How to use 2 SBP to protect the Battery in combination with an Inverter and Battery charger?

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omora asked Dec 14, '21

How to use 2 SBP to protect the Battery in combination with an Inverter and Battery charger?

Dear Victron community experts,

I am seeking your advice and verification for the following setup.

I would like to have a Battery solution which is permanently connected to the PV, but disconnects automatically when fully charged and no 12V load is applied.

In case the PV was unable to fully charge the Battery, I would like to have the option to charge via a Blue Smart Charger.

An automated complete disconnection of the Battery is desired for mainly 2 reasons:

A) for safety reasons and

B) to avoid the Battery being permanently charged via PV and gets over time discharged due to standby power consumptions in the setup.

Hence, the idea here is to have one Smart Battery Protect on the charging side of the Battery as well as another Smart Battery Protect on the load side of the Battery. Hope this logic of mine by using 2 SBP will actually do the wishfully automated disconnection of Battery when not in demand.

On the Charging Side:

Either PV or the Blue Smart charger would charge the 200Ah LiFePo4 Battery with an integrated BMS via the SBP 12/65.

On the Load Side:

Is a DOMETIC 12V/2000W Power Inverter with an external on/off switch as well as DC load via the SBP 12/220 connected.

These are now my questions:

With this setup, the Power Inverter will be seen as a load by the SBP 12/65 on the charging side. Since the SBP flow is from IN to OUT, I assume the Power Inverter with capacitor on its input will cause reverse current backflow and damage the SBP 12/65!

If so, how do you overcome this when the battery is simulations charging (current flow from one direction) as well as used as power source to run the Power Inverter (which will cause current flow to the opposite direction). Means, both SBP (on the charging as well as load side) are actively working.
I can read in the SBP manual “..For that use case, please use the SBP to control the remote on/off switch on the inverter, instead of disconnecting the higher power DC line.” And luckily the Power inverter has an external on/off switch, but how is this helping in this setup to protect the SBP 12/65? If the Power inverter gets disconnected, I will not be able to use the Power Inverter at all.

I would like to thank you already now in advance for your comments and suggestions.

oMora

battery charging Lithium Battery Battery Protect

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Answer 1 · 2021-12-14T16:07:04Z

kevgermany answered · Dec 14, 2021 at 04:07 PM

A better and easier way would be to configure the chargers with lower voltage settings.

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omora commented · Dec 14, 2021 at 06:21 PM

Thank you for answering kevgermany. Do you mind elaborating details pls. Are you suggesting to keep the setup as shown and just to lower down the voltages or to also remove the SBP completely from the setup? To fully charge the LiFePo4 I would still need >14.4V. Thx.

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Answer 2 · 2021-12-14T20:31:23Z

kevgermany answered · Dec 14, 2021 at 08:31 PM

With what you're doing/want to do, pointless to charge fully. Might as well aim for a lower charge state. As it's lithium, there's no battery damage, but it will prolong the battery life. Could include a single sbp if you want.

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Answer 3 · 2021-12-14T20:51:10Z

kevgermany answered · Dec 14, 2021 at 08:51 PM

Thinking more. Some devices like battery monitors have a programmable relay unit built in. It is low current, but powerful enough to switch a bigger relay. Or an Orion. So if you add a BMV 712 for instance you could program that to switch the Orion. But check the manual for full details.

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Answer 4 · 2021-12-15T03:56:33Z

omora answered · Dec 15, 2021 at 03:56 AM

Thx kevgermany, your recommendations are understood.
Lets assume you take the power Inverter out. The 2 SBP setup will be the approved victron view.
My only question here is, how do you connect a non-victron power Inverter in combination with a non victron Battery without damaging any SBP in below view?

If you connect the Power Inverter to point 4 which is SBP 220 - IN or the Battery positive pole, the second SBP will be damaged. Isnt it?

1639541487713.png (1.0 MiB)

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Answer 5 · 2021-12-15T06:52:55Z

kevgermany answered · Dec 15, 2021 at 06:52 AM

You do not need a second SBP.

But if you want to.

Group all charge loads to IN on one SBP with OUT wired to battery positive.

Wire IN on the second SBP to the battery positive, all DC loads to OUT on the second unit.

Make sure you don't depend on the battery for switch control.

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omora commented · Dec 15, 2021 at 06:59 AM

Very good point. I was thinking the same earlier, but then saw the victron diagram with 2 SBP and started following the same logic. We can now go one step back and generally ask what the purpose of the second BP in the victron diagram is.

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Answer 6 · 2021-12-15T10:15:18Z

omora answered · Dec 15, 2021 at 10:15 AM

This is exactly how I did :)

Here again my setup in a more simplified way (have just removed all details and ground wiring for illustrative purpose only).

And exactly here was my main ask earlier "wont the power inverter damage the left SBP 12/65?".

A friend of mine now told me how the reverse current flow from the power inverter might be compensated by the Battery and hence, wont harm the left SBP12/65.

What do you mean by "don't depend on the battery for switch control. "?

1639563066490.png (880.5 KiB)

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Answer 7 · 2021-12-15T11:06:33Z

kevgermany answered · Dec 15, 2021 at 11:06 AM

Is this an inverter? Or an inverter charger?

If the latter, then can't work.

You show inverter connected direct to the battery bypassing SBP.

Biggest parasitic drain on the battery is likely to be the inverter.

Frankly, you're over-complicating things.

Switching. If you achieve complete isolation of the battery and external power fails, there's no power to switch the battery back into the circuit.

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Answer 8 · 2021-12-15T12:57:39Z

omora answered · Dec 15, 2021 at 12:57 PM

The Dometic is just an inverter, NO Inverter charger!

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Answer 9 · 2021-12-15T13:03:45Z

omora answered · Dec 15, 2021 at 01:03 PM

To keep things simple, do you think I should just take both SBPs out and put a main On/Off switch towards the load side as well as an On/Off switch towards the power inverter? Its not an elegant solution, but the battery would at least get automatically charged and I would turn on and off the power supply on demand and would avoid the uncontrolled drain of battery.

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Answer 10 · 2021-12-15T15:42:09Z

kevgermany answered · Dec 15, 2021 at 03:42 PM

It's your decision, but that is simpler/more reliable.

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Answer 11 · 2021-12-15T16:45:20Z

omora answered · Dec 15, 2021 at 04:45 PM

Thx a lot again!

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