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Author Topic: panel meters from china  (Read 7125 times)
camillitech
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« Reply #15 on: January 18, 2008, 11:20:19 PM »

Being a bit vacant in the electrickary dept i used the 12volt turbine bank to power the 48v meter and it seems to work ok would it go pear shaped if i used another meter off the same supply then Huh
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Paulh_Boats
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« Reply #16 on: January 19, 2008, 12:17:26 AM »

camillitech,

Not sure. I've emailed a load of techie questions to the supplier - will know more when I get a reply.

I like the look of the square analog meters..... and nothing can wrong with them!

-Paul
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camillitech
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« Reply #17 on: January 19, 2008, 06:20:35 AM »

Must admit Paul I've allways prefered analogue meters myself, specially for ammeters. the reason i went LED for this application is that they are so sensitive you can use them to monitor the dump loads switching in and out and other loads very easily. I wanted to fit an ammeter as well in the house to monitor the wind turbine output but as my charge controller is over 100m away was unsure if it would read accurately.

any thoughts? cheers, Paul
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« Reply #18 on: January 19, 2008, 10:11:38 AM »

camillitech - the great thing about current is that it is constant for the whole length of the cable. So you can put the ammeter at the start, middle or end of the cable and you will see identical current readings.

Analog meters are useful for values that go up and down a lot, like the voltage of PV panels that changes every few seconds with cloud cover or the voltage of a turbine through gusts. You can see the high and low points over 10 seconds and make a good estimate on the average value with your eye.... but with digital numbers changing rapidly its hard to see what is happening.

Digital comes into its own for accurate, fixed readings like battery voltages or like you said small step changes when something switches in or out.

-Paul
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camillitech
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« Reply #19 on: January 19, 2008, 10:04:31 PM »

This is my meter of choice Paul though I'm struggling to get a battery for it Cry



regarding the ammeter Paul I wanted to measure the DC input into the batteries so it would mean 2 x 100m wires going from my house to the charge controller  Shocked would this be possible Huh

Cheers Paul C
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Paulh_Boats
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« Reply #20 on: January 19, 2008, 11:50:20 PM »

camillitech,

Ahh the good old AVO - built to survive World War 3  Smiley

The current and voltage range should work without a battery....only resistance ranges need a battery.

It sounds like you have both the controller and batteries in the shed. In that case you will have to use a shunt between controller and battery. Then thin wires from the shunt can run back to the house to the "ammeter" ... which will actually be reading the voltage across the shunt which varies in proportion to the current through the shunt.

Because a modern panel meter has high input impedance it consumes almost zero current from the circuit when reading a voltage, so there will be no voltage drop along the extra wires.

Asia Engineer had some 200 Amp shunts on some of the meters. They would work. There might be problems picking up noise on a long cable causing spurious readings. Got any radio sources nearby?
Twisted or shielded cable would help as would an inductor and capacitor filter like those fitted on car radios... but you will have to see what happens. I can't guarentee that 100m will be problem free, but if the plan goes pear-shaped it will be useful having a digital ammeter to read when you visit the shed.

There is a bit off a trade off as the shunt will drop a small amount of voltage and maybe get warm. If its a very low value shunt it will run cooler...but then the voltage across it will be very low and more likely to suffer interference. If you track down a shunt find its resistance and I'll help you with the sums. My only fee will be a bacon butty  Wink

cheers
Paul

PS I like the orange earthquake detector...you really have planned for everything.  Grin
« Last Edit: January 19, 2008, 11:56:48 PM by Paulh_Boats » Logged

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RichardKB
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« Reply #21 on: January 20, 2008, 03:08:37 AM »

Paulh_Boats said

However it makes no sense why each meter needs its own supply unless the current from the supply is only just enough for one meter, in which case it would get overloaded and possibly cut-out if multiple meters were used. end quote

If for argument sake the 0V input of the meter is tied to the 0V/-ve supply terminal, and you use one to measure the voltage of a rail and another to measure the current. The the 0V connection of the Volt meter is connected via its supply to the +ve rail via the 0V  supply to the ammeter.

I hope you are getting what I am trying to say.

Rich
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Paulh_Boats
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« Reply #22 on: January 20, 2008, 11:07:36 AM »

Rich,

Yes fully understand. I got a bland reply from "Asia Engineer" on ebay after asking for a technical data sheet, what are the maximum voltages on each pin, were the inputs floating, was 0V input connected to ground supply etc. I've replied.

Its likely that he has had customers blow up meters due to overloading the op-amp inputs (wrt supply) when using multiple meters on one supply.

As Ken illuded, if they had built-in DC-DC convertors there would be no such problems feeding them from one supply.

cheers
Paul
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LED lighting in every room
NO tumble dryer, +370 kWh per year
KenB
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« Reply #23 on: January 20, 2008, 11:58:45 AM »

Paul, List,

As I see it, the best way to use these is to put the shunt in the negative lead of the battery, and connect the input terminals of the current meter across the shunt so that its -ve goes to the negative terminal of the battery and its +ve goes to the other end of the shunt.  In this way current drawn out of the battery (discharge current) will appear as positive current on the meter.

The battery Volt meter can be connected -Ve to battery -ve,  and +ve to  +ve of battery or through a suitable potential divider.  In this way the meters at least share the same ground reference i.e. the battery -ve terminal - and in theory can both be powered from the same dc supply.

Problems start to arise when the shunt is fitted in the battery +ve lead and you try to connect the meter power inputs to the battery ground. This puts the measurement inputs at 24V or 48V or whatever above battery ground, and this is what fries the op-amp input stage of the meter.

Regarding powering them - I would use a couple of cheap 5V mobile phone chargers or any of the cheap plug top adaptors that can be bought in the high street.



Ken
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