longevity of toroidal transformers - Page 1
Forum section: electronics / projects

author: jpb
author_rank: Super Contributor
timestamp: February 18, 2015, 06:57:14 pm
content: I'm not sure if I'm posting this on the right thread but it is to do with bits for projects.I've just been scrapping/salviging parts from some equipment dating from the early 90s.There was a pair of nice 60VA toroidal transformers (2 x 115V to 2 x 12V) but the date on them is 1992 (so 23 years old).Are these worth reusing or is the insulation likely to have become a bit brittle/dodgy?My inclination is to not risk it and dump them - but this seems a bit of a waste. I can test for shorts with a multimeter but I don't have any insulation tester to hand.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 18, 2015, 06:59:14 pm
content: No way to know, I have 1960-70s's equipment with original transformers working just fine.Depends how long it was used, how hot it got and how well it was made.

author: MrAl
author_rank: Super Contributor
timestamp: February 19, 2015, 05:00:05 pm
content: Hi,I tend to agree with the previous post. The aging depends on several factors.You should handle all these things with a bit of caution anyway, even when new. Use a well chosen value for the fuse rating, etc. Build in some safety in all your circuits that run off line, or even off of batteries for that matter.A common problem with transformers is that they overheat and short out which causes more overheating. A fuse on the primary helps prevent problems because if the current goes too high it gets disconnected from the line voltage and all the power goes to zero, therefore no more heating.A more modern approach is to add a thermal fuse, which is a fuse that opens up when the temperature of the case goes over the value for that fuse part number. The thermal fuse is put in series with the primary and opens up when the temperature goes too high. The thermal fuse should be mounded somewhere inside the windings, like maybe between the windings and the core near the center. It should make good thermal contact with the windings.They use these things with fans too these days, so if the fan overheats the device opens up and turns the fan off permanently, and the only way to get it working again is to replace the thermal fuse.Thermal fuses come in a variety of temperature ratings too, from under 100 C to quite a bit over 100 C, so you have to choose as per the application. I dont like my stuff getting above about 80 C so maybe 80 C or something like that is good.The current ratings for these fuses has to match the application too. A low current one like 3 amps is good for those cheap box fans, while a higher rating would be necessary for a coffee maker for example.The key point with these things though is that they MUST make good thermal contact with the part of the device that gets hot. You may even want to use a couple of them for good protection.

author: jpb
author_rank: Super Contributor
timestamp: February 19, 2015, 10:22:55 pm
content: I think most modern toroidal transformers have a thermal fuse built in, though if it blows then the toroidal is useless. I don't know if those of 92 vintage do.Given the amount of effort it takes to build up a project (for me at least), it probably is not sensible to try and save a few quid by using an ancient transformer. It is the quality of the plastic insulation on the wiring that is my main concern - I guess if a short forms on the primary side there might be large voltage spikes on the secondary which might damage the electronics though I think this is probably unlikely.These particular transformers haven't had much use (I've had the original equipment since new) but they have spent a lot of time in storage much of it in my attic which suffers from temperature extremes and probably a fair amount of condensation so it is not the ideal environment for anything prone to corrosion.The other thing is that I'm currently playing with GPSDOs and so want to leave circuits running for days, having a safe transformer is therefore important.

author: John Roger
author_rank: Newbie
timestamp: March 13, 2015, 07:46:32 am
content: With Toroidal transformers, we get higher current capability, the reason being that they are more efficient. The cost of toroidal transformers is a big disadvantage. Another big plus is that they generate less noise than standard transformers.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 13, 2015, 08:06:54 am
content: Unless the transformer is damaged it will almost certainly outlast your project! You may find in 10y time that its stripped by someone else and re-used again.As long as it hasn't been overloaded or physically damaged it should be fine for many many years.

author: jpb
author_rank: Super Contributor
timestamp: March 13, 2015, 10:47:22 am
content: Quote from: Richard Head on March 13, 2015, 08:06:54 amThanks - I'll rescue them from the recycling pile (I'm having a massive clear out of household junk so have been making lots of trips to the tip).