measuring amps at tailcap

Okay, so I don't know how to do an amp test. I can only get a reading at milli-amp, not full amps. Also, I cannot change modes to get to high. On top of that, once I put it all back together, now my moonlight mode is 3x brighter than before. Sheesh.

A rundown on the setup. This is the Mountain FET driver, with a single IMR 18650.



Feeding a dsche quad with XPL-Hi's




I could only read .385 mA on the low setting (but couldn't hold the phone plus both leads). When I change the multimeter (and leads) to record amps, I get a big zero.

So, what am I doing wrong?

Well I'm just assuming here but it appears you are on the wrong scale. The red lead should be on the 10 amp input. What you need is a set of leads with a 4mm plug on one end and a test point clamp on the other. Makes like soooo much easier. Even better a modified talicap with the leads coming out the back that go right into your meter.

ETA you will need to change the selector knob to the 10 amp scale too! Don't worry it wont hurt nothing doing so.

Thanks M4 (though I prefer the M1a , although I did try with the other settings. I just happened to have the leads and selector on the milliamp scale when I shot this picture. I am a fully licensed low-voltage contractor, yet this stumps me !!
Always felt I'm better at the physical stuff rather than electrics.

Your idea of modifying a tailcap to take readings "on the fly" is a good one. I've certainly got plenty of 6P caps sitting in my spares box that I can fab up. But in this case, I've seen it on other posts as being a pretty easy task.

Is it possible you've blown the fuse on the 10A setting?

Are you aware that the meter will affect the behavior of the light? For single-cell designs it can be pretty significant.

DrafterDan said:

Thanks M4 (though I prefer the M1a , although I did try with the other settings. I just happened to have the leads and selector on the milliamp scale when I shot this picture. I am a fully licensed low-voltage contractor, yet this stumps me !!
Always felt I'm better at the physical stuff rather than electrics.

Your idea of modifying a tailcap to take readings "on the fly" is a good one. I've certainly got plenty of 6P caps sitting in my spares box that I can fab up. But in this case, I've seen it on other posts as being a pretty easy task.

Click to expand...

Noob here, so take with a grain of salt, but:

+1 to M4a1usr.

Positive lead in the 10A socket, negative lead in the COM socket, selector to Amps (not milliamps). On the light end: Positive lead on the threads, negative lead on the battery - (doesn't really matter, but you will get a negative symbol the other way around). Also, those stock leads aren't going to give you an accurate reading. You will need a set of very short, heavy-gauge leads to test amps more accurately. I just DIY'd a set out of solid-core 10ga. construction wire. :thumbsup:

Did you get this figured out yet?

Nope, I kinda gave up on it. I need to be able to measure across the load, which means I'd have to modify a tailcap to have an in-line lead that I can read from.

Plus, I messed up the settings on the driver, changing them to default and losing the super-low moonlight mode. I will have to replace the driver.

ahhh! I do not think i have a pic from what i did.
i got a tape switch, guted it out, soldered thick short wires and fed them though the switcl plastic case (in place of a standard switch buttion)

if your flashlight does not have a compatible tape switch model, you can do the saee thing with a switch PCB 920mm) by pressing it on the flashlight body.

DrafterDan said:

Nope, I kinda gave up on it. I need to be able to measure across the load, which means I'd have to modify a tailcap to have an in-line lead that I can read from.

Plus, I messed up the settings on the driver, changing them to default and losing the super-low moonlight mode. I will have to replace the driver.

Click to expand...

Which firmware did you get on the driver? Maybe just needs a mode group change.

To change your modes using the meter your leads act as the switch, so when your leads are connecting battery to light switch is on, break the connection and switch off. So mode changes are done simply by lifting a lead and reconnecting, brief off and back on.

May i ask what firmware is your Mtn FET driver flashed with?

DS, I figured it out. It has ToyKeeper's excellent firmware (which apparently I forgot sbout), so I did the 8 click thing and set the modes. ToyKeeper 4 life!

DrafterDan said:

DS, I figured it out. It has ToyKeeper's excellent firmware (which apparently I forgot sbout), so I did the 8 click thing and set the modes. ToyKeeper 4 life!

Click to expand...

Sweet..! Time to enjoy the light now.

Dan,

Sounds like you got the mode thing figured out.

In terms of the readings - it sounds like you have the leads in the right plugs (10A and COM) and the meter set on A. When you connect do you get any light at all (regardless of reading)? If not, then I would go with the above suggestion that you blew the fuse on the 10A circuit in the meter.

I'm actually kinda surprised you did pop the fuse for the lower mA readings as well trying to take a high current reading in the mA mode - I've done that many times.

ShineOnYouCrazyDiamond said:

If not, then I would go with the above suggestion that you blew the fuse on the 10A circuit in the meter.

Click to expand...

+1. Should have stated that earlier as well. Those Harbor Freight DMMs have been known to pop fuses quite easily. I wouldn't be surprised if they are actually 5A fuses.

My understanding has always been that to read true current a clamp meter is necessary. I could be wrong...

Yeah, that's how I see it too. Haven't had time to modify one of my z44's just yet, but it'll happen

I got one of those clamp style amp meters, I haven't used it yet, but I am curious to compare readings both ways. If I get a chance I'll post my findings.

I bet for most the clamp style DC amp meter will do most if not all what folks are probably looking for in a measurement. But if your trouble shooting losses across a circuit they cant do the job. Clamp on's tend to measure down to tenths of an amp while a pass thru device (DMM's) will go down to milliamps. So if your driver has a moonlight current output function I would think your just going to see zeros if trying to make that measurement with a clamp on. But really does it matter?

MikeB. said:

I got one of those clamp style amp meters, I haven't used it yet, but I am curious to compare readings both ways. If I get a chance I'll post my findings.

Click to expand...

The comparison will depend greatly on the design of the light and the condition of the battery. If you have a good regulator and a little overhead on the battery voltage, the difference should be minimal. On the other hand if you are doing direct drive with low-resistance mods, the difference can be huge.

m4a1usr said:

I bet for most the clamp style DC amp meter will do most if not all what folks are probably looking for in a measurement. But if your trouble shooting losses across a circuit they cant do the job. Clamp on's tend to measure down to tenths of an amp while a pass thru device (DMM's) will go down to milliamps. So if your driver has a moonlight current output function I would think your just going to see zeros if trying to make that measurement with a clamp on. But really does it matter?

Click to expand...

That's generally true, but you can wrap multiple turns of wire through the clamp to increase the sensitivity. Two turns makes it read twice the actual current, ten turns gives you an extra decimal place.