Current sensors

Started by EW Zuber, March 13, 2017, 06:35:17 PM

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EW Zuber

Wondering if Midnite has considered using current sensors similar to what a clamp-on meter uses so that there is no insertion loss or isolation added to the circuit.
(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

ClassicCrazy

The Whizbang is what is used because it can mount on and monitor via a precision shunt that is permanently installed in a system. This is a must  if being used for control. There is only a small mv drop on the shunt so not any appreciable loss.
I don't see the use of  clamp on amp monitoring when it is already built into the system .
If someone wanted to just read current on any particular cable it is easy to do that with a $30 clamp on digital multi meter.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Vic

I believe that inside the Classic,  there IS  a Hall-Effect current sensor for the CC output.

The calibration for Hall Effect sensors do drift,  and usually need to be re-zeroed periodically.

Some of these sensors may need to be degaussed from time-to-time,   as well.

As Larry mentioned,   50 mV,  500 A Shunts are really the industry-standard for DC current measurement,   and are shipped,  installed,  in the DC portion of many e-panels and DC conduit boxes,   and are useable by many existing solar subsystems.    Disregarding connection resistance of the large cables to the Shunt,   100 A of current through the Shunt,   yields 5 mV of voltage drop on a 50 mV 500 A Shunt.

FWIW,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

EW Zuber

#3
I remember another discussion on these forums where someone said that a supercap is a good idea when putting one or more shunts in series with an inverter due to an isolating effect the .005 ohm resistance that a 50mv shunt would have.

But this clamp-on sensor is not in addition to already existing shunts this is before any other shunts are installed or wired in.
Mostly thinking about the ease of installation and ease of adding more shunts at any time.
Instead of buying terminals, cutting wires and securing them to terminals then mounting the terminals to the shunt,
all that would need to be done is slide a sensor unit over the wire and leave it.
It's going to take over an hour preparing connectors and terminals for ,say, 5 shunts and these connections should probably be checked from time to time for voltage drop and / or re torquing. When it could take less than a minute to slip 5 sensors over wires and secure the ends and eliminate several mechanical connections in places where there is somewhat high current.
Just a thought.
(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

Hi Eric,

OK,   BUT,   a 50 mV 500 A Shunt has a resistance of 0.0001 Ohms,   really infinitesimal.

The traditional Clamp-On DC current sensors are quite unstable,   and need frequent zeroing.   Only really acceptable for their intended purpose.

A better all-Effect sensor (not a clamp-on,  but a donut type device),   would probably still need to be re-zeroed,  on occasion.  This can remove much of the utility as a general-purpose device,  but would be fine for a purpose-built subsystem.

IMO,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

EW Zuber

Vic, Hall Effect sensors are exactly what I am thinking.
Some of the Fluke clamp-on meters use Hall Effect IC's as sensors.
They might not as stable but I don't know, they are solid state though.   I'm thinking of exact donut sizes made for the wire size as needed. This would help with repeatable results.
Also mechanically assembled shunts are not free of drift either.
(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

dgd

Quote from: Vic on March 13, 2017, 07:37:09 PM
I believe that inside the Classic,  there IS  a Hall-Effect current sensor for the CC output.

A couple of years ago I asked about the current sensors in the Classic, I thought they were likely hall-effect devices, but was informed they were in fact shunt based.
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

dgd

EWZ,
All types of clamp-on current sensors tend to be notoriously inaccurate with readings drifting (for reasons as Vic noted above).
If you want to monitor currents at different places in your system then the easiest way is to use in circuit H-E devices such as the AC758, you would have to use a cpu
(PC,Arduino, rPi, BBB etc), and write some code to read and display the data.
http://www.ebay.com/itm/ACS758LCB-050B-PFF-T-Hall-Current-Sensor-Current-Module-MF-/172379257623?hash=item28229abb17:g:xQ8AAOSwzaJYBiCV
If you want MN to do this then you may have a long wait  as it may not be a commercially viable considering development costs vs potential sales.

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

EW Zuber

vic, "....a 50 mV 500 A Shunt has a resistance of 0.0001 Ohms,really infinitesimal....."
That was the exact point I made but it seemed to be dismissed in that particular discussion about the need for a supercap.

(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

EW Zuber

Well, like I said, this was only a thought. If a Hall IC attached to a current lead is not practical because the sensors are not accurate then it isn't going to work.
(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

Hello again Eric (I believe),

If you were referring to me being dismissive,   then I apologize ...  perhaps that part of a discussion was on another Forum.

Hall devices can be very accurate.  Historically they have needed to be recalibrated,  momentarily,  when in use ...   I have not followed the progress in this area.   Quite possibly,  the cost of devices that are more stable has come down  ...   dunno.

Your point about the connections to a large Shunt potentially having greater resistance than the Shunt is generally correct,   and this is one factor that can work against using the simple Shunt.

The Hall devices would need an interface,   power,   etc.   This is a bit of a disadvantage.   Resistive Shunts are the industry Standard,   and many monitoring/control functions readily interface to these Shunts,   so there would appear to be a wide application for them,   using existing monitoring/control devices ...

Those were the points that I was trying to make,  perhaps,  too clumsily.

73  Have Fun,   Vic    .   .
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

EW Zuber

Vic, to be honest I don't remember who was making the claim that a supercap would be needed if a shunt was installed. I wasn't trying to get personal about it.
Just saying that you supported my conclusion where I stated that a 50 millivolt shunt wouldn't create any more resistance than a normal connection.
In dealing with this topic I see that some people are using the resistance in wire as shunts. This might be a great idea. By calculating the resistance of a particular wire over a defined length one should be able to come up with a very accurate ohmic value.
For instance about 7' of #2 would have about a .001 ohm value.
(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

boB

We use a shunt  (500A 50mV) because this is what our industry has been using for many many years now.

It is also very low on power being 0.0001  Ohms.  At say, 25 amps draw, this is 25 * 25 * 0.0001 = 62.5 milliwatts.
0.0625 watts  Which is really low.

But the BIG advantage to this, as  others have pointed out is that it way more accurate than a Hall effect device.

Hall effect devices also draw power to operate and possibly more than a shunt at low power levels.

Hall effect devices and magnetic current sensors in general are also sensitive to external magnetic fields which can contribute to inaccurate  readings.

The Whizbang Junior calibrates for zero drift in-between every sample it takes which is about 10 times per second.
It's really accurate.

boB
K7IQ 🌛  He/She/Me

Resthome

Quote from: boB on March 21, 2017, 02:09:01 PM

The Whizbang Junior calibrates for zero drift in-between every sample it takes which is about 10 times per second.
It's really accurate.

boB

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.
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

Vic

#14
Hi John,

I see about a total variation of about 1.0,  or perhaps 1.2 A in WBjr Jitter.

This is not huge  --  about 0.1% of battery capacity,   but I do wish that it were lower.

Had assumed that this was due to a small voltage jitter,  which results in a larger current jitter.

Had also guessed,   that due to the relatively high String voltage on the main systems here (106 V at the STC Vmp of the PVs),   that this might well increase the Jitter,   compared to using a lower String voltage - guessing.

If the WBjr Jitter could be reduced,  that would be great.

AND,  on a slightly different subject,    sure DO wish that there could be a way for the Classic could have a battery voltage Sense device (perhaps the WBSr,   WBPlus  ...  WBDeluxe,   or similar that cold measure battery V at the battery terminals,   and communicate it to the Classic for use as THE battery voltage.   Realize that this could be a part of the B17 inverters,   but  we may not need replacement Inverters for some time ...  knock,  knock.

FWIW,    Vic

Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!