So this may or may not be seen as a beginner question, but I have a feeling I'm trying to debunk a myth with MPPTs. My MPPT is a Li-time 30A controller, and it states that the MPPT must be connected to a battery before connecting it to solar. I have watched a couple videos now that also say that if one does not connect a battery before connecting solar, that it will damage the MPPT. Here's my issue. If my battery becomes fully charged, then it effectively disconnects from the MPPT, meaning that it is just solar connected to the MPPT. Ok, so maybe since the MPPT has control over that disconnecting action, its not a big deal. But what if the battery performs the disconnection? Say the battery has cold temperature protection, it gets too cold, and it shuts off at the BMS. Then you suddenly have the same situation where the MPPT is connected to solar but not to the battery. To clear up one more thing, the MPPT manual specifically says to cover the solar array in a blanket before connecting, which would remove the possibility of creating a small arc during the instant of connection. So, is there a technical engineering reason why a battery should be connected to an MPPT before connecting a solar panel, or is this just a myth probably devised for the protection of individuals working with actively-generating solar panels? Assume there is no other load connected to the MPPT or to the battery.
Does order actually matter?
- Thread starter tutle64
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Q-Dog
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If the battery becomes fully charged, the charge controller should reduce output. If the BMS disconnects, you need to make some adjustments to the settings.
LakeHouse
Solar Enthusiast
For Victron SCC's, connecting to the battery before the PV is most important for the first time the device is connected so that it can automatically detect the battery system voltage. Your Li-time SCC can operate on 12V or 24V systems, so it may have a similar limitation.
I don't recall ever hearing about people frying an SCC because of a battery disconnect, so I'm guessing it at least doesn't happen very often.
I don't recall ever hearing about people frying an SCC because of a battery disconnect, so I'm guessing it at least doesn't happen very often.
mikefitz
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Most bms shutdown the charge path only, ( unless its really cold -20C) so the controllers 'sees' volts and can accept power.
Many MPPT controllers are multi voltage, 12, 24, 48, so when connected to the battery , detect the battery volts and select the correct charge voltage.
Same as cold protection, only the charge path is shutdown, ( unless its a single contactor BMS)
What can cause issues is a voltage surge if the charge path is shutdown, sometimes effecting system parts.
It's best practice to select charge voltages and load management so the BMS never enters protection.
By "charge path", are you meaning the wire through which current flows from the MPPT to the battery? I am aware that MPPTs detect the battery voltage in order to output the correct charging voltage. This doesn't really answer my more fundamental question of why order might matter in making initial connections to an MPPT.
This doesn't answer my question. yes, the controller reduces output voltage to slow or ultimately prevent current flow to the battery in the event of overcharge protection. Why would I need to adjust the settings of the MPPT? If cold temp protection kicks in via the BMS you can't just adjust some settings to correct this without manually coding the MPPT. This makes no sense, please clarify if this is not what you meant.
rodrick
Free energy enthusiast
Basically to tell the mppt what voltage it’s working with
timselectric
If I can do it, you can do it.
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The BMS has the ability to control charging and discharging separately.
When the BMS determines the battery or cell is over voltage or over amperage, it disconnects charging only. With discharge still connected. The MPPT still sees battery voltage.
When the BMS determines the battery or cell is over voltage or over amperage, it disconnects charging only. With discharge still connected. The MPPT still sees battery voltage.
Okay so what I think you are saying is that the MPPT's output voltage could be mismatched with the battery voltage upon initial connection, so to protect it from adjusting to the wrong voltage it needs to be connected to the battery first. This would make sense to me and explains why the manufacturer would suggest first connecting the MPPT to the battery before anything else. It also debunks the myth which I have repeatedly heard that connecting solar directly to an MPPT will damage or kill the MPPT, regardless of whether a battery is connected. Rather, the actual issue is that when one connects the MPPT to solar first, the MPPT could be set to the wrong voltage, which would result in damage to either the MPPT or the battery if the battery is connected without changing the MPPT charge settings first.
this doesn't help at all
Yes I am aware a battery can charge and discharge separately. The question isn't whether the MPPT still sees the voltage. The question is, why would an MPPT need to be connected to the battery before being connected to solar if the MPPT is set to the correct battery voltage from its internal settings?
rodrick
Free energy enthusiast
That is the main reason you hook the battery up first on a new install so the mppt knows what voltage its working with I have not heard of anyone losing a mppt controller due to a battery disconnect due to a blown fuse or lv shutdown ect not saying it can’t happen but it sure isn’t a common problem
Ok, just your previous comment did not clarify well what you were trying to say. I've never heard of that happening either but there was a myth being spread that if the MPPT is only connected to solar without a battery, that it would be damaged or killed. This isn't true though as I've come to realize because the real problem is connecting the MPPT to a battery with the wrong voltage while current is being supplied via the solar array.
timselectric
If I can do it, you can do it.
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I'm not sure if you mean to come off as rude.
But that's how it looks.
I hope that you find the answer you want.
rodrick
Free energy enthusiast
In my mind it made sense but I do get a lot of strange looks?
Q-Dog
¯\_(ツ)_/¯
The BMS is a protection device, not a charge controller. In your first post you said, If my battery becomes fully charged, then it effectively disconnects from the MPPT. That is not how it works. If your BMS is shutting down the battery while charging, you need to revisit your MPPT charge settings and maybe the BMS parameters too, if they are adjustable. If cold temp protection is engaged, the BMS only shuts down the charging circuit, it should not be shutting down the entire battery.
Your question was based on a flawed understanding of how this works, so it didn't make sense trying to answer it. I think you should do some experiments.
Robert Mate
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My take: proper bms can stop current flow from scc but still provides reference voltage to scc.
_mikefitz ... (unless its a single contactor BMS)
My take: If bms uses single contactor (relay) and this relay is the only connection from battery to scc & relay is OFF then no current can flow into battery from scc & battery cannot supply reference volts to scc..
https://www.bloomy.com/support/blog/mosfets-vs-contactors-battery-safety
My take: If there is a switch between the battery and scc & this battery switch is OFF, then, like relay, no current can flow into battery from scc & battery cannot supply reference voltge to scc.
_mikefitz ... (unless its a single contactor BMS)
My take: If bms uses single contactor (relay) and this relay is the only connection from battery to scc & relay is OFF then no current can flow into battery from scc & battery cannot supply reference volts to scc..
https://www.bloomy.com/support/blog/mosfets-vs-contactors-battery-safety
My take: If there is a switch between the battery and scc & this battery switch is OFF, then, like relay, no current can flow into battery from scc & battery cannot supply reference voltge to scc.
A few years back Will tried to destroy a number of Solar Charge Controllers and tried to fry them by connecting it only to solar panels. None of the Solar Charge Controllers had damage. I have mistakenly switch on the solar panels to my MTTP Solar Charge Controllers before battery power and the controller still functioned fine. Still recommend connecting battery power first.
Also this is probably before AIO became popular so don't know about AIO's. Never tried it on one of them.
Check out his thread.
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+...
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