Digital amp meter install help

Questions, Suggestions, Tips, Etc

Re: Digital amp meter install help

Postby macona » Sun Sep 16, 2012 10:59 pm

Be careful. If your lead between the meter and the return of the power supply becomes unhooked you will have a couple tens of thousands of volts in the meter which will arc over and jump to your power supply. This could be very bad.
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Re: Digital amp meter install help

Postby gene » Sun Sep 16, 2012 11:13 pm

macona wrote:Be careful. If your lead between the meter and the return of the power supply becomes unhooked you will have a couple tens of thousands of volts in the meter which will arc over and jump to your power supply. This could be very bad.


I soldered, heat shrunk and wrapped it in electrical tape

So default power setting of laserpowermax=180 with retina engrave yielded a reading of: 27ish on vector cut about the same as test firing the laser. I think this must be reading voltage and not mA. Makes sense since it was a 100mV meter in the name of the item when purchased way back when. Not sure why I got a voltage meter. I assume I'll need to replace it with the mA meter? or is there some way to tell mA with the voltage reading
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Re: Digital amp meter install help

Postby mattrsch » Mon Sep 17, 2012 1:28 am

gene wrote: I assume I'll need to replace it with the mA meter? or is there some way to tell mA with the voltage reading


If you know the resistance of the shunt you can easily find the voltage with Ohm's law: V=IR, so V/R=I. Is the resistance of your shunt written on it somewhere? It might just give a relationship like 100mA, 75mV. If not a digital multimeter typically won't give a super accurate value for a low resistance measurment, but it should get you close. Somehow I missed before that what you bought was a voltmeter.

It is also a good idea to double check with a multimeter that you have good grounding on your frame everywhere. If something like the situation macona mentioned happens good frame grounding would be the difference between a life threatening shock and a scary moment.
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Re: Digital amp meter install help

Postby gene » Mon Sep 17, 2012 1:56 am

mattrsch wrote:
gene wrote: I assume I'll need to replace it with the mA meter? or is there some way to tell mA with the voltage reading


If you know the resistance of the shunt you can easily find the voltage with Ohm's law: V=IR, so V/R=I. Is the resistance of your shunt written on it somewhere? It might just give a relationship like 100mA, 75mV. If not a digital multimeter typically won't give a super accurate value for a low resistance measurment, but it should get you close. Somehow I missed before that what you bought was a voltmeter.

It is also a good idea to double check with a multimeter that you have good grounding on your frame everywhere. If something like the situation macona mentioned happens good frame grounding would be the difference between a life threatening shock and a scary moment.


If my memory is right I think the shunt is 1ohm but nothing is written on it. I'll check with the multimeter tomorrow when I get a chance.

When I built up the frame I made sure to scuff all the joints with steel wool (due to that plasticy film that isn't conductive) to get good grounding and checked with the multimeter that grounding was sufficient all over the frame. When I get a chance I should spend some time reading on everything electrical as I need to improve my knowledge in the area.
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Re: Digital amp meter install help

Postby Techgraphix » Mon Sep 17, 2012 12:21 pm

Hi Gene,
I have written it before but maybe you just read over it or didn't understand it.
I posted a picture about how you have to connect a mA-meter.
a mA- or Current meter is infact nothing else than a Volt meter with a shunt resistor.
What you do is measure the voltage that is over the shuntresistor when there is a current through it;
How can you recognize a V-meter or a mA-meter?
When you measure with your Ohm-meter over the two input-connectors you will measure a very high resistance with the V-meter and a very low (about 1 Ohm or lower, depending on the range of the meter) resistance with the mA Meter.
So, if you have a V-meter (range 100mV, as you wrote) you will measure a very high resistance and to make this meter act as a mA meter you have to place the shunt-resistor of 1 Ohm over the two inputs.
To connect this meter and shunt right in the circuit, you have to cut the return-lead from the lasertube to the laserpowersupply. Connect the lead that is coming from your tube to the plus(+) of the meters input and the lead that goes to the supply is connected to the min(-) of the meters input.
The +5V and GND are connected to a supply that delivers that voltage. the GND must (and shall probably already) be connected to the main Earthpoint.

Hope it is clear now... else i see one digital meter go to trash... Then you can buy a analog meter, which will give you a more reliable average lasercurrent-indication.. and even my grandmother could connect that ( this is not how she died, however..)

Kees
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Re: Digital amp meter install help

Postby gene » Tue Sep 18, 2012 9:43 pm

thanks tech. I read your reply and then went back and examined your original post. I'll switch the meter over to amperage and also go back through the negative laser lead line to really beef up the soldering and shrink tubing so there is no possibility of of a dangerous separation. I think it's fine now but I'd rather be ultra-safe than sorry later

Edit: So digital meter resistance reading 33. Shunt reading exactly 1 ohm. So definitely a volt meter. Looks like I have it connected right to read amperage as it is hooked up per image below.. if so my laser power supply is baking that laser tube at like 25-26 mA when using the test button
Image
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Re: Digital amp meter install help

Postby Techgraphix » Wed Sep 19, 2012 4:06 pm

gene wrote: so my laser power supply is baking that laser tube at like 25-26 mA when using the test button

Possible... You can adjust the power with a potentiometer (see the manual of the powersupply how to connect) or you can set the max power in your controller.
Maybe it's on 100% or over now.. 90-95% max is save
Digital meters do not have to be very accurate, especially not when the shunt is something like a 5% or 10% tolerance resistor..
If you have a normal handheld multimeter you can set it to a range of 200mA and hook it up instead of you DVM/Shunt so you can compare the two values.
So it can happen that you read 26mA but it is only 21mA ... It can also be 30!..

Kees
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