Re: My best method for really good boards using photo sensitive dry film
Make and model of the laminator?? I just ordered a "Royal Sovereign 9" Desktop Laminator" from Office Max for doing toner transfer. -- Paul Mateer, AA9GG
Elan Engineering Corp.
|
My best method for really good boards using photo sensitive dry film
I've been persisting for a couple of months trying to get really good boards using photo resist. I prefer the dry film method because poorly exposed boards can be stripped and recoated quite easily, which is good when you're at the left hand side of the learning curve!
I've found the best method for applying the resist is using a laminator; I tried modifying a cheap home office laminator, but the rollers are too small, not firm enough and the A4 (8") width is too limited. I browsed ebay and located a professional pouch laminator, this has heated top and bottom rollers, a heated platen and a pair of output rollers; it has variable temperature from around 80C to very hot, but has fixed roller speed and although it has motor on-off, it doesn't have a connection for a foot pedal which would be a worthwhile upgrade.
The method I use is to mist the board with DI water, remove the inner protective layer from the dry film for about 10mm (3/8") and apply the leading edge to the copper clad, preferably outside the area to be exposed, although I have been lucky and been able to use the leading edge to within 3mm (1/8") of the board edge. Lay the board on a piece of heavy paper that's 30 to 50mm (1 1/4" to 2") longer than the board, ensuring the film does not overhang the edges of the paper anywhere, or you will end up with film stuck to the lamionator's rollers. Ste the laminator to a low tempertaure initially; run the leading edge of the paper into the laminator then stop the motor. Now peel back the inner protective layer until you can easily hold it, then lift the film so that it's vertically oriented directly from the input to the laminator. Start the laminator's motor and carefully hold the protective layer taut to prevent wrinkles and ensure it seperates from the dry film before it enters the rollers. This takes a bit of practice, but I've got it to a point where I don't have to strip and recoat any boards now.
A very important point is to make sure the copper is absolutely clean before coating; I scrub the board with a green pot scourer to remove any oxide, then thoroughly clean it with dish soap until water forms a film on the board and doesn't bead up.
Note that the photopolymer layer in the dry film is highly sensitive to oxygen and will not readily polymerise in the presence of oxygen, so you must leave the outer protective layer on the film until it's ready to be developed. This film is very thin and is UV transparent, so doesn't affect the exposure process.
I'm going to follow up with how I get really good photo masters, without resorting to using an imagesetter (I used to have access to machines that could image to 3600 lpi and produced extremely accurate films with an ND of > 5.0; as a development engineer, I could spend entire days running off random jobs on these machines, but alas I'm no longer in that job).
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Re: Question on PTC resistance
No issues. Thanks for reply? All the best?
I have no clue. When I first saw it, I thought you quoted it, but
forgot to add some comments. Probably a glitch on the forum.
Dave
On 11/11/2019 7:49 PM, MVS Sarma wrote:
How come my name is shown across this post!?
I dontvremember to have replied this post on
11th nov.
I would appeal the site manager to please check
the original poster .
Regards
sarma vu3zmv
On Mon, 11 Nov 2019, 10:23 pm
MVS Sarma via Groups.Io, <mvssarma= [email protected]>
wrote:
Hi
Harvey,
?? In my case I am just using the USB port for handy
readily available
power to run IR Led's so it is the simplest circuit. They
have a .100 mA
max spec for amperage and I can run them at 50% and they
still work fine
so I have plenty of leeway on the design. The USB 2.x
ports have 5V and
maximum 0.500 mA available. The newer USB 3.x goes up to
0.9 mA but I
won't be using a cable that fits that one. So if my PTC
kicks out at
0.200 mA or even a little later, it won't be a problem.
Now protecting a
transistor may be a different story.
Thanks,
Dave
On 11/10/2019 1:58 PM, Harvey White wrote:
> Yep, from what I read, the trip current vs time to
trip is a lot
> longer than for fuses, the advantage being only that
they reset. From
> what I can see, they're best used in catastrophic
failure cases where
> the battery (supply/circuit) can stand an overload
for a bit of time,
> then the fuse trips.? They're not the kind of thing
I'd think of using
> to protect an FET unless the trip current were
substantially below the
> rating of the FET.? Just me, of course.
>
> Harvey
>
>
> On 11/10/2019 1:27 PM, Dave wrote:
>> Hi Harvey,
>>
>> ? According to the LittleFuse datasheet, PTC
fuses are used to protect:
>>
>> USB peripherals
>> Disk drives? CD-ROMs
>> Plug and play protection for motherboards and
peripherals
>> Mobile phones - battery and port protection
>> Disk drives
>> PDAs / digital cameras
>> Game console port protection
>>
>>
>> But in reality they may be used more in
batteries. I just read about
>> them in relation to protecting USB ports and in
order to have an
>> option other than a battery pack, I wanted to
protect me from any
>> liability. :) Probably never even gonna trip the
PTC fuse except for
>> when it is first soldered in. Just covering my
you know what. I have
>> thoroughly thought out my plan and everything
will work fine. Just
>> trying to learn as I go.
>>
>> Thanks for the information,
>>
>> Dave
>>
>> On 11/8/2019 6:35 PM, Harvey White wrote:
>>>
>>> I spent a little time looking at PTC fuses.
>>>
>>> Made the following observations:
>>>
>>> 1) their resistance is higher than a regular
fuse (and a fuse *must*
>>> have a resistance)
>>>
>>> 2) the best use of the fuses is to protect
from a short circuit.?
>>> The more current through the fuse, the faster
it blows. If you would
>>> expect a normal 1 amp fuse to blow at 2 amps,
the PTC won't, not for
>>> a while
>>>
>>> 3) the normal use for a PTC fuse is to
protect a high current
>>> battery.? It's generally installed inside the
pack, not user
>>> replaceable.
>>>
>>> 4) the more you use them, slowly, the
resistance creeps up.
>>>
>>> 5) if you're going to use them in a circuit
where you're watching
>>> voltage drops, then very carefully think the
voltages and currents.?
>>> They? have a higher resistance than you'd
think.
>>>
>>> Harvey
>>>
>>>
>>> On 11/8/2019 5:43 PM, Dave wrote:
>>>> Brad,
>>>> ? Thanks for the test procedure. The
PTC's I am going to have to
>>>> test are .100mA hold and .250mA trip. I
should be able to figure it
>>>> out but if not, I will ask for some more
help. :)
>>>> Dave
>>
|
Re: Question on PTC resistance
I have no clue. When I first saw it, I thought you quoted it, but
forgot to add some comments. Probably a glitch on the forum.
Dave
On 11/11/2019 7:49 PM, MVS Sarma wrote:
toggle quoted message
Show quoted text
How come my name is shown across this post!?
I dontvremember to have replied this post on
11th nov.
I would appeal the site manager to please check
the original poster .
Regards
sarma vu3zmv
On Mon, 11 Nov 2019, 10:23 pm
MVS Sarma via Groups.Io, <mvssarma= [email protected]>
wrote:
Hi
Harvey,
?? In my case I am just using the USB port for handy
readily available
power to run IR Led's so it is the simplest circuit. They
have a .100 mA
max spec for amperage and I can run them at 50% and they
still work fine
so I have plenty of leeway on the design. The USB 2.x
ports have 5V and
maximum 0.500 mA available. The newer USB 3.x goes up to
0.9 mA but I
won't be using a cable that fits that one. So if my PTC
kicks out at
0.200 mA or even a little later, it won't be a problem.
Now protecting a
transistor may be a different story.
Thanks,
Dave
On 11/10/2019 1:58 PM, Harvey White wrote:
> Yep, from what I read, the trip current vs time to
trip is a lot
> longer than for fuses, the advantage being only that
they reset. From
> what I can see, they're best used in catastrophic
failure cases where
> the battery (supply/circuit) can stand an overload
for a bit of time,
> then the fuse trips.? They're not the kind of thing
I'd think of using
> to protect an FET unless the trip current were
substantially below the
> rating of the FET.? Just me, of course.
>
> Harvey
>
>
> On 11/10/2019 1:27 PM, Dave wrote:
>> Hi Harvey,
>>
>> ? According to the LittleFuse datasheet, PTC
fuses are used to protect:
>>
>> USB peripherals
>> Disk drives? CD-ROMs
>> Plug and play protection for motherboards and
peripherals
>> Mobile phones - battery and port protection
>> Disk drives
>> PDAs / digital cameras
>> Game console port protection
>>
>>
>> But in reality they may be used more in
batteries. I just read about
>> them in relation to protecting USB ports and in
order to have an
>> option other than a battery pack, I wanted to
protect me from any
>> liability. :) Probably never even gonna trip the
PTC fuse except for
>> when it is first soldered in. Just covering my
you know what. I have
>> thoroughly thought out my plan and everything
will work fine. Just
>> trying to learn as I go.
>>
>> Thanks for the information,
>>
>> Dave
>>
>> On 11/8/2019 6:35 PM, Harvey White wrote:
>>>
>>> I spent a little time looking at PTC fuses.
>>>
>>> Made the following observations:
>>>
>>> 1) their resistance is higher than a regular
fuse (and a fuse *must*
>>> have a resistance)
>>>
>>> 2) the best use of the fuses is to protect
from a short circuit.?
>>> The more current through the fuse, the faster
it blows. If you would
>>> expect a normal 1 amp fuse to blow at 2 amps,
the PTC won't, not for
>>> a while
>>>
>>> 3) the normal use for a PTC fuse is to
protect a high current
>>> battery.? It's generally installed inside the
pack, not user
>>> replaceable.
>>>
>>> 4) the more you use them, slowly, the
resistance creeps up.
>>>
>>> 5) if you're going to use them in a circuit
where you're watching
>>> voltage drops, then very carefully think the
voltages and currents.?
>>> They? have a higher resistance than you'd
think.
>>>
>>> Harvey
>>>
>>>
>>> On 11/8/2019 5:43 PM, Dave wrote:
>>>> Brad,
>>>> ? Thanks for the test procedure. The
PTC's I am going to have to
>>>> test are .100mA hold and .250mA trip. I
should be able to figure it
>>>> out but if not, I will ask for some more
help. :)
>>>> Dave
>>
|
Re: Question on PTC resistance
How come my name is shown across this post!?
I dontvremember to have replied this post on 11th nov.
I would appeal the site manager to please check the original poster .
Regards sarma vu3zmv
On Mon, 11 Nov 2019, 10:23 pm MVS Sarma via Groups.Io, <mvssarma= [email protected]> wrote:
Hi Harvey,
?? In my case I am just using the USB port for handy readily available
power to run IR Led's so it is the simplest circuit. They have a .100 mA
max spec for amperage and I can run them at 50% and they still work fine
so I have plenty of leeway on the design. The USB 2.x ports have 5V and
maximum 0.500 mA available. The newer USB 3.x goes up to 0.9 mA but I
won't be using a cable that fits that one. So if my PTC kicks out at
0.200 mA or even a little later, it won't be a problem. Now protecting a
transistor may be a different story.
Thanks,
Dave
On 11/10/2019 1:58 PM, Harvey White wrote:
> Yep, from what I read, the trip current vs time to trip is a lot
> longer than for fuses, the advantage being only that they reset. From
> what I can see, they're best used in catastrophic failure cases where
> the battery (supply/circuit) can stand an overload for a bit of time,
> then the fuse trips.? They're not the kind of thing I'd think of using
> to protect an FET unless the trip current were substantially below the
> rating of the FET.? Just me, of course.
>
> Harvey
>
>
> On 11/10/2019 1:27 PM, Dave wrote:
>> Hi Harvey,
>>
>> ? According to the LittleFuse datasheet, PTC fuses are used to protect:
>>
>> USB peripherals
>> Disk drives? CD-ROMs
>> Plug and play protection for motherboards and peripherals
>> Mobile phones - battery and port protection
>> Disk drives
>> PDAs / digital cameras
>> Game console port protection
>>
>>
>> But in reality they may be used more in batteries. I just read about
>> them in relation to protecting USB ports and in order to have an
>> option other than a battery pack, I wanted to protect me from any
>> liability. :) Probably never even gonna trip the PTC fuse except for
>> when it is first soldered in. Just covering my you know what. I have
>> thoroughly thought out my plan and everything will work fine. Just
>> trying to learn as I go.
>>
>> Thanks for the information,
>>
>> Dave
>>
>> On 11/8/2019 6:35 PM, Harvey White wrote:
>>>
>>> I spent a little time looking at PTC fuses.
>>>
>>> Made the following observations:
>>>
>>> 1) their resistance is higher than a regular fuse (and a fuse *must*
>>> have a resistance)
>>>
>>> 2) the best use of the fuses is to protect from a short circuit.?
>>> The more current through the fuse, the faster it blows. If you would
>>> expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for
>>> a while
>>>
>>> 3) the normal use for a PTC fuse is to protect a high current
>>> battery.? It's generally installed inside the pack, not user
>>> replaceable.
>>>
>>> 4) the more you use them, slowly, the resistance creeps up.
>>>
>>> 5) if you're going to use them in a circuit where you're watching
>>> voltage drops, then very carefully think the voltages and currents.?
>>> They? have a higher resistance than you'd think.
>>>
>>> Harvey
>>>
>>>
>>> On 11/8/2019 5:43 PM, Dave wrote:
>>>> Brad,
>>>> ? Thanks for the test procedure. The PTC's I am going to have to
>>>> test are .100mA hold and .250mA trip. I should be able to figure it
>>>> out but if not, I will ask for some more help. :)
>>>> Dave
>>
|
Re: Question on PTC resistance
Semiconductor devices can be surprisingly good at protecting fuses. <humour intended> Donald. -- *Plain Text* email -- it's an accessibility issue () no proprietary attachments; no html mail /\ <> On 11-Nov-2019 10:35, Dave wrote: Hi Harvey,
? In my case I am just using the USB port for handy readily available power to run IR Led's so it is the simplest circuit. They have a .100 mA max spec for amperage and I can run them at 50% and they still work fine so I have plenty of leeway on the design. The USB 2.x ports have 5V and maximum 0.500 mA available. The newer USB 3.x goes up to 0.9 mA but I won't be using a cable that fits that one. So if my PTC kicks out at 0.200 mA or even a little later, it won't be a problem. Now protecting a transistor may be a different story.
Thanks,
Dave
On 11/10/2019 1:58 PM, Harvey White wrote:
Yep, from what I read, the trip current vs time to trip is a lot longer than for fuses, the advantage being only that they reset. From what I can see, they're best used in catastrophic failure cases where the battery (supply/circuit) can stand an overload for a bit of time, then the fuse trips.? They're not the kind of thing I'd think of using to protect an FET unless the trip current were substantially below the rating of the FET.? Just me, of course.
Harvey
[snip]
|
Re: Question on PTC resistance
Hi Harvey,
?? In my case I am just using the USB port for handy readily available
power to run IR Led's so it is the simplest circuit. They have a .100 mA
max spec for amperage and I can run them at 50% and they still work fine
so I have plenty of leeway on the design. The USB 2.x ports have 5V and
maximum 0.500 mA available. The newer USB 3.x goes up to 0.9 mA but I
won't be using a cable that fits that one. So if my PTC kicks out at
0.200 mA or even a little later, it won't be a problem. Now protecting a
transistor may be a different story.
Thanks,
Dave
On 11/10/2019 1:58 PM, Harvey White wrote:
> Yep, from what I read, the trip current vs time to trip is a lot
> longer than for fuses, the advantage being only that they reset. From
> what I can see, they're best used in catastrophic failure cases where
> the battery (supply/circuit) can stand an overload for a bit of time,
> then the fuse trips.? They're not the kind of thing I'd think of using
> to protect an FET unless the trip current were substantially below the
> rating of the FET.? Just me, of course.
>
> Harvey
>
>
> On 11/10/2019 1:27 PM, Dave wrote:
>> Hi Harvey,
>>
>> ? According to the LittleFuse datasheet, PTC fuses are used to protect:
>>
>> USB peripherals
>> Disk drives? CD-ROMs
>> Plug and play protection for motherboards and peripherals
>> Mobile phones - battery and port protection
>> Disk drives
>> PDAs / digital cameras
>> Game console port protection
>>
>>
>> But in reality they may be used more in batteries. I just read about
>> them in relation to protecting USB ports and in order to have an
>> option other than a battery pack, I wanted to protect me from any
>> liability. :) Probably never even gonna trip the PTC fuse except for
>> when it is first soldered in. Just covering my you know what. I have
>> thoroughly thought out my plan and everything will work fine. Just
>> trying to learn as I go.
>>
>> Thanks for the information,
>>
>> Dave
>>
>> On 11/8/2019 6:35 PM, Harvey White wrote:
>>>
>>> I spent a little time looking at PTC fuses.
>>>
>>> Made the following observations:
>>>
>>> 1) their resistance is higher than a regular fuse (and a fuse *must*
>>> have a resistance)
>>>
>>> 2) the best use of the fuses is to protect from a short circuit.?
>>> The more current through the fuse, the faster it blows. If you would
>>> expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for
>>> a while
>>>
>>> 3) the normal use for a PTC fuse is to protect a high current
>>> battery.? It's generally installed inside the pack, not user
>>> replaceable.
>>>
>>> 4) the more you use them, slowly, the resistance creeps up.
>>>
>>> 5) if you're going to use them in a circuit where you're watching
>>> voltage drops, then very carefully think the voltages and currents.?
>>> They? have a higher resistance than you'd think.
>>>
>>> Harvey
>>>
>>>
>>> On 11/8/2019 5:43 PM, Dave wrote:
>>>> Brad,
>>>> ? Thanks for the test procedure. The PTC's I am going to have to
>>>> test are .100mA hold and .250mA trip. I should be able to figure it
>>>> out but if not, I will ask for some more help. :)
>>>> Dave
>>
|
Re: Question on PTC resistance
Hi Harvey,
? In my case I am just using the USB port for handy readily available power to run IR Led's so it is the simplest circuit. They have a .100 mA max spec for amperage and I can run them at 50% and they still work fine so I have plenty of leeway on the design. The USB 2.x ports have 5V and maximum 0.500 mA available. The newer USB 3.x goes up to 0.9 mA but I won't be using a cable that fits that one. So if my PTC kicks out at 0.200 mA or even a little later, it won't be a problem. Now protecting a transistor may be a different story.
Thanks,
Dave
toggle quoted message
Show quoted text
On 11/10/2019 1:58 PM, Harvey White wrote: Yep, from what I read, the trip current vs time to trip is a lot longer than for fuses, the advantage being only that they reset. From what I can see, they're best used in catastrophic failure cases where the battery (supply/circuit) can stand an overload for a bit of time, then the fuse trips.? They're not the kind of thing I'd think of using to protect an FET unless the trip current were substantially below the rating of the FET.? Just me, of course.
Harvey
On 11/10/2019 1:27 PM, Dave wrote:
Hi Harvey,
? According to the LittleFuse datasheet, PTC fuses are used to protect:
USB peripherals
Disk drives? CD-ROMs
Plug and play protection for motherboards and peripherals
Mobile phones - battery and port protection
Disk drives
PDAs / digital cameras
Game console port protection
But in reality they may be used more in batteries. I just read about them in relation to protecting USB ports and in order to have an option other than a battery pack, I wanted to protect me from any liability. :) Probably never even gonna trip the PTC fuse except for when it is first soldered in. Just covering my you know what. I have thoroughly thought out my plan and everything will work fine. Just trying to learn as I go.
Thanks for the information,
Dave
On 11/8/2019 6:35 PM, Harvey White wrote:
I spent a little time looking at PTC fuses.
Made the following observations:
1) their resistance is higher than a regular fuse (and a fuse *must* have a resistance)
2) the best use of the fuses is to protect from a short circuit.? The more current through the fuse, the faster it blows. If you would expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for a while
3) the normal use for a PTC fuse is to protect a high current battery.? It's generally installed inside the pack, not user replaceable.
4) the more you use them, slowly, the resistance creeps up.
5) if you're going to use them in a circuit where you're watching voltage drops, then very carefully think the voltages and currents.? They? have a higher resistance than you'd think.
Harvey
On 11/8/2019 5:43 PM, Dave wrote:
Brad,
? Thanks for the test procedure. The PTC's I am going to have to test are .100mA hold and .250mA trip. I should be able to figure it out but if not, I will ask for some more help. :)
Dave
|
Re: Question on PTC resistance
Yep, from what I read, the trip current vs time to trip is a lot longer than for fuses, the advantage being only that they reset. From what I can see, they're best used in catastrophic failure cases where the battery (supply/circuit) can stand an overload for a bit of time, then the fuse trips.? They're not the kind of thing I'd think of using to protect an FET unless the trip current were substantially below the rating of the FET.? Just me, of course.
Harvey
toggle quoted message
Show quoted text
On 11/10/2019 1:27 PM, Dave wrote: Hi Harvey,
? According to the LittleFuse datasheet, PTC fuses are used to protect:
USB peripherals
Disk drives? CD-ROMs
Plug and play protection for motherboards and peripherals
Mobile phones - battery and port protection
Disk drives
PDAs / digital cameras
Game console port protection
But in reality they may be used more in batteries. I just read about them in relation to protecting USB ports and in order to have an option other than a battery pack, I wanted to protect me from any liability. :) Probably never even gonna trip the PTC fuse except for when it is first soldered in. Just covering my you know what. I have thoroughly thought out my plan and everything will work fine. Just trying to learn as I go.
Thanks for the information,
Dave
On 11/8/2019 6:35 PM, Harvey White wrote:
I spent a little time looking at PTC fuses.
Made the following observations:
1) their resistance is higher than a regular fuse (and a fuse *must* have a resistance)
2) the best use of the fuses is to protect from a short circuit.? The more current through the fuse, the faster it blows. If you would expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for a while
3) the normal use for a PTC fuse is to protect a high current battery.? It's generally installed inside the pack, not user replaceable.
4) the more you use them, slowly, the resistance creeps up.
5) if you're going to use them in a circuit where you're watching voltage drops, then very carefully think the voltages and currents.? They? have a higher resistance than you'd think.
Harvey
On 11/8/2019 5:43 PM, Dave wrote:
Brad,
? Thanks for the test procedure. The PTC's I am going to have to test are .100mA hold and .250mA trip. I should be able to figure it out but if not, I will ask for some more help. :)
Dave
|
Re: Question on PTC resistance
Hi Harvey,
? According to the LittleFuse datasheet, PTC fuses are used to protect:
USB peripherals
Disk drives? CD-ROMs
Plug and play protection for motherboards and peripherals
Mobile phones - battery and port protection
Disk drives
PDAs / digital cameras
Game console port protection
But in reality they may be used more in batteries. I just read about them in relation to protecting USB ports and in order to have an option other than a battery pack, I wanted to protect me from any liability. :) Probably never even gonna trip the PTC fuse except for when it is first soldered in. Just covering my you know what. I have thoroughly thought out my plan and everything will work fine. Just trying to learn as I go.
Thanks for the information,
Dave
toggle quoted message
Show quoted text
On 11/8/2019 6:35 PM, Harvey White wrote:
I spent a little time looking at PTC fuses.
Made the following observations:
1) their resistance is higher than a regular fuse (and a fuse *must* have a resistance)
2) the best use of the fuses is to protect from a short circuit.? The more current through the fuse, the faster it blows. If you would expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for a while
3) the normal use for a PTC fuse is to protect a high current battery.? It's generally installed inside the pack, not user replaceable.
4) the more you use them, slowly, the resistance creeps up.
5) if you're going to use them in a circuit where you're watching voltage drops, then very carefully think the voltages and currents.? They? have a higher resistance than you'd think.
Harvey
On 11/8/2019 5:43 PM, Dave wrote:
Brad,
? Thanks for the test procedure. The PTC's I am going to have to test are .100mA hold and .250mA trip. I should be able to figure it out but if not, I will ask for some more help. :)
Dave
|
Re: Question on PTC resistance
Thanks Donald. I never ran across that Wiki article even though I was looking for some answers on this. Still seems like a long time though to get back to normal status. Made me think of "muscle wires" although they seem to work very quickly.
Dave
toggle quoted message
Show quoted text
On 11/10/2019 5:29 AM, Donald H Locker wrote: The mechanism of the resettable fuse PTC is thermo-mechanical. When heated, the resistive elastomeric elements expand, increasing the length of the resistive elements. It can take a very long time, even after cooling down for those elements to settle back to their pre-heated state. (c.f. )
Donald.
*Plain Text* email -- it's an accessibility issue
() no proprietary attachments; no html mail
/\ <>
On 2019-11-09 6:54 p.m., Dave wrote:
Thanks Jan,
?? That is a good way of looking at it. I just wonder why it takes hours/days at room temp too come back down to/towards 1.5 ohms. That said, my circuit will likely never see that fuse trip anyway, I am just adding it to cover me as it will be a device that plugs into a USB port and only controls LED's. I am pretty sure USB hubs and pc motherboards also use ptc fuses to protect the motherboard.
Dave
On 11/9/2019 12:52 AM, Jan Kok wrote:
I would treat the PTC as a very loose-tolerance resistor. Make sure your circuit will work properly if the PTC resistance is anywhere between 1.5 and 10 ohms. It's probably close to 10 ohms soon after tripping or being soldered, and may drift back down toward 1.5 ohms after hours or days at room temperature.
On Thu, Nov 7, 2019 at 5:46 PM Dave <theschemer@... <mailto:theschemer@...>> wrote:
??? In reference to the part number 1206L010/60 (second one down in top
??? list), I have a question.
??? Resistance R (min) = 1.5 ohms
??? Resistance R (1max) = 10 ohms
??? R min = Minimum resistance of device in initial (un-soldered) state.
??? Rtyp = No spec given.
??? R 1max =? Maximum resistance of device at 20°C measured one hour
??? after
??? tripping or reflow soldering of 260°C for 20 sec.
??? Question: If I were to figure in the resistance for the PTC fuse
??? as part
??? of my equation for selecting the correct resitors further down the
??? circuit...What number in ohms should I use? In other words, when the
??? circuit is in normal operation, what will the resistance of the PTC
??? actually be?
??? Thanks,
??? Dave
|
Re: Question on PTC resistance
The mechanism of the resettable fuse PTC is thermo-mechanical. When heated, the resistive elastomeric elements expand, increasing the length of the resistive elements. It can take a very long time, even after cooling down for those elements to settle back to their pre-heated state. (c.f. )
Donald.
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On 2019-11-09 6:54 p.m., Dave wrote: Thanks Jan,
? That is a good way of looking at it. I just wonder why it takes hours/days at room temp too come back down to/towards 1.5 ohms. That said, my circuit will likely never see that fuse trip anyway, I am just adding it to cover me as it will be a device that plugs into a USB port and only controls LED's. I am pretty sure USB hubs and pc motherboards also use ptc fuses to protect the motherboard.
Dave
On 11/9/2019 12:52 AM, Jan Kok wrote:
I would treat the PTC as a very loose-tolerance resistor. Make sure your circuit will work properly if the PTC resistance is anywhere between 1.5 and 10 ohms. It's probably close to 10 ohms soon after tripping or being soldered, and may drift back down toward 1.5 ohms after hours or days at room temperature.
On Thu, Nov 7, 2019 at 5:46 PM Dave <theschemer@... <mailto:theschemer@...>> wrote:
In reference to the part number 1206L010/60 (second one down in top
list), I have a question.
Resistance R (min) = 1.5 ohms
Resistance R (1max) = 10 ohms
R min = Minimum resistance of device in initial (un-soldered) state.
Rtyp = No spec given.
R 1max =? Maximum resistance of device at 20°C measured one hour
after
tripping or reflow soldering of 260°C for 20 sec.
Question: If I were to figure in the resistance for the PTC fuse
as part
of my equation for selecting the correct resitors further down the
circuit...What number in ohms should I use? In other words, when the
circuit is in normal operation, what will the resistance of the PTC
actually be?
Thanks,
Dave
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Re: Question on PTC resistance
Thanks Jan,
? That is a good way of looking at it. I just wonder why it takes
hours/days at room temp too come back down to/towards 1.5 ohms.
That said, my circuit will likely never see that fuse trip anyway,
I am just adding it to cover me as it will be a device that plugs
into a USB port and only controls LED's. I am pretty sure USB hubs
and pc motherboards also use ptc fuses to protect the motherboard.
Dave
On 11/9/2019 12:52 AM, Jan Kok wrote:
toggle quoted message
Show quoted text
I would treat the PTC as a very loose-tolerance
resistor. Make sure your circuit will work properly if the PTC
resistance is anywhere between 1.5 and 10 ohms. It's probably
close to 10 ohms soon after tripping or being soldered, and may
drift back down toward 1.5 ohms after hours or days at room
temperature.
In reference to the part number 1206L010/60 (second one down
in top
list), I have a question.
Resistance R (min) = 1.5 ohms
Resistance R (1max) = 10 ohms
R min = Minimum resistance of device in initial (un-soldered)
state.
Rtyp = No spec given.
R 1max =? Maximum resistance of device at 20°C measured one
hour after
tripping or reflow soldering of 260°C for 20 sec.
Question: If I were to figure in the resistance for the PTC
fuse as part
of my equation for selecting the correct resitors further down
the
circuit...What number in ohms should I use? In other words,
when the
circuit is in normal operation, what will the resistance of
the PTC
actually be?
Thanks,
Dave
|
Re: Question on PTC resistance
I would treat the PTC as a very loose-tolerance resistor. Make sure your circuit will work properly if the PTC resistance is anywhere between 1.5 and 10 ohms. It's probably close to 10 ohms soon after tripping or being soldered, and may drift back down toward 1.5 ohms after hours or days at room temperature.
In reference to the part number 1206L010/60 (second one down in top
list), I have a question.
Resistance R (min) = 1.5 ohms
Resistance R (1max) = 10 ohms
R min = Minimum resistance of device in initial (un-soldered) state.
Rtyp = No spec given.
R 1max =? Maximum resistance of device at 20°C measured one hour after
tripping or reflow soldering of 260°C for 20 sec.
Question: If I were to figure in the resistance for the PTC fuse as part
of my equation for selecting the correct resitors further down the
circuit...What number in ohms should I use? In other words, when the
circuit is in normal operation, what will the resistance of the PTC
actually be?
Thanks,
Dave
|
Re: Question on PTC resistance
I spent a little time looking at PTC fuses.
Made the following observations:
1) their resistance is higher than a regular fuse (and a fuse
*must* have a resistance)
2) the best use of the fuses is to protect from a short circuit.?
The more current through the fuse, the faster it blows. If you
would expect a normal 1 amp fuse to blow at 2 amps, the PTC won't,
not for a while
3) the normal use for a PTC fuse is to protect a high current
battery.? It's generally installed inside the pack, not user
replaceable.
4) the more you use them, slowly, the resistance creeps up.
5) if you're going to use them in a circuit where you're watching
voltage drops, then very carefully think the voltages and
currents.? They? have a higher resistance than you'd think.
Harvey
On 11/8/2019 5:43 PM, Dave wrote:
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Brad,
? Thanks for the test procedure. The PTC's I am going to have to
test are .100mA hold and .250mA trip. I should be able to figure
it out but if not, I will ask for some more help. :)
Dave
|
Re: Question on PTC resistance
Brad,
? Thanks for the test procedure. The PTC's I am going to have to test are .100mA hold and .250mA trip. I should be able to figure it out but if not, I will ask for some more help. :)
Dave
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Re: Question on PTC resistance
Dave wrote on 11/8/2019 4:30 PM: Donald,
? Thanks for confirming what I thought. That makes sense. This is a self resetting fuse. I guess I can test the parts with heat and see what they cool down to after they have been tripped using a hot air gun or oven. I am hoping in normal use they stay a 1.5 ohms and only in the case of a short they quickly ramp up to trip and cool back down to 1.5 ohms. Then I can just make a minor adjustment in my resistor specs.
Dave Hello, Dave-- It should be possible to create a more elaborate test.? The basic idea is to explore the DUT's recovery time and series resistance. Connect the device under test (DUT) in series with a regulated power supply. On the downstream side, connect a SPDT switch to two load resistors. One resistor represents a normal load (e.g., 100 ohms). The second resistor represents an overload condition,?? for example one tenth of the nominal load resistance (e.g., 10 ohms). Measure the power supply voltage (say, 10 volts). If you're uncertain about the power-supply regulation, connect an ammeter in series with the output. Connect a voltmeter across the DUT. Measure the voltage drop across the DUT with the switch set to nominal load. Switch to the overload resistor and measure the voltage drop across the DUT. Switch to the nominal load resistor and observe the voltage drop across the DUT until (or if) the voltage drop returns to its previous value. Modify the test values to suit your actual load conditions. Be prepared to release magick smoke from a DUT or two<g>. 73-- Brad? AA1IP
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Re: Question on PTC resistance
Hi Brad,
? Makes sense but I am hoping that in practice it is closer to 1.5 ohms, and after it heats up, it cools back down to the same spec (1.5 ohms) each time. If not, I have to do some redesigning. :)
Thanks,
Dave
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Re: Question on PTC resistance
Donald,
? Thanks for confirming what I thought. That makes sense. This is a self resetting fuse. I guess I can test the parts with heat and see what they cool down to after they have been tripped using a hot air gun or oven. I am hoping in normal use they stay a 1.5 ohms and only in the case of a short they quickly ramp up to trip and cool back down to 1.5 ohms. Then I can just make a minor adjustment in my resistor specs. There is no resistance curve chart in the datasheet.
Dave
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Re: Question on PTC resistance
Dave wrote on 11/8/2019 11:17 AM: I think I figured it out enough to make sense of it. The 1.5 ohms will likely be the normal state and if a short occurs the resistance will quickly rise to the 10 ohms and trip the PTC fuse. That works for me. The reason I was worried a little is that the resistors I use in the circuit range from 5.1 to 10 ohms and that could have caused me some re-design issues.
Thanks,
Dave
On 11/7/2019 6:46 PM, Dave wrote:
In reference to the part number 1206L010/60 (second one down in top list), I have a question.
Resistance R (min) = 1.5 ohms
Resistance R (1max) = 10 ohms
R min = Minimum resistance of device in initial (un-soldered) state.
Rtyp = No spec given.
R 1max =? Maximum resistance of device at 20°C measured one hour after tripping or reflow soldering of 260°C for 20 sec. Hello, Dave-- I haven't located an app note for the Littelfuse part, so what follows is guesswork. I interpret the specs as defining the resistance prior to exposure to an overload to be 1.5 ohms or more (Rmin=1.5 ohms). The spec defines? R(Imax) as the resistance measured one hour after the device is exposed to its maximum overload current and thus self-heated? to some unspecified temperature. (The reflow-soldering process will also heat the device.) After a specified time elapses (i.e., one hour), the device will have cooled to ambient temperature and its measured resistance will revert to ten ohms maximum (or likely less). 73-- Brad? AA1IP
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