Why not wire alternator directly to battery?

[TRCM]

I'm certainly no EE, but you are making no sense at all. Whether the alternator is hooked up to the battery or the PDC, it's providing power in the same way to the same places.

Does which side of a wire you tap for an accessory matter? If both sides of the wire are hot then it does not, all other factors being equal. I would assume the same thing holds for the charging side also.

Look at the example I gave of my laptop computer.

And here's another one.

You have a power plant that is water driven by the river. Upstream of the power plant, the river forks and then rejoins, so there is an island there. As long as the river is flowing, you make power right ? Well, lets say you have to build a bridge across the river. And you have to dam the river to do so. Well, if you build the bridge across the island, since you have 1/2 of the rivers flow on each side, then you can dam 1/2 of the river on one side, then when that 1/2 of the bridge is done, you can remove the dam and block the opposite side. Doing this, you will always have at least 1/2 of the rivers flow to the power plant.

Now, if the river does not split, to build the bridge, you will have to cut off ALL of the rivers flow to build, hence no power from the powerplant.


Apparently, you don't know how a charging system works. The alt supplies the vehicle loads AS WELL as the power to recharge the battery. In this case, the alt could well be supplying 2x as much to the vehicle as it is to the battery, so no, it's not providing power to the same place in the same way.

If I connect a winch to two different power sources (same as in the middle of a wire), where the two power sources have different ratings, the power supplied to the winch is gonna come from the higher rated power source, not both. This is the same reason you never put 1 good battery and 1 bad battery in your flashlight. The power will only come from the good battery, because the power output will equalize.

You don't want to connect a fully loaded 8 MW generator to the same bus as a partially loaded 8 MW generator. If you do, the loads will rapidly even out, and in the process, you will most likely damage something pretty bad. You must even out the loads before you connect them to prevent damage.


As to which side of the wire you tap for power, as long as ONE side of the wire has power, the item you are adding will also have power.

As to the alt being connected to the battery or the PDC, yes, it is providing power, but NOT in the same way, or at the same rate or current.

You can not charge and discharge a battery at the same time, which is what you will be trying to do if you connect straight to the battery. BUT, you can supply current to the vehicle AND the battery at the same time, because to the alt, the battery is a load when connect as it was from the factory. If the alt goes straight to the battery, then you will drain the battery lets say 10% when you start the vehicle. Once the vehicle is running, the alt will supply the loads of the vehicle by supplying only as much to the battery as is being drawn off. This means the battery WILL NOT charge, and since you can't have the alt working if the engine is not running, when you turn the engin eoff, the battery will be down 10%. And the next time it wil be 20%, and so on, and so son. The battery will slowly die.

The VR senses line voltage in the vehicle, and adjusts the alt output to match that plus a small %. That small % is what normally charges the battery. If you run the alt straight to the batt, and do not relocate the VR sensing point, then you will run off the battery voltage to supply the vehicle, and the VR will adjust the alt to that voltage. Now, doing this, you lose the extra voltage for charging the battery, but you will supply the vehicle.

The reason this works in boats for so long, is most people hook a battery charger up to their boat on a slow trickle charge when it is not being used.

 

[kunaji]

You seem to think that the wire coming to the battery from the alternator is a series circuit when in reality its a parallel circuit. The battery will not just suck all the amperage from the alternator unless something is wrong. If you so wanted to run without a battery, you would need to place the - and + terminals of the battery cables together or else there is an open circuit and power won't flow regardless of where the alternator lead is attached to. For the record, cars have been coming from the factory for many years with the alternator lead attached to the battery.

 

[8Mud]

You seem to think that the wire coming to the battery from the alternator is a series circuit when in reality its a parallel circuit. The battery will not just suck all the amperage from the alternator unless something is wrong. If you so wanted to run without a battery, you would need to place the - and + terminals of the battery cables together or else there is an open circuit and power won't flow regardless of where the alternator lead is attached to. For the record, cars have been coming from the factory for many years with the alternator lead attached to the battery.

Have Old_Man explain it to you, I lack the language.
But I hope to heck nobody places the negative and the positive leads (of the battery) together and tries to run the alternator (motor). The best that will happen is a blown high amp fuse, the worst is smoke.
Some of you guys seem to be talking past yourselves, some are pretty close.
You are leaving out some important factors. Like resistance, amperage, inductance, and that the battery is chemical and not really electrical.
Current flow is mostly tendancies and not absolutes. The system is a ladder circuit, though I'm sure there is a newer term for that.
All a battery does is migrate electrons from one plate to another and saves potential. It's more chemical than electrical. Though there is a resistance in the battery. And it does use amperage, the volts are largely irrelevant (within a fairly wide band).
Just a guess, but the wiring is likely designed that way, to minimize surges (spikes), due to the inductance of the starter. There may be a instant of overlap in the two circuits, when they are switched. Maybe to save some wire, possibly to help segregate (fuse) the circuits, likely all of the above.

 

[92DripCherokee]

So the consensus is piggy back the + wire to the battery, leaving the old wire in place?

Since the sensing wires are unchanged, why should it matter if the PDC is no longer the fusing point? Im simply adding a low resistance path, to an otherwise unchanged circuit..hot is hot right? the PDC isnt a load, and the battery is still in the same spot in the circuit...am i reasoning right? Im only doing this byapss since the old + wire from the alternator is damn hard to extricate from the brittle old PDC housing

Has anyone actually removed the old + alternator wire run through the PDC, and relied soley on a direct + run to the battery?

 

[Slo-Sho]

You can run the wire directly to the battery if you want to, using a hi-amp ANL or MAXI fuse will give you protection on that wire. If you want to go even further you can also directly ground the back of the alternator to the battery as well.

As far as the guy talking about his laptop and trees and rivers with powerplants with gardens full of rosies and a pocket full of posies and what-have-you....I don't think I'd trust him to refill my windshield washer bottle let alone take any electrical advice, but that's just me.:angel:

 

[gjxj]

So the consensus is piggy back the + wire to the battery, leaving the old wire in place?

Considering how much misinformation there is in this thread I dont think going by 'consensus' is a good idea.

If you run both wires you will be fine except for the failry unlikely scenaro where something goes wrong with the main starter lead. (loose, resistance from corrosion, etc). In that case if you try to start the car the couple hundred starting amps will try to take the other path and you will either blow a fuseable link or burn up the wire.

 

[Jim Mesthene]

"Dude, are you telling me you cant AT LEAST UNDERSTAND that a battery that is constantly being drained and charged simulatenously will live a shorter life?":confused1

Someone should know when to keep quiet, you can't both charge and discharge at the same time, if system voltage is above 12V then the battery is charging... current IN. Switch on a winch and even with the alt voltage will drop and the battery will drain to assist the load...
I am an Electronics tech... go read ohms law and some basic DC voltage stuff... elementary..
Run it to the Bat and leave the factory one there... the purpose is to not overload the 10 gage wire... and if you add lights, winch etc at the battery, stereo well the alt has to send all the current through the skinny wire and since these accesories are more load than the factory calls for it gets hot and melts..
Leave whats there for the stock wiring harness and tandem over from the alt to the batt and you will be fine...
Don't worry about stray current... more hogwash.
The only stray current that will bother you is a ground loop. IE using different points of ground on the vehicle like the radio and an amp way in the back. If conncections aren't grounded well on both ends the "loop" is formed by the ground shield on the rca cable that connects them. If you don't know about them, just google.

You should listen to this guy.

Consensus? Are we voting on what's true and what's not true?
Everybody is entitled to an opinion. That does not mean that all opinions are of equal value. For example: my doctor's opinion on why I'm sick is better than my plumber's opinion on why I'm sick.

 

[tweakado]

Not to steal this thread but. I have a 86 with a 2.5L and when i run the truck in gear my in dash volt meter runs to the red warning side. When i hit the brakes the needle jumps wildley then settles down and when i hit the turn signal it jumps with every click is this all normal stuff. Now to put my two cents in on 12 volt systems. 12 volt is 12 volt what runs the stuff like lights a/c and such is amps if your battery has a rating of 550 cold cranking amps then it shoud take half of that to turn over the engine and get it fired. Volts and amps have a close relationship one without the other will not work thats why when you check an altenator at the back lug good is over say 13 volts bad is under 13 volts but what really happens is your amps drop off and so does your voltage hence bad altenator as all think. Okay buy a new altenator right if you want you can. But what happens is the voltage regulator or the diodes go south and these items can be bought for a fraction of the price and do a rebuild. The reason they run things off the batt is because it has a constant storage of amps. So sure you could and can run the alt straight to the batt mine has a y shaped split one from the alt lug one to the starter relay and on to the batt. just my thoughts.

 

[Monkey55]

So the consensus is piggy back the + wire to the battery, leaving the old wire in place?

Since the sensing wires are unchanged, why should it matter if the PDC is no longer the fusing point? Im simply adding a low resistance path, to an otherwise unchanged circuit..hot is hot right? the PDC isnt a load, and the battery is still in the same spot in the circuit...am i reasoning right? Im only doing this byapss since the old + wire from the alternator is damn hard to extricate from the brittle old PDC housing

Has anyone actually removed the old + alternator wire run through the PDC, and relied soley on a direct + run to the battery?

Drip, just as a couple of people already said.. Don't rely on consunses on this topic.. You'll probably end up with with dual-deep cycle batteries, a 1,000watt sub-woofer, OBA with enough power to fill 10 tires at a time, a laptop installed under the passenger seat with a touch screen display mounted in the dash, LED lights for night wheeling, 2 cbs, heated seats, and a portable welder..
:roflmao: Just kidding..

I'm curious why you want to run a wire straight to the battery.. Are you having charging issues?? Shorting issues?? Or just wanted to do it just because??

I did some major re-wiring on my 64 Chevy Truck.. But, it doesn't have all the electronic stuff as newer cars.. Even though it seemed simple, it was still touchy.

So, you might be opening a can of worms by trying to do this or end up putting a lot more work into it than expected..

Elias

 

[5-90]

On two of my rigs (daily drivers,) I've installed uprated Delco alternators, and my mains upgrades. The alternator output runs from the back of the alternator to an ANL fuse block on the inner fenderwell, and from the ANL block to the battery anode (+ post.)

Electrically speaking, connecting it to the start relay screwpost or to the start motor mains post would be the same thing - since both are directly connected to the battery anode anyhow. The difference is the physical location of the connection.

For later XJs, the alternator lead runs up into the bottom of the PDC, through two MAXI60 fuses or a fusible link wire, and connects to the Buss bar inside the PDC. This Buss bar is directly connected to the battery anode (via the mains lead running from the battery to the PDC,) and connections would therefore be similar - the battery anode, Buss bar, PDC screwposts, or starter mains terminal would all be, electrically speaking, the same connection.

Just note that if you revise the OEM connection, you'll be eliminating a circuit protection device (which I do not advocate!) but the connections are otherwise the same thing. Period. Full stop.

It gets sticky if you were to want to do something silly - but any terminal that has a direct connection to the battery anode via a mains lead is, in effect, the battery anode terminal. I suspect that the OEM didn't go right to the battery anode for simplicity - for a similar reason that I don't like doing secondary distribution off of the battery anode, and will install a distribution post for secondary power. This would allow me to run a single lead to the battery - rather than six or eight - and makes it easier for me to service the battery.

 

[92DripCherokee]

postscript: thanks to all those who responded, the operation was a success.

I fused the new lead with a 100 amp maxi fuse, and added a bigger battery to chassis ground, all 4 gauge.
(old charge leads insulation was slightly melted at the rinf termial, and at the inline connector, i crimped a new ring on it.)

The stereo sounds perfectly clear, no noise or ground loop.
The engine idles slightly smoother now, and starter turns slightly faster.


For tech notes, to strip the heavy insulation from the 4 gauge I used a hook of galvanized steel wire heated cherry red to "hot knife"the insulation. Stinky, but worth the trouble because no wire strands were severed.

Rather than crimp, aI filled heavy duty tin plated marine grade lugs with molten electronic solder, jamming the cable in. Very risky since the coper wire cools the solder extremely fast . Did a hard pull test, and they're on for good! All the strands wicked up solder. Finally I wrapped the cables with cold shrink tape, making a watertight connection.

 

[Blaine B.]

FYI it's not a good idea to run without a battery.....too much voltage, etc.....will occur.