Test leads for your Multimeter

Excellent thread.

Quick question for the experts: are there any commercially available DMM leads you'd recommend? I have these from DX, but apparently the new batch is useless for any high current applications and when I am getting people started with flashlights and explain battery safety, I'd rather be able to give them something that looks professional, even if it's inferior to DIY leads.

http://www.robotroom.com/Multimeter-Reviews.html

It seemed a fairly good comparison. When I can afford it, I think I will get either one of these meters. I can't check amps currently.

http://www.amazon.com/Aidetek-VC97-multimeter-Capacitor-Frequency/dp/B004VNF7DW/ref=wl_it_dp_o_npd?ie=UTF8&coliid=I166MMMEDA13U&colid=3426XMTDQJOOO

http://www.amazon.com/Sinometer-Manual-Digital-Multimeter-MS8268/dp/B000JQ4O2U/ref=wl_it_dp_o_npd?ie=UTF8&coliid=I28GZUL259QNIC&colid=3426XMTDQJOOO

Too much to buy and so little moneyTongue Out

The closest from standard metric sizes (and quite suitable for measuring flashlight tail currents) is 2.5mm2 stranded (pletenica) wire.

Make your own leads, using banana plugs that you can buy locally, and 0.5m (or less) of that wire per lead.

EDIT: When choosing a DMM, look for standard 4mm connection ports. not the thinner ones (2.5mm, I think they are).

Can anyone point me towards good (cheap) banana plugs that I can build my own with. I have ones that are made for audio stuff, but they screw together and pinch the wire for the connection. There's no good way to solder them (even though I have) and there is way too much exposed metal just asking for a short circuit. Old's look pretty good, are there other options?

Wire is easy enough and I have gator clips I like, I'm just missing suitable plugs.

A measuring lead is a length of wire with suitable plugs on both ends. I suggest plugs of the "4mm banana" type, as they are the most standard in our part of the world and you connect them to most DMMs directly and use the "bananas" on the other end as simple probes, or fit some special attachments to them (pointed probes, alligator clips, whatever).

This is just for the picture, I'm sure you can buy them locally:

http://www.made-in-china.com/showroom/huanleijiangxian/product-detailJqxnDrTdJHhO/China-4mm-Banana-Plugs-Set-Four.html

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 ....

gorann,

You may want to have a look here:

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

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?

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)

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.

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

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?

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

Multimeter Ohms Law
Voltage 6.59 6.59
Ohms 2.5 2.5
Amps 2.4 2.636

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

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.

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):

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

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.

Agreed!

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. :)

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 ]