Sanity Check for Beginner Solar System

Hi All,

I've found these forums very useful, Will's videos have been great as well.

I wanted to post the system I'm in the process of building to see if I'm making any terrible mistakes.

The objective is to have a semi-portable build that will spend most of its time powering a home office in the backyard. Basically using system for backup power, may install in a remote cabin later. Kind of a hobby build to gain experience, and have back up power if the grid goes down. Might eventually install in a camper van if my wife lets me buy one...

Not going to tie into grid, but will use a budget all in one hybrid inverter:

I have a 12V 100ah SOK heated lifepo4:

Also picked up 4 Renogy 100W panels on sale:

Getting ready to put it all together and wondering about wire and fuse sizing.

If the inverter has 1500W capacity that would draw 125 amps, but I assume that would trip the max current out on the SOK BMS. Should I limit the fuse/breaker on the positive side to 100amps or below? If yes, then I assume a breaker would be preferable to a fuse as I might accidently run up on this limit powering the loads in the office (few lights around 100W, 500W video editing rig, starlink).

If I go with 50mm2 (awg 0) cable from battery to inverter/charger unti that should be large enough, I think

The AC charger seems to be able to push 80 amps into the battery, any concerns there if I use a 16 amp extension cord for AC in to inveter/charger? Idem for 50mm2 cable to battery for charging.

Lastly, the min V into the MPPT is 90V, each panel is rated to 24.3V Vo, if I put them in series will I have enought Volts in the real world? Not sure if I'll acheive the min voltage or need to add a panel or two?

Thanks for any input!

With regards to fuse for the output, what are your main house fuses rated at?

I'm in the UK, so the fuses I'm using are 63A in a normal fusebox bought from a DIY store. Same as what you would get in a UK main fusebox.

With regards to wiring from the battery to inverter, what do the instructions say? My 3Kw inverter says to use 35mm cable, 2AWG cable from battery to inverter.

With the panels, not sure with that one sorry. I think you would have to do 2 pairs of series, dont quote me on that tho.

Oh, the panels, just checked the specs, says can handle up to 2000W of solar or 450V open circuit. So I woud go parallel for panels ?

PV Array MPPT Voltage Range

90~430Vdc

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4x 100w panels are going to give you less than 80v under load, you'll never charge the batteries. It's also not a lot of power to fill up your batteries. Have you checked PVWatts for your area and looked at how much sunlight you can reasonably expect to get? You're going to need more panels to even get it to work, much less catch up the battery bank.

Any reason you're going with a super cheap AIO, cheap panels, and really expen$ive batteries? You'll want at LEAST 2 batteries to feed the draw that AIO can pull.

I really wish they made a 120v version of that unit, 1Kw is just a little undersized for my needs but 24v requires some weird wiring to keep my 12v bus working.

StuartV said:

With regards to fuse for the output, what are your main house fuses rated at?

I'm in the UK, so the fuses I'm using are 63A in a normal fusebox bought from a DIY store. Same as what you would get in a UK main fusebox.

With regards to wiring from the battery to inverter, what do the instructions say? My 3Kw inverter says to use 35mm cable, 2AWG cable from battery to inverter.

With the panels, not sure with that one sorry. I think you would have to do 2 pairs of series, dont quote me on that tho.

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Thanks I went with 25mm2 and not heating at 90A output.

StuartV said:

Oh, the panels, just checked the specs, says can handle up to 2000W of solar or 450V open circuit. So I woud go parallel for panels ?

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Wired in series to get to the min voltage of 90V

Long story on the choice of equipment, but its a kind of slippery slope of decisions. In November I thought I'd setup a backup power/heat as we were facing the possibility of energy shortages in France over the winter. Our apartment is all electric, no wood stove or gas. To be sure the kiddies were warm and we had lights I started researching solutions. I settled on a 3KW diesel heater that ran on 12V. I could pipe in the hot air easily, and the unit works great.


Mounted it in a cheat ski cargo roof box so I can also heat my SUV in case I want to sleep overnight in the car (also do some backcountry skiing in the alps here). Its super hot even on lowest settings, it only pulls less than 1 amp after startup.


The first battery I bought was a nightmare fake 200Ah, which in testing with dummy load worked out to about 50 actual Ah, sent it back to China (LOTL brand - do not buy). After that experience I just wanted something I could rely on, SOK in EU is only 630e, where the cheapest 100ah with bluetooth was about 450 due to Ukraine and energy shortages. Really happy with the battery and app.

Later, I thought why not also setup a small solar system and use it to power my home office and possibly mount on the ski box/future van build. Hence the AIO and cheap solar panels designed for camper vans.

Might use the same solar setup to power a starlink mounted on my roofrack and telework from the road in the summer... That's why I settled on 400W of solar power in compact format, as that's all I can fit on the roof of my car. However, I will add at least 200 more watts now.

FYI, where I live we have 2725 annual solar hours so about 7.5 per day on average. Not too shabby.

I built the system yesterday and have some issues:

1. Solar reads 93V on multimeter and AIO unit (partially cloudy). Panels in series, but 0 amps, 0 watts, PV icon is blinking....Basically its not charging the battery. I tried all three priority modes but no dice. I suppose technically it should be putting out some watts/amps into the battery but nothing…

2. When I hook up my main PC to a video projector via HDMI the signal is totally scrambled. Perhaps issues with sine wave quality? Modified instead of Pure? Whats really odd is that once the signal is past the power unit on the computer its changed to DC, so shouldn’t be an issue. It happens even if projector is on grid power and PC is on AIO.

3. Installed a 80A breaker to protect the BMS, as the inverter could draw too much power inadvertently. However, this one does not work: https://www.amazon.fr/dp/B09WKCKPM2?psc=1&ref=ppx_yo2ov_dt_b_product_details

I pulled 90A continuously and it never tripped, went past 100 and the BMS cutoff

SlickWIlly said:

1. Solar reads 93V on multimeter and AIO unit (partially cloudy). Panels in series, but 0 amps, 0 watts, PV icon is blinking....Basically its not charging the battery. I tried all three priority modes but no dice. I suppose technically it should be putting out some watts/amps into the battery but nothing…

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Yep, as @Rednecktek said in his post, you don't have enough voltage to drive your AIO unit, your panels have a 20.4V operating voltage, times 4 is 81.6V at best. You are measuring the VoC voltage, ie no load so it is higher. You need atleast one more panel in series to drive the AIO.

SlickWIlly said:

2. When I hook up my main PC to a video projector via HDMI the signal is totally scrambled. Perhaps issues with sine wave quality? Modified instead of Pure? Whats really odd is that once the signal is past the power unit on the computer its changed to DC, so shouldn’t be an issue. It happens even if projector is on grid power and PC is on AIO.

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Most likely the inverter, it is a cheap model with known issues. Could be grounding issue, hard to tell.

SlickWIlly said:

3. Installed a 80A breaker to protect the BMS, as the inverter could draw too much power inadvertently. However, this one does not work: https://www.amazon.fr/dp/B09WKCKPM2?psc=1&ref=ppx_yo2ov_dt_b_product_details

I pulled 90A continuously and it never tripped, went past 100 and the BMS cutoff

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Those style breakers are notoriously bad, they either trip at too low a current or even worse at too high a current.

When it comes to sizing breakers/fuses you are protecting your cables, you went with 2awg so can easily just use a 125A or even 150A breaker, you can trust your BMS overcurrent protection to not fry itself, that's what it's there for, you don't need to protect it, just your cabling. Use a DIN rail mount MCB like a Tomzn, make sure it is bi-directional as you have current flowing in both directions, charging and discharging. I use their 125A DC breaker which is bi-directional.

Here a shot of the screen showing 93V, min voltage is 90V

ShaneC said:

Yep, as @Rednecktek said in his post, you don't have enough voltage to drive your AIO unit, your panels have a 20.4V operating voltage, times 4 is 81.6V at best. You are measuring the VoC voltage, ie no load so it is higher. You need atleast one more panel in series to drive the AIO.

Most likely the inverter, it is a cheap model with known issues. Could be grounding issue, hard to tell.

Those style breakers are notoriously bad, they either trip at too low a current or even worse at too high a current.

When it comes to sizing breakers/fuses you are protecting your cables, you went with 2awg so can easily just use a 125A or even 150A breaker, you can trust your BMS overcurrent protection to not fry itself, that's what it's there for, you don't need to protect it, just your cabling. Use a DIN rail mount MCB like a Tomzn, make sure it is bi-directional as you have current flowing in both directions, charging and discharging. I use their 125A DC breaker which is bi-directional.

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Thanks, I'm going to add 2 more panels, will check out that breaker as well to protect the cable.

SlickWIlly said:

Thanks, I'm going to add 2 more panels, will check out that breaker as well to protect the cable.

ShaneC said:

Yep, as @Rednecktek said in his post, you don't have enough voltage to drive your AIO unit, your panels have a 20.4V operating voltage, times 4 is 81.6V at best. You are measuring the VoC voltage, ie no load so it is higher. You need atleast one more panel in series to drive the AIO.

Most likely the inverter, it is a cheap model with known issues. Could be grounding issue, hard to tell.

Those style breakers are notoriously bad, they either trip at too low a current or even worse at too high a current.

When it comes to sizing breakers/fuses you are protecting your cables, you went with 2awg so can easily just use a 125A or even 150A breaker, you can trust your BMS overcurrent protection to not fry itself, that's what it's there for, you don't need to protect it, just your cabling. Use a DIN rail mount MCB like a Tomzn, make sure it is bi-directional as you have current flowing in both directions, charging and discharging. I use their 125A DC breaker which is bi-directional.

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Is this the correct breaker you were referring to:

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SlickWIlly said:

TOMZN 1P DC circuit breakers MCB. Values from 3A to 125A **Shipped from UK** | eBay

Find many great new & used options and get the best deals for TOMZN 1P DC circuit breakers MCB. Values from 3A to 125A **Shipped from UK** at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

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ShaneC said:

Most likely the inverter, it is a cheap model with known issues. Could be grounding issue, hard to tell.

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Thanks @ShaneC, it was a grounding issue, all working fine now! You guys are a great help on this forum!

SlickWIlly said:

Thanks @ShaneC, it was a grounding issue, all working fine now! You guys are a great help on this forum!

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Ah good to hear, how did you fix it?

ShaneC said:

Ah good to hear, how did you fix it?

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I realized that the only ground on the AIO system came from the the AC input. I was testing the unit on battery power only to see how long I could run my office setup....plugged AC into the wall and issue solved.

New additional panels should arrive tomorrow so will finally be able to test with actual solar power!