Upgrade Your Alternator!!
 

I think this a missed and very important modification especially for heavily modified Fds. Here's why!!

When Mazda designed the Fd Rx7, they had the Mitsubishi Alternator Co. build the alternator based on the Fds max load capabilities. This is basically everything turned on MAX. Engine WOT, blower motor at max, cooling fans on MAX, all lights on w/ brake lights, and Bose sound system with all it's little amplifiers. What they came up with was 100amps max electrical load. For a mid 90's car that's plenty of power however, is it adequate with all the additional electrical loads we are adding while modifying our cars?

Now just because the alternator is capable of producing 100amps doesn't mean it's designed to do so for lengthy periods of time. It's just like injector duty. There's a reason we strive not to go past 80% duty on injectors. The internal regulators are designed to only allow the alternator to supply the needed current based on the loads it receives. The regulators secondary function if to keep the alternator from over heating. But what happens when those loads are exceeded? Short answer is voltage drop.

Lets take a look at the additional electrical loads we are adding to our 7's while in quest for more power.

1.Bigger fuel pump!

A lot you know this but I'm gonna go over it anyways. :) We all know that average base fuel pressure is around 38psi. Under normal cruising or engine vacuum conditions, the fuel pressure actually drops because the vacuum/boost line is pulling a vacuum on the internal spring or diagram of the fuel pressure regulator (FPR) which cause it to relieve more pressure. So while we are cruising around under vacuum, fuel pressure is lower (lets say 33-34psi). At this level the electrical loads are minimal. As we accelerate the opposite happens. The vacuum becomes less as we reach atmospheric pressure so the spring or diaphragm start to return to the original set pressure (again were at 38psi). Now since were talking stock Fd Rx7, were talking something that's boosted. As we get into boost, the vacuum/boost line to the FPR becomes more of a boost line. Under boost conditions, the pressure added to the spring or diaphragm causes the relief passes to close. This of course allows the FPR to relieve less fuel so the fuel pressure increases. In most cases FPR increase on a 1 to 1 ratio with boost. So a stock Fd is now running 48psi at 10psi boost pressure. Now what about a modified Fd? Not only are we running a BIGGER fuel pump, but we are also running more boost. Lets say we are now running 20psi with base fuel pressure set at 38psi. At 20 psi we are now at 58psi. The electrical demands on a BIGGER fuel pump at that PSI level are much higher than stock. Soooo do you think your stock alternator is gonna keep up? Maybe?

Ignition amplifier.

So now that we have more fuel potential to the engine, we need a way to combust all that extra fuel to make us more power. That's were that ignition amplifier comes in. With more power comes more responsibility on that stock alternator. The stock alternator be like "what the hell enough already!!!!" But wait were still not done yet!! I need to control my boost so I don't creep.


Electronic boost controllers

Here we have something else for the poor stock alternator to handle. This thing is duty cycle based and is putting even more electrical load stress on that alternator. Your alternator is really starting to get pissed. But we still aren't done yet!

Water injection.

Now I want to make sure I don't detonate and blow my engine we add yet another electrical motor in the form of a water pump and solenoids so we can spray a cooling mist down our engines throats. The engine may love you but your alternator is now saying F*CK YOU. Oh we still aren't done yet!

Stereo system.

Yep gotta have the ice to go with at that vroom vroom. Lets see big amplifier and 7" display. Your alternator has just thrown in the towel as it running constantly near it's peak output. Can you say blown engine from voltage drop to the fuel pump?

This is something you guys may want to think about next time you start having voltage drop problems due WOT on the dyno. Ask yourself " do I really have enough load producing capability out of my charging system to handle all this stuff"? If your still running the stock alternator, I seriously doubted it!

I see 20b guys doing the exact same thing. We add a bigger engines with 6 ignition coils to fire and all the above mods yet, some still run the stock alternator. Not me I recently upgraded to a 150amp once I started doing research. Jump in guys and lets upgrade those alternators. :)

And remember just upping the size of the alternator my not solve the issue. If you have bigger current draws you need to up the size of the wires handling them as well.

Mazda seemed to have used smaller diameter wires in their harnesses to help keep the overall weight of the car down.

an excellent post and the foundation for a valuable thread. lets hear more on the subject.

i have an upgraded alternator from Rich and don't remember the specific output.

i can also attest to the need for lots more alternator output.

for instance, as we find we can make 500+ hp with increased reliability, we find we are using larger fuel pumps.

the newer higher output pumps from Walbro:

9000262 gasoline
9000267 E85

should be fused for 30 amps.

fuel pump output is VERY dependent on elec input.

if your input to the pump does decrease in boost due to overload you could have a fatal engine problem. that's why i believe almost all modded FDs should have a digital fuel pressure sensor and LOG FUEL PRESSURE.

the cute little analog gauge will tell you nothing at 7000 RPM when it counts.

if you are currently logging, the additional expense should be under $100 and you will then KNOW fuel pressure where it counts... at high power levels.

lets hear from others as to what you run and what it draws current-wise..

i run both a Kenne Bell Boost A Pump (16 V to the pump in boost) and a Kenne Bell Boost A Spark (15 V to plugs in boost).

all our additional modules add up, especially in boost when it counts.

what do you have that sucks amps and what are the alternator options?

howard

"Mazda seemed to have used smaller diameter wires in their harnesses to help keep the overall weight of the car down."

weight, or lack thereof, is one of the many beauties of the FD. i wouldn't have been surprised to find they drilled holes in the wires to lighten them... the FD was aggressively designed and it delivers.

What vehicle is this 150 amp alternator found on, it would help to locate one.

I'm also interested - when my car idles, the amp doesn't appear to be producing enough
My gauges dim with the same frequency as my blinkers lol

With a little modification,a Ford Taurus alt fits on an FC,so I can't see why it wouldn't fit on an FD..it is 130 amps.
The pulley shaft is the same size too.(for FD)

Thanks for adding that info, let the hunt begin. What needs to be modified to make this fit?

Most FD owners would be well served to remove their shiny aftermarket underdrive pulleys from the alternator and install a factory one. This alone will make a noticeable difference at idle and low rpm cruising.

This is a very good point...get a proper idler pulley kit when you remove your airpump instead of a pulley kit that underdrives the alternator.

True. But small wires won't deliver big amps. ( As I'm sure you know Howard.) At least not for long without the need for you to break out your shinny chrome fire extinguisher that is. :-)

Here's a link to a DC wire size chart at the Engineers Tool Box site. (Which has a lot of other great info as well.)

Amps and Wire Gauge - 12V Circuit

And remember folks, when calculating DC wire runs you have to account for the return to ground leg as well. So if the run from the power source is say 10 feet, you have to double that to get the correct gauge wire to use. And it never hurts to go up one size if your calculations put you at the higher limit of a wires amp carrying capacity.

I know IRP sells an alternator upgrade for the FD. I think it's 120 amps.

Another important factor to consider is idle amperage. Peak amperage that is usually quoted does not tell the whole story. The alternator I will run on my car puts out over 100 amps at idle and 180 at full output. This is with the alternator at operating temp.

People with crazy fuel systems like 2 id1000 and 4 id2000 injectors should also consider the alternator amperage and voltage output because injectors are sensitive to operating voltage.

Good point John. Is your alternator going to be something completely custom or are you going to tell us where you're getting it? :)

Love this subject and where this thread is going. A quick search found this:

http://www.maniacelectricmotors.com/19rx7140amph.html

Any one have experience with or input in general on it?

It is a custom alternator however fitment is for a 2006 subaru sti. It mounts simmilar to the fd alternator.

Manufacturer is dc power engineering.

You are 100% right as I forgot to bring that up. I also upgraded to 2 gauge wiring through out. Also don't forget to add a secondary fuse to carry the total output load of the alternator. That long slender fuse box in the engine bay has a 100amp fuse. Well there's an empty spot right next to it to add another. The factory wiring is such that any current the alternator creates has to go through that fuse. Well since I added 50 more amps of current capability to the electrical, I also added another 50amp fuse so the alternator isn't being restricted and can pass it's max potential. If you don't match the fuse and wiring to the total output, you will never get the full benefits of the upgrade as the internal regulator will always reduce the output when it hits that resistance.

I bought the 150amp mazda from unit off ebay. It's a direct fit no mods. Do an eBay search for" rx7 amp alternator" and you will find upgrades for all generation rx7s.

+1. Some alternators, if you underdrive they turn off at idle.

This is why I do not run shiny under drive pulleys on any of my vehicles. Ever. Nothing wrong with the stock pulleys.

I may not be reading this correctly. But adding a 50a fuse inline with the 100a fuse isn't the same as replacing the 100a fuse with a 150a one.

Nor is adding a fuse inline with another fuse going to alleviate any restriction. Only increasing the wire size can do that. And I'm not just talking about the main battery cables and cable feeding the fuse block. In fact the whole fuse block may need to be replaced if it isn't rated to handle over 100a total current to it. Then there is the issue of the wires going from the fuse box to all those systems/loads that now may have a new higher current demand devices attached to them.

But like I said, perhaps I'm misreading you. :-)

This is why I have been offering our 140 amp upgrade for some time. The stock 90 amp unit does not cut it once you start adding gauges, larger/additional fuel pumps, stereo, etc. I use the stock case but install a larger stator with more windings and a corresponding voltage regulator. I also prefer NOT to underdrive the alternator. I run the stock pulley with an aux idler like the Pineapple or Tweakit. I know there are some alternators out there claiming higher output. The issue is most of these have to be spun faster to make that output, and as a result can suffer from charging issues at idle/low rpm. Its kind of like running a big turbo. You have to rev the car higher before boost comes on and you start making power. I found that 140 amps is the best compromise between low speed charging ability and maximum output. Otherwise you have to get into a custom bracket and do something like a side mount alternator.

Capt. Bill is right. Adding a fuse inline only reduces the capabilities to the maximum of the weakest link. Whether it be fuse or wire.

Most don't realize that a fuse is there to keep the wire from melting down and catching fire.

Individual components are protected at the components themselves.

Actually in this case it does as it's a parallel setup and not series like your thinking. It's just like doubling up on the wiring will increase the current capability because now you have two paths of travel to the same location. Go take a look at that long fuse holder in the engine bay and you will see the double plate that's attached to the main fuse. That empty section has the metal tab so you can screw another 10mm bolt into it. Adding a secondary fuse here gives another path of travel to the other side of that block where all your electricals are connected. :)


Edit: Now that I think about it, I'm going to need to upgrade the main wire on the other side of my fuse block if I want to carry the additional load to the interior panel. Otherwise my added fuse is doing nothing right now.

The added fuse is not inline, it's parallel. ;)

Still not going to increase capabilities how you think it will. If the resistance is the same between the two wires, then load will be divided equally.

So if there is more than 100 amps long enough, it will still pop your 50 amp fuse.

And if you just increase your overall fuse capability, you have to be sure that your wiring can handle the added load. As I stated before, fuses are there to protect the wiring. This is a safety matter. If a fuse is rated too high for the wire, then more amperage can transmitted than the wire can safely carry. It can overheat, melt, and possible catch fire.

That is what I thought you were saying.

Having one 100a fuse and another 50a running in parallel is not how you properly increase a circuits ability to safely carry up to 150 amps. Nor properly protect it from an overload condition. It's not like 100 of the amps know to only try and go down one path while 50 of them go down the other.

I like to add a lead from the alternator post to the fuse box where the positive battery terminal is. The charging harness gets beat up from heat, age, and oil spilling on it from oil changes. This give the alternator another charging path to the battery.

Doubling up on the wires is not how it's properly done. If for some odd reason you do choose to double up on your wiring for one circuit, either of the two wires individually should be capable of carrying the maximum potential amp load going to that circuit. Amps don't know that only X number of them should go down one path while the rest should take the other. And if either wire should develop added resistance for some reason, the amps are going to start taking the path of least resistance and perhaps overload that path. With potentially catastrophic results. Like your car burning to the ground.

If some one is not familiar with basic electrical theories and concepts, I highly recommend that they do not attempt to modify their electrical system on their own. Either do some research on how to do it properly yourself or get a professional to do the work for you. And considering some of the shit electrical work that is passed off as "professionally done", I'd learn as much as you can so you'll have a good idea if you really got what you thought you'd paid for. :-)

So, I have a local alternator rebuild and repair shop. Would they be able to rebuild my stock FD alternator to increase the output?

If they're knowledgeable they should be able to. I had a gentleman in my home town of grand rapids mi rebuild several alternators for various cars over the years. He was cheap to....$40-60 for a complete rebuild/upgrade.

Tim send it over to me I will take care of it.

What you are saying is not entirely correct.

Infact the factory wiring in the FD has circuits that have 2 seperate wires carrying current on the same circuit.

The main thing to remember is to make the wires the EXACT same length, once you do that it is a common electrical practice when working with high amp circuits.

Having said that, I would not run a circuit with a different amp rating as t-von does, that is not the correct way to do it and is infact bad electrical practice. He should upgrade the wiring on the circuit and use only one fuse but multiple wires if that is what he wants do do. Of course taking into account the current carrying capacity of the fuse block itself.

Basically if you really want to do it right the entire car should be rewired or just add a seperate fuse block for the extra components and upgrade the wiring from the alternator to the battery.

Length would be far less important than the size of the wire I would think. It still gets back to the fact that if both wires are not rated to carry the full current load individually, you run the chance of at the very least burning out your wiring if one of those under rated wires fails or builds up extra resistance.

Out of curiosity what type of high amp capacity circuits use two smaller wires to split and share the amp load as opposed to one larger wire to handle the whole load? And why?

I've had some classes and have successfully rewired my entire home remodel fully to add 200amp service so I have some knowledge. It also passed inspection. I can handle a/c .... d/c is child's play. ;)

Heavy gauge wiring is just numerous strands bundled together in a single rubber coated line. Answer this question for me. If you take 2 gauge (which is rated at about 180amps depending on length) and a razor blade and cut out half the wire, rewrap that same wire into two individual separate strands and hook them together back on that same circuit, will it still carry 180 amps?

I guess Mazda didn't do it right because the factory wiring to the alternator is exactly done that way. It too has 2 single strands of small gauge wires joined together to carry the 90amp load at a common point. Removing anyone one of those strands cuts the load carrying in half.

Thx that's what I was thinking. I did originally try to find just the one 150 fuse but had no luck. So I just added the second. I may do some fuse testing to prove if it's safe or not. All I have to do is wire 2 circuits. 1 with a single 25amp fuse and another with 5 single 5amp fuses and see if the 5 fuse setup will blow at the time as the single fuse setup. Either way, if Mazda didn't think it was safe, they would have never added that empty spot to take and additional fuse. 2nd gen is the same way.

In theory, I agree with t-von regarding wires in parallel. The total amount of copper is what matters, the electrons don't really care whether there are two separate bundles of copper or one bundle of copper, they will take the route with least resistance and so the current traveling through each wire be proportional to that wire's resistance. As long as the wires are routed in a safe manner, it's pretty unlikely one of your two wires are going to get cut or damaged to the point of leaving the other wire to carry all the current... how often do you worry that the original wire will get damaged or sliced in half?

In practice, you can't quite guarantee there will never be a short circuit or a broken wire, and the purpose of fuses are to burn first to protect the wire from burning. If you're going to run two wires in parallel but protect them with one fuse, the a fuse that is appropriate for protecting each wire individually is going to be about half the size of what should be used if you ran one larger wire. So the best practice would be to replace the undersized wires with single large wires, if you're able to.



By the way, I wouldn't consider the RX-7's wiring harness design to be a good example, for many reasons. There are quite a few high-power circuits that zig-zag back and forth across the car adding length (thereby weight and cost) without good reason... headlights and fuel pump are two examples. I'm also in strong disagreement with how many high-power circuits run through the ignition key. It's not a horrible design considering likely time and budget constraints. That said, there are quite a few things that would have been done differently if a knowledgeable wiring guy had spent an adequate amount of time designing the electrical system after the location for all the other mechanical parts in the car had been finalized.

The same scenario works for 1 single wire as well. If there is corrosion, or the wire is cut or somehow the cross sectional area of the wire is compromised you still have the same problem as if you had ran 2 individual wires. That argument is invalid.

Not an automotive example but the building that I am currently working at in NYC has a 4,000 AMP service (yes, four thousand amps). It is impractical for the electrictions wiring up the transformers to use 1 single wire as it would be essentially impossible to work with so it is reduced to something like 8-10 wires and all are the SAME length. It serves the same purpose.

Mazda did it probably to keep the wire diameter smaller and allow the wire harness to flex and be able to make tighter radius bends.


If each wire is drawing the same amps, as it should be in a properly wired multiple wired circuit, then the smaller fuse will blow first. There is no need for a test a simple understanding of parallel circuits and their principles would tell you that.

I agree, my conclusion with the weird wiring is because of differences between LHD and RHD as well as lack of time to make a better designed harness.

IMO, the stock harness is adequately designed though for a stock car. We who modify our cars are finding weakness in the factory wiring that the engineers do not have to worry about because they were not running the equipment we do. Also, it has been over 20 years since the FD was manufactured and electronic and wiring has come a long way since then.

AC and DC systems are not the same thing but both are "childs play" as long as the current is not flowing. :-)

While I've never rewired a whole house, I have rewired a few boats in my time and work with DC and AC systems on a daily basis on the boats I run or engineer on for a living. The current boat I run has two main engines with 24v starting systems, two 40KW gensets with 12v starting systems, 2 100a 240v shore cords connected to boost transformers and 10 starting and house batteries. And none of these circuits is wired with doubled small wires feeding the same circuit. I guessing there is a good reason for that.

I'm also guessing when you rewired your house you didn't use any small doubled up wire runs to feed the same circuit connected to two circuit breakers each with a different trip rating to protect the same single circuit, correct?

As to your question, sure it may carry the load. But you seem to be missing or ignoring the point. If one of those two wires drops out or builds up extra resistance then the other wire could end up trying to carry more amps than it is rated for and burn up. Smaller wires also have more resistance so I don't see the point in wiring it that way.

I have noticed the two smaller wires at the alternator before. Question is, are they both going to the same place? If so I can't recall seeing any other alternators wired that way. Makes no sense to me to do it that way. And if there are feeding the same circuit it may be one of the reasons people are seeing voltage drops as our cars get older.

I may not be an electrical engineer but quite frankly you showed your ignorance of how basic electrical systems work when you thought that putting in one 100a and one 50a fuse in parallel in your fuse block is the proper way to protect it while increase it's load carrying capability when running an alternator capable of putting out 150 amps through it.

Well currently on my alternator upgrade, I have a single 2 gauge wire that connects from the alternator to the battery/starter side of that fuse block. My battery also has 2 gauge that runs to the fuse panel from the storage bin. So on that side of the fuse block, my battery (and anything hooked directly to it) gets the full charging benefits of my upgraded alternator. Now I added that secondary fuse to the block because I thought it was needed to pass the full current capability over to the other side for the vehicle electrical. Now I know you can't pass 150amps through a 100 amp fuse so I added the 2nd fuse to create that additional path. I know I still need to upgrade that main line from the engine bay panel to the main under dash panel so that any additional electrical I add (not directly to the battery) has the energy it needs.

I never said I was running two different wires to carry my load. I only used the double wire comment as an example to support the added fuse theory. If you have two 50 amp fuses wired in parallel, you have a total of 100amps that can pass through to the other side.

On the house however, I did run the 3 wire romex yellow 12gauge 20amp from my parents 50amp electric stove connection to my newly installed circuit breaker box so I could have power through out the house as I did each rooms rewire. Even though I had a 50amp source, I knew I only had 20amps available to my box because of the 20amp wire used to connect it. So yea I had to be carefull on the number of items powered up during the remodel. ;) My inspector was in shock and told me he never seen a DYI done that well. You should have seen his eyes when I started turning on lights and how I had supplied the house with power. He actually asked me if I wanted a job if my career in the oil field took a turn. Lol!

Ok. So if you have a 100 and a 50 in parallel. ..

That means you still only have 100 amps max throughput.

Anything over means the 50 amp fuse sees more than 50 amps. So 102 amps means each fuse sees 51 amps.

It's how it works. Stop trying to justify it.

You are kidding right!? But in case you are not, what are you going to use to bring the load up on these wires gradually and then cause the fuses to blow?

Can you show us on this wiring diagram where that slot is for this extra fuse that runs parallel to the main fuse and feeds the same things as the main fuse? (Which based on the diagram should be a 120a not 100a.) Have you metered this extra fuse slot and confirmed that is does run parallel to the main feed wire and feed the same things?

http://wright-here.net/files/manuals...ng_Diagram.pdf

Are we getting bent out of shape over the internet? That's not how it works!

Example:

If a 12 gauge wire can carry 40amps. 4 sets of them in parallel will carry 160amps. Right?

Fuses carry current just like wires do so if you take 4 40 amps fuses and wire them in parallel, you will be able to pass a total of 160amps over to the other side. The total output is much higher than what the individual fuses are rated for. Scotty305 said it best, "It's the total amount of copper that matters." Running both of those fuses in parallel give me a higher total amount so more current can pass through.

Another example if are running 100amps max through a wire rated for 100amps, that wire will get warm. If you add another wire capable of 50amps to that same wire, that original wire that was warm will cool off because you have added more cooper and more path of travel. You will now be able to run more current through those combined wires. Now that's how it works.

I could easily wire up a fuel pump and start to dead end the pressure with a needle valve to manually raise the current. Then watch the load through an amp meter till the fuses start blowing.

A simple look at the fuse holder will show you what you need to see. Page 27. Look at the main fuse holder where the 120amp fuse is. Above that is the open slot that has a slash on the fuse cover. That's where I added my 50 amp.

I forgot the original fuse was 120amps. I blew mine a long time ago while doing my 20b swap and couldn't find a replacement at the local auto parts store. So I just stuck a 100 amp in their and forgot to put back the original over that time period. Oops! :)

No you don't.



Are you sure he wasn't being sarcastic? And you need to stop talking now and go get some fire extinguishers to keep handy for the next time you decide to do any kind of wiring.

I removed the starter lead so y'all can more clearly see the plate on the fuse holder that makes them parallel.

Attachment 521198

Also I made a mistake on my previous explanation of my wiring. My 2 gauge wire from my alternator actually connects to the opposite side of that fuse block (and not battery/starter side like I thought). So I added the extra fuse to pass more current back over to battery side.

Um yes you do. Fuses carry current just like wires do. Two 40 amp wires in parallel will carry a 80amp total load. Fuses will do the same thing in parallel.

LOL no sarcasm house has been wired that way for almost a year till I finish and have the electrical company run the main feed. It's a one man project an why my 20b project isn't finished.

That is what I thought you'd say.

Did you even look at how the wire/wires are attached to the block at that point? They all connected together. On one side you have a single wire bridged to both link holders and on the other you have two wires, one connected to each link slot but still bridged together. In effect you have just one path not two. Mazda left that fusible link slot empty for a very good reason. Not because you could add a second link and magically increase the current carrying capacity of the circuit at a later date but because it would be redundant, it's not needed. So adding a second fusible link into it does nothing, zilch, nada. It in no way increases the load carrying capacity of the circuit. It's a total waste of time and money!

You would do more good if you'd just put back in the correct 120a fusible link.

As some one else pointed out, get back to us when 41 or more of those amps decides to go down one of those 40 amp wires or through one of those 40 amp fuses.