Overkill Solar or Electrodacus SBMS for 12v 4s?

[Devin82m]

Hey everyone, I was curious what you would suggest for as 12v system I plan on building soon. I'm going to make it like Will's hand truck generator setup, but 12v for now. I will use it to power my home office in case of emergencies. But I am confused as to why Will used the Electrodacus instead of the Overkill Solar BMS. I really like the features of the Electrodacus, but I'm not sure if the inverter/charge controller shutoff will work for my Midnight Solar Kid charge controller, or my 1500 watt Samlex Inverter. I want to use my existing charge controller and inverter since I bought them in a solar package. Eventually I will build a full solar power system for my whole house using Victron gear.

Can anyone make any suggestions or provide advice? Thanks!

 

[snoobler]

Overkill is a simple solution with lots of flexibility, but it might be too limiting on current - 120A

Electrodacus seems more like a "tinkerer's" solution and requires a compatible inverter for LVD.

 

[Devin82m]

Would I really need more than 120A for a 12 v system and a 1500 Watt inverter? If so, do you suggest another quality programmable BMS?

 

[snoobler]

12V * 120A = 1440W

It really depends on how you're using it. Overkill has stated that their BMS is rated for a 100% duty cycle, i.e., run forever at 120A if you have to. It is also surge tolerant with a programmable delay before disconnect.

The call is yours. The system has the potential to overwhelm the BMS if the inverter has a good surge rating, and you use items that have high surge for several seconds.

I've recently purchased the 100A 24V unit for use with a 24V/3000 Multiplus. It's rare that it will use more than 2400W, but it might briefly. I'm not concerned about it.

 

[Devin82m]

It looks like the Samlex can do up to 3000 Watt surges. Nothing in my office, including my inject printer won't do anything that high. I have a space heater under the desk, but know enough not to use it on a 12v battery system. I just need to run two laptops, two monitor, Router, and modem/radio power supply (we use point to point wireless for our internet connection using a small dish/radio). So I imagine all that should be well within 1500 watts. I would like to eventually expand it to 24v system which my charge controller is capable of doing, but I guess I will have to upgrade to a new inverter after.

It's not good to say "it's up to you" to me because I still don't know what I am doing ultimately. :-D If you think it would be safer to go with a BMS rated for more current then please let me know and give suggestions.

Anyway, any specific suggestions are welcome.

 

[snoobler]

I mean you know your loads better than me...

I see
100W/laptop+monitor
30W Router
30W modem
?W radio

160W + radio.

1000W space heater might be fine.

I recently purchased some very small 500W space heaters for "opportunistic" solar harvesting at the ranch. If my battery is full, and it's just floating, I'll fire them up to grab some extra heat with the free solar. One of these little buggers can heat the very small "bedroom" in the fifth wheel to a surprising degree.

 

[Bob142]

I've done this to one of my Overkill Solar 12V 120A BMSes and it's still going strong. It's such a simple to install and effective BMS and my loads are generally way below the 120A, I just happened to surge over that for a bit several weeks ago. I haven't thought about it or worried about it since then until this thread popped up. I recommend it.

 

[Devin82m]

I've done this to one of my Overkill Solar 12V 120A BMSes and it's still going strong. It's such a simple to install and effective BMS and my loads are generally way below the 120A, I just happened to surge over that for a bit several weeks ago. I haven't thought about it or worried about it since then until this thread popped up. I recommend it.

View attachment 31010

I mean you know your loads better than me...

I see
100W/laptop+monitor
30W Router
30W modem
?W radio

160W + radio.

1000W space heater might be fine.

I recently purchased some very small 500W space heaters for "opportunistic" solar harvesting at the ranch. If my battery is full, and it's just floating, I'll fire them up to grab some extra heat with the free solar. One of these little buggers can heat the very small "bedroom" in the fifth wheel to a surprising degree.

OK, for now I think the 12v system with the Overkill BMS will probably suffice. I can't use the space heater because it's a 1500 watt space heater, but I may have to look into those little 500 watt ones. Surprisingly that space heater is pretty small, but man I forgot how many watts it used, I live in a mid 90s manufactured home and have one room as my home office.

Thanks for sharing your experience Bob142, it helps.

I also forget that I have 12v panels (not setup yet), which limit what voltages I am running at too from my understanding.

 

[snoobler]

Heater:

https://www.amazon.com/gp/product/B074MX8VN5 it's a creeper. It feel like it's not doing much, but it gets surprisingly warm and does a very good job of not heating the case much. In 5 minutes, you realize it's working better than you thought.

12V panels aren't the limitation. The charge controller is. Your MPPT KID has 12, 24, 36 and 48V options for batteries with 150V max solar PV voltage.

Your 12V panels can be connected in series for higher voltages to charge higher voltage batteries.

1-6 in series for 12V
2-6 in series for 24V
4-6 in series for 48V

You can then parallel additional strings of panels for a larger array.

The limiting factor is the KID's 30A charge current;

30A * 14.4V = 432W (12V)
30A * 28.8V = 864W (24V)
30A * 57.6V = 1728W (48V)

The actual numbers may vary as those are just based on typical peak charging voltages for those batteries.

12 to 24V will definitely require a new inverter.

 

[Devin82m]

So if I understand it right, for now the KID cc will work with 4 our of the 5 panels I have. But once I move over to 48v I will need all new stuff, which at that point I will just go with Victron gear for everything. So the 12v 100 Ah battery and the rest of the gear I have should work for that little hand truck setup for my home office should suffice? I want to get my feet wet and learn more before moving on to a 48v for the house, not to mention money is another consideration.

 

[snoobler]

The kid will work with any battery config.

It will still work with 5 of the panels, but you will be over-paneled. This is pretty common. This means that your peak will be clipped off, but you'll deliver the peak power the KID allows for as long as a 500W array would deliver that maximum (longer than a 400W array would). There are some

You may be able to use the panels and the KID for a 48V system, but you may find it more practical to replace everything. You can also have multiple SCC on the same battery without issue, so the KID might also have a supplemental use if you want to increase your array or use the KID with your old panels on the new system.

There's a sizer:

MidNite Solar - KID Sizing Tool.

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

www.midnitesolar.com

I input parameters typical for a 100W panel (yours might vary slightly). It indicates 1.2 KIDs would be required. That appears to be the limit of their over-paneling requirements.

 

[Devin82m]

I don't know much about the other settings, but in my case my panels are 315 watts each, the only number I could find in the specs on that list was the VOC, so this is what it said.



The panels are 315 Watt REC TwinPeak2.

 

[snoobler]

Label on back has all the info. Using:

https://www.solarelectricsupply.com/fileuploader/download/download/?d=0&file=custom%2Fupload%2FREC-TwinPeak-2-Mono-solar-panel-datasheet.pdf

315W
39.9 Voc
33.9 Vmp
10.05 Isc
9.36 Imp

You've put all 5 panels in series, and the Voc can't exceed 150V, so you'll need to do 5 in parallel. HOWEVER, at 12V, you're way over their overpaneling recommendation of 1.2, so at 12V, you could realistically only use 1. 2 might work, but it goes against their recommendations.

 

[Devin82m]

So what does 1.2 mean? Every you explaining all that I feel stupid asking. How many panels would you suggest?

 

[snoobler]

1.2 means the array power is 1.2X what the KID can apply to the battery with its 30A limit. They simply define it as 1.2 KIDs to handle the array power in my example. They indicate another KID should be added when more then 1.2 KIDs are required.

This implies the KID can handle being "over-paneled" by 20%.

 

[Devin82m]

Ah, OK, I was wondering. But if I did 5 in parallel wouldn't that be over 30 Amps? They have a nominal current of 9.36 Amps each right? Even 4 in parallel would be over the current limit by 7 Amps.

Should I do 2 panels in parallel connected in series with another parallel set? If I understand correctly (which I may not) that would come out to:

79.8 V
18.72 A

 

[snoobler]

You have to factor all 3. Voltage, current and power.

I recommend you put your two panels in that calculator, and you'll likely find that 2 of them - in series or parallel - Will likely require more than 1.2 KIDs - closer to 1.5 (for 12V). Your calculation use 48V, so I'm talking apples and you're talking oranges.