I still don't know how to find amperage on my shelf stereo.?

Question

I have one of those 5 cd-changer 200watt shelf stereo. On the back it says 170w, 125 volt, 60Hz. I was planning to use this stereo in my car with a DC to AC power inverter. But I need to find how many amp this stereo uses, so is there a way to find out since the information is not provided in the back of the stereo. Also, will these stereos use a lot of power on the start up? Because I heard people say that appliances with motor tend to use 3 times the wattage for start up. Thanks.

Answer 1

The formula for power is P=IE, where P is power and I is amperage and E is voltage. This is probably RMS voltage so the peak will be higher, divide the answer by 0.707

170=125i, that is 1.36A RMS at 125 volts. Amps need a voltage reference, you cannot compare amps at different voltages. The peak 1.9A.

Some devices use a bit more at start up to charge the capacitors in the power supply.

If you are running this in the lighter you may be able to get a slow-blow fuse for your lighter. This does not pose a fire hazard if the fuse has the same rating. The equipment will have a fuse to protect it.

Answer 2

170W with a perfect converter at 13.8v will be 12.3 A but it won't be a perfect converter. Minimum continuous current at full load will probably be nearer 15A. Inrush current on the original was probably more like 6A for an apparent 750W for a very short time as it charges the PSU capacitors, that's 54A at 13.8v.

This isn't a good idea. You are using DC to drive a converter to provide AC to a power supply that will invert and rectify it and provide DC. A 200W amp isn't a big deal and this is just a poor way to get one. Household electronics aren't specified for the ambient temperatures or the vibration that car equipment is subjected to.

Answer 3

Most DC to AC inverters are rated by the output power. As long as your inverter is rated at 200 watts or more you shouldn't have a problem.