XW-MPPT60-150 Running Hot

ElkeElke Solar Expert Posts: 28
I just had a Xantrex XW4024 inverter plus XW solar charge controller, distribution panel, system control panel, and a small 305Ah (24V) battery bank installed. The charge controller is running quite hot during midday (it even smells a bit like hot electronics), and I am wondering, if this is normal, or if this is detrimental to the equipment, and if there is a problem with the installation.

The installer wired all 12 Shell Solar 165 Watt panels in 4 strings of three modules to the same charge controller. The panel characteristics are: VOC=44.5V and ISC=5.4A.
On a sunny day I have seen the input wattage on the charge controller above 1600Watts and the output current just under 59Amps. I see in the manual, that 60Amps is the output limit. Do I need a second charge controller?

I have also noticed, that as the sun rises, there is no automatic transfer of floating the batteries from the inverter to the charge controller. I would have thought, that as soon as there is sufficient input wattage from the charge controller available, the inverter would automatically transfer the battery charging duties to the solar charge controller. Right now, this transfer only happens when I have the "charge block" on.
Is this how it is supposed to work?

I would greatly appreciate some advice.
Elke
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Comments

  • dsp3930dsp3930 Solar Expert Posts: 66 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    The XW SCC can handle up to a max of 150V at 60A DC; however, it reduces output current between 120v to 140v, and may shut down above 140v with an over voltage fault. With a VOC of 44.5, you have a max voltage of 133.5 volts assuming standard conditions (77F) for three panels in series. The colder the weather, the more volts the panels put out. (negative temperature coefficient) I'd say that your installer messed up quite a bit. Assuming your lowest temperature reached is 9F, then they would completely top out the controller at 150v. The max amps are on the DC side of the controller, so at between 20-30A you should be okay there. (Xantrex recommends always staying under 48A (Isc) for your solar panels connected to the SCC) I don't believe you are likely to overload the contoller in the summer, but in the winter you will if you live in most parts of the US. The strings really need to be changed to 6 strings of 2 as soon as possible.

    Your SCC should stay in bulk all day as long as your are selling to grid or your sub-panel is using power. If you are not, then it should go to absorb and then float as the batteries top off.

    If your XW inverter should only be charging your batteries if they have been run down through use such as a brief power outage. The internal charger should then switch off. When charging, it automatically lowers the amps as it approaches full charge. Even then, it should only be kicking in if you go below about 22v or after restoration of power from your main panel after a loss of utility power. Your SCC/solar should keep your batteries above that level nearly all of the time. This assumes you are using the batteries for buffering mainly and not really using them in an off grid manner.

    A good test to see if your system is setup correctly would be to turn off your main panel breaker to the XW unit. The inverter should kick in to power everything on your sub-panel from solar and if needed from batteries. Then, after 1 minute or so, flip the main breaker back on. The inverter will check the utility AC stability, and then it should turn on the internal charger to bring your batteries back up to full charge. (rapidly reducing the amps it is charging with until it stops charging). The inverter/charger should then shut off and normal solar charging via the SCC should resume as described above in the second paragraph.

    In a normal day scenario, your batteries should have been slightly used to power the Xantrex unit overnight and the first little bit of sun will be used by the SCC to bring them to a fully charged state in bulk mode. The inverter then will start to sell to grid (if enabled) and power your sub-panel. Your SCC will stay in bulk charge mode all day if you are selling to grid. If you have sell to grid disabled and your sub-panel is not consuming power, your SCC should slip into abosorbtion mode, and then into float.

    David
  • Solar GuppySolar Guppy Solar Expert Posts: 1,970 ✭✭✭
    Re: XW-MPPT60-150 Running Hot

    Your probably running close to 90V to 28V, that's a very large step down and the XW is not the charger to use in this configuration ( it is inefficient at large voltage differentials )

    At a minimum, you should rewire your array to be 2 in series by 6 strings or get a charge controller that can efficiency handle that large of a step down. The MorningStar Mppt in this configuration would have significantly lower losses run run much cooler.
  • boBboB Solar Expert Posts: 984 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot
    Elke wrote: »
    The charge controller is running quite hot during midday (it even smells a bit like hot electronics), and I am wondering, if this is normal, or if this is detrimental to the equipment, and if there is a problem with the installation.

    Elke

    It is normal for it to run hot and can be detrimental over time.

    You could get one of those clip on fans and point it at the CC near the heatsink and that will cool the transistors significantly. Won't do quite as much for the filter capacitors inside but will help some. They may be the first things to need replacing in a few years. You could check them for bulging in a couple of years.

    boB
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    you are running the controller very close to its max so it will dissipate heat. as we are to understand about the xw cc is that it will function fine without additional fans and it will not exceed 60a output. i'll bet you are hitting that 60a mark with the potential of more at times during high solar intensities for that many pvs. my guess is you are losing some power at times through the controller's current limitation. remember that an mppt controller will recoup some of the power that would normally be lost so in the end currents can appear to exceed pv nameplate at times. your pv is rated 35v vmp and 4.72a imp. due to downconversion it will lower the voltage and up the current even though the input is higher voltage in its series/parallel arrangement to start. arbitrarily 12 x 4.72a = 56.64a. adding 10% typical mppt may yield another 5-6a, but it is held to 60a.
    if you add another controller it will be for the reasons of lost power due to current limitations and future expandability, but the xw cc imho is fine as it is too.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: XW-MPPT60-150 Running Hot

    If I were you I'd put a fan on heat sink until the panels are rewired to 2 series X 6.

    You may also end up better off for morning/afternoon panel shading.
  • dsp3930dsp3930 Solar Expert Posts: 66 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    Niel

    I'm a bit confused by your last statement, you may have just been trying to make a point ... it so, it eluded me. :D

    Currently the panels are in four sets of three:
    4x4.72A = 18.88A DC

    Even if moved to six sets of two, the max Isc amps would be:
    6x4.72A = 28.32A DC

    The XW SCC amp limit is on the source DC side and per Xantrex docs should be no more than 48A. (with a max of 60A) I have not seen any notes on it being limited to 60A on the output side?



    As a side note: (and not completely related to the post)
    From what I have read (and understand), the real max operating level for the XW SCC is 120V at 48A. Any more than this and it starts backing off to prevent "bad things" from happening. If you put an array on the XW that had those max specs it would be about 5760 watts of panels. Since the XW can only accept up to 3500 watts a lot of potential would be clipped off on full sunny days.

    If you had the highest nominal voltage recommended of 120V, you could have up to 29A panel output and still get the max rated input of 3500w without potential loss on full sunny days.. (120V @ 29A)

    If you had the highest nominal amps recommended of 48A, you could have up to 73V panel output and still get the max rated input of 3500w without potential loss on full sunny days.. (73V @ 48A)

    Solar installs using the XW should fall somewhere inbetween the two above extremes if fully loading the SCC. As other posters have said, running the SCC at full tilt will reduce its life. If you have that much PV, consider using two and dividing your array between them.



    That said ...
    The original poster would not need two SCC units. Just a change to the PV panel layout. (Two panels in six strings as has already been noted.)


    David

    niel wrote: »
    you are running the controller very close to its max so it will dissipate heat. as we are to understand about the xw cc is that it will function fine without additional fans and it will not exceed 60a output. i'll bet you are hitting that 60a mark with the potential of more at times during high solar intensities for that many pvs. my guess is you are losing some power at times through the controller's current limitation. remember that an mppt controller will recoup some of the power that would normally be lost so in the end currents can appear to exceed pv nameplate at times. your pv is rated 35v vmp and 4.72a imp. due to downconversion it will lower the voltage and up the current even though the input is higher voltage in its series/parallel arrangement to start. arbitrarily 12 x 4.72a = 56.64a. adding 10% typical mppt may yield another 5-6a, but it is held to 60a.
    if you add another controller it will be for the reasons of lost power due to current limitations and future expandability, but the xw cc imho is fine as it is too.
  • trkarltrkarl Solar Expert Posts: 33
    Re: XW-MPPT60-150 Running Hot

    One thing you may want to check also, and this is a long shot, is the input and output terminals and make sure the screws are tight.

    A friend of mine had an installer install 2 xw ccs and he kept telling me one would always run hot. Well, it finally burned out.

    When he sent me pics of the damage it was melted at the + battery side connection.

    I finally drove up there and checked all his connections. The other 3 connections were also real loose. On his other charge controller they were tight and it had no problems with heat.

    This was the installers mistake and the cc was replaced no charge but it could have started a fire.
  • toppertopper Solar Expert Posts: 113 ✭✭
    Re: XW-MPPT60-150 Running Hot

    XW Sizing tool:
    Shell 165 Watt
    Pmax @ STC 165 W
    Pmax @ PTC 149 W
    Vmp at Pmax 35 V
    Imp at Pmax 4.72 A
    Voc @ STC 44.5 V
    Voltage change -145 mV/C

    Max OC Voltage 150 Vdc
    Max Current 60 Adc

    Bulk/Absorb battery voltage 28.8 Vdc
    Float battery voltage 27 Vdc

    Max VOC at Min Temp Min VMP at Max Temp (cell temperature 35°C)
    2 Modules 101 Vdc 57 Vdc

    1 Strings STC 330 Wdc 12 Adc PTC 298 Wdc 11 Adc
    2 Strings STC 660 Wdc 24 Adc PTC 596 Wdc 22 Adc
    3 Strings STC 990 Wdc 36 Adc PTC 894 Wdc 32 Adc
    4 Strings STC 1320 Wdc 48 Adc PTC 1192 Wdc 43 Adc
    5 Strings STC 1650 Wdc 60 Adc PTC 1491 Wdc 54 Adc

    According to the XW sizing tool. Max # is 5 strings of 2.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    my comments in bold.
    dsp3930 wrote: »
    Niel

    I'm a bit confused by your last statement, you may have just been trying to make a point ... it so, it eluded me. :D

    Currently the panels are in four sets of three:
    4x4.72A = 18.88A DC

    Even if moved to six sets of two, the max Isc amps would be:
    6x4.72A = 28.32A DC

    you forget that in the downconversion the current is upped. the equivalent would be all of them basically paralleled as it is a 24v battery bank and these are 24v pvs and not 12v pvs thus making it x12 due to the number of 24v pvs he has and not x6 for the current. even at the paralleled arrangement some current gains would be realized making it even higher than the x12 figure because the input voltage is at 35v which is high enough to generate a mppt gain especially when batteries are lower in voltage like 23v instead of 27v as many charged batteries would be at.

    The XW SCC amp limit is on the source DC side and per Xantrex docs should be no more than 48A. (with a max of 60A) I have not seen any notes on it being limited to 60A on the output side?

    that 48a is the nec input limitation and not the limitation of the controller. when doing voltage conversions as i stated before the equivalent amps will differ to get the same result at the output. to better understand this think if you had the 48a inputted at 48v and the output side is to be 24v in batteries. the controller would attempt to try and make it 24v at 96a and this will not happen as the output is limited to 60a. i didn't look over the documentation as to what xantrex does or does not say and i don't have to as the controller is a 60a controller and not an unlimited controller. the controller is limited to 24v x 60a = 1440w at the output. 12 165w pvs is 1980w. the nec would have you limit to 48a x 24v = 1152w.

    As a side note: (and not completely related to the post)
    From what I have read (and understand), the real max operating level for the XW SCC is 120V at 48A. Any more than this and it starts backing off to prevent "bad things" from happening. If you put an array on the XW that had those max specs it would be about 5760 watts of panels. Since the XW can only accept up to 3500 watts a lot of potential would be clipped off on full sunny days.

    If you had the highest nominal voltage recommended of 120V, you could have up to 29A panel output and still get the max rated input of 3500w without potential loss on full sunny days.. (120V @ 29A)

    If you had the highest nominal amps recommended of 48A, you could have up to 73V panel output and still get the max rated input of 3500w without potential loss on full sunny days.. (73V @ 48A)

    controller maximums are determined by the output voltage as a 12v output at 60a is 720w and the 48v output is 48v x 60a = 2880w. at 60v this is 3600w, but few have battery banks at 60v and i'm not sure if the controller does a 60v output offhand, but it really doesn't matter as the point is it will not handle as much power at lower output voltages.

    Solar installs using the XW should fall somewhere inbetween the two above extremes if fully loading the SCC. As other posters have said, running the SCC at full tilt will reduce its life. If you have that much PV, consider using two and dividing your array between them.



    That said ...
    The original poster would not need two SCC units. Just a change to the PV panel layout. (Two panels in six strings as has already been noted.)

    nec issues aside, as i said, the controller is maxed out and is being held back by the output current limitation of the controller. if it were my setup i'd get another cc even though the present one will work as is. one would lose the benefit of mppt by hitting the current max on the output.


    David
  • boBboB Solar Expert Posts: 984 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    So, how hot IS the heat sink ?? Maybe it feels (and smells) hot, but maybe it's not really TOO hot ?

    Can you keep your hand on the heat sink for a long time ? If so, then it's probably not too hot.

    You might try measuring the temperature of the heat sink and the ambient temperature of the room too.

    boB
  • dsp3930dsp3930 Solar Expert Posts: 66 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    From P2-2 / XW Series Charge Controller
    "Although the Solar Charge Controller can harvest a maximum of 3500 W, the PV array size can be as high as 6720 W (based on 48 A * 140 Vdc = 6270 W).

    -- This implies to me that the DC amps could have a theoretical maximum of 72 A @ 48V or 145 A @ 24 V to the battery bank based on the 3500 W of max harvestable input power. (though as noted below, only 60A would actually be output by the controller?)

    From P2-2 / XW Series Charge Controller
    "Panels rated up to 48 A at 25 C (77 F) are recommended to allow for increases in Isc at low panel temperatures and at solar noon. Ensure that the Isc rating under all conditions does not exceed 60A."

    Fron A-2 / Electrical Specifications
    "Array Short Circuit Current / 60 Adc maximum"
    "Maximum Output Current / 60A (for all battery voltages except 60V)"

    - It appears that the SCC is capable of pulling in up to 60 A ( 48 A recommended) from the solar panels but will cap the output a 60 A. This would seem to imply to me that either a 24 V or 48 V battery bank would be limited to a maximum of 60 A carging rate by the controller.

    Is this correct?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    i'm not sure of where that comes from for the 1st sentence as it seems way out of bounds.
    the 2nd sentence is totally false as wattage ratings of controllers drop with lowered output voltages.
    the 3rd sentence is the input limitation by the nec and is not a physical limitation of the cc and the breathing room i agree with to reap the benefits of mppt otherwise i feel it has no place in electrical rules by the nec.
    the rest confirms what i have been saying, but you could physically input more amps and the cc will just pass up to 60a of it and yes that's correct. if the output current is limited to 60a this means for different battery voltages that the max wattage is as follows;
    12v x 60a = 720w
    24v x 60a = 1440w
    48v x 60a = 2880w
    now if it outputs that much then it stands to reason not to exceed that much wattage on the input or you will waste the power.
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: XW-MPPT60-150 Running Hot

    Mine gets warm but never hot. I have 2100 watts going into 48V.

    I can put my hand on the top of the XWCC with no discomfort what so ever.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    now we still don't know for sure if there is a problem with the cc itself as there still could be, but we aren't getting more feedback from the op to evaluate.
  • ElkeElke Solar Expert Posts: 28
    Re: XW-MPPT60-150 Running Hot

    Hello All!

    Thank you so much for all your helpful information, advice and comments in such a short period of time. This is unbelievable! When do you guys sleep?

    I am sorry to not have provided any more details, but it took me and my husband a little while to digest all this and this weekends PV "events". I thought we had purchased a turn-key system, but more and more it looks like we bought ourselves a project.

    Here is the update: A couple of days ago, we came into the garage, where the inverter and SCC are located, and immediately noticed the unmistakable smell of melting/burning electronics components. I quickly turned off all the power. Our noses told us that the fumes came from the charge controller. Driven by curiosity we eventually opened the bottom cover of the SCC. What we found was a melted battery+ terminal block and melted insulation of the cable leading to it. Not much investigation revealed a #10 AWG cable on a connection, which can carry up to 60Amps! Of course, the 60Amp breaker did not trip.

    We took a picture of the whole mess and sent an email to the installer. This morning I talked to him on the phone. He did not believe me, and he is trying to get a Xantrex expert to visit and inspect the installation. I am pretty sure the installer's crew installed this cable not Xantrex. The manual says #6 AWG minimum I believe. I am wondering how much I can trust in the rest of the installation.

    Once this issue has been resolved, we would like to look more into dividing our PV array and using two SCCs. We looked up the Xantrex calculator and it does seem to allow our 165W panels in the 4 strings of 3 configuration we have. There is a note, however, that output could get clipped. If loss of output is the only problem, that may not be so bad, but we would like to avoid shortening the equipments lifetime. So maybe going to the 6 strings of 2 panels configuration would be better. It would also bring the input and output voltages closer together and hopefully increase the efficiency. On the other hand we did not get the impression that the SCC was particularly inefficient.
    I am just trying to summarize all the information I gathered from your various inputs. Hopefully, this is the right path. Please, correct me, if you see any problems.

    Oh, I wanted to add that our daytime minimum temperature does not sink below 60F, even in winter. And if we do get 60F, it is usually raining. We live on the Southern California coast. So I don't thinks that 3 panels in series will ever get close to 150V output. Before the "meltdown" we saw 120V max.

    Best regards,
    A Tired PV Project Owner
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: XW-MPPT60-150 Running Hot

    It looks like you got the configuration issues/questions down.

    Two controllers would run cooler vs one... And dropping the array down to 2 panels vs 3 would reduce temperatures some too. But, you are within the ratings of the controller and they are designed to safely limit there maximum output current--There is no chance of damage from over production on the solar panel side of things--just a slight loss in maximum current and solar harvest (and, depending on your local conditions, you may not really hit that 60 amp peak limit very often).

    The 10 AWG wire is a problem (how long is the wiring run?).. You might want to take a look at the wiring (gauge and distance) for your inverter's DC side too.

    If you wiring runs are fairly long (10-50+ feet or so), then you may need heavier gauge cables to reduce voltage drop too.

    Copper is expensive and it sounds like somebody was trying to save a buck.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ElkeElke Solar Expert Posts: 28
    Re: XW-MPPT60-150 Running Hot

    Bill,

    Luckily the inverter's DC side came pre-wired from the factory: thick, thick cables!

    Our wire run between the PV array and the SCC is 50 feet one way. We had a discussion about the wire gauge with the installer. He wanted to use his 10 AWG, which seemed too thin to us. Only when we offered to go and buy #6 wire he agreed to install it. Unfortunately, we did not look over the rest of his wiring job as closely. After all, we thought we bought a fully installed system and not a Do-It-Yourself-PV-Kit.

    The 10 AWG wire, which melted, is only 1 foot long, but we did see 58 to 59 Amps on the charge controllers output (where the wire is attached).

    I think you are right about somebody trying to save on the copper, but that can be quite dangerous in some cases.

    I am very glad this forum exists. Otherwise I would not know, where to get all this information from. The installer, unfortunately, does not offer much help.

    Regards,
    Elke
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    that is 100% the fault of the installer and has nothing to do with xantrex as the installer put that wire there. odds are there is another 1ft piece of #10 going from the controller to the battery for the other polarity. the heat was building up from the #10 wire heating things up and could possibly have damaged the controller at the point of connection. #10 wire, even if only 1ft long, is far undersizing things as it is to carry upwards of 60a and it would not have broke the bank for him to put 2 heavy gauge wires there and in fact imho he is paid to do the job properly with the proper wires. nowhere is #10 wire safe to pass 60a of current.
  • solar_davesolar_dave Solar Expert Posts: 2,381 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot
    niel wrote: »
    that is 100% the fault of the installer and has nothing to do with xantrex as the installer put that wire there. odds are there is another 1ft piece of #10 going from the controller to the battery for the other polarity. the heat was building up from the #10 wire heating things up and could possibly have damaged the controller at the point of connection. #10 wire, even if only 1ft long, is far undersizing things as it is to carry upwards of 60a and it would not have broke the bank for him to put 2 heavy gauge wires there and in fact imho he is paid to do the job properly with the proper wires. nowhere is #10 wire safe to pass 60a of current.

    If it caused damage (or worse yet a fire) he could be liable for the damages. Was he a licensed electrician?
  • carotenecarotene Registered Users Posts: 8
    Re: XW-MPPT60-150 Running Hot
    niel wrote: »
    nowhere is #10 wire safe to pass 60a of current.

    Actually, yes it is. Check your wire charts. Even at 12V, you can run 60A through 10 AWG 6 ft with < 3% drop. There is nothing wrong with using a short, smaller gauge wire to route out of a tight equipment box to a splice block termination to larger cable. It might have been better to run a larger gauge to reduce the V drop, but not necessary.

    Based on the OP's description, i'd vote for a resistive connection at the battery terminal on the controller. Melted insulation which starts at the point of termination and melts some distance down the wire is a dead give away. This is caused by corrosion or loose terminal connections. Since this is a new system, likely a poorly tightened terminal.
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: XW-MPPT60-150 Running Hot

    You're supposed to use a torque wrench to tighten those terminals.
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: XW-MPPT60-150 Running Hot

    Well, the 3% drop for the length of wire run is one recommended limit by NEC--but that is really more of a functional limit (how much voltage is at the end of the wire) than as a safety limit...

    2 feet of 10 awg wire has approximately 0.23 volt drop (assuming an elevated operating temperature for the wire)... The power dissipation would be:
    • P=V * R = 60 amps * 0.23 volt drop = 13.8 watts
    If the +/- wire is bundled together (or worse yet, in a conduit or wiring box with little air flow)--That 14 watts has to go somewhere spread over a 1 foot run of wire. Heating the wire and its environs--and its insulation--in the process.

    At this point, special high temperature insulation, calculating the ability of the wire to dissipate the heat (convective, radiative, conductive) where it was installed, etc. all would be a requirement if somebody wanted to cut the installation this close to the limits of the materials used.

    Or, just use the fairly conservative rules of thumbs that have been used to make the NEC (large diameter wire, temperature rated insulation, conservative deratings, safety devices to prevent over current/voltage/power in appropriate locations, proper installation techniques, proper materials for the environment in which the will be used, etc.) and you will have a pretty safe installation.

    That is why it is dangerous to use just one rule of thumb (like the 3% which is a functional limit rule of thumb) and ignore others (wire current limit based on current, voltage, insulation, exposure, ambient temperature, installation conditions, etc.) when trying to make for a safe installation.

    In this case, it may be an improperly torqued electrical connection inside the charge controller--But having undersized wire probably did exacerbate the local heating problem too (not enough contact area, not enough volume of wire to dissipate heat from the electrical connection, adding heat from the 14 watts of the wire itself, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • carotenecarotene Registered Users Posts: 8
    Re: XW-MPPT60-150 Running Hot
    BB. wrote: »
    Well, the 3% drop for the length of wire run is one recommended limit by NEC--but that is really more of a functional limit (how much voltage is at the end of the wire) than as a safety limit...

    2 feet of 10 awg wire has approximately 0.23 volt drop (assuming an elevated operating temperature for the wire)... The power dissipation would be:
    • P=V * R = 60 amps * 0.23 volt drop = 13.8 watts
    If the +/- wire is bundled together (or worse yet, in a conduit or wiring box with little air flow)--That 14 watts has to go somewhere spread over a 1 foot run of wire. Heating the wire and its environs--and its insulation--in the process.

    At this point, special high temperature insulation, calculating the ability of the wire to dissipate the heat (convective, radiative, conductive) where it was installed, etc. all would be a requirement if somebody wanted to cut the installation this close to the limits of the materials used.

    Or, just use the fairly conservative rules of thumbs that have been used to make the NEC (large diameter wire, temperature rated insulation, conservative deratings, safety devices to prevent over current/voltage/power in appropriate locations, proper installation techniques, proper materials for the environment in which the will be used, etc.) and you will have a pretty safe installation.

    That is why it is dangerous to use just one rule of thumb (like the 3% which is a functional limit rule of thumb) and ignore others (wire current limit based on current, voltage, insulation, exposure, ambient temperature, installation conditions, etc.) when trying to make for a safe installation.

    In this case, it may be an improperly torqued electrical connection inside the charge controller--But having undersized wire probably did exacerbate the local heating problem too (not enough contact area, not enough volume of wire to dissipate heat from the electrical connection, adding heat from the 14 watts of the wire itself, etc.).

    -Bill

    10 AWG has a resistance of 1.018 mOhm/ft @ 77F. That's ~2 mOhm for 2 ft.

    P = I^2*R = 3600 * 0.002036 = 7.33 Watts

    Thats 3.7 W / conductor @ 77 F. Granted there is elevated temps and conduit correction factors but this is not an unreasonable dissipation. Is it ideal? Not really. It's only 2 feet of wire, so why not spend the extra 50 cents on a guage or two lower. But it's not inherently unsafe either and that was my point. I don't think the wire size contributed to the problem. A resistive connection may only generate a few watts but it's dissipated in a very small contact patch. That's sufficient to melt a terminal. The contact patch is the loose compression terminal's contact with the wire. It's all about the Watts/area.
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: XW-MPPT60-150 Running Hot

    I assumed a higher temperature (using "adverse" in a wiring drop calculator), which causes an elevated resistance, because of the undersized wire and the potential for self heating of a 60 amp current in a 10 awg wire.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    the nec and the wiring industry itself does set minimum standards. pretty much as bb indicated one does not want to use as an example 1 inch of a small wire just based on voltage drop to carry a huge current as that voltage drop would be 12x less in a 1in length than what the 1ft length would be given the same gauge #.
    nowhere that i've ever seen has #10 even been considered safe above 55a and that's for a bare copper wire in the open air of which most wire has insulation on it (blanket) and the xw enclosure does not qualify for open air, or free air as stated on the chart below. it is generally unsafe to go with short lengths of small sized wire for high currents just based on voltage drop and is why the nec and the industry set some standards. going with the enclosed amps is a way to judge the wire in addition to voltage drop scenarios and going with large wires is always better to do anyway, especially in solar as that pv wattage is expensive.
    http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    i might add that if it was not tightened properly this would've compounded the heat build-up problem. it is also quite possible to have a connection loosen just because the wire itself was not dissipating the built-up heat and cycling hot/cold allowing this to happen and thusly make matters worse.
    all in all it is still 100% the fault of the installer unless he can prove xantrex to be at fault with bad connectors. good luck on that one.
  • ElkeElke Solar Expert Posts: 28
    Re: XW-MPPT60-150 Running Hot

    Hello all,

    I can only say that it was too late to check, if the terminal was tightened properly. By the time we read the cautionary note, the melting terminal had already embedded the screw, and we did not want to touch anything until the installer had looked at it. Now we are still waiting for him to stop by, but I guess he is waiting for the Xantrex expert. For our part, we are not going to pay until this is fixed properly.

    The installer is a licensed general contractor, and he has at least one licensed electrician in his crew. The wiring in and around the Xantrex equipment, however, was not done by the electrician. I believe the guy was a carpenter. The building inspector did not comment on the wiring either, despite taking off all the covers to check out the inside. And he came back for three visits all together.

    I did not see a torque wrench in use. I even commented to my husband that I wished I knew how tight my screws are without a torque wrench.

    Elke
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    elke,
    do not fret that you feel you could've done something. those guys are supposed to be professionals and got paid to do a professional job. the inspector may have overlooked that wire in passing the system, but the installer is still in violation. you can ask any electrician without any interest in this case the question of using a short piece of #10 copper wire to handle up to 60a and see what they say. also, if xantrex stated #6 wire or better then how can the installer even conceive of xantrex being at fault? watch that the installer doesn't turn this around and say you put that wire in there. did you take pics of it when it was done for that might show plenty?
  • ElkeElke Solar Expert Posts: 28
    Re: XW-MPPT60-150 Running Hot

    Niel,

    Thank you. Unfortunately, I do not have pics of the wires from the day of installation. But the installer basically used #10 wires everywhere but on the batteries! This was the only gauge wire he had! I had to go and buy #6 wire for the 50 feet between the panels and the charge controller, or they would be #10 too. Other thicker wires were supplied with the inverter by Xantrex. So I hope he and the crew will eventually agree that they installed the #10 wire.

    We still have not heard back from the installer, his electrician, or the Xantrex specialist. We will give him a few more days, but if we don't hear anything, we may look into not paying the remaining amount, and fixing the mess ourselves instead.

    Elke
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: XW-MPPT60-150 Running Hot

    please take plenty of pictures and get witnesses as to the condition of things if you can. anything that will back your claim against them and even the inspector if he should happen to remember if there was #10 there. (don't hold your breath as he would admit doing wrongly then:roll:)
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