Power supply and variac

[ozzie34231]

Hi All,
The electronics dummy is back.
I have a big old DC power supply, maybe 70-80 lbs; big transformer, diodes, big capacitors, and I think what is called a choke.
It puts out 70 vdc and is rated at 20 amps.
I also have a 10 amp Variac.
Can I feed the output of the Variac into the power supply to achieve adjustable voltage output?
I'm thinking about running some lower voltage servos.
If I can do this, and adjust the output to about 40 VDC, what sort of amps can I safely output?
I remember that there is some sort of isolation problem when using Variacs, should I take any special measures?
Thanks,
Ozzie

[Al_The_Man]

You can do it within reason, if you output the Variac to the input of the power trans. then it will be isolated, I would tend to look at taking turns off first.
Technically your current rating would increase, but actually be limited to the wire size used by the secondary.
Al.

[skmetal7]

(assuming the variac and power supply are 120v ac)

you have a 1200w variac and a 1400w power supply. you will cook your variac

[Al_The_Man]

Originally Posted by skmetal7 (assuming the variac and power supply are 120v ac) you have a 1200w variac and a 1400w power supply. you will cook your variac

Assuming he maintains 20amps, his wattage is reduced accordingly, in all probability the secondary may not handle much more than the 20amps it is built for.
Al.

[ozzie34231]

Thanks Guys,
I appreciate it.
Ozzie