How many Alternator AMPs needed for big block FE
 

Hey guys

I am looking for an alternator for my 427FE and I found a period correct reman (correct C5AF casing), but it is only 55Amps and I am not sure it will be enough.

Here is what I am running (circut wise)

Earls foot box blowers (on relay)
FFR regular radiator fan (on relay)
Radiator push fans (on relay)
FFR Heater (newer kit with servo controlled temp)
FFR Wiper
MSD 6AL w/blaster II coil
Smiths mechanical gauges (except for tac, ammeter, fuel sender)
Seat Heaters (on relay)
Halogen headlights (not FFR supplied) on relay

Mechanical fuel pump
Mechanical water pump

Now I doubt I will ever be running them all at once, but do you think 55Amps is too low? I was thinking I should be looking at 95Amps or so. Don’t want the headlights to dim out etc.

Your thoughts? I wonder if I can put 95amp guts into a C5AF housing???

you can easely make the calculation yourself...... take the worst case and count all the amps you need from the "users"... don't count on any "reserve" from the batterie.... once in the "-" ,time go's fast...ourselfs ever had to abandon the Rally Ypres Belgium in the dark because of a mal functioning alternator... we had no fuel pressure anymore because of the headlights... and ofcourse some reserve is always welcome .... radio ??? ;)

you will be boarder line at best
 

Dlotz you are going to be right on the edge for this. A 65 amp would be better for what you are doing. You have to remember that you need to recharge the battery too. PAPERFORMANCE sell a nice 95 or 105 amp system with external voltage regulator for a cobra. The other problem is if you are running an AMP gauge. Over time you will melt the protector to the gauge and cook things. You are better to go with a Volt gauge. It is simple to line into the car. Another thing is getting a mega surge fuse to save the wiring harness from burning up if you have a major short in the wiring. I have the 120a system from PA. I have a little more electric curcuits than you but had a charging problem with the MSD system, ECU for the FI system, running coolant fans (3) charging the battery, and having lights on. Charging was only 13.4 volts. You want to see from 13.8-14.2 volts at 2000 rpms with all the power curcuits on. This will give a good charging also for the battery. At idle, 13.2-13.5 volts with the same power curcuits on. You will start to drain the battery with anything less. Get the fuseable charging cable also for the new Alt. Good luck Rick L.

I went with a 110A alternator. Between the Spal puller and two pushers, I was already down half of that. The price was about $30 more than 65A.

Never seems like enough when your sitting in traffic and it is 95 outside.

:D

I took a period correct external regulator alternator to the local mom and pop auto electrical rebuilder and had him upgrade it to 95 amps. The cost was less than $100. It's a total rebuild, the case looks as new, and the amperage is way up over stock. For the regulator I took a modern solid state high capacity regulator, and on EBay bought an old points type regulator with a repro Autolite cover. I took the Autolite cover off the old style regulator and put it on the solid state regulator. Just an idea that I thought may help you. Good luck.

The early Alternators, the later ones may be as well, use the same case and there are several companies that offer higher amperage internals to boost the output. If you want the correct date code, which it sounds as if you do, I would go for the same upgrade. I don't recall exactly, although I have rebuilt hundreds...I think the diode plate has more diodes. But that was 20+ years ago, and I've slept since then...maybe once.

What are the symptoms of an undercharging alt? My battery has never gone dead, but I've experienced a partial loss of spark on one or two cylinders (I use an MSD dist w/plug & play) on extended 2500/3000 RPM driving. Would an underperforming alternator have this effect? I was gonna replace my almost new plug wires.

ZOERA,

I doubt whether a bad alternator would show the symptoms you describe and still be able to start the car afterward. If the car starts to miss at speed, turn the fan override switch on. If there's a problem, the ammeter will show on the negative side and the missing problem will get worse. I would suspect a bad connection somewhere, a bad coil, or a bad MSD would more likely be the cause.

There's also the possibility of the opposite problem: an overcharging alternator. Put a voltmeter on the system and check that you've got 14.1-14.7V at 2000 rpm with a charged battery. Any more than that is not good.

And while you are at it, see how much voltage swing you have. A lot of fluctuation is bad. I would also check the distributor cap.

Just wanted to pipe in on the thread to get an opinion or two (got them, thanks). I'm gonna try new plug wires & plugs to start with. I doubt it's overcharging, the guage reads pretty steady. I don't think it's a dist problem, as the # 1 plug seems to be the main culprit, along with # 8 at times. Thanks guys.

My personal ethos on if an alternator is sized correctly is this.

Start Car -- get to an normal idle.
Turn on ALL electrical items ; headlights , on high beams, fog lamps , cooling fans(all) , heater blowers, satellite radio.

then with your Voltage gauge in the dash -- you should see 14.1 - 14.5v ===(you *are* running a voltage gauge versus a AMP meter hooked up to a pair of wires that could act as welding rods right >? ) :)

you also could measure between the + terminal on the ALT and a engine ground for the same V reading.

You can go as low as 13.9 with all that running, but a good solid 14.1-14.2 is best in my opinion.


Steve

Just noticed that my volt meter is only reading 12v with all my accessories on (cooling fan, heater blower and headlights). With the accessories off and engine running it reads 14.2v.

I checked the alternator and it's fine. The car has been sitting over the winter with the battery disconnected and I just started driving it again (2nd drive of the year). I have an optima battery and I trickle charged (2 amp) it for 20+ hours before I started driving it. The starts and drives just fine. The battery is 4+ years old.

Does this mean that my battery (volt meter reads 12.3v) is going bad (not holding full charge any more) or voltage regulator problem or that the alternator is under sized?

It's a 60 amp alternator with external voltage regulator and the total amp I'm running = cooling fan 19.5amp, heater blower 18amp, lights and gauges = ?amp. No electric fuel pump or special ignition system or fuel injection. The alternator amperage should be more than enough.

The low voltage reading has me slightly concerned after reading this thread or is this nothing to be concerned about.

Thanks in advance for any comments or help.

Mark

RELAX Mark
 

mmlee Mark you forgot the ignition systems, what are you running?? MSD??
First off the gauge in the car is only ball park for reading the charging and draining of the electrical system. I don't know if you have under size pulleys from March?? This will also slow down the alt for charging. You need to get a cheap voltmeter and use this to check the charging system. The battery should be ok. A load test at a gas station needs to be done. DON'T let the guy sell you a new battery or ALT. Alot of stores have bad testers that fail about 20% of all batterys that there is nothing wrong with them. The trickel charger is working just fine. Once you get your volt meter. you can do 3 easy tests
1 With the car off check the battery volts. Turn the lights on for about 10 second to level out and charging the battery just had. readings should be in the 12.30's to 12.50's this is a full charged battery
2 start car and let it run for a minute at idle. No acc to be on. record voltage of charging system. should be in the 13.7- 14.20's voltage readings.
3 load charging system with fans, lights and blower motor, check charging numbers, at idle. Should be a min of 12.7volts or higher
4 Rev the motor up to 2,000 rpms and check the voltage with the same load. You are looking for a 13.7 and higher.
If all these check out, the charging system is fine. The battery can only be tested with a load tester.
You have to remember that the ALT when the car is running is suppling power to the electrical of the car plus recharging the battery at the same time.
This is way Volt gauges are better than Amp gauges. Also the charging systems have gone from 6 volts to 18 volts and have 300 amp alt's. Enough to run your house.
Do the check out first then get back to us. The only failure could be a weak voltage regulator or a diode bridge going bad. Make sure connections are tight on battery, back of Alt, and voltage regulator. Check the grounds for being clean and tight. That's all there is for charging system check 101.:) Rick L.

You'll need 90 Amps to be comfortable, you have some real power consumers there, be sure your wiring is up to the individual circuit loads too.

Get one of these... http://cgi.ebay.com/KH109-Snap-On-MT...item3a5807ed52

A Voltmeter does not an Ampmeter make...;)

Ampmeters are the thing to see if your charging system is up to the job. You can lay this across your big wire from the Alt to see how much power it's producing, about the only thing your voltmeter dropping says is it's not enough.

Did some additional research on alternators and here's what I've learned, correct me if I'm wrong. 60 amp alternator only produces ~40 amps at 2000 rpm engine speed. The pulleys on the alternator are set to run at 1 1/2 ratio and that means the alternator is running at 3000 rpm. It will only produce 60 amp at 4000+ rpm engine speed (6000 rpm alternator speed) and who cruises at 4000 rpm!

I know for sure my alternator is rated at 60 amp. With my max load ~55amps that means I'm under powered. It makes sense that at full load my volt meter is dropping down to 12v and when I turn one of accessories off and reduce my amp load down to >30 amps then my volt meter reads back to 14v. If I have all my accessories on and cruising down the road that means I'm drawing some power from my battery and the alternator doesn't have enough juice to run the Cobra and charge my battery which means I might have a problem starting the Cobra if the battery is drained too much. The realities of city cruising for me is such that the cooling fan is running and in the northwest I've got my heater on at high speed and my lights are on cause it gets dark pretty early (can't wait for daylight savings time :MECOOL:), my wife's got the electric blanket plugged in :D and my TomTom is navigating my route.

It's time to upgrade to at least a 100 amp alternator which will produce ~65amps at 2000 rpm (engine speed) or 3000 rpm alternator speed.

Thanks for all the help.

Not to mention how long an alternator putting out 100% rated power all the time will last...

Make sure your output wire is big enough when you swap in the bigger alt. For 100A I'd run at least an 8ga fine strand wire. (6ga would be better)

I wanted to build alternators in traditional ford cases and offer them in 90-100AMP ranges, and call them --- get this. ..

AMP-RAGE! , from the Mustang Ranch.

-- ok, going to bed now.

Steve