Safe In-Wall AC to DC Transformers??

[Soloam]

After some searching I can't find the 200mA fuses on 3.6x10 mm size and with Axial Leads! I think I'll go with the 300mA type!

[Samuel235]

I'm just having a quick look through the specs of the HLK-PM01 and it has a stable current draw of 600mA with a burst draw of 1A. Would i be wrong in giving this a 1A slow blow fuse to protect it, or should it be smaller? I see most of people are going for a 300mA fuse here but i'm a little confused on why you would do that if the HLK-PM01 is safe to burst draw 1A?

[alexsh1]

@Samuel235 I have a fast blow fuse 800mA and in terms of slow blow fuses,I think 300mA is spot on. Why are you looking at the hlk-pm01 specs? You should be looking at consumption current. Yes, hlk-pm01 can provide a stable 5v at 600mA, but is it relevant for our project when the consumption is probably below 200mA?

If you are looking at something more power hungry the values have to be altered accordingly.

[Samuel235]

@alexsh1 basic principles. I've been going round and round in circles regarding another project for weeks it seems to have made me insane. Thank you for pointing out basics to me.

[AffordableTech]

Hi all...

I've recently received 20 of these units (see picture below) and hooked all but two of them all up to 240v with a dummy load resister to test. The other two are driving MySensor nodes to make sure there are no unexplained resets etc. They are well made and are claimed to be a "Mature" and stable unit. So far, no smoke and the ones on nodes have not reset, so all looks well. They have temperature protection, overcurrent, overvoltage and short circuit protection.

I went for these rather than the HLK-PM01 because:

• Being an open PCB, i can easily attach a lead onto the low voltage AC side of the transformer for use by the EMon Energy Meter library in calculating the actual AC voltage in order to derive more accurate power usage.
• The other thing I like is they are not a 'potted blob' - while the blob is a lot safer with regard to errant fingers etc, I feel they must run a lot hotter, and heat not only causes components to die, I figure it could increase the fire risk?

And the final factor being that the price is a bit over one euro, making them the lowest cost AC power supply I've come across for nodes.

Product link: <click me>

FWIW: All the regular "Express" freight charges from China to Australia are about AUD$25 to $30, but this supplier offered an express courier for $7 (US$5) - When it sounds too good to be true. . . Well, the goods were collected from the supplier in China on Wed mid-day, and arrived at my door at noon on Friday. When you consider I live 100Km outside of the main city (Perth), which normally adds two additional days onto any delivery, this was utterly amazing!

Cheers,

Paul

[Samuel235]

@AffordableTech, I was looking at these not too long ago. I wish i could get my hands on these in the UK for that sort of price! I too like the open PCB style rather than the HLK-PM01, just like yourself as all of my projects are inside of boxes or hidden away from human reach some way.

I'm tempted to purchase this just to have a little investigation on the quality of the item....

[sundberg84]

@AffordableTech - the temperature in the HLK is not a problem. I have measured it running a 5v node, relay and some sensors attached with everything put inside a wall. It never goes above 35dgr C. Also having a open PCB with the possibilities to get to the hot traces has it positive things but are not safe and does not meet any safety regulations.

[Samuel235]

@sundberg84 I remember spending an hour reading through that. Huge in-depth review you did concerning properties such as temperature with thermal imaging camera under load. Am i thinking of the right one? Thank you for that by the way!

[AffordableTech]

@sundberg84 - its all about one's point of view. I recently met two English ladies on holiday here, they were on the verge of serious heatstroke, because as they said, "at home 23 degrees was a record summer for us" - it was a very pleasant pleasant 35C day. Days later we began a straight week of 40C plus. That's when all the "E's" die like flies "Electronics" & "Englishmen":cold_sweat:.

In your (truly excellent) tests, the HLK PM01's peaked at 60C under top load - but I suspect that test was performed in a veery laaaarge ice-box :wink:.

Paul

[sundberg84]

@AffordableTech - Not my test (the big excellent one with 60C). I did one myself (see Inwall AC/DC PCB on openhardware for diagram). I didnt top load it, I used a normal load (Normal MySensors node with some relay and stuff) and reached 35dgr C only.

This is good for me - i rather have the safety but as you said - its one's point of view what you find most important. :)

And no, no cooling at all on my test ;)

[petewill]

@Samuel235 & @alexsh1
I know this is a late response but I just wanted to clarify. The 200mA or 300mA fuse is supposed to go on the mains side of the HLK. The max draw from the mains side is 300mA (if I remember correctly). It is meant to kill power (and prevent fire or other damage to your property) to the entire circuit in case of any issues.

[Samuel235]

@petewill, thank you. I already knew where to place it but thank you for the warning. However because you have made me aware of the current draw of the HLK i went to the datasheet and found:

So thank you for making me aware of this! Not sure why i was looking at the output current and not the input.

[alexsh1]

@petewill Good point - thank you! However, I have raised a different argument concerning the fast blow fuse vs a slow blow fuse. This was discussed already with @sundberg84 in this thread.

[Samuel235]

@alexsh1, you did indeed. I remember questioning why in a previous reply because i had concerns that a fast blow would be better suited but then you guys pointed out that the slow blow is the slightly better option in this use case since there is a large current draw at first with the transformer, was this the outcome that i remember?

[m26872]

Here was my contribution to this discussion. https://forum.mysensors.org/topic/3428/my-look-at-a-cheap-12v-power-supply

Perhaps not very elaborate, but I'm in favour of the 'fast' fuse. But not extra fast.

[alexsh1]

@Samuel235 it is subjective. 300mA slow blow fuse will not cut it off if the current is 300mA or slightly above for a short time whereas the fast blow fuse will (at the higher current though in our example as you do not want to burn the fuse due to a spike). Unless you have a very sensitive electronics, in my experience both fuses would provide you adequate protection. In some cases (engines), you have to use a slow blow fuse as the start up current may blow the fuse.

Personally, I'm very much in favour of the fast blow fuse in this setup

[m26872]

To quote myself from a few posts above regarding fuse characteristics. As you can see it's not an art of precision.

"
Thee fuses must not open in less than one hour at 125% of rated current and open within two minutes at 200% of rated current. The 1000% overload is used to determine the fuse characteristic. The opening time for each rating is listed below.
Type FF: Less than 0.001 sec.
Type F: From 0.001 - 0.01 sec.
Type T: From 0.01 - 0.1 sec.
Type TT: From 0.1 - 1.00 sec.
These characteristics correlate to the terminology used in IEC 60127-1.
"

At >10xIn (1000%) I want it to be fast and safe, where as frequent running currents between 1.25-2xIn should be minimized due to wear and false blows. Type FF could be to sensitive from looking at my measurements. Hence I choose Type F.

[Samuel235]

Would you agree with me when i say;

I think it is safe to have a slow blow fuse on board no matter what and then include a fast blow Type F or Type FF at super cautious needs, if you have sensitive electronics such as RF Radios, ICs that are very sensitive. However if we would like to be picky about the choice, any circuit that has a in-rush surge of current when turned on we need a slow blow fuse, anything that doesn't we can go for a fast blow.

[m26872]

I guess the picky answer would be that the selected fuse characteristic should match the application and it's not as simple as safe, not safe, fast or slow.

Though, as a general personal thought I think almost all fuse discussions I've seen in this thread are "safe".

[AffordableTech]

@m26872 ,

I'm sure many individuals will be wondering where the 'standard temporary' fuse fits into your chart of fuse types.

Of cause, by 'standard temporary', I refer to the ever reliable nail, often called the 'no blow' here in Oz.

Paul