Anybody know our altenator max output? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-08-2007, 12:38 AM   #1
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Default Anybody know our altenator max output?

While having the WI pump engaged ie more than 4 psi i am noticing my voltage dithers from 14 to 13 volts kind of rythmically. So i wonder if my alternator is going out or maybe i am just outpacing the feed what do you guys think Every ground is right and for the most part i get 14 volts but just under laod like that it pulses down to 13 so thoughts anybody?
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Old 07-08-2007, 01:09 AM   #2
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Mine usually stays at about 15.3v, never payed too much attention under load.
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Old 07-08-2007, 01:10 AM   #3
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Belt? Check resistance of the - bat cable. Full Feild the Alt and see what the max output of it is.
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Old 07-08-2007, 01:18 AM   #4
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Belt is tight and new less than 2K miles, what is full feild the alternator, you mean put it on a laod tester If i knew the suposed output say if where 55 amps then i could do the math and figure out if i have enough voltage supply if the alternator is working as it should. considering my pump lights led and solenoid take 84 watts alltogether no idea what the coils take the FP should take another 100 wats, then cooling fans maybe another 60-70 watts. that quickly adds up to more than 300 watts while running. wich given 12 volts should equate to 25 amps well within what most other alternators run. but then i also have varius other peripherals. wich might net 100 wats totall while running. Hence i think maybe the alternator might have worn brushes and since ours are not rebuildable that i can see a new one would be the only cure.
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Old 07-08-2007, 01:34 AM   #5
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Looks like autozone and oreilly are getting $130 for a reman alternator.
I have no idea what the output for those alternators is though.
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Old 07-08-2007, 01:35 AM   #6
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A load tester can full feild it or if you know the wiring diagram of your alt all you need to do is ground either point A... or point B.

Full Field the Alternator

An alternator can be tested quite easily by full fielding it. This means to activate the field with full battery voltage and check for high alternator output. The full field test should only be done momentarily since overcharge will occur otherwise.

"To full field a P-type alternator, (most hot rated alternators are P-type), disconnect the wire connecting the field terminal to the regulator. Now connect the alternator field wire briefly to battery voltage. Expect to get a spark or two. You should be able to hear the engine load down as the alternator starts charging. "

a bit of google searching and your good to go... more or less you turn off the voltage regulator and it pumps out 100% of what it can... dont do it for more then 5-10 seconds else you can fry **** good... also when doing this protect all electrical systems as needed. More or less the ghetto mans way of testing an alternator if your shop doesnt have the $$$ for a nice alt load tester.
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Old 07-08-2007, 01:42 AM   #7
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Maybe you need to get autoshit to test it for you. They can do that right. I know they do starters.
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Old 07-08-2007, 01:43 AM   #8
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it sure doesnt i dont think i wana chance frying MS i might look abit more i still push 13 easy but i wanna make sure it wont get worse. cause if it will i will consider a better tougher alternator. or voltage regulator combo.
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Old 07-08-2007, 01:48 AM   #9
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Quote:
Originally Posted by magnamx-5 View Post
it sure doesnt i dont think i wana chance frying MS i might look abit more i still push 13 easy but i wanna make sure it wont get worse. cause if it will i will consider a better tougher alternator. or voltage regulator combo.
The way we make sure we dont fry **** at school is use a 2ndary battery... but yeah take it to autozone or **** drive to your local shop and be like "can you test the full output of my alt" and they will do it for free in hopes you pay them to replace it if it is bad...
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Old 07-08-2007, 07:26 AM   #10
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they can test full output i had it checked when it was out but i think they only spun it for 14 volts. might try that full laod though.
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Old 10-11-2007, 02:26 PM   #11
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Well i found out it is 60 amps for a manual tranny car and 65 for a auto so i gues i will look to an upgrade/.
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Old 10-11-2007, 02:58 PM   #12
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I get ~14V, my **** runs fine.... I'd say voltage drop isnt really a problem until it goes below 11-10V
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Old 10-11-2007, 09:43 PM   #13
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I dunno dude coils like a good power supply. Anywho my stocker is abit fubarred, or i am pulling to much. Cause WI pump at 12-15 amps, fans at 10 or so amps, my Fuel pump 8-10 amps, headlights 10 amps. And i am still getting a voltage drop even with the lights off.
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Old 10-11-2007, 11:53 PM   #14
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Sometimes the voltage drop is just because of the voltage regulator not being quick enough to generate the needed field current to increase the output of the alternator. These alternators seem to have very slow reacting regulators, plus coupled with age, and you get my point.
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Old 10-12-2007, 12:19 AM   #15
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Hey magna, I would also check the battery out really good and make sure it's adequate in size and is working properly. Have it tested when you test the alternator. A failing battery can cause simmilar symptoms as the alternator isn't designed to run the cars electrical system, it's designed to charge the battery that runs the electrical system. I just got my battery in my car tested today just to be sure it's good for this winter. "GL Man"
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Old 10-12-2007, 01:04 AM   #16
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anyone with a 1.8 car--if you wouldn't mind, please open your owner's manual towards the back and see what your alternator's rated for. my 91's manual lists 60 amps manual and 65a slushbox. Curious if a 1.8 alternator swap is worthwhile. I'm sure to be drawing hella more current than stock.
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Old 10-12-2007, 01:57 AM   #17
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Sayeth the Haynes manual:

90-93 = 60A manual, 65A auto
94-97 = 65A manual, 70A auto

Not really much of a meaningful difference.

When you see rapid fluctuations in voltage, suspect the wiring. It's the battery's job to deal with large demand swings- the alternator is just there to keep the battery charged.

Where is the pump supplied from, for instance? On my car, a dedicated wire runs up direct from the battery to supply the WI system. No fluctuations. The fans, by contrast, do cause a noticeable drop in system voltage when I switch them on- but they're using the stock factory wiring.
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Old 10-12-2007, 02:20 AM   #18
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well, certainly not huge differences. None the less, with this data, I will definately procure a 1.8 auto alternator for my engine swap project.
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Old 10-12-2007, 10:51 AM   #19
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Ben-so a 1.8 auto alt. will fit in directly into manual cars or do i need belt as well? id like to do this in the future for peace of mind
thanks
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Old 10-12-2007, 11:02 AM   #20
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well I've never seen alternate belt part numbers
1.6-->1.8 conversion wouldn't be a direct swap, but definately would be possible.

I wouldn't just go get a new alternator for 5A more potential though. In my case, it's 10A, and I have to fit an alternator to the motor anyway.

You can also have alternators rewound for higher output. I've had that done a few times at a local shop.
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