Need help with cables and bms for 8s 24v

[Lostchild]

Hi this is my first attempt on building a solar power system. I started off learning with 12v and recently changed to 24v and my head is all tangled up. Just looking for simple directions or formula when it comes to buying parts.
Im putting the battery/inverter and solar charger in a tool box so Im not expecting cables longer than 2 feet.
My battery is a 100ah DIY 8s 24v and I'll be using a1500w 12v/24v/48v capable inverter and building for 24v use with 12v backward compatibility in case shit hits the fan and I have to break down the 24v to 12v. I might actually make another build with 12v.
This set up is intended for back up power when the grid goes down powering mini fridge, tv lights and on occasion, microwave/rice cooker.

I was thinking of using 4gauge on everything just to make it simple and cheaper for myself, would that work? (considering 1AWG will be needed for battery terminal cable for 12v)
For fuses what is slo-blo fuses for?
fuse@battery 80a/150a
@Solar charger not sure what to do here. fuse/breaker and will it be 15a/30a?

8s 24v BMS: should I be looking for BMS amp rating that matches the inverter? Same port/separate port?
Overkill is on backorder.
Not sure where I can find one that can be delivered quick

Im open to suggestions and short answers. Anything is better than nothing cuz building has become more stressful than I expected.
Thx

 

[Northernchateau]

My suggestion is KISS keep It Simple Stupid
Run 24volts don't mess around with 12volts.
Size wire and breakers/fuse according to max amps needed.

Wire Sizing Chart for 12V/24V/48V DC Systems - DIY Solar Resources

Information on wire sizing and a universal AWG/mm2 wire sizing chart to help in designing a 12V, 24V, or 48V DC renewable energy system.

www.altestore.com

 

[Diysolar123]

I just bought a large amount of 1awg copper welding cable and use it for everything when I started making packs...
make sure to buy some copper crimp lugs to go with your cable (buy a couple bags of lugs with various size holes so you can attach to whatever you need)
harbor freight sells a "cheap" hydraulic crimper thats not that bad...for the money..

when figuring out "run time" remember to focus on watthours...
24V 100Ah battery means you have at MOST 2400Wh of power from the battery, you will not drain your battery dead and you will probably need to pull 20% more power from your battery for any load...so...

usable battery capacity 90% = 2400*0.9 = 2160Wh
eqipment load * 1.2 = battery load

almost everyone ends up running out of battery much sooner than they thought

the overkill BMS is a value added reseller of the JBD BMS which can be found...
You want a BMS that is matched to your battery, that is what the BMS is for, to protect the battery.
Make sure to get a "smart" BMS that you can program and get info from; the dumb units are cheaper but can be quite frustrating to use.
Your BMS/battery should be sized to provide the maximum your inverter "could" demand.

 

[Zwy]

Hi this is my first attempt on building a solar power system. I started off learning with 12v and recently changed to 24v and my head is all tangled up. Just looking for simple directions or formula when it comes to buying parts.
Im putting the battery/inverter and solar charger in a tool box so Im not expecting cables longer than 2 feet.
My battery is a 100ah DIY 8s 24v and I'll be using a1500w 12v/24v/48v capable inverter and building for 24v use with 12v backward compatibility in case shit hits the fan and I have to break down the 24v to 12v. I might actually make another build with 12v.
This set up is intended for back up power when the grid goes down powering mini fridge, tv lights and on occasion, microwave/rice cooker.

I was thinking of using 4gauge on everything just to make it simple and cheaper for myself, would that work? (considering 1AWG will be needed for battery terminal cable for 12v)
For fuses what is slo-blo fuses for?
fuse@battery 80a/150a
@Solar charger not sure what to do here. fuse/breaker and will it be 15a/30a?

8s 24v BMS: should I be looking for BMS amp rating that matches the inverter? Same port/separate port?
Overkill is on backorder.
Not sure where I can find one that can be delivered quick

Im open to suggestions and short answers. Anything is better than nothing cuz building has become more stressful than I expected.
Thx

I can say even though Overkill was backordered on BMS's when I ordered a few, they arrived within a month. You want to order and pay for them and Steve will ship quickly when he gets them in.

 

[MisterSandals]

This set up is intended for back up power when the grid goes down powering mini fridge, tv lights and on occasion, microwave/rice cooker.

Thats all pretty reasonable. Your microwave might not run on a 1500W inverter. The microwave rating is for cooking power, not the watts consumed.
You should do an energy audit with your planned use of these things to get a feel for how much power you need to produce, store and also convert to AC.

 

[Lostchild]

thx for the replies.
when it comes to inverter and battery, i initially planned for 1000w and 100ah 12v. my mindset was to have something rather than nothing but at this point ive gone beyond my budget and i just want it done.
its amazing how i found myself learning about prices by simply going big rather than going small because in the end you spend the same amount but when you go bigger u actually get more from it.

i wish i could have someone just buy everything for me and ill just put it together. just too much work trying to find it all and the fact that i dont know exactly what i should be getting makes it more difficult

 

[Lostchild]

slo blow fuse or regular fuse?
while doing some research i found this video informative. regarding breaker

 

[MisterSandals]

i wish i could have someone just buy everything for me and ill just put it together. just too much work trying to find it all and the fact that i dont know exactly what i should be getting makes it more difficult

You'll be better off knowing what you are doing. As they say, "Good judgement comes from experience and experience comes from poor judgement".

Good luck. Sounds like you know what you are doing and proceeding reasonably.

My emergency battery (solar charged) and inverter are "extension cord ready". My fridge and freezer are one extension cord away. I think I could talk my wife thru it over the phone if i had to.

So you can go as elaborate or as simple as you like.

 

[Lostchild]

You'll be better off knowing what you are doing. As they say, "Good judgement comes from experience and experience comes from poor judgement".

Good luck. Sounds like you know what you are doing and proceeding reasonably.

My emergency battery (solar charged) and inverter are "extension cord ready". My fridge and freezer are one extension cord away. I think I could talk my wife thru it over the phone if i had to.

So you can go as elaborate or as simple as you like.

yeah i know what you're saying. I'd just like a shortcut at this point. Seems like every week has been a focus on a certain area and this week is about wires and fuses.
Its a good thing I took more time on inverters, because I had bought my inverter before I decided to go 24v. I chose one that can be used for 12v 24v and 48v

 

[Diysolar123]

i wish i could have someone just buy everything for me and ill just put it together. just too much work trying to find it all and the fact that i dont know exactly what i should be getting makes it more difficult

you most certainly can buy entire systems all put together...and they even come with a warranty.
The prices are, well, quite impressive however.

 

[MisterSandals]

you most certainly can buy entire systems all put together...and they even come with a warranty.
The prices are, well, quite impressive however.

Just a little curious what such a system would look like and cost. It does not sound like your typical Amazon or Renogy kit.

 

[Lostchild]

i need an answer here./
1500w/24x1.25=78amps is this the correct fuse at the battery? 75-80amps?

 

[MisterSandals]

i need an answer here./
1500w/24x1.25=78amps is this the correct fuse at the battery? 75-80amps?

Looks pretty good. Is the inverter the only draw on this line?

 

[Lostchild]

I just bought a large amount of 1awg copper welding cable and use it for everything when I started making packs...
make sure to buy some copper crimp lugs to go with your cable (buy a couple bags of lugs with various size holes so you can attach to whatever you need)
harbor freight sells a "cheap" hydraulic crimper thats not that bad...for the money..

when figuring out "run time" remember to focus on watthours...
24V 100Ah battery means you have at MOST 2400Wh of power from the battery, you will not drain your battery dead and you will probably need to pull 20% more power from your battery for any load...so...

usable battery capacity 90% = 2400*0.9 = 2160Wh
eqipment load * 1.2 = battery load

almost everyone ends up running out of battery much sooner than they thought

the overkill BMS is a value added reseller of the JBD BMS which can be found...
You want a BMS that is matched to your battery, that is what the BMS is for, to protect the battery.
Make sure to get a "smart" BMS that you can program and get info from; the dumb units are cheaper but can be quite frustrating to use.
Your BMS/battery should be sized to provide the maximum your inverter "could" demand.

When it comes to lugs should i look for copper or tinned copper lugs?
As for BMS, I ordered the Overkill 8s 24v 100a w/usb. My cells and its wiring are capable of 1c.
Im not too familiar with how much appliances draw. In the back of my microwave it says: input 1050w, output 700w and 8.75amps. So with 120v x 8.75a= 1050w does that mean the microwave would reach 1050w max including surge or start up power?

 

[Lostchild]

Looks pretty good. Is the inverter the only draw on this line?

Im still working on the plan. I was thinking of adding a usb outlet and a service light onto the box. However that would mean Id have to spend a bit more on a 12v converter and fuse block etc. Im considering a workaround by using a powerbar with builtin usb outs. That actually sounds better with the advantage of a few more outlets since the inverter only has 2.

 

[Steve_S]

I'm 24V Offgrid so I can share a few numbers with you.
Panasonic 1200W Inverter Microwave pulls 75A on full power.
Oster Coffee Maker (no warmer plate, thermal carafe) pulls 48A for 6 minutes brewtime.
For a 12V system, those numbers are doubled and for a 48V they are halved.

BTW: The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling).
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)

 

[Lostchild]

I'm 24V Offgrid so I can share a few numbers with you.
Panasonic 1200W Inverter Microwave pulls 75A on full power.
Oster Coffee Maker (no warmer plate, thermal carafe) pulls 48A for 6 minutes brewtime.
For a 12V system, those numbers are doubled and for a 48V they are halved.

BTW: The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling).
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)

I think im missing something here, I don't understand the 75a. I thought most appliances are 15-20amps max.

 

[Zwy]

I'm 24V Offgrid so I can share a few numbers with you.
Panasonic 1200W Inverter Microwave pulls 75A on full power.
Oster Coffee Maker (no warmer plate, thermal carafe) pulls 48A for 6 minutes brewtime.
For a 12V system, those numbers are doubled and for a 48V they are halved.

BTW: The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling).
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)

You can add roof air on my TC which draws 50 amps on 24V. Right in line with the 1200w AC it says in the book.

 

[Steve_S]

That is what the Inverter is pulling from the 24V Battery Bank to power said device at 120VAC.
My system allows me to watch the Volts, Amps, Watts going through my gear. That let's me see what things are using from the battery bank.

The second set of number there is what an inverter at XX volts pulling 250A will output in AC Amps.
IE: 24V@250A=6000W or 50A VAC. That 50A can be 120VAC/50A or 240VAC/25A .
This is also UNCORRECTED for Inverter losses. Tier-1 are typically 92-95% efficent, Tier-2 88-92% while Tier-3 / Value gear is usually 82-88% efficient.