Limit testing 300Vdc, 175W device. - Page 1
Forum section: electronics / projects

author: peteb2
author_rank: Regular Contributor
timestamp: April 08, 2019, 02:49:10 am
content: These days its rare to have a Bench Power Supply that provides 300Vdc with any great current amount.I've a DC to DC regulator module that's spec'd to operate from 300V DC & rated at 175W to produce it's output of 15Vdc at 150W...I really need to make some kind of a source of 300V DC. I assume here the DC to DC converter will draw up to 0.6A (175/300)....So far the linear power supply ability that i cobbled together with a bridge and smoother has failed miserably because the big old transformer that has around 212V AC out sags very quickly under load rendering any kind of a test a fail.What's options are there to make a source of 300V DC @ under 0.7A ability. Mains is 230V AC. .... a nice fat Variac, (which means extra safety for being non-isolated) ... use Mains directly with a bridge and smoother and a heavy duty DC voltage pre-regulator stage (LR8) to bring it back to the 300V DC and be extremely dang careful using it for the testing or scrounge up an old isolation transformer to provide a level of safety at least.... I can't see actually having a mains transformer wound being something i can get past the bean counter... but i might be able to buy a SMPS.... (but have not searched if such a beast exists even)....Such a pity i can't have any access the actual piece of kit this DC to DC unit needs to end up working with which has 300V DC at quite a current....I might also be having a bit ofin all this as i don't tend to deal with such high voltages... so please excuse me if i'm over-thinking the entire issue or have something truly & absolutely WRONG!

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2019, 03:08:40 am
content: When I need to do something like this I connect a rectifier and bulk capacitor to the output of a variac and adjust it manually to maintain the desired bus voltage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 08, 2019, 04:18:45 am
content: This. ^ WITH an isolation transformer, of course!You'll need a few hundred VA capacity to avoid sag. If you don't have one already, it's an investment, useful for far more than this one project (unless, like, you're normally writing software and this is truly a one-off case or something..).Don't worry about heavy filtering, or regulation. Line voltage changes, you can handle by turning the knob. No biggie. Ripple, it's surely made to handle in the first place. The only exception would be a DC transformer, giving output proportional to input, but I don't think those are very common in the 300VDC input module space?Tim

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2019, 04:29:55 am
content: I don't usually bother with an isolation transformer unless I need to measure something with a scope but you'll certainly want to be aware whether the DC-DC converter you're testing is isolated and behave accordingly.

author: David Hess
author_rank: Super Contributor
timestamp: April 09, 2019, 03:17:09 am
content: Quote from: peteb2 on April 08, 2019, 02:49:10 amGet a bigger transformer. There should be no difficulty in doing this and I have done it several times with a variac and isolation transformer.