Cheap compartments for motor capacitors - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: March 31, 2025, 06:27:48 am
content: I have some 3-HP pumps that have been shipped with 120 VAC starting capacitors even though the pumps are used at 240 VAC. And the capacitors fail. So now, I replace them with 250 VAC capacitors which do not fail. The problem is the 250 VAC capacitors won’t fit in the compartments for 120 VAC capacitors. I looked online for capacitor compartments. Found they would have to be bought in quantity and were expensive. No real choice but to make them.First try was using a section of 2.375 inch (60 mm) galvanized fence post. This is heavy duty, but workable. Needed to use a post cap on one end, make a cap for the other, and mill a square hole for wiring. Main problem was mounting. This was the smallest diameter fence post that would accommodate the capacitor. But it was wide enough to block the original tapped screw holes in the motor casing. So new holes had to be drilled and tapped. Great care had to be used to avoid drilling into a field coil, and screws had to be short enough not to hit a field coil. Then a pair of screw passage holes had to be drilled in the side of the compartment that would be next to the motor. And a screwdriver access hole had to be drilled in the other side of the compartment on the end away from the wiring so the compartment could be screwed to the motor before the capacitor was inserted. A lot of tricky work but successful. See first pic.Then I thought of small tomato paste cans used in the U.S. Slightly larger than the capacitor, easy to work with because of the thin metal, and they come with ends. Found a couple in the pantry that were past their sell-by date. Cutoff one end, emptied, cleaned, and made slits at the open ends so two could be meshed. Then cut a window at one end for wiring to pass. Made a couple of thin aluminum wings to rivet to the compartment and screw to the existing holes in the motor casing. The two halves are held together with a hose clamp. See second pic.Simple project, but maybe some will find it useful.Mike

author: moffy
author_rank: Super Contributor
timestamp: March 31, 2025, 07:28:01 am
content: I like your solution better than the original, looks like an upgrade.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 02, 2025, 03:16:41 am
content: Hello calzap,Nice that your described /showed your custom capacitor boxes.Sure that the one using the fence post is just ironclad.Don't remember the size of your 250 VAC motor starting capacitor (as mentionned in your former thread)This time I listed some big capacitor boxes from ALI :Motor capacitor boxhttps://www.aliexpress.com/item/1005007785751923.htmlref DN140 (inside : 126 x 52 mm)Capacitor Box junction box water pump protective box 71YShttps://www.aliexpress.com/item/1005008572566026.htmlY2/YE2/YE3 series motor junction boxhttps://www.aliexpress.com/item/1005008519438064.htmlAir Compressor Capacitor Box Motor Junction Box 220Vhttps://www.aliexpress.com/item/1005007984193727.htmlhttps://www.aliexpress.com/item/1005006112026630.htmlAluminium junction boxhttps://www.aliexpress.com/item/1005006753620317.htmlCheck out refs 'FA12-1' 200x130x88mm or 'FA5-1' 222x145x55mmTo attach to the motor, use a custom aluminium bracket or brass hex spacers (size M6 or M8 if available)https://www.aliexpress.com/item/1005006049595637.htmlhttps://www.aliexpress.com/item/1005006998103576.htmlhttps://www.aliexpress.com/item/1005007556323254.html

author: andy3055
author_rank: Super Contributor
timestamp: April 02, 2025, 03:35:08 am
content: How about using a Coke can?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: April 02, 2025, 03:40:27 am
content: And if someone asks you about the can’s ribs, please tell them that it helps with the heat dissipation.

author: Whales
author_rank: Super Contributor
timestamp: April 02, 2025, 06:35:33 am
content: How many?Have you already bought all the replacement caps? Oil filled and plastic film can both be used, make sure to check the sizes of both families.Does it have to be a metal box? PVC plumbing fittings would be easier to drill, glue and screw than steel. Not sure if they meet the necessary heat and flammability requirements though.I'd suggest 3d printing (you can get flammability specced plastic filaments) but to make something impact-resistant enough to survive a tumbling motor it would have to be quite thick, probably taking many hours per print. Still could be viable if you're familiar with 3d modelling.

author: coppercone2
author_rank: Super Contributor
timestamp: April 02, 2025, 06:39:29 am
content: does anyone else think that building something out of a can is horrible? Cans are not meant to be cut or have things mounted to them, they don't have a proper seam for mounting or closing, making brackets is harder, its difficult to deburr them (they like to tear while drilling), etc.I strictly avoid doing this, even if the can is a perfect fit.A die cast box theoretically you can shape to conform to the motor, by carefully cutting two sides and even file the walls to have a flusher fit. Experts with a die grinder can probobly make it nearly seamlessalso, what's wrong with a motor in a square box? I always wondered why they always make it a cylinder. For instance with a belt drive motor, it would be perfectly happy as a box instead of a cylinder.

author: calzap
author_rank: Frequent Contributor
timestamp: April 02, 2025, 04:47:13 pm
content: Thanks for the inputs. Responses to some of the comments: The tomato paste cans are pretty robust. They had to survive going through a hydroflex and quick moving machinery. Thicker metal than a Coke or other beverage can. Not quite as thick as the original compartments but close. The main cuts were made with a cutoff wheel on a Dremel. Where desirable, like the wire passage, cuts were made a little small so the edges could be folded back and be smoother. The replacement capacitors were UL-rated motor-start capacitors. Replacements were the same mfd as the originals or close. In one case, the original capacitor was an odd size produced by or for the motor maker (who doesn’t sell them separately), so close had to be good enough … and it was. I thought of using PVC or some other plastic but was concerned about cooling. Metal is a better heat conductor. Having 2 cans of the right size was helpful … remove the lid and rim on one end so there was still one end intact, and cut 4 slits of correct depth in the other end so two cans could mesh perfectly.There are 2 pumps in use and a spare. They’re 3 HP, 2-stage centrifugals. Same pump is sold with various badges like AMT or Dayton. Motors are usually WEGs, unfortunately. In the one use, pumps last 3-5 years because of frequent starts and pumping against 30-60 PSI backpressure. It’s always the motor that fails, not the pump per se. I replace both because there’s a single shaft that serves motor and pump. Replacing only the motor would be very time consuming and tricky because pump has to be completely disassembled to remove motor/shaft. And who knows how long the old pump portion would last on a new motor. The other pump has maybe 20-30 starts per year. Those starts are for 18-24 hours runs against very little back pressure. The original pump has lasted 20 years and still runs well.Mike

author: Whales
author_rank: Super Contributor
timestamp: April 02, 2025, 07:29:31 pm
content: If it's only two pumps then I'd be happy with your steel options. They might take time, but if they're strong enough to survive the motor going for a tumble then it's worth it.N.B. it might also be feasible to run the wires from the motor to a wall-mounted box and install the cap in there, like how some VFDs are wall mounted. There is no electrical need for a short distance between cap and motor. Not sure if there are any standards that disagree.