48V Disconnect

[OffGridInTheCity]

I use a 400a ABB SACE S3 w/24v shunt-trip for my 48v powerwall w/24,000w of inverting.

Here's a plain ABB SACE S3 3-pole 200a for a reasonable price ($100) https://www.ebay.com/itm/282768920712 They are ~400-500vdc certified.

These used ABB SACE breakers are among the highest quality hi-volt-dc/amps around and come in a large variety of 3pole, 2pole, shunt-trip (24v, 120v ac or dc) options. If you're patient a month or 2, you can usually find a good match for what you need.

 

[Captain Kirk]

View attachment 147923

I too wrote BEP and this was the exchange. Seems no interest by the company to specify the voltage spec over 48V:

 

[HalfBaked]

The Victron website says their battery disconnect switch is suitable for 48v battery systems. Not just "rated to 48v".

 

[Captain Kirk]

View attachment 147923

The Victron website says their battery disconnect switch is suitable for 48v battery systems. Not just "rated to 48v".

Me thinks unfortunately not: https://diysolarforum.com/threads/victron-48v-275-amp-switch.64936/#post-812828

 

[HalfBaked]

Me thinks unfortunately not: https://diysolarforum.com/threads/victron-48v-275-amp-switch.64936/#post-812828

While my statement stands that the spec sheet does say it's suitable for 48v battery systems, that spec is a sad and dangerous lie. Nice catch.

 

[Tulex]

I too emailed the company, pointed them to this thread, asked for clarity.

Hi,

Thank you for sending the inquiry below. In speaking with our team, those are only rated to a nominal 48V per its UL rating. Those would be the only specs we could suggest at the moment.

Regards,

Kenny Garcia | Technical Support Representative | NAVICO GROUP 800 307 6702| Navico.com

 

[FilterGuy]

only rated to a nominal 48V per its UL rating

A 'Nominal 48V' UL rating will handle a 48V battery system.

They are being very careful about what they say, so I am assuming they are using the 'Nominal' terminology correctly.

Why they won't be more forthcoming is a mystery to me.

 

[740GLE]

So “Nominal 48v” is fine for 60vdc?

Or nominal is good for only +5%?

IMO a disconnect doesn’t break load, it just drops voltage. So zero current (BMS off) de-energizing doesn’t much.


Over current fault isolation is another thing.

 

[cs1234]

The nominal voltage on a 48vdc lifepo4 battery is 51.2vdc isn't it? You would have to use one of the telecom style 15cell batteries to hit 48vdc nominal.

 

[Tulex]

I just read this thread on busbars and voltage. Seems to me then that the rated amps is much more important than whether a product is 48V max or 48V system? I mean, if you have a 48V disconnect rated for 400 amps, I can't imagine it really matters if your bms/fuse are 200/300 amps for example. Or is there a mechanical part that comes into play? Even then, I can't see how. 48v @ 400 amps has to be much harder on it than 58v at 200 amps.

 

[cs1234]

I just read this thread on busbars and voltage. Seems to me then that the rated amps is much more important than whether a product is 48V max or 48V system? I mean, if you have a 48V disconnect rated for 400 amps, I can't imagine it really matters if your bms/fuse are 200/300 amps for example. Or is there a mechanical part that comes into play? Even then, I can't see how. 48v @ 400 amps has to be much harder on it than 58v at 200 amps.

Think of voltage as how far somebody can do a standing long jump. The amps are how many people can be straddling their back while they do that same long jump. A breaker rated for 48vdc might not be able to actually stop something at 58vdc from jumping the gap.. regardless of amperage.

 

[Captain Kirk]

I just read this thread on busbars and voltage. Seems to me then that the rated amps is much more important than whether a product is 48V max or 48V system? I mean, if you have a 48V disconnect rated for 400 amps, I can't imagine it really matters if your bms/fuse are 200/300 amps for example. Or is there a mechanical part that comes into play? Even then, I can't see how. 48v @ 400 amps has to be much harder on it than 58v at 200 amps.

Working from my electronics education memory of many moons ago, the voltage determines the gap jumping ability...the greater the voltage, the greater gap the electrons can cross/arc. Specs are important to me, because an engineer made some calculations based on a user requirement specification and designed accordingly. The word nominal doesn't belong in any spec IMO....too gray and specs should be B&W.

 

[Tulex]

Think of voltage as how far somebody can do a standing long jump. The amps are how many people can be straddling their back while they do that same long jump. A breaker rated for 48vdc might not be able to actually stop something at 58vdc from jumping the gap.. regardless of amperage.

But you are talking breakers, not disconnects. A disconnect is a manual on/off devise, not something that is triggered. And arc isn't an issue, the arc distance between 48v and 58v is miniscule.

 

[Captain Kirk]

Working from my electronics education memory of many moons ago, the voltage determines the gap jumping ability...the greater the voltage, the greater gap the electrons can cross/arc. Specs are important to me, because an engineer made some calculations based on a user requirement specification and designed accordingly. The word nominal doesn't belong in any spec IMO....too gray and specs should be B&W.

whoops, CS beat me to the reply....disregard.

 

[Tulex]

A 'Nominal 48V' UL rating will handle a 48V battery system.

They are being very careful about what they say, so I am assuming they are using the 'Nominal' terminology correctly.

Why they won't be more forthcoming is a mystery to me.

It took me over 2 weeks to get a reply from them, so I'm guess they had their lawyer provide the answer.

 

[cs1234]

But you are talking breakers, not disconnects. A disconnect is a manual on/off devise, not something that is triggered. And arc isn't an issue, the arc distance between 48v and 58v is miniscule.

A breaker or disconnect both are designed with a certain distance between the parts that break the circuit when in the disconnected state. The difference is minuscule for sure.. but maybe they are right on the edge for 48v, having designed their disconnect for 12/24vdc.

 

[Sanwizard]

So “Nominal 48v” is fine for 60vdc?

Or nominal is good for only +5%?

IMO a disconnect doesn’t break load, it just drops voltage. So zero current (BMS off) de-energizing doesn’t much.


Over current fault isolation is another thing.

I called Blue Sea systems support line, and they told me their 48V switch is tested to 48V, and reccomends NOT using it over 48V, cause under load, it may not handle the arc. So I ordered one of those Amazon 60V switches instead. The switch broke after about 20-30 on off cycles( the plastic switch itself stripped, so I could not turn off the battery.

I ended up buying the 48V blue sea switch, and will just set the inverter loads off before switching it.

 

[740GLE]

it’s def not idiot proof needing to knowing the order of operations, but if you have another over current protection device it’s a great isolating device and will last a long time.

I have one for my 12v system paired with an ANL fuse and plan to use it in the same fashion when I upgrade to 24v but would have no concerns for a 48v system.

 

[DIYrich]

I ended up buying the 48V blue sea switch, and will just set the inverter loads off before switching it.

The way I understand it, the issue is less about the arc during disconnect than it is about arcing inside the switch during normal operation (or just sitting there). They tested at 48v that no unexpected arc will occur during normal operation of the switch. At 58.0v charging voltage, there is no guarantee that there will not be an internal arc between anything inside the switch. Similar to voltage rating of wire - it is rated for 600v for a reason.

Also, the switch has some resistance. At 48v and max amps, the heating caused by the resistance is safe for the switch. It may not be able to dissipate the 21% additional heat at 58v.

I'd still trust Blue Sea over unknown brand from china on Amazon. I bought a hefty looking switch, and it heated up after a minute of heavy use (but well within the advertised specs). I returned it.

 

[740GLE]

Open air arcing is much different than breaking an arc with increased distance.

The distance conductors need to be to start an arc at say 60v is minuscule, in the mm range. But you can sustain an arc at much larger distance assuming it was started during the operation of opening the disconnect.

Sure they didn’t test it to verify it but they also have a very very conservative rating to cover their butt.

As for the heat the resistance of the switch is directly proportional to the current flowing through the switch and has zero do to if the system is 12v 24v or 48v, current is current. So 100a through the switch at 12v and 48v still has the same I^2*R losses.

The fault current is dramatically different so that’s why big bucks should be spent on over current protection.