rwkoehler avatar image
rwkoehler asked

How to connect a Victron battery protect between power inverter and battery

I currently have a small, off grid solar system - 100amp deep cycle sealed lead acid battery, 100 watt foldable solar panel, 20A charge controller and a 12V/750watt power inverter.

The power inverter is currently connected directly to the battery but I am concerned about over discharge if there are multiple consecutive cloudy days.

I purchased a 100A Victron battery protect. I am confused as to how to connect it to the battery and power inverter in order for it to prevent the battery from being over discharged.

  1. Does the power inverter connect to the battery protect and then the battery connect to the battery?
  2. Which connection do I use on the battery connect - IN or OUT?
  3. Where does the battery connect negative/black wire connect?

Battery Protect
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2 Answers
Justin Cook avatar image
Justin Cook answered ·

Hi @rwkoehler, welcome to the Community!

You must not use a BatteryProtect to directly disconnect the DC power supply of your inverter - this will, sooner or later, destroy the BP's logic. This is an expressly forbidden connection.

You may use the BatteryProtect to trigger the inverter's remote on/off pinout if so equipped, or perhaps to trigger an external relay that will then interrupt the inverter's DC supply, if it is not equipped with a remote on/off pinout, but you must not connect the BatteryProtect between the inverter and the battery.

Please see the user manual for acceptable connection methods.

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rwkoehler avatar image rwkoehler commented ·

Justin Cook: Ok, you say what I should NOT do. But what I'm asking for is how TO connect the battery connect in order to provide the over discharge protection. If the manual was clear, I would not be asking this question. Perhaps the manual is more clear to someone more technically familiar with solar. I am not. I am just asking what to connect to what, and in what order. Logically, it seems that in order to be able to determine whether or not the battery is in danger of over discharge, it would seem that the battery connect would HAVE to be between the thing drawing power from the battery and the battery itself. That seems to not agree with what you are saying.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ rwkoehler commented ·

He also wrote how you can connect it.

The problem is the high inrush current of the inverter.

The manual is clear about not connecting an inverter directly to the BP (installation point 4).

Maybe if you say us what kind of inverter you have we can say you how to connect it.

If you don't know what to do you should hire someone who knows.

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michelg avatar image michelg Matthias Lange - DE ♦ commented ·

In my setup that you can see on the photo, the main inverter has a delay between the moment you switch it on, and when it starts providing power. And the backup inverter is a Phoenix 24/800.

The main reason I installed an oversized Battery Protect is to avoid overloading it, with theorical inrush currents.

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Justin Cook avatar image Justin Cook ♦♦ michelg commented ·

@MichelG, inrush current is too fast to measure with most multimeters, and can be over 5x the maximum running current of the device.

"Oversizing" your BatteryProtect is not the solution here - the only reliable solution is to connect the BatteryProtect in a permitted configuration.

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michelg avatar image michelg Justin Cook ♦♦ commented ·

Hi Justin, thanks for the information.

AFAIK, there is a startup circuit limiting the inrush current. That's the reason it takes several seconds before getting the inverter "ON", and then other several seconds before starting to invert.

I do use FLUKE instruments to check every point of my installation, and did not had any issues.

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aceclement avatar image aceclement commented ·

I wired my inverter remote on off switch to the the relay terminal exactly the way the manual says and set it to relay in the app. The inverter is connected to the battery terminals. When I switch off the battery protect from the app the inverter does not turn off. What am I missing? Does there need to be an actual separate relay switch attached to the alarm terminal? Does the terminal not act as a relay? I wish the manual was more specific and detailed.

I don't know what I need to buy and how to make sure I am doing it correctly.

Can someone please fill me in?

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ aceclement commented ·


I asked you that two times in your question:



The alarm output is switched to ground in case of an under/over voltage alarm not when you switch the BP on or off.

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aceclement avatar image aceclement Matthias Lange - DE ♦ commented ·
I haven't seen anywhere that you asked what inverter I have. It doesn't matter, its not a victron inverter. So are you saying that the BP will shut off my inverter in the configuration I described but not until low voltage is reached? Thank you in advance.

I can't tell if you were being condescending or not, but I'm just looking for help understanding the BP and how I can properly use it to shut off my inverter. I soldered a remote toggle switch to my inverter on off switch which I am certain works perfect. But it does me no good since the app doesn't audibly notify of low voltage. I may be out of earshot of an alarm wired to the BP. I need to know i can rely on the BP or I'll be returning it.
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ aceclement commented ·

Just read the manual!


The BP will give you a negative signal at the alarm contact case of an under/over voltage alarm but the alarm will stop after a while.

You could try to connect a relay to the normal output of the BP and connect the relay to your inverter remote contact.

Or you buy a good inverter with adjustable low voltage cut-off.

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aceclement avatar image aceclement Matthias Lange - DE ♦ commented ·
Well gosh if the manual made sense to me I wouldn't be asking. Im not a professional installer.

A simple answer is sufficient. I tested it out and indeed without an actual relay the BP will not shut off my inverter. For the cost of this thing it should do at least what it says it can do even with an inverter. Iv seen so many people say they have had no issues connecting an inverter directly. I mean won't a breaker in the line prevent the inrush? Is there no other way for people who have no experience wiring a relay?

I see much cheaper devices for sale that claim to be able to do what the BP cannot. Seems like Victron would step up their game for how much they charge. It hasn't been worth the hassle. And then I get rudeness from the community? It's uncalled for. You could have just skipped commenting if it was too strenuous to be kind.

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aceclement avatar image aceclement commented ·
So I need a relay. Can someone spell it out to this amateur in plain English. What do i need to buy. I have no experience with relay. I'm a mom who built her own solar battery generator and wanted a way to stop my inverter from damaging my batteries without constant supervision. Bottom line, I need a relay and I don't know what that entails. If all you have is a condeacending attitude please skip responding. Its a waste of both our time. Thank you in advance.
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michelg avatar image
michelg answered ·

Hi rwkoehler, this is how my setup is done. A picture is worth a thousand words.

The Smart Protect 220A is linked to a DC DISCONNECT Switch to provide power to 2 inverters.

The Top black red cable over the SP is bringing the power from the SmartSolar MPPT.

The Bottom black red cable is linked to a 125A fuse, linked to a 450A switch (2 battery banks)

It works perfectly, when it disconnects, and the voltage gets to the reconnection limit, it will take a few minutes to release the power and reconnect the inverter. The main inverter is limited to 100A and the backup to 32A.

Let me know if you have some questions.



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Justin Cook avatar image Justin Cook ♦♦ commented ·

Hi @MichelG,

This is a forbidden connection method.

I understand that it works now, and indeed it may continue working for an unknown period of time... but it will fail, and depending on how it fails, you may suffer damage to your batteries if the BP does not disconnect when it should.

Please connect Victron components in accordance with their manuals to avoid component failure and/or possible system damage that will not be covered by warranty.

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