clamp on or tongs current meter

[Crofter]

Are they AC or AC DC. I see no indication in the instructions. AC loads seem in line with nominal ratings of some different loads and agree with my Kill O Wat meter but I am suspicious of its indicated current readings I get on supposedly DC circuits. Is AC current considered to be RMS averaged (not sure if this is appropriate term in regard to current) how does the meter accomodate both ac and dc or does it?

I have been dinking with taking the ripple out of the rectified field current on the ST5 gen head. Am using 60 u F capacitors across the lines before and after a reluctance coil which is the primary of a 500 watt microwave transformer. Have no occillascope to look at wave form but there is much less hum from motors. I have had to put something between 8 and 10 Ohms resistance in series with the field to bring the voltage back down to 120 ish. I am showing over 4.5 amps current reading on the field at full load using the tongs meter. Maybe I got some kind of resonant circuit going on!

At the moment I certainly would not want to show a photo of the Rube Goldberg contraption I have strewn out on the shop floor. It does seem to quite the power down and so far I have not let the smoke out of anything.

[mobile_bob]

none of my clamp on amp meters are capable of measureing dc current
i use a shunt and meter for dc work, shunts are widely available on ebay
and even the cheaper chinese shunts measuring DC  are more accurate than most clamp on meters measuring AC
in my opinion

i think there are clampon meters that will do ac or dc, but i suspect they are quite expensive

bob g

[BruceM]

I have a clamp on meter that does DC current sensing via hall effect sensor.  It drifts badly and is a PITA- stay away from cheap DC clamp on meters.  There are better hall effect sensors that switch polarity at 50KHz and are very stable, but they won't bother to use them on cheap meters.

As Bob suggests,  you are better off putting in a 0.1 or 0.01 shunt resistor and then measuring the voltage drop across it to get an accurate current measurement.  You'll need a meter that does true RMS at higher frequencies to get a proper reading- but what you really need is an o'scope for what you're trying to do. 

[Crumpite]

Crofter,

There are about three different kinds.

The oldest used a meter movement directly across the tongs, they could be both AC/DC, AC or DC.
I've seen all three of this type, and they are usually labeled as to what type currents they can read.
They usually use different snap in meter movements to change range.

The second used a coil around the tongs and just read AC
Some of the newer ones use electronics to extend the range, so they are a little like a DVM.
Might take a battery, maybe not...

The very newest type uses a hall effect sensor across the tongs, and will read both.
This kind usually requires a battery and is pretty pricey though getting a lot cheaper now that China has gotten into the business.

All of the first type will usually give you a true RMS reading on pulsating DC due to their design.

The second kind won't respond to DC at all, but will give an indication if there is ripple on the line.
Since they can't read pure DC, the RMS question is moot.

The third kind will only give a true RMS reading if designed to do do in the circuit, I'd guess that the cheap ones would not.

How old are is the ammeter ?
Got a picture ?

I'd guess that the reactance of the field winding would tend to reduce the AC flow some and that a pure DC current would want to climb much higher due to only pure resistance to limit it.

As for a resonant condition, you can usually tell when you've got one from the smoke and flames...  

This sounds very interesting !
Please keep us posted - It's something no one else has tried, as far a I know (which isn't much...)

Daryl

[Crofter]

Thanks guys;

I couldn't get my mind around how they could measure both ac and dc current. This certainly is not a very expensive ( 20$) or sophisticated meter. I will see if I can retrace my readings when I do a more permanent wire up.

What I did is taken from a simple ripple filter schematic so no original thinking there. I used the transformer in series as a choke and put a pair of capacitors across the circuit on either side of it.

I was not comfortable that indicated field current was considerably higher for the same generator output and voltage after having gone through the motions of taking the ripple and spikes out of it. It indicated an increase from about 3.8 amps to something over 4.5 on the field. For certain the capacitors up the output voltage about 15 volts so a variable resistance in the field in the range of 8 to 10 ohms is necessary. I think RCA victim or Ronmar (cant remember which) used much higher capacitance but perhaps not the series reluctance in taming the waveform.

Admittedly my measuring and technology is a bit like stabbing a cat in a bag! I would like to see the waveform before and after but no scope.

Having troubles getting pictures directly on here.

Why do we always have to take something that is supposed to be strong and simple and then try to dress it up and take it out, Lol!

[Crumpite]

Thanks guys;

I couldn't get my mind around how they could measure both ac and dc current. This certainly is not a very expensive ( 20$) or sophisticated meter. I will see if I can retrace my readings when I do a more permanent wire up.

What I did is taken from a simple ripple filter schematic so no original thinking there. I used the transformer in series as a choke and put a pair of capacitors across the circuit on either side of it.

I was not comfortable that indicated field current was considerably higher for the same generator output and voltage after having gone through the motions of taking the ripple and spikes out of it. It indicated an increase from about 3.8 amps to something over 4.5 on the field. For certain the capacitors up the output voltage about 15 volts so a variable resistance in the field in the range of 8 to 10 ohms is necessary. I think RCA victim or Ronmar (cant remember which) used much higher capacitance but perhaps not the series reluctance in taming the waveform.

Admittedly my measuring and technology is a bit like stabbing a cat in a bag! I would like to see the waveform before and after but no scope.

Having troubles getting pictures directly on here.

Why do we always have to take something that is supposed to be strong and simple and then try to dress it up and take it out, Lol!

Crofter,

Are you measuring the DC current after the caps and inductor ?

One of the easy ways might be to just measure the AC before it goes into the rectifier, then attach your filter circuit and measure again.
That should take the uncertainty out of the equation. You'd be comparing AC to AC...

Myself, I'd expect the DC current to rise if the ripple were removed, the reactance of the field would add to the effective resistance in the circuit on pulsating DC.

You say you see an improvement ?
In what way, motors growl less, less flicker, what ?
Inquiring minds want to know ! 

Daryl

[BruceM]

The action of the harmonic on the AC waveform is direct- the current in the harmonic winding is the culpret, not the output to the field coil, which is such a large inductance as to not care about input waveform. The proof of this is that most commercial AVRs are square wave pulsing devices (banging 350V on a 240V AC head), often only at the waveform peak, with pulse width varying.

So smoothing  input waveform to the field coil is irrelevant, but  changing the timing and shape of the harmonic winding current somewhat may prove slightly helpful.  A large choke would cause a phase lag in the harmonic current.  Putting capacitor(s) before the choke would cause the current to lead (as would just using capacitors alone). 

[Crofter]

Are you measuring the DC current after the caps and inductor ?

I cant remember where I took that reading.

One of the easy ways might be to just measure the AC before it goes into the rectifier, then attach your filter circuit and measure again.
That should take the uncertainty out of the equation. You'd be comparing AC to AC...

yes, that makes sense; I am going to work back through this and take better notes.

Myself, I'd expect the DC current to rise if the ripple were removed, the reactance of the field would add to the effective resistance in the circuit on pulsating DC.

You say you see an improvement ?
In what way, motors growl less, less flicker, what ?
Inquiring minds want to know ! 

Noticeably less growl in motors especially on my lathe.


Daryl     

Thanks

[Crofter]

The action of the harmonic on the AC waveform is direct- the current in the harmonic winding is the culpret, not the output to the field coil, which is such a large inductance as to not care about input waveform. The proof of this is that most commercial AVRs are square wave pulsing devices (banging 350V on a 240V AC head), often only at the waveform peak, with pulse width varying.

So smoothing  input waveform to the field coil is irrelevant, but  changing the timing and shape of the harmonic winding current somewhat may prove slightly helpful.  A large choke would cause a phase lag in the harmonic current.  Putting capacitor(s) before the choke would cause the current to lead (as would just using capacitors alone). 

I guess I was trying to deny the affects that generating the harmonic windings output necessary create in the output stator windings, since they share the same laminations and space.

If I understand correctly, I think you are suggesting that adjusting the phase slightly so they tend at least not to compound with the spikes on the rotor windings, that is about all you can expect to gain.

I am going to see if I can get my hands on an occillascope. I am thinking I might later compare with the waveform I get with an output sourced avr. So far I am just entertaining myself ( and my wife) She has comments like, "I told you you would break it if you keep messing with it" Lol!

Thanks,

[BruceM]

Hi Frank-  Your use of a massive choke is a new trick- I've never heard of anyone trying that before. I'd love to see some 'scope shots!

Some of the AVRs that Tom at Georgia Generator sells can be connected to use the line voltage as excitation.  Ask him for it and you and can get the alternate wiring diagram.  Then you get some pretty good flicker reduction, good voltage regulation AND a much better looking waverform. 

If you're handy with electronics I've published here my simple AVR design and you can build one of those, though you'll spend as much as one of Tom's units.  But you'll have full documentation and can do any needed repairs down the road. 

Best Wishes,
Bruce

[Crofter]

Hi Frank-  Your use of a massive choke is a new trick- I've never heard of anyone trying that before. I'd love to see some 'scope shots!

Some of the AVRs that Tom at Georgia Generator sells can be connected to use the line voltage as excitation.  Ask him for it and you and can get the alternate wiring diagram.  Then you get some pretty good flicker reduction, good voltage regulation AND a much better looking waverform. 

If you're handy with electronics I've published here my simple AVR design and you can build one of those, though you'll spend as much as one of Tom's units.  But you'll have full documentation and can do any needed repairs down the road. 

Best Wishes,
Bruce

Thanks, without a scope I am stabbing the cat through the bag of course. It would be interesting to compare all the combinations for output wave form but I can see why anything using the harmonic windings as field source is problematic and perhaps energy consuming tail chasing.

I am waiting till my passport app. returns so I can whip accross the border to receive an AVR from George. It is a slow expensive pain it seems to have anything mailed US to CAn. I have assembled a few circuit boad kits, but here in the sticks it is not easy to acquire components.

I would like to see a bit bette voltage regulation as there is quite a high rise when I drop a heavy load. OK for the things back in the shop but I would like to see the power a little more civilized before I bring it into the house.

[BruceM]

I've noticed the same problem with items shipped from Canada to the US.  Takes a couple weeks extra to get through Custom's grip once entering the US.  Not so for packages from China.  Bizarre.

[12gauge]

BruceM,
I think I spent just under 50 bucks for parts to build your regulator.  I am going to build another for a second generator and that will double as a spare.
RH

[Crofter]

BruceM,
I think I spent just under 50 bucks for parts to build your regulator.  I am going to build another for a second generator and that will double as a spare.
RH

Hey 12 Gauge, while you are making that next one, how about doubling the order? It sure would be preferable to have a unit that is testable and repairable. Seriously I would be interested if it could be do-able.

I rechecked my meter on pure dc from a battery and it shows 000 but if you move the tong center around the conductor it gives a jumble of numbers. I see there is a very small ~ symbol on those positions so any readings I attempted on the rectified Z winding and field were meaningless.

[12gauge]

Crofter,
I already have my parts for a second unit, but I'd be happy to help you with your parts list.  Judging by your location you probably want to try to get everything at one place for economy of shipping.  I used Mouser and Digi-key for all except the radio shack board.  One of the reasons I went with the generic board was I could substitute parts with no interference problems since there is lots of room.  After I installed IRGB14C40LPBF for Q1 it has worked fine, although I continue to attempt improvements in power factor, etc.  Here is a picture of my board layout, maybe it will help.

http://picasaweb.google.com/lh/photo/c8acql5jBnBSxEmx-hajMg?authkey=Gv1sRgCN-YqvmH1oi44QE&feat=directlink

It's a rewarding project.

RH