How to mount autotransformer in plastic box for test jig? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: August 10, 2021, 07:32:31 pm
content: Hi,I need to mount this autotransformer, and this mains transformer in a plastic box, and connect wires to them from outside the box...Autotransformer:RS 890 2765https://uk.rs-online.com/web/p/variacs/8902765/Mains transformer :RS 503 950LINKDo you know the best way to do this? Its just for a test jig. The autotransformer doent have any mounting tabs or fasteners...how will i fix it into the enclosure so it doesnt roll around inside?

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2021, 08:13:23 pm
content: I suggest actually looking at the instruction manual (well, 1 side sheet) - it has a pair of M4 threaded inserts for panel mounting. Less haste, more speed, and rtfm!

author: Faringdon
author_rank: Super Contributor
timestamp: August 11, 2021, 06:14:54 am
content: Thanks, yes i see those screws going right through the body.....thing is, access to them is blocked by the rotary knob on one side, and blocked by the wiper mechanism on the other side. If i use those to mount the autotransformer, then it looks like the wiper movement will be very restricted.

author: Mangozac
author_rank: Frequent Contributor
timestamp: August 11, 2021, 08:00:02 am
content: They are underneath the knob: take the knob off, mount it, then put the knob back on.

author: Faringdon
author_rank: Super Contributor
timestamp: August 11, 2021, 08:15:45 am
content: Thanks, i see what you mean...i am also wondering what the two screws at the back are for, whether for mounting or not?.....maybe they need taking out and putting back in the front so that they can assist with mounting?........they couldnt be of use at the back as they would impede the wiper movement.

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2021, 08:39:22 am
content: It's probably a standard moulding (or very long threaded bushes moulded in full length for strength).Obviouslyyou can't put screws into holes that are going to block the wiper rotation.As Mangozac says, just take the knob off and mount it, as the instructions say!

author: Ian.M
author_rank: Super Contributor
timestamp: August 11, 2021, 08:40:10 am
content: The RS Components web page for that Variac is a mess. The instruction manual and so-called datasheet show variacs with very different mountings.The manual appears to be largely a rip-off (including spelling mistakes) of the one from this discontinued product:https://uk.rs-online.com/web/p/variacs/3473574/The web page claims it weighs 1.4 kg, but the manual claims 1 kg. In either case I wouldn't be happy panel mounting it, hanging off a plastic box side or lid with only two M4 bolts on 28 mm centers securing it to relatively flimsy plastic.IMHO you need to either mount it a >6mm thick fiber reinforced plastic panel, or need a steel or thick aluminum rigid mounting plate for it to spread the load over a large enough area and over enough fasteners for it not to tear a hole in the plastic box the first time its handled a bit roughly.Quote from: Faringdon on August 11, 2021, 08:15:45 amI've got no idea what you are on about. There shouldn't be *ANYTHING* blocking the wiper movement except for end stops that align with the ends of the winding. Post photos of the front (with the knob off) and back of the Variac so we can see what you've got and give you proper advise.

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2021, 10:31:52 am
content: Yes, I wondered about the strength of the box too, though some polycarbonate ones are much better than the others (doubtless it's a cheapest available ABS one though) - at the very least, I'd be using large washers, but a reinforcing plate would be better. This is a problem for the other (2.8kg) transformer too if it gets dropped.You have to take the knob off regardless, otherwise how are you going to fit the shaft through the hole in the box.

author: Clif
author_rank: Newbie
timestamp: August 12, 2021, 11:58:01 am
content: you can consult with your machine supplier about customized nozzle