AVR Freaks

The USA is actually behind the rest of the world when it comes to EMC and energy efficiency stuff

They just don't care, in EU EMC is a massive thing its something I have had to learn and I am quite experienced with EMC filters and problem solving, its so satisfying to see your product produce very low levels but I digress

You need the details of the MOV but I can assure you that you will be exceeding its ratings so I would just source a proper rated part and also fit a TVS diode, its not optionl IMO

Good luck

I live in the UK but I am sure it will be of a similar quality

As an ex elec trician I can tell you its 230V +6%, -10%

they changed these numbers so we were harmonised with Europe, nothing physical ever changed except the colours

For equipment designed to European standards

But he asked abourt the tolerance of the mains supply, this is in the hands of the power companies and beyond anyones design, the tolerance is currently +6% -10% for voltage magnitude it was changed when the harmonisation came into effect so that the EU electricity could be harmonised without the UK having to change all the transformer tap settings

The frequency is much more tightly controlled because its used to measure time in many cases

Kartman, good post

Seriously dude I can't keep up with you!, I need to learn that MODBUS stuff (its high on the list) and get my IoT data capture stuff going but lately I am fighting battles on many fronts and I just do not have time but its coming!

I am interested in your take on MOV's TVS diodes, we have to gfit them to our products for EMC, transients and surge protection, withouit them the products fail

Now I never seen a problem so far (doesn't say a lot) but I know some of our customers use MOV and TVS diodes in systems with a 20 year lifetime and these products have worked flawlessly for years and years in horrendous environments like railways etc

maybe a proper sized device is half the battle, like I said I have physically heard them doing their job which has given me confidence in them but your comments have me wondering if my confidence is justified?

Looking at the schematic I would have the MOV's on the mains supply where the transients and surges are coming in, I also do not see why the secondary side has its ground refrenced to earth, I know its sometimes required but looking at the schematic its hard to see why!

Edit

What are you like with analogue Kartman?, Guru?, rusty?

I have a big interest in  this and I have worked on some nice simple current limitting circuits lately, I am looking to improve my knowledge a bit

Noob, i'm probably technician grade when it comes to analog. I have a knowlege of most building blocks, but don't expect me to design them!
Normally you'd use movs and tvs for transient and lightning protection. In these applications the total amount of energy involved can be handled by the device. In some cases you might expect an overvoltage to happen and the energy involved can destroy the device. If you've ever plugged a pc psu set for 110V into 240V and looked at the results. The poor old m205 fuse could not break the fault current so the movs exploded and the switching transistors died. With a lot of gear i designed we has rs485 comms in a multicore along with 24VDC. This is generally not seen as good practice - for good reason! Invariably the site wiring was done wrong so you got 24VDC on the comms. The average rs485 transceiver doesn't like this and promptly dies. So you add TVS diodes for protection. Sounds reasonable? But the tvs diodes are thermally limited so applying 24V to a 5V1 tvs ends up burning the pcb. So you add polyfuses in series to limit the current. Net result you get a design that has transient protected comms as well as overvoltage without dying in the process. Except if the customer applies 240VAC! That was a lesson in 'poke yoke' (Google that). At some point you need to draw the line as to what would be expected and what the design can tolerate.

Thanks Kartman,

My use of MOV's TVS diodes has been to do with the EMC directive, as you know some standards have very harsh levels

I know a fair amount of analogue electronics and its an area I put a lot of effort into getting better at, I always used diodes for polarity protection but these days I like using MOSFETS which can give polarity, inrush current limit and overcurrent protection its all really neat but I do wish I was much better with transistors, its actually amazing the amount of things you can do with transistors

The OP needs to seriously consider this system, its a WTF system

Its like the MOV's should be a couple of Y caps from an EMC filter, the Y caps and the common mode choke has been removed from the input as has the X cap

And there isnt actually any surge protection to protect against power surges at all, because power surges not surprisingly come on the power supply, maybe thats why they called them that!

And then for extra WTF they reference the 0V line to the main earth!

WTF?