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Forum Index : Electronics : Rewinding PJ8000 Tranny, Conflicting Winding Calculations
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Murphy's friend Guru  Joined: 04/10/2019 Location: AustraliaPosts: 649 |
Nice winding job. With that mesh wrapping I would just tape the end off, no epoxy, and continue with the next layers. Only when all are in place do the epoxy thing. It will soak in to the inner layers. Before epoxying I jam a split PVC tube (split so its circumference can be set to 'precisely' the hole diameter), wax it so no epoxy sticks to the tube and jam it in the hole to push the windings in there out as far as possible. This gives you maximum hole size. I use marine epoxy BTW, no need for high temperature types if that inverter has a decent cooling fan. With your calculated 50mm hole remaining I think you have buckleys chance to fit 17 turns of 4 gauge welding cable primary, prove me wrong  . |
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| sunnypower46 Newbie  Joined: 09/12/2021 Location: United StatesPosts: 24 |
While it doesn't look like it in the photo, the epoxy has done its job and locked in the windings. I like the split PVC idea for the final secondary epoxy wetting. I should have mentioned, but don't have a photo; I smoothed the sharp edges of the core, wrapped with screening, applied epoxy and then wrapped with Kapton tape before winding the first layer. The Kapton tape made a smooth surface for physically positioning the windings close together. The thinness and adhesiveness of the Kapton tape worked better for me than mylar tape. I chose high heat epoxy because the original transformer would get way too hot to touch. 60-65C. Took the conservative approach. The welding cable diameter is 9.525 mm. My diagram shows 14 turns first layer and 7 turns on second. And a maybe 10 mm open circular area remaining. I expect more than 50 mm hole to be available. So, should be easier. We'll see, stay tuned. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
Hi Sunny, in the old days when I wound electric motors for a living , we just wound the motor or transformer, then dipped them in electrical varnish. Waited until the bubbles stopped, lifted them out and drained the excess off and put them in an oven to bake the varnish. Worked perfectly fine and the windings were a solid lump when cooked. Seems much easier than epoxy. The only time we used epoxy was on urgent jobs, we connected the windings up to reduced voltage and used the current through them to heat them up. Then poured epoxy through. It was never as good a job as varnish as it did not get into the slots and penetrate the windings as good as the varnish, but rush jobs are just that. Cheers Pete |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 649 |
Yes, that works IF one has a suitable oven and a big pot of varnish. Few home transformer winders would have that or access to such items. Not a good idea to bake varnish in the kitchen oven .For a one off job epoxy wins hands down for ease of application. I never saw the need to epoxy the *whole* of the toroid winding, just the part going through the hole was enough to result in a very quiet transformer. And I have hand wound about 8 toroidal transformers of varying sizes so far, no problem with any of them. |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
This helped me check if the cable/wires will fit inside, plus total length. |
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| sunnypower46 Newbie Joined: 09/12/2021 Location: United StatesPosts: 24 |
Thanks guys for the nice history lesson on ways to seal motors and transformers. I have to stick with my epoxy investment on this one, however. I think I'll play off Murphy's note on epoxy for the inner core and do that area with the best, thickest coating. I got all the secondary turns on; needed 2 1/2 layers. That presents a problem for using a split PVC form in the center -- not round now. Have to think about it more. Eventually, I'll coat the entire remaining area, but not with as much attention to detail. I should mention something I tried when "messing" with epoxy. I got some teflon roll up baking sheets. When the epoxy drips harden, you can flick then off with your fingernail. Nothing sticks. Reusable, too. Use them under the piece you're working on. I attached the variac (a 130v model, only) to one of the 120v windings and noted about 0.14A on the clamp meter with 120v on the winding. The other winding checked the same (17W). Then I put 120v across the total secondary to check for equal voltage on each half winding. Both showed within +/- 0.25V of 60v. Nice! Happy! Next, I'm going to leave the core's latest winding un-epoxied for now and wrap a 17 turn #12 silicone wire for the primary and see whether this turns ratio stuff works. I'll put 15v from the variac on the primary and hope for 240v across the secondary. @tinyt: I think I stumbled on your rope through the hole post earlier. Makes sense to me! Cheaper than buying welding cable that won't fit or is too short. Now to find a close diameter rope . . . . |
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| sunnypower46 Newbie Joined: 09/12/2021 Location: United StatesPosts: 24 |
Bumped my total secondary winding count from 268 to 272. Wound 17 turns of #12 awg onto the toroid, a 16 turns ratio. Applied 15v to the 17 turn primary. Measured 240v on the secondary. Amazing! The turns formulas actually work! Now to finish the epoxy job. Then figure out a suitable permanent primary winding solution. Not really anything further now to add to this post. I'm moving on to build the EGS002/8010 guts and marry it to the PJ8000 FET board. I think I've collected most of the hardware mod suggestions from those that have gone before me. |
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| sunnypower46 Newbie Joined: 09/12/2021 Location: United StatesPosts: 24 |
Just a follow up on this rewinding project. I managed to get 17 turns of 2AWG welding cable through the hole. Cable OD was .411 inches. Took some squeezing and compressing, but made it happen. Picture shows it resting vertically on 1/2 inch wood dowels inserted into 1/2 inch silicone tubing. It fits inside the classic PJ8000 shell with additional metal on the sides (not shown) to increase the overall height about two inches. Provides a 15v primary to the EGS002 and has no trouble going beyond 240 volts, if adjusted with the voltage pot. Near perfect sinusoidal waveform, too. Have run it at 2800 watts for several minutes using 24 4110 fets on the PJ power board with gate resistor and diode mods added.  |
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