How to protect 12 to 24VDC input device from 230VAC input voltage

Hi,

My device input voltage is 12 to 24VDC, for reverse voltage protection purpose I have provided series Diode in positive input point and SMBJ30CA TVS diode at across the input point.
Also I want to protect my device from 230VAC input.
Glass fuse provision available in input point
Please suggest suitable protection circuit with low cost.

Thank you,
Rajan

You want to protect a 12v DC input from inadvertent 230 VAC? That's a pretty bad mistake. Maybe you could use a crowbar circuit.

Hi,
Thank you for your suggestion,
Yes, I want to protect from inadvertent 230VAC
what voltage i need to set for LM431 Adj. zener for drive SCR (Crowbar circuit). It seems short circuit



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HI,
Instead of crowbar circuit, can i use Bridge rectifier?
For inadvertent 230 VAC I will get (230x1.414=325VDC) 325VDC. But my regulator Maximum input is 40VDC only and provided 50VDC Aluminum Electrolytic filter capacitor at regulator input side.
Please suggest
Thank you
Rajan

Hi,

Is it just in case the user erroneously connects 230V AC?
If so, then it should be the user's problem. If he is not able to read how to connect your device properly, then there is a good chance that he makes other errors that may harm people.

Protecting a 24V DC device against 230V AC is not that easy. The problem is, that usually 24V DC devices have no access to NEUTRAL, nor to EARTH GND. But this is where the 230V refer to.

You need to know... if you don't have NEUTRAL or EARTH GND, then - in case of 230V connection - the whole 24V circuit carries those 230V. It's dangerous to touch any part of the circuit.

Don't make yuorself responsible for the mistakes others do. It costs your money. And in case you write the "230V AC feature" into your device's documemtation, then you are responsible in case if malfunction.


Klaus

I have to agree with Klaus. If someone is stupid enough to connect 230VAC to a 24 DC input, they shouldn't be allowed to touch the equipment to begin with.

'If you make something foolproof, someone will invent a better fool'.

Hi,

Maybe that's actually a good idea. What if someone with severe learning difficulties or dementia tries to use it, or a baby/toddler, just as examples. Who is the fool there? Who should be responsible and have the foresight to consider who the end user may be? An ill-informed and not in the least that much interested consumer? I'd hope things are made to be accident proof because manufacturers understand the realities of human beings...

d123 said:

Hi,

Maybe that's actually a good idea. What if someone with severe learning difficulties or dementia tries to use it, or a baby/toddler, just as examples. Who is the fool there? Who should be responsible and have the foresight to consider who the end user may be? An ill-informed and not in the least that much interested consumer? I'd hope things are made to be accident proof because manufacturers understand the realities of human beings...

Click to expand...

I would hope so also but in many cases what they understand is the reality of lawyers and lawsuits.

The best way is to use very large TVS or Zener, 42V rated, that are guaranteed to blow an input fuse, a crow bar is kinda OK but can take > 2 - 10uS to fire up depending on the detect and drive ckt.

If the input current is > 20A say - then things may get very problematic.

barry said:

I have to agree with Klaus. If someone is stupid enough to connect 230VAC to a 24 DC input, they shouldn't be allowed to touch the equipment to begin with.

'If you make something foolproof, someone will invent a better fool'.

Click to expand...

Usually the best way to discourage dumb mistakes like this is proper selection of connectors. If your 24V input has a IEC 6032 connector on it, then you're basically inviting people to plug it into the mains. So choose something else, like a barrel jack...

you need a front end which is designed for 240vac input.....if it gets 240vac, then it never switches on the relay and so never gets connected to the downstream low voltage bit.
You see what i mean, you just have a front end which "decides" whether or not to connect up via relay or whatever to the LV bit.