Clarification on why not to connect inverter to Battery Protect isolator

DIY
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Hi all,

I’m after some clarity on why one shouldn’t connect an inverter to the Victron Smart Battery Connect, as the explanations given don’t make sense to me. The two explanations I can find are as follows.

  1. A “current in-rush” may damage the SBC.

Surely this depends on the load generated by the inverter, no? If I have a 220A SBC, and a small inverter that draws a maximum of 10-15A, I fail to see the risk of “current in-rush”.

The initial current draw for such a small inverter would never get anywhere near the rated 220A of the SBC.

  1. The other explanation is “a reverse current may flow”.

But then, when looking into when/how this would happen, the explanations are along the lines of "if the positive and negative cables are connected to the wrong terminals on the battery, or other wiring issues.”

Yeah… No **** it will cause damage if you wire it wrong :roll_eyes: , but that’s a completely different problem, not a reason to never connect an inverter.

I get not pushing the limits, e.g., don’t connect a 100A inverter load to a 100A SBC.

But I’m yet to find a satisfactory explanation why you can’t connect a small inverter that is well below the limit of what the SBC is rated for.

Can anyone tell me specifically what the issue with running a sensible-sized inverter is, if there really is one at all?

Cheers all.

2

A victron inverter charges it’s capacitator bank when switched on, even with no load connected the inrush current can be multiple times the operating current. Check this document for more info.

Reverse current is more the case for inverter/chargers, in standard operation they will try to charge the batteries when shore power is connected and damage the battery protect.

1 Like
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Hey @mac ,

Thanks for your time.

Reverse current is more the case for inverter/chargers, in standard operation they will try to charge the batteries when shore power is connected and damage the battery protect.

Understood regarding inverters/chargers. In this case, I’m just talking about a standard inverter, no battery charging functionality.

A victron inverter charges it’s capacitator bank when switched on, even with no load connected the inrush current can be multiple times the operating current. Check this document for more info.

I get that. But that takes me back to my first point about the current in-rush.

In that article it uses the example of a 3000w inverter, and that “With typical battery voltage of 13.5V this can result in an inrush peak current of 2,700 Amps (!!!)”

Big scary Amp number, but if you had a 3000A SBP, it would be no issue, right? (I realise there is no SBP anywhere near this rating, but in principle.)

Back to real word number and the 220A SBP… I have a small 150w inverter. It has a maximum continuous output of 15A, and is rated for a peak of 25A. Surely this is never getting anywhere near 220A… it would be a smouldering wreck already :sweat_smile:

I guess Victron’s assumption is based on people typically using much larger inverters, where they could realistically exceed their SBP ratings, and it’s a case of taking an abundance of caution when they say “Under no circumstances is it permitted to connect inverters…”, rather than being technically accurate?

It may not be the typical setup, but if you have a small inverter you know with absolute certainty does not exceed the SBP rating, there is actually no reason it shouldn’t be connected, right?

Cheers.

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Maybe it’s no problem, i wouldn’t take the risk.

Peak and inrush is not the same, i see no reason why your inverter can’t pull more than 220 amps. If you have the right equipment you can measure it.

What are you trying to achieve? Maybe there is a better solution.

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The combination of capacitors and inductions inside an inverter can also cause a reverse inrush current spike and that is most likely what kills the BP.

That warning wouldn’t be in the manual if it wouldn’t be a problem.

I think the risk is small with a 150W inverter but it would still void the warranty.

The manual of the BP shows an alternative way to control inverters via a remote input.
Does you inverter have a remote?

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Hey Mac,

Peak and inrush is not the same, i see no reason why your inverter can’t pull more than 220 amps. If you have the right equipment you can measure it.

I realise that. I was sharing some particulars on the inverter so we could be specific, instead of hypothetically talking about “an inverter” in general.

Obviously, the capacitor in a 150w inverter is going to be far smaller than one from a 3000w inverter.

I actually can’t remember if my clamp meter has an in-rush current measurement, haha. Never something I’ve wanted to measure before, so didn’t cross my mind :sweat_smile:

I’ll see tomorrow.

What are you trying to achieve? Maybe there is a better solution.

Avoiding having to run an additional circuit outside of my isolator, if in fact there is no need with my particular inverter.

I think I’ll just put my money where my mouth is and just plug it in on the weekend :sweat_smile:

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Hey Mathias,

That warning wouldn’t be in the manual if it wouldn’t be a problem.

I’m not disputing the fact that a large enough inverter can destroy a battery isolator. No argument at all.

But I don’t accept the premise that you can’t connect “an inverter” to “an isolator”. It’s vague and completely useless when planning specs for a system.

Specifics matter.

Happy to be proven wrong if someone has actual data/figures, and we’re not just rattling off generalities.

The manual of the BP shows an alternative way to control inverters via a remote input.
Does you inverter have a remote?

No remote on this one. Too small to warrant one, I suppose.

I’m aware of the diagram you’re referring to. As I touched on above, this is an additional circuit outside of my isolator, which is what I’d ideally like to avoid.

In any case. I appreciate people’s time. I will carry on…

Cheers.