Help with DMM!

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how2
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Help with DMM!

Help me choose a DMM i want to buy UT50C for £24.99

Or should I get UT60E with True RMS £49.99

http://www.maplin.co.uk/Search.aspx?criteria=dmm

My present DMM cannot measure Current Draw in amps.

Don
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If they have any N56FU (Maplin stock number) left you may be able to get a bargain - I got one for £15 - it is the cheapest datalogger available. But it is discontinued so may not be available.

http://www.maplin.co.uk/Module.aspx?ModuleNo=222041

Try clicking on the Check Stores Stock button. There aren't any left in Scotland but it is worth checking around your area, there might be some left.

 

You don't really need True RMS unless you want to measure pulsed stuff or fancy AC. It isn't worth double the price though autoranging is nice to have.

 

I've not seen a DMM that can't measure current. Obviously there are some out there, but I've never seen one.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

how2
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How measure  current draw a lot of the trustfire tr801 are drawing "Just measured mine on the tail - 1.32 A on high and 0.32 A on low"

Don
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how2 wrote:

How measure  current draw a lot of the trustfire tr801 are drawing "Just measured mine on the tail - 1.32 A on high and 0.32 A on low"

 

This is pretty good.

http://www.candlepowerforums.com/vb/showthread.php?t=236906

 

I'll get around to doing something similar though there are plenty of people where who know a lot more about electronics than I do.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

how2
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Don I have tried that and I still get no reading.

Also should I offer £10 for the DMM at maplins?

Don
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how2 wrote:

Don I have tried that and I still get no reading.

Also should I offer £10 for the DMM at maplins?

 

Worth a try.

 

Could be that the fuse has gone in your meter if it isn't measuring current - Maplin probably have a suitable fuse. I own an old Fluke meter that needs a new fuse - which will cost me more than the meter did (used)

 

You really don't need anything fancy for this.

 

Wish the same could be said for my car - which spat its head gasket today. Off to borrow a car.

Still, my assistant would enjoy the walk if it wasn't for all the fireworks going bang.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

how2
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The only reading i get is 5.61 on the low mode.

 

My meter is set ACmA and 20

Should i put it on 2?

And should it be on DCmA?

Don
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how2 wrote:

The only reading i get is 5.61 on the low mode.

 

My meter is set ACmA and 20

Should i put it on 2?

And should it be on DCmA?

 

All batteries are DC. Personally, I'd put it on DC Amps - these lights can pull up to 2 amps. They shouldn't but some do.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

agenthex
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Buy a uni-trend, they're worth what you pay. You don't seem to know a lot about this, so stick with a safe brand. Some of the cheap ones are good, but you're not in a position to tell.

 

Read this http://en.wikipedia.org/wiki/Series_and_parallel_circuits until you can understand it, and especially before you start sticking stuff onto mains circuits. The meter measures voltage (V) in parallel with a circuit and current (A) in series. Flashlights are in the 20V DC and 10A DC ranges. For stuff you don't know, start with higher ranges and move down until you get a sane reading.

Reading this makes you smarter: http://lesswrong.com/

FlashPilot
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In my part of the world, this is generally regarded as the best of the cheap DMM's. Its probably made in China and marketed under several different brand names so a a few minutes on Google will probably uncover several additional sources.

agenthex
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I would submit that this is almost as good. You can get them for free with coupon at harborfreight. I use it on lights even though I have a bench grade fluke.

 

http://www.harborfreight.com/7-function-digital-multimeter-90899.html

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Oldienea
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this one from DX http://www.dealextreme.com/details.dx/sku.32418 . It works well for me, because of the big display. I'm even elder than Don and my eyesight is bad in the short distance. It comes with quite thick leads and it mesures also temperature (separate leads included), wich I use very often. The only negative side is the size and the weight.

FlashPilot
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agenthex wrote:

I would submit that this is almost as good. You can get them for free with coupon at harborfreight. I use it on lights even though I have a bench grade fluke.

 

http://www.harborfreight.com/7-function-digital-multimeter-90899.html

You must have just happened to to get lucky and picked up an accurate one from the lottery bin. I took a battery with me to the store and tested about 20 of these meters. They were inaccurate and inconsistent, being off as much as .90V on a 4.15V battery. I have done this twice, about one year apart to see if they had changed in accuracy, but unfortunately they have not. I have two of these meters kicking around here somewhere. I wonder if there is a calibration pot inside that I could adjust to dial in more accuracy. The idea was that if they were accurate enough, I could give these to my friends so they could test their own batteries with the flashlights and chargers I give them.

agenthex
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I have several of them and they're pretty good. However they are the model with the backlight (everything else inside is the same). These things are usually calibrated from the factory.

 

They do have a pot inside, but I've never had to use it.

 

I've bought all sorts of cheapo chinese metering devices (temp, weight, distance, tach, gauge) and they've all been uncanny accurate. What's sorf of funny is that NIST et al will accept factory cals for measurements, and these things are orders of magnitude less expensive than an aftermarket calibration.

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FlashPilot
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None of the free/inexpensive Harbor Freight DMM's come with a backlight. Out of approximately 50 units (yes I actually did open and test that many during my two visits to the store) none were even remotely accurate and deserved to be ran over by a large garbage truck. I'll dig through my boxes later to see if I can locate one and mess around with the pot. I'll target 100% accuracy at 4.20V against a calibrated FLUKE DMM, which should be good enough for testing voltages close to these ranges (+/- .01-.02V)  If this works out, then we might be onto something useful, but ONLY if measurements can be repeated against a KNOWN calibrated reference. For those without access to a calibrated DMM, these cheap free DMM’s at HF seem to be more than useless. I'll check out the backlight version the next time I'm at the store but most people wont want to pay that much for a DMM just to check flashlight battery voltages, which is the whole point.

Do you have a link for the model you have?

Thanks!

Don
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There is also the small problem that shipping to the UK from Harbor Freight would kill the deal. If they do ship outside the US.

 

Maplin are no better - and a good deal more expensive - but they will deliver to the UK.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

agenthex
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http://www.harborfreight.com/7-function-digital-multimeter-92020.html . I got mine at the store.

 

I think it's exactly the same thing with a small backlight stuck on the display. I get within a hundreds or two on a battery for all of them, close enough as to make no difference. Maybe your HF gets the reject ones or something :).

 

OTOH, the only slightly funky meter out of a bunch of cheapo ones I've got is this tester http://www.dealextreme.com/details.dx/sku.24219. It's very convenient especially after I moded to accept 18650, but consistently about 0.05v high on a fully charged lithium. But you have to cut it some slack as it's powered by the DUT, compensating for the test load, and probably cal'ed for ~1.5v. I still use it though, because it's precise, just not necessarily accurate.

 

BTW, how did you manage to open and test that many without employees getting suspicous? The packaging is relately easy to open, but not that easy to open, and kind of pain to put everything back. Believe me, I've thought about it Smile

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FlashPilot
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Thanks for digging up the link. I'll check it out the next time I go in and bring along a charged battery to check their accuracy. They do look identical in the photo to the free one. Id really like my friends with lithium ion cells to have a tool to accurately measure their voltages, and package it along with any future flashlight gifts I give them. The first one I got from HF was way off in accuracy so I assumed it was a fluke. When I returned it for exchange, the clerk behind the counter said that they had many returns from those that had other quality DMM's to check their accuracy.  There was a huge bin full of these things and a couple of lose ones without packaging. The blister packs they use to package them slides over a cardboard backer on the packaging and is held in place by a small staple. I picked up one of the lose DMM's and tested it and was shocked to find that it reported completely different results. I swapped leads and got the same results. I went to the clerk and complained and asked him if I could borrow his stapler so i could test a few samples. He didn't mind. I only removed the meter from the remaining samples, not the leads, and reused a pair of tested lose leads. I have done this on two separate occasions about 1 year apart and got the same pathetic results. I have noticed that the free meter can share 3 separate sku's, although they appear to be identical, and the clerk said that they were. It is entirely possible that the problem is not with the meter itself but in the equipment used to calibrate it. I also wonder if the cheap 9V battery inside has anything to do with the accuracy of the meter, especially if reporting voltage fluctuates with the voltage/amperage to power the darn thing. Things such as temperature, humidity and the way the DMM’s were stored and transported can have a huge impact on cheap electronic as they age in the warehouse or supply chain. I just rummaged through a few boxes and couldn't find my cheapo HF DMM's but I'm sure they will turn up soon enough.

If you don't mind, could you please try adjusting one of your pots to see if you can dial in more accuracy? Id particularly be interested to see that if once calibrated for 4.20V, would it accurately report down to 1-0.9V? Possibly by narrowing the voltage test scale for our uses, more inherent accuracy might be realized. This would definitely be a win for everyone with access to a HF and an accurate DMM to calibrate the HF DMM.

agenthex
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I've noticed too that the leads that come with these are often different (for the same sku!), though the meters look the same far as I could tell. However, they should all work more or less the same since they're are all semi based these days and there's really not much to them and not much to screw up. But then, our friends in the chinese light business often remind us otherwise.

 

I'll check the pot next I get a chance.

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how2
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Don wrote:

If they have any N56FU (Maplin stock number) left you may be able to get a bargain - I got one for £15 - it is the cheapest datalogger available. But it is discontinued so may not be available.

http://www.maplin.co.uk/Module.aspx?ModuleNo=222041

Try clicking on the Check Stores Stock button. There aren't any left in Scotland but it is worth checking around your area, there might be some left.

 

They had some but they wanted £24.99Surprised

Don
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how2 wrote:

Don wrote:

If they have any N56FU (Maplin stock number) left you may be able to get a bargain - I got one for £15 - it is the cheapest datalogger available. But it is discontinued so may not be available.

http://www.maplin.co.uk/Module.aspx?ModuleNo=222041

Try clicking on the Check Stores Stock button. There aren't any left in Scotland but it is worth checking around your area, there might be some left.

 

They had some but they wanted £24.99Surprised

 

The one I got for 15 had no software or leads. I wasn't bothered as I had both already.

 

I'd actually say it is worth £25 - it once sold for around £60. On the other hand, whether it is worth it to you is another matter. Anything reasonably accurate will do fine.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

agenthex
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FlashPilot wrote:

If you don't mind, could you please try adjusting one of your pots to see if you can dial in more accuracy? Id particularly be interested to see that if once calibrated for 4.20V, would it accurately report down to 1-0.9V? Possibly by narrowing the voltage test scale for our uses, more inherent accuracy might be realized. This would definitely be a win for everyone with access to a HF and an accurate DMM to calibrate the HF DMM.

 

The pot directly tunes the voltage measurement. It's fairly sensitive but I can adjust it within .01v pretty easily.

 

Mine are already accurate, so they've always matched up at 1.3v same as 4.1v.

Reading this makes you smarter: http://lesswrong.com/