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General => General Chat => Topic started by: grumpydoc on January 14, 2013, 05:08:35 pm

Title: Agilent u8002a startup oddity
Post by: grumpydoc on January 14, 2013, 05:08:35 pm
Well, my u8002a turned up today so naturally I wanted to have a tinker and check its performance :)

However I noted something of an oddity when looking at it's turn on behaviour. Set at 24V driving a dummy load I get this:


With a rapid rise to about 8V, then much more slowly to the set voltage over about 80-100ms. Not what I expected and had me scratching my head a bit but I think the problem is my dummy load.

Not having a "proper" dummy load which will sink 3-5A at 30V for higher current stuff I wind up using a combination of high wattage vehicle headlamps as I have them lying around - in this case a single 75W 24V truck headlamp.

Initially the filament is cold and therefore low resistance so the voltage rises rapidly until the current limit kicks in at a little over 5A - 8V at 5A is enough to get the filament glowing so as its resistance rises the supply will be in CC mode and raise the voltage to keep the current at 5A. Finally once the bulb is up to temperature the current drops to about 2.8A1 and the voltage steadies off at 24V

Does this sound correct?

Guess I need a better dummy load!

[1] Truck electrical systems are at about 28V with the alternator running and the battery charging so 24V is under-running the lamp a little.