Advance Constant voltage transformer 240v - Page 1
Forum section: electronics / repair

author: Lee76
author_rank: Newbie
timestamp: September 22, 2023, 10:11:21 am
content: [ Specified attachment is not available ]Just picked up a Mains 240v Constant voltage transformer, I want to replace the input/output cables. the photo shows how its connected up at the moment although i doesn't have a plug fitted so not sure its correctly wired. also am i correct that the earth should go onto the post not bypassed like it is now. please see photos.thanks in advance.

author: tridac
author_rank: Regular Contributor
timestamp: September 22, 2023, 11:33:15 am
content: Looks pretty straightforward, mains input to the input terminals, out from the output terminals. Secondary is isolated, so don't need to worry about polarity of input and output, live and neutral. You do need to ground the frame, so use a solder tag or crimp tag to to connect both earth poles to the transformer case. These old Advance cvt give good regulation and isolation, but do waste a bit of power in the process. They work by saturating the core on input, then use a tuned circuit to restore the output sine wave...

author: Ian.M
author_rank: Super Contributor
timestamp: September 22, 2023, 11:50:05 am
content: Before using that so convenient grounding stud (if that's what it is), check continuity to the enclosure, as even if it grounds the transformer core, there's no guarantee of a good connection through its mounting bolts to the enclosure. If it doesn't have continuity, you'll probably need to add a ground strap.Knots in mains leads are no longer acceptable as adequate anchoring. They don't anchor the lead against twist or being pushed in, either of which could strain or break the individual wire connections. Retrofitting suitable cord grips is likely to be somewhat of a PITA, but must be done if its for general use. If its only going to be used by the owner (who cant sue themself) cable tying the knot to the ventilation slots so it cant be pushed in or twisted very far would be better than nothing.

author: Lee76
author_rank: Newbie
timestamp: September 23, 2023, 01:20:54 pm
content: Hi, I've just put a plug on the CVT to try it before fitting glands earthing the case and new cables. I put a socket tester in it turned it on and it says live neutral reverse? is it just a case of swapping the live and neutral on the output. checked the output and I am getting 245v rms thanks .

author: CaptDon
author_rank: Super Contributor
timestamp: September 23, 2023, 04:01:25 pm
content: Never ever use a constant voltage ferro-resonant transformer from a supply of varying frequency like a generator set!! A very slight change in frequency leads to a huge voltage swing such as when the generator is 'hunting' after a large load change. And be aware most of those CV units run hotter unloaded than they do with a load of 50% of their rated capacity!!

author: tridac
author_rank: Regular Contributor
timestamp: September 24, 2023, 11:50:10 am
content: The output is usually isolated on a CVT, so you may be getting wrong answers, which usually assumes one side of the line is grounded at the substation. You can verify the isolation by unplugging from the line, then use the ohms range on a meter between input and output, then output and frame, which should show infinite resistance. To check leakage, use a megger or other insulation tester, which should show 10's to 100's of megohms. Not much to go wrong on a CVT, other than resonating cap failure with age, but that is pretty rare as well...