Only getting 1/2 PV output to batteries.

CJW8CJW8 Registered Users Posts: 23
New Solar Install Test
Equipment:
• 3 group 27 batteries from Costco, 2 years old
• 2 Kyocera 135 watt panels 270 total, installed flat
• Xantrex C35 charge controller, Controller settings- 14.8 boost, 13.4 float

• 35 feet #4 welding lead from panel to controller
• Trimetric 2020
Test :
• Turn off converter/charger.
• Take batteries down to near 50% using 5-7 amp load.
• Wait for sunrise
Start conditions: 12.3v, -71.9AH, empty/full meter 20%.
Time, Voltage, Current , AH from full, %
6:00 12.33 0 -72 20
6:05 12.4 0.01 -72 20
6:30 12.6 0.9 -71.8 20
7:00 12.7 2.3 -70.7 21
7:30 12.6 0.1 cloud -70.4 21
8:00 12.9 5.0 -69.1 23
8:30 13 6.3 -66.4 27
9:00 13 7.1 -63.7 29
9:30 13.1 8 -59.5 34
10:00 13.2 9 -55.5 39
10:30 13.2 9.2 -52 43
11:00 13.3 9.6 -48.9 46
11:30 13.4 10.1 -43 52
12:00 13.5 10.3 -39 57
12:30 13.6 10.1 -33.8 62
13:00 13.7 9.8 -27.4 70
13:30 13.9 9.6 -23 74
14:00 14 9.1 -19.9 78
14:30 14.2 8.5 -7.33 84
15:00 14.5 8.3 -6.23 89
15:30 14.6 7.8 -5.13 94
16:00 14.8 6.4 -4.03 96
16:30 14.9 5.03 -2.9 97
17:00 14.9 3.7 -1.96 98
17:30 14.4 2.1 -0.49 100
18:00 13.8 0.9 +0.24 100
Maximum wattage was at 12:00 noon at 139 watts. The system did restore 72 amp hours in one days sun but I wonder why my maximum wattage was only 136 watts. Something does not seem right. With 2 135 watt panels, shouln't my wattage have been higher at noon? I realize I'll never see 270 watts but I should see more than half.
«1

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,741 admin
    Re: Only getting 1/2 PV output to batteries.

    I just ran the PV Watts program for Prescott AZ with 270 watts of panels set flat with 0.77 derating and found for this time of year, you should be peaking around 180-200 watts (one hour average) on average days around May 25th.

    Did you try disconnecting one panel then the other and see if they gave the same current readings?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    No, but I did check the open circuit voltage on both panels on another test today. It was 19+ volts at 5PM and short circuit amps at 5.5 amps on each panel. I reconnected and pulled the fuse on the pos wire between the array and the controller and measured 10.5 amps going to the controller. At that time there was only 5.5 amps going to the batteries according to the trimetric. All downstream loads were disconnected.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    This is the disadvantage of a battery base system, Plus you are using a PWM type controller.

    What type of loads do you have at solar noon??
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    There was no load. The load disconnect switch was open.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    although i don't use the pv watts program i don't think pv watts will account for additional losses seen by some systems for he lost 44 and 1/4w alone from the pwm controller just from the voltage differential between the 17.7v vmp and the highest attained charge voltage of 14.8v with the current of 2 of those pvs at 15.26a. losses are higher when battery voltages are even lower.
    add to it the flat collection, charge losses, resistive losses, etc. and efficiency drops very quickly as it evidenced by the results the op got.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    Since your short circuit test show ~10 amps ( each doing about ~5 amps ) , the difference is your panels are not perpendicular to the sun when doing the test.

    Being flat on a roof is almost a guarantee to not be optimal, and you probably off by 10-20 degrees from perpendicular. Also, haze, clouds or even time of year will be less than the 1000wmsq on the irradiance, typically, this time of year in clear conditions is about 930-940wmsq ( your 7 amp rating is achieved when the the panels see 1000wmsq )

    Short answer, nothing wrong with the panels
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    The short circuit test was done at 5pm because my fluke 87 will only measure 10 amps and I wanted a direct in series measurement so I had to wait until the sun was low enough to measure directly.

    Agreed that flat is not optimal but is typical for RV installations.

    I too believe the panels are fine and wiring is sufficient. I know I will never see 270 watts and expected not to. I did expect to see 180-200. On the two test that I ran I bearly got over 1/2 of rated output at high noon in mile high Prescott AZ with clear skies

    I believe the Xantrex C35 is not functioning properly. Should I contact Xantrex or AZ Wind and Sun, my vendor?
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    The C35 had nothing to do with this, as its basically a switch, if the voltage is below absorb voltage, the solar panel is directly connected to the battery for all practical explanations.

    As for you expectations, your going to be giving up at least 30% by the fact your running the solar panels @ battery voltage , figure another 10% for the angle issue, sounds about right to me what your seeing.

    On final note, I assume your using C35's display, not your DVM on the reported amps, The C35 display can easily be off an amp or two. I would put your DVM in series with one of the panels, let it run for a day and compare the difference between the DVM and the C35 Meter, your only measuring the current in one panel, so just double it for the compare
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.
    The C35 had nothing to do with this, as its basically a switch, if the voltage is below absorb voltage, the solar panel is directly connected to the battery for all practical explanations.

    As for you expectations, your going to be giving up at least 30% by the fact your running the solar panels @ battery voltage , figure another 10% for the angle issue, sounds about right to me what your seeing.

    On final note, I assume your using C35's display, not your DVM on the reported amps, The C35 display can easily be off an amp or two. I would put your DVM in series with one of the panels, let it run for a day and compare the difference between the DVM and the C35 Meter, your only measuring the current in one panel, so just double it for the compare

    I thought about voltage being an issue. On the first test I ran the batteries down during the night and they started chagring as soon as the sun reached the panels. So the batteries were already up some by high noon.

    So on the second test I kept the panels disconnected until until 11:00AM and then connected them hoping to see more watts. The batteries were at 12.3V. The charge rate after 15 minutes was 11.2 amps and 13.2V (147.84 Watts). Better but not what I had hoped to see.

    All readings are with the Trimetric 2020. I do not have the remote display for the C35. What would it tell me that the trimetric doesn't?
  • BB.BB. Super Moderators, Administrators Posts: 29,741 admin
    Re: Only getting 1/2 PV output to batteries.

    The Trimetric is fine... And it measures current into the battery--as long as you have no other loads, then it will show 100% of the output current of the charge controller (the charge controller display can only show its own output, not where the power is going--and it is not all that accurate).

    Your method of discharging the batteries and applying charging current seems fine... the Charge Controller will not start reducing current (if it is programmed/working correctly) until the set point voltages are reached.

    You can take your DVM, set to 10 amps full scale, and measure the short current out of each of the solar panels. If both panels read the same current (when measured at roughly the same time under the same light), then your panels should be OK (Imp/Isc is measured under "optimum conditions" of 1,000 watts per sq.meter--usually, most of the time we do not get optimum light conditions)... Basically, the short circuit output current of a solar panel is directly proportional to the amount of sunlight hitting it (taking account of sun position, panel orientation, amount of light lost to atmospheric dust, humidity, clouds, etc.).

    Complete Specifications for Kyocera KD185GX-LPU PV Panel

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    The important thing here is to look at total power over the day. To have the batteries at 100% at the end of the day is more important that peak power. Unless you need to run a particular device.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    My system was just adaquate with the summer sun. With the fall sun it is very inadaquate. Either there is something wrong with the C35 or 1/2 PV output to the batteries is all it will do. Today, a full sun day, it only replaced 34 amps out of 53 amps used during the night. I am giving up on it.

    After some research, I have just ordered a Rogue MPT 3024.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    My bad? Maybe the Xantrex C35 was not doing as bad as I thought it was. Today I removed it and installed the Rogue 3024. The Rogue has a very informative display. It said I was charging at 12A but my Trimetric only said 8A. So my Trimetric is only measureing 2/3 of the current going to the batteries. I confirmed this with a clamp on amp meter. I believe I have a wiring error but I can't find it. I'll try and up load a schematic. I am hoping someone can see my error. I am thinking it is because the charge controller + is going to the middle battery instead of the end battery? I did this for convenience because the #3 battery is in the next compartment.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    Lets see, the the white wire for the TV jack should be on the other side of the shunt. You should not use frame ground between the shunt and the chargers. Frames rust and can cause high impedance circuits.

    Everything else looks right.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    Ken, Yes, I noticed this when I was tracing it out. TV (tow vehicle) is a very small part of the charging so I left it as but I will chnge it.

    Are you saying that a weak frame ground is the possible cause in the difference in the Trimetric and the Rogue readings?

    The frame ground is factory original and orginally there was a only low end charger/converter utilizing this frame ground. (I added all the other components) The frame ground is welded at the charger/converter but is screwed at the shunt. When I installed the shunt I used a bigger screw and sanded off and paint reound the hole.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    I think that the way your battery bank is configured/wired is a problem. It may, or may not, be the cause of your failures. It is certainly not optimal.

    I agree with n3qik (Ken) that the shunt is not wired correctly and, most importantly, the "frame ground" must not be used to carry heavy current, unlike a automobile. All negative connections should be made with adequately sized cables and connected to the frame at one point only. This is done to bring the frame to zero potential.

    I may add more later.

    see here http://www.smartgauge.co.uk/batt_con.html

    K
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Only getting 1/2 PV output to batteries.
    CJW8 wrote: »
    ... When I installed the shunt I used a bigger screw and sanded off and paint reound the hole.

    I would not modify a shunt.

    K
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    Looks "almost" like a proper caddy corner between battery 2+ and battery 3- (from the top).

    But how does charge current flow *through* battery 1? I mean, I can see how it would bleed over from 2 to 1, but it's not flowing through during solar charge.

    The way it seems to me is that solar charge current follows a path from batt2+ through batt2, to batt2- and then through the jumper down to batt3- and then right out to the shunt. Wouldn't that be the path of least resistance?

    So batt2 is getting a proper charge through it from the solar charge controller and the Truecharge...but 1 and 3 are only getting whatever bleeds over from 2.

    Where is the Trimetric B1+ connected?


    Um...how about this? (Experts check me out on this whacky theory of mine please); Have all + connections on batt1+ and all - connections on the shunt. Then, remove the batt1+ to batt2+ jumper, and the batt2- to batt3- jumper.

    It seems to me that that will force the current to flow...

    in batt1+
    through batt1 to batt1-
    then jump to batt2-
    through batt2 to batt2+
    then jump to batt3+
    through batt3 to batt3-
    to shunt

    I.e., *through* all three batteries equally. It's like a back-asswards series, but since it's not + to - it should still be a 12v rig right? Or am I seeing it cross-eyed?


    Right now, it looks to me like you've got too many potential paths of least resistance.

    For instance, the inverter current path looks like batt1+ to batt1-, jump to batt2-, jump to batt3-, jump to shunt. So really batt1 is doing all the work to feed the inverter.

    You need both the feed and the load to go through all 3 batteries equally instead of taking the easiest route.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.
    Kamala wrote: »
    I would not modify a shunt.

    K

    Sorry, I didn't modify the shunt, I just improved the connection of the negative cable there it attached to the frame of the RV.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    I agree that the batteries are not wired optimally. This is the result of adding a 3rd battery in the adjacent compartment when the inverter was added. I will correct it in the future. But is that the cause of my problem? Which is: the Trimetric is not measuring the same as the Rogue output. I.e. The Rogue says it is doing 12 amps and the Trimetric only says 8. At the same time the clamp on amprobe confirms approximately 4 amps going to each battery.
    It looks like to me that I have a positive buss and a negative buss and all current, loads and charging, must flow through the shunt. (after I correct the Tow Vehicle charge line)
    The frame ground may not be the best but all RV’s I have seen are wired this way. I am not saying that they are all wired this way, just the ones I have seen. I always assumed a frame ground would offer less resistance than a piece of wire. 6” channel iron verses #4 copper wire?
    I could try charging with either of the two chargers, which do not have their own meters so I’ll have to use the clamp on amprobe, and compare the charger output to the trimetric reading.
    In any event, after only one day of use, I am very pleased with the Rogue 3024. I will write a full review on the Rogue thread when I get this issue corrected.
    Thanks for the assistance.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    A simple test with a dvm. When you have a good bulk charge current going into your batteries on a sunny day, check the voltage on your #4 cables as close as you can to the panels and then run to the batteries and take a reading right on the batteries. If you see less at the batteries, there could be some contact resistance in your system which usually happens where things are connected like splices and circuit breakers or fuse boxes. I have been redoing both the solar and wind parts of my system and installed a big cartridge fuse box with a pull out disconnect between the charge controllers and the batteries and afterwards I found that the controllers were tripping way to low. The culprit was the fuse box which had .6 volts across it it at 25 amps which was wasting 15 watts at full charge and raising the voltage seen at the controllers by .6 volts which meant they were tripping too low. I had to sand and clean with contact cleaner the contacts on the fuses, fuse holder and pull out disconnect to solve the problem.

    If you find a difference in voltage, a good tool to look for the problem is an infrared laser thermometer. Wherever current is flowing across resistance power is going to be dissapated in the form of heat so you can quickly find the hot spots with a good remote thermometer and that is where the contact resistance is going to be.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    Here is a revised schematic showing amp reading at various points. The revision shows that the shunt is actually connected to the #2 battery, not the #1 battery. What stands out is I have 12.4 amps going to the shunt and 8 amps going through it with 4.4 amps on the frame ground?
  • sloarlitesloarlite Registered Users Posts: 14 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    CJ, you have something that is drawing that 4.5amps to the frame and then to some device that is on.

    Disconnect one thing at a time and you will find it.

    Is you fridge on? Perhaps the de- moisture switch is on on your fridge.

    Bigfootford,

    Jim
  • sloarlitesloarlite Registered Users Posts: 14 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    CJ, as for a miss read on your Trimetric...Use your meter and measure the "SMALL" mv drop across your shunt. Measure right on the sense wire screws. If your shunt is 100a=100mv...then 10amps will read 10mv. Compare that reading to your trimetric and your Rogue...

    Jim
  • phred01phred01 Solar Expert Posts: 35
    Re: Only getting 1/2 PV output to batteries.
    CJW8 wrote: »
    Here is a revised schematic showing amp reading at various points. The revision shows that the shunt is actually connected to the #2 battery, not the #1 battery. What stands out is I have 12.4 amps going to the shunt and 8 amps going through it with 4.4 amps on the frame ground?

    Your right the 4.4A signals there's a problem. U need to measure the current flow on the following items
    1 Xantrax 1000w inverter
    2 Xantrax true charger 40
    3 Xantrax XADC40 spare
    One of these devices must be still drawing current
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: Only getting 1/2 PV output to batteries.

    I'm not familiar with RV wiring so there might be something I don't know but looking at the schematic, right off the bat, I would suggest that both positive and negative leads of both charge controler and inverter be cabled directly to the batteries and not at the middle battery. Put the positve lead of the controller on the positve of the first battery and the negative lead of the controller on the negative of the last battery and do the same with the inverter but on opposite ends of the battery bank. Then tie the battery negative directly to the frame ground with a short lead of #6 awg. Last, move the shunt to the positve #4 lead and put a fuse or circuit breaker in series with it.

    Putting small DC loads through the frame ground is probably OK but I wouldn't have any charge currents or inverter DC current passing through it.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    We all agree that the wiring is not ideal, but working within the confines of an RV. Reworking the wires may not be the best move right now, plus the charging current is only 13 amps. If the loads are not huge, then the batts will be fine.

    Lets find where that 4 amps to frame ground in going. As stated by phred01, disconnect some stuff.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.

    I've been out there all afternoon and evening. The de- moisture switch was on. Apparantly, that feature still works even if the refer is turned off. The refer door was warm.
    I found I have a short in the lighting curcuit going to my slide outs. I found this by pulling all the DC fuses and putting my Fluke meter in series with each circuit and turning stuff on. I was unable to locate the exact location of the short so I left that fuse out.
    My shunt is 500A/50 mV. I didn't get a chance to read the mV while it was still charging.
  • CJW8CJW8 Registered Users Posts: 23
    Re: Only getting 1/2 PV output to batteries.
    phred01 wrote: »
    Your right the 4.4A signals there's a problem. U need to measure the current flow on the following items
    1 Xantrax 1000w inverter
    2 Xantrax true charger 40
    3 Xantrax XADC40 spare
    One of these devices must be still drawing current

    All 3 of these devices are off and have no current flow.
    I think it is parasitic load to propane monitor, radios, CO monitor, and the big one was the refer anti frost. I will disconnect that frame ground tomorrow and see if the Trimetric and Rogue agree.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Only getting 1/2 PV output to batteries.

    I must admit to seeing a difference between the amps in to/out of my battery bank reported by my TriMetric and the MSView software reported on my PC from the Moringstar MPPT15. The TriMetric reports about 2 amps above the MSView (or is it the other way 'round?:cry:). I am puzzled but not overly concerned.

    I have similar "parasitic" loads. But combined they are less than 0.3A.

    But I don't think that is why I see the discrepancy. Rather, I submit, it is because the current measuring device/algorithm of the charge controller cannot account for the loads beyond it. In other words, the charge controller can only know the current it is delivering to the battery. It cannot know what is being drawn from the battery. Only the Trimetic shunt can know that.

    Or, so I think. I've been set on more better tracks by people here...

    K :confused:
Sign In or Register to comment.