Where can I get a 0.7mH 70A inductor? - Page 1
Forum section: electronics / repair

author: Pentium100
author_rank: Frequent Contributor
timestamp: April 05, 2020, 07:45:57 am
content: Hi,In trying to repair my UPS, I started thinking that I could just replace the bad inductor and be dome with it since I cannot seem to put it back properly (I managed to disassemble, glue the core and put back the iductor from another phase, but this one is in worse shape - the coil former is falling apart in the center etc) so that it does not buzz so much.Logically, I do not have the only high power inverter in the world, there are other UPSs, inverters for solar power etc, so somebody has to make these things, right? However, I cannot find a suitable one anywhere I look (so I probably am looking wrong), I fave found a couple of inductors rated at the required inductance and current, but they all are designed for DC and not an inverter with switching frequency of 15kHz.I have attached a photo of the label that is on the inductor. I have not been able to find any information on it whatsoever.Anyone knows where I can get one?

author: t1d
author_rank: Super Contributor
timestamp: April 05, 2020, 11:06:18 am
content: Please give us more information, so we can help you.Picture of Make and Model of unit. Picture of the front and back and any identification information.Picture of the part on the circuit board, showing surrounding parts.More details about what repairs you have made, particularly to this one part. Have you removed it? Pin count? Better photo of the part, not just the label.It might be a proprietary part, but, as you say, there should be something that would work.

author: t1d
author_rank: Super Contributor
timestamp: April 05, 2020, 12:30:39 pm
content: Firstly, I am not the guy who knows all about chokes. I am just the guy who is geeky enough to search for mystery parts, when he can't sleep... It's a good way to learn...So, I learned/am thinking that "ACM" in the part number indicates that it is a common mode series choke. There are manufacturers that make bigger chokes TDK, etc... But, I did not find exactly what you are after. If you made a more extensive search, you might do better.I did come across two options...1) Build your own... There are website, YouTube videos and on-line calculators to help you design it. There are DIY suppliers who sell the parts you need. It really doesn't look all that complicated. You pick a core, or reuse the one you have, and a wire diameter, based on the amps you need, and the calculator will tell you how many wraps to make on the core. I am just a hobbyist and even I would give it a go.2) There are companies that will build custom chokes for you, but I think you are looking a minimum orders/bigger bucks, etc...Maybe advertise that you want to buy one in the sell/buy section. You never know what people have in their surplus component stocks.Give us more information, as I asked, and we will keep at it with you.

author: TheMG
author_rank: Frequent Contributor
timestamp: April 05, 2020, 02:27:20 pm
content: Those are almost always custom made inductors according to the manufacturer's required specs, not off the shelf parts.Best I could recommend is to contact UPS manufacturer and see if they will sell you a replacement part. Other options are searching auction/second-hand sites for the inductor or even a complete UPS that you can strip for parts.As a last resort you could try to get an inductor custom manufactured but that is likely to be very expensive in a one-off quantity, and you need to be sure that the new inductor matches all the correct characteristics: there's a lot more it than just inductance and current. So somehow you would have to find all the specs (core material, etc) for the originals, which again is unlikely.

author: Pentium100
author_rank: Frequent Contributor
timestamp: April 05, 2020, 04:18:16 pm
content: UPS is a Borri B8033 40kW. I have attached a picture of the inductor. The core looks like E, but it is made from four C shaped sections. What is a bit strange to me is that the laminations are different, compared to a EI core transfomer, I cannot find the correct words to describe this, but you should see in the picture. The wire is flat, 7mm by 3mm. It is mounted separately on the chassis, but in the circuit, one side is connected to the output transistor (half bridge) and the other to about 120uF of filter capacitors.The problem I have with it (and one other) is that the laminations have become loose. The other one was just a little bit loose, I glued them back with epoxy and it is silent now.This one is in worse shape, the laminations were more loose, some were completely unstuck. Due to this, it was buzzing quite loudly but it also was probably heating up more than the others. Now the inside of the coil former is degraded due to heat (feels kind-of like cardboard) and is missing in some places, leaving a very small gap between the winding and the core (it may actually have arced from the winding to the core, blowing up the output transistor).I glued the core pieces back and when I tried to put the inductor back together I noticed the problem with the coil former, since there was a bit of space inside the coil former, I wrapped a core piece in electrical tape (rated for up to ~300C) and shoved it in. The core pieces seem to fit well and not really move, but when I turn the UPS back on, this inductor buzzes loudly (not much different from before actually), so there is movement. I also thought that it may be arcing between the turns, but from what I can see, the winding does not look burned etc. I can (kind-of) test if it arcs between the winding and the core, but have no way of testing it it arcs between the turns.I tried contacting the manufacturer, but received no reply. Either they are not working right now because the company is in Italy or theyare ignoring me because I do not represent a million Euro company.

author: JohnPi
author_rank: Regular Contributor
timestamp: April 05, 2020, 05:10:31 pm
content: Note this is not a 70 A 'inductor' -- it is choke, and there is a significant difference.The difference is that you would expect a 70 A inductor to maintain its inductance (core not saturate) at 70 A DC current. In this choke, there are 2 windings and current flows in opposite directions; thus the magnetic flux cancels in the core, avoiding saturation. The copper wires in the component are capable of carrying 70 ADC.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 05, 2020, 05:39:30 pm
content: The spacers between the cores halves are very important as well...If it just vibrating but otherwise working, take it to a local motor repair shop and have them vacuum impregnate and bake it with their standard insulating varnish which should be good to at least 90-100 C.If it needs internal repairs, the motor shop would probably be the best place to ask for help.

author: Pentium100
author_rank: Frequent Contributor
timestamp: April 05, 2020, 06:34:34 pm
content: Quote from: JohnPi on April 05, 2020, 05:10:31 pmThere is only one winding here. I have attached part of the circuit diagram of how it is used.I'll look for a motor shop, hopefully I'll find one that works during the quarantine. One more option.

author: t1d
author_rank: Super Contributor
timestamp: April 06, 2020, 02:29:59 am
content: Quote from: JohnPi on April 05, 2020, 05:10:31 pmGood information. You taught me something. Just saying...

author: t1d
author_rank: Super Contributor
timestamp: April 06, 2020, 02:31:10 am
content: Quote from: WattsThat on April 05, 2020, 05:39:30 pmBrilliant suggestion. Just saying, too...

author: trobbins
author_rank: Frequent Contributor
timestamp: April 06, 2020, 08:06:57 am
content: They hum audibly as a normal part of operation, given they are for commercial/industrial use. The hum may well have increased over time due to gradual change, and/or may have vibrated and over-heated due to a semiconductor failure. I think you have done yourself a dis-service by pulling it apart, as you now need a metal banding facility. The gaps need to remain the same width or you will change the inductance. You wouldn't be able to install a new former, so can either add filler, and add insulation sheet as packer, and as indicated find someone to heat/dip varnish or vacuum impreg to quieten down the operation and increase insulation resistance (both those activities have been done by DIYers. You probably need to IR test it to at least 2.5kV.You may have better luck identifying a service centre that has handled Borri UPS in the past, as they may have factory details, or you could persuade them to order in the part from Borri.

author: Pentium100
author_rank: Frequent Contributor
timestamp: April 06, 2020, 01:11:12 pm
content: Quote from: trobbins on April 06, 2020, 08:06:57 amI understand that it is not supposed to be silent, but this one was buzzing really loudly, while the other two (since the UPS has three phases, I have something for comparison) were almost silent. And actually when I bought the UPS even this inductor was not that loud, it primarily produced noise at 15kHz (sounded like a TV yoke or flyback), not at 50Hz.Initially I removed this inductor and saw that some laminations have completely separated from the core (see attachment) and the noise was from them hitting the rest of the core. I glued what I saw, but did not disassemble the inductor (probably that was a mistake), put it back, it became quieter. Later the output transistor blew up. I do not really want to blow up another expensive output transistor, so I decided to fix this inductor properly. In all fairness, the output transistor could have blown up because other reasons, but, at the same time, only this inductor was making a lot of noise, while the other two were making much less noise.This time I did disassemble the inductor and saw that the laminations were loose in the center as well, also that the inside of the coil former was falling apart (it's supposed to be plastic, but behaves kind-of like old foam or cardboard). I also saw that a corner of one core piece (on the inside) was damaged a bit, almost looks like it has arced there, though the inside of the winding does not look damaged.I later took apart one of the better ones (this one was buzzing more compared to the third one, but not that much), it also had loose laminations, I glued them, assembled the inductor and it is quiet now. But the center of the coil former is not falling apart on this one.

author: trobbins
author_rank: Frequent Contributor
timestamp: April 06, 2020, 11:54:41 pm
content: That photo and description is much more informative. That loose inner lamination would certainly have made a racket, and may well have been the cause of local friction and heat against the former. That may have resulted in the demise of the former, especially if the former was loose and not restrained in place by packing and varnishing.If the former initially sat on the bottom half of the core, then it seems strange that they didn't pack the space between the top of the former and the top core half. And the somewhat narrow width of the core gap packer also isn't supporting all the laminations equally, which may have also alleviated this sorry tale for starters.I would also suggest trying to locate a local transformer manufacturer, especially a manufacturer who has a wide range of in-house built product. They would have the capability to pack, re-band, and impregnate or epoxy the total assembly. Whether they would advise that the former is degraded to such an extent that a new unit needs to be built from scratch, I'm not sure.It would be good to hear you progress.