DC breakers/fuses

[billi]

Maybe Billi's switches work fine because he doesn't turn his PV off often in full sunlight (why would he)?

EA ,  the one i suggested to Stephan is not the one i have , but many others use them , cause they address the bespoke problem

It seems a nightmare  , what some "Accessoires" can cost  and probably a good idea to get as much info  as possible  about those

I have three of those  between the battery and the inverter  and the 2 PV  controllers

and surely i used those  a few times to disconnect the PV from the system  (if needed )

But hey , my PV is only wired to 66 V    so kinda low and remaining in the hobby league     ,  but this was intended from the start .... DC is my Voltage for AC  i get Bon Scott (my electrician)

my fuses are fitted in the Victron  DC Link box  that seemed pricy when i got it  8 years back , but worth  it for people like me (in a growing system)  , with two right hands and a brain that has other things to do then always thinking  in numbers


CU

[Eccentric Anomaly]

Maybe Billi's switches work fine because he doesn't turn his PV off often in full sunlight (why would he)?

EA ,  the one i suggested to Stephan is not the one i have , but many others use them , cause they address the bespoke problem

Hi Billi, I think we might be talking at cross-purposes. I was commenting on and asking about the “disconnect” switches that Stephen linked to in his first post. I've no idea what switches you use other than that you implied you used something very similar. I think those 150 A breakers you linked to ought to be fine and agree with you that if Justme is right that they're not adequate then they're badly specified.

[Tinbum]

I use something like this.

I have a 60kVa 3 phase ups and the battery bank of about 32x12v (384v) batteries is protected by a similar item as manufactured. They do come up for sale at good prices on auction sites. Take careful note of the sensor part through as some are AC, some DC and some both.

[billi]

Hi Billi, I think we might be talking at cross-purposes

Can happen ,  actually happens very often  in such a big universal brain   


Surely , if Justme knows

I would not dream of putting more than about 20 amps through them.

the specs of a 150 A  rated  fuse better than the supplier , i will be the last person  that recommends this product  again

[Justme]

Hi Justme, why not??

Is it breakers in general that you don't like as disconnects, or that specific model? 

Well when you think that the cable that carry my 300amps at 12v for the inverter feeds are 120mm2 & those tiny screw terminals are less than 15mm2 I cant see them lasting that long before they melt.

I would not dream of putting more than about 20 amps through them.

then report to the supplier , i would say   

They were bought by me for the purpose of disconnecting under 10 amps.

They suit that purpose. They were cheap.

[Eccentric Anomaly]

300 A at 12 V is a bit mind boggling. Why?

An aside on selection of nuts and bolts for this sort of thing: http://edavies.me.uk/2013/11/resistance-stainless/.

[billi]

Quote from: stephendv on June 23, 2014, 04:43:18 PM
Hi Justme, why not??

Is it breakers in general that you don't like as disconnects, or that specific model?


Well when you think that the cable that carry my 300amps at 12v for the inverter feeds are 120mm2 & those tiny screw terminals are less than 15mm2 I cant see them lasting that long before they melt.

Hmm ... this somehow sounds logical  , but why are cable terminals  then having no bigger holes ??

[Justme]

The cable terminals dont rely on the hole or the contact around the hole to transmit the current.
Its the flat faces that are held together. Those resetable fuses dont have large external contact surfaces.
I guess they also dont have large internal contacts on the switch.

We are off grid to have an inverter for our mains power.
We dont often pull the full capacity through the cables but they still need to be sized to take the max load.

[biff]

This is the main reason why we went the 120volt route.
                                     Our first system was 12volt and I learned quickly that if we were going to be anyway successful of-grid,we had to get as high in the voltage as possible within reason. I know that most off-gridders are 48volt but the amps are still very high on long runs to a DC immersion heater dump load. So 120volt seemed a reasonable compromise at the time.
  As it turned out,140volt travels well over long stretches and the fuses are still 20amp per string, with the same 20amp fuse for the turbine.
   I also believe that 120volt is kinder to the battteries. It delivers the charge better and the bank can be 2 ton .
    We still have the same original 2kw iron core Chinese Inverter,sitting there unfussed for over 6 years. Our very first controller was the old type grey box affair which blew one night during a bad storm but   I installed two of the new type digital controllers. This is a good idea because if one gets whacked,the other can cope.
        We had our own way of testing dump loads, during a storm but I have grown out of that lark.
  I kept enough cardboard and tarp to cover the array if I needed to work on it in daylight.I am well aware that it is still live even after I have disconnected but the m4 connectors can be pulled apart without any nasty arcing once you disconnect the bank. Even car headlights can make the panels deliver a charge in the dark.
                                                                                             Biff

[Eccentric Anomaly]

We are off grid to have an inverter for our mains power.

Of course, but why 12 V? The only reason I can think of is that you started with a small 12 V system and it just grewed. Starting from scratch, 24 V would be the minimum, I'd have thought, and you'd probably need a good reason not to use 48 V or, as Biff says, more though then you get less choice of inverters.

[billi]

The cable terminals dont rely on the hole or the contact around the hole to transmit the current.
Its the flat faces that are held together. Those resetable fuses dont have large external contact surfaces.
I guess they also dont have large internal contacts on the switch.

We are off grid to have an inverter for our mains power.
We dont often pull the full capacity through the cables but they still need to be sized to take the max load.

So back to Stephan s question ,  would you suggest then  , that the outback 175 a rated  unit are the way to go  with their "huge  3/8”  studs and contact area" ?? at a pricy price
... plan B ?

[Billy]

Morning all,

My high current gear is all joined up with 3/8th"/10mm stud and 140mm2 cable.  We are talking 350/400 draw for the thruster and a bit less for the winch.  Mega fuses for me, and some suitably rated battery disconnects.

[Justme]

We are off grid to have an inverter for our mains power.

Of course, but why 12 V? The only reason I can think of is that you started with a small 12 V system and it just grewed. Starting from scratch, 24 V would be the minimum, I'd have thought, and you'd probably need a good reason not to use 48 V or, as Biff says, more though then you get less choice of inverters.

We first sourced a 12v victron at a bargain price, then matched a medium battery bank (at a bargain price) to it. From there it just grew so the next victron had to be 12v then increased the battery bank. If we need to change the inverter again we could go 12 24 or 48v without needing to buy extras as the outback controller will do all of them.

[stephendv]

In the end I went for a 150A megafuse + chunky mechanical disconnect switch linked to on the first page.  Since this is for someone else's system I don't want to take any chances with having short circuited batteries and then having a breaker which may not be able to break the massive currents.

The part of the megafuse that's designed to melt is only a thin flat strip about 1mm thick and 2mm wide.