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Question of the Day: If you were buying a TV today, which brand would you choose?
Axpert invertors
- Thread starter Draganchor
- Start date
Ah I thought I recognized your name. You have the youtube video.
Any things to watch out for with this inverter?
Any issues thus far?
So the dry contact is a no-go? (I assume you've played around with them?)
How have you tied your ground and neutral?
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All good so far, but I only use it during loadshedding and when I'm at home, which doesn't happen all that often.
I haven't really done anything with the dry contact. I looked at the comms board that the dry contact relay lives on to see if there was anything promising, but as far as I can see there's no signal available to indicate it's not in bypass mode.
I haven't. The electrician never complained about it, and I'm not 100% comfortable with earthing Eskom's neutral line again. The inverter only runs for 2 hours at a time so chances are it's not going to drift too far.
I still want to get it sorted out properly though.
As I see it there are the following options
1. Permanent link: Forms a loop when in bypass mode between the utility earth point and the inverter. Most probably it'd be fine since there is little chance for any current to be induced into that loop anyway. Still not sure.
2. Resistor: (or an incandescent light bulb) I wouldn't know if the resistor or bulb breaks
3. Contactor: (Powered off eskom) There's no guarantee that the inverter will go into bypass mode when AC is present
4. Relay: Means opening up the inverter or something more fancy that runs off the serial port, which is what I'm going for
[email protected]
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Hi
So I found something very interesting about AC single poll breakers in a test scenario. Please don't rely on this rather use a DC breaker. If you are only using the AC breaker as a isolator I suppose it will be okay but you must still have a fuse but I would not recommend this.
So the AC breaker will trip on a DC circuit however it will only trip at +- double its amp rating. It was mentioned in this thread that it will not trip.
DC trips AC circuit breaker
Check this out https://www.youtube.com/watch?v=kRB7Z66brO0
This is why you should not use it as a breaker
https://www.youtube.com/watch?v=S6BRo5fjtVk
So I found something very interesting about AC single poll breakers in a test scenario. Please don't rely on this rather use a DC breaker. If you are only using the AC breaker as a isolator I suppose it will be okay but you must still have a fuse but I would not recommend this.
So the AC breaker will trip on a DC circuit however it will only trip at +- double its amp rating. It was mentioned in this thread that it will not trip.
DC trips AC circuit breaker
Check this out https://www.youtube.com/watch?v=kRB7Z66brO0
This is why you should not use it as a breaker
https://www.youtube.com/watch?v=S6BRo5fjtVk
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greg_SA
Expert Member
I think there are a lot of installers that don't really understand all of the different inverters that they are installing. Some of the inverters (like some Victron units) have this earthing issue sorted out internally, but not all inverters do. The manuals of the inverters aren't always very clear either - the Axpert is not clear at all in this regard.
The neutral (when in battery mode) doesn't drift relative to earth over time - it is completely floating, so will immediately be difference of say 20 or 100 V. The floating itself isn't a risk, but the fact that your E/L won't protect the plugs running from the inverter output (in battery mode) is the issue.
With regards to your options:
1.) The earth and neutral conductors will share the total neutral current, which is incorrect. The earth is only meant to carry fault currents.
2.) That just seems like a strange idea...
3.) I'm not sure what you mean...
4.) You can fit the relay outside the inverter. It is a loose part that will be energised by Eskom power (on the inverter input) and it will switch the neutral to earth on the inverter output.
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These options are all things that have cropped up in the thread so far.
1.) I agree, however the loop is only between the earth-neutral bond and the inverter so in practise it'd probably work. Still dodgy though.
2.) A resistor would stop the two isolated supplies from drifting apart while not allowing large currents in the loop, but same problem with EL.
3.) A contactor (AC powered relay) powered off eskom could disconnect the earth-neutral link when eskom is present, but the inverter might be in bypass mode or it might be inverting depending on the settings and solar options.
It'd be okay if you always made sure the inverter went back into bypass mode when eskom returned, but that's only an option if you don't want to use solar power.
4.) A DC relay could be powered from the internal bypass relay to be sure that you disconnect the earth-neutral bond if it ever goes into bypass mode. Otherwise a microcontroller could read the state and control the relay without having to modify the inverter.
EDIT: For googling purposes it's called a backfeed relay
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I just got one of these for my earth relay.
http://www.ebay.com/itm/JQX-40F-1Z-40A-220VAC-Coil-PCB-Power-Relay-/120956894320?hash=item1c2997bc70
Simple enough and doesn't require extensive modification or weird changes.
Not true.
It doesn't matter where you bond an earth or neutral, it creates the bond for the entire house.
That is why any earth/neutral fault will trigger a RCD/Earth Leakage to trip.
Essentially your neutral current flows all the way to where the earth bond is created and then all the way back to the earth at the Eskom transformer.
The reason it is very dangerous:
Typically every electrical device in your house has a live and neutral wire going to it. Both conductors are evenly matched. The amount of power going in on the live matches the amount of power going back on the neutral.
So you only need to add a circuit breaker on the live and the neutral will therefore be safe.
When you create a neutral/earth bond the rules change.
You created a new path back to the Eskom transformer going VIA a single earth wire in your house.
Suddenly that earth wire can carry current of a lot of neutral conductors. You created a parallel path back to the transformer.
Why it is so dangerous and is termed a fault:
Your earth wire isn't rated to carry current
Your earth & neutral wire are suddenly carrying more current than they were rated for (Remember you are suddenly creating a path for ALL neutral current to return)
Therefore your breaker on your live is no longer enough to ensure that the neutral will not get overloaded and certainly not the earth.
It is a fire hazard. Simple as that.
EDIT: This guy is super boring but he goes over the fault: https://www.youtube.com/watch?v=JTkuoMplER8
http://www.ebay.com/itm/JQX-40F-1Z-40A-220VAC-Coil-PCB-Power-Relay-/120956894320?hash=item1c2997bc70
Simple enough and doesn't require extensive modification or weird changes.
Not true.
It doesn't matter where you bond an earth or neutral, it creates the bond for the entire house.
That is why any earth/neutral fault will trigger a RCD/Earth Leakage to trip.
Essentially your neutral current flows all the way to where the earth bond is created and then all the way back to the earth at the Eskom transformer.
The reason it is very dangerous:
Typically every electrical device in your house has a live and neutral wire going to it. Both conductors are evenly matched. The amount of power going in on the live matches the amount of power going back on the neutral.
So you only need to add a circuit breaker on the live and the neutral will therefore be safe.
When you create a neutral/earth bond the rules change.
You created a new path back to the Eskom transformer going VIA a single earth wire in your house.
Suddenly that earth wire can carry current of a lot of neutral conductors. You created a parallel path back to the transformer.
Why it is so dangerous and is termed a fault:
Your earth wire isn't rated to carry current
Your earth & neutral wire are suddenly carrying more current than they were rated for (Remember you are suddenly creating a path for ALL neutral current to return)
Therefore your breaker on your live is no longer enough to ensure that the neutral will not get overloaded and certainly not the earth.
It is a fire hazard. Simple as that.
EDIT: This guy is super boring but he goes over the fault: https://www.youtube.com/watch?v=JTkuoMplER8
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greg_SA
Expert Member
Cool - I'm going for option 3. I'll use a normal relay, with a 240V coil. Luckily I don't plan on using the solar at all - my setup is for a plain UPS.
EDIT: Just to add, in the second video you have. AC circuit breakers that are rated for DC will typically have MUCH lower voltage ratings. This guy is putting 240v DC through that breaker. The same test at lower voltage will likely yield a different result but I am intrigued!
EDIT2: Damn that arc from 240v creating the smoke internally was impressive!
That video is very worrying because he makes assumptions.
Circuit breakers never break at rated current. Circuit breaker ratings are very tricky and the datasheet has more info about when a circuit breaker will trip based on temperature and time.
The rating for AC and DC are identical.
You are heating a bi-metal strip. It doesn't matter if you heat it from AC or DC. If the amount of power is the same, it will heat the same and trip the breaker.
The real concern of using AC circuit breaker for DC is arcing.
Circuit breakers have special plates to break the arc in a high current situation.
In an AC breaker, they rely on the zero crossing point to break the arc.
This makes extinguishing the arc easier than DC applications.
Some breakers are rated for both AC and DC and have sufficient breaking capacity (measured in kA) to break a DC arc.
For example Chint NB1 (10kA breakers) are rated for DC also and have a tripping curve for DC in the datasheet.
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greg_SA
Expert Member
Did you order if from that link?
I'm just thinking of using one of these: http://za.rs-online.com/web/p/non-latching-relays/2111304/
Yeah, I did, that brand is also sold by ACDC and Communica although neither sell that specific relay or for that cheap.
It does take about a month to arrive however (eBay and post office being what it is).
I refuse to use RS for anything. They are overpriced and I've tried ordering relays from them before. Only to get a call that half my order is cancelled because they aren't willing to source it unless I order 10. When I point out the website allowed me to order 1 their attitude is that they aren't willing to honor that.
Found much better alternatives at Communica. I recommend you give them a call if you don't want to wait.
I wrote a long reply to this, but I think the topic is confusing enough already, and I don't think it's helpful to discuss whether this hypothetical wiring is just bad or very bad!
For your 4 x 250W panels you would need to connect them in sets of 2 (2 x series, 2 x parallel). The parallel connection should be done in a combiner box with fuses, DC breaker etc to combine the strings and have a single input to the inverter.
The MPPT operating voltage range is 60-115VDC with a maximum open circuit voltage (VoC) of 145VDC.
If you connect your panels in parallel the max operating voltage will only be around 30VDC. 2 x panels in parallel will get you to the 60VDC minimum - but only if everything is operating optimally.
To get the most out of the system, I'd suggest configuring the panels in sets of 3 series connected strings, i.e. 3, 6, 9 or 12 panels.
3 x 250W panels @ 37.4V VoC = 112.2V VoC (below the maximum input of 145V.) and 90VDC operating voltage which is within the operating range of the MPPT.
Getafixx
Active Member
These can both switch 40A - not sure if you need that much.
http://www.communica.co.za/Catalog/Details/P0733741839
http://www.communica.co.za/Catalog/Details/P2961727466
There's also this sort of thing, might be neater depending on your db board.
http://za.rs-online.com/web/p/contactors/6851488/
Getafixx
Active Member
Here's a much smaller version, 12A, DIN, similar price.
http://www.acdc.co.za/Catalogue/ACDCCATALOGUE.html#/156
(Bottom right, NCH8-20)
greg_SA
Expert Member
Thanks for all the suggestions...
Sure, I order from RS regularly (for work) and they are a pain to deal with. I was mostly trying to show what type of relay I'd like to use... I want it small, with spade terminals so that I can fit it into the cavity of the inverter, where the wire connections are done.
It won't need to carry massive currents - technically it will never really do anything, unless there is a fault... And the wiring for my inverter is from a 10A breaker, so anything that can handle 10A is fine anyway.
Sure, I order from RS regularly (for work) and they are a pain to deal with. I was mostly trying to show what type of relay I'd like to use... I want it small, with spade terminals so that I can fit it into the cavity of the inverter, where the wire connections are done.
It won't need to carry massive currents - technically it will never really do anything, unless there is a fault... And the wiring for my inverter is from a 10A breaker, so anything that can handle 10A is fine anyway.
Getafixx
Active Member
Hold on, if the floating is no risk, does it mean you can touch both the neutral and the earth without shocking even though they are 100V apart? Because there is no return path for the current?
In this diagram there is no return path in case of an earth fault on the circuits connected to the ups/inverter when Eskom is off and the load is supplied by the inverter. I think a better way of connecting the inverter is to connect the inverter mains input before the main E/L and to bond the neutral and earth on the inverter output and then run that through the secondary E/L. Connected in that way all the circuits supplied by the inverter will always be protected by the secondary E/L, whether Eskom is on and running straight through the inverter or Eskom is off and the inverter is supplying the load.
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greg_SA
Expert Member
Yes, that's the theory
Many people don't worry about E/L on this type of inverter output, because the only way you can shock yourself is if you touch both the live and neutral, and that it relatively unlikely.