I have a question regarding your solar panel configuration.
According to your specifications, you are using four 200 W solar panels, and each panel has an open-circuit voltage (Voc) of 24.3 V. If all four panels are connected in series, the maximum open-circuit voltage should be:
24.3 V × 4 = 97.2 V
Could you please clarify how you are obtaining 122 V at the output of the solar panel array? I would appreciate it if you could explain the configuration or provide any additional information that accounts for this higher voltage.
Maximum Power | 200W | | Module Efficiency | 25% (N-Type 16BB cells) | | Open-Circuit Voltage (Voc) | 37.44V | | Optimum Operating Voltage | 31.03V | | Optimum Operating Current | 6.45A | | Short-Circuit Current (Isc) | 6.85A | | Max Series Fuse Rating | 15A | | Max System Voltage | 600V DC | | Output Voltage | 24V DC |
I might have missed it in the comments, but did you try bypassing the breaker on the battery side of the MPPT? Those breakers are notoriously poor in quality.
I’m asking about the breaker on the battery side of the charge controller which I believe his drawing indicates is a 70 amp. He says he bench tested the 250/60 and it worked as it should, which again indicates a problem with the installation.
Yeha those breaker types… Interesting idea you have there.
He said he has battery voltage at the terminals but that doesn’t always mean it can move amps.
The part that has been of great focus has been the disappearing panel voltage.
I haven’t seen any suggestion so far that the panel array has been commissioned or recommissioned; Checking Voc is not the same. Kudos to those suggesting focusing on getting a clamp or similar to check current.
I would strongly suspect that there is a fault in the array, and that measuring the array Voc is misleading you. An array can easily have an active fault (poor connection, faulty breaker, faulty panel) and still produce an apparently correct Voc. This Voc will collapse to either zero or battery voltage as soon as power is (tried to be) drawn. This seems to be exactly what OP is seeing.
My advice would be for the OP to follow this method, recommission the array. My bet is that either this finds the fault, or it rules out the array and you can move on with confidence to downstream parts of the system.
The breaker type is one thing, the breaker brand is another. T-Tocas is an Amazon-special Chinese knockoff of the Bussmann Series 285 breaker, and while the Bussmann 285 and 187 breakers are pretty solid (can’t be used on the PV side of course, but good on bat side), T-Tocas and other counterfeits like Red Wolf and so forth are definitely known to be trash - going on 5 years or more, you can find reports of those brands causing severe system issues on this forum, the old forum, and just about every other forum and FB group and etc that has anything to do with electrical systems.
I am fairly certain that the problem all along was the manner in which the battery cables were installed (the 250/60 MPPT tested and found to function perfectly). The first battery on the left at the cabin was connected to the system with a 4/0 cable while the other two batteries were connected with much smaller cables in parallel off the leftmost battery. The negative cable from the leftmost battery to the smartshunt with a 2/0 cable and the leftmost was also connected similar to the positive side. All of the charge went into the first battery and damaged it to the point that the MPPT is sensing something and not turning ON and charging.
I am switching out the batteries for one Deca 300Ah lithium battery with a built in BMS and redoing all of the cables with the same size 4/0 cables with the same lengths off the main bus and will use some means such as single or dual lug buses to make the 90 degree turns instead of cable bends. The surge capability of the Victron switch is well over 400A so I will keep it and will also keep the 400A fuses due to the battery chosen. The 4/0 cables will all be as straight as possible and the run to the two buses will be virtually identical if I have my way. Any ideas for facilitate running the cables without bending would be appreciated. I know it is a simple 12V system but it is all I have room for. Any comments on the following revised rough sketch of a re-cabling, upgrade of fuses to MidNite brand, and a new Deca 300Ah, 300A lithium-Ion battery with built in BMS rated for -5F.:
See below. The problem is not with the PV arrays. Both have been very dependable and the test one is still working. All the breakers were tested and bypassed with the same results. I will be taking the new battery and cables with me, voltage generator and I will hopefully determine what caused the MPPT’s not to turn on. I am fairly certain it is a damaged battery that caused the problem, but we will see. I am also going to upgrade all the breakers in the system. I was thinking of going with MidNite breakers.
I am switching to MidNite breakers. But, yes, I did bypass the Tocas breakers to make sure none of them were the problem.
Also, does anyone know whether the new SmartSolar MPPT’s (mine is a new 250/60-Tr) has a relay or something else to protect against PV voltage shorting to battery voltage?
I had a quick look at the schematic. The graphic is NOT very clear. BUT you should only have ONE panel pos connected to the MPPT(+).
If I have read your schematic correctly, then you currently have a string of THREE panels in parallel with ONE panel.
Panels 1 Positive goes to MPPT. Panel 1 Neg goes to Panel 2 Pos. Panel 2 Neg goes to panel 4 Pos. Panel 4 neg goes to MPPT.
Panel 3 Pos goes to MPPT. Panel 3 neg goes to MPPT.
In this configuration the three panels would be shorted by the single panel and all the current from the three panels, (Isc), will be flowing through panel 3. This MAY have caused it some harm, depending on it’s internal current rating.
4 x 37.44 is real close to the 150V limit of the MPPT. On a cold day, once the batteries are fully charged OR if the MPPT is forced off due to a generator charging the batteries via the Inverter, then this voltage limit could be exceeded.
I’m sure that they won’t be fried at 0.1V above the stated limit but you are probably too close to the voltage limit with the 150 MPPT, (good call to go up to the higher rated unit).
The above is how the cables are run. The Voc in incorrect on the drawing though (see the specs above). Only one positive and one negative MC4 cable is connected to the MPPT PV terminals. Only one cable per +/- emanates from the battery side of the MPPT to the buses. The handwritten sketch I shared above I drew two lines to simulate the 4/0 and 2/0 cables, mainly because I want in the re-cable to eliminate the bends and differences between the +/- sides when we re-cable everything properly. My electrical engineer son built the cables and installed them for several years for a photon therapy company. Unfortunately, he was not available before but has agreed to do this job. His cabling in his previous job had to be perfect in every sense or they could suffer millions of dollars in damage. He said their rules were: same brand, same cable characteristics, same length, same connections, no bends. I was attempting to come up with a design to discuss with him today actually. I am looking forward to his take on how he will want to do it. I have not purchased all the components and cable yet. Update: My son likes the new cable install design.
Well that cabling schematic looks better than the earlier version. The same current will be flowing in all cables, if the lengths aren’t too long, you could probably use 4mm2 solar cabling for all these runs. The current is around 10 Amps, voltage drop should not be a problem.
This might be a strange question but have you set the battery voltage of the MPPT unit? The manual tells you how to do this, and to reset it if you have a different voltage by default or from the supplier, etc.
And have you set the MPPT charge properties? ie set for your battery type, your charge profile and durations etc. I’m not sure that leaving this blank will cause problems, it will probably just adopt the settings from the hardware switch if not set in software.
With regard to cable bends, the current will not know if the cable is bent or straight, just as long as you don’t wind a large inductor or wrap the cable around a steel/ferrite rod etc. The current is generally DC, (with only a little switching hash from the MPPT unit superimposed), so the cable shape generally won’t matter. With regard to cable lengths, they are NOT required to be the same length, short is good, just make sure that you leave a suitable amount for terminations and in case you need to remake a termination at a later date, better to be looking at the cable than looking for the cable.
I did. And, reset everything again. I currently have set everything up using the MK3-USB but will have to change the battery settings from gel batteries to the new LIFePO4 battery. I think the biggest problem with the current installation was most of the charge was going into the first battery due to the cabling size mismatch 4/0 +, 2/0 - for leftmost battery, smaller gauge yet going in parallel to the other two batteries. All of the issues noted in the above posts will be addressed later this month when I and my son return to determine the root problem that caused the MPPT’s not to turn to Bulk before, redo the cabling, reinstall the new 250/60-Tr MPPT, and the new 300Ah Deca LiFePO4 heated battery (see below) which communicates via cable directly with my Cerbo GX (which eliminates the need for a new 500A SmartShunt. Any thoughts on this battery?
