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Old 09-21-2007, 02:11 PM
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100 amp alternator question

I'm getting ready to install a 100 amp one wire in my truck, I've got the wiring figured out except for one part. Some people; including Jeg's recommend using a "maxi-fuse" for high output alternators (80-140 amp), but the fuse they sell only goes up to 50 amp.

Isn't a fuse rated at 50% of the output a little low. It seems that if I have the headlights, defroster and the radiator fans are going at the same time I'd end up playing FORD (Found On Road Dead).

I understand the use of fusible links, but have never really cared for the idea of having a wire burn in two. Can two 50 amp maxi-fuses be run in parallel?

Thanks
Howard

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Old 09-21-2007, 02:30 PM
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No! You never want to run fuses in parallel. They will not be able to "sense" the current and blow properly. You will never get the conductivity identical and in high current applications the current will never balance 50/50. Temp or moisture differences between them will cause a spike in one fuse and blow and then the other fuse will blow since it will obviously be overloaded.

The fuse link is the only safe reliable way to go. It can withstand a short burst over it's rating, and only catches on fire if there is a dead short for quite a while. Docvette has a ton of posts about them if you do a quick search.
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Old 09-21-2007, 02:42 PM
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100 Amp Alternator Fuse

Dear Howard,

I had similar questions about fusing the system when i stepped my 40 Ford up to 140 Amp single wire unit.
The information I gathered was the fuse protected the system when the following occurred:

The electrical system draws its power directly from the alternator so that under normal operation the various circuits are protected by the fuses in line with their respective circuits.

The reason for the Maxi fuse is to protect the system when the battery is so deeply discharged that it begins to draw an exceptional amount of current to recharge itself. What happens is the alternator supplies the demand and being electriciyt it flows everywhere, which may in turn exceed the capability of the electrical panel. Unless fused many bad things start to happen. So definitely FUSE the system.

The folks at Painless did sell a 50 Amp MAXI, but recently changed it to a 70 Amp MAXI. I called on this issue and they said it did a better job than the original 50 Amp fuse.

At any rate the diagram I followed was to run an 8 gage wire from the battery side of the starter solenoid to one side of the Maxi Fuse. The other side received a new alternator wire (this new wire was run in addition to the alternator wire running directly to the fuse panel) which tied in with the system wire running from the fuse panel ( which used to run to the battery side of the solenoid) to the other post of the maxi fuse.

If you need a diagram visit Painless or Ron Francis website and down load a copy.

The result in my install was: the battery definitely recharges faster, the car starts better, and I am sleeping a whole lot better not worrying about my Hort Rod actualay becoming "hot" whwn I am driving it.

No matter what the fuse size please do it especially with these higher output alternators.

Good Luck,

MrPhat40
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Old 09-21-2007, 02:44 PM
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Maxi Fuse

Yes, you CAN run two 50 amp maxi fuses in parallel (side by side NOT one after the other), but make sure you tie them together on both ends (parallel).

You don't want the output of one to go to a different place than the output of another. For example, if you had the output of one fuse going to the battery and the output of the other going to the fuse box, if the battery ever got low, that alternator will try to send 90 or more amps down that line to the battery through that one 50 amp fuse.

However, there are 100 Amp Maxi Fuses on E-bay along with some pretty cool distribution blocks. These are FOR stereos, but if you could keep one water tight, and lock down the setscrew, it should work nicely under the hood. I'm going to try it myself.

I know what you mean about fusible links. I have read pros and cons. To me, with maxi-fuses you fix the problem, change the fuse, and you're on your way. Unless you Mickey Mouse it, a fusible link will take considerable more work, assuming you even HAD a spare....and didn't get stranded in the middle of nowhere.

Keep in mind, Maxi-fuses at these high of amperage ratings are relatively new, so not all old reading material on the subject will apply.

Steve
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Old 09-21-2007, 02:50 PM
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100 Amp Alternator Fuse

Thanks guys.
I was looking through the McMaster web site and found fuses and holders w/covers that go way up the amperage chain (clean up past 100). I'll check out those sites you recommended and verify my plans.
Howard
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Old 09-23-2007, 11:26 AM
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I've gotr the same thing as mrfat.. and I like it. Got the 70 amp too. Painless has the best customer support. Give them a call they know their stuff.
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Old 09-25-2007, 12:53 AM
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High Amp Fuse Holder

There is an outfit called Blue Sea (www.bluesea.com) that has an array of heavy duty DC equipment for marine applications. Blue Sea p/n 5006 is a guarded maxifuse holder rated for 80 amps - it is a "pro" wiring part. Jegs 555-10520 is similar.

To carry the big amps away from a modern alternator - with no "problemo" forever - I have been using very flexible no. 6 welding cable with properly sized copper solder lugs. Check your local welding supply store for a chunk the right length for the job and you can get the right size solder lugs at Ace hardware. Use plenty of flux, solder and a propane torch to get the joint just right. Armor and insulate the joints with heavy duty heat shrink tubing from an industrial electrical supply. This "battery cable" goes from the alternator to the battery post of the starter solenoid. On most vehicles the voltage drop is virtually zero at this short distance.

From this same solenoid post - run a no. 8 lead to the maxifuse holder. This is where power gets transferred into your vehicle electrical system. Limit the fuse size to the amps required to operate the main vehicle fuse block with everything "on".
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Old 09-25-2007, 01:48 AM
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Here is another little tip. I was wiring up the battery which is behind the front seats so some distance from the starter and Maxi fuse. I found a set of 2 ga jumper cables at AutoZone for $42. These are 20 feet long. One black one red...perfect. After I got all done making the battery hook ups and grounds I still have enough cables for a good set of jumpers......However my cars always start haha.

I have a similar alternator wire as green... does.
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Old 09-25-2007, 07:32 AM
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Quote:
Originally Posted by hyarbour
Thanks guys.
I was looking through the McMaster web site and found fuses and holders w/covers that go way up the amperage chain (clean up past 100). I'll check out those sites you recommended and verify my plans.
Howard
McMaster also has some high quality marine grade battery cable. It is very flexible compared to standard welding cable or jumper cables. The marine cable has a much higher strand count than standard battery cable.

Vince
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Old 09-25-2007, 09:12 AM
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Napa also has the larger fuse holders, both the "MIDI" and the "MEGA" fuse holders. Some of those go all the way to 300 amps

You can also get cable there, up to 0000, as well as welding cable up to 2/0
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Old 09-29-2007, 08:22 PM
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fuseholder

Hi.

You might want to give "Parts Express" a try. Their website is good. I've dealt with them for marine electrical parts as well as amp kits and caps.


Enjoy
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Old 10-03-2007, 11:36 AM
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100 amps

This right here is why i love this site. I was going to post a question about almost the exact same thing. Here it is all ready answered.

I have a customer that called asking me about why his 50 amp betwwen the alt and battery was blowing. Up until that point i have never herd of a fuse between the bat and alt...

I do have a question, if i understand electricity correct. If he runs accessorys that pull more the 50 amps will it not blow the fuse????

Keith
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Old 10-04-2007, 01:10 PM
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I used one of these circuit breakers:
http://order.waytekwire.com/IMAGES/M...og/219_081.PDF
I used p/n 46987.
I ran a no. 4 welding cable from the alt (and also a no. 4 cable for the alt ground). The positive cable goes to the circuit breaker that goes to a junction point that feeds most of the vehicle through a maxi-fuse for the fuse panel feed, and 2 maxi-fuses for the headlights. I did follow Mad Electrical's advice and connected the starter solenoid stud (that feeds the battery) with 10 feet of 10 gauge wire with a fusible link. This was done to drop the voltage to the battery in case the alt tries to fast charge it. The battery cables are 1/0 welding cable.
So far so good.

Last edited by kick_the_reverb; 10-04-2007 at 01:16 PM.
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Old 10-04-2007, 09:22 PM
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Don't blow it!

Quote:
Originally Posted by k-star
I do have a question, if i understand electricity correct. If he runs accessorys that pull more the 50 amps will it not blow the fuse????

Keith
Keith, that's the THEORY. It depends...on the type of fuse, how LONG you are drawing over 50 amps, the reliability of the fuse itself to blow right at (or very near) 50 amps...and not at 40 or 60, temperature, resistance in the circuit, spikes in voltage in the circuit, and maybe a few other things.

It's not a perfect science since a fuse is basically the same thing as a fusible link, in that it's a smaller piece of wire encased in a package that's easy to replace. In theory, this section of smaller weaker "wire" inside fuse package, that will be the first place to open up and no longer allow current to flow if you go over the educated guess of the rating of the fuse.

If the circuit was designed right, with the total amount of current of all circuits taken into account when selecting the fuse rating, and a little cushion for variations, spikes, etc. then you should never blow the fuse ...if all goes as it should. So the fuse is a failsafe ...in case something goes wrong.

If the circuit's total current draw is very near the rating of the fuse, then you need to get a bigger fuse ....and then there's the wire diameter, as too small a wire for the current flow will cause problems, and possible fires.

Steve
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Old 10-06-2007, 02:20 PM
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What good would two fuses, in-line do?? One blows the other is just a fuse in a line with no power to it...am I missing something here?

If I was mountain climbing and spliced another ten feet of rope in, the rope broke, that extra rope would only provide me a few seconds of 'air climbing', he he.
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