My DIY 3kw trolley backup system

[Winston1990]

For anyone interested I thought I'd share my standalone 3kw backup system build.

I had a Mecer 1440w/2400va modified sine wave inverter with 2x deep cycle batteries that were around 9 months old. I work from home full time and used it to power my laptop and occasionally TV/PC. I knew that I would need a new solution as the deep cycle batteries were not going to last forever and cost almost R6k each time to replace, and I wanted something which is pure sine wave so I can run my fridge if need be and a fan in the evenings due to the heat.

I did not want to connect it to my DB and go through the costs of installation, COC etc as I will probably be out of this place within the next year. So, I decided to build myself a standalone trolley backup system.

Components:

• 3kw Must 60A MPPT inverter 24v
• 2.56kw Must 100ah LiFePO4 24v battery (4,000 cycles)
• 125A DC fuse disconnectors
• 16A AC circuit breaker (Input)
• 30KA Surge Protective Device (Input)
• 25A Earth Leakage (Output)
• Onesto ready DB
• 25 sq mm battery cables
• All other wiring 2.5 mm
• 2x200ah battery cabinet

A lot of advise I received on another forum to keep the build legit and as safe as possible. Worked out a lot cheaper to do the build myself than buying a similar ready built system, and this system is solar ready or can be charged via a generator. I completed the build today and herewith the end result:

 

[maq_]

For anyone interested I thought I'd share my standalone 3kw backup system build.

I had a Mecer 1440w/2400va modified sine wave inverter with 2x deep cycle batteries that were around 9 months old. I work from home full time and used it to power my laptop and occasionally TV/PC. I knew that I would need a new solution as the deep cycle batteries were not going to last forever and cost almost R6k each time to replace, and I wanted something which is pure sine wave so I can run my fridge if need be and a fan in the evenings due to the heat.

I did not want to connect it to my DB and go through the costs of installation, COC etc as I will probably be out of this place within the next year. So, I decided to build myself a standalone trolley backup system.

Components:

• 3kw Must 60A MPPT inverter 24v
• 2.56kw Must 100ah LiFePO4 24v battery (4,000 cycles)
• 125A DC fuse disconnectors
• 16A AC circuit breaker (Input)
• 30KA Surge Protective Device (Input)
• 25A Earth Leakage (Output)
• Onesto ready DB
• 25 sq mm battery cables
• All other wiring 2.5 mm
• 2x200ah battery cabinet

A lot of advise I received on another forum to keep the build legit and as safe as possible. Worked out a lot cheaper to do the build myself than buying a similar ready built system, and this system is solar ready or can be charged via a generator. I completed the build today and herewith the end result:

What was the cost of this system

 

[Winston1990]

Around R25k - R25.5k

 

[ForestGump]

which fuses did you get?
most of the <R100 cheapies in SA (unbranded chinese kak) are a bad idea

I built a very similar diy system to you after looking at prices of pre-built

 

[Winston1990]

which fuses did you get?
most of the <R100 cheapies in SA (unbranded chinese kak) are a bad idea

I built a very similar diy system to you after looking at prices of pre-built

According to the inverter manual you require 125A fuses or a DC breaker. I got 125A ONESTO fuses from Lite-Glo in Randburg.

 

[DampStranger]

Sorry to hijack your thread, I have a prebuilt similar to this and when I got it, it would last hours and power anything I threw at it, now I'm lucky to get 30mins, it got 2 new batteries(not lithium) 9months ago and I'm wondering if it's possible I killed them? I got it 3months ago 2nd hand and powered 2 PCs and a fridge during loadshedding for about a month before it started goin downhill,now all it can power 1 pc for 30min.Rentech battery box

 

[lowracer]

Sorry to hijack your thread, I have a prebuilt similar to this and when I got it, it would last hours and power anything I threw at it, now I'm lucky to get 30mins, it got 2 new batteries(not lithium) 9months ago and I'm wondering if it's possible I killed them? I got it 3months ago 2nd hand and powered 2 PCs and a fridge during loadshedding for about a month before it started goin downhill,now all it can power 1 pc for 30min.Rentech battery box

Yeah. you did.

the problem with non- lithium (lead acid, gel, etc) batteries is that you diminish the capacity if you discharge it more than 50%. and if you had a double shift (4 hours) or two double shifts (because of say stage 6), the batteries didnt fully charge fully before the next loadshedding cycle.

temperature is something else, as most summer temps run opver 25 degrees. not completely sure how much that fucks them up either.

 

[DampStranger]

Thanks for the quick reply, well I guess I've learnt an expensive lesson then.

 

[ettiene]

Very good that you have included fuses and breakers. Some don't even bother.

But like they say the devil is in the details.
You must make sure what is the DC rating of the fuses. It's not the same as the AC rating.
You state that it's a 25A earth leakage, thats probably only the maximum amps it can handle, but its not a circuit breaker. Thus you need a circuit breaker as well to protect against overload. Inverter output is about 13A, so something close or better lower than that. Like a 10A double pole.
Does the earthleakage actually work when on battery? Can't test this with the button on it. Need a plug in tester to test it.

Lastly
Lifepo4 batteries over a certain size isn't allowed in a occupied area. So it means it must be behind a 2 hour firewall like in a garage. It's seems that the size limit is 1kwh according to the clever people.

 

[Qui_Illustrati]

Lastly
Lifepo4 batteries over a certain size isn't allowed in a occupied area. So it means it must be behind a 2 hour firewall like in a garage. It's seems that the size limit is 1kwh according to the clever people.

Huh?

 

[Winston1990]

Very good that you have included fuses and breakers. Some don't even bother.

But like they say the devil is in the details.
You must make sure what is the DC rating of the fuses. It's not the same as the AC rating.
You state that it's a 25A earth leakage, thats probably only the maximum amps it can handle, but its not a circuit breaker. Thus you need a circuit breaker as well to protect against overload. Inverter output is about 13A, so something close or better lower than that. Like a 10A double pole.
Does the earthleakage actually work when on battery? Can't test this with the button on it. Need a plug in tester to test it.

Lastly
Lifepo4 batteries over a certain size isn't allowed in a occupied area. So it means it must be behind a 2 hour firewall like in a garage. It's seems that the size limit is 1kwh according to the clever people.

Hi Ettiene,

Haven't been on the forum for a while.

DC fuses are Onesto 125A - 125A is what the inverter manual recommends.

With regards to the 10A 2P circuit breaker you recommend - is this wired before or after the earth leakage? Just a normal 2P 10A circuit breaker?

Thanks for the tip - the 25A earth leakage I currently have does not have overload protection.

So far the system has been running well and has helped me a lot in prolonged outages (fridge, internet, laptop, charging a phone etc).