I'm a high school teacher and have about 16 power supply that i want to upgrade. I repair them all but there is still a problem : they present, on a oscilloscope, ripples with a load and they don't present constant voltage when varying the load.
They are very simple construction : 120V to a VARIAC, VARIAC to a transformer (27v AC max), tansformer to a bridge rectifier that have a 1000uF capacitor in parallel with the "DC" output. They are built like tanks!
I tried to add parallel caps up to 10000uF, it helps for the ripples but that is not perfect, expecially with high current.
These power supply are rated 30v 5A VARIABLE "DC"
What can i do to remove the ripples and to regulate the variable output. I'm looking for an upgrade circuitto add in series that will do the job that i can put in the exixting box without too much mods.
In the old days we only power light bulbs, ceramic resistors and switches. Not we uses LED, transistors, buzzers and "delicate" components, arduino's. So these power supply are no more suitable for my teaching...