truck electric leak

"David Lesher" wrote: (CLIP) But Leo seems to think proportional == linearly proportional.

^^^^^^^^^^^^^^^^^^^^^ From Your Dictionary.com: "Math.: "having the same or a constant ratio"

I've always been taught to put a test light between the negative lead and the negative post. Do your same fuse study. If the light is burning, something is on.

"DanG" wroteI've always been taught to put a test light between the negative

^^^^^^^^^^^^^^^^^^^^ It's not an electrical reason--it has to do with safety. Having the ground cable dangling in the engine compartment poses no risk of a short (to ground.) However, I consider an ammeter much better than a light bulb. It's going to be in series with whatever is draining the battery, which could cut down the current to a level that doesn't light the bulb. If you do use a light bulb, use the lowest wattage you can find. Possibly even a

ive> lead and the negative post. =A0Do your same fuse study. =A0If the ligh= t is

You connect both in series and the bulb protects the meter from a short or heavy load. The 10A range on the $4 HF meter reads down to

jsw

Sorry I've not been tracking this thread. For future reference: a thick-walled "impact" 1/2" drive 9/16" good quality chrome-moly

Given enough force (long enough cheater) it should have either turned the bolt or sheared it in torsion. After splitting a few Craftsman sockets I started buying good ones. Oddly enough, some really good ones are quite inexpensive: Wright at Fleet Farm. They're not pretty (black, not shiney) but they're strong and well made.

As you discovered, red to orange heat always works but minimizing collateral damage can be an issue.

Replacing fuses in a DMM used in ammeter mode can get old after a while. Been there, done that.

For those inclined to tinker a bit, as I think Andrew might be, a solution is to make some shunts of known (low) resistance. Connect shunt in series with load, measure the voltage across the shunt, calculate the current. Weston shunts of yesteryear were 50 millivolt shunts. 100 amps at 50 millivolts is 5 watts, no big deal but not negligable either. The shunt can be made of convenient material -- iron, steel, stainless, brass, whatever. Nichrome and carbon are readily-available materials with fairly low temperature coefficients. Constantin and manganin are much lower but not readily available. Just make it big enough so it doesn't get spit-sizzle hot and fuggedaboudit. Don't need 1% accuracy to be useful, right? My shunts are made of copper, stainless, brass and steel. They work for me.

I calibrate/trim the shunts by measuring both current and voltage with a controllable bench supply so as not to cremate the ammeter. Once calibrated, the shunt and a voltmeter become my robust ammeter.

(...)

Also, for those super low-impedance current measuring requirements, you can use a Hall Effect current sensor to great effect.

I used some of these:

--Winston

Especially if its a Fluke with UL listed fuses at $10 each...(in Oz, anyway) Which is ridiculous - you can fry a $10 DMM and just curse about it. Same with over voltage protection in Flukes - had to fix mine twice now, not cheap. Again, the $10 DMM would be cheaper/easier. But I paid approx $200 for the Fluke, years ago, its my favourite meter (no logic to that, of course)

Yep. Done that - gets a bit dodgy with high current and very low resistance shunts - the R of the terminals etc etc. Very rarely do I attempt to measure high currents anyway, the bench power supplies have in built 30A meters - and the clouds of smoke are usually a dead give away that something is wrong......(bugger).... But its a good idea Don, thank you - I do have a few WW2 vintage round Bakelite cased 100ma meters, so having one set up like you describe as a dedicated high current meter would be a good idea....

Winston - thank you for the link, what a truly amazing device that IC is....wonder if its available here in less than tube quantities...

Andrew VK3BFA.

The fuse is there for SAFETY. Your $10 DMM probably has an unfused shunt. Or a crappy fuse that is short enough that 240VAC can arc from end to end if the fault current is high enough. Fine for electronics and 12V, but not for an industrial control panel. How much is your vision worth? Those aids for even partially blind folks are VERY expensive.

Best regards, Spehro Pefhany

I just made one to test. 15" of 0.030" galvanized steel wire dropped

When you experiment with your own wire, the length to use is between the inner two connections and it doesn't matter whether they are the voltmeter or the current. The reason is a good student exercise. Hint

- what's the I*R drop in the voltmeter leads?

The original HF probe tips plug into the curled edges of female 0.250" Faston terminals.

The $4 HF meter resolves 0.1mV on the 200mV range, ignore the decimal point and take the entire displayed reading as Milliamps.

I have at least four of those HF meters for fault monitoring like this, as well as good meters for serious measurements. The HF ones are accurate to +- 1 or 2 counts, the usual standard for DVMs, but the good ones have more digits.

Jim Wilkins

(..)

Can you buy from any of these vendors, Andrew?

--Winston

That steel wire stayed shiny while charging a battery at 5A. Galvanizing dulls when it nears its melting point.

Well, that didn't work at all! Try this:

That should work better.

--Winston

Notice that the noise level equals about a quarter of an amp. and the total error can be 5% of 50A for the X050 over the Commercial temperature range, so you need a way to calibrate or at least zero it. The simple way to use it would be to connect a 1 - 5K pot across the supply ( 3 x AA cells) and meter between the device output and the pot wiper. Use the pot to zero the meter when current =3D 0. I would add a shorting switch to zero the meter reading without disconnecting the circuit.

That ought to be enough to check a truck electrical system.

Sears sells a DC clamp-on meter which may use that device or one similar. I tried one in their parking lot on a cold day and found it was unusable because the reading drifted so fast, >300 mA in less than a minute as it cooled down.

Jim Wilkins

(...)

The noise is A.C. that A.M.s the output voltage, yes? It can be filtered and / or averaged out.

Sounds like D.C. offset compensation. That is a good thing because the offset spec is +- 30 mV.

For those otherwise impossible low-impedance current measuring tasks, an accuracy of +- 7.5% from -40 to +125 C was sufficient for my purposes. Readings from these devices agreed within 2% with a good quality ammeter during my cross - checks so I figured that was good 'nuff.

Clearly a naked DMM is more than sufficient for truck electrical system testing, without these fancy devices.

I haven't seen a car battery yet that breaks into open loop oscillation when presented with a load impedance 10% higher than normal. :)

--Winston

They don't give the frequency range, it could include drift. If you use an op amp to filter and level-shift the output, be careful that the op amp doesn't rectify the noise into a false DC offset.

I'm so used to having the right electronic test equipment that it's hard to think up simple alternatives sometimes. This morning I checked the DC output of a genny using a 300A Weston shunt to measure the current.

jsw

Sounds like a "git 'er done" attitude to me. That's the way to go.

--Winston