i've been reading with interest the other posts about proper wiring for fan controls. one point made was that by wiring the control directly to the battery, the charging system will not function properly.
can anyone explain this? i understand that the ammeter would not sense the current draw to the fans if they are wired to the battery, but how would that effect the total charge on the battery? would the alternator keep the battery charged? how about running an extra wire from the alternator to the starter lug-how would that effect things? any ee's out there?
jeff

 

You have missed a couple of points. First, the Ammeter will reflect the current used by the fans if they are connected to the battery, the reason is that the current path is the same for the fans and charge current. The alternatoe WILL keep the battery fully charged and run the fans if it sized correctly to do so.
1 limiting or danger point is to make sure the battery charge wire from the alternator to the battery is sized correctly to carry the current for both.
The point to wireing everything up front on relays is to eliminate the voltage drop inherent in the stock wire harness.
If your running a PWM controller connect it to the battery or use a large filter. If the fans are on relays connect them up front. There is no reason to run the current for the fans or headlights in a double loop around the car.
The relays used on the headlights are to put full alternator voltage to the headlights by eliminating the voltage drop in the bulkhead connector, headlight switch, and bulkhead connectoe again etc..

 

hi six
i'm not sure that you're totally correct. how can the ammeter sense current draw if the fan is wired directly to the battery? also, if i unerstand what baskin said about the field windings, how does the alternator sense the correct output unless there is feedback thru the meter? i have to admit that i don't really understand the charge-discharge regulation of this system, so i'm looking for an engineer to step in and enlighten me. just one of many things i'm in the dark about!
jeff

 

The charge wire was never intended to be a load buss, why not use the point of power distribution, the horn relay, to power your fans. Unless you've got one of those DCC units which require a battery connection it's the best point for all power distribution, it's much closer to the alternator, your ammeter will be happy and it's the way it was designed to operate originally, not to mention negating the lessons in EE.

If you require an upgrade in load capacity, upgrade the wire between the alt and the power distribution point, along with a healthier alt.

 

Hey Jeff.
Take a look at this. Its a cleaned up and sortof simplified schematic of the charging and ammeter circuits.
If you have the fans connected to the battery, all the current for running the fans as well as the current to charge the battery all goes down the same current path, the Red wire between Point A and B, so, the ammeter will report it. Remember, when the engine is running, the alternator output will be higher than the baqttery voltage so it will be supplying all the current to run everything including charging the battery. Voltage sensing for the regulator is done with the red wire on the connector at the side of the alternator, it is spliced into the alternator supply line in the main harness close to the horn relay. In the pic it is the splice on the pink highlited wire that ties the 2 red wires on the alternator together. The relay is the distribution point, so thats where the voltage sensing is done.

 

I understand this point, The wire size off the the alternator may not be big to handle the load of charging and runnning two fans! So does the wire run directly back to the battery? Or is that a one of the wires that go down to the starter and run through the fusible link?

 

Depends on the year, in the pic it is the wire going from the alternator to the starter thru a fuse link. Late C3s the wire went directly from the alternator to the battery thru a fuse link in the battery box

 

S3 and I am in basic agreement, to which I may add, the steady drain of lets assume 20 amps, through that main power buss/or fuse link (worse) going to the battery as a charge circuit will drop voltage at the battery, but the sense voltage of the alt wiring is up top next to the alt stud, AND off the instrument panel switch source that would have run a red dash light....in some cars, some sharks have a steel resistance wire instead, with no red dash bulb/idiot light....the typical amp meter in these sharks from the factoy runs off the regulator circuit and is NOT a typical ampmeter wired into series with any load, except the regulator.....IMO, It's nearly worthless, so I put in a voltmeter on my '72 here some 12? years ago.....

BUT back to the point here, that is, the battery needs 14.7 volts max for full charge rate, and should see 13.4-6 something for maintaining a full charge, but with that fan set dropping some .5 to a full volt off that through the wire.....it does....beleive me, it does....I ran tests on my old GTO once with same alternator, same electrics as this vette....

sorta like that ground wire for out heater blower grounding....you know, the black wire to ground that's frequently mis connected near the starter?? well I proved about .8++ voltage drop across that wire alone to the blower motor.....in total that motor saw maybe 11 volts, when changing the wiring out for more robust wiring it saw only .2 volt drop from system voltages, across the blower motor.....another example of voltage drop across wires.....

hell, you can see that yourself...plug in a hairdryer to the typical lighting circuit in your household....note the lights dim?? that's about 5 volts drop, roughly.....off 110 volts, it's nothing, but you take one volt off 12-14 volts...and you got a problem.....

I was in Jr, High school, electronics hobby since elementary school, and wondered THEN why they did't drop 6 volt car systems and go directly to the military standard 24 volt.....or for that matter 48 volts....still I dunno why.....

 

Gene we both will live to see 42/12 volt dual power systems in our cars. It's just around the corner.

Bullshark

 

OH Christ, here we go again,....yo just KNOW some Bubba will take a 42 volt source and put it across his buddies 12 volt car to give him a jump start.....THAT should be interesting....

 

You don't you guys really mean 48V?

 

I don't know much about this stuff but I remember back in the car audio world there were some companies selling 16V batteries. Wouldn't that be bad for a car with a 12V system? I always thought 15V was pushing it.

 

DB, I would guess that the entire new car electrical systems would be engineered for the higher voltage. I would guess the systems would incorporate some voltage step down features when necessary. I can't imagine a whole new line of light bulbs, radios and the like hit the auto parts stores, but it's possible.

And with 48v on tap it would be a real boom for you audiophiles, 'scuze the pun. You'd want the higher voltage audio equipment.

 

Yeah I understood the need for the higher voltages but I couldn't believe they were selling the 16V batteries openly without warning of the dangers of hooking up said battery with no other changes or as you said, voltage step down precautions.

 

Allan, It seems 42v is the trend. Do a quick google on upcoming 42-volt automotive systems and you will get more than you want on the topic.

Here was one.

http://www.tierone.com/42voltrr.html


Bullshark

 

For all practical purposes, it doesn't effect it, the alternator sense wire will compensate for most of the drop and you can calculate the drop of the wire between where the sense is connected and the battery here for any extra current applied (eg mark viii fan = 35A)

http://www.stealth316.com/2-wire-resistance.htm

Keep in mind, that even high quality regulators depend on a zenor diode for a reference, so the spec, even on a high quality regulator is 13.8 to 14.2 V, the lower cost ones are not as tightly controlled.

 

With regard to the charge wire, it's sized for the worst case scenario (eg very low battery or shorted battery cell and the engine reved), so it's sized to the alternator, not the load with regard to reliability. If you upgrade the alternator, you need to upgrade the feed wire from it.

 

UH,, NO, i'ts sized to keep the BATTERY from overheating and exploding.....you get the rong failure in a battery which is nothing but 8 cells in series for 12.6 volts.....and it's possible to boil enough hydrogen outta that thing to make a serious mess, if not explode....common enough for cheep chargers to overcharge even a BOAT battery...read deep cycle marine, and boil the fluids outta it....

THE ONLY loading the battery should normally see is maybe lights, stereo running with someone sitting in the car....through the fuse link/fuse into the main power circuit...right?? so from there when the switch is hit, it actuates the solenoid, which in turn hits contacts to toss 200 amps to the starter motor....whoopie doo....

NOW, WTF does that have to do with ALT power, rated in current???

it don't matter one whit DAMN to that battery if that alt has 500 amps available, like off a fire truck, or a simple 60 amp stock unit....the battery will draw what it needs to maintain a decent charge...and the regulator senses that, the fuse link IF drawn down several volts by putting another load directly across the battery....will essentially lie to the regulator, the car chargine SYSTEM thinks everyone is happy, while the BATTERY, due to that voltage drop, is not happy....

I remember years ago, when I first got my Fluke DVM, and I got some time on my hands (bored to tears) and decided to run some tests on my old '70 GTO/Lemans and so I did, and found what I say is true....

So lets leave it alone, I been running more electronicus crappicus of my own designs over some 40 years in my cars....and never had a problem....can YOU say the SAME???

didn't think so.....

someone sent me a search link on your patents, and your company....I have to look it up again...fine for industrial controlls, no arguement, not my field.....

 

Wow, I have a stalker now, are you going to start throwing bricks through my windows and drilling holes in my tires or do you only do that to young women?

A car battery has six cells, not eight. http://www.landiss.com/battery.htm
everyone here already knows that

A 10 gauge wire isn't used to regulate current, again, everyone here already knows that.

Everyone here understands also that a battery doesn't regulate its own charge, that's what the voltage regulator is for.

I believe the original poster asked for the opinion of someone with an electrical engineering degree, the last time that I checked, google search didn't issue degrees in electrical engineering.

 

The above first line is rather funny as in WHO stalks this site for an offhand funny comment about some parking/condo lot situation???

as stated someone ELSE sent me that link as to your background....
Frankly I could give 2 tschits, I only care about the accuracy of discussion....and YOU are more into defending some design that fell into the same trap that Spal may well have.....not really caring WHY/WHO/WHAT, but the salient FACTS are that YOUR design is lacking, apparently same as theirs.....

pick a better design or parts source.....CASE CLOSED.....

depending on a battery to releive your design's inadequate margins to the enviornment it's required to work in is just plain silly....own UP MAN....



typed 8 as a reaction to most consumer electronics...forgot about 2.1/cell as in lead acid....don't matter much either way, really still the capability of the total battery.....

YOU still don't get it DO you?? especially if there is a fuse link, and a steady enough draw of ~20 amps, the battery is NOT SEEING the full charge voltage the regulator upstream THINKS i'ts seeing....

jeebus man....how hard is that to comprende'???


I don't have a PHD EE, that's true, but I understand cars pretty well, and lotsa other electronicus crappicus too....

IF your attitude would change from being a condecending *****, you and I could have a beer and exchange war stories sometime, but you seem too smug for my company.....