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The current on that lead changes continously depending on load. If you have a light load, the resulting current will be light assuming a good battery.

If you change to a big current producing alternator, and put a big load out there, like a huge stereo and/or fan, the current will go up and could take the fusible link out if it has not been sized properly.

I hope this helps.

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Make it slightly higher then the alt output. ie 65amp alt use 70 fuse, breaker, or link.

Hope this helps
Steve
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by wanarace:
Make it slightly higher then the alt output. ie 65amp alt use 70 fuse, breaker, or link.

Hope this helps
Steve
<HR></BLOCKQUOTE>

Although "what fuse size wasn't the question"

fuses are there to protect the wire from burning, not to protect the appliance

Therefore the wire size dictates the fuse size so it will blow before the wire starts to burn
 

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Discussion Starter #5
Hey guys;

Thanks for the info, I moved my battery to the trunk and everything is great. I was looking into using one of those blade fuse pigtails (the kind that's removable / replaceable) instead of a fuseable link. This would be for the battery charging lead. That's why I was wondering what the "normal" charging rate or current draw would be to the battery. I've went ahead and used a 14 ga 'link on the 10 ga lead, connecting the two with male/female quick disconnect spade connectors. Tips for sure starts:
1. Use Hi-torque starter ( I suffered long trying to use a freeby small block starter-worked but tough cranking on high compression-never again)
2. Use solenoid heat shield ( can be reg "Help" parts store item. Cheap and easy way to help heat soak)
3. Use no less than 2 ga multi-strand pos lead
4. Grind and secure ground lead to body/frame (I'm using pass through bolt in trunk floor to accomplish both- 2 ga to body, 4 ga to frame fore and aft)
5. Ground engine to frame ( currently from alt bracket to frame stud at idler arm - convienent and close by to alt)
6. Use grounding straps from eng to body (lower rear valve cover bolt.
7.!! Route / secure wiring away from heat sources ( i.e. manifold / headers)

Thanks again

mfinger1
'70 SS 402/400TH/4.10
 

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Discussion Starter #6
Found the answer to my own question. If the battery is charged up, then normally the alternator supplys about 7 amps to maintain the charge. I would then need about an 8-10 amp fuse in the blade fuse pigtail to insert replacing a fusable link in the alt battery charging lead. Thanks again!

'70 SS 402
 

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The battery can supply up to 40A or so at times and the alternator can charge about the same so a 10A fuse won't cut it. I would think you'd need either a 100A or so fast acting fuse or a 50A slow blow fuse.

They wouldn't make the main wire 10 guage if there was only a 7A draw.

Peter
 

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Discussion Starter #8
Hi Peter;

OK, but then how can a 14 gauge 'link, connected to the 10 ga charging lead sustain such a high current with out frequent melt downs. Doesn't the regulator control (if working normally) the max current feed ? Really hate to sound dumb, but if the battery needed 40A, then the charging circuit really isn't doing it's job, is it?
Do I need Automotive Electrical 101?


mfinger1
'70 SS 402
 

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The regulator controls the voltage output.Think about what your asking.If the alternator is rated for 65 amps then it puts out 65 amps when fully loaded.That current flows down the output wire.Putting a 10 amp fuse in is gonna blow,get it.The alt runs the car after starting.Whatever the car needs in terms of amps, the alt supplies.The battery does NOTHING after starting unless the electrical system needs more than the alt can put out.Use the 14 gauge fuse link and be done with it.
 

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Discussion Starter #10
Hey SSchevyfan;

Think about what your stating. Yes an alt may have potential for say 65 amp output, but that doesn't mean that the battery will ever see a draw of this much just to maintain charge. The amperage output of the alt is primarily for feeding other loads...i.e lights, radio, heater, A/C, lighter, etc... these loads don't get pulled of the battery, unless engine is off.
 

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When you start the car you will draw approximately 200A from the battery while you are cranking. At this time, the battery voltage can drop to around 11V or so. So, for the whole cranking time you drain 200A from the battery.

When the car starts it will come up to 1500rpm's or so since the choke would be set. This is enough RPM's to make a good alternator go to (or at least try to) full voltage output, which is about 14.2V or so. The alternator is capable of producing say 65A so it will pump this amount of current into the battery until it "replaces" the current you drained from the battery while cranking the car.

I'm not bothering with battery theory here, just know that you have to put back what you take out. I'm sure you know about the chemical reaction in a battery.

For the charging wire, you will never get a constant current much over 10A in most cases so the 14 guage wire is lots. In any case, I think that the fusible link wire has a high temperature insulation so in all likelyhood it could handle 25 or 30A continously.

When wire is overloaded the copper itself almost never fails but rather the insulation burns off. In some cases, this causes another short much closer to the source (battery in this case) and the current does go up enough to burn open the wire. At work, I ran about 600A through a piece of 10 guage wire about 2 feet long and all it did was melt the insulation off. I had it going for probably 4 or 5 minutes to do this. So, the current has to be more than 600A to fail 10 guage wire open.

FYI, when I had a car with an ammeter I typically saw about 35A for a few minutes after starting the car. The ammeter was measuring the current in the battery charging wire, not the alternator.

I hope this helps.

Peter
 

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What did I say in my last post mfinger1? Your almost repeating what I said but you still seem confused.I don't need your explanation of how a charging system works,I know.Why do you keep bringing up the battery? Your question was about how many amps are going down the alternator output wire and I SAID you can have as much as full alternator output which in my example was 65 amps.Your making it sound like the alternator is just there to charge the battery and it's not.It runs the car after it starts.If you have the heater blowing on high and headlights on and windshield wipers going and a mega ear shattering stereo cranking that alt is putting out lots of current that your 10amp fuse idea won't cut it.I'm not trying to be a knob towards you but your not "listening" to what some of us are saying.
 

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Discussion Starter #13
Hello all;

I really hate to be stubborn here, but we're talking different loads.

Peter stated pretty much
what I've said all along that:

"For the charging wire, you will never get a constant current much over 10A in most cases so the 14 guage wire is lots."

From what I've gathered, not really much over 7 amps draw, to replenish or charge the
battery. The starter may pull as much as say 200 amps during starting, but may only drop a volt or so, which then needs recharging.
Thats when it will draw charge from the alt across the charging lead. It just so happens that this lead (on the '69 '70 & 71) is tied into the main electricals feed at the bulkhead connector. It can be moved and tied in directly of the alt, as it was redesigned in '72.
This was my whole point of using a replaceable instead of a fusable. Easier to replace.
SSchevyman, I still don't think you follow, that just because your electricals are drawing high amps, doesn't mean the battery is drawing the same load. They're seperate loads, with battery only drawing what it
needs and not a constant draw as lights, heater, A/C, stereo etc...
 

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I'm done responding to this post after this.No offense to know one.Just getting irritated.What your calling the charging wire IS THE OUTPUT WIRE!
Whatever is coming out that wire the battery is seeing.It does not matter where the wire is hooked up in the car.The alt does not have a terminal that charges the battery and a seperate terminal that runs the car.If the load on the electrical system needs 65 amps then the battery is seeing 65 amps from the alt.I guess for you to be convinced you need to get your hands on an ammeter and check for yourself.Put the meter in between the alt terminal and the wire to battery and flip on all your lights and heater and whatever else you have and see what is coming out that terminal.Guaranteed it's more than the 10 amps you think it is.Again,I'm not being a knob towards you.If I was talking to you in person you'd see my tone is different from what it 'sounds' like in type.Good luck,see ya.
 

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OK, here's my two cents (and that's probably more than it's worth):

The alternator charges the battery and runs the electrical system with the car running.

The way mine is set up the alternator wire goes to a junction point at the starter solenoid. It charges the battery from there through the battery cable. There is another wire from there to the main fuse block. The battery cable only sees charging current. It doesn't see the current from the rest of the system.

So, what am I saying? If your alternator is connected directly to the battery and the rest of your electrical system is fed from that point, the charge wire will see full system current and should be sized accordingly.

If, on the other hand, you have a separate "charge wire" for the battery and "system wire" for everything else, both tied into the alternator at some junction point, the battery and alternator will see different current readings because the current will follow the path of least resistance.

Does this make sense?

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[This message has been edited by cjlandry (edited 03-28-2002).]
 

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The “charging wire” in question has a double role. When the engine is running the charging current flows trough this wire. When the engine is not running the entire electrical load of the car is supplied by this wire. Lets say you are out cursing one night, stereo blasting, heat or ac blower on high, headlights on and whatever else. At a stop light the engine dies, now suddenly all that load is on the wire in question. That 7-amp fuse will blow and you’re stuck in traffic. In addition this wire supplies the start circuit/solenoid. I don’t know the current load during starting but this by its self could be greater than 7 A.

If I were rewiring as you are I would do the following.

I’m assuming you have a #2 cable from the trunk mounted bat + to the start solenoid.
1-Move the core support mounted junction block to a convenient location on the firewall.
2- Connect a #10 wire from the start solenoid (bat cable)to the J-block, with a 6"-8" length of #14 fusible link wire on the solenoid end.
3- Connect the alternator output to the J-block using #10 wire.
4- Connect the fuse block/ignition switch power feed red #10 wire from the bulkhead to the J-block. I would also use 6"-8" of #14 fusible link wire on the J-block end of this wire.
5- If you have A/C connect the blower high speed power feed black #10 wire to the J-block.
6- If you have no other large load items connected to the horn relay. Connect a #14 wire from the J block to the horn relay.

This is similar to the way 72s are wired except that the horn relay is on the firewall instead of a J-block and the alternator output is spliced to the main power feed wire from the start solenoid.

I would use fusible link instead of a fuse. A fuse is easy to replace but a momentary short will not blow a fusible link. It’s a rare occasion that an f-link fails.



[This message has been edited by Elree Colby (edited 03-28-2002).]
 

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Man, if you read my post and still think that a 7A fuse will cut it you need to re-read it. As already stated, there will often be 30A, 40A, 50A or more current being drawn from the battery.

The solenoid require about 25A inrush so there goes your fuse as soon as you crank the key to start the car.

My comment on the 10A, or so, continous was just that. While driving down the road that's the probably current that will be flowing in the battery wire. At other times it can peak at a much higher value.

For the person who said that the battery wire "sees" all the current of the alternator. That is wrong. These vintage cars have a smaller wire going to the battery. This wire only see's the charging current, the currrent required to start the car, The current required to take up the alternator slack at a stop light and the current required to run accessories while the car is off. If you're driving down the highway and the alternator is cracking out 50A to run your accessories that doesn't mean 50A is flowing to the battery through this wire.

I think sometime around 72 or 73, GM began to use the solenoid as a junction block so there was no longer a seperate small wire running to the battery.

I have yet to see a fuse holder and fuse sutable for this purpose. They're all to low a current. The only place you may be able to find a suitable fuse and holder is in a car audio store.

Peter
 

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Peter
"I think sometime around 72 or 73, GM began to use the solenoid as a junction block so there was no longer a seperate small wire running to the battery."

It was 72. The wiring under the hood is very different than the 71.
John
 

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“These vintage cars have a smaller wire going to the battery. This wire only see's the charging current.”

Sorry Peter, I don’t agree.

The factory installed wiring on all 64 to 71 Chevelles have two wires/cables connected to the battery + post. One is a #4 or #6 (depending in the engine option). It connects to the starter. It carries the current of the starter only. The other wire connects to the J-block (no J-block in 64) most have #14 fusible links (I think it started in 66. Can’t find my 66 diagram to be sure). From the J-block to the horn relay #10 red wire. The alternator output is spliced to this wire (64 and 65 the alternator output connects directly to the horn relay). This is the wire in question, from the battery to the horn relay 64 - 65 or to the alternator output splice 66 and after. When the engine is running it sees charging current. Typically less than 10 A. When the engine is not running the battery is supplying all the current demands of the electrical system. That current is flowing through this wire. There is no single wire that sees only battery charging current.
 

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Well I said I wasn't gonna respond to this anymore but I need to correct my earlier statement.I said "the battery see's all the current from alt".This comes from all my years of checking charging systems with a vat(volt/amp tester).You hook up heavy vat cables to battery pos/neg and put inductive amps clamp either on little red wire from alt to battery or put it on neg cable.Either way works and I usually put it on little wire.Then when carbon pile is turned on to load system ALL the alts output goes through this wire.But when the car is running it won't and yes usually sees around 6-10 amps to maintain battery charge.But when engine is off ALL required current flows through this wire so that 10 amp fuse idea won't cut it.There,I corrected myself.Sorry for the earlier false statement.By the way,this example vehicle has the positive battery cable hooked to the starter only.Then a small red wire integrated in the positive cable off the positive post goes to back of alt on output terminal.There two other wires are connected to same post to supply current to the rest of vehicle.As was stated earlier some vehicles don't have a little red wire on the positive post.The positive cable goes to starter and smaller wires on the same post go from there to the vehicle electrical system.Therefore the positive cable is now the 'charge wire'.Then I would have to hook vat amps clamp to neg cable.Sorry for rambling.
 
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