Comon Neutral

While reviewing an installation diagram for the Outback MX60/VFX3024 I noticed that the MX60 charge controller ‘PV in’ negative and ‘Battery out’ negative were bonded. This simplifies the cabling and works fine; it also seemed to make sense. I have just installed a smaller system using a Steca Tarom 35Amp charge controller. I always fuse the PV in and Battery out, and in this installation used a common negative connector in my fuse box effectively bridging the PV negative to the battery negative, as illustrated by the Outback diagram. To my surprise the Steca went up in a blue flash as soon as I connected the battery, at that point the PV was connected. The Steca Tarom is working accept for the charge regulation, it shows no amps going in, but the voltage indicates it is charging, so it as good as dead… Any experts out there like to help me understand why?:confused:

The system is: two 110w / 7.5A Solar Fabrik panels on SunTracer trackers (one per panel), Steca Tarom 35A Charge Controller, Exide Opz 985Ah Bateries, 1.6Kw PSW inverter/charger.

Comments

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Comon Neutral

    Planetharman,

    This data sheet indicates that negative grounding at one point is a feature of the Tarom controller. The data sheet also indicated plenty of electronic protection features: reverse polarity, short circuits, etc. Hard to say what happened: defective controller, bad wiring, or...??

    Sorry about the bad luck...
    Jim / crewzer
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Never Assume Common Ground

    The unit appears to be a true 4 wire controller and is documented as such

    http://www.solarpanelsaustralia.com.au/downloads/steca_pr_manual.pdf

    Quoted from the manual:
    Observe that there is no common connection, e.g. across
    a ground connection, the minus module connections,
    battery minus and load minus. Non-observance can
    damage the regulator!

    Technically, any controller that has current sense using interal shunts on the negatives will be damaged by shorting the lowside in/out pins .. in essance, you are disabling the units current monitoring/regulating ability and it wil fail to regulate and very well maybe damaged.

    For the Record the new Xantrex WX-MPPT is also a 4 wire design, meaning the PV has two wires in, the regulated voltage out is another pair of wires and none should be bonded together!
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Comon Neutral

    Interesting info about the new Xantrex controller!

    Planetharman,

    Assuming the charge controller in question is indeed a Steca Tarom 35 A model, I respectfully disagree with Solar Guppy’s analysis. The chargers described in his post appear to be models that are different from yours.

    Is/was your 1.6 kW inverter/charger connected to the Taron’s load connections? If so, I suspect that may be the source of the problem. The inverter’s start-up 12 V start up surge (100 A? 200 A?) would likely be substantially above what the Tarom is designed to handle (35 A?),. For your application, I would think that the inverter charger should be connected directly to the battery bank (via a fuse and/or circuit breaker) and not via the controller.

    Additionally, the controller may not have been happy when you attempted to connect the battery (+) after the solar array was connected. Check the user manual on this point.

    HTH,
    Jim / crewzer
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Comon Neutral
    Assuming the charge controller in question is indeed a Steca Tarom 35 A model, I respectfully disagree with Solar Guppy’s analysis. The chargers described in his post appear to be models that are different from yours.

    huh? I googled and found the manual for the OP charge controller ... its clearly a 4 wire design ... did I miss something crewzer?
  • System2
    System2 Posts: 6,290 admin
    Re: Comon Neutral

    Thanks for all the tech input.

    I have since done so more digging and noted that the Steca is a rare? Positive earth controller, both positives are internally linked! By using a common negative I was in effect shorting the whole thing out, we live and we learn…
  • System2
    System2 Posts: 6,290 admin
    Re: Comon Neutral
    at that point the PV was connected.

    Just for the record, the PV was NOT connected, this is a typo, which I tried to edit out but could not. Good practise is always to connect the batteries to the charge controller (with a fuse/disconnect) first, then the PV, preferably with another fuse/disconnect 8)

    Second good practice, read your own post before posting it:roll:
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Comon Neutral

    Planetharman,

    Sounds like you’ve diagnosed the problem. The positive ground architecture certainly adds a twist.
    Quote:
    Assuming the charge controller in question is indeed a Steca Tarom 35 A model, I respectfully disagree with Solar Guppy’s analysis. The chargers described in his post appear to be models that are different from yours.

    huh? I googled and found the manual for the OP charge controller ... its clearly a 4 wire design ... did I miss something crewzer?
    Solar Guppy,

    Now that I know that the Steca Tarom 235 and its relatives are primarily intended for floating or positive ground applications, I’d say that you’re correct. I obviously misinterpreted the data sheet's statement about "negative grounding at one terminal".

    I was therefore wrong in my initial assessment and in my criticism of your post . :blush: But, I learned something new today, and I think we all now understand why planetharman's system "flashed".

    With apologies,
    Jim / crewzer
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Comon Neutral

    At the top of the "Features for this Steca PWM controller it says:
    "PWM shunt battery charging"....

    This may mean that instead of the PWM "opening" the PV input, it
    actually "shorts" the PV input, and if so, because it switches the negatives
    and you tied those together, the battery terminals would be shorted
    together through its FETs or switches. Bad ! Fire ! Smoke !
    Some controllers unfortunately do work this way. Maybe this is one
    of them.

    However, I will have to remember this unit for use in certain
    positive ground systems where they MUST tie both positives together
    and cannot with C40s, MX60s etc...


    So Mr Guppy, are you saying that the XW60 does not work properly
    if the two negatives are tied together ? Maybe this has something to
    do with the GFI fuse thingie ?? Or, maybe has something to do placement
    of its current sensors ? The C40, MX60, etc does allow tying of the negatives
    together and would be, at this late date, kind of non-standard and not
    understood by many people just switching to it after using the more widely
    used American controllers.

    boB
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Comon Neutral

    boB Ive just checked the installation manual that I down loaded from the XW60 MPPT and Solar Guppy is correct. The negative out from the controller goes direct to the negative terminal of the battery bank. and not to the -ve bonding block in the disconnect unit. The only connection to the bonding block is the earth terminal. However it doesnt show the bos like the inverter conected which goes direct to the -ve battery bank from the common ground earth combiner block it also shows earthing the metal battery container enclusure which I dont have mines concrete. Have alook.
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Comon Neutral

    >>The negative out from the controller goes direct to the negative terminal of the battery bank.

    That's fine but it wouldn't change why the Steca blew up. I think that
    it means that the current measurement comes from the XWMPPT rather than through
    the main 500 Amp shunt and a main system battery monitor, however there isn't an
    XW battery monitor "system" yet, except for individual XW charger blocks.

    I'll have another look at the diagram though.

    P.S. Not having current limit would not necessarily hurt anything because hardly anybody installs a PV array big enough
    to overcurrent a controller. They are current limited unlike a battery which is virtually unlimited in this situation. (which is
    what I think probably happened to your unit) The internal controller shunt may OR may not have been fast enough to
    avoid the smoke.

    thanks,
    boB