Device Protection

[tetwin11]

I'm working on a battery charger module. It will include within it, qty 2 of MeanWell DBU-3200, connected in parallel at the AC input and DC output, powered by 220VAC.

https://www.meanwell.com/Upload/PDF/DBU-3200/DBU-3200-SPEC.PDF

The spec sheet says AC current typical 17A, inrush current typical 55A.
Does anyone have advice on what I should do for a protection scheme? Fusing? Breakers? They each have an internal fuse, but I can't tell what value. If I use a 50A breaker to power them both, is that sufficient protection?
And since I've been pondering and researching this, it leads me to question, what is the exact purpose of circuit breakers and fusing in a product like this? Is it just to prevent fires from a short circuit? Is it to prevent damage to components? It seems that the answer to this question is critical to deciding what to use.
Looking for any thoughts/advice/resources. Thanks!

 

[tetwin11]

I should note that it seems likely this will be a product that will be hardwired and bolted to the floor in an industrial environment. I'm not sure if that matters, but I wanted to add a bit of context.

 

[waross]

Breakers in that current range are typically thermal-magnetic.
A common sizing is the next size above 125% of rated full load current.
The thermal characteristic allows the inrush up to typically 10 times the rating or adjustable from 5 times to 10 times the rating.
The supply breaker does not and often can not protect the device.
The supply breaker protects the wiring and the supply system.
17 Amps x 125% = 21.25 Amps.
Use a 25 Amp or a 30 Amp breaker.
In the event that the breaker trips on inrush, the code may allow a greater breaker rating.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[tetwin11]

Thanks waross! So, you think I should use 2 breakers, one to power each unit? I figure that makes sense. Then upon installation at the customer's location, the electrician can install a separate disconnect or 50A breaker, based on local codes. Or do you think there should be a 50A breaker first, with 2 downstream 25 or 30A breakers?

 

[waross]

Talk to your electrician.
but I would consider a feeder for both machines.
17 Amps + (125% x 17 Amps) = 38.25 Amps.
Either a 40 Amp breaker or a 50 Amp breaker.
If you are concerned with the inrush when both machines are energized simultaneously after a power outage use 50 Amps.
Check you local code.
If you are subject to a maximum of 80% loading for a continuous load then use a 50 Amp breaker.
The feeders must be suitable for the rated ampacity of the breaker.
A local, lockable disconnect is always a good safe idea.
It may be a code requirement.
There may be exceptions but I resist using those exceptions.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

What standard are you using to build this charger? Depending oh the rules you are following you can't always round up. Doing that is only allowed for certain load types. The wiring will have to be suitable for whatever breaker you use so a 50A breaker would require 6 gauge wiring.

I would try to protect them individually but considering these are working in parallel, it may be prudent to consider some way to trip both at the same time.

 

[tetwin11]

It seems like the requirements on this will be highly local-code-dependent. So, I'm leaning toward using a pair of 25A breakers. Then the installing electrician can add anything on the line side to make it compliant.

LionelHutz (love the name btw) you ask a good question, what standard am I using... Can this be a multiple choice? What are some options? I'm a bit green on things like this.

I'm working on a test to see what happens if they are operating and only 1 of the 2 trips. I think the only consequence is that it will operate at half capacity, which is a fine mode of operation as long as the user is notified.