Resistance and Inductance of Motors and Controller Parts.

[johnrobholmes]

You guys really give me tool envy. What an awesome asset.

[amberwolf]

(I've never owned a chair, and this is the first desk/workbench I've ever had in my life. lol I've worked just kneeling on the floor for years).

That's usually how I work on stuff, because then I can spread the project around me and work on it, instead of being limited to just a bench or other work surface. Plus, I *have* to pick up my stuff when I get done or else the dogs will play with the bits and pieces...if I used workbenches I would leave stuff cluttered all over them instead. Actually, I *do* both of those: use a workbench/table/etc., *and* leave stuff all over it when I'm done, often losing tools and stuff for months or years because I suddenly need the work surface for something else, and have to rake all the previous stuff into a box....

If anyone has some litz wire they want measured and quantified for resistance and freq vs linear inductance etc, feel free to send me some, or really any parts you've got that you've not been able to get specs on.

I'm tempted; I have a few of the soda-can-sized caps from various linear power supplies that I am curious how good they still are (some are 30-40 years old, maybe 50, but probably don't have more than a few hundred hours use on them, if that). Also some Elna caps out of Sony 1" VTRs that I'm unable to find specs on, that used to be filters for the brushless tape reel drive motors and power supplies. (there are also lots of solid-state-relays in there that I wish I had a pinout and specs for, but can't find anywhere, and IR doesn't respond to inquiries about them).

[Jeremy Harris]

Note enough bench space.... you will fill it by the end of the year!! You must always have 5 sq feet of unused bench space... for safety sake... and so you can buy another instrument!!

You beat me too it, Bigmoose! I was going to suggest doubling the size Luke thought he needed.

Jeremy

PS: I'm on my 5th generation workbench come storage rack design; each time I make them bigger than I think I'll need, each time I run out of space within a few months......................

[liveforphysics]

LOL!

I was thinking doing a 6ftx2ft bench, with a 6ft x 1.5ft mid-shelf, and a 6ft x 8in top shelf would be over-kill. Soooo much bigger than my lap, which served me well for that last couple decades. lol


Speaking of more equipment, as soon as the wallet recovers, I'm thinking about getting a good bench DMM to go with my kick-ass LCR meter (but I don't want to spend more than a couple hundred ).

Thinking maybe something like this:
http://cgi.ebay.com/Guildline-9578-Sola ... 500wt_1156

A computer option like this also seems attractive:
http://cgi.ebay.com/Signametrics-SMX204 ... 623wt_1153


But then I was thinking maybe just a lot of el-cheap 4.5digit multi-meters like this might be better for me, because it would give me 4 separate channels to observe voltage or current with reasonable 4.5digit resolution:

http://cgi.ebay.com/Lot-4-True-RMS-Digi ... 769wt_1139


Or maybe a kick-ass 4-channel USB logging scope/multi-meter?
Or a scope with ground isolation between channels would be kick-ass too. It's super lame being tied to the same ground plane when you want to over lay scope traces.

[liveforphysics]

Here is another of that 8+ digit multi-meter, but with some error message (wait @ F), does that message mean anything to you guys?

http://compare.ebay.com/like/4001644720 ... 602_304692

[bigmoose]

Luke, I am biased AGAINST computer connected instrumentation. Sooner or later you goof up or the circuit goofs up. At the voltages we are working with, and with potential ground loop problems, the probability of FUBARing the laptop is just too high in my opinion. The dollar value may be the same, but I have invested way, way too much time in the software, files and system build on my laptop.

That said, I got my HP 3456A voltmeter (6 1/2 digits) for a couple of hundred bucks, and I didn't wait and shop for the best price. All these old HP items have the GPIB bus so you can automate your readings if you want with Labview software, which is what I use.

Also I have secured auction material from these two sites. Trouble is they do not ship. You or someone must go and retrieve it. Most of my power supplies are from these auctions as was my tab spot welder. Statistically 80% work out of the box, 15% need power supply repair, and 5% is totally trashed and fit for the dumpster. You know I'll go and retrieve for you within my driving area.

http://gsaauctions.gov/gsaauctions/gsaauctions/
http://www.govliquidation.com/index.html

[liveforphysics]

Luke, I am biased AGAINST computer connected instrumentation. Sooner or later you goof up or the circuit goofs up. At the voltages we are working with, and with potential ground loop problems, the probability of FUBARing the laptop is just too high in my opinion. The dollar value may be the same, but I have invested way, way too much time in the software, files and system build on my laptop.

Ehh, I've got 3 outdated netbooks just laying around. I run only open-source or cracked bootleg software, and the data I want on them is also copied other places, so it's not really like I loose anything other than a paper-weight if it fails and wrecks a netbook. But I do see your point there my friend.

That said, I got my HP 3456A voltmeter (6 1/2 digits) for a couple of hundred bucks, and I didn't wait and shop for the best price. All these old HP items have the GPIB bus so you can automate your readings if you want with Labview software, which is what I use.

Also I have secured auction material from these two sites. Trouble is they do not ship. You or someone must go and retrieve it. Most of my power supplies are from these auctions as was my tab spot welder. Statistically 80% work out of the box, 15% need power supply repair, and 5% is totally trashed and fit for the dumpster. You know I'll go and retrieve for you within my driving area.

http://gsaauctions.gov/gsaauctions/gsaauctions/
http://www.govliquidation.com/index.html

What a cool site! I will keep an eye out on the lots for awesome things.

Thinking about it more, it does seem like a 6.5digit meter would be more than I would really ever need, and those HP's do seem to have great specs. I might just pick one up. (after next payday, lol, right now I'm pretty short again. lol)

[Ricky_nz]

One of my workmates had a dell laptop and somehow and he somehow got 24V between 2 of its ports (not sure which).

He had the accidental damage insurance option that was part of the deal when he brought it.

The surprising bit was that they covered the replacement mother board .
I thought that insurance was for things like dropping it not using it as a resistor!


Edit: I prefer to keep things separate or only have one connection to the laptop.
I'm going to buy a USB isolator to use when testing my motor controller.

[grindz145]

I need one of these LCR meters. It's officially on the EBay shopping list.

[Jeremy Harris]

I've just done some quick calcs on the current ripple versus PWM frequency for that HXT motor, adding 10mohms to allow for lead resistance, FET resistance and cell Ri (probably an underestimate). Anyway, for 40mohms and 26uH I get the following plot of current ripple vs frequency:

HXT 80-100 ripple vs frequency.jpg

(41.28 KiB) Downloaded 2 times

I'm guessing that we want the current ripple to be below about 10%, which is easily met by the 15kHz PWM frequency of the XieChang controllers. This is reassuring for those looking to use large format FETs, because generally the big packages don't switch very fast.

Thanks for the raw data, Luke. As soon as I have a bit more spare time I'll look into this in more detail. Knowing how the inductance varies under different conditions would be very useful, but probably hard to measure. I have a suspicion that the inductance will massively drop as the core gets close to saturation, which may be the reason we see those very large current spikes that trip the XieChang over-current protection.

Jeremy

[texaspyro]

Luke, I am biased AGAINST computer connected instrumentation. Sooner or later you goof up or the circuit goofs up. At the voltages we are working with, and with potential ground loop problems, the probability of FUBARing the laptop is just too high in my opinion. The dollar value may be the same, but I have invested way, way too much time in the software, files and system build on my laptop.

Most of the better benchtop meters have optically isolated protection between the analog section and the digital section. Not too much to worry about blowing the computer (and even not-so-old laptops can be had for 50 bucks).

[texaspyro]

I need one of these LCR meters. It's officially on the EBay shopping list.

I used to be able to snag them for fairly cheap... lately they have gone ballistic. One sold for around $700 a couple weeks ago. But then Tucker still sells them for $4000+ I've been unable to buy any off Ebay for a reasonable price in years (and they don't show up very often any more).

You need to be careful about choosing them. The monitor is a bit of a sore point. All the problems that I have had with these machines have been video monitor related. I have another one right now (that I was going to ship to Luke since it was cleaner than the one he got). When I originally got it, it had a flakey connection to the CRT filament in the CRT socket. I've "fixed" it a few times. The last time it lasted for a couple of years... thought it was good to go. When I was packing it up, it went flakey again. I need to just replace the CRT socket... it takes forever to get to it. Or perhaps just add an external video connection.

[texaspyro]

I do not have a set of good kelvin leads like yours. I ordered them, but they have yet to arrive. I made my own "almost kelvin" leads up. The reference point is a couple of inches upstream of the clips.

Actually those are the semi-not-crappy Chinese Kelvin clips off Ebay. (Hint, when buying them, look at the photos carefully. Some sellers don't color code the heat shrink on the clips). Also, buy them pre-wired... it helps to be lazy. The Chinese clips close the jaws with a metal spring. The GOOD kelvin clips use o-rings or surgical tubing to close the clips. The lack of metal in the clips helps when measuring pico and nano whatsits. Tegam will sell you a pair for over $500. Agilent has them on a set for $170 (but has banana plugs). The Chinese clips are dirt-freakin'-cheap and work well. Luke did have to adjust the meter to zero out the reading offsets on the low end.

[HumboldtRc]

I was wondering if the HUG 1000uF caps were the best cheap capacitors to add to my electric pit-bike. I will be using them with the 100A Super Brain esc's. (Using 12s) (2 esc's)

http://parts.digikey.com/1/parts/41839-cap-1000uf-63v-elect-vr-radial-uvr1j102mhd.html

Stock ones with fried legs. This esc survived and still works, but the other went up in smoke. I have a replacement on the way... So i will be needing to add some good caps this time...



Any other cheap cap choices, that are still worth using...? Or are the HUG's the best cheap option...?

My pit-bike
http://endless-sphere.com/forums/viewtopic.php?f=12&t=22888

[amberwolf]

You can possibly prevent or minimize the fried legs on caps simply by using larger gauge copper wire to run to the leads on the caps, and solder to the leads right at the base of the cap, so there is virtually no cap lead length being used as conductor outside of the cap.

Most of the cheap caps have steel legs, just plated/tinned, and they heat up and melt easy under these loads.

Also, keep all the leads to all the caps as close to the same length as possible, so that resistance/inductance/etc is the same between all caps to the ESC. It may help with load distribution.

[AussieJester]

Nice bench there Luke, if you find you do want to make the benchtop bigger, dropping a larger top over the existing one and glue/nailing it in place would be easy fix.... LoL@ CNC machine and bench being in your house though, still haven't had a lil lady move in with you i gather LoL...

KiM

[katou]

Looks like a the beginnings of a good little lab there LFP. I am going through a little "reorganization" myself. I have determined that a minimal workbench-like shelf of about 18-20" deep on most walls is more valuable than traditional 30" deep workbenches. I'm replacing my 2 workbenches (32" deep) with one, and two wall mounted "shelves" (18-20" deep). It seems that I get more use out of having horizontal surface to hold tools and projects, rather than truly "working" on the bench. This leaves more floor space in the middle for a movable project assembly/worktable.

Time spent on workbenches and such, I have never felt I wasted. I also scored a bunch of kitchen cabs (uppers and lowers with drawers) that revolutionized my workshop. Pegboard is evil. (JMHO)

Oh, one suggestion. Your long shelf looks like it might sag if loaded right up. If you add a piece running along underneath on edge, (say 1x2) there will be no sag. You probably already thought of that, but, there you go anyway.

Keep up the good work, keep pushing the envelope. It inspires me to keep on trucking too.

Katou