Do not disconnect under load question

Options
MichaelJ
MichaelJ Registered Users Posts: 23 ✭✭
in Solar Beginners Corner #1
Greetings,

Just installed my KD135GX panel, and it is working. I have no intention of disconnecting the MC4 connectors.

My question is can I safely remove the ATC 10a fuse installed in the positive cable near the cc to connect a meter to measure the amps? The meter is rated for 10amps dc, and I would make a serial connection.

May be a silly question, but I would appreciate knowing.

Thanks, Mike
· Share on Twitter

Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Options
    Re: Do not disconnect under load question

    Your PV open circuit voltage is a wee bit over 21, so the possibility of arcing while breaking the circuit is a real possibility. However, if you're charging a good 12 volt battery that is not dead (as in discharged), that would leave at most, 9 volts difference as you remove the fuse, so in that case there should be very little or no arcing problem. Just do it quickly.
    OR, you can throw a dark blanket over the panel, remove the fuse, hook up your meter, then remove the blanket.
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Options
    Re: Do not disconnect under load question

    i would assume this is a temporary move to measure your amps. if the meter is already connected across the opposing ends of the fuse holder then you could lift the fuse out briefly and full current will flow through the meter. watch that the meter leads don't super heat so maybe a few seconds before pushing the fuse back into place so you can remove the meter leads. you may see a tiny bit of current on the meter in a lower scale while the fuse is still in place and that would be due to possible resistance on the fuse, but don't go by that at all as you need the fuse removed to see the full current.
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
    Options
    Re: Do not disconnect under load question
    niel wrote: »
    if the meter is already connected across the opposing ends of the fuse holder then you could lift the fuse out briefly and full current will flow through the meter.

    Hahaha Niel you just made me feel VERY stupid! :p:p
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Options
    Re: Do not disconnect under load question
    waynefromnscanada wrote: »
    Hahaha Niel you just made me feel VERY stupid! :p:p

    so sorry. didn't mean to as i was only trying to help michael.
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Options
    Re: Do not disconnect under load question

    Hahaha Not to worry Niel, I just couldn't believe I hadn't thought of it myself :p:p
    · Share on Twitter
  • MichaelJ
    MichaelJ Registered Users Posts: 23 ✭✭
    #7
    Options
    Re: Do not disconnect under load question

    Thank you for the informative replies. Attaching the meter before removing the fuse can be done.

    My main concern was the MC4 connectors attached to the panel, and the risk of voiding the panel warranty.

    Mike
    · Share on Twitter
  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #8
    Options
    Re: Do not disconnect under load question

    Ithereon no junction box to meter across the + and - leads?
    · Share on Twitter
  • MichaelJ
    MichaelJ Registered Users Posts: 23 ✭✭
    #9
    Options
    Re: Do not disconnect under load question

    bmet,

    There is a junction box, plastic and completely sealed.

    I need to connect the meter to the positive cable to measure amps.

    Thanks, Mike
    · Share on Twitter
  • MichaelJ
    MichaelJ Registered Users Posts: 23 ✭✭
    #10
    Options
    Re: Do not disconnect under load question

    Greetings,

    I removed the 10a fuse from the panel to cc positive, was not able to have fuse and meter connected at the same time (ran out of hands). Pos meter conn toward panel, and neg toward cc. Didn't work, never got above one amp.

    Finally decided to disconnect the panel to cc pos cable from the cc. Took a reading from pos to the still attached (to the cc) neg cable. 8 amps. So the panel is working, the cables are good.

    But why did the in-line meter connection fail to give a valid reading. I even tried reversing the meter leads with no change.

    Is it possible that having the cc in the circuit somehow affected the reading. Or what? Any feedback appreciated.

    Mike
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #11
    Options
    Re: Do not disconnect under load question

    Yes, it can... If you have the DMM meter set for Amps on the output of the charge controller to the battery bank, the additional voltage drop may be enough to confuse the charge controller to think the battery bank is nearly fully charged and needs to cut back on the output current.

    I sound like a broken record--and should put a website selling this meter:roll:--I would suggest that you get an inexpensive DC Current Clamp Meter (~$60). It is much easier to monitor current without having to open electrical connections to jumper through the meter... Plus it is good to 400 amps. And it is much safer to use too.

    Because the charge controller can and does limit charging current based on battery voltage--Take your volt meter and measure the battery voltage and the output of the charge controller in full sun and when you think the battery should be needing full charging current (battery less than 80% charged and/or you have a DC load on the battery bank to drop the bank voltage). You need to get charger in "bulk charge mode" which usually means dropping the battery bank voltage to 12.7 volts or less, then recharging and keep the voltage below ~14.2 volts or so to get maximum current through the charge controller).

    If the controller sees more than ~14.2 volts and/or enters float mode--the current will be cut way back by the charge controller.

    Ideally, you should not see more than 0.10 volt drop between the output of the charge controller and the battery bank. If you see >>0.10 volt drop, you may have too small of copper wire, too long of wire run (too much voltage drop), and/or you may have poor connections somewhere.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • MichaelJ
    MichaelJ Registered Users Posts: 23 ✭✭
    #12
    Options
    Re: Do not disconnect under load question

    BB.,

    Thanks for the good info. Sorry if I wasn't clear, I connected to the input of the cc with the fuse removed.
    The + meter probe toward the panel, - meter probe toward the cc. That's when I got less than one amp, and the meter reading was constantly changing, but always under one amp.

    With the fuse removed from the positive input to the cc(no connection) and + meter probe as before, I connected the - probe to the negative cc input and got 8amp reading.

    The cc is pwm, which has constant voltage but lowers the amps to "float". My battery was fully charged, and read 12.8v last night - with no use since.

    Having no other solar experience, I wonder if the serial connection to the positive input to the cc measured the cc output to the fully charged battery?

    I believe that metering from the disconnected positive cc input to the connected negative input gave a true reading of the panel working in full sun.

    When I connect a load to the cc, and the battery is below 80%, I will try again. And yes, the clamp on dc ammeter is on my list.

    Mike
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #13
    Options
    Re: Do not disconnect under load question

    Hi Mike,

    No, I think you were clear... I was trying to say (in too many words:roll:) that the charge controller can change the average current into the battery bank, depending on state of charge, voltage drop of charger to battery cable, and other state/time modes (bulk, absorb, float).

    It does make it more difficult to see if everything is working correctly. The state of charge of your battery bank, monitoring current flow (ideally with a hardwired amp meter, battery monitor, or DC Current Clamp Meter), when you have good sun and lots of load on the battery bank (and/or the battery is known to be discharged), and checking specific gravity/resting voltage is just par for the course of the day to day/week to week monitoring you need to do to make sure that your system is operating well.

    All it takes is a few days to a week of a failed charge controller or wiring connection and you can kill your expensive battery bank.

    And we all get complacent--Everything works for several years and we get "lazy"--then something breaks and we don't notice... Even a small digital volt meter wired into the system draws little power but a quick glance a couple times a day will tell you if all is well or not.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • MichaelJ
    MichaelJ Registered Users Posts: 23 ✭✭
    #14
    Options
    Re: Do not disconnect under load question

    Thanks Bill,

    Excellent info (as always). My system is tiny, one panel and one battery - a learning project. This forum and NAWS are a critical resource for me, and sincerely appreciated.

    Voltage drop was a concern, and I went with 10ga panel to cc (16') and 10ga cc to batt (18"). May become complacent in the future, but for now batt volts daily and hydometer weekly.

    Mike
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #15
    Options
    Re: Do not disconnect under load question
    BB. wrote: »
    I sound like a broken record--and should put a website selling this meter:roll:--I would suggest that you get an inexpensive DC Current Clamp Meter (~$60). It is much easier to monitor current without having to open electrical connections to jumper through the meter... Plus it is good to 400 amps. And it is much safer to use too.


    -Bill

    Hey BB, I just received mine yesterday - - Finally after all these years, nay decades, finally I have a DC clamp meter and after giving it a test run, have no idea how I ever got along without it! I guess if one never had such a thing, (and indeed they didn't even exist during my earlier working life in electronics) one somehow manages to get along without it, in the same way someone born blind, does in fact still manage to get around without vision. Using this meter as intended, is like someone lifting the window shade, and where once I could tell if the sun was shining, I now can see the moon and stars!
    Oh, and one more thing - - it was sent to me from the USA, through the postal service all the way, and for the first time ever, I received an item across the border with no import duties, no brokerage fees, no assorted whatever they could think of fees!
    Do you REALLY have to ask me if I'm pleased? :p:p:p:p
    THANK YOU BILL!
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #16
    Options
    Re: Do not disconnect under load question

    :D Neat. Glad you are having fun with the meter. It is almost magic.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #17
    Options
    Re: Do not disconnect under load question

    It is indeed like magic :D
    And if you glue a small magnet, out of sight behind the wire you're checking, you can show others what HUGE currents that relatively small wire is carrying. :p:p
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #18
    Options
    Re: Do not disconnect under load question

    Only took ~55 years for me to buy one (less than a year ago).

    The only thing I have problems with is the temperature probe (thermocouple). Stopped working and fell apart in a couple days (mostly sitting in the meter case).

    Oh well...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #19
    Options
    Re: Do not disconnect under load question
    BB. wrote: »
    Only took ~55 years for me to buy one (less than a year ago).

    The only thing I have problems with is the temperature probe (thermocouple). Stopped working and fell apart in a couple days (mostly sitting in the meter case).

    Oh well...

    -Bill

    Very interesting re the temp probe. When I first opened the package, took one look at the tip and thought: "Now that's gonna last about a week if I'm lucky". Don't know why I even bothered to put it in the case with the meter. Oh well, the DC clamp meter is what I wanted/needed, and have other things to take care of temp readings, so overall I'm extremely happy with it :D.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #20
    Options
    Re: Do not disconnect under load question

    The tip is welded (standard for thermocouples). It was the plug/base that came apart for me.

    Put it back together, but never worked right again. May be a simple fix, just did not bother because I did not need that function anyway either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter

Categories