How to measure the Electrical Capacity of my car?

[icehellion 10+ year member]

How do I measure the electrical capacity of my car?

I own a 1997 Mustang Cobra, Alternator is 130AMP and I installed an Optima Yellow Top.

I want to measure the normal draw of the car on the electrical system, so I know what I can install without having to upgrade electrical.

Currently I own (not installed) a PDX M-12 (100AMP) and a Boston GT2300 (100AMP). Know I know that unless Im cranking full blast, the amps should draw less. With that being said, I want to know if I'm at the end of my rope.

Thank You!

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[Moble Enclosurs 10+ year member]

You can measure voltage drop with the dmm on the batt, just don't try to measure amps with it or you'll blow a fuse or damage the dmm. Check the voltage with the car at idle, off, and then with each electrical component running/operating individually, and then all at the same time, such as the ac, lights(exterior/interior), windows, seat heaters, etc. Log all of the voltage drops down and that will give you a good idea of what happens when it's being ran normally. If your voltage goes below 11v, I would upgrade to the big three and possibly other components before drawing more of a current.

As far as amps go, you have to know the ah of the batt for reserve amperes/wattage, and also the capacity of the alternator and take 60% of that for usability of an aftermarket system.

All in all, if adding anything do the big three at the least. Will help a bit.

As far as your current setup, that is something research will take care of with the known information above. Find out how much current the amp8s) draw as well as anything being connected and take that from the 60% when figured out. If you do not know the batts ah, use 45 to be safe, 90 nominally.

There are formulas to figure everything out online likely, but I might have them at home as well, if I can find them I'll post em. May have to remind me though.....very busy right now2. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[maylar 10+ year member]

Your capacity is the rating of the alternator. How much of that gets used by the car depends on what you use - like being in Arizona you probably won't use heated seats and rear window defroster like I do here in CT. You could put a DC amp clamp meter on the alt wire and measure how much is being used by your car with lights etc but it's probably better to just ask the guys here what size alternator you need for the system you have.

 

[icehellion 10+ year member]

What do you mean by Battery ah?

 

[Fiendstolemyamp 10+ year member]

What do you mean by Battery ah?

Battery Amp-Hour rating.

 

[Moble Enclosurs 10+ year member]

Yes, correct. The ah rating, sometimes located on the battery itself, will give you an idea of what kind of reserve wattage that can be supplied to the system if the alternator is not enough. It is usually always recommended by a lot of people to upgrade all major components of the circuit when installing a new system. These major upgrades include, the pre-mentioned big 3, a new batt(not dry cell, but starter Batt), and a new alternator with a high ampere rating. Usually a high output alt is recommended.

The average standard vehicles reserve amps allow for around 900-1600 watts for the aftermarket system. This includes the use of front stage amplifiers and other components as well as the substage components. If your needed wattage falls within those values, the stock system may be ok for you. If it exceeds those values, I highly recommend an upgrade.

The main reason why? Not for extra power.......but for avoiding damaged components by trying to drive them too hard, using bass boost, increased gain settings, etc, when you may not know the current efficiency the components may have. A sub amp on an unknown load efficiency can give you either a subpar performance, or be more than what you expected, but best not to take a chance, and learn how to match up the electrical system with the components best as possible.

When an amp has subpar performance, it is usually do to it asking for more than what the alt/battery can supply. That can damage the alternator and other components as well if misused.

Hope that helps.

 

[Moble Enclosurs 10+ year member]

If you can view the link, this is a great video that explains most of it. I believe it has the formulas in there as well....i know it has a few.

 

[TheUnderFighter 10+ year member]

All in all, you'll probably be ok with that equipment. A big 3 upgrade is cheap, easy, and helps a lot. But you won't know if it's ok until you get it installed. That's a pretty good stock alt... almost twice as big as mine haha. Get the equipment installed, set your gains properly, and leave bass boost off. Then run your equipment with a DMM on the amp or battery terminals and see how bad your voltage drops. If it's going below 12, I'd consider an extra battery or turning some gains down.