Ammeter wiring?

ThSpeakerDude88 · 2nd April 2008, 11:05 PM

I want to put an ammeter in my HV power supply, but am completly new to the concept of ammeters.

my power supply is adjustable from 150vdc-450vdc, and will have a maximum draw of 150-200 ma.

I have a Vellman 500ma panel meter that I got for like $5. Can I use this in a HV circuit? Does the shunt resistor have to be very high and if so would it cause any problems with heat dissipation?

nhuwar · 2nd April 2008, 11:13 PM

Make sure the meter is on the negative line of the high voltage supply not on the positive side.

You can use the vellamen gauge and the type of resistors shouldn't really matter.

Just find the current draw full scale for the meter and find the corresponding resistor value.

Are you going to use a .1 ohm shunt or a 1 ohm shunt, this will decide what the size of the multiplier resistor is.

Hope this helps,

Nick

ThSpeakerDude88 · 2nd April 2008, 11:43 PM

the meter's resistance is .5 ohm if that helps any.. are there any calculators on the web that show how to connect a panel meter and/or calculate shunt resistance? I havent been able to find any...

nhuwar · 2nd April 2008, 11:48 PM

If the meters resistance is .5 ohms then it probably has a built in shunt.

You can test is with a power supply and a resistor and the meter put in the circuit and see what you get.

But I'm guessing it has a built in shunt. Most of the amp meters I have working with do.

Nick

ThSpeakerDude88 · 3rd April 2008, 12:10 AM

so... I can just stick it in series on the positive rail with the output?

nhuwar · 3rd April 2008, 01:07 AM

No the negative rail !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you put it on the positive rail it could arc to ground. You always put an amp meter on the side of the supply that is grounded.

Nick

ThSpeakerDude88 · 3rd April 2008, 01:38 AM

I'm confused? If it is in series with the plate supply, how can it arc to ground?

I basically want to put it in line with the B+ output ... it would go between the B+ output and the + lead of the output transformer to measure plate current. I would put it in the cathodes but this wouldn't do me any good as I want to be able to monitor my entire power supply's current draw to keep it within the transformers ratings, and to see if there are any problems in the circuit causing excessive current draw.

kuroguy · 3rd April 2008, 01:58 AM

put it on the ground side. that way if something inside it shorts to the case it is at gropund potential instead of at B+.

ThSpeakerDude88 · 3rd April 2008, 02:03 AM

Case is made of oak...and any panels are made of PVC. Yeah I know, maybe a fire hazard but I have a main kill switch nearby and a fire extenguisher handy at all times. Its very well built and shielded inside as well.

I guess I could put it in the negative rail...will the .5 ohm resistance mess anything up with the ground potential? I wouldn't think so but just asking...

korneluk · 3rd April 2008, 02:04 AM

Here is an example from Yamamoto:

Go here for more details...
http://www.jacmusic.com/Yamamoto/html/meters/index.html

Enjoy,

-- josé k.

2nd April 2008, 11:05 PM	#1
ThSpeakerDude88 diyAudio Member Join Date: Jun 2005 Location: USA	Ammeter wiring? I want to put an ammeter in my HV power supply, but am completly new to the concept of ammeters. my power supply is adjustable from 150vdc-450vdc, and will have a maximum draw of 150-200 ma. I have a Vellman 500ma panel meter that I got for like $5. Can I use this in a HV circuit? Does the shunt resistor have to be very high and if so would it cause any problems with heat dissipation? __________________ always preach the gospel- and when necessary use words.

2nd April 2008, 11:43 PM	#3
ThSpeakerDude88 diyAudio Member Join Date: Jun 2005 Location: USA	the meter's resistance is .5 ohm if that helps any.. are there any calculators on the web that show how to connect a panel meter and/or calculate shunt resistance? I havent been able to find any... __________________ always preach the gospel- and when necessary use words.

3rd April 2008, 12:10 AM	#5
ThSpeakerDude88 diyAudio Member Join Date: Jun 2005 Location: USA	so... I can just stick it in series on the positive rail with the output? __________________ always preach the gospel- and when necessary use words.

3rd April 2008, 01:38 AM	#7
ThSpeakerDude88 diyAudio Member Join Date: Jun 2005 Location: USA	I'm confused? If it is in series with the plate supply, how can it arc to ground? I basically want to put it in line with the B+ output ... it would go between the B+ output and the + lead of the output transformer to measure plate current. I would put it in the cathodes but this wouldn't do me any good as I want to be able to monitor my entire power supply's current draw to keep it within the transformers ratings, and to see if there are any problems in the circuit causing excessive current draw. __________________ always preach the gospel- and when necessary use words.

3rd April 2008, 02:03 AM	#9
ThSpeakerDude88 diyAudio Member Join Date: Jun 2005 Location: USA	Case is made of oak...and any panels are made of PVC. Yeah I know, maybe a fire hazard but I have a main kill switch nearby and a fire extenguisher handy at all times. Its very well built and shielded inside as well. I guess I could put it in the negative rail...will the .5 ohm resistance mess anything up with the ground potential? I wouldn't think so but just asking... __________________ always preach the gospel- and when necessary use words.

2nd April 2008, 11:13 PM	#2
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Make sure the meter is on the negative line of the high voltage supply not on the positive side. You can use the vellamen gauge and the type of resistors shouldn't really matter. Just find the current draw full scale for the meter and find the corresponding resistor value. Are you going to use a .1 ohm shunt or a 1 ohm shunt, this will decide what the size of the multiplier resistor is. Hope this helps, Nick

2nd April 2008, 11:48 PM	#4
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	If the meters resistance is .5 ohms then it probably has a built in shunt. You can test is with a power supply and a resistor and the meter put in the circuit and see what you get. But I'm guessing it has a built in shunt. Most of the amp meters I have working with do. Nick

3rd April 2008, 01:07 AM	#6
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	No the negative rail !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! If you put it on the positive rail it could arc to ground. You always put an amp meter on the side of the supply that is grounded. Nick

3rd April 2008, 01:58 AM	#8
kuroguy diyAudio Member Join Date: Sep 2007	put it on the ground side. that way if something inside it shorts to the case it is at gropund potential instead of at B+.

3rd April 2008, 02:04 AM	#10
korneluk diyAudio Member Join Date: Jan 2005 Location: South Florida	Here is an example from Yamamoto: Go here for more details... http://www.jacmusic.com/Yamamoto/html/meters/index.html Enjoy, -- josé k.

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