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Essential loads challenges


Fazil

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Hi Guys

Question specially to those who have more experience than I have in solar market to date.

How do you overcome challenges of building essential ac load db when only 2 of the 3 plugs on a circuit will stay on grid and 1 on solar?

Also, what protection mechanism are you using to prevent ac overload on client side? This is particularly for the Mecer/Axpert brand? For example clients using a hairdryer whilst the kettle is boiling and microwave is on.

Thanks in advance.

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17 hours ago, Fazil said:

only 2 of the 3 plugs on a circuit will stay on grid and 1 on solar?

Hi Fazil

To my knowledge the entire circuit will have to be either on grid or solar, The best will be to split the 3x plugs up and make it into two circuits.

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17 hours ago, Fazil said:

For example clients using a hairdryer whilst the kettle is boiling and microwave is on.

The inverter will trip on overload if your load is higher than inverter output. Otherwise you need to install loadshed relays like Phil mentioned to switch off heavy loads while on inverter power.

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A load prioritizing relay wont allow power to cct. 2 on, if the chosen threshold on cct.1 is exceeded.

An MCB (or the inverter) will trip when the current draw is too high on any single cct.

My understanding of your original question is that you seek to prevent a tripping because of an accumulation of loads, not because of any one single load?

 

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6 hours ago, Fazil said:

items like hairdryers and lawnmowers and drills to the plugs which damage the relays.

I’m using a 5KVA Axpert and use two domestic type change over contactors in my DB. I can switch my critical loads alone to solar, or I can switch the entire house to solar. These are set on sonoff timers to come on during the day when pv is good.

The way my setup work is should someone switch on to many loads the inverter simply trips on overload and the system simply switches to grid without even noticing any interruption, Or sometimes in cloudy weather the battery’s low voltage will switch inverter off and automatically back to grid. This is done by the change over contactors. 

These contactors (Tomzn) are rated for such loads and I haven't had any problems so far.

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37 minutes ago, Fazil said:

nice

Where did you buy these contactors?

I ordered them on e-bay because I found that they are about 50% of the price you pay local. Electro-Mechanica also do the hager type which I think is quite good quality but more expensive, but they had no stock the time I wanted them.

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9 minutes ago, Fazil said:

lets say the inverter had an issue and needs repair, does the contactor switch to grid automatically and inverter can be removed without the need for a manual change over switch that most if not all of us install?

Yes, the inverter control the contactors, so if the inverter is faulty it cannot energize the contactors so then the contactors will drop out and grid comes on. But I do also have a manual changeover switch in parrallel over the contactors as a second backup for incase the contactors should fail.

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Hi @Gerrie

 

Thanks for the schematic.  I think you will also like this.

This guy with his own idea on how to design an ATS (Automatic Transfer Switch) - for safe fully automatic switching between two completely non synchronized power sources (PV and Grid), with priority input, wired on to Inverter that uses soft start, also watching on to too low and too high input voltages, plus taking care for safe transition in any direction and from any state ...  https://www.thebackshed.com/forum/ViewTopic.php?TID=9879

image.png.5e345ac53e932a266e6e020ab87fbcd1.png

 

It was designed to automatically switch all his home appliances between non synchronized PV (Off Grid inverter) and city Grid, with PV priority, that can be disabled by 2A breaker. He use/share common N (neutral) in his system, thus only L (live) is switched thru ATS.  the second design uses both neutral and live.image.png.e700b3f7249d3a41eb2e2770985a875e.png

 

He also uses TOMZ contactors.

 

 

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On 2019/10/14 at 10:40 PM, Fazil said:

manual change over switch that most if not all of us install?

In the beginning my system had only the manual change over switch, my plan was to save some money on Eskom bills, and have back up during load shedding, but I often forgot to flick the switch to solar before going to work and lost the benifit of solar during the day.

Thats when I decided to install the auto change over contactors controlled by a sonoff switch, to switch from where ever I am on that day. This was one of the best things I could do, that just added much satisfaction from a relativly cheap system. I also make use of my cctv on my cell phone to check that all switching went ok at home and I can see if its cloudy or sun and switch on/off as I think best. I have set the sonoff timers for in case I forget to switch between solar and grid especially in the evenings as I don’t want to run too much on battery's. 

I left the manual change over switch in the DB so that if I’m not at home and there is load shedding the family can still manually switch over to inverter, otherwise they have to phone me to switch them on. I  now still need to figure out a way to switch automatic between grid and solar on cloudy days, after that the Axpert will be completely auto and I can forget about it.

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13 hours ago, Stefan said:

I think you will also like this.

Thanks Stefan, this is quite interesting to see another persons diagram, It looks like quite a cost effective way to make an auto change over. Although I think there were quite a bit of thinking that went into that design, It still have me scratching my head.🧐🙂

 

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what about and essential loads db with:

1) mains to supply priority loads

2) 20A for plugs

3) 15A for lights

4) 30A contactor with aux.

not the cheapest approach but at least if hairdryers or lawnmower is connected by mistake then its safe?

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1 hour ago, Fazil said:

what about and essential loads db with:

1) mains to supply priority loads

2) 20A for plugs

3) 15A for lights

4) 30A contactor with aux.

not the cheapest approach but at least if hairdryers or lawnmower is connected by mistake then its safe?

If I understand correct, the 30A contactor will carry the plug and lights, that should be good enough as your highest circuit breaker is a 20A. I once had a little 12A plug in relay do a similar task and it worked until a welding machine was plugged in that melted the relay contacts.

You could also double up the contacts on the 30A contactor if it has spare contacts that should give you additional capacity that should make it even last longer.

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2 hours ago, Gerrie said:

If I understand correct, the 30A contactor will carry the plug and lights, that should be good enough as your highest circuit breaker is a 20A. I once had a little 12A plug in relay do a similar task and it worked until a welding machine was plugged in that melted the relay contacts.

You could also double up the contacts on the 30A contactor if it has spare contacts that should give you additional capacity that should make it even last longer.

same here

10A dinrail relays until client was using blow dryer and lawnmower on that circuit.  the rest was history. upgraded to 30A contactor and no issues 1 year later.

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