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Pylon to Axpert 5K - disconnect switch and fuses?


HowardB

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Hi all, two questions:

1. So I bought an MLT 200A Battery Disconnect with Pre-Charge Circuit, and as with most websites in SA, there is some info but not all the info! I tried to research the product more before buying, but most sites state exactly the same generic information. The seller (not SegenSolar) confirmed that the unit included 2 fuse modules on 2 separate poles, with 125A fuses on each pole and the pre-charge circuit on the "+", however when the product arrived it does have the 2 poles, 2x 125A fuses and the pre-charge circuit, BUT, the two poles are connected with a bus bar as in this picture -- I also have no clue what the 2 smaller bus bars are for at the bottom of the box:

IMG_20190313_163508.thumb.jpg.670312c131f13a5b713c813c43fe78ee.jpg

So my main question is: when connecting this unit between the Pylon's and the Axpert, would the "+" only run through this unit, effective having 2x 125A fusing on the "+" and nothing on the "-".

Alternatively, if the 2 fuse pole units are disconnected from each other (i.e bus bar removed from the left one via cutting for the "-", with the right cut shorter on the "+"), with the pre-charge circuit still on the right pole, then the "+" and "-" would both be fused individually at 125A each - I always understood that both cables should be fused with such battery/inverter connections, hence getting this unit on the basis that the seller described such, but the way it's actually designed it doesn't seem to allow this. If not, then I'll have to return the unit and opt for a Keto or similar.

I also do not know if there would be any adverse effect on the pre-charge circuit on the "+" if the "-" is effectively just a fused pass though?

Any comments/guidance would be appreciated on this.

2. If the above (or a Keto) fusing is installed between the Pylon's and Axpert, do I also need a 2-pole disconnect breaker in line? And if so, would it go on the battery side or the inverter side of the above fuse unit? I know the above is already a disconnect unit, but I also want to be able to totally disconnect the batteries quickly via breaker/switch if ever needed, just to be extra safe.

Again, comments/input would be welcome :)

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Two small busbars at the bottom of the box are just remains and have no use for your application. This box without fuses is quite often used as a small DB for AC breakers, hence these busbars - they are meant for neutral and ground.

This unit goes to "+" cable only.
Leave the "-" cable straight, without any fuses between the battery and Axpert.

I'm not sure what regulations are saying about it, but I saw dozens of solar systems where "-" is connected directly to a huge negative busbar that's shared by many Invertors and Solar Charge Controllers, while only "+" cables are fused. The logic behind it is this:

  • Technically, it's okay to fuse just one side of the circuit, since once the fuse has blown, the current cannot flow anymore. In the AC DB, you also have the breakers on the Phase wires only, not on the Neutral wires.
  • If you fuse the negative pole and that fuse will blow, the current might find an alternative way to close the circuit: LAN cables, serial communication cables, shielding, etc. So, if you break the negative wire first, while keeping the positive wire connected, there's a risk that some other equipment will be damaged (monitoring, PC, etc).

But like I said - I'm not sure what local regulations are saying about it.

Edited by Youda
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3 hours ago, Youda said:

Two small busbars at the bottom of the box are just remains and have no use for your application. This box without fuses is quite often used as a small DB for AC breakers, hence these busbars - they are meant for neutral and ground.

This unit goes to "+" cable only.
Leave the "-" cable straight, without any fuses between the battery and Axpert.

I'm not sure what regulations are saying about it, but I saw dozens of solar systems where "-" is connected directly to a huge negative busbar that's shared by many Invertors and Solar Charge Controllers, while only "+" cables are fused. The logic behind it is this:

  • Technically, it's okay to fuse just one side of the circuit, since once the fuse has blown, the current cannot flow anymore. In the AC DB, you also have the breakers on the Phase wires only, not on the Neutral wires.
  • If you fuse the negative pole and that fuse will blow, the current might find an alternative way to close the circuit: LAN cables, serial communication cables, shielding, etc. So, if you break the negative wire first, while keeping the positive wire connected, there's a risk that some other equipment will be damaged (monitoring, PC, etc).

But like I said - I'm not sure what local regulations are saying about it.

Thanks again for the reply Youda. Makes sense on the "+" only.

If I'm running the 2x Pylon 2.4kw and the "+" is fused with the 2x 125A on the same pole effectively, how/when would this blow - I assume the fused "+" would then be able to handle 250A given the 2 fuses in parallel; is this then not to-high-a-fuse-rating? Each Pylon seems to output about 120A max on full load (from what I've read), and they are in parallel only, so would seem 240A is the total max output of the 2 batteries at full load (will probably never use this full power capability though).

If the above is true, then if I add 2 more Pylon's in a few months time, then the Amps could double again, but would I need to up the fuse ratings and 4AWG DC cables? 

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Whats the number of, type and rating of the inverters that you have on this system?

For anything under 5kW, just one 125A fuse is okay (50V x 100A= 5kW). Btw: you should not pull/push more than 20A per a Pylon brick. Yes, they can deliver 120A each but it's killing them quickly.

Sorry, writing this from the cellphone...

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For 40Amps the 4AWG is acceptable. My system is pulling 200Amps during rush-hour so I went for AWG0 cabling (rougly 50mm2 cross-section).

Btw keep the battery cables as short as possible, otherwise there will be a voltage drop during peaks and the inverter will complain or even switch to a bypass.

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7 hours ago, Youda said:

Whats the number of, type and rating of the inverters that you have on this system?

For anything under 5kW, just one 125A fuse is okay (50V x 100A= 5kW). Btw: you should not pull/push more than 20A per a Pylon brick. Yes, they can deliver 120A each but it's killing them quickly.

Sorry, writing this from the cellphone...

Only one RCT Axpert MKS-5K inverter for now, 4kW. Draw would never be more than 10A-15A peak, and not continuous. Great, will use the single fuse only.

 

7 hours ago, Youda said:

For 40Amps the 4AWG is acceptable. My system is pulling 200Amps during rush-hour so I went for AWG0 cabling (rougly 50mm2 cross-section).

Btw keep the battery cables as short as possible, otherwise there will be a voltage drop during peaks and the inverter will complain or even switch to a bypass.

I'm using the standard cable set that came with the Pylon's which shows 4AWG on it. I know if you parallel more than 4-5 Pylon's, you need a second set of 120A cables, so my 2 batteries should be fine on the 4AWG, would probably never pull 40A for the current proposed setup.

Thx, cable length will be as short as possible, around 40-50cm max from battery cabinet to inverter, including inline fuses; probably 1m total from battery terminals to inverter.

Is there any point/reason in adding a secondary disconnect breaker switch if I'm using the fuse unit?

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1 hour ago, HowardB said:

Only one RCT Axpert MKS-5K inverter for now, 4kW. Draw would never be more than 10A-15A peak, and not continuous. Great, will use the single fuse only.

 

I'm using the standard cable set that came with the Pylon's which shows 4AWG on it. I know if you parallel more than 4-5 Pylon's, you need a second set of 120A cables, so my 2 batteries should be fine on the 4AWG, would probably never pull 40A for the current proposed setup.

Thx, cable length will be as short as possible, around 40-50cm max from battery cabinet to inverter, including inline fuses; probably 1m total from battery terminals to inverter.

Is there any point/reason in adding a secondary disconnect breaker switch if I'm using the fuse unit?

The Pylontech has a power switch so you don't need a second isolator. Only an in-line fuse is necessary. 

As matter of interest, I've seen a few cases where the Axpert's blow 160A fuses and even 250A fuses when the main circuit boards develop problems. And in every case the client said they didn't use big appliances at the time. One such installation is an off grid security installation, i.e. it only has LED lights, electric fence, alarm system and CCTV connected to the Axpert. The power draw was never more than 1000W, over a 2 year period  but one day I got a call, "everything is off, come quick" 125A fuse blown. I replaced it, switched everything back on, fuse blows again. It then blew a 160A fuse and a 250A fuse at which point I realized there is a problem with the main control board. IF there weren't any fuses they could have had much bigger problems. 

The Axpert 4Kw unit has a limit of 83A, under normal conditions, but it can handle 10,000VA for a short period, pushing that limit 120A. The Pylontech can deliver 5KW for 15 seconds, so in both cases it is very plausible to push more power through than you anticipate to use. 

Another client once blew 2x Axperts (from a 4x parallel configuration). He claims they were only vacuuming at that time. Being a farm, I suspect the vacuum cleaner was 600 years old and probably had a faulty motor that caused a surge. There are fuses and surge arrestors installed so the rest of his equipment was safe. I have to add though, he insisted on not having surge arrestors after the inverters, which could probably have saved the inverters from the vacuum's surge. 

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2 hours ago, SilverNodashi said:

vacuum's surge

What kind of surge did you think of? Inrush current perhaps? An inverter should be able to take a dead short and switch itself off without blowing. In fact I've done it a few times to test overload alarms on the bench... it's not even that big a spark, although for safety I use an old AC/DC breaker.  

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2 minutes ago, plonkster said:

What kind of surge did you think of? Inrush current perhaps? An inverter should be able to take a dead short and switch itself off without blowing. In fact I've done it a few times to test overload alarms on the bench... it's not even that big a spark, although for safety I use an old AC/DC breaker.  

To be honest I don't know as I wasn't on-site when it happened, but that was the only conclusion I came to. Perhaps there was a shorted wire in the motor and it caused a surge, or it drew more than 270V, etc, I don't know. But his words was "we were vacuuming" when it happened. Off course they had some fridges, electric fence, cell phone chargers, etc on at the same time as well. But the fact that there was an electric motor with a sudden stop / start pulse on the system made me think it could have been a surge of sorts. 

 

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31 minutes ago, SilverNodashi said:

sudden stop / start pulse on the system

The proverbial last straw 🙂

I suppose one must also keep in mind that old-style low-frequency stuff handles this sort of thing much better. The high frequency "transformerless" stuff have actual switching components and stuff directly in the path of such bad appliances. So drawing a comparison with the stuff on my test bench is clearly not really fair 🙂

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3 hours ago, SilverNodashi said:

The Pylontech has a power switch so you don't need a second isolator. Only an in-line fuse is necessary. 

As matter of interest, I've seen a few cases where the Axpert's blow 160A fuses and even 250A fuses when the main circuit boards develop problems. And in every case the client said they didn't use big appliances at the time. One such installation is an off grid security installation, i.e. it only has LED lights, electric fence, alarm system and CCTV connected to the Axpert. The power draw was never more than 1000W, over a 2 year period  but one day I got a call, "everything is off, come quick" 125A fuse blown. I replaced it, switched everything back on, fuse blows again. It then blew a 160A fuse and a 250A fuse at which point I realized there is a problem with the main control board. IF there weren't any fuses they could have had much bigger problems. 

The Axpert 4Kw unit has a limit of 83A, under normal conditions, but it can handle 10,000VA for a short period, pushing that limit 120A. The Pylontech can deliver 5KW for 15 seconds, so in both cases it is very plausible to push more power through than you anticipate to use. 

Another client once blew 2x Axperts (from a 4x parallel configuration). He claims they were only vacuuming at that time. Being a farm, I suspect the vacuum cleaner was 600 years old and probably had a faulty motor that caused a surge. There are fuses and surge arrestors installed so the rest of his equipment was safe. I have to add though, he insisted on not having surge arrestors after the inverters, which could probably have saved the inverters from the vacuum's surge. 

Many thanks SilverNodashi. Interesting.

Another question then, if the Axpert pushes 83A under normal conditions, with a short peak of 120A, then shouldn't I replace the 125A fuse that came with the unit with a lower value, say 100A fuse, or would this not make much difference (the additional 5A that is)?

The Pylon US2000-B Plus datasheet states max discharge/charge current at 100A(2C)@ 1min - I assume if the discharge current then hits 120A for longer time it would damage the batteries; if the fuse only blows at 125A, it would then do serious damage to the batteries?

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Take it easy... 125A fuse is okay.
The fuse is not there to protect the Inverter. The main purpose of the fuse is to protect the wires from the short -> cause of fire and damage.

Pylon has a current monitoring probes in each brick. Should the current pass over the limit, the Pylon will disconnect itself from charger/inverter.
Just be carefull not to run 4kW load on 2 Pylon bricks during night. This would shorten the life of the batteries. In the near future, just add at least 2 more bricks and you are set.

 

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23 minutes ago, Youda said:

Take it easy... 125A fuse is okay.
The fuse is not there to protect the Inverter. The main purpose of the fuse is to protect the wires from the short -> cause of fire and damage. 

Yup. Also, a fuse doesn't blow immediately when you exceed the limit. Just yesterday I was running a 10A fuse at 11A for short periods and it didn't blow (it got very hot though!). They usually only blow immediately when you get to around ten times the rated current, and even at 50% over it might take minutes to blow. So sizing a fuse to the max expected draw (plus 20% or so) should be more than adequate, though of course, as @Youda says: the fuse is there to protect the cable.

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1 hour ago, plonkster said:

The proverbial last straw 🙂

I suppose one must also keep in mind that old-style low-frequency stuff handles this sort of thing much better. The high frequency "transformerless" stuff have actual switching components and stuff directly in the path of such bad appliances. So drawing a comparison with the stuff on my test bench is clearly not really fair 🙂

It was an Axpert inverter, which is probably not on your test bench 😆

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1 hour ago, HowardB said:

Many thanks SilverNodashi. Interesting.

Another question then, if the Axpert pushes 83A under normal conditions, with a short peak of 120A, then shouldn't I replace the 125A fuse that came with the unit with a lower value, say 100A fuse, or would this not make much difference (the additional 5A that is)?

The Pylon US2000-B Plus datasheet states max discharge/charge current at 100A(2C)@ 1min - I assume if the discharge current then hits 120A for longer time it would damage the batteries; if the fuse only blows at 125A, it would then do serious damage to the batteries?

The battery will safely shutdown if the current is too high. If you want to, fit the 100A fuse and if it blows too often, replace it with 125A. Remember an appliance with a high startup current might, just might, cause the 100A to blow

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50 minutes ago, plonkster said:

Yup. Also, a fuse doesn't blow immediately when you exceed the limit. Just yesterday I was running a 10A fuse at 11A for short periods and it didn't blow (it got very hot though!). They usually only blow immediately when you get to around ten times the rated current, and even at 50% over it might take minutes to blow. So sizing a fuse to the max expected draw (plus 20% or so) should be more than adequate, though of course, as @Youda says: the fuse is there to protect the cable.

You get fast blow and slow blow fuses. Keep that in mind. 

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25 minutes ago, SilverNodashi said:

You get fast blow and slow blow fuses

I know... I even thought of it while writing it. Don't think we need to complicate things even further. Those fuses in the picture are slow-blow 🙂

Edit: Essentially, you just need the fuse to heat up faster and melt faster than the cable within which it is installed. Since copper at 200% of its rating is not going to blow up immediately, you'd generally go with slow-blow.

Edited by plonkster
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22 hours ago, Youda said:

I'm not sure what regulations are saying about it, but I saw dozens of solar systems where "-" is connected directly to a huge negative busbar that's shared by many Invertors and Solar Charge Controllers, while only "+" cables are fused. The logic behind it is this:

I read in the new draft SANS document that the isolator must disconnect the + and - connection to the batteries. 

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2 hours ago, Youda said:

@HowardB,

stop being worried and put that damn thing into operation now :) We want to see the fireworks it running!
And share the photos and some info, please!

Ha ha, hoping to have it done in the next few days, at least by end of the weekend! With the loadshedding starting again today, hopefully will get it up and running sooner than later - Murphy today ensured my old faithful independent inverter running the fridge/freezer/lamps/TV/HTPC pack up, so now there's incentive to get this done asap :)

Will post pics and info, and thanks to everyone for their valued comments!

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Speaking of Mr.Murphy...

Couple of days ago, I wanted to save a few bucks and decided to swap CFL light in the bathroom's mirror for a pair of new led lights. I needed to modify the AC wiring for the bathroom too, because there's a LED TV hanging on the wall in the adjacent room and I wanted to have all the cables leading to that TV to be hidden.

That bloody job took me a whole day:
- dismantle the mirror
- extract old CFL lights
- bolt-on new LED lights
- drill a hole through the wall for TV cables
- install the cables for TV
...and in the 22pm, when I was almost finished and ready to hang the mirror back, I dropped it on the floor and broke it's corner!

OH MY DEAR! 🤪

 

 

 

Edited by Youda
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3 hours ago, Youda said:

... when I was almost finished and ready to hang the mirror back, I dropped it on the floor and broke it's corner!

O man, I'm so with you on this one!!!

My wife has told me I'm not allowed to fix anything anymore, one too many "AG MY LIEWE DONNER" (O MY DEAREST THUNDER - just not the same translated) accompanied by say the house tripping / smoke / blue sparks / glass shattering / wood cracking / bricks falling ...

I like to think it is out of love for her hubby from her side ... but I suppose not. 🙂 

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27 minutes ago, The Terrible Triplett said:

AG MY LIEWE DONNER

That's a slightly more polite version of "My f*k Jaco..." 🙂

It's this sort of thing that keeps me happy to remain in Africa. Perhaps even move North into Africa if I have to...

(Marlize is from Windhoek...)

Apologies for language... but this just had me laughing so hard last week...

53761042_1232852890213097_6426777594724614144_n.thumb.jpg.d51756bbb93e5b0c5b2b29f7a5fa92d6.jpg

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