Technical Painless Wiring Warning

Since the thread started with this diagram, and thats exactly the diagram in my installation manual, I'd like to see some discussion about this specific application. We have two distinctly opposing opinions about whether this circuit is ingenuious or disasterous.

Here are some additional notes which are included in the installation manual.

 

In that figure 7.2.2 that short jumper wire will make the alternator work, but it will sense voltage very close to the alternator and keep the battery just a little off full charge. I did many of these alternator up grades . I usually took that wire back to the accessories side of the ignition switch or direct to the battery. Just a minor thing, but it is a thing!






Bones

 

If that fusible link blows, you have other problems, you're still going to be stranded. A competent mechanic can repair the blown link and get going, it's the regulator failure that caused it that's going to be the problem.

I never said the 4 awg wire was inappropriate. In the OP of this thread it was mentioned that often these kits use under sized wires for this, my comment was just addressing that concern. My comment on your post is the installation of the fuse itself and the inherant potentail for failure it introduces. I don't understand why this is so complicated for you. And yes, problems occur in circuits all the time due to connections at a fuse box, or a fuse failure, corrosion between the fuse and the terminals, etc, etc, etc. Anyone dealing with old cars for any length of time has dealt with that at least once, most of us multiple times.

Tell me, what happens if the regulator fails and the alternator goes to full output (how often does that happen anyway?)? Does that fuse stop the over voltage condition from hitting the rest of the circuits in the car? Not if the alterntor output is going straight to the fuse box it doesn't. And all of the kit schematics shown so far are designed that. So what is it protecting? The battery is the only thing left. Hopefully the car will have a voltmeter installed, and the driver will notice the over charge condition before the battery fails. I've seen batteries take an awful lot of abuse, even swell up, and not fail. I've seen batteries explode before too, but not from overcharging but from an accumulation of gas due to insufficient venting, and an ignition source ignites the gas.

 

It appears that the concepts involved are beyond some people. To be fair, you need a pretty thorough understanding of AC/DC electrical theory and use of same to grasp all this. And before someone objects that 'This is a DC system, AC doesn't apply!', keep in mind that your ignition system, all motors/solenoids/relays and charging system all operate under at least some AC principles. The only 'pure' DC circuits we have are straight resistive circuits such as lighting and cigarette lighters. With that said, I'll just hit the high points, or low depending on how you look at this...

Sorry, not one of these statements is entirely true. AT BEST, the fuses may protect the wire on the other side of the fuse away from the fault. But it may fail to blow even on the side with the fault, I'll discuss this below. I will give you credit for apparently eliminating the panel/alternator loop shown in the first diagram I posted, as well as upsizing the wire..

Sorry, this has nearly all the same faults as the first diagram. The one improvement is at least it's not looping the alternator through the panel. But those 100A fuses are not an improvement unless the wire size used is at least #2.

I see I have to revisit overcurrent protection yet again....

Overcurrent protection is there to protect the wire. End of story, full stop. In most cases (and certainly on our systems) it doesn't offer (and isn't intended to offer) ANY protection to any devices connected to it. At best it may limit the damage a failed device may cause.

So let's say you have a branch circuit that starts blowing fuses. How do you fix it? Do you start putting in larger fuses until it stops? A very good way to create a wiring fire. I would hope that everyone understands that the correct way is to find out why it's drawing more current and fix the issue. The fuse size MUST not be larger than the wire ampacity rating! Even the aftermarket harness manufacturers understand this, they give recommendations for branch circuit fuse sizes in line with the wire size used for those circuits. Until they get to charging systems and panel feeders, they then throw that knowledge out the window. Now there are legitimate reasons for reducing the wire size in charging systems and panel feeders. Rather than type all this in here, go read my Wiring 101 | The H.A.M.B. (jalopyjournal.com) , specifically where I discuss 'Diversity'. Typically these two circuits weren't fused for years (certainly in the HAMB era), that came later. The OEMs have done this forever to save money, the aftermarket tries to mimic them for reasons only they know, although they're probably very similar. But one big difference is the OEMs engineer each harness for the specific car it's used in. The aftermarket doesn't, they use a one-size-fits-all approach which may be fine for one car but not for every car. The fact that they offer all sorts of 'relay kits' to cover larger loads or excessive voltage drop (dim lights) is basically an admission of the inadequacies of their core product.

As far as how the bad examples above would work in an actual overload or short-circuit event, that's a bit hard to predict. Protecting wires rated at 30, 40 and/or 50 amps with a 100 amp fuse may give some overload protection but you will have wire heating before reaching the fuse's limit. If the panel input leads are #10, that will be the weak link. Fusible links are not much more than another wire, only designed to melt in half with less drama, i.e. not catch fire. If one is sized too big, the wire may become the link.
As far as short-circuit protection, that's iffy too. Now if you get a really solid short connection, say an accident where the wire gets pinched between thicker pieces of metal, the fuse will probably blow. But a more typical (IMO) failure will be failed insulation (local burned away, rubbing against something) where only a few exposed strands will make contact at any given time. Those strands (22 gauge or smaller) will certainly melt at less than 100 amps so what happens is as strands break, the remaining ones start carrying more and more current and heat up. At some point there will be too few left, you'll get a hot spot and likely a fire. All without the fuse blowing. This is actually more of a problem at lower voltages like ours because of the amount arcing you don't get.

And as has been mentioned multiple times, on circuits with power fed in from each end, a single fuse in the middle WILL NOT clear a short on the side where the short occurs. You will need a fuse AT EACH END to get full short-circuit protection. And maybe not even then.

Interesting that you ask that. I have had conversations with a few of them and they blew me off. I'm sure all this is business decisions for the most part. I know a guy from Painless posted here once in a while so I assume he watches here. His content appears to have disappeared (too much resemblance to self-advertising?) and his absence here on this thread is a bit notable...

 

I guess you have to go back to the very basics of what electricity is, keeping in mind that electrical energy really is not a fully understood science or fully comprehended at this time. (some time ago I posted a video in another thread here from one scientist trying to explain it, but the point he made was electrical energy does not flow through wires. This is probably a digression, just wanted to emphasize that the nature of electricity is still unfolding) But, we know that it involves the movement of electrons in a conductor, and those electrons move because of the force of attraction, when there is a difference in potential between 2 points in a circuit, i.e. there is a difference between a negative charge (surplus of electrons) and a positive charge (deficiency of electrons) that exists, electrons will flow in an attempt to equalize the potential. But it is the force of attraction that causes the flow.


The hydraulic analogy is useful for comprehending circuits, I've used it myself all the time. But like all analogies, it fails at a certain point. The flow of electrical current and the flow of liquids are not the same thing.

 

Thanks, I glad you mentioned that electricy is not fully understood! Now I don’t feel alone!
I know fluids and electricy are not 100% the same on energy movements, but are usually close enough to help understand.
I have stumbled through both systems for years, but always found a way to get them fixed!






Bones

 

You are absolutely correct. What we're working with here is series of discoveries that guys smarter than me at least figured out the mathematical relationships between them to give us a set of working tools allowing us to reasonably predict what will happen in a given circuit. Regular code changes (especially in grounding) and advances in electronics are proof that it still holds surprises. Between my electrician Dad and 35+ years in the trade myself doing everything from stringing romex in houses, industrial automation, teaching AC/DC theory and even nuclear plants I've seen a whole lot of 'stuff'. I won't claim I know everything, but what I do know I know....

 

Agreed.

The Painless drawing definitely fails to protect the rest of the vehicle from the alternator, which is why I wouldn't do it that way. If you read my initial post, I stated the 4AWG wire with the fuse mates the alternator to the starter. The fuse panel is fed either off the same starter lug or the battery depending on install with another 100AMP fuse in between those two connections. The alternator is isolated from the rest of the harness via the fuse.

 

I just yanked out my harness and still don't understand why the fuse didn't pop which would've stopped the power in the wire ???
The wire from the alternator was disconnected and shorted itself on the alternator housing, this mess took all of 30 seconds total before I could get the battery disconnected.



Started from here at the alternator, turned the wire glowing red hot and melted everything it touched all the way back into the fuse box.

 

A couple of things you're missing here. Alternators can't produce large amounts of current beyond their rated output. This is controlled by the wire size wound onto the rotor and stator, as well as the iron core size the wire is wound on. This is baked into the design. The regulator simply adjusts what's available. So assuming you're using a 100 amp alternator (if fused at that, it's senseless to use a larger unit as you could have nuisance tripping), you may not get enough more current to actually blow the fuse. That will depend on the trip slope; how quickly the fuse clears the overcurrent. Generally faster as current increases past its rating before damage appears.

You will however have increased voltage in the case of a regulator failure of this type. The fuse can do nothing about this, all it cares about is current.

And again, you have NO short circuit protection between the fuse and the current source. To fully protect the alternator wire, you'll need one at each end of it.

These two circuits are the worst ones for trying to apply protection to. To be honest, in most cases it's not needed. Assuming you use diversity to reduce the wire sizes needed (but not down to #10!), barring one of these rather remote possibilities you won't have any issues if the remainder of the system is right. Short circuits can be addressed by careful routing during install to prevent physical damage. For overcurrent protection, size the wire to the maximum continuous load. I like to add the largest intermittent load also, that stops things like lights dimming or flashers working funny when used. If you just have to install fuses, do this for sure. Then size the wire to match the fuse. This is where this usually goes wrong. Installing fuses that are substantially larger than the wire rating defeats the purpose of the fuse. Too big of a difference, which one is protecting which?

As to the use of fusible links by the OEMs, what that tells me is they're cheating on wire size (again). They don't think they have a problem but knowing that they're cutting it close, replacing a fusible link is cheaper than replacing a harness. People get upset when their car billows smoke and/or bursts into flame....

 

There is no fuse on that wire. That's one of the failings of these designs. And with however many cold cranking amps available at the battery, it doesn't take long for that to happen.

 

Yes it does!
Everything in the vehicle [after the Alternator /Battery] is routed via the fuse block

As long as everything in the fuse block doesn't exceed 72ow when everything is switched on at the same time , the Alt harness should handle it.

If you add up the values of everything from the fuse block ,and add 600w for the sound system
If this total amount exceeds 720w then you will need to upgrade the 960 and 915/916 wires

For example if the car normally draws 400w [without the stereo] and you add 600w sound system the total is now 1000w [1000w + 12v = 83.33a]
Because there is 2 feeds to the fuse block you will need 41.66a rated wires for all these 3 wires [45a]
and an Alt capable of feeding this and sending surplus to the battery [90a]

 

You're assuming those wires are fused at the panel... they're not... Look at Swade's post.

 

Is there a fuse labeled "alternator" on your fuse panel. I highly doubt it and there's no fuse between the alternator and every thing else. This is a perfect example supporting the approach I mentioned earlier in the thread. Does that wire need a fuse in it? Not until it does...

 

600W is the output to the speakers n subs, not all out volts/amps/watts. I'm not using a Painless, I have a simple Rebel 8 circuit and I'm confident enuff to bet the car on safe and capable. The amp and sub system will be added "essentially" to the battery only. That feed will have it's own protection. That stuff can be shut off from the rest of the car at will with internal controls through the rest of the system. There's a dedicated radio circuit for just radio without benefit of the amp. Pretty standard fare in aftermarket sound.

 

But his system does have the fuseable link, suppling the fuse panel. Maybe the fuseable link had a higher capacity than the wire! I have seen many OEM fuseable links burn out with no damage to the system on OEM uinits. Just my observation.






Bones

 

You're assuming they're Not.
This is the schematic from Swade's post [showing the same "lack of" detail that Painless have shown]


Professional harness manufacturers are not F***en stupid with their specialized products.
Why would they add a Fuse-Block then hang all the feeds off the unfused side? [they could simply save $$$ and use a Bus Bar]

The original statement was the accessories were unfused between the Alt and the Accesories [not the Battery and the accessories] which would be true.
But this is also assuming that Painless Wiring is a bunch of idiots connecting all the accessories to the unfused side of the Fuse Block.

 

Think it through... The wire that burned up was the output from the alternator. It went to the panel, not directly to the battery like it should. In order for it to charge, there has to be an internal connection and wire going to the battery in the panel.

And yes, it appears they can be that effing stupid....

This is why I'll never buy a pre-made harness kit.

 

SO......where does someone add a Fuse or Breaker that will protect the rest of the system from the alternator?

I plan to have a basic system with additions of A/C, electric fuel pump, and possibly electric fans. Also may opt for electric windows. No radio, so no big useless sound system. Probably some electric cut outs as well....like those sounds a lot better. I figure I'll want more than 60 amps even if a 60 amp alternator can handle it. Probably looking at an 80-100 amp alternator.

From what I have been able to grasp is that the problem is not having an alternator disconnect of some kind in the basic engine starting circuit..........but can also be problematic after starting if the alternator generates uncontrolled current.

IF (and that's a big if) I got that anywhere near close to right...........where and how can I insert a breaker (or a fuze) that protects everything from the alternator? If I got it wrong......well I admit to being electrically challenged

 

After looking at this some more..........

I thought that the alternator was supposed to charge the battery (reservoir) and then the fuse panel drew the power from the battery and distributed it to each circuit that had a need. That then raises the thought that if the alternator provides all of its (unregulated) power (in the event of a failure) it would destroy the battery rather than the fused panel. But then that makes me wonder how the alternator can push power to circuits that aren't drawing the power any more than normal? My head hurts..........

 

Well... To be fair, in some cases it's the best thing that could happen to a car!

 

All of this has got me wired and now I can't go to sleep.

 

Which wire?
The 960, 915 or 916??

It could be an over 65a Alt trying to charge a flat battery via the over-rated Maxi Fuse
Add to that the load from the accessories [on the output side of the fuse block]

any one of the above wires would get hot and lose it's efficiency [then the weakest link will Chernobyl itself]
A short circuit in the Alternator can also cause this.
The problem is the maxi fuse [and maybe a mismatched Alternator if there is too much charge]

I never buy pre-made harness kits [the shipping would cripple us in NZ]

Because I play with race cars I prefer to make my own to meet regulations, And in some classes I will get an OEM harness and unwrap it and start removing excess wiring [and add the battery cut-off]

 

If you had an ammeter ,it would be a lot easier to understand.
They show current draw both ways depending on load.

With a fully topped up battery, the battery wont show any discharge on the ammeter because the alternator is running the accessories.

If you have an old weak generator charging system, the ammeter will show discharge if the vehicle is loaded with accessories [driving lights, a/c , etc]

After cranking the engine over, the ammeter shows a lot of charge back to the battery. [this is the "danger zone" of Alt conversions through an ammeter]

The painless wiring schematic won't work with an ammeter unless it is placed in the 8g wire.[risky]
If placed in the 916 or 960 wire, to other one acts like a shunt bypassing the ammeter.

 

Saw this whilst doing some further reading. Interesting info on wire size and a fuse in the alternator - battery wire.


Heres the direct link.

https://www.cvfracing.com/content/Instructions/CVF_Alternator_1Wire.pdf

Based on what has been written elsewhere is this thread that may be redundant? Perhaps it being for a 1 wire alternator has an impact.

 

I'm going wireless, it's the latest thing.

 

Interesting side note regarding a fuse in the alternator-battery wire. I once left an OT vehicle at a body shop for 5 weeks. They left a door open and dome light on for an unknown time, I assume 5 weeks. When I went to pick it up, they freshly jumped it and sent me on my way. The vehicle had a 120A alternator. No ammeter. Shortly after entering the interstate and letting her eat, a cloud of noxious steam erupted from under the hood. I pulled over and the battery was as big as a basketball. It finally split and blew acid everywhere. I don't know how many amps it takes to basketball a battery, 120 or less is safe to assume. No fuses were blown. No wires burned. The way it was wired, a big wire went to the battery. From there, another big wire went to the "load center" (nice piece BTW) under the hood. I guess limiting current to the battery would also limit current to the rest of the zillion accessories, which totaled up must have been 120A, or why have the big alternator ?
Not my first battery eruption, I had a way older, but still OT, '69 MGB GT. 2 6v batteries under the back seat. One's battery box rotted out and the battery fell on the hot exhaust. A clamp punched a perfect hole in the bottom of the battery. The car filled with steam that, if you breathed it, you would die. The bailing out on the side of the road was vigorous.
While I was replacing the floors, I sawed through the brake, fuel and battery lines and cable, all at once. Set the whole mess on fire in my parent's garage. I fixed the battery with a rubber stripped-out-oil-plug-repair-thing (stretched in like a tire plug), and refilled it. Worked a treat. But, I digress. Mike

 

We've argued this for the last three pages. LOL Go back and read all the replies, do a little internet research, and you'll have your answer. My advice would be to select a company that you think offers the best product and ask for/follow their advice on the subject.

 

So, another example from real life.
I'm out to lunch with the guys. On the way home, the volt gauge pegs to MAX.

I have a one wire GM alternator, no maxi fuse in the alternator to battery circuit, or anywhere else in this vehicle.

I should probably have stopped and isolated the alternator from the starter, or removed the alternator belt and drove on battery power. Not thinking, I didn't do either. I drove home on MAX.

Next I replaced the alternator internal regulator. Problem appears to be solved.

No other damage has been identified, over the last couple years.

Yes, I thank G_d it turned out this simple in my case.