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  #21  
Old 11-15-2012
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Re: Voltage tester idea

Let's see, E over I equals R, yes? So

12
----------
10,000,000

and the meter draws 0.0000012 amps, 12 millionths of an amp?

and the folks at calculator.net say:

Voltage drop: 0.0051
Voltage drop percentage: 0.043%
Voltage at the end: 11.9949

Not too bad! I suppose instrument rounding and errors might mean it could show 11.9 instead of 12.0 but from a hundred miles away...(VBG)

OTOH, having seen the way my "good" meters of various ages disagreed (by .2 volts) and the way a HF special couldn't meet it's own specs, I put zero faith (actually, 0.000000000 faith) in meters that have no specs at all, like those specials at dx. Which is why I finally decided to get out the soldering gun and put a 10.00 volt precision reference source in a mini Altoids tin, so there's no guessing, and I *know* when my meters are fibbing. The reference source is good beyond 4 digits, so when I hook it to a meter the meter had damn well say 10.00 or it gets re-educated, as the Chinese would say.
I'll be interested to see how the meters HOLD calibration, now that I've got a way to check on them.
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Old 11-16-2012
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Re: Voltage tester idea

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Originally Posted by hellosailor View Post
OTOH, having seen the way my "good" meters of various ages disagreed (by .2 volts) and the way a HF special couldn't meet it's own specs, I put zero faith (actually, 0.000000000 faith) in meters that have no specs at all, like those specials at dx. Which is why I finally decided to get out the soldering gun and put a 10.00 volt precision reference source in a mini Altoids tin, so there's no guessing, and I *know* when my meters are fibbing. The reference source is good beyond 4 digits, so when I hook it to a meter the meter had damn well say 10.00 or it gets re-educated, as the Chinese would say.
I'll be interested to see how the meters HOLD calibration, now that I've got a way to check on them.
My Fluke meters are all calibrated, my cheapies not so much, but I'd love to grab one of these chips. Got a link?????
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  #23  
Old 11-16-2012
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Re: Voltage tester idea

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Originally Posted by Maine Sail View Post
My Fluke meters are all calibrated, my cheapies not so much, but I'd love to grab one of these chips. Got a link?????
Well for $2 this is a 0.1% shunt reference (like a zener).
LM4040AIM3-10.0/NOPB Texas Instruments | LM4040AIM3-10.0/NOPBCT-ND | DigiKey

It needs a bias current (100uA to 15mA) though which could be as simple as a resistor to 12V (perhaps a lighter plug outlet) or you could get the 1.225V version and use a couple batteries with a resistor and a switch.

I'm also curious what hello has got.

Edit: I'll also add that as far as cheapies go the one I linked earlier is pretty damn good. Auto ranging, shuts off automatically, buzzer for continuity and it includes internal space for the (small) leads under a cover that doubles as a stand. It's ideal for throwing in a tool bag. When I've had it next to a fluke the accuracy has been near dead on.

The purchase I regretted was the $35 meter I bought. That one failed on me. Lesson learned. I'll try to stick to things that are either really good or really cheap. It's hard to go wrong that way.
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Old 11-16-2012
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Re: Voltage tester idea

Maine-
Me and the chips are in different places this week, so I can't tell you offhand but I went with Linear, who offer accuracy to better than 0.05% (that's not a typo) so when they say "10.00" they really mean it. And internal temperature compensation, so basically if you don't need gloves or icepacks to work, it doesn't either. Damned thing just hums along and says "Ten! Nyah-nyah-nyah-nyah! TEN!" all day long.

The main limit is output power, i.e. only use it with the usual high-impedance meters. It won't work with the source-self-powered LED voltmeter displays from China, minor drawback. Other than that, it pretty much doesn't give a damn what's connected in the way of power supplies, takes a wide range of those as well.

Seems like a lot of chipmakers have been coming up with all sorts of interesting "twelve volt" management devices in the last year or two. Multiple regulators, convertors, I've got to be thinking the "solar" industry is driving some of this.
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Old 11-16-2012
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Re: Voltage tester idea

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Originally Posted by hellosailor View Post
Seems like a lot of chipmakers have been coming up with all sorts of interesting "twelve volt" management devices in the last year or two. Multiple regulators, convertors, I've got to be thinking the "solar" industry is driving some of this.
What did you use as a power source? Linear the type or brand?

12V is also used in the automotive world which is becoming more and more computerized. So there are tons of neat and robust 12V power management chips out there because of the automotive overlap. I've tried to think of ways to incorporate them into the boat.

In particular there are fantastic solid state switches with internal over-temperature and over-current limits. I've incorporated these into a couple designs and personally short circuit tested them (hold the + wire and - wire and then quickly mash them together) and scope traced the results. They work. Basically reset-able fuses that, in theory, can't be burnt out under any circumstances.

I considered using these when I re-did my panel. I could have had the switch on the panel only switching control current with the actual switch/fuse solid state device behind the scenes. However at the end of the day it's hard to beat the simplicity of actual switches and fuses.

Also there is an opportunity to build a cross between the bluesea relay and the echo charger for about $10 component cost. A comparator and a solid state 20-30A switch. It would limit current to 20-30A meaning you could get away with smaller wires but would lack the charging smarts of the echo charger.

Anyway, another overly long engineering rant. You can tell I've been thinking (dreaming) of ways to make money doing marine electrical design.
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Re: Voltage tester idea

Linear as in the company, LT. Power source was easy, a 12 volt alarm "fob" battery is readily available and much more compact than the next simple choice, which would have been a couple of 9v batteries in series. But that would have filled a standard size Altoids tin and given me a decade of battery power, didn't want to go there.

Maybe I should sell my spares as kits? (VBG)

A few years ago all the players were saying cars would move to 48VDC in order to power the electrical power steering, electrical AC, all sorts of things. Now, they're saying gee, it would cost too much to use 48VDC rated switches and wiring. Funny thing, huh?

I'd prefer "dumb" switches and breakers. No worries about noise pulses, rfi, odd things the microelectronics can do. Heck, I've "repaired" a car fuse with a chewing gum wrapper in order to get home. Can't do that with microelectronics.

"Also there is an opportunity to build a cross between the bluesea relay and the echo charger for" You'd probably be reinventing a "Hellroarer" a solid state (high power FET I think) version of the Yandina/West isolator, which is the grandpappy of the Echocharger and all that stuff.

I'm still waiting for "one ring to rule them all", i.e. a modular charge controller that would be able to integrate alternator, solar, wind, and run them all efficiently together without making blind assumptions. I had some ideas on how to do it, isolate and integrate, but it all comes back to "Gee, this is gonna cost" no matter how small and cheap they can sell the brains for it.
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Re: Voltage tester idea

Which Fluke multi-meter is good for this kind of application so that even we can have some additional information while selecting this type of multi-meter?
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