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Author Topic:   New Fuse Design: Low-profile Jcase Cartridge
jimh posted 05-01-2012 12:38 AM ET (US)   Profile for jimh   Send Email to jimh  
On the drive to work this morning I plugged my cellular telephone charging cord into the cigar lighter power socket on the dashboard of my car in order to charge the cell-fone. The charger LED did not illuminate, indicating there was no power from the cigar lighter socket.

I thought about this for a moment, and realized what had gone wrong. Last week at work we were having a dispute about a particular DC-to-DC converter power supply, used for charging a laptop computer. It outputs 19-VDC and runs off the cigar lighter socket in a vehicle. The end-user said it did not work. The bench tech said it was fixed. I said, "I'll try it in my car." I did, and, no, it did not work. Now I realized that not only did the DC-to-DC converter not work, it probably had blown the fuse in my car's power outlet, too!

When I got to work, I checked the cigar lighter power outlet with a DMM. There was no voltage there, as I suspected. I opened the glove box and grabbed the owner's manual. Around page 246--it's a big owner's manual--I found the section on fuses. Even though my car is not particularly big or particularly fancy, it has two power distribution centers and enough capacity to have about 100 fuses. After carefully reading the list twice, I found what I thought should be the circuit for the cigar lighter socket, called "Front Power Center" or something like that. The fuse was under the engine hood in the power center there.

When I opened the cover on the power center I was quite surprised. All the fuses were of a new type I had not seen before. The fuses were contained in rectangular cartridges, color coded for current rating. The cartridges have a clear cover and you can see into them to look at the actual fuse element. It was too dark in the garage to see if the particular fuse I thought was associated with the cigar-lighter was blown, so I pried it out of the fuse panel, using the test leads of the DMM. (No fuse puller accessory in the box under the hood.)

Once out of circuit, I checked the fuse with the DMM. Yup, it was open. OK, mystery solved. Now let's get a new fuse.

Back at my desk, I GOOGLE'd for "Ford cartridge fuse Fusion 2011" I got some results that were close, but not a perfect match for my fuse. From what I could tell, the fuse I had in my hand was a "Jcase" fuse. Here the "J" means Japan. This fuse style is apparently used on a lot of cars made in Japan. (My FORD was made in Mexico, by the way.) The Jcase fuses all looked too long for my fuse holder. Then I found a "mini-Jcase" fuse. The size looked correct, but my fuse had some molded ridges along the sides that fit into guides on the fuse panel. These fuses did not.

I checked for vendors, but did not find much. Someone on Amazon was selling "mini-Jcase" fuses for $9-each. Wow, that is an expensive fuse.

Finally, in desperation, I called the local FORD dealer and asked for the Parts counter. The parts counter guy looked up the FORD part and found he had them in-stock. "It's a little blue rectangular cube," he said, "with '20' etched on the clear part."

"That's the one I need," I told him. (Now for the important part.) "How much are they?"

After a moment's pause, the parts guy said, "Hey, not too bad, only $1.52."

"Set one aside for me," I said, "I will come over after lunch, about one o'clock."

According to Littlefuse, the Jcase cartridge fuse has been around for a while. It is intended to supplant the MAXI-Fuse in automotive applications where a high current fuse with some time delay is needed. The Jcase cartridge also has an interesting design advantage over traditional fuses. The Jcase cartridge fuse carries the female contacts, and the Jcase fuse panel slots for the fuses have male contacts. This advantage is that every fuse brings with it a fresh female contact. In older designs where the fuse had male contacts, the socket on the fuse panel has a female contact. With every fuse insertion the female contact on the fuse panel is expanded slightly. The fuse panel contact had to be designed to withstand many insertions. With a Jcase cartridge fuse, the fuse carries with it a fresh set of contacts, and the Jcase fuse box or panel needs only the simple male contact portion.

I have never seen this style fuse before, but I think it has become common in automotive applications. I wonder if we will see them moving to boats.

jimh posted 05-01-2012 12:52 AM ET (US)     Profile for jimh  Send Email to jimh     
The proper name for the fuse I was seeking is Low-profile Jcase. This Littlefuse literature shows what they look like: Littelfuse-Automotive-Cartridge-Fuse-Low-Profile-JCASE-58V.pdf

But those generic fuses did not have the ridges and guides specific to the FORD fuse block.

Low-profile Jcase 20-Ampere fuse
The Ford low-profile Jcase 20-Ampere fuse.

jimh posted 05-01-2012 04:16 PM ET (US)     Profile for jimh  Send Email to jimh     
The voltage rating of the Low-profile Jcase fuse is 58-Volts, which is very likely sufficient for automotive applications involving higher primary power voltages. For some time now there has been talk that in order to reduce the size of electrical conductors in vehicles the primary DC power voltage will be raised, and the increase is likely to be in multiples of the standard battery voltage of a nominal 13.2-Volts also known as "12-Volts". Four times 13.2-Volts is about 53-volts. The Low-profile Jcase fuse should be suitable for applications with that sort of primary voltage.
Jerry Townsend posted 05-02-2012 03:07 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Jim - in all of my vehicles, there are spare fuses in the fuse box - but then, I use GM. But, aside from that, I am surprised that there were not spare fuses in your fuse box.

What is wrong with the small fuses (about 3/4 x 3/4 x 3/32) fuses that have been used for many, many years? Your fuse looks to be quite a bit larger - requiring more space.

I was not aware that a fuse size was related to voltage - current yes - but not voltage. Enlighten me a bit. --- Jerry/Idaho

jimh posted 05-02-2012 04:55 PM ET (US)     Profile for jimh  Send Email to jimh     
The voltage rating of a fuse is reflective of the maximum safe voltage in the circuit that the device can interrupt. For example, I have a rather impressive 4,800-VAC fuse sitting around somewhere as a souvenir of a power outage from a few years ago. This fuse is rated to interrupt current in circuits carrying 4,800-Volts. When you want to break such a circuit, you need to mindful of the ability of a voltage that high to jump over and arc. In switchgear for high-voltage circuits there are often special elements of the device known as arc-breakers, which are introduced in the path of arc to suppress the arc as the contact separate.

The Low-profile Jcase fuse might be able to interrupt current in a 58-Volt circuit, but in higher voltage applications is might fail. A higher voltage circuit might arc-over the fuse opening and continue to flow, or the arc could set something on fire. So all fuses have a voltage rating in addition to their current limit rating.

jimh posted 05-02-2012 08:01 PM ET (US)     Profile for jimh  Send Email to jimh     
The photograph of the Low-profile Jcase cartridge fuse used in my 2011 Ford FUSION automobile that I show above perhaps conveys an incorrect impression of the size. The fuse is not particularly big. In the document to which I linked you can find the dimensions of the fuse cartridge. It is larger than the typical ATC-style fuse, but considering that the Low-profile Jcase fuse is typically only used for fusing circuits of 20-Amperes or more, I do not find that its size is inappropriate for the function.
jimh posted 06-01-2012 12:35 PM ET (US)     Profile for jimh  Send Email to jimh     
The FORD part number for the fuse discussed above is


BobbyC posted 02-18-2014 07:57 AM ET (US)     Profile for BobbyC  Send Email to BobbyC     
Hi jim,
This info has been invaluable. By the way it happened the same to me, a shorted power inverter. I just returned from Pep Boys, where I tried a JCase fuse, they don't fit. They look like they will but they don't. I came home and started searching and couldn't find it anywhere on line. Fortunately, you listed the ford part #. I found a couple on ebay fairly reasonably and it will save me a trip to the dealer.
They are listed as a circuit breaker. Well, I guess that is true.They will break it... once.

Thanks a bunch,

jimh posted 02-18-2014 11:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Hi Bob--I am pleased to hear the information was useful. It will probably be useful to me, too, some time in the future when I blow another of those low-profile J-Case fuses and cannot remember the actual proper name for them.

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