checking alternator voltage\amperage?

[req 5,000+ posts]

Ok so i go this new alternator.

*its a Delco alt. at 2000rpm (idle) it puts out "160 amps" they claim, and its 14.4v i believe. i want to test this.

some pics;

sorry for the bad quality, they were taken with a camrea phone (not mine) and are the only pics ive taken at the moment. ill have more pics later with the metering.

so i was wondering how to measure the voltage and amperage *CORRECTLY* i have a DMM with all the little settings, a big circular knob in the middle. its yellow.

yea, looks like this one;

i was thinking id hook it up the the +\- but what settings do i use to test the voltage? and the amperage?

is it safe to test the amperage? (i think i can do the voltage with no problems, just double checking)

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[Apoc 10+ year member]

maybe if you could run it in to a local auto shop?

 

[req 5,000+ posts]

whats the point if i can just hook up the DMM to the +\ground and look at the reading =P

i know thats all there is to it, but i dont know what icon is for amperage, and\or if i need to fuse the DMM or somthing weird because it IS a ton of current- and if i hook it up wrong i bet it can break.

i can test voltage no problem though. (ill get a nice test CD and play a sweep and test the voltage to see if it drops as the DMM is touching the battery with the sub burps)

but the amperage im not sure of.

 

[n2audio 5,000+ posts]

you can't read high current with a dmm.

For voltage you just set it to Volts DC. Usually there will be a 20 range which is what you want to use. THen just touch the probes to the battery + and -. You might try it first w/the car off then with the car idling just to see how the voltage changes.

Then to learn a little more you can turn on your car's accessories 1 by 1 (lights, heater blower, stereo ) to see if the voltage comes back down. With an alt that big it shouldn't change much.

 

[req 5,000+ posts]

thats what i needed to know,

so how would i go about measuring high current?

i figured thats how it worked with a DMM for the voltage, but i was unsure about amperage.

 

[req 5,000+ posts]

anyone?

10chars

 

[maylar 10+ year member]

Measuring current isn't that hard, but applying 160 amps worth of load is gonna be a biatch.

Understand that the alternator's current rating means it will maintain its output voltage from no load all the way up to its max rated current. After that it either drops voltage or smokes...

With every light and accessory on in your car you'll be lucky to draw 60-80 amps.

To measure the current you need an ammeter in series with the power wire. A 200 amp ammeter won't be easy to find.

You can also use a shunt and your DMM. A shunt is a precision high current resistor. They're calibrated to have some amount of voltage (usually millivolts) across them at their rated current. Like these Simpson shunts:

http://www.simpsonelectric.com/pdf/webpdfg/Shunts.pdf

.. which will provide a low voltage that you can measure with your dmm.

 

[req 5,000+ posts]

Measuring current isn't that hard, but applying 160 amps worth of load is gonna be a biatch.
Understand that the alternator's current rating means it will maintain its output voltage from no load all the way up to its max rated current. After that it either drops voltage or smokes...

With every light and accessory on in your car you'll be lucky to draw 60-80 amps.

To measure the current you need an ammeter in series with the power wire. A 200 amp ammeter won't be easy to find.

You can also use a shunt and your DMM. A shunt is a precision high current resistor. They're calibrated to have some amount of voltage (usually millivolts) across them at their rated current. Like these Simpson shunts:

http://www.simpsonelectric.com/pdf/webpdfg/Shunts.pdf

.. which will provide a low voltage that you can measure with your dmm.

so basically i wont be able to do it safly in my garage in a few minutes?

****.

would a car shop (like pepboys) be able to do this?

 

[maylar 10+ year member]

They'll be able to test the alternator, but I doubt they can load it more than 50 amps or so. Why not just install the fukkin thing and see if it does what you want?

 

[deadboi77 10+ year member]

what i did is i bought a nice battery charger*not too cheap around $80-90*but it basicly tells you battery % ,volts and your Alt*plus its a charger for 3 different types of batteries..alil pricey but worth the cash..but what ive been tryin to figure out ive bought 2 H/O Alts one 175 amps and another just like Reg from the same place both Alts are perfect but i cant get my volts above 14.0..the highest it gets is around 13.8-13.6..ive done the Big 3 aswell and still its right around the same volts and sometimes it drops low high 12`s

 

[Apoc 10+ year member]

why dont you just run it into the auto shop, or better yet, call them before and see if they could do what you want?

 

[diminishedpower 10+ year member]

for the person that says he keeps getting 13.8's that could be that thats the the internal regulator is set to. you could get an external regulator from the people that you baught it from and raise it to 14, because like chev stock alts are set to 13.8 volts were as fords are 14.4. I could be wrong, but i know when i baught my ho alt i asked before i baught it what the internal regulator was set to before i baught it.

I could be wrong.