 

[Walkir]

Probably going to need to figure out how this is being figured. If it's by voltage it's likely very inaccurate.

yes it must be by voltage, and it is jumping all over the place when I am operating anything

 

[Partimewages]

yes it must be by voltage, and it is jumping all over the place when I am operating anything

That's a sign that it's not been charged to 100%

 

[sunshine_eggo]

yes it must be by voltage, and it is jumping all over the place when I am operating anything

It is a completely useless number. It should be ignored at all times.

 

[Walkir]

So I did more testing, this time as you advised on fully charged batteries and it looks like all works fine. I can run more tools and the voltage doesn't drop below 12.3v shortly after the start even under full load.

Thank you for all your suggestions and help