Newbie 24V Setup Review - Craigslist Special

[hereforthefreecoffee]

Hi all,

New to the DIY solar world and looking for a system review with a few questions. I recently purchased the inverter, charge controller, batteries, and panels from Craigslist and am purchasing the rest of the wiring, fuses, PDBs, etc. new.

The goal for this system is to siphon off some of my electrical needs to reduce my overall monthly costs: office, portable air conditioner, extra refrigerator, etc.

Here are the main components I've purchased already used.

• Panels: 8 REC 250W
• Inverter: Sigineer 3000W 24V 120V
• Charge Controller: Outback FlexMax FM80
• Batteries: 3 Beckett Lithium Ion (not Lifepo4) 3 x 24V at 40ah.

Questions:

1. Grounding - when do I need a true earth ground with ground rod.
   1. If I use the AC input on the inverter, does this pull the ground from the house?
   2. If I do NOT use the AC input for the inverter, do I need the earth ground/rod?
2. Fuses - Am I missing any fuses or safety mechanisms?
3. General mistakes - I've looked at a lot of videos and common newb mistakes and I think I've over engineered and over wired everything based on the component manual recommendations.
   1. The panels are over for voltage recommendations but they are used from a solar farm so they are not going to be hitting the max.
4. Calculations - does anything look funky for the calculations or unsafe?

Here is the diagram I came up with with details.


Thanks!

 

[Mattb4]

Just a quick couple of things. Your solar panel's Voc adds up to being higher than the max allowed by the SCC. Does not matter that they are old solar farm panels. There is every chance you could damage your SCC on over voltage. Your solar panel amperage is the sum of 8.27a per series string which adds to 16.54a in your diagram. So long as the distance between panels and SCC is 40ft 10awg wire is more than enough and potentially 12 awg would work (40ft run for voltage drop calculation brings up just under 3% drop).

Also I have a few concerns about your lithium ion batteries. First is whether the SCC is suitable for charging this chemistry type. The other is the potential fire hazard from using them. Most folks use LiFePO4 for safety aspects in a solar setup.

 

[hereforthefreecoffee]

Just a quick couple of things. Your solar panel's Voc adds up to being higher than the max allowed by the SCC. Does not matter that they are old solar farm panels. There is every chance you could damage your SCC on over voltage. Your solar panel amperage is the sum of 8.27a per series string which adds to 16.54a in your diagram. So long as the distance between panels and SCC is 40ft 10awg wire is more than enough and potentially 12 awg would work (40ft run for voltage drop calculation brings up just under 3% drop).

Also I have a few concerns about your lithium ion batteries. First is whether the SCC is suitable for charging this chemistry type. The other is the potential fire hazard from using them. Most folks use LiFePO4 for safety aspects in a solar setup.

Hi @Mattb4, thanks for the quick reply. The PV cable I purchased is 40FT so at 3% drop, doesn't that bring me down under 150 to around 146 and in safe parameters?

As for the SCC, there are a few articles and videos about the FM80 being able to charge Lithium Ion batteries, it does not have default settings but should work by adjusting the absorption, float, and eq. This system was being used by another person without issue (not that, that means he was doing it correctly) but I'm not in a place to purchase LiFePO4 at the moment even though that would be ideal. I also know lithium ion is more dangerous than other chemistries but these came as part of the package deal so I was hoping to use them and ensure they are in a cement board box or enclosure.

Do you think I should rethink the whole set up based on the lack of default li-ion settings on the SCC and the fire risk?

One last note - the batteries have a BMS and this is the company statement: "the internal battery management system measures the temperature, voltage and current of the module, ensures that individual cells in the module remain in balance, and will disconnect the lithium-ion battery if any conditions reach a fault state. State of charge is visible via an LED indicator, or can be communicated via serial data stream to a higher level control."

 

[Doggydogworld]

Hi @Mattb4, thanks for the quick reply. The PV cable I purchased is 40FT so at 3% drop, doesn't that bring me down under 150 to around 146 and in safe parameters?

Voc increases in cold temps. At 0C / 32F you'll be around 160V. Voltage drop in your wires doesn't help. There isn't any current at Voc (by definition) so there isn't any I2R loss in the wires.

 

[MichaelK]

What are your winter low's like? At freezing, your solar string Voc will be ~165V. That will fry your controller. I would look around for one more panel, and then wire them 3S3P.

I have to agree, the batteries are not the best choice. I would replace them.

The ground rod should be wired into your main electrical panel, and the inverter connected to ground there.

 

[hereforthefreecoffee]

Voc increases in cold temps. At 0C / 32F you'll be around 160V. Voltage drop in your wires doesn't help. There isn't any current at Voc (by definition) so there isn't any I2R loss in the wires.

@Doggydogworld Thank you and understood. Located in Southern California so very rare freezing but I will reconfigure to ensure I'm well below 150.

 

[hereforthefreecoffee]

What are your winter low's like? At freezing, your solar string Voc will be ~165V. That will fry your controller. I would look around for one more panel, and then wire them 3S3P.

I have to agree, the batteries are not the best choice. I would replace them.

The ground rod should be wired into your main electrical panel, and the inverter connected to ground there.

@MichaelK Thanks for the reply. Sounds good about the 3S3P, I should be able to make that work.

If I connect the AC in on the Inverter, does that count as the ground to the panel?

Thanks for the thoughts on the batteries too.

 

[MichaelK]

If I connect the AC in on the Inverter, does that count as the ground to the panel?

Can't say. My inverter has a specific hard-wire terminal that goes to ground. Can your inverter be hard-wired or does it only have NEMA plugs on the front?

BTW, I also have a house in Southern California, and I definately do see frost here. BUT, freezing was just an easy to recognize example. Since the Voc at 25C is already right at 150V, even a very cool morning will bump up the voltage to a destructive level. Here is a string calculator I like to use that will accurately predict your Voc at whatever temperature you plug in. A four-panel string will exceed 150V even above freezing.

MidNite Solar - Classic Sizing Tool.

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.

www.midnitesolar.com

 

[MichaelK]

Found the installation manual for your inverter. Yes, it has a dedicated grounding terminal. A green wire would run from the ground terminal on the inverter to the grounding buss-bar in your main electrical panel. That ground wire should be at least 8 gauge. The primary grounding electrode wire, the one that connects the buss-bar to the ground rod, should be at least 6 gauge for 100A service.

 

[Mattb4]

Hi @Mattb4, thanks for the quick reply. The PV cable I purchased is 40FT so at 3% drop, doesn't that bring me down under 150 to around 146 and in safe parameters?

As for the SCC, there are a few articles and videos about the FM80 being able to charge Lithium Ion batteries, it does not have default settings but should work by adjusting the absorption, float, and eq. This system was being used by another person without issue (not that, that means he was doing it correctly) but I'm not in a place to purchase LiFePO4 at the moment even though that would be ideal. I also know lithium ion is more dangerous than other chemistries but these came as part of the package deal so I was hoping to use them and ensure they are in a cement board box or enclosure.

Do you think I should rethink the whole set up based on the lack of default li-ion settings on the SCC and the fire risk?

One last note - the batteries have a BMS and this is the company statement: "the internal battery management system measures the temperature, voltage and current of the module, ensures that individual cells in the module remain in balance, and will disconnect the lithium-ion battery if any conditions reach a fault state. State of charge is visible via an LED indicator, or can be communicated via serial data stream to a higher level control."

If the PV cable you bought is 8 awg your voltage drop is considerably less than the 12 awg I mention as possibly adequate. Voltage drop is compensated for by larger conductor and/or higher voltages.

I looked up the Beckett Li-ion batteries and they seem to be geared to military vehicle applications for energy storage. You would think anything put into military equipment was safe. Though it is hard to trust companies claims for things without some form of user experience.

 

[hereforthefreecoffee]

Thanks everyone for the input and feedback. Based on the comments, I have cleaned everything up a bit. I have not purchased the panels yet (everything else has been purchased) and the person I'm chatting with has some 240w panels that might be better for this so I can run 9 in 3S/3P as suggested with minimal over paneling and within safer voltage ranges.

@MichaelK - I've attached pictures of the Sigineer inverter. I think the one you looked up is different. There is a ground with the AC input/output and a dedicated ground on the opposite side with the main DC pos/neg input.

@Mattb4 I agree on the Beckett batteries - I would assume most military-grade products would be safer than most but I haven't seen a lot of people using them and the business closed that portion of operations. I'll still be cautious with them and ensure they are as fire proof as possible with plans to upgrade.

Any additional feedback is greatly appreciated.