TU56/TC11 restoration - VARIAC question

dvcorbin wrote: As long as there is an adjustable current limit, all you have to do is set the voltage to the rated capacitor voltage (or perhaps 10-20% higher, but some people dispute that, even though the manufacturer forms the capacitor to a much higher voltage), and set the current limit such that the capacitor cannot dissipate enough power to be damaged. This can be computed based on the rated leakage current. There is no need to programmatically control the supply voltage; the current limit will cause the voltage to ramp up at whatever rate maintains that current. Once the voltage reaches the voltage limit, watch the actual current being drawn. It should decline to below the rated leakage current. If the capacitor is in good condition, the initial rampup may occur fairly quickly, i.e., a few minutes. If it needs a lot of reforming, it may take hours. I wouldn't normally expect a capacitor that took more than a few hours to succeed at reforming. We used voltage programming on the PDP-1 project for two reasons, neither of which is strictly necessary. 1) The allowable reformation current is higher at lower voltages, e.g., 2V @ 30mA is the same power as 4V @ 15mA. However, setting the current limit as appropriate at a higher voltage, it will still reform properly unless the capacitor is in very poor condition, in which case it's probably not recoverable anyhow. 2) We wanted to log a lot of data on the reformation process. Although it's not clear that we've learned too much new or useful information from the logs. Eric