What size Battery disconnect trip switch

[bds70]

Haven't quiet found the answer to this problem.

I want to correctly size a battery disconnect/trip switch, but not sure what amperage to get.

I have two 3000W victron inverters drawing power from 3 lifepo4 340ah batteries in parallel. The only Amp data I can see is that of being a 150A charger, but that's current 'to' the batteries not current draw 'From' the batteries.

Assuming both inverters are working at their peak of 3000W continuous, how do I calculate the amp draw and therefore be able to size a trip switch accordingly.

Thanks

 

[Q-Dog]

What voltage? Do you not have the manual?

 

[bds70]

Yeah sorry 12v. What am I looking for in the manual to tell me the max current draw?

 

[Q-Dog]

400 amp fuse is recommended for each inverter. (Section 4.2, Connection of battery cables)

 

[bds70]

400 amp fuse is recommended for each inverter. (Section 4.2, Connection of battery cables)

Perhaps I am not making myself clear. I have 400Amp fuses per inverter on the lynx distributor.
However if your equipment is on fire it's not feasable to be sticking your head into a locker trying to unscrew fuse connections.

So to try again. I want a trip switch immediately in the main battery positive cable before it reaches the lynx distributor. It would be placed at the very front of the access door, or alternatively internal, although that would require a much longer run of cabling.

The question is, what amp trip switch? 120 amps is too small, but would 600 amps be too big and not trip in the event of a problem.

This switch would cut ALL power from the Batteries to any of the equipment.

I hope this clarifies my question.

 

[Warpspeed]

You might like to look at Gigavac vacuum relays.
That is what I am using for battery disconnect.
These are typically rated to carry and break up to 400 amps and 1500 volts. They come with either 12v or 24v coils.

These are worth big money brand new, but come up on e-bay fairly often second hand as removed from junked electric vehicles.
Prices vary a lot, but if you are patient, and quick on the draw, real bargains pop up from time to time.
I bought two for eighty dollars a few months ago on e-bay.

 

[bds70]

I will have a look at that, thanks

 

[Alarchist]

You could use two Blue Sea HD series isolators, (one for each inverter) your 400A fuse rating is based on the Multiplus short term peak current, so you want an isolator that can handle it.

HD-Series - Blue Sea Systems

Up to 600 Amps continuous rating for large diesel engines.

www.bluesea.com

Or you could go for a dual NH style fuseholder / isolator, but they get expensive at 250a+

 

[mikefitz]

I want a trip switch immediately in the main battery positive

It's not too clear if it's a switch, contactor, or DC circuit breaker.
Whatever, with approaching 600 amps on a single feed, cable and component needs quality engineering.
Isolator switch,

HD-Series - Blue Sea Systems

Up to 600 Amps continuous rating for large diesel engines.

www.bluesea.com

 

[OffGridInTheCity]

You might like to look at Gigavac vacuum relays.
That is what I am using for battery disconnect.
These are typically rated to carry and break up to 400 amps and 1500 volts. They come with either 12v or 24v coils.

These are worth big money brand new, but come up on e-bay fairly often second hand as removed from junked electric vehicles.
Prices vary a lot, but if you are patient, and quick on the draw, real bargains pop up from time to time.
I bought two for eighty dollars a few months ago on e-bay.

How do you plan to activate the relay? thru a BMS? or manually?

I use a Gigavac on one of my batteries (with Chargery BMS) and love these relays - they have wide range of voltages (12, 24, 48...) and hi amps! The Chargery BMS works by providing a steady coil voltage to keep the relay closed (allow current) and then removes the voltage (relay opens / current stops) if there's a problem.

For my battery bank, I use a shunt-trip - e.g. a relay with a coil that can be triggered. The BMS or control system sends a momentary voltage to trigger the relay open - it's not a continuous voltage situation like Gigavac. For this I use a used (ebay) ABB SACE S3 with 24v coil. Mine is 400a capable.

 

[Warpspeed]

Yup, you beat me to it Off Grid.

Best and most flexible battery disconnect is to use a high current relay.
Once you have that, it can be operated from a BMS for under or over voltage disconnect, or activated and reset manually.

I did use a shunt trip dc circuit breaker for a while, but the cheap Chinese circuit breakers I was using kept failing.
The contacts either burned or welded together over time which made me very nervous !
A proper high quality DC circuit breaker would have been nice, but was really beyond my budget.

 

[Cronix]

I use one of these 60vdc/200a breakers on each battery rack before going to busbar before the inverter so I can quickly disconnect and work on a bank. They're the same breakers (different amperage) that are in the EG4 batteries.

Nader DC Circuit Breaker | 60V 200Amp with Enclosure

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signaturesolar.com

 

[OffGridInTheCity]

Yup, you beat me to it Off Grid.

Best and most flexible battery disconnect is to use a high current relay.
Once you have that, it can be operated from a BMS for under or over voltage disconnect, or activated and reset manually.

I did use a shunt trip dc circuit breaker for a while, but the cheap Chinese circuit breakers I was using kept failing.
The contacts either burned or welded together over time which made me very nervous !
A proper high quality DC circuit breaker would have been nice, but was really beyond my budget.

Agree that *quality* relay or breaker is recommended! ABB SACE and Gigavac are both quality. The risk of cheap stuff is 1) they might not work and 2) even if they work, if you toggle them 5 or 10 times they might stop working and 3) not ETL/UL.

For breakers (non relay), I use Midnite as they are ETL/UL and high quality. Everything from 15a for combiner boxes to 80a for Charge Controller -> battery bus to 250a for Battery -> Inverter. I think 250a is about the max for Midnite.

 

[bds70]

Thanks all for the help. I think some of the answers are getting a bit complicated for my range of understanding.

Let's try and simplify this.
So I have 3 340ah lifepo4 batteries in parallel. A single high capacity positive cable goes to a 400amp fuse. It then proceeds directly to a Lynxx Distributor.
The two mppt''s each go to the distributor each with their own 150amp fuse. The power then goes to each inverter from seperate poles with 500 amp mega fuses. Each inverter is 3000w.

Between the first 400 amp fuse and the distributor there is nothing. In the event I suffered - an Internal electrical fault in one of the mppt''s causing a fire. - I had no way of isolating the power from the battery to the distributor and thus the MPPT on fire was still receiving current from the batteries, making it hard to extinguish as it kept reigniting, until I was finally able to unscrew the positive cable from the batteries. In the process of which I inhaled a fair amount of toxic / acrid smoke. This has resulted in a severe chest infection.

So what I want is an manual / auto isolator switch where I can reach it without risking my life and turn it off, as well as an automatic trip if I was not present.

I need to be able to cut all power 'from' the batteries to 'all' internal equipment.

I hope that explains the whole issue.

 

[Cronix]

Between the first 400 amp fuse and the distributor there is nothing. In the event I suffered - an Internal electrical fault in one of the mppt''s causing a fire. - I had no way of isolating the power from the battery to the distributor and thus the MPPT on fire was still receiving current from the batteries, making it hard to extinguish as it kept reigniting, until I was finally able to unscrew the positive cable from the batteries. In the process of which I inhaled a fair amount of toxic / acrid smoke. This has resulted in a severe chest infection.

So what I want is an manual / auto isolator switch where I can reach it without risking my life and turn it off, as well as an automatic trip if I was not present.

I need to be able to cut all power 'from' the batteries to 'all' internal equipment.

I hope that explains the whole issue.

Is there a reason the breaker I posted won't work for you? You just put it between your battery bank and the first fuse. I don't think you actually need that fuse if you replace it with this breaker, but it wouldn't hurt either.

 

[Warpspeed]

There are two completely separate requirements here.

The first is over current protection to isolate the battery to protect the wiring. That can be achieved either with circuit breakers or fuses.
There are advantages and disadvantages with either. Or you can fit both.
Multiple class T bolt in fuses, located right at the final battery terminal of each battery string, followed by a master circuit breaker that disconnects the whole battery system from everything else for example.

The second requirement is an over or under voltage battery disconnect system, to protect a very expensive battery in the event of a system failure where the battery voltage may become uncontrolled.
That can be achieved either with a high current relay, or by fitting a shunt trip coil to the main circuit breaker that kicks the circuit breaker off electrically.
Manual disconnect can be performed either with the main circuit breaker, or perhaps by opening the high current relay with a small switch, or sometimes with one or more large red emergency shut down buttons in a large system.

 

[bds70]

Is there a reason the breaker I posted won't work for you? You just put it between your battery bank and the first fuse. I don't think you actually need that fuse if you replace it with this breaker, but it wouldn't hurt either.

I think I missed your post or flew past it. Would 200 amps be high enough to stop it tripping in normal use? I saw on the site that 200amp is the highest they have. But it looks ideal.

 

[bds70]

There are two completely separate requirements here.

The first is over current protection to isolate the battery to protect the wiring. That can be achieved either with circuit breakers or fuses.
There are advantages and disadvantages with either. Or you can fit both.
Multiple class T bolt in fuses, located right at the final battery terminal of each battery string, followed by a master circuit breaker that disconnects the whole battery system from everything else for example.

The second requirement is an over or under voltage battery disconnect system, to protect a very expensive battery in the event of a system failure where the battery voltage may become uncontrolled.
That can be achieved either with a high current relay, or by fitting a shunt trip coil to the main circuit breaker that kicks the circuit breaker off electrically.
Manual disconnect can be performed either with the main circuit breaker, or perhaps by opening the high current relay with a small switch, or sometimes with one or more large red emergency shut down buttons in a large system.

I truly appreciate your help, but this is what I meant by too complicated for me. It seems an awful big solution for what should be a simple problem. This is an off grid RV system not a house size one.

 

[Brucey]

Thanks all for the help. I think some of the answers are getting a bit complicated for my range of understanding.

Let's try and simplify this.
So I have 3 340ah lifepo4 batteries in parallel. A single high capacity positive cable goes to a 400amp fuse. It then proceeds directly to a Lynxx Distributor.
The two mppt''s each go to the distributor each with their own 150amp fuse. The power then goes to each inverter from seperate poles with 500 amp mega fuses. Each inverter is 3000w.

Between the first 400 amp fuse and the distributor there is nothing. In the event I suffered - an Internal electrical fault in one of the mppt''s causing a fire. - I had no way of isolating the power from the battery to the distributor and thus the MPPT on fire was still receiving current from the batteries, making it hard to extinguish as it kept reigniting, until I was finally able to unscrew the positive cable from the batteries. In the process of which I inhaled a fair amount of toxic / acrid smoke. This has resulted in a severe chest infection.

So what I want is an manual / auto isolator switch where I can reach it without risking my life and turn it off, as well as an automatic trip if I was not present.

I need to be able to cut all power 'from' the batteries to 'all' internal equipment.

I hope that explains the whole issue.

I've seen several installs where a cutoff switch is mounted directly to the positive busbar of the Distributor.

I have one of these I plan to use at some point

https://www.amazon.com/gp/aw/d/B00445KFZ2

 

[Warpspeed]

I truly appreciate your help, but this is what I meant by too complicated for me. It seems an awful big solution for what should be a simple problem. This is an off grid RV system not a house size one.

Only thing simpler would be a bloody great axe.
Cut the wire and run like hell.