Two ammeters in parallel

[williamwright]

I'd forget and connect up something with exposed metal parts.

Bill

[Indy Jess John]

But to be a problem the exposed metal parts have to make a short circuit. Inside the car there is only the (painted) seat frame or the door handles that your "something" might short against, because the seats are upholstered and the floor is carpeted and the parcel shelf is hardboard. Also the wire to the new cigarette lighter socket is protected by its own in-line fuse, so a short would blow it.

Jim

[williamwright]

Don't worry, I'd f*ck it up.

Bill

[Paul]

If running appliance loads off the lighter socket, you might want to know that.

Paul

[RayL12]

OK, I think I see the picture noe. I was disregarding leads as zero effect. But at very low resistivity in the shunts, I guess the leads can be a big part?

If this is the case. I get it :-)

[Indy Jess John]

I won't be offering you a lift then :-)

Jim

[RayL12]

I think today's education, in a few fields, is based on software output, or, pre programmed hardware where the 'light says it's right'. Maybe?

Try convincing the youth, indeed people, of today they need to learn the long route to anything because one day they may be in a situation without a device that tells them what they need to know.

Phones today are closer and closer to 'Star Trek' tech. And, in the future, the handiest place to keep the hardware will be in the skull.

Warehouse operatives wear ear pieces and talk into a mic and get constant feedback where others have eye pieces that direct attention to a parcel and then guide to the spot it is to be placed. Amusingly, if a particular parcel is wanted, the graphic will show where it is in a block of parcels and tell you which other parcels it is easier to move to access it. Constantly scanning, the new parcel arrangement is remembered.

In the Audio workplace, talking to a workmate was frowned upon and the 'orange jackets', some who would stand with folded arms and watch you work all day would even have the balls to come and ask what was so important it had to be talked about? Disgusting, morbid places. But, at

12 to 20 miles a day walking, healthy :-) I did about 6 weeks. TF it was my last year before retirement.

In the 90's while re-slating a roof, the young lad working along side me asked, 'what's it like nailing your old school books to a roof'?

[RayL12]

Or a block of cheese that can be called cheese as long as there is at least 6% real cheese within.

In the 60's I asked granddad why he has a wired switch from his tv to the armchair. Because I don't want to listen to those adverts. And, he told me why.

He also explained and told me to listen out for the 'hooks' that are used before an advert, or, at the end of an episode that is designed to draw you back. Some were so poor that the whole program would lose it's flavour. It took less than 2 minutes for the, highly acclaimed, 'Game of Thrones' thing. And, oddly enough, because of the well made up tit popping actresses.

Oh, and just the one, enjoyable, opening episode of 'Lost'. Years later when I hear people moaning about the 'ending', I had a satisfying feeling and 'sent' my good thoughts to granddad.

Honestly, there are more truths in the The Simpsons.

[RayL12]

LOL. Excellent picture :-)

[John Rumm]

You really have demonstrated your astonishingly poor comprehension skills again. Go look at the thread again - the *vast* majority of the posters (i.e. all but a couple) were right on the money form the start, or at least quickly understood and accepted corrections.

Yes there is thread drift (usenet, what do you expect?), yes noise from TNP barking Kirchhoff at everyone like an over enthusiastic puppy, and a bit of misunderstanding about whether Bill's meters were a matched pair or not, but when it came down to it, the majority of posters answered Bill's question correctly.

Now does that mean I believe "this thread does demonstrate the group's understanding of electronic basics"? - no that is another comprehension fart on your part. While there are many posters here with excellent electronics and engineering backgrounds, that is no reason to assume its necessarily everyone's field of expertise or interest.

[tabbypurr]

My first tv had a remote control. Wired of course. It had something like volume & line hold on it.

NT

[tabbypurr]

Let's get a few basic facts right.

1. The original question is very basic stuff.
2. Some contributors know the answer, some did not.
3. Too many confidently advanced bogus ideas about very basic aspects of electricity

I therefore conclude that this is one more example of this group being confused on basic electrical matters.

Then there's thermodynamic matters. IIRC your armchair expert opinions included the notion that evaporative cooling doesn't work in the uk. I've enough experience of it to know it does, though it's not the same as refrigeration a/c. Unlike you I also know how it works.

NT

[williamwright]

Best not.

Bill

[alan_m]

Too many people who knew the answers were correct and deliberately questioned the validity of those answers in order to wind up some other contributor.

No-one questioned the general effectiveness of evaporative cooling in the UK only that it was not effective in the UK with a crude swamp cooler - a wet towel draped in front of a fan running inside a room, or with a similar high priced snake oil product with dodgy advertising.

[Paul]

This is my meter (the meter I use most of the time). Page 17 lower left corner has the current measurement shunt. it's not a Kelvin setup, just an ordinary resistor. The BOM in the front of this document, does not give sufficient detail to determine what it's made of.

The shunt is 10 milliohms. What's the resistance of a mated banana plug ? Or how about the connections and methods to get a wire to the meter ? The shunt would dissipate 4W when measuring the max 20 amperes allowed. It would be cooking in there if you blindly tried to use it. If it has a tempco, it'll be "over-the-moon" at that point.

In fact, even with a single multimeter, measuring current is problematic. I don't really think the specs in the user manual do justice to how bad this is.

The accuracy is listed as +/-2% plus 5 digits. Which means the digit in the last place pretty well flaps in the breeze.

With 20A into it, the shunt develops 20A * 0.01 ohm = 200mV FS.

I tested it with a 1 ampere source (3.3V wall adapter, 3 ohm power resistor), and the voltage developed across the meter starts to rise with time. Which means as (something) in the path gets hot, the total resistance of that leg of the circuit is changing.

So even without adding two panel meters or two multimeters to the mix, the measurement is already a shambles.

Why do you think I *never* measure current with a multimeter ? There's very little wear on those meter connectors. The 20A scale, today is the first time a test lead has been plugged in there. I have used the 200mA scale for setting up some low-current constant current sources.

The clamp-on ammeter (which cost 3x what my multimeter cost), the zero on it tends to drift. I would expect the Hall probe to drift a bit as it warms up. It uses the right-hand rule to make measurements. A voltage develops across the Hall Probe silicon die, in proportion to the constant current source pushed through the probe, and the mag field into the face of the die. Each of these things being on a different axis (X-Y-Z). But the clamp-on ammeter is non-intrusive. For the person with the BMW who sought to measure vampire loads while the car is off, a clamp-on ammeter offers the best possibility of making a measurement without setting off any tumblers in the car. You can't tell that it's making a current measurement. Not under most circumstances.

I measured the vampire loading on my 2002 car, and it was less than 20mA (that's the absolute lower limit on the clamp-on meter - Hall Probes can go lower than that, but the meters for sale don't usually play in that range). My car doesn't update its Facebook page, when you pull the key out. It's electrically mostly quiet (I think the OBDI connector might respond, if you plugged into it).

A Kelvin shunt made with manganin, is a start at a decent shunt, but the whole idea of shunt measurement is just asking for trouble. That's why some of the Kill-O-Watt meters, when they failed, people would open them up and find the shunt had melted the solder it was sitting on, and the shunt "floated out of place". That's why you don't measure electric kettles with a Kill-O-Watt meter, because of whatever shortcut was taken in shunt design. The specs for the Kill-O-Watt meter imply measuring kettles is OK, but you should be automatically suspicious when they make claims like that. Even in the case of my multimeter, with its 0.01 ohm shunt, the full scale power dissipation is 4W and there's no air movement inside the multimeter to speak of. "A soldering we will go..." That's why the duty cycle is ON for 30 seconds, OFF for 15 minutes (ugh!). That's an advertisement for "we did something naughty in here". I don't have to worry too much, testing at 1 ampere.

The clamp-on DC ammeter, it can measure 400 amperes all day long, and all that happens to it, is the nine volt battery will die on it. There are no "soldering-like" incidents. I've measured 150 amps with that meter, that's the highest thing I've measured so far. Imagine what kind of shunt it would take to do that, the other way. Mr.Kelvin would be as big as your arm and have fins for cooling.

*******

That's why this meter is about the best you can do in the Chinese jokey meter market. The last picture in the advert, shows it is a low-side monitor. OK, so it doesn't have any real specs. Who is counting ?

Paul

[John Rumm]

So far, so profound (not!)

A minority... still we can't all know everything.

Using that logic we can argue that as a group we are all confused on all basic matters.

From the man who apparently does not even know what a swamp cooler is, you are not in a good place to accuse others of being armchair experts. Especially with your posting history!

BTW, still waiting for the apology from you for wasting all our time in that thread as a result of your sloppy terminology / cluelessness / fibs (delete as you feel fit).

I guess we all have delusions.

[tabbypurr]

Lol. ICBA

NT

[tabbypurr]

You haven't even got as far as discovering the things work in the UK, and your 'explanation' of why you think they don't is also wrong. All you got to reply with is ad hominem bs.

NT

[John Rumm]

Oh, so you CBA after all?

I can't.

I would not call any of that ad hominem. In fact I try to counter the message and not the man in the vast majority of cases.

I did cite your posting history since you make many strong assertions, and yet provide little that one can use to gain confidence in those claims. We have little visibility of your profession or skills or qualifications. We know little of your background or the type of work you do. You post little or nothing about any projects you have been involved in be it professionally or personally; not even photos of stuff you have built or fixed or restored.

IMHO, the whole online persona seems to be carefully crafted to give away as little as possible, and so there is also little to inspire confidence and trust.

You are often keen to denigrate the collective skills of the group and yet in many cases seem more inclined to dismiss or criticise rather than actually share your knowledge with actual teaching.

[tabbypurr]

I guess that's one way to acknowledge that you don't know me or what I've done or do now. And yes, I keep my private life mostly out of public places. That's deliberate and I'm fine with that.

But your comments on things when you clearly have no idea what the facts are do not generate respect. I spend /most/ of my replies sharing what I've learnt, it is imho the primary purpose of this place. I learnt a large chunk of what I know from reading people here doing likewise. That does not mean I'm going to hold the hands of people that cba to type a few words into google or spend numerous hours explaining what has been written about enough times elsewhere. Nor am I interested in spending my time on people that are more into being dunces than learning anything. When it comes to non-ac cooling technology alas you fall into the bracket of strongly held opinions without knowledge, which quickly degenerates into duncity.

As for criticising what people say, no group gets everything right and no group has all the expertise it thinks it has. Such is human nature, and this group is not exempt. Nor are you, I or anyone else. Some of us are aware of that & cautious in what we say, some not. I point out errors because otherwise everything that follows is male cow parts, and no-one learns any thing.

And if you want me to say a group that can't work out how ammeters in parallel work is expert in electronics, er, no. Ain't gonna happen.

When I make what you regard as outlandish claims it's because I've done them. I like experiments and have done a lot of them. They solve a lot of problems. Experiments are also how businesses are started. I've experimented in diy with noise reduction methods, fillers, plumbing, heating, cooling, paint, various tools, cement products, lighting, glazing, curtain hardware, fans, glues, cleaning, limited locksmithing, roofing etc. I've restored a car and fixed up houses. My main area is electronics, where I've done a lot. If you think I'm bsing, pick one from noise reduction methods, plumbing, heating, cooling, paint, tools, cement products, lighting, fans, cleaning, roofing, in most diy cases I don't mind discussing it. Not so much the electronics. The experiments cover the full range from trying what 1000s have tried before to trying to develop new tech. The latter I don't get into. Most diy experiments have been very basic but useful.

When I discuss things I've not done I try to make sure I say so with phrases like I'd expect, but I've not done it and so on. I'm not perfect, nor are you. When you come back with stream of stupidity stuff you can't really expect me to agree. Mostly you're sensible but now & then you absolutely are not. When getting into ad hominem if you bear in mind you really don't know what the facts are, maybe then we can keep it sensible. That would be more productive.

NT