Small scale household backup system

TheChamp said:
The calculator does agree with 125mm, is it mm or mm2?

DC Cable Sizing Tool - Use The Correct Sized Cables - Free Calculator

Use our free cable-sizing tool to establish the correct size of cable for your DC power system cables. This is especially important for low voltage, high current systems.
www.solar-wind.co.uk www.solar-wind.co.uk
Click to expand...

Simple cable thickness is also not to be trusted... as it also depends on the internal strand sizes vs solid copper.

^ why "rated for" is a better bet than oh this is thick enough.
 
TheChamp said:
I don't understand mm, I understand current ratings and mm will automatically fall into place. 3kW, if it's truly 3kW and not 2.4kW(perhaps that's where the conflicting sizes stems from) will be 125A, maybe you will understand which mm corresponds to that, I suspect 25mm?

The DC breaker is straight forward positive pole and negative.
Click to expand...
IMG-20220516-WA0014.jpeg
20220516_151700.jpg
 
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Iwojima said:
View attachment 1309710
View attachment 1309712
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Perhaps they recommend 35mm to cater for the peak power draw? I see the inverter is capable for 2 times the rated power draw for 5 seconds, that is the only reason I can think of because otherwise 25mm should be adequate.

Anyway I would advise you to ignore that and just work on the basis that 3kW is the max power draw because no one should have any business drawing more than what the inverter is rated for, the batteries will probably not handle that anyway.

If I were in your position I would limit the draw to what the battery is rated for and ignore the inverter rating for now, unless you trust the BMS to do the job, I don't trust internal protection of either the battery or the inverter. Revisit the setup again if you add another battery that can handle the full 3kW.

For now, 25mm cable or you can oversize if you want to, but put a 100A isolator, assuming you are using Hubble s120. The inverter will still be good for its rated power running on AC but Wil be limited to what the battery can offer when running as backup.
 
A good thread on why both Breaker and Fuse is good, on that site i'm banned from :)

energytalk.co.za

CoCT Battery DC isolater

Huge humangus difference with AC, because it pass 0VAC multiple times a second (100x) for SA the arc will very quickly die out as the contacts distance increase. No such luck with high current DC, even at 50V. Arcing and burning happens fast. DC disconnects and breakers are specially designed...
energytalk.co.za energytalk.co.za
 
TheChamp said:
Perhaps they recommend 35mm to cater for the peak power draw? I see the inverter is capable for 2 times the rated power draw for 5 seconds, that is the only reason I can think of because otherwise 25mm should be adequate.

Anyway I would advise you to ignore that and just work on the basis that 3kW is the max power draw because no one should have any business drawing more than what the inverter is rated for, the batteries will probably not handle that anyway.

If I were in your position I would limit the draw to what the battery is rated for and ignore the inverter rating for now, unless you trust the BMS to do the job, I don't trust internal protection of either the battery or the inverter. Revisit the setup again if you add another battery that can handle the full 3kW.

For now, 25mm cable or you can oversize if you want to, but put a 100A isolator, assuming you are using Hubble s120. The inverter will still be good for its rated power running on AC but Wil be limited to what the battery can offer when running as backup.
Click to expand...
Cheers. I'm going to order the 160A version of the isolator @itareanlnotani linked earlier for ease of disconnect.

Then I'm going to add the inline fuse to protect cable. Likely a 100A fuse with the 25mm cable.
 
itareanlnotani said:
Yes, both is good to have, otherwise disconnecting/connecting can be "fun".

DC Breaker so you can disconnect / reconnect safely.
Fuse so that you can protect in case of short or too much current draw.


I have one of these for mine (DC on / off) -
powerforum-store.co.za

KETO Battery Disconnector with 160A Fuses

Add robust and secure battery disconnection with the Keto range from Jean Müller. They are well known for their attention to detail in ensuring maximum user safety.KETO size 00Maximum DC current = 160ADC voltage rating: 440VOverall width: 106mm System size: 195mmTerminals: M8 lugs with cable...
powerforum-store.co.za
Click to expand...
Any idea how long these guys take to generate a quote? Been waiting a bit longer than 24hrs
 
itareanlnotani said:
A good thread on why both Breaker and Fuse is good, on that site i'm banned from :)

energytalk.co.za

CoCT Battery DC isolater

Huge humangus difference with AC, because it pass 0VAC multiple times a second (100x) for SA the arc will very quickly die out as the contacts distance increase. No such luck with high current DC, even at 50V. Arcing and burning happens fast. DC disconnects and breakers are specially designed...
energytalk.co.za energytalk.co.za
Click to expand...
Banned?
:D
Iwojima said:
Any idea how long these guys take to generate a quote? Been waiting a bit longer than 24hrs
Click to expand...
Did you make contact telephonically, or just fill in the web form? Always better to do the former.
 
itareanlnotani said:
A good thread on why both Breaker and Fuse is good, on that site i'm banned from :)

energytalk.co.za

CoCT Battery DC isolater

Huge humangus difference with AC, because it pass 0VAC multiple times a second (100x) for SA the arc will very quickly die out as the contacts distance increase. No such luck with high current DC, even at 50V. Arcing and burning happens fast. DC disconnects and breakers are specially designed...
energytalk.co.za energytalk.co.za
Click to expand...
Banned? :p For doing what?
 
Did you make contact telephonically, or just fill in the web form? Always better to do the former.
Click to expand...
Web form.

Thanks for the tip. I'll give them a call tomorrow morning.

Failing which Geewiz has the same thing in 125A "flavour" for a grand, but with free shipping.
 
Iwojima said:
Cheers. I'm going to order the 160A version of the isolator @itareanlnotani linked earlier for ease of disconnect.

Then I'm going to add the inline fuse to protect cable. Likely a 100A fuse with the 25mm cable.
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NB - The Jean Mullers are a fused disconnect.
i.e. you have a disconnect, and a fuse in that single device.

Switchable fuse holders are not considered “on-load” disconnecting devices, so only switch on/off when under “no-load”.

My suggestion would be that it wouldn't hurt to have an isolator switch as well for extra precaution. Do read that thread I linked.

Don't forget your PV also will need a disconnect so you can turn that off too.


In most instances, a safe procedure to disconnect batteries is as follows:
• Disconnect and isolate the load from the inverter (where applicable) • Power down the inverter (where applicable)
• Disconnect and isolate the AC grid from the inverter
• Disconnect and isolate the solar panel from the inverter
• Disconnect the batteries using the battery disconnect device
 
itareanlnotani said:
For not fawning over a certain someones customer install, and pointing out the shading issues present.
Click to expand...
LOL.
What tickles me is that certain someone seems to be collecting these bork ups with alarming regularity, quite contrary to his rep in the eyes of laypeople. We all have a lot to learn, but some more than others it seems.
 
RonSwanson said:
LOL.
What tickles me is that certain someone seems to be collecting these bork ups with alarming regularity, quite contrary to his rep in the eyes of laypeople. We all have a lot to learn, but some more than others it seems.
Click to expand...
I haven't really gone back to look. It's also been a while now since the "split" between the forums and people migrating to energytalk. I still pop my head in at PowerForum (most recently documenting reverse engineering and writing a driver for the TianpowerBMS for my Revov), but mostly I give my 2cents here.
 
While I'm waiting for my DC bits to arrive my mind has now switched to monitoring.

I see the inverter comes with cables to monitor via USB/serial while connected to a PC.

Is anyone aware of any 3rd party unit that communicates with the inverter comms port and exposes the data over WiFi to say Home Assistant as an eg?
 
Iwojima said:
While I'm waiting for my DC bits to arrive my mind has now switched to monitoring.

I see the inverter comes with cables to monitor via USB/serial while connected to a PC.

Is anyone aware of any 3rd party unit that communicates with the inverter comms port and exposes the data over WiFi to say Home Assistant as an eg?
Click to expand...
PI and roll your own?

Or ESP32 or ESP8266 and some custom code.

Thats also assuming your Mecer inverter can actually provide useful data over serial. Does the manual at least have some detail on serial commands?
 
itareanlnotani said:
PI and roll your own?

Or ESP32 or ESP8266 and some custom code.

Thats also assuming your Mecer inverter can actually provide useful data over serial. Does the manual at least have some detail on serial commands?
Click to expand...
Nothing documented in the manual sadly, but after posting the above a quick Google revealed that there are some Pi based and bespoke devices out there for Axpert type inverters to do the type of monitoring or remote config that would be a nice to have, but nothing with some form of API to expose raw data to something like HA.
 
Iwojima said:
Web form.

Thanks for the tip. I'll give them a call tomorrow morning.

Failing which Geewiz has the same thing in 125A "flavour" for a grand, but with free shipping.
Click to expand...
Should have gone with Geewiz...

Contantly needing to chase up to get the order moving along.

With Geewiz I could have banked on getting it before weekend and having the time to put everything together over the weekend.
 
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