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 Post subject: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 12:25 pm 
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Posts: 5412
Location: Lincoln City, OR 97367
Greetings, All!

I had an Edison bump the other day that popped a fuse in my LG refrigerator. This model uses a so-called "Linear Compressor" which I believe is driven from a large circuit board under a cover on the back of the refrigerator. I assume this because the AC line cord goes direct to this board and the first component in the hot lead is a fuse. After that, there are some rather large devices on heat sinks so I presume the board is driving the compressor.

The Edison hit blew the fuse which is soldered into the board. When I discovered the refrigerator was completely dead, I checked this line fuse and found it open. I decided to replace it, having nothing to lose by doing so. The original fuse soldered directly into the board; I replaced it with an in-line fuse holder on leads so that I could easily replace the fuse in the future.

Now comes the fun part... what to replace it with? Fortunately, the current rating was clearly labeled, both on the board and on the fuse. It is a 10 amp fuse. However, the only 10 amp fuse I had in stock was an MDL-10.... i.e. a 10 amp slow-blow. That's what is in there now, and the refrigerator runs OK. However, I don't think a slow-blow fuse is what is desired for the protection of solid-state electronics. So, what type of fuse should be in there? The original fuse is a 3AG size with a white ceramic body. There seems to be a logo which is a stylized "IC" There is also a mark that looks like a capital letter "B" or a right angle fork terminal, followed by the designation 65TL. The other end simply says "250 V 10 A". The fuse is, as I said a ceramic 3AG size, but it has press-fit end caps that connect the wire leads to the fuse so it can be soldered into the board. These end caps cover about half of the normal 3AG end caps and increase the fuse diameter at the ends.

That's all I can tell you, because that's all I know. Replacing the fuse is way cheaper than replacing the whole board, which is what I'm sure the appliance repair people would have me do, and I can't see doing it since the board survived the line transient, presumably thanks to the fuse. So, I am looking for a 3AG size 10 Amp 250 volt fuse that will go in my new fuse holder and will have the same protection characteristics as the original fuse.

Edit: I just noticed that there is a red dot in the center of the ceramic body of the fuse... reminiscent of the dot on a body-end-dot resistor.

Any thoughts?

Thanks,

_________________
Jim T.
KB6GM


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 1:17 pm 
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Joined: Oct Tue 12, 2021 1:14 pm
Posts: 105
Location: Central Texas
Jthorusen wrote:
Greetings, All!

I had an Edison bump the other day that popped a fuse in my LG refrigerator. This model uses a so-called "Linear Compressor" which I believe is driven from a large circuit board under a cover on the back of the refrigerator. I assume this because the AC line cord goes direct to this board and the first component in the hot lead is a fuse. After that, there are some rather large devices on heat sinks so I presume the board is driving the compressor.

The Edison hit blew the fuse which is soldered into the board. When I discovered the refrigerator was completely dead, I checked this line fuse and found it open. I decided to replace it, having nothing to lose by doing so. The original fuse soldered directly into the board; I replaced it with an in-line fuse holder on leads so that I could easily replace the fuse in the future.

Now comes the fun part... what to replace it with? Fortunately, the current rating was clearly labeled, both on the board and on the fuse. It is a 10 amp fuse. However, the only 10 amp fuse I had in stock was an MDL-10.... i.e. a 10 amp slow-blow. That's what is in there now, and the refrigerator runs OK. However, I don't think a slow-blow fuse is what is desired for the protection of solid-state electronics. So, what type of fuse should be in there? The original fuse is a 3AG size with a white ceramic body. There seems to be a logo which is a stylized "IC" There is also a mark that looks like a capital letter "B" or a right angle fork terminal, followed by the designation 65TL. The other end simply says "250 V 10 A". The fuse is, as I said a ceramic 3AG size, but it has press-fit end caps that connect the wire leads to the fuse so it can be soldered into the board. These end caps cover about half of the normal 3AG end caps and increase the fuse diameter at the ends.

That's all I can tell you, because that's all I know. Replacing the fuse is way cheaper than replacing the whole board, which is what I'm sure the appliance repair people would have me do, and I can't see doing it since the board survived the line transient, presumably thanks to the fuse. So, I am looking for a 3AG size 10 Amp 250 volt fuse that will go in my new fuse holder and will have the same protection characteristics as the original fuse.

Edit: I just noticed that there is a red dot in the center of the ceramic body of the fuse... reminiscent of the dot on a body-end-dot resistor.

Any thoughts?

Thanks,

Greetings,
My son-in-law owns an appliance repair business, and I know he services LG refrigerators.
Tell me the model number and I'll ask him about the fuse.

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Kind regards,
OldRelic

Warning: May contain traces of nut.


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 4:13 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 11179
Location: Long Island NY
According to the trusty (?) internet, 65TL appears to be short for 65-second time lag fuse. There have been some efforts on the parts of both the IEC and UL to quantify just how fast or slow fuses are. If that's what it is, you may discover that a common slow blow fuse might pop faster than an original would. The ceramic body indicates that the original fuse likely had a higher current interrupting capacity than a glass one.

At one point in time I would have thought nothing of installing an external fuse holder behind a refrigerator as you have done. Today I would not let something like that stand longer than necessary to track down an exact replacement fuse from an appliance parts distributor or even better from LG directly. The mod would then come out and everything would go back exactly the way it was. Manufacturers and insurance companies no longer pay damage claims without forensics. If there was a fire or accident that could conceivably be blamed on the fridge, they might find your unauthorized fuse and holder and put the whammy on you when they try to decline payment.

While one normally associates fast blow fuses with protecting semiconductors, refrigeration motors call for time lag fuses or breakers. The amount of current on start-up, as well as the length of time it takes to fall off to normal running current, vary quite a bit depending on the temperatures of the coils and how long it has been since the motor last ran. Specifically when a refrigerator stops, the gas pressures in the system gradually equalize which tends to super-cool the compressor and make its lubricants thicken. If the system kicks back on before the compressor has a chance to warm up to room temperature, the motor can take extra current for a minute or two while overcoming the thickness of the lubricant.

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"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 8:48 pm 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 5412
Location: Lincoln City, OR 97367
Greetings to OldRelic, Chris and the Forum:

Thanks for your responses and all the information.

The refrigerator is an LG, model LFX28979ST/00. The serial number is: 107KRWZ0Z761.

I doubt your son-in-law will be able to find just the fuse; I'm sure the standard thing is to replace the whole board. However, I would appreciate it if he could check anyway; I'd like to be proven wrong on that point.

As far as the fuse holder is concerned, I intend to leave it in and replace the fuse with something as close to the original as I can get. Odds multiply. The odds of the refrigerator starting a fire are a small fraction of 1. The odds that my modification would even be discovered are also very small; the cost of a forensics lab discovering such a mod in a burnt out refrigerator would be prohibitive for a claim as small as a house fire where no one was injured. Then, I can contest any finding in court; my modification is most unlikely to have caused a fire, provided I can find the correct fuse. Offset that with the nuisance factor of replacing the fuse on the board... this board has all the electronics for the whole refrigerator on it.... it is about 6 X 10 inches and has multitudes of multi-pin connectors and associated harnesses plugged into it. I already broke one connector locking tab trying to get that particular connector out; fortunately, the connector is so located that pressure on the harness by the board cover would prevent its ever coming out. It just plain isn't worth the trouble if a fuse holder can be installed under the cover, which is where it is.

As far as the time constant on the fuse is concerned, the Edison transient lasted no more than 1 second. I was watching TV at the time and while everything had to reboot, there were no problems with any other gear excepting the refrigerator. This led me to believe that the fuse was very fast acting. I did not discover that the refrigerator was dead until some time after that, so it is possible that there was a 65 second over-current condition before the fuse blew. I would think that 65 seconds of a solid-state switch latched up would be the end of the device... but the refrigerator has been working fine for some days now so I conclude that the rest of the electronics survived.

This particular refrigerator does not have a motor-driven compressor. It has a "Linear Compressor" which I take to be a reciprocating linear motor driving a piston type compressor... the motor probably being internal to the compressor body. The switching electronics for this linear motor are on the board with the fuse. Therefore, the usual starting current requirements for a rotary compressor do not apply. I do not know if the solid-state switch limits in-rush current or if it is just a saturating on-off switch. In any event, the fuse is principally protecting the solid-state electronics, which is why I assumed that is is a fast-blowing fuse.

I don't know how much current would have to be interrupted if one of the switching devices were to short.... that's anybody's guess as I doubt that LG would be forthcoming. The normal refrigerator drain is specified to be 5.2 amps.... presumably when the compressor is running.

So, there you have it.... I've told you more than I know. If the original fuse was indeed a 65 second delay, then the current fuse should offer better protection... at the possible cost of more nuisance blown fuses.

Thanks to all for your thoughtful responses,

_________________
Jim T.
KB6GM


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 9:18 pm 
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Joined: Oct Tue 12, 2021 1:14 pm
Posts: 105
Location: Central Texas
Jthorusen wrote:
Greetings to OldRelic, Chris and the Forum:

Thanks for your responses and all the information.

The refrigerator is an LG, model LFX28979ST/00. The serial number is: 107KRWZ0Z761.

I doubt your son-in-law will be able to find just the fuse; I'm sure the standard thing is to replace the whole board. However, I would appreciate it if he could check anyway; I'd like to be proven wrong on that point.

As far as the fuse holder is concerned, I intend to leave it in and replace the fuse with something as close to the original as I can get. Odds multiply. The odds of the refrigerator starting a fire are a small fraction of 1. The odds that my modification would even be discovered are also very small; the cost of a forensics lab discovering such a mod in a burnt out refrigerator would be prohibitive for a claim as small as a house fire where no one was injured. Then, I can contest any finding in court; my modification is most unlikely to have caused a fire, provided I can find the correct fuse. Offset that with the nuisance factor of replacing the fuse on the board... this board has all the electronics for the whole refrigerator on it.... it is about 6 X 10 inches and has multitudes of multi-pin connectors and associated harnesses plugged into it. I already broke one connector locking tab trying to get that particular connector out; fortunately, the connector is so located that pressure on the harness by the board cover would prevent its ever coming out. It just plain isn't worth the trouble if a fuse holder can be installed under the cover, which is where it is.

As far as the time constant on the fuse is concerned, the Edison transient lasted no more than 1 second. I was watching TV at the time and while everything had to reboot, there were no problems with any other gear excepting the refrigerator. This led me to believe that the fuse was very fast acting. I did not discover that the refrigerator was dead until some time after that, so it is possible that there was a 65 second over-current condition before the fuse blew. I would think that 65 seconds of a solid-state switch latched up would be the end of the device... but the refrigerator has been working fine for some days now so I conclude that the rest of the electronics survived.

This particular refrigerator does not have a motor-driven compressor. It has a "Linear Compressor" which I take to be a reciprocating linear motor driving a piston type compressor... the motor probably being internal to the compressor body. The switching electronics for this linear motor are on the board with the fuse. Therefore, the usual starting current requirements for a rotary compressor do not apply. I do not know if the solid-state switch limits in-rush current or if it is just a saturating on-off switch. In any event, the fuse is principally protecting the solid-state electronics, which is why I assumed that is is a fast-blowing fuse.

I don't know how much current would have to be interrupted if one of the switching devices were to short.... that's anybody's guess as I doubt that LG would be forthcoming. The normal refrigerator drain is specified to be 5.2 amps.... presumably when the compressor is running.

So, there you have it.... I've told you more than I know. If the original fuse was indeed a 65 second delay, then the current fuse should offer better protection... at the possible cost of more nuisance blown fuses.

Thanks to all for your thoughtful responses,

I texted my daughter with the info to pass on to my SiL. I'll let you know what he says.

Meanwhile, just a thought: A CVT (constant-voltage transformer) rated for your fridge's load might not be a bad idea if you get a lot of transients. Sounds like an expensive fridge. If you get a lot of transients a slo-blo fuse will let those get through until the fuse blows and fatigue the electronics it's supposed to be protecting. A good CVT will attenuate those considerably. Or just replace fuses when it happens and take your chances. I reckon it depends on how often it happens vs how expensive replacing the board would be.

[edit] The Tripp-Lite LC-1200 looks like it would do a good job protecting your fridge. $129.96 on Amazon.

_________________
Kind regards,
OldRelic

Warning: May contain traces of nut.


Last edited by OldRelic on Oct Tue 26, 2021 11:28 pm, edited 5 times in total.

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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 9:44 pm 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 5195
Location: Tucson, Arizona U.S.A.
Fuses do not have a delay of a specific number of seconds. A number like that carries an implied set of test conditions. The actual blowing time of a fuse depends on the size of the overload, how long it exists (larger overloads blow faster), ambient temperature (since fuses are thermal devices), and possibly other factors.

That fuse is likely there to prevent a fire. The old-time adage is that semiconductors blow to protect the fuse. That isn't really true since semiconductors tend to fail shorted.

Ceramic fuses are generally filled with sand to suppress arcs and prevent the fuse from exploding.

The board you describe sounds like it may be a variable speed drive to maximize the efficiency of the refrigerator.

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Jim Mueller

Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Tue 26, 2021 11:17 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 11179
Location: Long Island NY
You have to read the spec sheets for fuses to determine what the time lags are, but they are there. Even the fastest of fast blowing fuses have time specs. I believe for TL type fuses the time lag applies at 200% to 210% of rated current with the fuse at room temperature or slightly above. Of course the higher the current, the shorter the time before it blows.

LG's "linear compressor" is basically an electromagnet that pulls a spring plate attached to the compressor piston. There are fewer moving parts, thus less wear and friction loss, compared to a conventional motor-driven referigerator compressor with a crankshaft and connecting rod. The inverter board drives the electromagnet at varying rates depending on how much cooling is needed at any point in time.

Even though there are no rotating parts in the linear compressor, it still could be subject to transient periods of high current depending on the inlet and outlet pressures when it starts. But there are other possibilities besides; the power glitch could have caused the inverter to miss a beat and do something it shouldn't have done like clamp to one of the rails, or the fuse itself could have had a fatigued element which finally let go.

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"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Let's Play "Guess That Fuse"
PostPosted: Oct Sat 30, 2021 11:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1198
Location: dayton oh usa
ceramic body fuses typically have higher interrupting ratings.
usually with a filling to quench any arc.
i would get one asap to replace
mdl is a glass fuse.
bad things might happen if the blow is aggravated by inductive kick from the motor.
you could get a sustained arc that in a rare case might start a fire.


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