Which fuses can be used for protection in the DC area for two directions


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Redpacket

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So sounds like a breaker rating should be be closer to actual use current?
 

Wolf

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completelycharged said:
......................I have only managed to get upto about 18kW out of my pack when trying to trip breakers .........................
Uff 18kW 300+Amps @Nominal. Copper girders are needed for that. :)

My only experience with such current flow is when I hook up my Inverter. The inrush of current to charge the capacitors has blown many a 200A fuse.
I did replace the fuse with a "cheep" breaker but even that was not enough as I fused the contacts on those also when switching the breaker on to power up the inverter. So it essentially became a fuse and no longer did any of that "breaker" stuff. I now jump the new replacement"cheep" breaker with a substantial jumper to charge the capacitors before turning the breaker on. Kind of defeats the purpose when trying to turn the inverter on.
SoI now leave the breaker on but the inverter is off. Keeps the capacitors charged.
The same goes for my Grid ties.
Both these breaker are on the "to replace " list with a proper one that can handle the current inrush without melting.

Also sizing the wiring to the system is paramount. At this time the max Amps I pull from my battery is 37.8 Amps for 1800W at 47.6V which is the very lowest I will let my batteries go. Sizing your wire to handle that, at least X2 and possible further expansion is good forethought.

Wolf
 
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Had to look back at one of my old posts for the current reading while burning wire... (the meter is a slow average) and the current measurement lags the power calculation for some insane reason on the meter. Notice the volt drop..
"Resting voltage was 47.23V so at 325A and 45.48V on the same meter that gives a battery to busbar resistance of 5.08 milli Ohm. "

image_ewwblm.jpg

https://secondlifestorage.com/showthread.php?tid=5027&page=8


Balancing act, but mainly wiring should be over rated (to cope with breaker trip rating delay) and high amp single pole breakers avoided if possible.

Running breakers close to long term use can create issues with heating and cooling cycles that loosen the connections but also means the fault issue is a little more comfortable. Bigger (over sized) cables can also carry more heat away from the breakers, which also impacts the breaker timing on thermal trip overload.

My packs have 100A breakers and I have effectively 9 packs (2 in series) connected to a busbar which is effectively then "protected" at 900A. BUT in reality those breakers would never trip in a fault and it would be molten aluminium or wires elsewhere that would be the "fuse". I am contemplating de-rating / swaping those breakers to 40A (on the to do list - when it get's high enough up in the list !).

When I was doing the research for the inverter build I ended up at a conclusion that something like 1x breaker + (1.2x to 1.5x) fuse in series was required for best protection. The fuse at the 2x-4x over current would blow fatser than the breaker. The breaker would service overloads and full on disaster situations. Marginal overloading the breakers would trip on (inverter overheating protection).

My thoughts / conclusions (all open to being shot down in flames as long as they are not caused by a battery fire) :
1. Fuses burn faster than breakers trip
2. FET's in an inverter can burn much faster than breakers trip
3. Fuses have a better chance at saving the FET's in a high amp rated inverter than a breaker
4. Small amp breakers over fuses for distribution (cheaper in long run and allows for switching)
5. Test and know for yourself what works and what does not work in reality
6. Don't always go for a single big cable, 2 cables of the same overall conductor csa can cary more amps (see litz wire principle)
7. Multipole breakers (lower amp per pole) are more reliable/safer than a single higher amp breaker
8. Still learning


And this is more "normal" for a peak (sustained) on the inverter that should be expected not to cause issues

image_guuwdf.jpg



Oh, in relation to the batter to busbar resistance of 5.08 milli Ohm :
47V battery with short on busbar would be 9250 Amps or... 434kW... and that scares the s**t out of me.
 

Wolf

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completelycharged said:
8. Still learning


Oh, in relation to the batter to busbar resistance of 5.08 milli Ohm :
47V battery with short on busbar would be 9250 Amps or... 434kW... and that scares the s**t out of me.



CC
I thought you were the master now who am I going to learn from?

Well lets see 9250 Amps at 47V we are going to need an Air Breaker for that. :pthey are only about 50 grand :D

Wolf
 
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The "air breaker" so far was related to a wire that cought across the terminals on one pack and set fire to the carpet... the air was me blowing out the small flame on the carpet. Stunned at the time that carpet cought fire so easily (and my error at having all the terminals bare at my feet kicking stuff around). We are all forest gump at different times, "stupid is as stupid does"
 

Redpacket

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Wolf said:
My only experience with such current flow is when I hook up my Inverter. The inrush of current to charge the capacitors has blown many a 200A fuse.
I did replace the fuse with a "cheep" breaker but even that was not enough as I fused the contacts on those also when switching the breaker on to power up the inverter. So it essentially became a fuse and no longer did any of that "breaker" stuff.I now jump the new replacement"cheep" breaker with a substantial jumper to charge the capacitors before turning the breaker on. Kind of defeats the purposewhen trying to turnthe inverter on.
.....
Both these breaker areon the "to replace " list with a proper one that can handle the current inrush without melting.
......
Wolf

Wondering if you've considered inrush current limiting via a pre-charge resistor for this?
I have a small 10A breaker (normally off) around the main fuse with 2x 10W resistors a few ohms each.
(yes I need to upgrade to shunt trips but that's another story).
I close the small breaker first, wait a few secs, then close the fuse disconnect. No sparks or Valium for operator! ....
 

daromer

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Wolf it it blows your fuses you have wrong fuses for that inverter. They often should be b or c characteristics.

Inrush current limiting should not be needed for appliances for normal homes.

Also note that with a proper breaker between the inverter and battery you can also minimize the sparks created. Like the ABB series do.
 

Walde

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Wolf said:
I for one am going with breakers.
I have investigated this pretty heavily and have come up with the ABB S200 series to be my breaker of choice.

They offer all kinds of trip curves and numerouscurrent protection values,125 VDC bidirectional support, and are reasonably priced esp on eBay.
They also offer a shunt trip attachment, which I will be installing on all my breakers, and putting a RED emergency button in a conspicuous location to do an emergency shutdown tripping all the breakers at once. Anything over 63 Amps will be a ABB Sace S3 also shunt tripped.
A complete system shutdown with fuses ,I feel, is time consuming esp in an emergency.

Correct me if I am reading these ABB specs wrong but I believe they are correct.
Wolf

image_nruuoe.jpg

I think it's good that I started such a nice discussion.

With the 125VDC, the voltage plus must be conducted via two poles. Each pass can only be 62V. This is well described at schneider electronic. See

[/ url]
[url = https://www.se.com/de/de/download/document/ZXKACTI9/] https://www.se.com/de/de/download/document/ZXKACTI9/
 
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For DC equipment the internal design may be based on an assumed minimum DC supply impedance (resistance) to act as a limiter for capacitor charging. Blowing a 200A fuse is an example of a lower than intended supply source impedance (they may have designed the unit with a lead-acid bias) AND if you look at some equipment specifications they provide an upper bound on capacity as a proxy for this impedance in the design. i.e. they may say 3-9kWh battery system for example.

Capacitors in DC equipment, if connected to a near zero impedance DC supply will damage or destroy the weakest components. This is completely irrelevant to the fuse or breaker rating. Blowing a 200A fuse deffinately does not mean you put a higher rated fuse in.

I have a 12kW plasma cutter with an integral HV DC bus which "must" be precharged with an integral circuit to the unit to "soft start", otherwise the unit would blow the 100A supply fuse with ease and probably blow the traces off the PCB or detroy the rectifier diodes.

AC equipment has different issues but most households have a very high supply impedance compared to a DC battery pack. The supply transformer has quite a distance of wire (which also acts as an inductor).
 

Redpacket

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daromer said:
Inrush current limiting should not be needed for appliances for normal homes.
Agree but this is for connection of battery to inverter after it's been off, ie system start-up, not normal operation.
Like completely charged says, low impedance batteries suddenly dumping energy into the inverters input caps is a pretty high stress thing.
For AC appliances on the inverter output, the inverter itself is current limiting.
I'm sure we have all seen inside larger switchmode PSU's they usually do have inrush limiters to reduce stress on parts like caps & rectifiers.

Of course there are other items:
https://www.reddit.com/r/funny/comments/2sxuux
 
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The other part is with breakers the mechanical movemnt delay determines part of the net fault energy transfer.

Consider if the contacts stay conductive for 0.1mS while the fault current flows.
Then consider a 48V supply and a 0.01 Ohm inline resiatance (will skip full impedance at this point for simplicity).
The fault current would be 4800 Amps
For 0.1mS this equates to only 0.48 Joules of energy - tiny yes....
The issue is then how much damage can 0.48 Joules of energy inflict on the wekest link.

Then consider the first google search result summary for simplicity
"Circuit breaker CB-3 is set to trip if an overload of 2000A or greater occurs for 0.080 seconds. Circuit ..."

48V x 2000A x 0.08 seconds == 7680 Joules !!!! No longer a tiny amount of energy.

Pulse 7680 Joules of energy in a laser at 6.34uS and thats 1.21GW marty !!! Time travel !!!
 

Wolf

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daromer said:
Wolf it it blows your fuses you have wrong fuses for that inverter. They often should be b or c characteristics.

Inrush current limiting should not be needed for appliances for normal homes.

Also note that with a proper breaker between the inverter and battery you can also minimize the sparks created. Like the ABB series do.
Daromer,

Oh I know I had the wrong fuses but at that time I was a noob and just wanted my 15000W (Yes 15000 chinese Watts)Inverter hooked up.
What a noob...........................
Since my maximum consumption with everything on in the house is 4000W I have no idea why I bought this beast.
Nevertheless it will have an ABB S3 100A shunt trip on it soon :)

Wolf
 

Charly144

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i’d like to pick up this discussion again. as i do have 5 battery strings in parallel, which are monitored and controlled separately, i am looking for a safe but payable solution on dc breakers.

in my setup i am switching and monitoring the negative pole of the battery. as discussed above, we habe current flowing in and out of the battery, which means we have to care about current running in both directions via the breaker.

looking at the tomzn tob1z i am not sure whether it will be suitable for both directions. unfortunately i can’t find any datasheet for the 125a version.

what if i use a 2pole model and loop through from bottom to top and top to bottom, in order to have both directions covered...

or use just one and secure battery -> inverter, because other way is secured by victrons...

any thoughts?
 
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