High Power Fusing

[drdx]

Hello all, just wondering, how does the big amp crew fuse their stuff? I have a 300 amp breaker I plan on using, but at 300 amps, I'd think the vehicle would be burning down by the time it tripped itself in the event of a short. Any thoughts on this? Do they just run it all direct and disconnect when not in use? I can understand a much lower rated fuse or breaker used for safety, and I use them at the equipment and the battery, but what about this higher amperage stuff? I typically unhook my stuff when not in use anyway, as it is on welder connectors, no big deal, but I'm moving to a more hard mounted setup. -drdx

[slydog]

Hello all, just wondering, how does the big amp crew fuse their stuff? I have a 300 amp breaker I plan on using, but at 300 amps, I'd think the vehicle would be burning down by the time it tripped itself in the event of a short. Any thoughts on this? Do they just run it all direct and disconnect when not in use? I can understand a much lower rated fuse or breaker used for safety, and I use them at the equipment and the battery, but what about this higher amperage stuff? I typically unhook my stuff when not in use anyway, as it is on welder connectors, no big deal, but I'm moving to a more hard mounted setup. -drdx

No one around here fuses their keydown mobiles but then again most of them are all trust fund CBers and in the event of a vehicle burning up.........they'll just buy another.
Fuses are not meant to protect equipment, just keep the vehicle from flaming up in the event of a dead short.
I don't fuse anything....I have a 92 F350 with half a million miles on it, no big loss if it smokes.

[TX_Dj]

If you must have everything run on the same circuit, then a quality breaker at the battery is a must in case of a serious dead short. Second, I believe heartily in fuses at the device which are sized to the device's need in case something bad happens inside one of the boxes.

I.E. if your device has a max rating of 60a, and you have it connected to a 300a breaker, if something busts in the device and pushes it past 60a, you're going to be in a world of hurt if the power line can only take 100a, for example. If your box shorts, and blows its 60a fuse, it will stop it from drawing too much power.

Batt -> Breaker -> Long Run -> Fuse -> Device

A better option may be to run separate circuits sized appropriately for each device, than to gang them all up on a common bus.

Also keep in mind your load should not be expected to exceed 80% of your breaker's rating, so that is to say all the devices behind that 300a breaker should be 240a or less at max draw. Or does that only apply in AC ? I dunno!

[slydog]

If you must have everything run on the same circuit, then a quality breaker at the battery is a must in case of a serious dead short. Second, I believe heartily in fuses at the device which are sized to the device's need in case something bad happens inside one of the boxes.

I.E. if your device has a max rating of 60a, and you have it connected to a 300a breaker, if something busts in the device and pushes it past 60a, you're going to be in a world of hurt if the power line can only take 100a, for example. If your box shorts, and blows its 60a fuse, it will stop it from drawing too much power.

Batt -> Breaker -> Long Run -> Fuse -> Device

A better option may be to run separate circuits sized appropriately for each device, than to gang them all up on a common bus.

Also keep in mind your load should not be expected to exceed 80% of your breaker's rating, so that is to say all the devices behind that 300a breaker should be 240a or less at max draw. Or does that only apply in AC ? I dunno!

But it is so cool when your floor board is glowing red!

[Foxhunter]

Dr.Dx I like alot of your posts they are very good and straightforward. Somehow I wonder how anywhere in Texas could be near "the center of the CB universe". Texas, isn't that now Northern Mexico? Okay, on topic: Yeah I couldn't imagine running high loads/amps without using appropriately rated fuses. Unless----are you a "trust-fund baby"? Did you say "breaker"? From what I read that's real dangerous and many fires have resulted. When I didn't know, I used 6 switch 300 amp circuit-breakers because I'm somewhat familiar with car audio amps & related. Then I was reading in an AARL manual how in dead-short conditions they often fuse---and weld themselves together, continuing the circuit. I'm not trying to re-hash but it is right to slightly underate the fuse rating for the device. Currently I'm using 2AWG cables with heavy copper lugs and they are fused within 1ft of the power source---both sides +/- and within 1 ft of each device (radio/amp/two 1.5 farad capacitors). I also use a main shut-off switch (automotive type) from Calterm as a master "killswitch". This comes with a removeable key so that when I exit my vehicle all power is removed from the radio system so no "amateur" will operate it in my absence nor will there be any further risk of electrical malfunction. I just bought some 0000AWG cable and am wondering how I might fuse such line---as it's diameter is indeed large, maybe AC house fuses.

[Foxhunter]

One more thing.....I know I've recommended one particular site to a couple others and judging from the nature of your post(s) it would be some good, simple, straight-forward reading. The site is: www.K0BG.com
The wiring section is good as well as the dozen or so others. He's a first-class operator and there's a few real tips and no myth. Hope it helps.

[209 first class]

im wondering if the circuit breaker has less resistance than a fuse, and if it would open quicker in case of short. i know plenty of people who will not use a fuse saying it adds resistance and therefore limits the amperage/current just like a very long extension cord would. i have heard of a car burning up around here, and also a friend had a short while driving. the car was smoking ,(it was the insulation on the hot wire burning!) it died, they pulled over, if they had not had a hatchet to chop the hot wire at the battery, his truck would have burned. it would be nice if someone did a test, no fuse/ fuse/ breaker. see if any one of them limits your swing or deadkey. i only know what people say, it would be good to really know. 2zero9

[drdx]

That K0BG site has excellent information. This has been going a bit, but I'm not breakered under the hood and also at the amp tray in the back. I too use a racecar battery switch, mounted in a pvc box, next to the driver seat so I can disconnect the vehicle from the 2nd battery and amp setup. It came in handy recently when I left my lights on overnight. I got in and it was all dead, so I just turned the key and connected the rear battery for a jump start. I have wondered about the breakers, but haven't tested them. I do have a spare jump box and an extra 200 amp one, so I may do a controlled test shorting it out and see if it blows. -drdx

[209 first class]

gee, i dont know if i would short it, however fast it breaks the circuit, it will still strain the battery and heat up the wire/insulation with that much amperage. however i would be curious to know if any wattage is lost thru using a fuse/breaker versus running straight to the battery. if none is lost, then the whole thing about "dont use a fuse,you will lose power " is a hoax . 2zero9

[drdx]

I've wondered about the loss myself but always saw the fusing as essential. It does make you think you'd see some loss if you have this huge #2 cable running back to an amp then you see all that power traveling through 4 30 amp fuses or whatever and see the size of the conductor in that fuse. -drdx

[powerstrokin]

would there be a difference in running a distribution box with X amount of midi style fuses vs running a single higher amp fuse?

[drdx]

That's what I do. I couldn't find a 120 amp fuse, so i run 4 30's to one of my amps using one of those monster distribution boxes. -drdx

[PONY EXPRESS]

That's what I do. I couldn't find a 120 amp fuse, so i run 4 30's to one of my amps using one of those monster distribution boxes. -drdx

If I was running that much power I would have to do it that way as well. To much current before the wire would blow and it would look like this. I feel much safer those fuses blowing up front than after it catches the carpet and everything else on fire.Yes that is an actual USPS vehicle like I drive on fire .Odds are they will find the old fuel lines cracked and gas ran down to the red hot manifold and ignited .Heck I worry about 50 amp fuses blowing but I know in a direct short it will pop that fuse by battery quick.




We could have a BBQ with this

[drdx]

The 4 30's are at the back on the ts 16. The front has a breaker, but it's only a 135. The rear battery, right at the amps, takes the brunt of the draw on keydown so I haven't blown the 135 breaker yet, though I have a bigger one thinking I'd need to replace it. The rear battery is fused to everything, and breakered goint to the front of the vehicle. The only thing not currently fused is the bigger box, and I don't have any 320 amp fuses or a dist. box with that combo, although I guess I could do the 4x80 amp deal for that. I have a 300 amp breaker but this amp is on quick disconnects (welder banana kind) and is not in there often, so I haven't breakered/fused it yet but I will. I don't leave it hooked up as I don't usually need it and it sleeps in the house. -drdx

[Foxhunter]

im wondering if the circuit breaker has less resistance than a fuse, and if it would open quicker in case of short. i know plenty of people who will not use a fuse saying it adds resistance and therefore limits the amperage/current just like a very long extension cord would. i have heard of a car burning up around here, and also a friend had a short while driving. the car was smoking ,(it was the insulation on the hot wire burning!) it died, they pulled over, if they had not had a hatchet to chop the hot wire at the battery, his truck would have burned. it would be nice if someone did a test, no fuse/ fuse/ breaker. see if any one of them limits your swing or deadkey. i only know what people say, it would be good to really know. 2zero9

That topic is addressed mostly at: www.K0BG.com (in the wiring protection section at the bottom of the list).

I still think you're mic collection is the real deal 209 1st class green w/envy

[Kojak]

Dr.Dx I like alot of your posts they are very good and straightforward. Somehow I wonder how anywhere in Texas could be near "the center of the CB universe". Texas, isn't that now Northern Mexico? Okay, on topic: Yeah I couldn't imagine running high loads/amps without using appropriately rated fuses. Unless----are you a "trust-fund baby"? Did you say "breaker"? From what I read that's real dangerous and many fires have resulted. When I didn't know, I used 6 switch 300 amp circuit-breakers because I'm somewhat familiar with car audio amps & related. Then I was reading in an AARL manual how in dead-short conditions they often fuse---and weld themselves together, continuing the circuit. I'm not trying to re-hash but it is right to slightly underate the fuse rating for the device. Currently I'm using 2AWG cables with heavy copper lugs and they are fused within 1ft of the power source---both sides +/- and within 1 ft of each device (radio/amp/two 1.5 farad capacitors). I also use a main shut-off switch (automotive type) from Calterm as a master "killswitch". This comes with a removeable key so that when I exit my vehicle all power is removed from the radio system so no "amateur" will operate it in my absence nor will there be any further risk of electrical malfunction. I just bought some 0000AWG cable and am wondering how I might fuse such line---as it's diameter is indeed large, maybe AC house fuses.

Having done electrical work by trade, I tell you fuses are the only way to go. Household breakers react thermally to overload. Household circuit breakers sometimes weld themselves closed because they cannot react fast enough to the excessive heat generated by dead shorts. Car batteries under these conditions can generate upwards of 3-4k amps For a very short (no pun intended) time.

[Foxhunter]

Dr.Dx I like alot of your posts they are very good and straightforward. Somehow I wonder how anywhere in Texas could be near "the center of the CB universe". Texas, isn't that now Northern Mexico? Okay, on topic: Yeah I couldn't imagine running high loads/amps without using appropriately rated fuses. Unless----are you a "trust-fund baby"? Did you say "breaker"? From what I read that's real dangerous and many fires have resulted. When I didn't know, I used 6 switch 300 amp circuit-breakers because I'm somewhat familiar with car audio amps & related. Then I was reading in an AARL manual how in dead-short conditions they often fuse---and weld themselves together, continuing the circuit. I'm not trying to re-hash but it is right to slightly underate the fuse rating for the device. Currently I'm using 2AWG cables with heavy copper lugs and they are fused within 1ft of the power source---both sides +/- and within 1 ft of each device (radio/amp/two 1.5 farad capacitors). I also use a main shut-off switch (automotive type) from Calterm as a master "killswitch". This comes with a removeable key so that when I exit my vehicle all power is removed from the radio system so no "amateur" will operate it in my absence nor will there be any further risk of electrical malfunction. I just bought some 0000AWG cable and am wondering how I might fuse such line---as it's diameter is indeed large, maybe AC house fuses.

Having done electrical work by trade, I tell you fuses are the only way to go. Household breakers react thermally to overload. Household circuit breakers sometimes weld themselves closed because they cannot react fast enough to the excessive heat generated by dead shorts. Car batteries under these conditions can generate upwards of 3-4k amps For a very short (no pun intended) time.

Hi there Kojak. Welcome on and glad to see your post & comments. Out of curiousity, did you choose the "bald-headed" eagle in relationship to the famously "bald-headed" Kojak you're using for a username/handle? Just wondering!

My last comment on the post you'd quoted mentioned me considering the possibility of using large "AC house fuses " for that industrial 0000AWG stranded-flex DC power cable I have. I shouldn't, I've learned. I bought that G-I-A-N-T cable for a future mobile amp install (hee). The problem is: finding connectors that size. Asking around, electrical supply retailers (not your local autostore either) automatically think I am confused and mean "4AWG" where as it is actually "4/0", aka "4-ought". Connectors and fusing that size will be the trick. I'll do a more extensive search when I get closer to being ready.

Here's a link to the AWG Wire Gauge & Current Limits Chart for any of our Forum vieweres who may be interested:
http://www.powerstream.com/Wire_Size.htm
Use it as a reference, to gauge whether your current install's supply lines are adequate or not.

If I may, I'd like to re-post an article written elsewhere on proper fusing & wiring protection. I won't include any of the charts or photos in the re-post. In the article, the process of "Hysteresis" (ie-"reaction-times") is explored demonstating that many circuits and boards in a radio system will suffer damage before a fuse or breaker will respond. I'd invite any of our viewers to read this article and consider the information provided. Comments/replies are welcome. After I'd read this, I had to "rethink" what I'd done in the past-----and what I considered "safe" or "protected" in prior installs.
*****************************************************************************


Quote:

"Installing an amateur transceiver in a vehicle entails a lot of work, and attention to detail. This includes proper wiring, protecting that wiring, and ultimately protecting the equipment as well. Far too often the details are overlooked, or circumvented, resulting is erratic operation, ground loop problems, and other maladies not easily traced or repaired.

Besides the wiring issues, proper fusing is also an important consideration. While the factory wiring harnesses are adequately fused, it's a rare mobile installation that doesn't have some ancillary equipment (SWR meter for example) requiring power. When there is, each device should be fused according to the manufacturer's recommendations.

This article is an effort to explain why proper fusing is so important.

Fusing and a Thing Called Hysteresis

It seems, no matter how many times a myth is dispelled, they keep raising their ugly head. One common myth is that power cable fuses protect the radio from damage. They don't. Myth number two is, that a fuse will open instantly as soon as the current exceeds the fuse's rating. It won't. Myth number three is, it's always okay to use fuses designed for 120 volts AC, in a nominal 12 volt DC system. It isn't.

Fuses are there to protect the cabling. For example, the Icom IC-7000 has a 5 amp (system) fuse mounted inside the radio, and 30 amp fuses in the cabling (plus and minus). If you short out a supply connection (pin 3 of the tuner port for example), a circuit board trace and/or switching transistor will fail long before the 5 amp fuse opens. The 30 amp fuses will never open in this particular case. It can be argued that the power cable fuses do protect the radio if something fails catastrophically, a final perhaps, but chances are some other component in the circuitry will be damaged beyond repair before the power cable fuse(s) opens.

The definition of a fuse is relatively simple. It is a wire, that when subjected to too high of a current, melts. When it does, the circuit opens... hopefully. I say hopefully, because if you've chosen the incorrect size for your application, it may not open. Or, it may open after a long delay. In any case, you want the fuse to do its job, well before your wiring becomes its own fuse.

All fuses exhibit hysteresis. This is the time lag between any given ampere overload and when the fuse opens. For example, a nominal 20 amp fuse will handle a 30 amp load for about 90 seconds. It will hold a 100 amp load for about 1 second. This is one reason slow blow fuses are not recommended for amateur devices.

Unless you're an engineer, you don't hear the word hysteresis very often. Hysteresis is used to describe a phenomenon, in which the value of a physical attribute lags behind changes in the effect causing it. I use it here because fuses have a hysteresis effect. This fact figures heavily on our choice of fuse amperage ratings, the wire size we choose as a result, and ultimately how safe our installation is should a dead short occur.

The chart at left (omitted---Home page link: ( http://www.littelfuse.com/index.html ) is courtesy of Littelfuse, Inc. and I thank them for allowing me to reproduce it here. The chart covers their 299 series fuses (shown below in colors which match their ratings), more commonly called Maxi fuses. They're popular in amateur mobile installations as they are a modern replacement for the older cylindrical style 5ag fuses. They're also available with LED failure indicators.


Note that a 30 amp Maxi fuse will take about 3 seconds to open when subjected to a 100 amp load! The same fuse will carry 40 amps for about 2 minutes! As the static temperature goes up, the vertical scale compresses slightly, and in very cold temperatures settings it elongates slightly. So, hysteresis is the time lag between applying an overload, and the fuse opening to protect the wire. Here is a pdf with more data on the Maxi fuse.

In the mean time, the wire being protected is getting rather warm. If it gets too warm, hot really, it could cause a fire. For a better understanding, let's look at some specific cases.

Most amateur transceivers' DC power cords are built using 10 AWG, or an equivalent (e.g.: Metric 6). Further, most are about 9 feet long, and most are fused with 30 amp fuses. If you subject them to 22 amps of current (nominal input for key down full power), they'll exhibit about a half volt drop (including the drop caused by the internal resistance of the fuse, and that of it's holder). This means the power cable will be dissipating about 11 watts.

If we subject the cable to a load of 100 amps (not a dead short) where the fuse would nominally require 3 seconds to open, our voltage drop is 2 volts, and our wire has to sustain 200 watts of dissipation for 3 full seconds! Now you know one of the reasons why it is so important to choose the correct wire size. To reiterate, the wire must be capable of handling the nominal ICAS load with a minimal amount of voltage drop, and it must also be capable of handling an impressive overload, albeit briefly.

Fuse Size

So, if the radio draws just 20 amps peak, why not use a 20 amp fuse instead? Here's why. Subjecting any given fuse to instantaneous loads close to their current rating will eventually cause them to fail due to element fatigue (sometimes referred to as erosion). Depending on the load characteristics (steady or varying), fuses are sized from 25% to 50% larger than their impressed loads.

In some cases, peak loads will exceed the rating of the fuse, like those encountered when starting an electric motor. Depending on the application, the designer may use a slow-blow fuse with an appropriately longer hysteresis rating. However, in an amateur application, it is only necessary to keep the average current draw below about 60% of the rating for any given fuse to avoid element fatigue.

The correct wire size should be based on the peak current, not the average, if you want to keep I2R losses low. In any case, should a dead short occur, the wire size needs to be large enough to carry the current imposed by the fuse's hysteresis time delay without exceeding the wire's temperature rating. After all, you don't want to turn the wire itself into a fuse!

As stated, part of the sizing calculation is the temperature rating the protected wire is designed for, as well as its ambient operating conditions. In other words, the fuse must open before the wire reaches its maximum rating for any given overload. Remember, underhood wiring should have a temperature rating of at least 90C, and preferably 105C.

For any given ampere rating, fuses designed for high voltage (nominal 250 volts maximum) service typically have lower resistance than those designed for low voltage (nominally 32 volts maximum). Thus, their low voltage hysteresis time is elongated, which means they take longer to open under a given overload. While these facts alone don't preclude their use in low voltage applications, the bottom line is, you should select fuses specifically designed for the voltage range in use.

Lastly, fuses protecting your wiring should be as close to the battery as possible. Remember, that short length of wire from the battery to the fuses is NOT protected. It should be mounted out of harms way (in case of a crash), and protected with an outer sheathe such as plastic split loom.

Circuit Breakers

If you're thinking out loud to yourself about now with the admonition, I use circuit breakers, so I don't have this problem, you're kidding yourself! Fact is, circuit breakers exhibit a much longer hysteresis than any fuse except some specially designed slow-blow fuses. What's more, most circuit breakers will fail closed on dead shorts if the current exceeds 2,000 amps or so. A standard SLI (Starting, Lights, Ignition) car battery in good condition can easily supply this amount of current when subjected to a dead short.

Fuse Blocks

One very popular way of powering multiple ancillary devices is West Mountain Radio's RigRunner series. The unit shown has a main fuse, and five separately fused circuits. This particular one has a maximum rating of 40 amps. They use the very-popular Anderson Power Pole connectors (PP), which makes wiring easy.

They're typically wired directly to the battery, just like a transceiver should be. And like a transceiver, their leads (negative and positive) need to be fused close to the battery connections to protect the wiring should a short occur.

In-line fuse holders should be avoided for two reasons. First, they require butt splices which are very hard to solder. Secondly, the supplied wire size is universally too small. Here's a suggestion. The PP15-45 connectors will hold an ATU fuse for loads up to 40 amps. For larger loads, the PP75 connectors will accommodate a Maxifuse perfectly. What's more, the connectors are a lot cheaper than most decent fuse holders. This is one drawback, however. Getting the fuse inserted properly can be difficult if you don't make sure the connectors are pushed all the way into their respective housings. For the smaller ATO fuses, standard 1/4 inch, female blade connectors work well too.

Digi-Key, Fastenal, Mouser Electronics, and PowerWerx all carry a wide variety of fuse holders. However, for high-amperage loads, I prefer the Littelfuse MAB1 holders (at left), and here's why. Every Maxifuse holder I have seen has molded in pigtails. The largest wire size available is size 8 which is too small for for loads over 50 amps, the need for butt splices notwithstanding. Although the MAB1 is a discontinued item, Newark has a large supply on hand. They cost about $35 with a clear plastic cover (not shown).

If you're not into PP connectors, you might want to look into the Centech line of products. Under the cover are heavy-duty connectors for the primary wire, and a screw terminal block for the secondary wires. There are more photos on their web site."

Also:
Here is an additional PDF article link courtesy of Littelfuse on "Fuses vs. Breakers" which anyone may find of interest or fr reference.
http://www.littelfuse.com/dat ... eakers.pdf

[Kojak]

@Foxhunter

Thanks for the welcome.

I chose the Eagle for two reasons.

1) Been cleanin' the ol' bean since 11/92.
2) No time to re-size a picture of myself.

That's good information you've added to the basics I posted.

[drdx]

Good topic. Well, I'm fused at the amp in back(an 8 pill tx star), where I have an optima as well. I have a breaker (300 amp one) there coming off the optima, then 2/0 cable running to the front battery, and it is breakered there. I like the breakers because my stuff is not always in the vehicle so when I remove it, it is just a button away from disconnecting power to the 2/0 cable running to the back. Since install, I have gotten a little agressive running things and I have blown the 300 amp breaker at the rear while running both the tx star and my WW amp, which makes sence. Their combined draws overcame the rear battery, which usually acts as a bit of an amperage cushion. I ran my rear battery down a little and it was looking for some serious amperage elsewhere, as in the front battery, so it blew I guess. The amps still had ample power but after a few keydowns I noticed a slight decrease in performance. I've seen this happen before when I put all of my stuff in and forgot to activate the breaker and it was all running on just the rear battery. I was surprised how long a single red top optima will run a low driven 8 pill without recharge and at nice output levels, but you can definitely tell when you reconnect the battery to the charging system as it pulls the volt meter down a little at idle until it gets back up to charge. I ran around for 2 days last week low driving my driver doing the old 250dk/600 swing deal before realizing it and hooking the battery back up, no harm done. I've also thought about a small solar panel hooked to the rear battery full time to keep it topped off.

-drdx

[Kojak]

@drdx

...Good Topic.

What ? Bean cleanin' ?

[drdx]

Hey, it's your "bean" and you can clean it, or resize it, anytime you want to. -drdx

[The Breeze]

Great read you guys!! :D When I bought my 2X4 amp, I had to learn a lot about a lot of different things. These boards have helped a lot. But when I asked the locals and also the guy that built my amp about what they used to fuse the wire, they all looked at me like I was nuts, and said they don't fuse theirs. Well, that's when I started thinking they were nuts. I have seen wire burn, and really don't want to see mine light up and smoke. None of them could tell me where to even look for a good fuse except to go to a stereo install shop and ask. I use a 4G wire to my amp, and found what I think is a great, in-line fuse at radio shack. Gold connectors and the contact ends of the fuses are gold. The heaviest fuse there is a 60 amp, and none bigger can be ordered I guess, I wanted an 80 at least. So far it works just fine. As of yet I have not blown a fuse. Radio Shack has a couple different types of in-line fuses to choose from, and I opted with one that looks like a large automotive type, and they are water tight. Just thought I would pass this along. For the record, I would rather loose a little juice to the box than loose my whole rig.

[jessejamesdallas]

drdx...you can find 300amp fuse's and the holders at Car Toy's. They ain't cheap thou!

[jessejamesdallas]

drdx...you can find 300amp fuse's and the holders at Car Toy's. They ain't cheap thou!

[wegarrett]

fuses = voltage loss.........

do a good clean install and there is really no need for
a fuse........im running a 2x6 in my truck no fuse guna
install a 1x4 in my semi this week sometime no fuse
and my base im running a 3x8 no fuse, and if i can find
something to run my 12 pill in its not going to have a fuse
either.......it is kind of a safety devise to leave yourself
room for error but i just double check everything and go
with it........been doing it that way for 5 years and so far
i havent smoked nothing but 1 pill in my 8 pill.....and yes
its a Davemade and yes their pills will also blow just as
any other amps will