Understanding the math of electrical loads

So, how much current at 12 volts does a pair of 55 watt headlights consume? Algebra lets you turn the formula around to find the unknown. 110 watts = I  X  12 volts, whip it around you get 110 watts divided by 12 volts = 9.17 amps. If you have a battery rated at 65 amp/hour you can see the time at the above load of 9.17 amps to complete battery exhaustion would be about 7 hours. (Not counting the Puekert effect, which in simple form just means the heavier the current draw the lower the a/hr for the battery). Now comes some fun calculations, hp and watts, both units of work. Let's say some aftermarket, high performance starter motor manufacturer claims he has a 4 hp starter -- can you determine if this is reality? Math again. 1 hp = 746 watts, so 4 hp = 2984 watts divided by 10 volts (your 12 volt battery under the load of the starter) = 298.4 amps.

So, how much current at 12 volts does a pair of 55 watt headlights consume? Algebra lets you turn the formula around to find the unknown. 110 watts = I  X  12 volts, whip it around you get 110 watts divided by 12 volts = 9.17 amps. If you have a battery rated at 65 amp/hour you can see the time at the above load of 9.17 amps to complete battery exhaustion would be about 7 hours. (Not counting the Puekert effect, which in simple form just means the heavier the current draw the lower the a/hr for the battery). Now comes some fun calculations, hp and watts, both units of work. Let's say some aftermarket, high performance starter motor manufacturer claims he has a 4 hp starter -- can you determine if this is reality? Math again. 1 hp = 746 watts, so 4 hp = 2984 watts divided by 10 volts (your 12 volt battery under the load of the starter) = 298.4 amps.

Now, a little 15 lb Odyssey will lay down 680 amps for 5 seconds. If you want to blast your tunes for more than 5 seconds to be truly obnoxious, don't worry ,you can. That current draw is at peak output and that doesn't happen often or for a few milliseconds at a time. With the engine running and sending 15-20 amps back to the AGM battery, you're good to go. Another misconception is large amps burn out your tweeters, but believe it or not it is small amps that burn out the tweeter. When an underpowered amp is turned up so loud that the amp is clipping the wave form, you burn out the tweeter. Clipping is a distortion that muddies the sound and is caused by the amp running out of output voltage swing and clipping the top and bottom of the waveform. Looking at clipping on a scope, instead of seeing a nice completed sine wave the tops and bottoms are a horizontal line which is DC, no longer a frequency. What keeps a tweeter healthy is the fact that its voice coil is moving in and out 8000 to 20000 times a second and that motion keeps the voice coil from burning up due to the moving air keeping the voice coil in an acceptable temperature range. So when the underpowered amp clips at high settings the tweeter is seeing DC, so a lot of heat energy to dissipate but because it is DC, the little sucker isn't moving, so smoked. Radios in new cars no longer will clip because what you think is the volume control potentiometer is in reality just a shaft with a slotted light chopper wheel and as you turn up the volume, each time the light from a led passes through a slot to a light sensor on the other side of the wheel, it requests if you will the ramping up of volume but now can employ control circuitry that stops short of clipping, thus saving the speakers and warranty claims.

Now, a little 15 lb Odyssey will lay down 680 amps for 5 seconds. If you want to blast your tunes for more than 5 seconds to be truly obnoxious, don't worry ,you can. That current draw is at peak output and that doesn't happen often or for a few milliseconds at a time. With the engine running and sending 15-20 amps back to the AGM battery, you're good to go. Another misconception is large amps burn out your tweeters, but believe it or not it is small amps that burn out the tweeter. When an underpowered amp is turned up so loud that the amp is clipping the wave form, you burn out the tweeter. Clipping is a distortion that muddies the sound and is caused by the amp running out of output voltage swing and clipping the top and bottom of the waveform. Looking at clipping on a scope, instead of seeing a nice completed sine wave the tops and bottoms are a horizontal line which is DC, no longer a frequency. What keeps a tweeter healthy is the fact that its voice coil is moving in and out 8000 to 20000 times a second and that motion keeps the voice coil from burning up due to the moving air keeping the voice coil in an acceptable temperature range. So when the underpowered amp clips at high settings the tweeter is seeing DC, so a lot of heat energy to dissipate but because it is DC, the little sucker isn't moving, so smoked. Radios in new cars no longer will clip because what you think is the volume control potentiometer is in reality just a shaft with a slotted light chopper wheel and as you turn up the volume, each time the light from a led passes through a slot to a light sensor on the other side of the wheel, it requests if you will the ramping up of volume but now can employ control circuitry that stops short of clipping, thus saving the speakers and warranty claims.