Safe In-Wall AC to DC Transformers??
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@sundberg84 Given that HLK-PM01 can withstand current spikes to 1.0A, I decided to go for a 0.8A fast blow fuse. Additionally, having a thermal fuse would be an advantage, but not a must. Unless you want to push the PSU to around 600mA then it is going to operate close to its limit and you need some extra protection
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@alexsh1 - what do you base it on, its not a must? Im trying to be as safe as possible :) but i really wants to learn as much as possible about safety regarding ac/dc converting.
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@alexsh1 said:
150mA
Ok, sounds logic - tnx. If I want to run a relay and some sensors it might be higher than 150mA so I like the extra safety :) Yea, have read that review about 100 times now, and emailed the dude as well for questions, haha. Much to learn!
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@alexsh1 - yes offcourse, you are right - mixed that up.
I have some 0.5 fast blow - sounds like thats a better idea than slow blow @petewill.@sundberg84 said:
@alexsh1 - yes offcourse, you are right - mixed that up.
I have some 0.5 fast blow - sounds like thats a better idea than slow blow @petewill.Are you guys sure you're not confusing the input current with the output? In the above mentioned review he says there is a "Maximum input current: <0.2A" which is the reason for the slow blow fuses (I think). Or, maybe I'm misunderstanding and you're talking about adding an additional fuse to the output of the HLK?
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Yes, max input is 0.2A with spikes ok upp to 1.0A but
@petewill we were discussing about using slow or fast blow fuse on the input.Slow blow seems to be more for motors and allowing equipment making spikes when they start up. Then the fuse wont blow due to a higher current during start. In home appliances it seems its a fast blow fuse we should use.
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Found what seems to be a interesting article: https://www.ieee.li/pdf/essay/safety_considerations_in_power_supply_design.pdf (Texas instrument).
Not read through it or know if the source is reliable but Texas instrument seems like a good author/source. No references inside so I guess its "how they see it".Controller: Proxmox VM - Home Assistant
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Found what seems to be a interesting article: https://www.ieee.li/pdf/essay/safety_considerations_in_power_supply_design.pdf (Texas instrument).
Not read through it or know if the source is reliable but Texas instrument seems like a good author/source. No references inside so I guess its "how they see it".@sundberg84 Ok, I understand. I will defer to the experts here and update the first post when a consensus is reached. I do have one more thing I'd like clarified though. It still seems to me like a 200/300mA slow fuse would be better as it would survive small over-current spikes but it wouldn't allow sustained draws over the HLK's rating of 200mA. With a 600mA fast blow fuse the HLK could draw 500mA as long as it wanted without blowing. Maybe this doesn't matter though?
On a side note, when I tested one of my slow blow fuses it still blew pretty fast with a moderate load above it's specs. I tested with a 33 watt floresent bulb and it blew in less than a second (not sure of the exact time/wattage as it was really just a test to see if it was a fuse and not something else).
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Transformers typically have an in-rush current as well, so a fast-blow fuse could pop because of this if it's not sized for that.
Cheers
Al -
Interesting @Sparkman!
https://en.wikipedia.org/wiki/Inrush_current "When a transformer is first energized, a transient current up to 10 to 15 times larger than the rated transformer current can flow for several cycles." -
This in-rush 'effect' can be seen on any induction load.
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I´m no expert but I thought and researched some. Could be wrong, please correct me then.
I think you're confusing AC inductive load inrush current with what we're interested in, which is the inrush to our switched power supplies. In our case the inrush current is to the primary side rectifier filter capacitor, not to the transformer. The transformer inside SMPS is for high frequency and would probably give a small inrush even if it was subjected to normal AC. Now it's DC and behind the switch controller and FET. And the controllers I've seen usually have some start-up time.
General about fast/slow types of small fuses (from here):
The 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.So in theory a type FF fuse could open "instantly" for 10*In (rated current) ? (in reality you check its specs of course). But let's see how a more normal type F fuse would work given the setup from a "normal" SMPS. I use this, but from what I've seen, primary side looks very similar to the HLK-PM01.
Rectifier filter cap value of my SMPS: 4.7uF
A normal 5x20mm fuse resistance value: 5 ohm (usually more resistances than just the fuse, but let's be conservative)
Max voltage peak-peak 700V ( ~250Vrms )
Regular capacitor calculation:
I(t0) = U/R = 140 A
T = RC = 54.7u = 23,5 us
I(t) = U/Re^-(t/T) = 140*e^-(t/0.0000235)How much inrush current do we have at for e.g. the fastest F-type fuse characteristic:
I(tmin=0.001) = 140e^-(0.001/0.0000235) = 140e^-(1/0.0235) = 3.3*10^-19 (i.e. zero current)How much time until I=0.1A (which would correspond to fuse value 0.01A):
I=U/R*e^-(.) <=> e^-(.)=IR/U <=> (.)=-ln(IR/U) <=> t = -ln(IR/U)0.0000235
t = -ln(0.15/700)*0.0000235 = 0.00017 = 170usSo even a 0.01A type F fuse should be far from blowing in a worst case and with conservative assumptions. For extra fast fuses, type FF, the characteristic must be checked.
Edit: This is only regarding the inrush, of course the load must be added to this eventually.
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@m26872 So, to sum up - there is no need to use a slow fuse, since the in rush current isnt "long" enough to blow a fast fuse. So considering safety (and if you have the same mA value for both fuses) its better and should work to use a fast rather than slow ??
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I´m no expert but I thought and researched some. Could be wrong, please correct me then.
I think you're confusing AC inductive load inrush current with what we're interested in, which is the inrush to our switched power supplies. In our case the inrush current is to the primary side rectifier filter capacitor, not to the transformer. The transformer inside SMPS is for high frequency and would probably give a small inrush even if it was subjected to normal AC. Now it's DC and behind the switch controller and FET. And the controllers I've seen usually have some start-up time.
General about fast/slow types of small fuses (from here):
The 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.So in theory a type FF fuse could open "instantly" for 10*In (rated current) ? (in reality you check its specs of course). But let's see how a more normal type F fuse would work given the setup from a "normal" SMPS. I use this, but from what I've seen, primary side looks very similar to the HLK-PM01.
Rectifier filter cap value of my SMPS: 4.7uF
A normal 5x20mm fuse resistance value: 5 ohm (usually more resistances than just the fuse, but let's be conservative)
Max voltage peak-peak 700V ( ~250Vrms )
Regular capacitor calculation:
I(t0) = U/R = 140 A
T = RC = 54.7u = 23,5 us
I(t) = U/Re^-(t/T) = 140*e^-(t/0.0000235)How much inrush current do we have at for e.g. the fastest F-type fuse characteristic:
I(tmin=0.001) = 140e^-(0.001/0.0000235) = 140e^-(1/0.0235) = 3.3*10^-19 (i.e. zero current)How much time until I=0.1A (which would correspond to fuse value 0.01A):
I=U/R*e^-(.) <=> e^-(.)=IR/U <=> (.)=-ln(IR/U) <=> t = -ln(IR/U)0.0000235
t = -ln(0.15/700)*0.0000235 = 0.00017 = 170usSo even a 0.01A type F fuse should be far from blowing in a worst case and with conservative assumptions. For extra fast fuses, type FF, the characteristic must be checked.
Edit: This is only regarding the inrush, of course the load must be added to this eventually.
@m26872 I'm no expert either. :smiley: We may be saying the same thing however... I don't think it matters (AC or DC), if there is a transformer in the circuit, there is going to be a current peak on startup. If you have a filter cap before your transformer, you will see 2 peaks. The first one will be caused by the capacitor charging up, and the second from the inductive load caused by the transformer powering up. I'm thinking the 2nd peak should be much less due to the filter cap.
Of course I could be all wrong. :persevere:
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Here is an interesting article http://www.vptpower.com/wp-content/uploads/downloads/2012/01/info_inrushCurrent.pdf on the subject. Looks like there is a LOT more to it (not that I thought there wasn't) than my over simplified post above.
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I´m no expert but I thought and researched some. Could be wrong, please correct me then.
I think you're confusing AC inductive load inrush current with what we're interested in, which is the inrush to our switched power supplies. In our case the inrush current is to the primary side rectifier filter capacitor, not to the transformer. The transformer inside SMPS is for high frequency and would probably give a small inrush even if it was subjected to normal AC. Now it's DC and behind the switch controller and FET. And the controllers I've seen usually have some start-up time.
General about fast/slow types of small fuses (from here):
The 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.So in theory a type FF fuse could open "instantly" for 10*In (rated current) ? (in reality you check its specs of course). But let's see how a more normal type F fuse would work given the setup from a "normal" SMPS. I use this, but from what I've seen, primary side looks very similar to the HLK-PM01.
Rectifier filter cap value of my SMPS: 4.7uF
A normal 5x20mm fuse resistance value: 5 ohm (usually more resistances than just the fuse, but let's be conservative)
Max voltage peak-peak 700V ( ~250Vrms )
Regular capacitor calculation:
I(t0) = U/R = 140 A
T = RC = 54.7u = 23,5 us
I(t) = U/Re^-(t/T) = 140*e^-(t/0.0000235)How much inrush current do we have at for e.g. the fastest F-type fuse characteristic:
I(tmin=0.001) = 140e^-(0.001/0.0000235) = 140e^-(1/0.0235) = 3.3*10^-19 (i.e. zero current)How much time until I=0.1A (which would correspond to fuse value 0.01A):
I=U/R*e^-(.) <=> e^-(.)=IR/U <=> (.)=-ln(IR/U) <=> t = -ln(IR/U)0.0000235
t = -ln(0.15/700)*0.0000235 = 0.00017 = 170usSo even a 0.01A type F fuse should be far from blowing in a worst case and with conservative assumptions. For extra fast fuses, type FF, the characteristic must be checked.
Edit: This is only regarding the inrush, of course the load must be added to this eventually.
@m26872 Thanks! So, am I understanding this correctly that we would want a 200mA or 300mA fast blow fuse? Since I know some of us have already purchased the 300mA slow blow fuses do you think it is safe to use them? If I'm understanding correctly they should still blow relatively quickly if they are subjected to high current right?
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@sundberg84 Yes, a fast fuse should give a higher level of protection without issues.
@RJ_Make That second "inrush" is what I called the load. It's completely governed by the controller and should not stress the fuse more than running overloads. If there's a peak it´s because of capactive load on the output and has nothing to do with the transformer.
Thx for the link. It confirmes that these turn-on-times are a few milliseconds just like the HLK-review said (around 3ms). No chance to superimpose the first peak.@petewill Regarding fast fuse, yes. But the value I don't know. The HLK review shows overload capabilties, but I don't know about the input currents at that point. Honestly I think it's very unlikely that you'll be saved by using a fast fuse instead of a slow. It's more a matter of e.g. better varistor (overvoltage) protection and the personal feeling of maximum safety etc.
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So there is another safety issue we should discuss for the HLK.
Creepage (separation between two solder eyes measured along the surface) and clearance (shortest distance between as measured through the air) on the AC input.According to datasheet there is 5mm center-center, but real distance with solder and pads its more like 3, maybe 3.5mm.
I found this and this which was a great summary of some IEC standards states that if your are going to use 240v and put the HLK into a environment with pollution degree III higher you need more creppage than 3.2mm. What am i saying? If i understand this right its not safe to use the HLK in any environment where moisture condensation may occur (outside, bathroom). My guess when i try to read the contamination groups is that if you put the HLK inside a sealed case you get the contamination level down to 2 and then we are safe above needed 2,5mm.
To be on the safe side I have in my latest pcb added holes between AC input to increase creepage:
Am i right? Dont know - its hard to read all these articles and Im new to this so please bring anything to the table... corrections, questions or thoughts.
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So there is another safety issue we should discuss for the HLK.
Creepage (separation between two solder eyes measured along the surface) and clearance (shortest distance between as measured through the air) on the AC input.According to datasheet there is 5mm center-center, but real distance with solder and pads its more like 3, maybe 3.5mm.
I found this and this which was a great summary of some IEC standards states that if your are going to use 240v and put the HLK into a environment with pollution degree III higher you need more creppage than 3.2mm. What am i saying? If i understand this right its not safe to use the HLK in any environment where moisture condensation may occur (outside, bathroom). My guess when i try to read the contamination groups is that if you put the HLK inside a sealed case you get the contamination level down to 2 and then we are safe above needed 2,5mm.
To be on the safe side I have in my latest pcb added holes between AC input to increase creepage:
Am i right? Dont know - its hard to read all these articles and Im new to this so please bring anything to the table... corrections, questions or thoughts.
@sundberg84 I think that looks like an excellent idea. I was looking at the tear down of the HLK in the test that was run and it doesn't look like there was any reason for them to do this - at least as far as I could see, there was plenty of room to put those connectors at the corners like the DC side.
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@sundberg84 How about a watertight enclosure?
In the UK it is IP67 (this is what it means -> http://aceeca.com/handhelds/ip67)
