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Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: stephendv on June 23, 2014, 07:42:42 AM



Title: DC breakers/fuses
Post by: stephendv on June 23, 2014, 07:42:42 AM

I'm helping a mate with an off-grid install on a budget and I'm not sure about which DC breakers/fuses/switches to use for the main battery bank.  Install is around a Victron C1600/24V, so they'd need about a 150A protection.  A single outback 175A DC breaker goes for 80+ euros which is too dear.  However, 2 x 80A breakers in parallel would be about 30 Euros which is doable- but it's not a neat solution as I'd have to superglue or find some other way to make sure the breakers operate together.
The Victron has a surge rating of 3000W and the owners will only be using washing machine + fridge (not bought yet), so do you think a single 125A outback breaker would be good enough (it goes for just over 30 euros and would solve the switch and protection problem in 1 unit).

Another option is simply a Fuse + disconnect switch, this is the cheapest solution so far, thinking of using a 150A mega-fuse (like in the victron itself) and one of these disconnect switches: http://www.ebay.es/itm/Desconectador-de-Bateria-150A-pico-400A-con-Llave-y-Tapa-Terminales-Coche-4x4-/321390605416?pt=LH_DefaultDomain_186&hash=item4ad45f7468&_uhb=1

Thoughts?


Title: Re: DC breakers/fuses
Post by: billi on June 23, 2014, 08:43:37 AM
Ola Stephen

Perhaps here http://www.fraron.de/en/power-inverter-accessories/fuses-fuseholders/


(http://www.fraron.de/images/produkte/cache/mi33/33630534-AF150A-1000-1.jpg)


Title: Re: DC breakers/fuses
Post by: stephendv on June 23, 2014, 08:53:26 AM
Thanks billi!  That looks like the perfect solution.


Title: Re: DC breakers/fuses
Post by: Justme on June 23, 2014, 04:41:05 PM
Dont do it.

I have them as a simple disconnects on my DC PV strings.

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

Some of mine are 300amp.


Title: Re: DC breakers/fuses
Post by: 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? 


Title: Re: DC breakers/fuses
Post by: billi on June 23, 2014, 04:50:53 PM
Quote
I would not dream of putting more than about 20 amps through them.

then report to the supplier , i would say    ;)






Title: Re: DC breakers/fuses
Post by: Eccentric Anomaly on June 23, 2014, 06:02:21 PM
Am I right in thinking that those “disconnect” switches that Stephen links in the first post are really isolator switches; that is, they can carry high current and they can safely separate systems but they should only be switched off when there is no (or little) current flowing?

OTOH, I can't see the point of a 150 A breaker which can't break considerably more than 150 A. Maybe it'll only do it a few times but I think repeated operation at full current could be avoided in this application as normally you'd turn the inverter off or at least disconnect its load before manually triggering the breaker.


Title: Re: DC breakers/fuses
Post by: nowty on June 23, 2014, 06:36:49 PM
I use a fork lift truck battery fuse, about £20.


(http://s1.postimg.org/59lq5tje3/Off_Grid_Main_Battery_Fuse.jpg) (http://postimg.org/image/59lq5tje3/)


Title: Re: DC breakers/fuses
Post by: stephendv on June 23, 2014, 06:44:11 PM
I use a fork lift truck battery fuse, about £20.

And to disconnect the battery from the inverters?


Title: Re: DC breakers/fuses
Post by: stephendv on June 23, 2014, 06:48:25 PM
OTOH, I can't see the point of a 150 A breaker which can't break considerably more than 150 A. Maybe it'll only do it a few times but I think repeated operation at full current could be avoided in this application as normally you'd turn the inverter off or at least disconnect its load before manually triggering the breaker.

Yeah, from my perspective I want something that will work as a protection device in the event of a short circuit, so it must be able to break thousands of Amps.
The other nice-to-have feature is to be able to isolate the battery from the rest of the installation occasionally, which I'll do as you describe, only under low or no load.


Title: Re: DC breakers/fuses
Post by: billi on June 23, 2014, 07:20:01 PM
what are u on about ?

 ok   my setup is fused  like Stephends second  approach     fuse and disconnect switch

I have my megafuses ( that never blew)  and a disconnect   switch


So  surely i would follow my  given link,  nowadays , cause it seems much easier  in some installs


Quote
Am I right in thinking that those “disconnect” switches that Stephen links in the first post are really isolator switches; that is, they can carry high current and they can safely separate systems but they should only be switched off when there is no (or little) current flowing?
Please tell me  if thats important !  Cause i switch my PV of/on  , when ever i want


Title: Re: DC breakers/fuses
Post by: biff on June 23, 2014, 08:04:06 PM
I guess he means that most pv panels have a little sticker on them that states that they should never be switched off under load,
                         However,If I have to switch mine off during the day,I throw a tarp over the array and then disconnect.
                                                                   Biff


Title: Re: DC breakers/fuses
Post by: billt on June 23, 2014, 09:11:48 PM
I'd guess that he means that DC breakers are harder to design and make than AC breakers. (Properly designed solar string DC isolators tend to be more expensive than similarly rated AC isolators.)

A battery isolator is a safety device; you may want to disconnect the battery in an emergency when it is delivering power and you cannot remove the load by any other means. If the battery isolator is not designed to break the full load at the system voltage then it may not work at all and weld itself closed.

Your choice. If you are satisfied that the load can be removed by another means so little current is flowing through your switch then use the cheap option. I'd go for the expensive but reliable option.


Title: Re: DC breakers/fuses
Post by: Eccentric Anomaly on June 23, 2014, 09:33:58 PM
Quote
Am I right in thinking that those “disconnect” switches that Stephen links in the first post are really isolator switches; that is, they can carry high current and they can safely separate systems but they should only be switched off when there is no (or little) current flowing?
Please tell me  if thats important !  Cause i switch my PV of/on  , when ever i want

Dunno, that's only a semi-rhetorical question. My understanding is that those isolators are not rated to break at full load current but a) I'm not sure and b) I too would be interested to know at what current they can safely break.

As Billt says, they could weld shut. However, they have to break to draw an arc so that doesn't seem like an immediate threat to me. Either they'd open but not suppress the arc so continue to pass current and eventually overheat or, I'm guessing, they'd more likely be pitted by arcs draw, get higher resistance and not work well or run warm subsequently.

Of course, there's the difference between what they're rated for and how they work in practice. Maybe Billi's switches work fine because he doesn't turn his PV off often in full sunlight (why would he)? The actual switch rating would be defined on the assumption that it would be operated often.

It's a matter of what works vs what an electrician can actually sign off.

I guess he means that most pv panels have a little sticker on them that states that they should never be switched off under load,

Switching panels off under load is fine. PWM controllers do it multiple times per second. The MC4 connectors aren't rated for disconnection under load - a slightly different matter.


Title: Re: DC breakers/fuses
Post by: nowty on June 23, 2014, 11:28:34 PM
And to disconnect the battery from the inverters?

Shutdown the inverter and unscrew the fuse.  :crossed

In an emergency, take a sledge hammer and smash the fuse cos replacing the fuse will be the least of my problems. sh*tfan:
Actually I did think about putting in an isolator but decided that an isolator might cause more problems that it solves with the large currents supplied from the battery.
I also decided to remotely fit the fuse away from the battery housing as a fuse blowing could act as a perfect detonator to any explosive gases.


Title: Re: DC breakers/fuses
Post by: billi on June 24, 2014, 08:28:48 AM
Quote
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 (http://d31erm66v9u4gr.cloudfront.net/sites/default/files/imagecache/product/images/2012/02/blue-sea-systems-9003e-dc-battery-switch-44528.gif)

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





Title: Re: DC breakers/fuses
Post by: Eccentric Anomaly on June 24, 2014, 08:42:09 AM
Quote
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.


Title: Re: DC breakers/fuses
Post by: Tinbum on June 24, 2014, 08:59:04 AM
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.


Title: Re: DC breakers/fuses
Post by: billi on June 24, 2014, 09:50:06 AM
Quote
Hi Billi, I think we might be talking at cross-purposes

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


Surely , if Justme knows
Quote
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



Title: Re: DC breakers/fuses
Post by: Justme on June 24, 2014, 05:07:07 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.


Quote
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.


Title: Re: DC breakers/fuses
Post by: Eccentric Anomaly on June 24, 2014, 08:33:51 PM
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/ (http://edavies.me.uk/2013/11/resistance-stainless/).


Title: Re: DC breakers/fuses
Post by: billi on June 25, 2014, 05:21:29 AM
Quote
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 ??

(http://www.elecspess.com.au/spnet6/img/L/U/G/2/4/lug240-16.jpg)


Title: Re: DC breakers/fuses
Post by: Justme on June 25, 2014, 08:56:26 AM
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.


Title: Re: DC breakers/fuses
Post by: biff on June 25, 2014, 09:42:19 AM
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 ;D.
    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, :hysteria :hysteria 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


Title: Re: DC breakers/fuses
Post by: Eccentric Anomaly on June 25, 2014, 10:28:07 AM
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.


Title: Re: DC breakers/fuses
Post by: billi on June 26, 2014, 05:39:42 AM
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 ?

(http://www.altestore.com/descfiles/outback/dcbreakers/OUTOBDC-20_&_OUTOBDC-30_side_250px.jpg)


Title: Re: DC breakers/fuses
Post by: Billy on June 26, 2014, 08:29:55 AM
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.


Title: Re: DC breakers/fuses
Post by: Justme on June 26, 2014, 04:48:57 PM
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.


Title: Re: DC breakers/fuses
Post by: stephendv on June 30, 2014, 09:43:15 AM
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.