Author Topic: Current sensors  (Read 311 times)

dgd

  • Hero Member
  • *****
  • Posts: 1654
    • Lorylink
Re: Current sensors
« Reply #15 on: March 23, 2017, 08:06:00 PM »
boB, I see anywhere from 0.5-1.0 Amp of jitter on the WBjr data dumped by the LA at 2 sec/reading resolution. Is that normal? What is the typical jitter on the WBjr data stream.

Now this intrigued me as my arduino is reading the WBjr modbus registers every second or just slightly over. The values for current are sent directly to a web page current gauge that is refreshing at the register read rate of near every second.
The gauge is sensitive enough that a small jitter or even fifth amp would make the needle visably jitter.
I have not investigated more deeply but unless the modbus register is amps averaging and there is another 'raw' amps register then I cannot see this jitter in data from the WBjr...

dgd
Classic 250, 150,  20 140w, 6 250w PVs, 2Kw turbine, MN ac Clipper, Epanel/MNdc, Trace SW3024E (1997), Century 1050Ah 24V FLA (1999). Arduino power monitoring and web server.  Off grid since 4/2000
West Auckland, New Zealand

Resthome

  • Hero Member
  • *****
  • Posts: 1012
Re: Current sensors
« Reply #16 on: March 24, 2017, 01:11:42 AM »
Vic, dgd

Thanks for the replies. So Vic is seeing close to what I see.  I seem to recall this was the topic once and boB did some kind of averaging to try to smooth it out. At least this is what I recall. Not sure what Modbus reg the LA is reading for it. And not sure where the jitter is coming from or if it is normal.  It would make End Amps easier to hit if it was smoother and more steady in my case.  I did have to extend the purple wire a few feet to get to the Classic, but don't think that effected it. Unless it is running near something else that is causing it.

Agree with Vic on the remote voltage sense, that would help with the variations in voltage with current and no current. The tweets offset doesn't help this.

Will try to post some data tomorrow of what I see.
John

10 x Kyocera KC140, Classic 150 w/WBJr, Link10 Battery Monitor, 850 AH @ 12v Solar One 2v cells, Xantrex PROwatt SW2000
Off Grid on Houseboat Lake Don Pedro, CA

EW Zuber

  • Jr. Member
  • **
  • Posts: 53
Re: Current sensors
« Reply #17 on: April 07, 2017, 04:53:46 AM »
Found this little snap on current sensor with 2% accuracy.
http://cdn.sparkfun.com/datasheets/Sensors/Current/ECS1030-L72-SPEC.pdf
(6) Solar World 175 watt, (14) Arco Solar 33 Watt, (15) REC 250 watt, 2KW Whirlwind turbine on 85' rohn 25 tower, Outback VFX 3648, Outback FM80 and Midnite Classic 150 w/WBJR, ( 8 ) Trojan L-16REB, 
WL7BDK

Vic

  • Hero Member
  • *****
  • Posts: 1626
Re: Current sensors
« Reply #18 on: April 07, 2017, 04:54:03 PM »
Hi Eric,

It seems to me,   that these are AC current transformers:

"Rated Primary Current(Amp.) 50/60Hz"

Perhaps you need an AC Current transformer,   but had thought that you had been referring to DC Current Sensors.

FWIW,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

TomW

  • Administrator
  • Hero Member
  • *****
  • Posts: 1409
  • Nullius in Verba
Re: Current sensors
« Reply #19 on: April 07, 2017, 05:03:29 PM »
Hi Eric,

It seems to me,   that these are AC current transformers:

"Rated Primary Current(Amp.) 50/60Hz"

Perhaps you need an AC Current transformer,   but had thought that you had been referring to DC Current Sensors.

FWIW,   Vic

Vic;

Probably why they are called current transformers. You need an active component to read DC. with the AC Current Transformer you can read  volts produced from the sine wave  through the transformer with a known amps to millivolts ratio. With steady DC you can't drive a transformer once the flow is steady. Talking about non contact methods here, of course (no shunt).

You probably know that but there it is in case others wonder about it.

Tom
Do NOT mistake me for any kind of "expert".

( ͡° ͜ʖ ͡°)


24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

RossW

  • Sr. Member
  • ****
  • Posts: 313
Re: Current sensors
« Reply #20 on: April 08, 2017, 06:24:07 PM »
With steady DC you can't drive a transformer once the flow is steady. Talking about non contact methods here, of course (no shunt).

You probably know that but there it is in case others wonder about it.

Hey Tom, I hate to beg to differ... and it's not exactly the same thing, but....

When I was a young'n, my father had a NON-CONTACT, DC CURRENT METER.
It was used to measure battery cranking amps, headlamp current, and looking for other residual current draws like running lights etc.

It was basically about a 2" diameter centre-zero meter that showed amps charge and discharge. One simply held it against the wire in question (it had a little guide on the back to make sure it sat exactly along the wire the right way).

It worked great, and had absolutely no electronics in it whatsoever. 

So there you go, it CAN be done!
6 tracking arrays, each 6 x 100W modules. Nominal 100V/6A each.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 300AH cells (primary bank)
24 x AGM 500AH cells (secondary bank)
Selectronics SP-PRO 481 5kW inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

dgd

  • Hero Member
  • *****
  • Posts: 1654
    • Lorylink
Re: Current sensors
« Reply #21 on: April 08, 2017, 07:43:37 PM »
So was it some sort of hall effect sensor with a sensitive microvolt meter? I can't imagine it being very or even nearly accurate.
dgd
Classic 250, 150,  20 140w, 6 250w PVs, 2Kw turbine, MN ac Clipper, Epanel/MNdc, Trace SW3024E (1997), Century 1050Ah 24V FLA (1999). Arduino power monitoring and web server.  Off grid since 4/2000
West Auckland, New Zealand

Vic

  • Hero Member
  • *****
  • Posts: 1626
Re: Current sensors
« Reply #22 on: April 08, 2017, 08:00:23 PM »
So was it some sort of hall effect sensor with a sensitive microvolt meter? I can't imagine it being very or even nearly accurate.
dgd

I believe that this type DC Ammeter just used the large magnetic field surrounding the cable with a LARGE current flowing in it to disturb the magnetic field from a fixed magnet in the meter,   IIRC.

So a direct reading of the field,   and calibrated in tens of amps,   or so.

Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

RossW

  • Sr. Member
  • ****
  • Posts: 313
Re: Current sensors
« Reply #23 on: April 08, 2017, 08:39:10 PM »
So was it some sort of hall effect sensor with a sensitive microvolt meter? I can't imagine it being very or even nearly accurate.
dgd

I believe that this type DC Ammeter just used the large magnetic field surrounding the cable with a LARGE current flowing in it to disturb the magnetic field from a fixed magnet in the meter,   IIRC.

So a direct reading of the field,   and calibrated in tens of amps,   or so.

Near as I recall (I haven't seen it in decades), it was pretty much a bog-standard moving-iron type meter movement, but instead of having a coil and passing current through the insides of the meter, the wire was held directly against the back of the meter movement.

It was certainly more sensitive than merely "tens of amps" - it could quite easily indicate the modest current of the interior light coming on and off, so in the order of an amp or so.

I think it must have been a logarithmic meter, cranking amps would take it out to pretty much full scale one way or the other, and generator (or alternator) charging current of 40A would show about 1/2 scale.

I've had a quick search of google images and haven't found a picture of it or anything quite like it. I best ask Dad next time I see him if he still has it, and take some pictures for historical reference!


OK, this isn't the same but it's very similar.


« Last Edit: April 08, 2017, 08:50:57 PM by RossW »
6 tracking arrays, each 6 x 100W modules. Nominal 100V/6A each.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 300AH cells (primary bank)
24 x AGM 500AH cells (secondary bank)
Selectronics SP-PRO 481 5kW inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

TomW

  • Administrator
  • Hero Member
  • *****
  • Posts: 1409
  • Nullius in Verba
Re: Current sensors
« Reply #24 on: April 09, 2017, 09:03:27 AM »

So there you go, it CAN be done!

I actually have one of those in the toolbox. Not sure why I ignored that fact.

Wonder what kind of voltage it puts into that meter from a steady flow of current?

You seem to be my own personal fact checker.  ;D

Now on to your regularly scheduled programming.

Tom
Do NOT mistake me for any kind of "expert".

( ͡° ͜ʖ ͡°)


24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

RossW

  • Sr. Member
  • ****
  • Posts: 313
Re: Current sensors
« Reply #25 on: April 09, 2017, 05:10:09 PM »
I actually have one of those in the toolbox. Not sure why I ignored that fact.
Wonder what kind of voltage it puts into that meter from a steady flow of current?

None. We already know a static field won't actually generate a voltage in any useful form, but a magnetic field - even static - is a different thing. Think back to your compass - earths magnetic field is relatively static yet can deflect the compass needle in a very useful way. These hold-over-the-wire type indicators are pretty much the same thing and work in pretty much the same way.

Quote
You seem to be my own personal fact checker.  ;D

Well, we all miss you in IRC, so I have to come here to catch up!
6 tracking arrays, each 6 x 100W modules. Nominal 100V/6A each.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 300AH cells (primary bank)
24 x AGM 500AH cells (secondary bank)
Selectronics SP-PRO 481 5kW inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine