Test leads for your Multimeter

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old4570
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gorann wrote:

Than I will first try to make new leads, and will try to measure currents with my 3$ multimeter (DT850 or something). (because I also bought that 3,01$ from dx, so maybe its their fault, not MMs fault...)

If that doesnt succed, than I will buy some 10$multimeter...

@old4570 are you sure that thesde 2 MMs you recommended me can measure higher amps? I just need confirmation.

No guarantees , sorry ... I have the UT33C Uni-T multimeter , and everything in this price range seems to be similar , but the original leads were current limited past 1A , the leads I used for a long time came from a better quality analog MM , that my father used in testing TV's ...

Im going to go and buy some more wire [ leads ] in different sizes and see how they perform ... [ Later in the week ] 

This is interesting stuff .... 

 

 Always remember , the easiest thing in the world to do , is to expel hot air from your lungs and through some vocal chords ..
The resulting sound may , or may not be worth listening too ….

 

agedbriar
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gorann,

You may want to have a look here:

http://www.lygte-info.dk/info/Measurement%20UK.html

ChibiM
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Can anybody help me as well.  (hopefully this is still on-topic?)
I have 3 sets of leads. With all of them giving different readings.

The lowest reading test leads, I want to cut down, so short, that there is just enough wire left to connect to a flashlight.. About 20cm leads.. Do you think this is a good idea?

I guess that this helps to give me some better reading, less resistance! am I right?

2100
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ChibiM wrote:

The lowest reading test leads, I want to cut down, so short, that there is just enough wire left to connect to a flashlight.. About 20cm leads.. Do you think this is a good idea?

I guess that this helps to give me some better reading, less resistance! am I right?

Shouldn't be an issue.  Most tailcaps have pretty low resistance from what i measured, even the Yezl.  (when i connected them in series to measure current, and compare the current drop)

JohnnyMac
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All you're doing with all of this is fooling yourself and accomplishing nothing. The crazy cheap DMMs are garbage (I owned one) and do give low readings due to crappy leads. I bought an Equus 3320 from Amazon for $15 and nowmy readings match what others are getting from quality DMMs like Flukes and such.

A good DMM comes calibrated for the leads it has and takes into account the internal resistance of the leads.  By running crazy thick lead wires just to get higher readings is like baseball players using steroids and blowing the stats curves. It doesn't make your light any brighter and ruins accurate estimates of it's performance. If you are getting more than 2.8A draw from an 8*AMC driver equipped torch running a single cell than you are doing it wrong. Getting 5A+ from a light known to only draw 3.8A doesn't help anything.

ChibiM
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Okay, that will let me go ahead, and cut them down... (soon)

Leelou
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JohnnyMac wrote:

A good DMM comes calibrated for the leads it has

What is it really? I've read posts that say DMMs doesn't take into account lead resistances. And now you are saying they do. Can we settle this once and for all?

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Pulsar
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this is a controversial subject. i dont believe in modifying leads. but i also have compared my multimeter readings to the ohms law.

 

here is some data from doing readings on my ecig. 2xRCR132a and a 2.5ohm atty. test done right now

 MultimeterOhms Law
Voltage6.596.59
Ohms2.52.5
Amps2.42.636

 

now, im not able to check voltage under load, but substitute 6.59 for the nominal voltage 2 rcr123a will give you (6v) and bam, ohms law says with 6v and a 2.5 ohm load will give you 2.4a

edit: i know that my ecig has a significant drop in voltage under load. i just dont have a setup anymore to check it. im using 2 lithium batteries with circuits to limit voltage to 3v per cell under load. they have been off the charger for about an hour so are still pretty well topped off

 

this is a 15 year old or so craftsman digital multimeter.

 decide for yourself but also find a way to actually verify your readings and accuracy.

 

ohms law... try it out

JohnnyMac
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Leelou wrote:
JohnnyMac wrote:

A good DMM comes calibrated for the leads it has

What is it really? I've read posts that say DMMs doesn't take into account lead resistances. And now you are saying they do. Can we settle this once and for all?
Everything I've read and understood is that quality DMMs do take lead resistance into account and are calibrated. Cheap DMMs like HarborFreight specials (my old one) and cheap fleabay specials do not.  It's why my crappy old one was way off on the low side and my new Equus reads perfectly.  I even tried new leads on my old DMM and it was still off.

Get yourself a good DMM and leave it alone to get accurate readings. If you want to get increased output from your torch then replace the driver-to-LED leads with better wire and clean all internal connections.

HKJ
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The leads for a DMM does not affect the current calibration.

But the current consumption of a light will change with the resistance in the DMM and test leads!

The current consumption will also change with the battery quality and charge state.

I can use any leads I want on any of my meters and they will show the same current (When using a current source and not a flashlight):

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Pulsar
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JohnnyMac wrote:

Leelou wrote:
JohnnyMac wrote:

A good DMM comes calibrated for the leads it has

What is it really? I've read posts that say DMMs doesn't take into account lead resistances. And now you are saying they do. Can we settle this once and for all?
Everything I've read and understood is that quality DMMs do take lead resistance into account and are calibrated. Cheap DMMs like HarborFreight specials (my old one) and cheap fleabay specials do not.  It's why my crappy old one was way off on the low side and my new Equus reads perfectly.  I even tried new leads on my old DMM and it was still off.

Get yourself a good DMM and leave it alone to get accurate readings. If you want to get increased output from your torch then replace the driver-to-LED leads with better wire and clean all internal connections.

also the impression i get from all the topics ive read. all i can say is my dad had this craftsman for ever, and got a new one for cheap and swore that this craftsman was off because it didnt match the readings of his new one. he was going to toss it, but i didnt have one and wanted it. ive compared readings to the ohms law many times and am always very close if not spot on.

find a little set up to test ohms, voltage, and amps under load. then goto the ohms calculator and compare your readings. type in the ohms and voltage under load, then calculate what the amps should be, and see how close it is to the law

2100
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JohnnyMac wrote:

All you're doing with all of this is fooling yourself and accomplishing nothing. The crazy cheap DMMs are garbage (I owned one) and do give low readings due to crappy leads. I bought an Equus 3320 from Amazon for $15 and nowmy readings match what others are getting from quality DMMs like Flukes and such.

A good DMM comes calibrated for the leads it has and takes into account the internal resistance of the leads.  By running crazy thick lead wires just to get higher readings is like baseball players using steroids and blowing the stats curves. It doesn't make your light any brighter and ruins accurate estimates of it's performance. If you are getting more than 2.8A draw from an 8*AMC driver equipped torch running a single cell than you are doing it wrong. Getting 5A+ from a light known to only draw 3.8A doesn't help anything.

My experience has been the opposite.  It does 2.82A on eight 7135s on the short 5-inch leads.  It's a Uni-T UT-58E.  It gives you 2 pairs, one short and one 110cm long.  The 110cm long one is giving very low readings....  in fact just over 3 amps on the DRY triple XM-L on freshly charged Sanyo 2600s (the ones which gives me the highest current, even higher than Panasonic 2900 and 3100s).

Get a lux meter and do relative readings compared to various branded lights with known OTF outputs.  You will experience the sag due to heat and output cut due to glass etc....   It's better info than any $2000 DMM.

JohnnyMac
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2100 wrote:

Get a lux meter and do relative readings compared to various branded lights with known OTF outputs.  You will experience the sag due to heat and output cut due to glass etc....   It's better info than any $2000 DMM.

Agreed!
mitro
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JohnnyMac wrote:
A good DMM comes calibrated for the leads it has and takes into account the internal resistance of the leads. 

How can a DMM be calibrated to an accessory which is removable? Even Fluke has an assortment of leads that certainly have varying resistance.

I cannot believe that to be true.

EDIT: After thinking about it, and with my very limited knowledge, I'd guess they are calibrated using an very precise constant current power supply which would negate the effects of resistance of in the circuit. The power supply delivers the current regardless of resistance and allows the DMM to be accurately calibrated. Looking up info on 4-wire low resistance testing made a light bulb go off in my brain. Smile

old4570
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The MM Leads add resistance to the circuit [ testing current = flashlight ] so therefore , depending on the resistance added , will dictate current ...

So the lower the resistance , the more true the reading ..  Now we are forgetting the clicky switch  ...

It also adds resistance , so to get a more accurate picture of flashlight performance [ current draw ] it would need to be in the circuit ...

Then you would have a true idea of current draw ...

Again lower resistance leads would result in a more accurate reading ...

One way to test this is with a current limited light - Like 1.4A  , 2A  3A  ..  And knowing current is limited to such then test leads to see what effect they have ...

I have some of those 7135 x 6 drivers on the way ..  

But the plan is to see what's what .. Test Leads wise .... and how thick you need to go to get low resistance ...  [ Something interesting to test ] 

 Always remember , the easiest thing in the world to do , is to expel hot air from your lungs and through some vocal chords ..
The resulting sound may , or may not be worth listening too ….

 

viffer750
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if anybody wants to measure low(er) resistance, I can recommend this little cheap LCR DMM:

http://www.ebay.com/itm/LCR-Inductance-Capacitance-Digital-Multimeter-Meter-RCL-/320780792708?pt=LH_DefaultDomain_0&hash=item4ab0067384

It is not a professional equipment, but it has 10milli ohm resolution, this is quite enough for checking tailcap, connections, DMM resistance etc. 

 

 

unique engrish language... Smile

 

HKJ
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viffer750 wrote:

if anybody wants to measure low(er) resistance, I can recommend this little cheap LCR DMM:

http://www.ebay.com/itm/LCR-Inductance-Capacitance-Digital-Multimeter-Meter-RCL-/320780792708?pt=LH_DefaultDomain_0&hash=item4ab0067384

It is not a professional equipment, but it has 10milli ohm resolution, this is quite enough for checking tailcap, connections, DMM resistance etc.

 

The problem with this is connection and probe resistance, you have to be very careful to avoid large errors from that.

Using a 4 terminal measurement is much safer, this can either be done with a meter that has it (Present on many bench DMM, but not a budget solution) or with a power supply and a regular DMM (See my guide).

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

viffer750
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Yes, I know that. I have a labor PS and can measure low resistance.  I can say, that it is quite accurate for this price for amateurs. It is necessary to replace the leads, no question. First, you have to measure self resistance of Dmm+leads, after that you can calculate the "real" resistance of a tailcap for example.

And you have to press the probes strongly to the metal parts of course.

unique engrish language... Smile

 

ChibiM
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I actually took the worst leads and made them shorter, now about 30cm top to toe.. and they give a higher reading, but still not as high as my 2 other test leads. Anyway, just wanted to add this related to my earlier post in here

Leelou
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HKJ wrote:

The leads for a DMM does not affect the current calibration.

But the current consumption of a light will change with the resistance in the DMM and test leads!

The current consumption will also change with the battery quality and charge state.

I can use any leads I want on any of my meters and they will show the same current (When using a current source and not a flashlight):

Just to clarify. You are saying leads are not calibrated into the DMM? Or is it?

When you say you can use any leads you meant any leads that are not current limited right? Have you tried using thin long leads and did it give a smaller current reading?

I like: walks on the beach, sushi and things that are paisley.

HKJ
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Sorry, I missed this question.

Leelou wrote:

Just to clarify. You are saying leads are not calibrated into the DMM? Or is it?

It is not, you can use any leads you want, but ohms law can get you into trouble!

Leelou wrote:

When you say you can use any leads you meant any leads that are not current limited right? Have you tried using thin long leads and did it give a smaller current reading?

You might loose some volts when using thin long leads. When measuring on a flash light, the meter will show a different value, than when using short thick leads. This has to do with ohm law, not calibration.

When measuring on 230V, it is not a problem with a few volts drop and the meter will show the same value.

 

 

 

 

 

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Leelou
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That's how I understood it. Thanks for clarifying. So in conclusion using thicker shorter leads is advisable to get max current draw of the flashlight(sans switch).

I like: walks on the beach, sushi and things that are paisley.

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