Author Topic: Voltmeter (Read 3609 times)

2windy · « **on:** May 15, 2006, 03:58:02 AM »

The only dc to dc converter from 12volt to 5volt cost as much as the meter itself. Do you think 1 1/2 volt AAA batteries wired in series to make 6 volt would work? When it says 5 volt does it mean 5 volt?

willib · « **Reply #1 on:** May 14, 2006, 10:05:49 PM »

When what says 5V ?

what are you trying to do?

2windy · « **Reply #2 on:** May 14, 2006, 10:22:52 PM »

I should of mentioned that this question is from my oringinal post on the voltmeter hookup. Look at my last posting of Voltmeter Hookup. Thanks

commanda · « **Reply #3 on:** May 14, 2006, 10:40:42 PM »

Quoting DaveW from the original thread......

You can use small batteries, most 5VDC panel meters will work with about 4.3 to 6 volt inputs...

x NiCads will give you 4.8 volts.
x Alkalines will give you 6 volts.

Amanda

nanotech · « **Reply #4 on:** May 14, 2006, 11:10:22 PM »

Use a multimeter to find the resistance of the voltmeter in question.

Multiply that resistance by 1.4 and go buy a resistor of that value.

5V meter in series with (1.4 times value) resistor hooked to 12V.

Voile. You just made a voltage divider for your meter.

By the way, I came up with the value of 1.4 by assuming the resistance of the meter as 1, dividing it by 5 (5 volts), then multiplying that by 7 (7 volts remaining in the 12 volts after taking out the 5 for the meter). That brought it up to a value of 1.4

That way the voltage drop across the 1.4 resistor will be 7V leaving 5 for the meter.

commanda · « **Reply #5 on:** May 14, 2006, 11:44:56 PM »

Don't do that. The power supply for the meter must be isolated from the voltage it is measuring.

Amanda

wpowokal · « **Reply #6 on:** May 15, 2006, 06:50:08 AM »

$#|+ this post has gone from hither too tither, buy a digital metre that can use the same supply that it measures.

'e' bay may seem cheep but, what do you need, source it from a reliable source to suit your circumstances.

Yes building isolated 5v supplies is dificult unless you are electronic savy. Buy a metre that can be supplied from the voltage it is measuring, at minimum that is 12v. So using a 5v regulator off that source, is the answer. Try this site for information on circuits.http://www.discovercircuits.com/list.htm

regards

Allan down under

ghurd · « **Reply #7 on:** May 15, 2006, 07:07:38 AM »

For something similar, we used an 8 AA holder pack, to a momentary-on switch, to a 7805 with an output capacitor, to the meter. Push & hold the button, read the meter. Cost less than the batteries.

AA have about twice the power as AAA, and cost the same here.

G-

nanotech · « **Reply #8 on:** May 15, 2006, 12:12:11 PM »

Sorry, didn't realise this was the situation.

Amanda is correct, of course.

RP · « **Reply #9 on:** May 15, 2006, 08:20:55 PM »

If you want, add a series silicon diode to 6 volts to get 5.4volts

2windy · « **Reply #10 on:** May 15, 2006, 08:55:58 PM »

Wish I knew what you were explaining to me. 7805 ,output capacitor, this is hard for me to understand, as you can see I'm not up on electronics very well. Thanks for trying to help!

ruddycrazy · « **Reply #11 on:** May 16, 2006, 04:29:03 AM »

Hiya 2windy,

Eh mate just google LM7805 to see what it does. But a brief explanation a 7805 is a 3 pin voltage regulator IC, it uses Capacitors to smooth the output and by reading the datsheet will explain it all, also the datasheet has plenty of schematics on how to use the IC. This chip will serve your purpose to a tee- 1 7805, 2 cpacitors, 4x AA batteries and you have your 5 volt power supply for your meter. TOO EASY

Cheers Bryan

ghurd · « **Reply #12 on:** May 16, 2006, 07:02:48 AM »

Very simple.

Push the button. 12V goes to the LM7805, 5V comes out. The capacitor smoothes the output.

Figure a standard LM7805 will have a 2.5V drop, meaning it needs 7.5V input to be reliable. Also as the batteries get low, their voltage drops.

The local parts store should have everything.

No idea how large a capacitor you need. Maybe 10uF?

Might want to 'Right Click' and save this to you files now.

I probably won't leave the drawing online very long.

G-

(I can tell it got bigger. I uploaded a 367x413 file. ?)

dinges · « **Reply #13 on:** May 16, 2006, 07:32:29 AM »

Guys,

I'm reading this thread in utter amazement. This guy doesn't know how to wire-up a digital voltmeter module.

The response he gets goes into diodes, isolating voltage converters, LM7805s, etc.

I have to agree, for me this is easy stuff too.

But keep in mind the level of expertise of the original poster.

I think wpwokal said it best; try to find a voltmeter module that does NOT need an isolated powersupply. That way, you can use the module to measure its own power supply voltage. Preferably get a module that can work straight off 12V (have never seen one myself though).

Or get a simple, cheap universal digital multimeter (DMM); they have their own 9V battery.

No matter what else you do, if you want to delve more deeply into RE, try to increase your electronics knowledge. It will come in handy at the most unexpected moments.

There are no shortcuts here for knowledge; not even this board.

Peter.

TomW · « **Reply #14 on:** May 16, 2006, 08:13:44 AM »

Dinges;

Yes, good points!

Not particularly applicable to this thread / poster but some folks should just pay for a pro to do stuff. Advice here can often over simplify or over complicate the matter.

I often have a simple solution to these electrical /electronics questions but will usually not post them because I don't think a lot of the posters are clueful enough to be aware of the pitfalls in connecting things. I saw one comment [given in good faith, I am sure] advising a dropping resistor from the voltage to be tested. Following that advice will destroy almost any of these type meters but I do not have the energy to argue the point and if I did there would be 5 people who simply for the sake of argument would take the other side.

Anyway just the nature of communities. You have the clueless the know it alls and the genuine savvy folks who are happy to help. The text all looks the same on your monitor so determining which advice is good advice is very tough.

Bottom line on this meter setup seems to be it needs a dedicated power supply for the meter and to conserve that source you would want a momentary contact switch that activated the meter when needed. Even that simple setup may be beyond a lot of users but we just cannot tell from this side of the screen. Also in many [most] electronics the voltage requirements are seldom critical values. You can generally get away with a + or - value of 20% with no danger to the circuit you are powering . However, I am very comfortable around electronics and have decades of experience so I tend to understand what to look for and how to to avoid damage. Just too many little "gotchas" that are very hard to pass on via text.

Cheers.

TomW

ghurd · « **Reply #15 on:** May 16, 2006, 09:09:19 AM »

Well, I figured he has a 250+W homebrew windmill, C-40, battery bank, dump load...

And now he has a meter he can't quite figure out.

Sounds deserving of a simple circuit diagram. It may be the only electronics he ever needs to build or understand.

I bet a lot of guys who have made full sized systems couldn't do it either.

Everybody starts somewhere!

G-

dinges · « **Reply #16 on:** May 16, 2006, 12:59:34 PM »

Ghurd,

My response ended up by accident in your reply-thread, it wasn't directly meant at you. The schematic is excellent, esp. for beginners.

But, electronics is a bit different from winding & wiring a stator. Building a switching power supply... Would not be my idea for a first project, esp. if someone can't figure out how to wire a 7805 (I'm assuming he can't and doesn't know what a 7805 is/was).

Aside: personally I always include a few 100n caps across the input & output of the 78xx-ICs, to prevent oscillations. Plus a fuse. And a safety diode (against reverse connections).

Building a windmill and wiring it up are 'pretty' easy (to me, at least). Building electronics stuff is bit more 'esoterical' for most people.

Building electronics stuff isn't necessarily difficult, and everyone has to start somewhere (I built my first project, a blinking LED, using an LM3909... Times have changed eh? ). Your 7805 project could be a good start, simple and practical. Plus, he has the motivation of needing the end result.

That's what I meant by saying to 'read up' on the subject. All the help on this board isn't going to do any good if someone doesn't know the difference between a diode and a capacitor. This board is not the place for educating a newbie to an electronics guru. There's plenty of stuff on the web around to read & study first.

I appreciate the effort youse make in trying to educate someone, but I don't think it works this way. Besides, I've seen some responses (not only in this thread) that really makes me scratch my head.

If, for instance, I would want to learn to play golf (yeah, right), the last person I want as my teacher is Tiger Woods. I want someone who has taught a few more nitwits and knows the typical beginner's problems. An expert is not necessarily the best teacher, is what I'm trying to say.

To no one in particular: try to engage the original poster on his own level and drag him up a bit. It's so easy to spew out lots of technical remarks that are 100% accurate but don't help the person much. And I've even seen some remarks/'help' (also in this thread) that had me scratching my head (like e.g. how to dimension the input resistors). Good thing that I already know how to do such stuff... But that's the 20+ years of experience, I suppose. No board & helpful members can replace that.

Peter.

(hmm... my reply seems to have gotten very long & completely off-topic)

dinges · « **Reply #17 on:** May 16, 2006, 01:10:01 PM »

DON'T DO THIS!! Not even with a separate 12V power supply!

Follow Ghurd's schematic, it's the proper route. And you still need a separate powersupply with his schematic.

Not trying to be harsh on Nano's reply, but I'd hate it if this guy blew his module following it.

Peter.

ghurd · « **Reply #18 on:** May 17, 2006, 03:25:20 PM »

Hi 2windy,

Hope we didn't scare you away. From fieldlines or RE.

I think a lot of comments came out that were not aimed at you or your question.

Peter,

LM3909? You are showing your age! BTW, they are again available, if you have a deep wallet. New part # is "LED-Flasher" or so. ROLF!

I really wish someone would tell me "Use a 7805" or whatever IC. How many hours and dollars are wasted because someone doesn't know a 3 pin IC exists to do just what they are trying to accomplish.

Today I was waiting for detailed explainations on the consequences of bi-directional rotation of a 3 phase PMA, and almost felt disappointed when a poster who is totally beyond reproach effectively blocked further comments in regard to the situation, which could have proven entertaining to say the least.

I may need to resort to the TV.

Start rant

Everybody,

Spent half the day wondering why...

When someone buys the first PM motor and can't understand how the diode goes in, nobody complains.

When someone builds a 1000W 3-ph windmill but can not figure out how to connect it for DC output, everyone jumps to tell how to connect 6 diodes.

Is that more relative than a battery meter?

Both seem pretty darn important to me.

If someone can not handle connecting 6 diodes to a 1000w machine they just made, maybe they should just buy a 1000w machine?

If a novice can connect 6 diodes to handle 1000 watts, why can't another novice handle a 7805 and 1W?

When someone buys a TDM, and wants to disconnect the house, and make a grid tie inverter so he can be rich with monthly electric company checks, everyone jumps in.

When a guy has a working system and needs to know a 7805 exists, and it is not as NEARLY as frightening as the data sheets make it look, everyone seems to chastise him for not knowing about it.

Gotta feel like that if you were the one who asked the question.

(everyone who knows that the difference between 7805 and 7912 is not 107 should take another look at the all data sheets from different companies with fresh eyes. Sure they are simple to use, but it does not show through all the BS)

Didn't everyone ask a easy question at on time or another? And I will do it again.

If you didn't know, were confused, or could not see the forest for the trees. I was.

Anyone who did not must have made some major errors over something simple. I did.

I thought that is why we are here. A semi-newbie can help a newbie. A guru in one field can help a guru in another field. A guru can even learn from a newbie. And it is fun and interesting.

G-

oztules · « **Reply #19 on:** May 17, 2006, 04:54:58 PM »

2windy... listen to Ghurd is my advice on this one, or buy a cheap multimeter and use it instead or go stoneage and use a good ol panel meter. (my choice)

everyone starts somewhere...............oztules

commanda · « **Reply #20 on:** May 17, 2006, 07:43:07 PM »

3 step process to a good panel meter.

Step 1. Series resistor. Meter reads 0-15 volts. Not very good resolution.

Step 2. Series 10 volt zener plus series resistor. Meter now reads 10-15 volts. Good resolution, but not linear (due to the dynamic resistance of the zener diode).

Step 3. Add Amanda's op-amp circuit (see my diary). Meter now reads 10-15 volts with good resolution & is linear. And is powered by the battery we're trying to measure.

This approach, over time, as one learns some basic electronics, should be do-able by most newbies.

Amanda

2windy · « **Reply #21 on:** May 17, 2006, 09:25:00 PM »

Thanks for setting me straight.

SmoggyTurnip · « **Reply #22 on:** May 18, 2006, 06:07:54 AM »

Very well said!

.

SmoggyTurnip · « **Reply #23 on:** May 18, 2006, 06:09:02 AM »

Hmmm - my comment was suposed to

go under ghurds rant.

.

pepa · « **Reply #24 on:** May 18, 2006, 06:22:31 AM »

thanks ghurd, that meed to be said, pepa

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Author Topic: Voltmeter (Read 3609 times)