DC breakers for 48V SLA battery banks

[wattmatters]

I need some help choosing a suitable DC circuit breaker / over current protection.

I've searched on the forum and not really getting far with suitable suggestions.

This is my battery system schematic, feeding an all-in-one inverter:


By all means make suggestions on the above if it should be configured a different way. Not shown in the diagram are the AC input and output and the solar PV input.

The system's primary job is for grid outage backup. Not much cycling of these batteries is expected. Just when needed.

At present I have one of the battery banks supplying the all-in-one inverter and I have a 20A limit set on charging, which I plan to lift to 40A when the second bank is added. I have a 100A megafuse and one of those cheap circuit breakers like this:

But I'm not convinced this circuit breaker is really that good of a device so am looking for advice on suitable alternatives.

I don't think I need smart relay control, for now I'll trust the inverter's inbuilt low voltage / low charge state cut off protection. I think I just want a suitable over current protection device which can also be manually switched if I need.

The inverter is rated to supply up to max of 4kW continuous on the AC output side, so on the DC side I don't expect ever to draw more than about 80A and any such high load would be for brief periods, a couple of minutes perhaps. Most of the time during outage back up the load on the DC side will be in the 10-15A range, less if it's daytime and the off-grid solar PV array is also supplying power. Charging current will be limited to 40A max.

Also, being located in Australia suppliers in the USA are typically out of bounds (most don't ship or if they do the shipping prices are ridiculous).

I've searched online for 100A DC circuit breakers but the array of options presented are pretty confusing, many are clearly not DC breakers but as for the rest, well the price variances are huge and I'm having trouble knowing what is suitable and of suitable quality.

Suggestions?

Thanks in advance.

 

[FilterGuy]

I need some help choosing a suitable DC circuit breaker / over current protection.

I've searched on the forum and not really getting far with suitable suggestions.

This is my battery system schematic, feeding an all-in-one inverter:

View attachment 61188
By all means make suggestions on the above if it should be configured a different way. Not shown in the diagram are the AC input and output and the solar PV input.

The system's primary job is for grid outage backup. Not much cycling of these batteries is expected. Just when needed.

At present I have one of the battery banks supplying the all-in-one inverter and I have a 20A limit set on charging, which I plan to lift to 40A when the second bank is added. I have a 100A megafuse and one of those cheap circuit breakers like this:
View attachment 61190
But I'm not convinced this circuit breaker is really that good of a device so am looking for advice on suitable alternatives.

I don't think I need smart relay control, for now I'll trust the inverter's inbuilt low voltage / low charge state cut off protection. I think I just want a suitable over current protection device which can also be manually switched if I need.

The inverter is rated to supply up to max of 4kW continuous on the AC output side, so on the DC side I don't expect ever to draw more than about 80A and any such high load would be for brief periods, a couple of minutes perhaps. Most of the time during outage back up the load on the DC side will be in the 10-15A range, less if it's daytime and the off-grid solar PV array is also supplying power. Charging current will be limited to 40A max.

Also, being located in Australia suppliers in the USA are typically out of bounds (most don't ship or if they do the shipping prices are ridiculous).

I've searched online for 100A DC circuit breakers but the array of options presented are pretty confusing, many are clearly not DC breakers but as for the rest, well the price variances are huge and I'm having trouble knowing what is suitable and of suitable quality.

Suggestions?

Thanks in advance.

Why do you want a fuse *and* a breaker?


You are correct in being suspicions of that breaker if it is not Blue Sea or Busman/Eaton branded. (Eaton-Busman Makes the Blue Sea version) All of the other knock-offs are questionable.

How did you choose the Mega Fuse? It has a rather low 1K AIC rating and with the low internal resistance of LiFePO4, the general consensus is that high AIC rating is important. On the forum we generally recommend a class T fuse (20KA AIC), but I have seen pre-built batteries with ANL fuses (5K AIC). (With FET based BMSs the inline resistance helps reduce the needed AIC rating, but I have never seen a good analysis of that)

You may want to review this:

DC Fuse and breaker Sizing and Placement

To get the paper, click on the orange button at the top of the page. The attached presentation gives the fundamentals for picking fuse/breaker sizes and describes where in the circuit they should be placed. You can download the presentation...

diysolarforum.com

 

[wattmatters]

Why do you want a fuse *and* a breaker?

Thanks for responding.

I don't necessarily. I guess some redundancy isn't a bad idea but agree it's not absolutely necessary if I felt the breaker was reliable. I don't have a sense of what sort of breaker I can be confident with and with this one I figured it was better to have it.

How did you choose the Mega Fuse?

It was given to me by a fellow off gridder who was encouraging me with my project. That's all I know about it. I do trust his judgement though.

You are correct in being suspicions of that breaker if it is not Blue Sea or Busman/Eaton branded.

Thanks. I found these options via marine supplies company here.

Ignore the ratings shown in the pics, they are just to show the type.

$75. Circuit Breaker 285F Series Surface Mount 100A - BS- 7187


$115. Electrical Circuit Breaker 187F Series Surface Mount 100A - BS - 7144B


If these breakers are the good stuff then I'll ditch the fuse. Make for cleaner cabling. The 187F looks like it would make for neater set up in my housing but quite a bit more expensive.

It has a rather low 1K AIC rating and with the low internal resistance of LiFePO4

My batteries are sealed lead acid. Enersys Powersafe SBS190F. Eight of them weighing nearly half a tonne.

 

[wattmatters]

You may want to review this:

Thanks, I've been through that powerpoint. Helpful.

 

[drnickriviera]

A related question. These Blue Sea and other similar breakers say 48vdc max, not nominal. Blue Seas seems to test them at 42vdc. Is it ok to use these on a 48V nominal system or should you go with breakers rated at 60v and higher?

wattmatters. I'm looking at the midnite solar panel mount breakers. You may also check ebay for airpax breakers

 

[JoeHam]

A related question. These Blue Sea and other similar breakers say 48vdc max, not nominal. Blue Seas seems to test them at 42vdc. Is it ok to use these on a 48V nominal system or should you go with breakers rated at 60v and higher?

Discussed many times but I believe the spec sheet, not heresay. As you know, a 48v nominal system will exceed that by a significant margin. I would NOT use something not properly rated for a critical safety purpose.

I would only use Schneider, Midnite Solar, Cooper Busman.

I normally use the Schneider C65H-DC breakers which are rated at 600V DC if I recall correctly.

 

[drnickriviera]

Discussed many times but I believe the spec sheet, not heresay. As you know, a 48v nominal system will exceed that by a significant margin. I would NOT use something not properly rated for a critical safety purpose.

I would only use Schneider, Midnite Solar, Cooper Busman.

I normally use the Schneider C65H-DC breakers which are rated at 600V DC if I recall correctly.

Ahh, i'm just getting started on this forum so haven't had a lot of time to go over old threads. I'm in the process of building my system and just got to breakers. I went to Will's latest video when he was replacing the lv5048 and wanted to see what he used. Got me head scratching. If Blue Seas had a rated cycle life at 48v, then maybe I would use, but all i've seen is a cycle life at 42v. I think i'll stick with higher voltage rated breakers.

 

[wattmatters]

These Blue Sea and other similar breakers say 48vdc max, not nominal.

Ah, hadn't noticed that. Thanks.

That would make them unsuitable given my system is 48V DC nominal but typically operates in the 50-56V range. Bugger.

wattmatters. I'm looking at the midnite solar panel mount breakers. You may also check ebay for airpax breakers

Thanks but but any clues on where to find these things in Australia? Everything listed is in the US.

I would only use Schneider, Midnite Solar, Cooper Busman.

I normally use the Schneider C65H-DC breakers which are rated at 600V DC if I recall correctly.

Thanks for the suggestions.

Unfortunately when I search online for such things, I get back to my original problem. A whole lot of noise in the results and very little signal.

Schneider lists what appears to be a DIN rail device with the right specifications but I can't find anywhere here who actually sells them.

I'm finding this most frustrating!

I sent an enquiry off to company called Outback Marine as they seem to have a range of similar things. No idea if they'll respond.

 

[mrzed001]

Why do you want a fuse *and* a breaker?

A breaker can fail, like a relay. A fuse can not


For breaker NOARK is a good choice:
https://www.outbackmarine.com.au/noark-200a-500v-dc-circuit-breaker-2-pole

For fuse Class T fuse is a good start ... but I like the NH1 fuses better.

This are the principles how I design fusing
https://diysolarforum.com/threads/4-0-cables-250anl-fuse-heating.27153/page-2#post-323078

 

[JoeHam]

@wattmatters look here :

250V Low-voltage C65H-DC Miniature Circuit Breaker For Solar Panels 16A/32A/63A(63A) - - Amazon.com

250V Low-voltage C65H-DC Miniature Circuit Breaker For Solar Panels 16A/32A/63A(63A) - - Amazon.com

www.amazon.com

Sometimes they are marked Schneider brand, sometimes not but it’s always been the correct model number and I’ve not had any problems in a few different 48v nominal systems.

And DIN rails here :

mxuteuk 3 pcs MXU-DIN-100 DIN Rail Slotted Aluminum RoHS 4" Inches Long 35mm Wide 7.5mm High - - Amazon.com

mxuteuk 3 pcs MXU-DIN-100 DIN Rail Slotted Aluminum RoHS 4" Inches Long 35mm Wide 7.5mm High - - Amazon.com

www.amazon.com

Hope that improves your S/N ratio ?

 

[wattmatters]

For breaker NOARK is a good choice:
https://www.outbackmarine.com.au/noark-200a-500v-dc-circuit-breaker-2-pole

Thanks.

The 100A version looks pretty robust but pricey. To be able to switch batteries independently I'd need two. Else I guess just use the one for both.

but I like the NH1 fuses better.

I'm considering just going with fuses and forgetting about a breaker. This has been suggested to me:

Triple NT00 HRC Fuse Isolating Switch - 160 Amp - Hardware - Fuses & Breakers

www.rpc.com.au

NT00 HRC Fuse Link - 100 Amp - Hardware - Fuses & Breakers

www.rpc.com.au

I'm not expecting to need to flip this thing on/off with any regularity. It's the overcurrent protection I'm more interested in.

@wattmatters look here :

Thanks but those are for solar panels, not batteries and only rated up to 63A so not suitable in any case.

I appreciate all the suggestions!

 

[mrzed001]

Thanks.

The 100A version looks pretty robust but pricey. To be able to switch batteries independently I'd need two. Else I guess just use the one for both.

There is also an ABB breaker that can be disconnected remotely. Expensive, but sometimes usefull. For example used together with an over voltage protection.

I'm considering just going with fuses and forgetting about a breaker. This has been suggested to me:

Triple NT00 HRC Fuse Isolating Switch - 160 Amp - Hardware - Fuses & Breakers

www.rpc.com.au

NT00 HRC Fuse Link - 100 Amp - Hardware - Fuses & Breakers

www.rpc.com.au

NT00 is the little brother of the NH00/NH1 fuses. That is enough for the system.

I'm not expecting to need to flip this thing on/off with any regularity. It's the overcurrent protection I'm more interested in.

Do not forget you will need some pre-charge mechanism or procedure to do before connecting battery to inverter.

 

[wattmatters]

There is also an ABB breaker that can be disconnected remotely. Expensive, but sometimes usefull. For example used together with an over voltage protection.

Thanks. I have a link somewhere to a chunky relay controller which would provide an extra layer of low/high voltage cut off protection in addition to what is built into the all-in-one inverter/charger controller.

I don't propose to install one at this time but may do so in future.

NT00 is the little brother of the NH00/NH1 fuses. That is enough for the system.

Great, thanks.

Do not forget you will need some pre-charge mechanism or procedure to do before connecting battery to inverter.

I have a 10W resistor I've been using for that job. It's not fancy but it seems to work. It probably could do with being a bit higher resistance rating than 2.2ohms but it was all the shop had.

 

[wattmatters]

So I think I'm down to the following options:

100A Noark breakers
NT00 HRC 100A fuse

Perhaps 1 x breaker for each battery, and 1 x fuse in between the breakers and the AIO inverter like this:

 

[wattmatters]

Even though the above looks fine, I just can't find an image/video anywhere of how these things are actually mounted, nor where and how the cables connect.

The billion page long catalogues have gazillions of lovely but completely useless images. Not a single one actually shows how these things are mounted nor where the cables go.

I never had this amount of trouble working out all the other stuff with my off-grid system.
But DC breakers for the batteries, this has me beat.

 

[mrzed001]

Even though the above looks fine, I just can't find an image/video anywhere of how these things are actually mounted, nor where and how the cables connect.

The billion page long catalogues have gazillions of lovely but completely useless images. Not a single one actually shows how these things are mounted nor where the cables go.

I never had this amount of trouble working out all the other stuff with my off-grid system.
But DC breakers for the batteries, this has me beat.

Both the NOARK and the fuseholder are connected to both lines and separating both lines
A video from a fuseholder:

 

[wattmatters]

Thanks. Shame they don't show where the cables go.

I've decided (I think) I'll just go with the pull down fuses, one fuse per battery bank.

 

[mrzed001]

Thanks. Shame they don't show where the cables go.

I've decided (I think) I'll just go with the pull down fuses, one fuse per battery bank.

That is a good choice. Protects both line the same time. Allows you to disconnect one pack for maintenance and other still giving power to load.
I sometimes put one before inverter too. To limit the current inverter can pull ... or to shut down if pulls too much.

 

[wattmatters]

Allows you to disconnect one pack for maintenance and other still giving power to load.

That's one thing I can't tell from the pictures - whether this triple fuse holder enables me to access each fuse independently, or if are all fuses are opened at same time.

 

[mrzed001]

That's one thing I can't tell from the pictures - whether this triple fuse holder enables me to access each fuse independently, or if are all fuses are opened at same time.

All opened at the same time. Mainly there were designed for 3 phase systems. But we love to use them in battery systems because they have a high DC V and a high Amp rating. Also a high Amp short circuit disconnect rating (the sand in the big fuse disconnects even big arches).