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Old 06-13-2009, 11:47 AM   #1 (permalink)
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Testing amperage draw - 1997 Paseo

Since I've been looking into going alternatorless, I wanted to do some testing to see how much amperage things pull on the Paseo. The first test was the biggest amperage puller I can think of, the starter. The initial setup is the picture below. I'm going to need something a bit more permanent to use while driving down the road.



Anyway, the starter pulls a very quick 125A (for maybe a half second) and quickly settles to 100A. I pulled my spark plug wires to do the test. I also used the 200A ammeter from Ben Nelson I got for my electric riding lawn mower. I was worried (and rightly so) that using a standard 60A automotive gauge might fry it.

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Old 06-13-2009, 01:41 PM   #2 (permalink)
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Ohm's Law

Daox,does the owner's manual list all the major electrical loads in Watts? If so,you could just divide everything by 12-Volts,and the current(Amps ) would fall out.
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Old 06-13-2009, 03:30 PM   #3 (permalink)
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Quite true aerohead. I haven't dug through the service manual.

More testing shows:
ign off - .1A
ign to Acc - .22A
ign on (engine off) - 2.15A

The last number was really the one I was after. If I go alternatorless, about half of my trip is with the engine off. So, if the car uses (the average guess of) 25A, I'll really only be using ~13A since my engine is off half the time. This should easily allow me to use a group 24 marine battery that I already have laying around without discharging it too much on my daily commute.

I did also go for a short spin around the block testing headlights and fan since that is really the only things I use in the car besides the stereo which pulls very little power. Unfortunately, the 200A gauge is not nearly accurate enough to get any specific numbers.
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Old 06-13-2009, 04:09 PM   #4 (permalink)
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loads

Quote:
Originally Posted by Daox View Post
Quite true aerohead. I haven't dug through the service manual.

More testing shows:
ign off - .1A
ign to Acc - .22A
ign on (engine off) - 2.15A

The last number was really the one I was after. If I go alternatorless, about half of my trip is with the engine off. So, if the car uses (the average guess of) 25A, I'll really only be using ~13A since my engine is off half the time. This should easily allow me to use a group 24 marine battery that I already have laying around without discharging it too much on my daily commute.

I did also go for a short spin around the block testing headlights and fan since that is really the only things I use in the car besides the stereo which pulls very little power. Unfortunately, the 200A gauge is not nearly accurate enough to get any specific numbers.
Since 746 Watts is equivalent to a horsepower,you may be able to normalize your electric loads in terms of HP saved,and use relationships of rolling resistance and aero loads to help extrapolate savings ( like maybe the alternator delete would be equivalent to removing sideview mirrors or adding LRR tires).This would make it easier for everyone to build their savings on paper without spending money until the paper said to do it.
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Old 06-14-2009, 10:50 PM   #5 (permalink)
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I borrowed an inductive ammeter and took some readings. The car was warmed up so the O2 sensor heaters wouldn't have to run. I recorded the following:

Code:
Engine off, 12.6V:
0.3A - key off
0.5A - Acc
4.7A - key On
10A - key on, corner lights on, engine off
19.3A - headlights on

Lights out, car stationary, 13.87V:
17.4A engine on, 4000 RPM
16.0A engine on,  700 RPM
The radiator fans, blower motor, radio, wipers, etc were off during the test.

So I would say 20A for a car going down the road, +5A for corner lights (which I recommend despite the MPG hit), +15A for headlights.

Btw, I had to move the ammeter from the battery to the alternator to get any meaningful readings with the engine running.


An alternator + belt is 50% efficient, a car converts gas to torque with 30% efficiency, and gasoline has 121MJ/gal. So an alternator making 20A at 13.8V = .99MJ/hr is costing you 0.05gal/hr. At 45mph (trip average), an alternator delete would turn your 40mpg into 41.9mpg. That's worth doing if you can live with the drawbacks (limited range, have to plug in the car at night, cost of deep-cycle batteries). But don't forget to sign your house up for renewable electricity first, or all you're doing is replacing a 15% efficient source of electricty with a 30% efficient one.

Also, the energy savings are smaller if your car already has a high-efficiency alternator - 70-80% efficiency units are available.
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Old 06-15-2009, 12:01 AM   #6 (permalink)
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Good info, guys. Since the topic of going alternator-optional comes up a LOT, it's important to have good data so people can make good decisions. Examples of electrical loads for various cars is gold.
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Old 06-17-2009, 02:07 PM   #7 (permalink)
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Quote:
I was worried ... that using a standard 60A automotive gauge might fry it.
Quote:
Originally Posted by Daox View Post
Unfortunately, the 200A gauge is not nearly accurate enough to get any specific numbers.
So here's what you do: bump start the engine to get it going, then read from the 60A gauge with its better resolution.

Would mean parking on a hill, attaching the gauge and then roll starting, but ... the numbers! Science will thank you for getting some accurate numbers!
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Old 06-17-2009, 02:27 PM   #8 (permalink)
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Here's another thought:

Put a pair of multimeters in parallel and set that pair up in series with your load. They're usually rated 10A, and fused for self preservation.

So you'd be good for 20A total, each meter reading up to 10A, no?
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Old 06-17-2009, 02:31 PM   #9 (permalink)
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Yup, that should work. Let me know what you find out.

I'll have to retest mine now that I have the alternator disable switch installed.
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Old 06-22-2009, 01:22 PM   #10 (permalink)
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I found out: two 10A ammeters in parallel worked in a quickie bench test - each reads half the total current draw.

But I'd need a third one to measure voltage to calculate watts!

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