What is the regulated voltage from an alternator?

BBShark

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What is the regulated voltage coming from an alternator (presumably the voltage the battery sees)? I also presume this is the same voltage to all other accessories (fuel pump, electric fans, etc.).
 
What type of alternator? One wire (which are internally regulated) or externally regulated? I'll agree that automotive have pretty much gone to a "one wire" setup and like GT6Steve said 13.8 Volts is about right.

If you need more VOLTS - you'll need to get something setup with an external regulator. Externally regulation can drive up to 14+ (even more with AGM?LiPO etc) and then taper off - but are used typically for RV/Marine applications (or other off grid).

But, if you have bigger loads (Amps) a one wire 100 Amp may do the job. Not sure what you're planning.

Cheers - Jim
 
So, kinda in the planning stages of wiring the car. I need to figure out wiring for EFI, fuel pump, radiator fans, etc. Things that the car never had originally. Does everything come (through a relay) to the battery? Not sure if I want to get an aftermarket harness or cut and splice the old one.

BTW, I'm using an alternator for a mid 90's chevy truck.
 
IIRC for years the Delco alternators had a segment of circuitry in the regulator that varied the output voltage depending on ambient temperature. This directed/allowed the alternator to charge at higher voltage (about 14.4 -14.6) during colder battery temps in winter times, but ramped down the charging voltage in the hot summer (to about 13.2v) to keep from cooking the battery.

I believe the later alternators (starting sometime in the nineties) had additional inputs from the ECM to modulate/soften the alternator output to keep from causing excessive instantaneous alternator loads (such as when turning on the rear window defroster or heated seats) on an idling engine, causing idle instability.

Which alternator model are you using?
 
I would think all the EFI wants from the chassis harness is 12v, Key-on and ground... The rest is self contained (sensors, injectors, etc... ) No? The one thing that I would think matters is to not hook up your 12v source at the alternator output post because of potential electrical noise

The "default" voltage output on the newer (DR44) GM alternators is supposedly 13.8v. When hooked up to an ECU they are controlled with a PWM signal to vary the voltage for vehicle/environment changes.
 
IIRC for years the Delco alternators had a segment of circuitry in the regulator that varied the output voltage depending on ambient temperature. This directed/allowed the alternator to charge at higher voltage (about 14.4 -14.6) during colder battery temps in winter times, but ramped down the charging voltage in the hot summer (to about 13.2v) to keep from cooking the battery.

I believe the later alternators (starting sometime in the nineties) had additional inputs from the ECM to modulate/soften the alternator output to keep from causing excessive instantaneous alternator loads (such as when turning on the rear window defroster or heated seats) on an idling engine, causing idle instability.

Which alternator model are you using?

I would think all the EFI wants from the chassis harness is 12v, Key-on and ground... The rest is self contained (sensors, injectors, etc... ) No? The one thing that I would think matters is to not hook up your 12v source at the alternator output post because of potential electrical noise

The "default" voltage output on the newer (DR44) GM alternators is supposedly 13.8v. When hooked up to an ECU they are controlled with a PWM signal to vary the voltage for vehicle/environment changes.

The alternator I am using is the same alternator that is in my 97 Tahoe. Sorry I don't know what type that is.

Just checked my Tahoe on a cold 30 degree morning. The battery voltage was 12.6V. With it started the voltage was ~14.7V (jumped around .2V). So even my old Tahoe must have some kind of output compensation as both of you describe.

So would you suggest running all added accessories (that were not original to the car) directly from key on power?
 
So would you suggest running all added accessories (that were not original to the car) directly from key on power?

If they have their own power switch, I'd go for it. I'd be sure and in-line fuse each one though. Like a Radio, Ham Radio, Spot Light, Fog Lights, etc. If there is no separate circuit (On-Off Switch) - or you forget to turn off a high load - Radiator Fans for example, when you shut the car down, you'll have a higher demand when cranking, more than just the starter. You'd be trying to crank with all that stuff on, and on a COLD morning, or after a long sit without charging, you might bog the battery down. Just thinking...

Cheers - Jim
 
My '72 was done many years ago, and I using the GM speed density computer from like a '88-91 vette #1227730 the alt is either a 10SI or 17SI....I forget, but it's same as a '79 Seville....bases on old design, but factory 108 amps witch is plenty to drag the spals and the a/c on high in FLORIDA....even with the C4 blower motor and heavy up wiring....I ran the power up/over the serp drive off a same year vette 88-91, to the fan relay on the top of the shroud.....through a 30 amp fuse....the rest of the wiring is pretty much stock except the main feed to the fuse block.....the charge wire going to the battery post on starter is stock OEM.....even though I use a voltmeter in the dash....

the computer takes 3 12 volt feeds, the one that feeds the 5 volt TTL regulator inside is wired to my anti theft system.....and my wiring uses the same color to wire much of the computer, WHY?? to totally baffle any hot shot kids thinking they going to drive it away....not happening....

Alts typically do as above 14.9 on the highest of high I have ever measured, and that was a new one on a FORD, and yes it was cold out in the lo 30's..... but the typical charge/maintenance volts when running is 13.3 or so......at the battery terminals....with car off/parked the battery should not go lower than 12.7 after a few daze.....

ONE of the computer hot wires is hot to the injectors, the other is controlling memory the one to the 5 volt is my anti theft hot...and is also wired to the switched hot/orange? wire off the ignition switch....through the control relay for that voltage.....

;)
 
So would you suggest running all added accessories (that were not original to the car) directly from key on power?

You have basically two ignition sources-

One is power on acc and ignition but NOT while the starter is engaged

The other is not powered on acc but powered on ignition AND start.

So connecting to the acc-ignition for your injectors would not be a great
idea...

I have also added a 'timed' circuit- used a Hella relay- as so the electric fans and AC woun't turn on till the car has been running for about 8-10sec.

Here's a diagram of power off the ignition switch-this is for a 71-for many years it was the same...


starter%20wires_zpspybudkf7.png



I've used several of these through out my car to add on accessories- it's a combo relay and fuseblock

relaysocket_zps828e9009.jpg

DSCN6014_zpsdxwkha8g.jpg


Here's a rack of them controlling-starter-fuel pump- injectors-coils-ECU-Vintage Air-lights-etc...

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Even using them for the headlights & electric headlight motors-

16621132373_25f347e1c3_k.jpg
 
Good stuff. Thanks.

On my C4, I can hear the fuel pump as soon as the key is turned to "ON" before the key is turned to "Start". Is that what is happening with the two "IGN" relays in your diagram?
 
Good stuff. Thanks.

On my C4, I can hear the fuel pump as soon as the key is turned to "ON" before the key is turned to "Start". Is that what is happening with the two "IGN" relays in your diagram?

My ECU ( Megasquirt MS3 Pro) bumps the fuel pump for a couple of seconds as the key is turned to ignition- shuts it off till the engine hits (programmable) 275 RPM- then turns it on. For another safety measure I have a Ford Inertial/rollover switch which will shut the power off to the pump in case something bad happens-

Mounted in the back compartment-

16398743430_e27098f431_k.jpg

I have a 'blown' fuse (LED type) that lights and tells me the inertia /rollover switch has been tripped.

16399901189_2f87dbe4d2_k.jpg

it's a really neat switch- used for years on Ford Mustangs/Taurus 90-00s And can buy brand new from Summit for about $30.

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