Ohms resistance meters

[weidit]

Hi guys sorry if in wrong place.
I have a half decent elec tester (fluke) but it's no good when Daikin ask me to check pins on boards.
Is there one you guys would recommend? Can it also be used as a mega to test compressors?

Also is there some specials prongs you can get as board pins are so small?

Many thanks

[james10]

i have a fluke 332 which is my main meter it is small and has a built in amp clamp meter and its fine on most things including daikin perhaps you need a meter that you can adjust the resistance scale on the fluke 179 is a good choice (around £250) if you can get one or RS do an equivelant called isotech idm93m around (£80) which i use for serious fault finding rs also do needle tip test probes
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3402538&cm_sp=Merchandising-_-Featured-Product-_-3402538

[weidit]

Ok that's sounds like what I need. Will that be like mega so can test comps? Many thanks

[james10]

they dont havea built in megga i think they start at around £500 for a decent one my gaffa dosent think us mere fridgies need a meega so i have to borrow one as and when from the sparkys

[weidit]

I don't think I need to worry about a mega tester then...
I must need a tester that can be set to different resistances!

Does anyone know what setting you would have it on to check a compressor or is it different on each one?
My fluke tester only has on continuity setting and on brand new comps it just beeps between them and flashes 3 normally.
Could you have it on say the 200 setting and you would get a better degree of Reading say 150 so you can see if they are close? I have never really understood the testing of motors.

Many thanks

[devlin maguire]

Why would you want to do IR on windings or am I misunderstanding
Dev

[james10]

Why would you want to do IR on windings or am I misunderstanding
Dev
The idea is to check the resistance across the compressor windings in order to check the state of the compressor also to check earth continuity, A compressor should have the correct readings as per manufactuers guidlines although a megga should be used in most cases, a multi meter can confirm suspicions

[james10]

I don't think I need to worry about a mega tester then...
I must need a tester that can be set to different resistances!

Does anyone know what setting you would have it on to check a compressor or is it different on each one?
My fluke tester only has on continuity setting and on brand new comps it just beeps between them and flashes 3 normally.
Could you have it on say the 200 setting and you would get a better degree of Reading say 150 so you can see if they are close? I have never really understood the testing of motors.

Many thanks
I normally start on the lowest scale and work up

[devlin maguire]

Alec sorry I should have said that "megger" is now misused as a generic term for anything that will carry out insulation resistance test they will apply 250,500, 1000V some DC some AC some do both,carrying out this kind of tests on windings is risky, a low resistance ohms meter is best and the scale does not really matter if your just adding up the ressys all that happens is you move the decimal point set it to the lowest and you will probably get one decimal point IE 2.13 ohms shift it once and you get .213 I use a tiny one from scewfix that I have soldered shrouded croccy clips to with long leads get a resistor of a known value and check it regularly a check box is better and they are as cheap as chips
Dev

[weidit]

Cheers for help guys..!
How much are these mega meters? Is there a particular make to get?

So start at lowest and work up? What kind of Reading would you expect on a compressor?

[weidit]

Can you use this to check if it's down to earth?

When would you want to use a Megga?

[martinw58]

for checking inverter units you need a meter that is true rms maplin sell them not to expensive

[devlin maguire]

Your low resistance ohms meter will do for checking to earth one term on the pins and one to the case or any earthed part continuity here means comp is dead
I am still not clear what you mean by a megga meter?
Dev

[devlin maguire]

Yes martin but he's talking about continuity and resistance not voltage
Dev

[TRASH101]

When they say "megga" I think they refer to "Megger" A company (who makes various testers and charge a fortune for them) that made their reputation building Insulation resistance testers.

[james10]

Can you use this to check if it's down to earth?

When would you want to use a Megga? You use a megger or "Earth Insulation tester" to check a motor continuity to earth to which there should be none.
A multi meter will also tell you this but a lot of manufactuers recomend using a megger as the tolerances can be very fine.

[devlin maguire]

Hey Trash I can remember the wind up ones that charged up a capacitor wooden cased things then bakelite they were made by Megger and the name stuck with all IR testers since just like Hoover, also the first multi meters were made by Avo again the name stuck till quite recently
Dev

[weidit]

for checking inverter units you need a meter that is true rms maplin sell them not to expensive



True rms?

My tester only has one ohms settings doesn't read low enough.

I thought a mega throws volts threw something to test it?When ppl call them megger meters then it's like hoover? ( a make not a object)

[TRASH101]

I can remember the wind up ones that charged up a capacitor


Well remembered Dev
How much fun were they:D

[devlin maguire]

I think there is confusion over function and terminology a ohms meter tests continuity and low resistances IE s a piece of cable or similar, is it continuous,and what is it's resistance to current flow
an insulation resistances tester tests the insulation be it pvc, rubber, paper, etc and the ability to resist the flow of curent through it if you apply a Megger or similar to windings at say 250v if it's a winding rated at 230v yes you will check its continuity, at a voltage higher than the rated V you will melt the insulation and it will come out as a fail so dont go meggering willy nilly it's pointless and not really required,I have never done it
Devlin

[TRASH101]

Alec



True rms?



Can't see that you really need it. If you need to get involved in fault finding inverters to any great degree you'll get an oscilloscope and an electronics qualification.




My tester only has one ohms settings doesn't read low enough.


For testing winding resistances you need (almost always 0-20 ohms. To test continuity to earth you need 0-20 Mohms.


I thought a mega throws volts threw something to test it?

It does. So does continuity testing, its just a question of how much you throw.

[TRASH101]

voltage higher than the rated V you will melt the insulation and it will come out as a fail so dont go meggering willy nilly it's pointless and not really required,I have never done it

Wise words from Dev. To the best of my knowledge "Megger" testing was developed for testing WIRING INSTALLATIONS upto the point of isolation and NOT for appliance testing.

[devlin maguire]

Spot on Trash spot on
Dev

[weidit]

Oh ok so I can use continuity (ohms) symbol to test a loop a cable like belling out cables to vrv's but I need a resistance tester to check windings etc....

This is what I have http://www.alertelectrical.com/prod/127/fluke-t5-1000-electrical-tester this is no good for fault diagnostics?

Do I want to buy one that has differant settings of ohms readings? Could someone give me an example of one? I want to get one and check the dead comps at the yard to have a practice...
Many thanks

[Brian_UK]

I have one of those Fluke testers, all it is good for to testing if voltage is present.

If you want to check sensors etc then you need a good multi-meter.

For insulation testing then you need an insulation tester, Google that and see what's around.

[weidit]

So when your on the phone to Daikin they asked
me the other day to disconnect pins from board whilsw live and take continuity Reading across two pins my tester was to big and wouldn't really don it properly ( both my lead toached and gave a Reading)

I would use a multi meter?

When Daikin ask me to check resistance across compressor to check windings I need a insulation tester?


When you guys say megga is a name like Hoover is a make
and really they make vacuum cleaners. When people say megga it out what kind if tester are they actually referring to?
Many thanks

[weidit]

When checking a compressor you check between each terminal don't you?
Can I use a general multi meter with resistance settings on to check this?
This is checking the windings right?

To check if it's down to earth I need to check between each pin and and earthing point on unit for example suction pipe? What tester is used for that? Does it have be insulation resistance tester? Or can I check using a general multi meter with differant resistance ranges?

Sorry guys I just want to know so I can be more competent when checking... thanks guys

[devlin maguire]

Alec lets forget the insulation tester for a moment On the comp you have three pins use your ohm meter on any of the three set it on buzzer and stick the other probe to earth if it buzzes on any pin to earth the comp is toast, set it on any scale and it will read infinity, or in other terms no resitance it's just a lump of metal, if on the other hand you get, say, from COM pin to one other 2.5 ohms and from COM to the other 1.5 ohms, then between the run and start pins 4.0 ohms 2.5 being the start windings you then have proved the windings to be sound No need for IR tests at all you have done the testing all with your humble multimeter and stay on the same (lowest range) throuout testing. Now if you need to you can compare these values against the manufacturers data
Hope this helps
Devlin

[weidit]

Cheers devlin. That's what I needed...
Is there a certain ohms amount my tester should go to? As I see some with 10 ohms (sign) right way round to meg ohms)

Sorry to a pain but when would you use a insulation tester? MAny thanks

[devlin maguire]

without bogging you down in ohms law an example right now Iam checking the starter solenoid for a honda super dream, through the coil I am mesuring 1.41 ohms to check if this is right I need to refer to the manual now suppose it should be 2.1 ohms that would tell that although the winding is not completly shot some of the insulation is breaking down in the coil, (same thing can happen on contactors hence chattering) probably for your purposes an auto ranging multi would be best, s to an IR tester thats what it does checks the insulations ability to withstand current it wont check the cables wires or anything else for continuity, a low resistance omh meter measures the conductors resistance to current, for example a 1 metre length of cable will have halve the resitance of a 2 metre length, I carry out electrical installaion reports the checks are. Polarity,Continuity of conductors, Insulation resistance, these are three related but entirly different procedures I really cant see a reason for checking insulation resistances Like I said the readings through your comp windings tell all you need to know
Devlin if you ned more info just ask

[RatsPom]

Have a look at these technical .pdfs from Fluke

http://support.fluke.com/find-sales/download/asset/2646876_6001_eng_a_w.pdf

and also http://us.fluke.com/fluke/usen/community/fluke+plus/articlecategories/hvac/hvac+insulation+test.htm

I think these articles by Fluke should answer any questions that you have.

Mac

[weidit]

without bogging you down in ohms law an example right now Iam checking the starter solenoid for a honda super dream, through the coil I am mesuring 1.41 ohms to check if this is right I need to refer to the manual now suppose it should be 2.1 ohms that would tell that although the winding is not completly shot some of the insulation is breaking down in the coil, (same thing can happen on contactors hence chattering) probably for your purposes an auto ranging multi would be best, s to an IR tester thats what it does checks the insulations ability to withstand current it wont check the cables wires or anything else for continuity, a low resistance omh meter measures the conductors resistance to current, for example a 1 metre length of cable will have halve the resitance of a 2 metre length, I carry out electrical installaion reports the checks are. Polarity,Continuity of conductors, Insulation resistance, these are three related but entirly different procedures I really cant see a reason for checking insulation resistances Like I said the readings through your comp windings tell all you need to know
Devlin if you ned more info just ask

Cheers mate it's making a lot more sense now.
So our saying resistance checking doesn't need to be done? Don't you have to use a resistance tester to check If comp is down to earth?

Many thanks

[monkey spanners]

Youtube is your friend!

http://www.youtube.com/watch?v=6IiIIMcAVGE&feature=fvw

Check out the other similar vids on there.

Jon

[devlin maguire]

By doing a continuity check on windings you are in essence checking the isulation that keeps all the copper wire in that winding seperate from itself just like the flex in your table lamp has pvc on it,s wire to keep L N E seperate, If you know what the winding resisance should be then when you check it thats what you should get, so cable or wire resistance and insulation resitance are different, a simple way of looking at this is, take a fork place your probes on each end, then move one probe towards the other and you will see the resistance decrease untill you get 0.00 now if you wrap that fork in say cellotape except the ends, and repeat the procedure as soon as you move onto the tape you get no reading so you have proved that there is continuity 1st test and insulation resistance 2nd test So on a dead winding you would get no resitance IE it's a fork, or a reading of some sort a fork with its wrapper on.
Dev

[monkey spanners]

Here is another one worth a look which show the different use of a multi meter and a megger or insulation tester. For checking motors for shorts to earth you need a high voltage tester such as a megger, a multi meter will only test around 9v which would be like looking for leaks with only 9psi instead of 500psi

http://www.youtube.com/watch?v=RL7A18LdF9E&feature=channel

Jon :)

[TRASH101]

take a fork place your probes on each end, then move one probe towards the other and you will see the resistance decrease untill you get 0.00 now if you wrap that fork in say cellotape except the ends, and repeat the procedure as soon as you move onto the tape you get no reading so you have proved that there is continuity 1st test and insulation resistance 2nd test So on a dead winding you would get no resitance IE it's a fork, or a reading of some sort a fork with its wrapper on.



For Fork sake dont megger the fork!!!! :D

[Crash Pilot]

Thought the term megger was recognised across the world. We use that description here also. Lazy name for saying Meg ohm tester. Get a good rms fluke and you are good to go. As for leads I just grind mine down in the grinder.

[weidit]

So a resistance tester (mega) can check if a comp is down to earth?

[monkey spanners]

So a resistance tester (mega) can check if a comp is down to earth?

Its the only meter for the job. a normal multimeter only tests at 9v a megger (insulation tester) at 250, 500, or 1000v depending on model and selected mode. This puts the windings under similar strain as a working motor so will show faults a multi meter won't.

Jon :)

[weidit]

Ok cool. Cheers guys sorry I'm so slow lol!!!!
How do you know when to test 250v or 500 say? I take it's different for every make/model/compressor?

[monkey spanners]

I usually test at either 500v or 1000v, this is on motors rated at 240v and 415v.
If there are any electronic circuits etc that may be in the circuit i will test at 240v, not sure if this is correct, but its how i do it!

[SkyWalker]

i thought the correct practice was test at twice the rated voltage, so 500v for a 240v and 100v for 480v this way its a safe test and nothing gets damaged, fluke have a nice booklet a read a while back, suppose i ought to read it again! i have T5-1000 a fluke 116 (great multi meter) http://metersandtools.com/Fluke-116-HVAC-Multimeter-with-Temperature/M/B000NI69YA.htm

once i saved money i invested in a fluke 1577 insulation tester http://metersandtools.com/Fluke-1577-Insulation-Multimeter/M/B000VRJFPI.htm

there is a meter fluke do which combine both the above meters in one and will save you money in the long run