Fencers should be sold on JOULES, not volts! Joules are what give the shock. A high voltage but low joule (joule=stored energy) charger is not going to keep calves in. If you look at your 3000v charger it probably only has 1 or less joule of energy storage.

You can generate a lot of volts rubbing fur on a rod but thats not going to hurt nor keep calves in.

Buy a fence charger with at least 6 joules of stored energy. This is what gives a shock and keeps cattle including calve inside a fence.

Volts are cheap, Joules are not. Good 6+ joule chargers cost a bit more but are worth it.

Some brands don't even list joules, just volts or miles, both of which are irrelevant. I use Gallagher 6 joule chargers. Never hook 120v to a fence!!!