newb, multimeter test hu ground

I am not the smartest man, but im also not the dumbest. I got a Multimeter the other day to test my ground for my HU. Kinda cheap, 25$ @ Homedepot. I put it on the 200 scale and when I tested it came up with .4 or .3 assuming I did the test right. Is that too high? should it be exactly zero? and also i see a bunch of BB and CC ads that say like 1000 watts sub & amp package for like 120$. What is up with that? How can you reallly tell how powerful a package is?

You'll rarely if ever see a 0 ohm except if probes are side by side on the same plane.

0.3 is tolerable in a vehicle. You can see up to 25 ohms between battery post negative and the firewall during the crank cycle!

Amp choice: this horse has been so beaten to death that the bones have been pulverized to dust, so I won't even start. Read this: How to choose an amplifier

After you read that, use some math.

Here's what I usually do:

((Amp fuse/2) ^2 x impedance) / 2

So it goes something like this. Let's say you have a 15 amp fuse in the amp and you want to use a 4 ohm sub.

((15/2) ^2 x 4) / 2

15/2 = 7.5

7.5 ^2 = 7.5 X 7.5 = 56.25

56.25 x 4 = 225

225 / 2 = 112 watts

So, if the amp has a 15 amp fuse and is connected to a 4 ohm sub, you can expect an average of 112 watts. This is at 50% efficiency because the rest is lost in heat.

Works for me!

Awsome info, thanks. Just now I went and tested it again but I disconected it and there was still .3 reading. My HU has gatta be grounded out somewhere else. The bracket is grounded you think that could be doing it?

What kind of a problem are you having?

With the meter set to the same resistance setting you've been using, touch the probes together and hold in place until the reading steadies.  What resistance does it read?  This is the internal resistance of the meter.  Subtract this internal resistance from all measurements that you take with the meter.

I have a meter that consistently reads 0.8 ohms internal resistance.  When I check, say, a 2.5 ohm resistor I should get 3.3 ohms resistance.  And if I check continuity, 0.8 ohms is perfect.  If I get 1.0 ohm reading, the actual resistance is 0.2 ohms.  Got that?

stevdart wrote:

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With the meter set to the same resistance setting you've been using, touch the probes together and hold in place until the reading steadies.  What resistance does it read?  This is the internal resistance of the meter.  Subtract this internal resistance from all measurements that you take with the meter.

I have a meter that consistently reads 0.8 ohms internal resistance.  When I check, say, a 2.5 ohm resistor I should get 3.3 ohms resistance.  And if I check continuity, 0.8 ohms is perfect.  If I get 1.0 ohm reading, the actual resistance is 0.2 ohms.  Got that?

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