Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #21   Report Post  
Old November 2nd 20, 07:39 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jul 2007
Posts: 4,045
Default SMD Fuse ID

On Sun, 1 Nov 2020 22:49:59 -0500, ABLE1
wrote:

On 11/1/2020 5:38 PM, Jeff Liebermann wrote:
Are you prepared to pay for the best? (The worst you already have in
the form of an SMT fuse). For a little more $$$, the manufacturer
might supply a PPTC resettable fuse:
https://www.littelfuse.com/products/polyswitch-resettable-ptcs.aspx
Nothing to replace when it blows. Just give it time to cool down.


So Jeff, let me ask you.

If I would replace or jumper the B = RXEF010 resetable fuse the board
would work, meet code, and almost never have to concern myself with
it in the future??


No. I would replace it with as close to the original SMD fuse as
possible. In an emergency, I might replace the tiny SMD fuse with a
much larger fuse with wire leads. If doing development work on a
prototype, I would probably install a rather expensive socket and
rectangular fuse. However, for consumer use, it will always be the
original fuse.

The reason is that I don't know anything about the device that you
own. Most important, I don't know what it will do if a low AC voltage
is applied to the device. That's what will happen with a PTC
resettable fuse. The circuit does not go to completely open when the
PTC fuse is tripped. It goes to a fairly high resistance, and then
only as long as the fuse remains hot. To keep it hot, there has to be
a high current going through the fuse. That means there's power
applied to the rest of the PC board while the fuse is tripped. If you
look at the specs, that's the "hold current". Done correctly, that
will keep the fuse warm, and the power MOSTLY removed from the rest of
the circuit. Done wrong, it is possible that the fuse will cause the
device to cycle on and off repeatedly as the PTC fuse cycles through
hot and cold cycles. There are places and devices where a resettable
fuse is appropriate and safe. However, since I have no idea what
you're working with, I can't predict what will happen if you cram in a
PPTC resettable fuse and certainly don't want to take the risk
suggesting you do something that might be unsafe.

Also, is this really a problem that is worth solving? I doubt it. Put
in the correct fuse and you won't have to worry about the device
burning your house down.

Incidentally, I once repaired a small 13.6V 30A switching power
supply, which had a PPTC resettable fuse in the AC line. The problem
was obvious as there was a hole burned into the PCB where the PTC
resettable fuse had been. I could find no part number or specs on the
fuse making replacement difficult. I soon discovered why they used a
resettable fuse. It wasn't for convenience or size. It was because
the inrush current on this power supply was so high, that even a
slow-blo fuse would blow up if switched on with a 15A load. The
designer decided to use the PPTC fuse as an inrush current limiter,
which is a really bad idea. At some point along the load curve and
near maximum current, the operating point landed on the transition
line between low and high resistance. Since there was no hysteresis
in the transition line, the maximum power dissipation point for the
PPTC fuse was also somewhere along the curve. As bad luck would have
it, the customer's was operating almost on the same point of the
curve, causing the PTC fuse to become very hot. After a few days of
this kind of abuse, it burned a hole in the PCB and carbonized the PTC
fuse.

I made a few measurements and calculations and found a higher current
replacement PTC fuse. That brought the PTC fuse transition line to
somewhat higher than the maximum current. That fixed one problem and
created a new problem. The PTC would never trip because the
over-current protection in the power supply would turn down the power
supply before the PTC fuse was able to do the same. However, the
over-current protection was set to begin at about 10A above the
maximum output current and had no hysteresis. So, this mess is going
to require some redesign. I changed a few parts to bring the
over-current threshold to the maximum rated current and enabled
hysteresis by installing a resistor that the designer forgot. I
replaced the PTC fuse with a Slo-Blo conventional fuse, and inserted a
PTC thermistor inrush current limiter intended only to prevent blowing
the fuse under normal operation. Problem solved and it's been working
just fine for about 3 years.

Are you prepared to do something similar with your "circuit board"?

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

  #22   Report Post  
Old November 2nd 20, 07:51 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Nov 2020
Posts: 26
Default SMD Fuse ID

On Monday, November 2, 2020 at 1:13:44 PM UTC-6, soft-stool Fox Comics queefed:

Oh look, monkey boy figured out how to change his name.


I'm learning a lot everyday old fella. Like how much smaller you've become since I first ran into you. Here I thought, "41 yrs on usenet! Wowee!" Ahhaha. You continue to shrink and your posts seem so much softer.
  #23   Report Post  
Old November 2nd 20, 08:51 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: May 2018
Posts: 21
Default SMD Fuse ID

On 11/2/2020 2:39 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2020 22:49:59 -0500, ABLE1
wrote:

On 11/1/2020 5:38 PM, Jeff Liebermann wrote:
Are you prepared to pay for the best? (The worst you already have in
the form of an SMT fuse). For a little more $$$, the manufacturer
might supply a PPTC resettable fuse:
https://www.littelfuse.com/products/polyswitch-resettable-ptcs.aspx
Nothing to replace when it blows. Just give it time to cool down.


So Jeff, let me ask you.

If I would replace or jumper the B = RXEF010 resetable fuse the board
would work, meet code, and almost never have to concern myself with
it in the future??


No. I would replace it with as close to the original SMD fuse as
possible. In an emergency, I might replace the tiny SMD fuse with a
much larger fuse with wire leads. If doing development work on a
prototype, I would probably install a rather expensive socket and
rectangular fuse. However, for consumer use, it will always be the
original fuse.

The reason is that I don't know anything about the device that you
own. Most important, I don't know what it will do if a low AC voltage
is applied to the device. That's what will happen with a PTC
resettable fuse. The circuit does not go to completely open when the
PTC fuse is tripped. It goes to a fairly high resistance, and then
only as long as the fuse remains hot. To keep it hot, there has to be
a high current going through the fuse. That means there's power
applied to the rest of the PC board while the fuse is tripped. If you
look at the specs, that's the "hold current". Done correctly, that
will keep the fuse warm, and the power MOSTLY removed from the rest of
the circuit. Done wrong, it is possible that the fuse will cause the
device to cycle on and off repeatedly as the PTC fuse cycles through
hot and cold cycles. There are places and devices where a resettable
fuse is appropriate and safe. However, since I have no idea what
you're working with, I can't predict what will happen if you cram in a
PPTC resettable fuse and certainly don't want to take the risk
suggesting you do something that might be unsafe.

Also, is this really a problem that is worth solving? I doubt it. Put
in the correct fuse and you won't have to worry about the device
burning your house down.

Incidentally, I once repaired a small 13.6V 30A switching power
supply, which had a PPTC resettable fuse in the AC line. The problem
was obvious as there was a hole burned into the PCB where the PTC
resettable fuse had been. I could find no part number or specs on the
fuse making replacement difficult. I soon discovered why they used a
resettable fuse. It wasn't for convenience or size. It was because
the inrush current on this power supply was so high, that even a
slow-blo fuse would blow up if switched on with a 15A load. The
designer decided to use the PPTC fuse as an inrush current limiter,
which is a really bad idea. At some point along the load curve and
near maximum current, the operating point landed on the transition
line between low and high resistance. Since there was no hysteresis
in the transition line, the maximum power dissipation point for the
PPTC fuse was also somewhere along the curve. As bad luck would have
it, the customer's was operating almost on the same point of the
curve, causing the PTC fuse to become very hot. After a few days of
this kind of abuse, it burned a hole in the PCB and carbonized the PTC
fuse.

I made a few measurements and calculations and found a higher current
replacement PTC fuse. That brought the PTC fuse transition line to
somewhat higher than the maximum current. That fixed one problem and
created a new problem. The PTC would never trip because the
over-current protection in the power supply would turn down the power
supply before the PTC fuse was able to do the same. However, the
over-current protection was set to begin at about 10A above the
maximum output current and had no hysteresis. So, this mess is going
to require some redesign. I changed a few parts to bring the
over-current threshold to the maximum rated current and enabled
hysteresis by installing a resistor that the designer forgot. I
replaced the PTC fuse with a Slo-Blo conventional fuse, and inserted a
PTC thermistor inrush current limiter intended only to prevent blowing
the fuse under normal operation. Problem solved and it's been working
just fine for about 3 years.

Are you prepared to do something similar with your "circuit board"?



Jeff,

Actually no I am not. This is for a wall clock timer controlled
correcting board. Basically upon a signal from the master clock
the clock then adjusts to the right time.


I was thinking of trying a retro fix of board to see if it would
work. I realized early on that I would probably not do this, but,
I wanted to get opinions on the plus and minus of choices.

Since you put the possible issues the way you did I will totally
scratch that idea and move on to other stuff. However, I doubt
there would be any major issues at the current draw max of .5 amps.
The clock would just stop running!!

Thanks for the detailed typing. All very helpful and informative
to my brain antique brain. Learning new stuff is always beneficial.

Thanks again and have a good week.

Les





  #24   Report Post  
Old November 29th 20, 02:05 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Feb 2008
Posts: 141
Default SMD Fuse ID

On Monday, November 2, 2020 at 11:21:49 AM UTC-5, Mary R. Smith wrote:
On Sun, 1 Nov 2020 14:09:56 -0800 (PST) the anus of Edward Hernandez sputtered:
I think you do. Are you able to chase me? Don't get out of breath.


Stop being such a troll and go away.


I encourage everyone in all the trades to come here, whether its 'horsing around' like this or not. Like on a construction site: everyone gangs up on the person getting the attention. Like in the powder room. All the ladies gang up on the girl with the angelic face withbomb shell body.
  #25   Report Post  
Old November 29th 20, 08:36 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Feb 2008
Posts: 141
Default SMD Fuse ID

On Sunday, November 29, 2020 at 9:05:08 AM UTC-5, Transition Zone wrote:
On Monday, November 2, 2020 at 11:21:49 AM UTC-5, Mary R. Smith wrote:
On Sun, 1 Nov 2020 14:09:56 -0800 (PST) the anus of Edward Hernandez sputtered:
I think you do. Are you able to chase me? Don't get out of breath.


Stop being such a troll and go away.

I encourage everyone in all the trades to come here, whether its 'horsing around' like this or not. Like on a construction site: everyone gangs up on the person getting the attention. Like in the powder room. All the ladies gang up on the girl with the angelic face withbomb shell body.


OK well, not in the powder room (but everywhere else).


  #26   Report Post  
Old November 30th 20, 11:53 AM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Oct 2020
Posts: 151
Default SMD Fuse ID

Well, it has become clear that this individual is an Idiot in Search of a Village - and has found this venue. Given that the purpose of the Village Idiot is to make everyone else in the village look good by comparison, I would posit that this Idiot is performing its job in a most masterful way!

Peter Wieck
Melrose Park, PA


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help identifying SMD fuse? fusible link? Not[_2_] Electronics Repair 2 July 17th 09 06:32 AM
Hot air smd rework station. SMD removal??? Defective Machines??? SAUHING LEE Electronics Repair 12 March 25th 08 11:49 AM
switch-fuse and service-fuse discrimination Fash UK diy 16 July 19th 06 12:28 PM
Low cost SMD Oven for making SMD samples and Prototypes erica Electronics 0 July 11th 06 12:46 PM
Low cost SMD Oven for making SMD samples and Prototypes erica Electronics Repair 0 July 11th 06 10:42 AM


All times are GMT +1. The time now is 02:16 AM.

Powered by vBulletin® Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2004-2022 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"

 

Copyright © 2017