I think we're on the same page, which is the battery voltage doesn't vary much in comparison to a PV, thus the MPPT operates in a narrow voltage range, and thus narrow current range. My guess how the MPPT circuitry works is to vary the input voltage, since the PVs are a current source, to hunt for that max power (VxI) point. The problem would arise when the battery voltage drops at low charge state, then the current would rise dramatically. At which point the circuit breaker should trip. But hopefully Yabert would do an experiment, of lowering the PVDC input voltage, to let us know whether his PowerMr inverter would max out at the 3kw PV-DC input current. He would want to know in case his Bolt's pack voltage drop, though the Bolt's BMS would probably shut-down before then.
Exceeding voltage or amps on SCC
- Thread starter moonlitsouls
- Start date
I think this is correct. Over panelling will just result in "inverter clipping". My M215 Enphase micros clip daily, as each is connected to a 250w panel
zanydroid
Solar Wizard
What happens if shading / bypass diode activation halves Vmp? Then Imp will double, for the same output current. If the SCC does not prevent limit its current in that state there could be a problem.
Why would Imp double?
there is less wattage being produced.
The other panels can only provide their rated Voltage and Amperage (=Wattage), so the overall capability of the array will drop.
The MPPT will be in the same situation as it would be in a 7 panel array if panel #8 is shaded (assuming an 8 panel array). Maybe there's enough wattage to provide full charging current, but likely not depending on how overpanelled the array is...
Current is pulled, Voltage is pushed.
zanydroid
Solar Wizard
This thread is mostly about discussing obscene overpaneling situation. Imagine 5x overpaneling.
If the SCC seeks to keep charging output constant then it would double the V_imp. Because the battery can pull “infinite” (limited by SCC config/design). So then the charger will pull from the array. Hopefully it limits itself and doesn’t explode when the array has an obscenely high Isc
Is it sufficient then, to prevent over current with an inline DC circuit breaker to trip near inverter max current ? say in Yabert's case: his inverter is 3000w, his obscene overpanelling (ala battery) is 360vdc, so would 10A breaker enough for run-away scenario ?
zanydroid
Solar Wizard
Battery is more well behaved because the voltage will be 360vdc except when discharged to the point where it really should not be used anymore. I think some kind of PLC that monitors voltage then cuts off the inverter has a chance of doing the right thing here, since the V-I behavior when using a battery is quite predictable and the battery will mightily fight any effort of MPPT to deviate from 360v. A DC rated OCPD seems fine.
For solar panels I think the OCPD could trip during normal operation if the Vmpp drops to a sufficient point. It depends on how the MPPT is designed. The instantaneous behavior of MPPT is much less predictable.
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yabert
Solar Enthusiast
One of the biggest advantage for me to have a 60 kWh battery on wheel on the driveway is I can have a small/low cost battery inside the house connect to the solar system.
I think an high voltage DC battery and inverter could work, but are you award of any small/affordable HV battery and inverter available?
If the cost of those HV stuff is really high, it could be tempting to simply use regularly available/affordable 48V equipment's and have a large battery inside the house and kill the idea to connect the EV to the house... That an important waste of resource's, but still financially logic.
wattmatters
Solar Wizard
I think with EV I would be waiting for affordable 2-way EV chargers which enable V2H/G capability. At present they are expensive and only viable with limited EV models.
I'm not that up on what inverters might be suitable but there are grid tied systems, e.g. Fronius and others which use a higher voltage DC battery. There's even a thread on here with someone who just connected a Leaf pack to one.
diysolarforum.com
I can't imagine any such system would be small, but depends on what you mean by small. Fronius Gen24 inverters are in the 5-10 kW range. Anything used by a BYD HV battery for instance.
Affordable is also a subjective measure so i can't answer that.
I'm not that up on what inverters might be suitable but there are grid tied systems, e.g. Fronius and others which use a higher voltage DC battery. There's even a thread on here with someone who just connected a Leaf pack to one.
Dyi battery to fronius hybrid inverter
So to start with the Fronius inverter reverse engineering, is there some user on this forum that has batteries hooked up to a Fronius inverter? It would make it so much easier if we could get a log file from a working system! Not many yet I don't think. I know my local installer has installed...
diysolarforum.com
I can't imagine any such system would be small, but depends on what you mean by small. Fronius Gen24 inverters are in the 5-10 kW range. Anything used by a BYD HV battery for instance.
Affordable is also a subjective measure so i can't answer that.
Again, I = PV...
There will be a maximum amount of power drawn by the load.
Be it a battery charger, inverter, or hairdryer.
The load is your constraint.
a 3000w inverter will only pull 3000w (plus overhead), likewise a 50a battery charger is only going to pull enough to provide 50a at battery voltage.
ergo; 3000w at 360v is 8.4a. 3000w at 240v is 12.5...
Even if you have unlimited amperage available (you don't, each shaded panel drops available amperage), eventually you will lose enough voltage that the load will stop operating. (you can't start my car with a 2v battery, even a 2190Ah Surrette wired directly to the starter motor)
zanydroid
Solar Wizard
Shading to the point of bypass or forcing operation at a lower voltage will not drop current.
With overpaneling there is plenty of available current.
With the lower voltage battery case there is very high available current.
If the inverter does not do input limiting eventually it will destructively exceed the current limit of some component.
With overpaneling there is plenty of available current.
With the lower voltage battery case there is very high available current.
If the inverter does not do input limiting eventually it will destructively exceed the current limit of some component.
2Kayaker!
New Member
There is an expanding range of used EV traction batteries, different inverter models, differently programmed’ lilygo circuit boards being tested by the developers on ‘open source’. The lily go (so?) is flashed with code to emulate what’s normally accomplished in an EV to acces the traction battery and utilize the original Bms. The first set up I saw working by the original developer - programmer- EV technician, is on YouTube, see’ Dala’s EV repair.’ The open source project is on ‘GitHub’. EV batteries pulled from cars because of degradation to 80 or 60% capacity are fine for home storage.
Lot’s of caution required here though. ( Did you buy a crashed or abused battery pack? Exposure to high voltage d/c etc). He used a 40kwh Nissan Leaf battery and a Fronios inverter in this first version.
Lot’s of caution required here though. ( Did you buy a crashed or abused battery pack? Exposure to high voltage d/c etc). He used a 40kwh Nissan Leaf battery and a Fronios inverter in this first version.
carlosspicyweiner
New Member
Any idea where I could get a thorough explanation of how the CC (physically) manages the input current? looking at my victron 100/50, spec sheet says do not exceed 60 amps input - aside from pulling it apart, I would like to know the physical mechanism that clips/diverts/ignores/wastes the excess incoming current.
Running 2400w into it at the moment (70v x 36 amps), works great on cloudy days, charge controller noticably hotter to the touch but with active cooling keeps it comfortably warm. Is it simply an internal heatsink type deely that diverts and bleeds off all that excess incoming PV current?
Have noticed even with a ridiculous amount of wattage available, the app shows only the combination it wants ie - 60v x 12amps (700w) to run at its maximum 50 amps charge. So, I'm assuming whatever bit of metal is in there has been tested to stand up to 60amps trying to bash its way in.
Cheers
zanydroid
Solar Wizard
It just goes open circuit or (more likely, if some charge current is still needed) drives the voltage / current to a portion of the solar module (silicon magic) characteristic curve where the power generated takes a nosedive in efficiency. And the efficiency losses are typically pushed into the solar cells so there is no extra heating in the SCC. Usually an MPPT seeks to latch onto the maximum power point but if the battery doesn't need it it can operate at a different point.
WindWizard
Solar Enthusiast
My thought on the matter is that the MPPT controllers are just that. A Maximum Power Point Tracker. A typical Solar Panel does not produce any usable wattage when the panel is disconnected.
This means that when you do not have a load on the Solar panel then there is no power being generated. When you put a load on the panel. the voltage on the panel is reduced and then it starts to produce power. The MPPT Controller looks for the ideal voltage to produce the most power.
If you are producing more power than the MPPT controller is capable of then it just uses a different voltage that produces less power and the panels become less efficient.
It is just the way the Solar Panels are built. In order to produce the maximum amount of power then then need to operated at the ideal voltage which produces the most current. Ohms law states that Voltage time Current is equal to wattage.
For a wind turbine, all of the power the turbine generates must be used so they have a load resistor that engages to use the power. On the grid all of the power must be used. If the power on the grid or the wind turbine is not used then bad things happen.
Solar panels are totally different. You can put a solar panel out in the sun and not connect the leads and nothing bad will happen. Basically, a MPPT controller just raises the voltage of the panels up to the point where they produce less current. If you have a Victron MPPT 250/100 amp like I do, then it will only produce 100 amps of current and will let the rest be wasted.
zanydroid
Solar Wizard
Exactly. Noobs sometimes say solar and storage is complicated… but it doesn’t have the pesky properties of turbines or other spinning generators. Solar is easy to disconnect and battery are like the perfect dispatchable power source.
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