Milli-Ohm Meter - Hybrid and EV Stator, Fuse, and Wire Diagnostics

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great. now I want one of these.

👍︎︎ 1 👤︎︎ u/Freekmagnet 📅︎︎ Jul 18 2018 🗫︎ replies
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Hello, I am Professor John Kelly and this is  the WeberAuto YouTube channel. Today I'm going   to show you an amazing tool that somehow I have  never used before and never heard about and it   is the milli-ohm meter now I had never heard of  a milli-ohm meter until a few months ago when I   was reading an article in motor Age magazine I'm a  contributing editor to motor age magazine now and   again and there's an article written by another  contributing editor Mr. David Macholz I hope   I'm pronouncing that correctly he's a Toyota T-TEN  instructor out of Suffolk County Community College   in Selden New York and the article is about megohmmeters and milli-ohm meters now if you do any   work on hybrid or electric vehicles you probably  have heard of the megohmmeter or giga-ohm meter   the Fluke 1587 meter back here, and I've had one  of these since 2007, but I've never heard of the   milli-ohm meter so let's take a look at why this  thing is so cool and why you may want one if you   do any type of electrical diagnostic work not just  on hybrids but any type of electrical diagnostic   work I think once you see what this thing does  you may want one now this is a very expensive   tool it's around $1200 - $1300  depending on where you buy it okay   just some basics about an ohmmeter. An ohmmeter  has really never been a very useful tool in my   opinion because all it would do is show you if a  circuit was open or not open. the resistance value   that you would measure with an ohmmeter could be  inaccurate if the power was on, which of course the   power in the circuit is always supposed to be off  when you use an ohmmeter, but I've never really   trusted ohmmeter readings in all of the time I've  been a service technician Ana professor so we will   compare just a regular ohmmeter reading to the  milli-ohm meter in this video the megohmmeter   the Fluke 1587 meter we will come back to in a  different video okay if we use just a regular   old meter at a high-quality Fluke 87 series 5  multimeter and we rotate the selector dial to   the ohms position we can measure resistance and I  have a piece of wire right here just a small piece   of wire it's 39.3 inches long which is 1 meter  in length and we connect some good quality meter   leads to the meter I've got alligator clips on the  the ends of these meter leads whenever you measure   low resistance values with any multimeter you  should zero out the meter to compensate for the   resistance of the meter leads so on the Fluke 87  meter there is a relative button with this little   triangle or the Delta symbol we just push that  and now with our meter leads connected together   we are reading zero ohms all right now if I come  in with our 1-meter long piece of copper wire   and I connect one meter lead right there and the  other one on the opposite end we are reading 0.1   ohms of resistance for this 1-meter length of wire.  This wire here that we'll measure next is 1/10 of   that so it's 100 millimeters and if we measure  its resistance I get the same 0.1 toggling to   zero so almost the exact same reading with the  tenth of the lengths all right then I have a 10   millimeter long piece of wire right here and we'll  just clip that in here and I'm reading zero ohms   okay so this meter wasn't designed to read real  small resistances clear down to 0.1 ohms is its   resolution, which for most automotive work is fine  but let's take a look at we're measuring smaller   resistances than 0.1 ohms would be possibly  valuable now let's do the same thing but with   the milli-ohm meter now this milli-ohm meter is  from a company a Japanese company I'm probably   pronouncing it wrong HI OKI or HIOKI. Its model  number RM3548 and it's called   a Resistance Meter and this will measure clear  down to 0.1 micro ohms. so milli-ohm   is thousandths of an ohm. micro-ohm is millionths  of an ohm, this will measure 0.1 micro-ohm, that's 100 nano-ohms it can measure at  its finest resolution, so incredible accuracy.   well, let's prove it. The milli-ohm meter  uses two meter leads with alligator clips of   course, but these meter leads if you look at it  have two wires per meter lead, so when you plug   in the meter leads to the meter there's two wires  per lead, okay so let's measure this 1-meter length of   wire we will turn on the milli-ohm meter there's  an optional temperature sensor here for the meter   and I would highly recommend that you purchase  that otherwise you have to do a calculation to   compensate for whatever the temperature of the  conductor is that you're measuring the meter we'll   assume that it's at a certain temperature and  then if that temperature is wrong then you have   to do a compensation calculation to determine the  correct resistance with the temperature sensor as   long as the meter the sensor and the conductor  and the leads have in the same area for around   six hours is what they recommend to let everything  stabilize to the same temperature then the meter   will measure the resistance of the air in the room  that will be the same temperature as the part that   you're measuring and then the resistance value  that it comes up with will be accurate because   resistance is affected by the material it's made  of the temperature of the material itself the   length of the material and the cross-sectional  area of the material so let's measure this 1   meter long piece of copper wire the instructions  that come with the meter tell us that when you   take a measurement that you should wait about 10  seconds to let the meter stabilize and come up   with an accurate reading so this milli-ohm meter  is showing us that this 1-meter long piece of   wire has a resistance of 53.06 milli-ohms now  that's 0.05306 ohms, now   our other meter our Fluke 87 meter that  wasn't designed for this type of low resistance   readings was measuring 0.1 ohms not 0.053  ohms and the rule of course   is to round up so in round-up mathematically  point one was correct but this is 0.05302   ohms, 53 thousandths of one ohm Alright now if 1 meter   is 53 milli-ohms then one tenth of the length  of that wire so 100 millimeters should be   5 milli-ohms so let's try this let's take the 1  meter length out let's put in the 100 millimeter   or 1/10 of a meter and look at that we get  5 milli-ohms how cool is that? so a tenth of   the resistance which of course it should be if one  meter is 50 milli-ohms and 1/10 of that this little   10 millimeter long piece of conductor I have right  here copper wire should be 0.5 milli-ohm so let's   measure it next 0.59 it's a little longer than  10 millimeters 0.5 milli-ohm that's incredible   accuracy I mean you might be wondering well how  is that useful for On-Car Diagnostics well in a   hybrid vehicle, which is why Toyota is recommending  this tool you, have a stator winding for MG1 and   MG2, and for any vehicle with stator winding so any  hybrid or electric vehicle is going to have stator   windings of some sort it could be this individual  wire a Wye-wound stator like this older design   stator right here and we can come in there's  actual Toyota specifications to come in with   this milli-ohm meter and measure the resistance  of these windings so let's do that next all right   so I'm going to take this meter and go from the U  phase connection to the V phase connection and we   are reading 104.3 let it stabilize for 10 seconds  and notice this is at room temperature here in the   shop which is pretty hot, 28.3 degrees celsius  so the U to V resistance of the   stator windings is 104.4 milli-ohms, now  that is a 12 strand connection so there's 12 wire   strands there now let's go from U to W remember we  were at 104.4 now we're reading 104.2   and the toyota specification is there should be  no more difference than 2.0 milli-ohms difference   between each measurement, we were 0.2 milli-ohms  different between those two, now let's go from V   to W 103.9 that's still a 0.5 milli-ohm difference  between the highest reading and the lowest reading   which means this stator is not shorted it does not  have wires that have shorted out overheated lost   their insulation and shorted out and are touching  each other but that is something that can happen   on cars, and I have a 2002 Prius right over here  that we will go measure this vehicle has a problem   with its transmission there's something wrong that  caused the vehicle to lose power and now when you   try to drive it it's really jerky goes to choo,  choo, choo, choo, choo, choo, as you try to move it   and I believe that it has a shorted stator and so  we will use this tool to measure that but before   we do that let's look at a different style of  stator a newer design stator is called a hair-pin   style stator and it doesn't use the small  little wires like we saw in that earlier Toyota   stator this is out of a 2nd generation Chevrolet  Volt the 5ET50 transaxle, but the latest transaxle   from Toyota also uses this hairpin technology,  what we mean by hairpin technology is each   one of these big heavy pieces of flat wire are  actually shaped like a hairpin, it's a u-shaped   piece that has been bent laid in place and then  welded together on the back here with another   hairpin stater element and now we have all of  these individual welds that can have potentially   poor connections and so we can also use this same  milli-ohm meter to measure the resistance of this   style of stator so let's do that let's  take a measurement from U to V notice now we   get 34.8 milli-ohms much, lower  resistance than we had before on the wire-wound   stator okay now let's go from U to W 34.68  milli-ohm and then W to V 34.82   so all of these are easily within the  2 milli-ohm spec that Toyota gives us I don't   know what GM would give us for a specification  because I have not seen this tool used or called   for in any GM diagnostic yet but I'm sure they  will so this is a GM stator the other one was a   Toyota but both of them have used both the wire  wound and the hairpin style welded stators here   what we're looking for is consistency, we want  each measurement across each phase to be very   close to equal, a tiny bit of difference is okay  but not a lot. Now before we go over to the   car and take some measurements of the the stator  windings in the vehicle I want to show you a few   more things that are amazing about this milli-ohm  meter so I I was wondering how accurate can this   thing be and so I got just one of my alligator  clip style jumper wires here and I stripped off   the insulation for about 50 millimetres of the  length of this jumper wire now I counted there   are 24 strands a very fine wire in this flexible  jumper wire so let's measure the resistance from   one end of this jumper wire to the other with all  24 strands and intact and then let's start cutting   one strand at a time and seeing what happens  all right for the entire length of this jumper   wire here with all 24 strands we have 36.44  milli-ohms of resistance, now if I just come in   and pick out one wire strand I'm going to come  in and cut that wire strand and let's watch what   happens to the resistance reading here so we're at  36.42 we cut the wire strand   and we go up to 36.54 now  the reason we went up is because these wires are   in parallel with each other so every time you  put wires in parallel with each other the total   circuit resistance goes down so now the circuit  resistance has gone up so now we're at 36.50   let me pick out one more wire  strand 36.49 right now and   we cut it and now we're at 36.65  so we went from 36.49 to   36.65 roughly 0.15 or 0.16  milli-ohm per strand. so I've got, I've cut   two strands, so now I can predict what will  happen when I cut the next one if we go up by 0.16   milli-ohms per strand when I cut the next wire we  should go up to 36.80, 36.81   somewhere right around there so  I'm going to come and cut the wire here it comes   it's cut there we go 36.81  exactly predictable is that incredible or what so   we can get right down to determining wire strand  resistances and how many wire strands are broken   in a length of wire so another incredible thing  here this meter can tell you how long the wire is   so there's a length button right down here if  I go ahead and push that button turn it on we   punch in the resistance per meter now we measure  roughly 50 milli-ohms of resistance per meter in   this copper wire earlier so now if I hit enter the  word length shows up on the screen and I can come   in and connect our meter leads to this 1 meter  length wire and now it tells us that it is   1.0662 meters in length so based  on the resistance of the wire, it can tell you   how long the wire is that's really cool so now  let's go to this 100-millimeter length wire   100.11 millimeters it's now showing us and  now let's go down to this 10-millimeter length   wire there 11.06 millimeters, now I  I still need to think about it, I'm still wrapping   my head around how cool this meter is there's got  to be some really cool diagnostics things that we   can do with this besides just check for shorted  stators on a hybrid or electric vehicle, alright   one of my co-workers Will Spiegel was here in the  shop yesterday and he said hey I wonder if you   could check the resistance of a fuse and measure  a voltage drop across a fuse based on that, so I   thought wow that's a really good idea so I went  over to their 2017 Chevrolet Bolt EV and pulled   out five of the spare fuses that are in the under  hood fuse block so now let me put the meter back   to resistance measurements let's measure the  resistance of five common sized fuses so these   are the little micro fuses the General Motors uses  this is a 10 amp fuse and we are reading 7.562   milli-ohm so roughly 7.5 milli-ohm  but we don't have to go roughly it's we can it's   7.55 milli-ohms at 28.3  degrees Celsius. Alright now that's   7.5 milli-ohms for a 10 amp fuse here's  a 15 so we were at 7.5 milli-ohms   on a 10 amp fuse now we are at 4.783  milli-ohms for a 15, let's do the 20   3.486 milli-ohms on a 20 amp fuse  2.7195 milli-ohms on a 25 amp fuse and 2.3117, 2.3165  it's stabilizing milli-ohm   2.3 milli-ohms on a 30 amp fuse so each fuse has  its own specific resistance and I measured two   other styles of fuses and their resistance values  are very close to what these measured here   so for a certain size of fuse, it should have a  certain resistance now with that resistance if   we go over to the vehicle and take a voltage drop  measurement in a live circuit right across the top   of a fuse so here's a 15 amp fuse right here if we  take a voltmeter put it on millivolts and measure   right across the top of that which I did as you  can see in this photograph here under the hood of   the Chevrolet Bolt EV over there I measured 17.5  millivolts dropped across the left-front low beam   headlight fuse with the headlights on so 17.5  milli-volts that's 0.0175 volts   now if we divide that by the resistance  of this fuse that we just measured which is   in milli-ohms of 4.783 milli-ohms  that's 0.004783 ohms   so basically if we take 17.5 milli-volts and we divide it by 4.783 milli-ohms  the current going through  that fuse with the headlights on was 3.56 amps   and it's just basic Ohm's law stuff.  So you can measure the milli-volt drop across a   fuse if you know the fuses resistance, which you  should probably measure, there's a lot of garbage   fuses for sale out there, and there's high-quality  fuses for sale, I'm going to buy some less than   reputable brand fuses and compare them to the  factory fuses that come in these vehicles and   see if the resistance values are the same they're  milli-ohm resistances I hope they are but I know   there's been some problems with some that weren't  and and the fuses weren't blowing when they were   supposed to blow. Okay, so, with this meter we can  measure milli and micro and even nano ohms of   resistance which is useful for measuring the  stator winding resistance to find a short circuit   I've shown you that we can cut an individual  wire strand and it can detect the difference   there I've shown you that we can not only measure  the resistance of a piece of wire but we can tell   you how long that wire is that might be useful in  somehow determining where a short-circuit is I've   still got to think about that but I this is not  the last video I'm going to do with this milli-ohm   meter there's got to be other uses of  this meter I'm just barely playing with it now   and I really like it. Now the last thing I want  to do is let's go over to this 2002 Prius with   what appears to be a transaxle problem and  measure the resistance of the stator windings in   the vehicle itself. okay here we are under the  hood of a 2002 Toyota Prius first generation   Prius but this could just as easily be any other  Prius or electric or hybrid vehicle on the road   it doesn't really matter what matters is that we  can access the three-phase cables that go down   to the transaxle from the inverter converter  assembly because that's where we are going   to use our milli-ohm meter so let's take some  measurements okay our first measurement will be   from you the U phase to the V phase and we are  reading 32.88 milli-ohms   of resistance at 28.6 degrees  Celsius here in the shop now the resistance will   go up as it gets hotter it'll go down as it gets  colder so we're looking for consistency alright   now let's go from U to W 35.12  milli-ohms of resistance so we were at 32.89   milli-ohms and now we are at  35.11, that is more than the   2 milli-ohm maximum allowed by Toyota so that  indicates a problem. Alright now let's measure   from V to W now we're getting 26.98  milli-ohms so our very lowest value   is right here between the V and the W phase at  26.982 milli-ohms our   very highest value was between U and W at 35.11  milli-ohms and then we had one   in the middle that has a shared branch of the  Y wound stator of 32.89   milli-ohm. so we have 26.9. 26.9  was the lowest, 35.1   is the highest that gives us roughly an 8.2  milli-ohm difference between the highest   reading and the lowest which tells us that there  is definitely a problem with the stator windings   for MG2 which is what this goes to on this 2002  Prius which is why it jerks really hard it has   melted through the insulation around the  stator windings it may even have contact with   the stator frame which in the next video on meg-  ohm and Giga-ohm meters we will go in and learn   how to check for loss of isolation or check for  insulation it's an insulation tester so we   will learn how to do that so by comparison I have  this exact same P111 transaxle in the backroom   over here with a good stator winding for MG2 and  all three measurements that we've done here on   that transaxle measure are identical they're  almost all 35 milli-ohms and so that's what   we're looking for so the milli-ohm meter is a very  useful, but expensive, but very useful tool. we can   tell when stator windings are starting to melt we  don't have to wait until it totally gets to where   the vehicle is chugging and kicking and spitting  out trouble codes if it's acting strangely with a   little bit of jerking or pulsating as you drive  even if it has a trigger to trouble code yet we   can go in and take those measurements and see  because this seems to be a fairly common problem   on high mileage Prius transaxles and the newer  ones with those hair pinned technology Staters   with all those additional welds and connections  have even more potential of problems hopefully we   won't see that this has been a review of the basic  use of a milli-ohm meter thank you for watching
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Channel: WeberAuto
Views: 29,027
Rating: 4.930131 out of 5
Keywords: Ford, Volt, NATEF, Weber State University, FCA, CCAR, Oh My!, CAT, Prius Plug-In, Tesla Model 3, Hybrid, Guy in wheelchair, Aisin, fuse resistance, Weber State Automotive, milliohmmeter, NACAT, John D. Kelly, STEM, Stator, Fluke 87, Resistance, Toyota, THS, stator diagnostics, Cell Groups, WSU, Hioki RM3548, Nissan Leaf, Prius Prime, milli-ohm meter, Professor, UAT, Chevrolet, ASE
Id: bVKuYOA3F2E
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Length: 29min 0sec (1740 seconds)
Published: Sat Jul 14 2018
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