Hi Everyone, Looks like I get to post the first one in this forum..... So....as most of you may know I'm currently doing some "upgrades" to my '70 conv. (see my sig below if not). Well my question pertains to the alternator amperage and the wiring system that the car came with. About 5 years ago I upgraded to a slightly more-modern-than-stock internal regulated 70AMP from a late 70's Buick over the stock 38AMP. Now that I'm installing all kinds of electrical items such as Speed-Pro EFI, two (yes TWO) Weldon 2025-A fuel pumps, a CSI remote water pump, twin electric radiator fans as well as all the normal street accessories, what would any of you "electrical wizards" recommend? I'm thinking a modern 140AMP like the TUFF STUFF (Jeg's part #908-7140B) would do BUT...........will my stock wiring (in excellent condition) hold up to this??? BTW......I run a TurboStart 16-Volt 3-post battery with a step-up box that converts the alternator's "12-volts" into 16 to keep the additional 2 cells charged equally with the other cells. I figure we PROBABLY have some members here who are into BIG stereos and amps that require basicly the same upgrades and can give me some in's-and-out's of what to do...... Thanks in advance for any and all suggestions ya all!!!
Hi Kerry- The short answer is, "Size your alternator so the battery doesn't go dead!!!" The long answer follows: Battery are rated in ampere-hours. The energy taken out of a battery is equal to the connected ampere load times the time it is connected. The same is true of charging a battery - amperes (alternator capacity) times time the engine is run equals the energy stored. Remember that the voltage regulator is involved too, to measure the battery voltage and REDUCE the charging current when the charge is complete. You can estimate your alternator requirements by adding up the ampere requirements for all of the stuff you want to power, like the water pump, EFI, fuel pumps, etc. Then make sure that the alternator has at least enough capacity to keep the battery up when everything is operating, with some left over for replacing the energy used in cranking the starter. The down side to good old shadetree engineering (a little is good, more is better, too much is just right) is that excessive alternator size adds up to parasitic losses from engine power. If you oversize the alternator to pick up lots of stuff, you will lose the crankshaft horsepower required to spin it. The reason it makes sense to use an electrically driven water pump, for instance, is that the battery supplies the energy to spin it instead of taking motor power. If the combination of charging system and water pump is LESS efficient than the stock mechanical pump it's a net loser. I know, if we're talking about a race car, you can get cooldown between runs, you're boost charging the battery or not relying on an alternator, and electric pumps ARE better at pumping than the belt driven mechanical type. But it's worth thinking about when you're spending your dough, especially on a street car.
Thanks John for the info, I knew, for the most part, about adding up amperage ratings of all the addition eletrically supplied items. I guess my real question was when adding a bigger amp alternator for the additional loads imparted on the battery, how will the stock wiring hold up to extra electrical "flow". Are there any wires other than the main feed wire from the alternator that need an increase in guage size that I should be made aware of??? Remember, I am using a Turbo Start 16-volts 3-post w/step-up box. The third post is for a standard 12-volt connection. I also use 20 & 30 AMP relays whenever and wherever possible. Thanks in advance for your additional help........
Kerry- Your weak pont will probably be the 30 year old fuse center in your GS both in terms of ampere capacity and the ability to connect stuff. There are better distribution systems available, but I don't have any recent experience with them. I would look for a distribution block with the ability to land a good sized feed from the alternator/regulator and individual fuses for the load taps. Check out this link from Painless Wiring. They make a series of fuse blocks, including a relay controlled distribution block. http://www.painlesswiring.com/fuseblock.htm Good luck!
bigger wire yes kerry you MUST upgrade your alternator wire.the largest stock buick unit in the early70's was 63 ampres.i dont see why you need a 140 amp unit.judging by the description of what you are running,i doubt if you run much under 3000 rpm for any length of time.you should be able to run the(17si) 108 amp alternator(same size case as your 70amp(15si)and have more than enough power.also upgrade any ground wires that connect to the gnd. side of the battery,AND the ground wires that connect the block to the body and from the body to the frame.you see,the return path for the charge is actually via the ground NOT the pos like everyone thinks!!!go to your local rebuilder,and ask for this set-up.if you cant find someone you trust,let me know,as i have been a rebuilder for the last 22yrs ,owned my own shop for 5 and would gladly build you one!:beer
Hi Guys, Thanks Jamie.........I forgot to mention that I have already upgraded the power feed alternator wire to a 10gauge ran directly back to the 12-volt 2nd post on the Turbo Start battery. I also run 1/0 welding cable from positive post 12" to Ford style solenoid then approximately 15' to Tilton starter. Negative side...approx. 16" thru grommeted hole in trunk floor to well cleaned and bare frame(light coat of oil to prevent rust, no problem in three years). Engine-to-frame, engine-to-body, body-to-frame all 4gauge negative "stud-to-stud" starter cable. I've tried to do some homework in the past ! To my knowledge.....battery cables ARE one of the areas where bigger is better?!?!?! Sorry, guess I should have shared a little more for you there . My intentions are to build this and still retain a certain "flavor" of streetability (fuel injection goes A LONG WAY here) so it will see more below 3000RPM than you are figuring. Will or does that change anything you have stated?? You recommend 108AMP.....is there any downsides to a 140AMP other than cost. I'm taking will it hurt anything or cause unneeded costs in addition accessories?? Thanks in advance...............:TU:
140amp kerry,it sounds like you have covered all the bases,the only drawback to higher amprage is it will rob a bit of horsepower.if this wont bother you , bigger is better!what will this 140amp unit cost you?:Brow:
Just for reference on horsepower loss- 140 amperes x 14 volts = 1,960 watts assuming 30% losses (friction, belts & pulleys, regulator losses, etc.) the power consumption is about 2500 watts. 2500 watts/746 watts per H.P. = 3.4 H.P. loss REMEMBER, this is maximum power lost assuming that the alternater is pumping maximum charging current. Most of the time, the regulator will be reducing the charging current.
Kerry, according to my "pocket reference" by Thomas Glover, you need a #4 wire for "continuous load carrying capacity" of 140 amps. According to this book, #10 is only good for 55 amps, though this is continuous. I imagine the auto engineers figure that will never be continuous and so you can get away with smaller wire in the real world. Your loss with the #10 wire is exaggerated by increasing the length of the cable (such as all the way to the back of the car). One easy thing to do is run your wire back to the cable stud on the starter. Then you only have ~5ft of #10(or #4) cable before taking the rest of the trip via the 1/0 cable. I know for a fact I melted the #10 wire on my Dodge truck after installing a HD 155 amp alternator. But still, #4 sounds awful big to me. I will try to verify all this with our plant electrician tomorrow. He always talks about cable size, length, ampacity, and why didn't anyone tell him :spank: we might want to use a bigger pump later. HTH
Hi Guys, THANKS!!! I am taking note of each and everyones input on this subject. Any new thoughts?? Feel free to add, NO NEED TO BE SHY!!:grin: Thanks again Guys.....
Kerry I talked to our electrician this morning and he said that national electric code (industrial electric I'm talking) would call for a 1/0 for continuous :jd: use. Obviously that isn't applied in the automotive world. That being said, he suggested you add up the current draw of all the continuously operating electric accessories, or all that might be operated at one time. Then add a 20% safety factor to that, then size the cable accordingly. I wouldn't be surprised to see 40-60 amps with all the electric stuff we use these days. A #8 wire would be good for 80 amps.
Slow down guys - some logic on the alternator cabling issue- First, the NEC is not a design guide but a safety code. The requirement for #1/0 cable to carry 145 amperes comes from a totally different configuration - (3) wires, in conduit, carrying alternating current. #1/0 wire has low enough resistance to allow it to operate in this configuration without thermal damage to the wire. Remember if you will that the 140 ampere rating of that alternator is a peak rating and is probably only attained for a short period of time. The NEC definition of a continuous load is one that is carried for three hours or longer. The right criteria for sizing the alternator wire is the resistance of the wire and the resulting voltage drop. Voltage = Current * Resistance If your alternator puts out 140 amperes at 14 volts and your battery needs 13 volts to charge, the maximum voltage drop you can allow is one volt and the maximum resistance is .0071 ohms. Assuming that the alternator to battery wire is 6 feet long, the resistance per foot would need to be .00119 ohms/foot or less. There IS a table in the NEC showing D.C. resistance of stranded wires. Using that table, a #8 coated wire has a resistance of .000786 ohms/foot, so it would work based on the voltage drop criteria. As far as burning up the wire, remember that it is in free air and allowed to release heat freely. Power = Current x Current x Resistance The actual power lost at 140 amperes would be 92 watts - spread over the 6' of wire. Think of a 100 watt light bulb. I think the wire would get pretty hot, but as long as the load was not "continuous" at 140 amperes it would be O.K.
Well, I think John and I agree that a #8 wire should do it. John, thanks for the elaboration on the basis for the NEC, I sure didn't know that.
Pure Science! I have a 140 amp alternator on mine because the battery would never keep a charge and 12V is the most I could get, even with a new internal regulated alternator. I used a #4 cable from the alternator to the ford starter solenoid (about 2 feet) because they have them in the parts store with ends on them already!
