Solar charge controller question

[GGameBoy]

A thought that just crossed my head as I was planning on building a solar generator. Not sure how to ask it in a single question so I can’t search it in the forms. Sorry.


Will said and many others that u have to hook up the battery first then connect the solar charge controller 2nd so u don’t fry the controller.
But here’s my question, say I have it all working and one day I deplete the battery to the point the BMS disconnects all power to save the battery from over discharging. IF the solar is still connected in the morning wouldn’t that be plugging in the solar first and 2nd plugging in the battery? Wouldn’t that destroy the charge controller? Or is there some sort of memory the charge controller has for just that?

not sure if my battery makes a difference but I’m using the miady 20 ah battery. BMS is internal.

 

[MisterSandals]

That’s the conundrum. You have discovered the mystery early, +10 points to your score.

it turns out that wWill and many others have NOT destroyed controllers this way.
BUT, it make a LOT of sense to always connect battery first (controller detects bat voltage and assumes charge voltage) and disconnect battery last. Just good practice and great reason for breaker or fuse and switch to your array.

 

[GXMnow]

I have not tried it yet myself, but one thought I had to greatly reduce the chance of a big problem would be to connect a large capacitor at the battery terminals of the charge controller. For a 12 volt system, I was thinking maybe one of those 1 Farad things they use for car stereos.

Here is the idea. As long as the battery is connected, everything is happy, but if the battery disconnects for any reason, what will fail? If the charge controller tries to put out current, the voltage will climb. With no load, it might climb too quickly and damage something. But with a big capacitor, it should slow the voltage climb, so the charge controller should have a chance to go into absorb mode, and then the current will fall quickly, and it should switch to idle or float with the capacitor acting as a low capacity battery. As the cap discharges, it should kick back into charge mode and repeat the cycle. The bigger the cap, the slower the cycle. But it should not hurt anything while you get the battery to reconnect.

 

[Forbisher]

Will said and many others that u have to hook up the battery first then connect the solar charge controller 2nd so u don’t fry the controller.
But here’s my question, say I have it all working and one day I deplete the battery to the point the BMS disconnects all power to save the battery from over discharging. IF the solar is still connected in the morning wouldn’t that be plugging in the solar first and 2nd plugging in the battery? Wouldn’t that destroy the charge controller? Or is there some sort of memory the charge controller has for just that?

not sure if my battery makes a difference but I’m using the miady 20 ah battery. BMS is internal.

Where did Will say you would fry the SCC?
In fact Will said that disconnecting the battery does not fry a SCC.

Trying to destory my SCC's: I can't do it!

So I took every EPEver/Victron/PWM/Renogy solar charge controller, and tried to fry it by connecting it only to solar panels, and not to a battery... guess which one survived? EVERY SINGLE ONE! I couldn't destroy any of them, and I left them connected to a high voltage array (80 volts) for 4+...

diysolarforum.com

 

[GXMnow]

Most of the manufacturers say to never do it as it could cause a problem, and they don't want a ton of warranty returns. In most cases, it should just go to the CV mode and power the battery input from the solar power, but the processor electronics are powered from the battery side, so it can go stupid if the voltage swings to much, too fast, and that can cause things to fail. They try to make them fail safe, but crap can still happen.

If the system is set up correctly, the BMS should never have to disconnect the battery. If that happens, something is wrong and you will likely need to manually intervene to make it work correctly again. Charger should stop before the BMS sees over voltage, and loads should shut down before the BMS sees under voltage.

The one worst case we need to watch for that settings can't fix would be if an LFP BMS open the charge current side due to cold temps that also increase the solar panel output voltage. This is a case where I think the capacitor could save it from cooking something. This could cause it to go from absolute maximum charge current flowing, to an open load. Even a fast charge controller might have an issue keeping the voltage from spiking too high.

 

[GGameBoy]

Where did Will say you would fry the SCC?
In fact Will said that disconnecting the battery does not fry a SCC.

Trying to destory my SCC's: I can't do it!

So I took every EPEver/Victron/PWM/Renogy solar charge controller, and tried to fry it by connecting it only to solar panels, and not to a battery... guess which one survived? EVERY SINGLE ONE! I couldn't destroy any of them, and I left them connected to a high voltage array (80 volts) for 4+...

diysolarforum.com

I have heard it from him maybe an older youtube video as well as others on youtube however i can not find an example atm. But thanks for sending the form link. apparently its not as big of an issue as I thought since will could not destroy the SCC.

 

[GGameBoy]

If the system is set up correctly, the BMS should never have to disconnect the battery. If that happens, something is wrong and you will likely need to manually intervene to make it work correctly again. Charger should stop before the BMS sees over voltage, and loads should shut down before the BMS sees under voltage.

How would I set up a system that disconnects the load automatically without using the BMS for that?

The most power hungry device is the inverter in most cases and unless the inverter itself has a low voltage disconnect that is higher then the BMS I dont see how it would be done.

But also, the voltage drops quite fast once you get to the extreme low voltages. so even a DC load could drop the voltage to the point the BMS has to disconnect all loads to save the battery. I dont understand.

 

[Bud Martin]

If you get the SCC that has Aux DC output (with programable Low Voltage cutoff point) that you can use to drive the SSR (Solid State Relay) which will then interface with inverter that has remote ON/OFF port to the inverter will turn off at higher shutdown point than the BMS low Voltage shutdown point.
I myself use this adjustable Low Voltage shutdown Recovery point module to interface with my modified inverter since my inverter does not have remote ON/OFF port.
Victron makes Low Battery Voltage protection module that cut off the DC to the load, but it is not made to handle the Inverter due to high inrush current but you can use it with inverter that has Remote ON/OFF port to shutdown the inverter.

 

[Substrate]

You may be struggling with remnants from the dinosaur age when solar controllers needed battery voltage first to get their internal logic together before applying a panel. Or secondly, some controllers used this as a form of user-protection to prevent the SCC from trying to charge what it sees with a disconnect as a "zero volt" damaged battery.

Times have changed. In fact, coming from that dinosaur era myself, I was totally surprised when I read my Genasun GV-10 manual, and they actually recommend attaching the panel first!

From the Genasun GV-10 LFP manual: "Connect the solar panel to the +PANEL and -PANEL terminals. While connecting the battery first will not damage the GV-10, we recommend connecting the panel first. This eliminates the risk of short-circuiting the panel, while the GV-10 is operating, which can cause damage."

I just pulled the battery from my Genasun right now charging my battery to make sure I wasn't lying. It took about 30 seconds to figure out that my LFP battery was reattached when I put it back, and it went on it's merry way.