Voltage variation when loaded?

Question

When i draw current through a load from my DC battery, a voltmeter shows a drop across the battery terminals when compared to a 'no load' condition. The more the current drawn, the greater the voltage drop. why is this?

Answer 1

Because the battery has an internal resistance.

Actually I recently learned that electronic devices (iPod, pocketPCs, cell phones) draw current from batteries in short spike of high current instead of a nice continuous draw as for resistive devices (e.g. radio, flashlights). So if a battery has high internal resistance, it will deplete itself much faster because very soon this high resistance will cause the voltage to drop below nominal. What happens is the device will say the battery is empty when in reality it still has plenty of charge but not enough to supply the high amps required.

Bottom line, when shopping for batteries for electronic toys, look for internal resistance spec and choose the lowest one.

Answer 2

Because the battery is loaded down by the current draw. The ideal condition is that the battery stay the same voltage under all loads, but the chemistry of the battery will dictate how much current it can possibly put out. If you draw more current than the battery will put out, the voltage will drop.

Answer 3

Volt meter across a battery tells u almost nothing. With a load it shows u have a poor connection or the battery is getting old and unable to carry the load.

Answer 4

You need to remember there is nothing that is perfect. No conductor without resistance, no insulator without leakage, so it only goes to follow there can be no Voltage Source without resistance.