Panel meters?

[Anonymous]

Re: Getting an education on buying low cost(2.5% accuracy)general purpose Panel Meters overseas.(ZAK is familar with my effort).

I recently ordered forty 2-3/4 x 2-3/8 DER 670 brand Panel Meters, units which I have 5 years of favorable experience with:
twenty 0-30Vac and twenty 0-20 Aac which will cost me about $18-20 each landed here(depending on final air freight,Customs fees,local taxes). On small lot orders such as mine, freight,Custom clearance and currency exchange combined, about double what the cost is listed at the country of origin. As my shipper, I selected higher cost DHL who handles Customs clearance for me(since I am not in the Meter business I don't want to learn to mess with Customs for 40 units)

I ordered from a New Zealand distributor (who would accept a minimum order of 40)]on May 10 and the units are scheduled to arrive here on May 23. Freight cost is a major factor on small orders and exchange rates can add significantly to cost depending on the Country.
(the exchange rate on the U.S.$ is currently .7268 of the NZ$ which inflates my landed cost about 27% or roughly $3.50 per unit).

Although most countries "peg" their currency far below the U.S$ for export advantage, from what I have learned so far, ordering directly from manufacturers in Taiwan, China or other Pacific Rim or Indian sub-continent countries involves minimum orders of 500-1,000 units of each type meter, Volt and Amp.

[lionelsoni]

I assumed that t444 was looking for an ac voltmeter, as we had been discussing. You may be right in thinking that he is looking for an ac ammeter instead. If that is the case, he can do it, by using a bridge rectifier. The + and - terminals would go to the dc ammeter; and the ~ terminals would be connected in series with the ac circuit. The meter shunt would have to be adjusted to make the meter scale right. The drawback is that I can see no practical way to filter out the ac component. However, the shunt might provide enough damping to make the meter readable.

[Anonymous]

Thanks Guys!!!!

[webenda]

t444,

You cannot use a diode between the meter and shunt. Current shunts do not put out very much voltage. A 0.005 ohm shunt at 10 amps only puts out .050 volts. The diode needs more than that to conduct. Some DC shunts do not work at 60 Hz anyway.

You could place a 10 amp rectifier in series with the circuit, but then you would be supplying the load with DC.

I cannot see any practical way to modify a DC Ammeter to work on AC. At least no way that would be cheaper than buying an AC Ammeter.

[lionelsoni]

No. Those are ammeters, which have a very low resistance. You need a voltmeter, which has a very high resistance.

[Anonymous]

Will your modification work with the meter listed below? Thanks.

http://www.simpsonelectric.com/pdf/webpdfe/Century%20ADC.pdf

[webenda]

Hamfests and electronic stores with a surplus isle are great sources of meters. (Word of experience – sealed meters are not as easy to open, for the purpose of changing the meter face, as non-sealed.)

Bob Nelson suggested that I reveal the "Secret of the Potentiometer."

If you use a potentiometer instead of a fixed resistor, you can "calibrate" your meter against another meter. You can see in one of the photos that my digital meter reads 20VAC when connected to the 18V output of my transformer. The Radio Shack 0-15 / 0-30 VDC meter has had the calibration pot adjusted to make the meter read 20VAC after conversion.

You can also see that I have modified the meter face. It used to say, "DC VOLTS."

The second photo shows inside the meter. You can see how the modification was done. All parts used to modify the meter were found at Radio Shack.




(I cannot get this picture to enlage when clicked on. Maybe you can go to http://home.earthlink.net/~webenda/sitebuildercontent/sitebuilderpictures/rectifierboard3.jpg and see it?)

[underworld]

I mentioned Harbor freight reguarding the multi meters....and of course all of the wonderful tools! ***....didn't know that about Radio Shack. I guess the best source I know of now is the occasional hamfest.

underworld

[:D][:D][:D][:D][:D]

[eZAK]

Here is what I dug up so far;

"A 250-3 series Yokogawa model 250-344-NLNL, range and scale 0-30 VOLTS AC. Price is $56.00 and delivery about a week. The face of the meter is 3.5 inches square and it mounts in a 2.7 inch diameter panel opening."

Andrew Lovelace
MeterCenter
[phone]
[e-mail]

AND,

"I can special order them with 5 weeks delivery."

http://www.rpelectronics.com/English/Content/Items/7406Z.asp

Thanks,
Deepak Chopra
R.P.ELECTRONIC COMPONENTS LTD
Tel # [phone] Ext# 105
Fax# [phone]
www.rpelectronics.com



Wayne & Bob,
I may try a DC one.

underworld,
Harbor freight does not carry them!
And RS and others have discontinued them.

[underworld]

Harbor Freight is great for just about everything!!!! Have you tried Radio Shack, they used to have many different ranges.

underworld

[:D][:D][:D][:D][:D]

[lionelsoni]

A one-microfard peak detector with a 1 milliampere load will produce way too much ripple. Ten microfarads will reduce the peak-to-peak ripple to 833 millivolts, for an average voltage loss of only 417 millivolts.

However, I suggest that you use a single diode rather than a bridge. The imbalance is negligible; and it will cut the offset error in half. Of course, as Wayne says, you won't see that at very low voltages; but you will see half of it at 12.5 volts. Assuming one diode and 10 microfarads, I figure the required series resistor is 8822 ohms (at 25 volts). If you use the standard value of 8200 instead, at 25 volts the meter reads about 470 millivolts high, at 18 volts about 190 millivolts high, and at 6 volts about 290 millivolts low.

Whichever way you do it, be sure to put the capacitor directly after the rectifier, not across the meter.

[webenda]

eZAK,

I know what you are going through. It is hard to find an AC Panel Meter suitable for three rail use. When you google for “VAC Panel Meters Surplus” you find lots of beautiful meters, none with the range we want. New meters have the same problem. For example the Allied Electronics catalog lists Shurite Analog AC Panel Meters: 0-10, 0-15, 0-150, 0-300 VAC. None are suitable for our use.

I use DC Panel Meters with a bridge rectifier. For example: Shurite Analog DC Panel Meter: 0-25 VDC, Part Number 7109Z, Allied Stock No. 698-7109, $15.99. http://www.alliedelec.com/catalog/pf.asp?FN=991.pdf

You lose about 1.4 volts with the bridge rectifier, so with 18 volts input, the meter reads 16.6. Put a capacitor (1 to 10 uF works) across the meter and it will read peak volts, 18 x 1.414 - 1.4 = 24. This meter has a 1 mA movement and 25kOhm impedance. You need 1 mA at 34 Vp (25 x 1.414 - 1.4 = 34) to make it read 25 at 25 peak. Using Ohm's law R = V / I = 34 / .001 = 34,000 Ohms. The meter already has 25kOhm. Add 9kOhm in series with the meter (25k + 9k = 34k) and at 25 VAC the meter will read 25 (and 18 at 18VAC.)

The cover snaps off the Shurite meters easily. You could cover up “DC Volts” with a piece of tape or even create a new scale with your computer and printer.

--NOTE—The 1.4 V drop across the bridge rectifier causes the meter to read zero at 1.4 V input. Fortunately three railers do not use 1.4 V. Even in conventional mode our transformers start with at least 6 V output. The zero offset when using a bridge rectifier with DC meters is not a problem.

[eZAK]

Hey guys,
I checked both sites and nothing so far!

[webenda]

Charlie,

http://www.harborfreight.com

Good lead. Thank you. Do you happen to know the Harbor Freight Item Number? I could not find one for $2.99.

I found a couple of multimeters for $4.99. Sounds like a great bargain at that price.

HINT

Before buying, download the manuals. Make sure that the meter specifications meet your requirements. The two meters I found on sale today do not measure AC Current. (Not important to eZAK, he is looking for a voltmeter.)

Do not depend on Harbor Freight's advertising verbiage. For example, Harbor Freight advertises that item 33499-7VGA has an AC accuracy of ±1.2%. (The real specification is ±1.2% ± 10D.) The person writing the advertisement did not understand what "10D" meant. It means ten digits. Since the lowest range on AC is 200V and it is a three and one half digit meter, the display is 199.9 V maximum. One point two percent means 0.2V. Ten digits means 1.0 volts. On 18 V a reading of 16.8 to 19.2 V meets specification.

ITEM 90899-2VGA Multimeter $4.99
AC Volts 200/750 Volts
Accuracy ±1.2% + 10D

ITEM 33499-7VGA Multimeter $4.99
AC Volts 200/750 Volts
Accuracy ±1.2% + 10D

[Anonymous]

You can get a digtal volt ohm meter from Habor Freight for $2.99 and mount is in your panel.

Charlie

[webenda]

http://www.loystoys.com/meters/index.html
Interesting site.

No voltage panelmeters listed today.

[Sturgeon-Phish]

Do a search for Loys Toys, and search for ac meter. $15 + $3 shipping. I've bought several from them to make testing stations. They look and work great. Nice folks too.
Jim

[lionelsoni]

No problem.

[eZAK]

I would like to use the meter to monitor the voltage on the secondary of the transformer.

[lionelsoni]

Pat, beware if you're planning to use these to measure the non-sinusoidal waveforms we have discussed. Almost all ac panel meters assume a sine wave. They are just dc meters with rectifiers.

[eZAK]

Does anyone know of a good source for panel meters?

I'm looking for a 0 - 20vac, 2.5" face