Input protection setting for DC-DC converter

[Hasan2019]

Hi there,

This post is very easy one for you who knows better.

I am confused to set some values.
My DC-DC conveters input is 250-650VDC and output is 24V/5A. Its use for PV battery charger.
Take a look here,


I have few more query,

1. My boss want me to put some common ground ZNR” Transient/Surge Absorbers, in folloing manner, https://www.farnell.com/datasheets/2244565.pdf

2. Dont you think he needs it unnecessary for protection since there is 2 cap, 1 noise suppreser and rersistor are available.

3. He wants to add a fuse in pin 1 to R24, not sure why?

4 Can you imagine any idea to use R1-3? Those are 1 Mohms.

6. He wants to add a LED indecator for power output, for 5A current whats your idea?

 

[Harald Kapp]

1. Where's the question in this one? The pdf describes the component, not how and where to place it.
2. The components you name will not suppress surges, An additional surge absorber may help.
   But the two resistors R24 and R25 look as if these are menat to be varistors which are used for suppressing surges. Which leads back to item #1 and the question where these additional suppressors are to be placed.
3. One would also add a fuse from pin 4 of the connector to R25. Varistor deterioraet with time and become conductive. This leads to increased power dissipation and ultimately can lead to fire, A fuse will trigger when the current becomes too high, thus preventing overheating. A better alternative is to use thermally protected varistors which have an integrated fuse, matched to the component.
4. Yes I can. C2 will hold a charge when the power plug P1 is disconnected, thus presenting a potentially lethal voltage. These resistors will discharge C2, making handling of the unit save shortly after power has been disconnected.
   Btw: C2 is rated 700 V but P1 is labeled DC 800 V. The capacitor will be overloaded by 800 V. Make sure P1 is never connected to more than 650 V as you stated in your description
6. Having a power indicator is a good idea. Not sure though what you mean by "LED indecator for power output, for 5A current". Please describe in more detail this requirement.

In the light of your questions I recommend you get some expert support with this task. You are dealing with lethal power ratings and any failure may lead to fatalities. Don't take this lightly, learn from a fellow engineer.

 

[Hasan2019]

The components you name will not suppress surges, An additional surge absorber may help.
But the two resistors R24 and R25 look as if these are menat to be varistors which are used for suppressing surges. Which leads back to item #1 and the question where these additional suppressors are to be placed.

well said. Additional suppressors location will be where?

Yes I can. C2 will hold a charge when the power plug P1 is disconnected, thus presenting a potentially lethal voltage. These resistors will discharge C2, making handling of the unit save shortly after power has been disconnected.
Btw: C2 is rated 700 V but P1 is labeled DC 800 V. The capacitor will be overloaded by 800 V. Make sure P1 is never connected to more than 650 V as you stated in your descriptio

Yes, those are discharging resistors. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html
Lets think P1 as 650VDC.

Having a power indicator is a good idea. Not sure though what you mean by "LED indecator for power output, for 5A current". Please describe in more detail this requirement.

With a LED indicator on the output leads so one can see that the converter is likely putting out charging power. A 5K resistor in series with a LED would show if any voltage is present at the output (before it is connected to a battery). A 24-V 1W zener in series with a 2K resistor to the LED (with a 100-ohm in parallel with the LED) would show that the voltage is near the proper level, but either way the LED would not show if any current is flowing out to the batteries to be charged.