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SMD VM-1 LED Volt Meter! (its back!) Pics/short vid pg. 19 (new update pg 35)


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Having a second VM-1 can be a great tool. By plugging one into the 12V (lighter) outlet, you will be reading the voltage at battery/alternator basically because there is very little current flowing to the 12V lighter outlet. Voltage drop is calcuated by this formula Amps X Ohms = Volts, thus is you basically have zero amps flowing, you can not have a voltage drop, and thus you will be reading the battery/alternator voltage. HOWEVER, voltage AT your amplifier(s) can be a totally different thing. Huge currents can flow to the amplifier(s), even though the resistance of the wiring is small, it will still cause a voltage drop. I connected one VM-1 to my lighter, and one right at the amplifier's connections by lengthing the wires going to the VM-1 (you can make these as long as you like without causing any issues or voiding your warranty). With music and subwoofers, I see 0.8V - 1.2V lower at the amplifier. On the dyno I'm seeing 1.6V drop at the amplifier. 1/0 AWG is good, but it ain't that good. I am pretty confident that most people who try this will be very surprised how much voltage drop at the amplifier they have. I challange you to measure yours and post your results.

By having multiple units you can check your system like this, and try to correct it by using better distribution/fuses and wiring.

If you are wondering, the basic formula for how much more power your amplifier would make with different battery voltage is

((Higher battery voltage / lower battery voltage) ^2 ) x how much power you made at the lower voltage

Example, I just dyno'd the T2500.1bdcp in my Jeep. It did 2365 watts into 1 ohm with the battery voltage AT THE AMP at 12.24Vdc. If I could keep 12.6Vdc at the amplifier, the amp should dyno this much power:

((12.6V / 12.24V) ^2 x 2365 watts) This works out to 2506 watts at 12.6V. Rockford rates their power at 14.4V so, clearly this amplifier makes rated power @ 1 ohm and then some.

If by some act of God I could keep 13.8V at the amplifier I could get that amp to put out:

((13.8V / 12.24V) ^2 x 2365 watts) This works out to 3006 watts.

Now this is only true if you have an amplifier with an unregulated power supply. Some amplifiers, like JL slash series for instance, have fully regulated supplies so this math doesn't apply. Those amplifiers will put out the same power reguardless of the battery voltage within a resonable range.

Edited by Tony D
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  • 3 weeks later...

Hey Steve, I'm finally getting around to my install and I need to chop the case on VM to fit the dash. I was wondering if I could get an extra case and what the cost would be, thanks in advance

2011 Chrysler 200 S (Black on Black on Black w/ black trim) :)

Changing all the time but, for now.....

*Coming Soon*

80sq ft. SS Damp Pro (INSTALLED)

36sq ft. SS Luxury Liner (INSTALLED)

Big 3 (RF 0 Gauge)

All RF power wire, speaker wire, RCA's

RF T3 6.5" components (2 sets) have

RF T800-4 ad (mids & highs)

XS Power D925

XS Power D3400 have

still undecided on sub/sub amp

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  • 1 month later...

Having a second VM-1 can be a great tool. By plugging one into the 12V (lighter) outlet, you will be reading the voltage at battery/alternator basically because there is very little current flowing to the 12V lighter outlet. Voltage drop is calcuated by this formula Amps X Ohms = Volts, thus is you basically have zero amps flowing, you can not have a voltage drop, and thus you will be reading the battery/alternator voltage. HOWEVER, voltage AT your amplifier(s) can be a totally different thing. Huge currents can flow to the amplifier(s), even though the resistance of the wiring is small, it will still cause a voltage drop. I connected one VM-1 to my lighter, and one right at the amplifier's connections by lengthing the wires going to the VM-1 (you can make these as long as you like without causing any issues or voiding your warranty). With music and subwoofers, I see 0.8V - 1.2V lower at the amplifier. On the dyno I'm seeing 1.6V drop at the amplifier. 1/0 AWG is good, but it ain't that good. I am pretty confident that most people who try this will be very surprised how much voltage drop at the amplifier they have. I challange you to measure yours and post your results.

By having multiple units you can check your system like this, and try to correct it by using better distribution/fuses and wiring.

If you are wondering, the basic formula for how much more power your amplifier would make with different battery voltage is

((Higher battery voltage / lower battery voltage) ^2 ) x how much power you made at the lower voltage

Example, I just dyno'd the T2500.1bdcp in my Jeep. It did 2365 watts into 1 ohm with the battery voltage AT THE AMP at 12.24Vdc. If I could keep 12.6Vdc at the amplifier, the amp should dyno this much power:

((12.6V / 12.24V) ^2 x 2365 watts) This works out to 2506 watts at 12.6V. Rockford rates their power at 14.4V so, clearly this amplifier makes rated power @ 1 ohm and then some.

If by some act of God I could keep 13.8V at the amplifier I could get that amp to put out:

((13.8V / 12.24V) ^2 x 2365 watts) This works out to 3006 watts.

Now this is only true if you have an amplifier with an unregulated power supply. Some amplifiers, like JL slash series for instance, have fully regulated supplies so this math doesn't apply. Those amplifiers will put out the same power reguardless of the battery voltage within a resonable range.

I bought one recently but it has lighter adapter is the white wire remote turn on? I have a NS1 do I hook it to any one of the sets of power/ground? or to a battery in the back closest to the amp?

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