Total amps drawn (Page 1/3)
cvxjet OCT 25, 12:27 PM
I am working on a project on my Fiero and am having trouble calculating the total amps drawn by my car; I have a 8 SE V6 with basically no options (No PW/PDL/PM or A/C).....So what would the amp draw be for a 2.8 V6 running, with heater fan on #2, headlights on high beam and the wipers running? If I just add up all of the fuse numbers I get somewhere around 160 amps but I seriously doubt my electrical system is using that much at any moment......

Does anyone here have a good estimate of the number of amps drawn?
Rexgirl OCT 25, 02:53 PM
The easiest way would be to read the current flow directly with an ammeter on the red fuse link wires connected to the battery junction terminal. Depending on how you measure, collectively or individually, you may find a clamp-type ammeter will be necessary since your total draw will be roughly around 30 amps (that is only a guess). Since I've only used direct current measurement in my electronic work, I'm not sure if clamp style meters are influenced by nearby magnetic fields that may affect their accuracy. Anyone?
Gall757 OCT 25, 03:18 PM

quote
Originally posted by cvxjet:

Does anyone here have a good estimate of the number of amps drawn?



The problem is more difficult as the car gets older.

The Ogre's cave has a page on this subject that is helpful. (Electrical/General/Electric Motors)

Example:

Radiator Fan Motor is rated at 150 Watts and uses 10-11 Amps about 14 Volts normally. But have a mess up ground and now get 10 volt, motor uses 15 amp. Really bad ground? Say 7 volts? Motor uses nearly 21.5 amps! That will blow the motor and/or relay to controls the motor.

[This message has been edited by Gall757 (edited 10-25-2019).]

theogre OCT 25, 09:21 PM
See my Cave, Watt Story gives some more examples etc.

Fuse amp rating is Not what amps draw by whatever.
Fuse are to stop Battery and Alt dumping Hundreds of Amps in a short circuit frying the cars.

Actual HL draw depends just what HL are installed. "Max Legal" High Beam on paper w/ engine running is typical 65w/14v=4.7a each, x2 = 9.4a for 2 bulbs but many people have illegal HL pulling more power. But Unless you drive on roads w/ very little traffic at night, you can't use High Beam often in most areas. Example: PA's NE Extension to PA Turnpike is hard to use HB in many sections now unless maybe 2 to 4 am.

Best and simple is using DC Amp Clamp to see Amp Draw without disconnect/cutting.
Warning: Most meters w/o that feature only handles 10 to 20a on a builtin shut and many cheap ones have big problem handling even that. IOW If you have a shut meter in circuit and turn on a few things you better hope has a fuse or you likely will melt the meter, the probes or catch fire.
Yes we use them for cars but mostly to look for Battery Leaches and most are well under 5a.

Why do you think you need this?
Example: To save weight using smaller alt and/or battery?

Size of either is not really a function power drawn by a car.
For most cars...
"Size" of battery is about Starter the car in all kinds of weather, how fast does ECM etc Standby Power kill the battery when parked and how long battery runs a car w/ dead alt.
"Size" of Alt is directly related to amp draw but also more. Big one is Old SI alts are way less efficient to make power vs. CS-130 w/ around same size and weight.

But even that in very general info.
Often SI and others don't make full power all the time. IOW the 95a or whatever is advertise spec for an alt is only Peak Power.
So If you run PW at idle and alt can't make enough, the battery delivers that power for the seconds you push the button.

Unlike many newer cars w/ smallest alts and often bigger batteries then Fiero and others to pad MPG numbers to US EPA and other Governments around the world. But that's for a whole other topic.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

cvxjet OCT 25, 11:50 PM
I moved the battery up front- but didn't like the "Safety" of having a Welding-size cable (Always energized) running UNDER the car next to the FUEL tank, So I installed a Ford-style separate starter solenoid that powers the big starter cable only during start, and then a AWG 8 wire to run the actual car- I ran that wire in with the Negative battery-to-block cable in Scd 40 tubing...But I have planned on installing a large fuse in that AWG 8 wire in case of "High-centering" so that the wire shorts and immediately blows the fuse shutting off power.

I have one of those really BIG fuse holders, but am not sure what size fuse to use- 30, 40, 50, 60- maybe even 100.......Just trying to set it up so I don't become famous as the guy who BLEW-UP his Fiero- with him in it...........(I know this isn't the perfect set-up...but the best I could figure out)

I wanted to cover the extreme power situation- Driving at night, in the rain on a backroad- high beams on, heater fan on 2, and wipers going full speed......(plus the stupid rad fan going also.....)
dear1700 OCT 26, 03:33 AM
You could always runs pvc style conduit underneath your vehicle. Also if you have a good battery to chassis ground, you can then ground the engine to chassis, without need for long negative cable.
olejoedad OCT 26, 10:14 AM
The fuse needs to be the proper rating for the wire.
Ampacity takes into account the wire gage and the length of the run.
cvxjet OCT 26, 02:10 PM
First- I ran the wires front to rear in Schedule 40 plastic conduit...But that is not going to protect the wires in a serious high-center situation.

Second, I am not interested in having a fuse to "protect the wire from burning up under normal load"- I am interested in having a fuse that has the proper capacity for all the car's needs- but considering that, is as low as possible to "pop" when an accident occurs if there is a short in the system.

I can get a Maxi fuse in 40 up to 120 amp range. Maybe I will have to buy an assortment and then try from small to big until one survives running everything. I know a lot of the systems have run and SURGE power levels......

I have seen some numbers; Headlights on high beam just under 10 A....Rad fan is at 11 A....What does the V6 draw during normal running (Computer, ignition, Fuel pump and injectors) and what about the heater fan? And the wipers? (I don't have the trunk fan at the moment but may add it in a modified installation) I see on Ogre's page that he estimated 32-33 amps PLUS some additions- maybe 60 A would be enough...?

[This message has been edited by cvxjet (edited 10-26-2019).]

Gall757 OCT 27, 11:50 AM
You are worried about an accident that is so rare, that there is no research to point to and say "YES!...use a 60 amp. fuse!" So whatever your comfort level is, go for it, but my lawyer would advise against giving you an absolute number....
olejoedad OCT 27, 12:14 PM

quote
Originally posted by cvxjet:

(snip)

Second, I am not interested in having a fuse to "protect the wire from burning up under normal load"- I am interested in having a fuse that has the proper capacity for all the car's needs- but considering that, is as low as possible to "pop" when an accident occurs if there is a short in the system.




Have you thought about that statement?

Protecting the wire is why the fuse is sized properly.
A properly sized fuse will deliver the desired protection in an accident, and protect the wire from damage if the amp draw from your normal load is too high.
Oversizing the fuse, with too much amp draw from the normal load, will burn your car down just as easily as a dead short with no fuse protection.
If your amp draw is too high under normal load, you need to upsize the wire, and provide proper fusing.