MOV footprint from datasheet doesn't seem possible - Page 1
Forum section: electronics / general

author: AlfBaz
author_rank: Super Contributor
timestamp: August 24, 2024, 02:13:22 am
content: https://au.mouser.com/datasheet/2/54/mov10d-777448.pdfOn the 2nd page, dimensions are given that only have one variable depending on the particular part number and that is the width of the bodyFront view shows distance between pins as 7.5mm but the side view shows these pins are offset by some undocumented amount, sure you can make assumptions, but they are not documented.Further on in the document there are various dimensions of the part mounted on tape and part of that shows the pins flat against the tape but again, there is no dimension. This would seem to indicated the MOV body would not be parallel with the tape.Basic geometry and the pins 'offsettednes' would seem to indicate that the actual straight line distance between pins will not be 7.5mm but some distance slightly longer.I managed to find a Bourns step file of the MOV I'm interested in and it shows this discrepancy. Measuring the 3D model shows the pins offset by 1mm giving a straight line distance between pins of 7.566mmI am either missing something in the data sheet or the tolerance they are giving for the front view pin spacing of 7.5 +/- 0.8 is how they are getting around it as 7.566 falls within that tolerance.Thing is if you wanted the part to fit in without bending the leads and saying the pad size for a 0.8mm pin is the same my calcs show you would need a hole size of 2.4mm!I realise I'm being pedantic especially as I will hand mount these devices, just curious what others have to say

author: gamalot
author_rank: Super Contributor
timestamp: August 24, 2024, 03:21:59 am
content: I drew a sketch to help, but I still don't understand why you say you need 2.4mm holes, maybe it's because I'm not a native English speaker.

author: floobydust
author_rank: Super Contributor
timestamp: August 24, 2024, 04:17:30 am
content: That datasheet is shit, try this one:https://www.bourns.com/docs/product-datasheets/mov10d.pdfedit: for the mystery dimension "a" I think I use:https://www.tdk-electronics.tdk.com/inf/70/db/var/SIOV_Leaded_AdvanceD.pdfOther compatible manufacturers, like CNR 10D, Epcos S10K etc. to consider too.You have to be careful because there are many (10mm) parts with different energy handling ratings.Also, there are typically three lead-bending options. I don't like the big lead bends because they can arc to adjacent parts unless you leave space.

author: AlfBaz
author_rank: Super Contributor
timestamp: August 24, 2024, 07:27:21 am
content: Quote from: gamalot on August 24, 2024, 03:21:59 amThe 1mm you show is not specified in their datasheet. I measured it from their 3D model so I don't trust itThe 2.4mm came from their spec of 7.5mm plus or minus 0.8mm but I only took into account the size needed for the 2nd hole to accommodate that toleranceObviously I should have taken both holes into account which would make it a pair of 1.2mm holes, sorry about thatQuote from: floobydust on August 24, 2024, 04:17:30 amI see the TDK one specifies the offset and as you say, it's dimension aLooks like I'll go with another manufacturer, thanks

author: floobydust
author_rank: Super Contributor
timestamp: August 24, 2024, 05:46:50 pm
content: If that spacing is out, the part sits crooked. Just compare joule rating to know if the other MOV's are in the same ballpark for physical size.Leads are so far no where near diameter as manufacturers say. I measure biggest is 0.6mm and a 1mm hole I use, also gives some slop as these part's thickness seems to vary quite a bit. I thought 1.2mm hole a bit big.

author: IconicPCB
author_rank: Super Contributor
timestamp: August 27, 2024, 10:59:43 am
content: There is nothing wrong with the data sheet,Page 4 clearly shows pin spacing and wire diameter tolerances,The component is LEADED, leads are flexible, use them as such stop crying,SERIOUSLY so what if the component is a bit crooked, you need to give it a bit of a clearance around the body since once it fails under fault condition since that is its intended purpose you need to minimise damage to surrounding components anyway so clearance is your friend. Use it.

author: Simon
author_rank: Unknown
timestamp: August 27, 2024, 08:05:04 pm
content: The difference is in the microns. 0.066mm or 66 microns so it is smaller than any usual tolerance. They could state 0.1mm tolerance and it would fit. If you look at equipment with these things in you will notice that they seem to be mounted diagonally as the pins are assumed to be in line and this gives them some space as the job they do is quite physical.There are a lot of companies that are bad with datasheets. It is like they don't understand how drawings work. I always have to use a calculator to work it out as even something as simple as a resistor will not give the pitch of the pads which is exactly how you do the footprint drawing as things are referenced to the centre of the pad not the edges like they do on the drawings.Ever tried putting a model on a footprint? I mean who the hell thought that people design footprints on the xz plane and offset the centre of the footprint from the origin by several sizes of footprint and then the don't put the pins down on the plane they put them if not the whole part body through the plane

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 31, 2024, 11:15:27 am
content: I agree with OP here. The pitch in X direction is given as 7.5mm, but the difference in the Y direction is not given, and this likely also varies with the voltage rating (= thickness) of the MOV. The drawing suggests that the pins are aligned with the outside of the mov (Directly to the MOV material, under the epoxy). The TDK datasheet confirms this. It has a measurement "a" and this is a column in the table and it's distance goes up to 4.2mm for the B72220S2681K101I do not agree with IconicPCB. Bending leads for DIY is not a big issue, but it's a nuisance for bigger production runs.

author: Simon
author_rank: Unknown
timestamp: August 31, 2024, 06:27:13 pm
content: Lots of data sheets are rubbish. I cherish my components library because the parts in it are parts I carefully researched and setup myself with all the information I needed and all the information I will need. If I pick up a data sheet and I am not happy with it I will probably move onto the next part. For this reason I will never ever use an STM switchmode converter chip because just 2 pages in I detect the signature style of someone trying to sell me something whilst hiding the obvious drawbacks of the part by not talking about them instead of just explaining what the part can and can't do. Given that switching converter data sheets are long and tedious I don't have time for people who won't play ball with me. The cost and time wasted with a substandard part will outweigh the difference in just going for a quality part in the first place.

author: IconicPCB
author_rank: Super Contributor
timestamp: September 01, 2024, 11:05:00 am
content: Dr, Andus,I appreciate the tidiness of fully dimensioned PTH footprint, You will however admit the lead pitch is a constant 75 mm irrespective of MOV rating.Hence lead bending is really not an issueso long as the general space is sufficient for the SAFE positioning of a component whose primary purpose in life is to blow up ( and not damage surrounds).

author: tooki
author_rank: Super Contributor
timestamp: September 01, 2024, 12:25:40 pm
content: Quote from: Doctorandus_P on August 31, 2024, 11:15:27 amLuckily they do sell versions with the leads bent into a single plane for easy machine insertion.What I also wonder is if the lead offsets could potentially be described in the IEC standards referred to in the TDK datasheet.

author: wraper
author_rank: Unknown
timestamp: September 01, 2024, 12:44:20 pm
content: Quote from: floobydust on August 24, 2024, 05:46:50 pmAnd there is nothing wrong for component to not be aligned straight other not looking as pretty. In fact PCB designers often do not bother with hole offset at all.

author: floobydust
author_rank: Super Contributor
timestamp: September 01, 2024, 07:44:04 pm
content: MOV's can have HV on them and sitting crooked, leads nearby or touching adjacent parts is bad, it can arc during impulse testing. In production, who has time to sit and straighten them out? Hobbyists yes. I prefer to have a decent PCB footprint, auto-insertion included.MOV's there can be up to four different lead configurations. Bourns offers straight and outside kink.Last year, I'd emailed Bourns showing them their datasheet is shit with the omitted dimension and for the lead bending option as well. Requested samples as a workaround. Never heard back, and the datasheets are still dated 2018. I think what happens is they source the parts from Asia, and that manufacturer has vague or incomplete datasheets and it trickles on down.No problem, there are other fish in the sea:Yageo MOV 10D Seriesprovide the dimension "e".Panasonic ERZ V seriesprovide the dimension "L".EPCOS/TDK StandarD B722* seriesprovide the dimension "a".Littelfuse UltraMOV series provide the dimension "e1".EvenWürth Elektronikprovide the dimension.Is there some point the Bourns datasheet can blamed for its low quality? Strange how responses are "nothing wrong here"

author: Simon
author_rank: Unknown
timestamp: September 02, 2024, 05:12:12 am
content: As I said, if I am not happy with the data I just move on, as you said there are other suppliers. I believe I too have contacted bourns in the past when I could not get a 3D model pointing out that no model was no sale for me as it was essential for designing the overall product, I got no reply, and found an alternative part.