Using Battery Protect with Inverter (as a load). Victron SmallBMS manual says ok but is it?

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coaster asked Jan 21, '22

Using Battery Protect with Inverter (as a load). Victron SmallBMS manual says ok but is it?

Hi, I've been reading up on Inverters and how to install them in my system. I'm looking to add a 1,000-1,500 watt pure sine inverter to my system (not an inverter/charger).

I thought I understood that a BP was not appropriate for this because it would be damaged by the inrush/inductive surge that occurs when due to the inverter's capacitors (sorry if I have the terms wrong, but I get the idea).

However in reading the current Victron manual for the SmallBMS (just downloaded this manual today from the Victron Energy site), I see this paragraph (Safety Instructions, section 3.4):

I'm sorry if that came out tiny. The Section 3.4 heading is this:

3.4 DC Load: Disconnecting the load with a BatteryProtect

The part I have outlined in red says this:

"Contrary to a Cyrix or contactor, a BatteryProtect can start a load with a large input capacitor such as an inverter or a DC-DC converter."

So that makes it sound like it is fine to use a BP between the battery (and BMS) and the inverter (load). But I thought I understood that that was verboten and would damage the BP? If I'm understanding the manual correctly though, I can use a BP (as a load disconnect/protect) between my main busbar and the inverter (controlled by SmallBMS). Can someone confirm that? Or fill in any misunderstanding on my part?

Thanks,

Coaster

System components (appropriate fusing not mentioned):

Victron Smart 12.8 200ah battery

SmallBMS (or could change to VE.Bus BMS)

BP100 before existing house loads

BP100 (backwards) from charging side (Victron SCC 75/15)

Orion TrSmart DC-DC 12v/12v charger from Start battery (controlled from BMS).

Victron BMV-702/shunt on negative side

Battery Protect

section-34.png (70.4 KiB)

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Justin Cook answered · Feb 08, 2022 at 09:23 PM

Hi @Coaster ,

I would advise using the method described in the Smart BatteryProtect manual (line 4) and use the SBP to trigger the remote on-off of your inverter. I will bring the specific line in the smallBMS manual to Victron's attention to get that instruction clarified/corrected.

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coaster commented · Feb 08, 2022 at 11:18 PM

Thank you, Justin!

Also thanks for letting me know that you will follow up on this with Victron. If I hadn't been studying the forum and seen your previous posts on why this is forbidden I would have thought it was fine based on the SmallBMS manual. So obviously other people could do the same. Now it will be corrected for everyone. Right on.

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Answer 1 · 2022-01-21T18:30:36Z

Mike Dorsett answered · Jan 21, 2022 at 06:30 PM

With a small inverter the inrush current into the capacitors is not that great compared with e.g. a 5,000W inverter. As the BP manual says it can cope, I would trust the manual.

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coaster commented · Jan 21, 2022 at 10:56 PM

Mike Dorsett,

I understand your concept that smaller inverters may not cause damage whereas larger ones would. However the manual doesn't list any figures for what is too small or too large. It just says you can do it. If there is an upper limit, I would like to know that (just like they show figures for batteries and other components).

Also, although I may put in a 1,500 watt inverter now, what if I upgrade to a 2,000 watt? 3,000? (with the rest of the system upgraded commensurately). There is nothing in the paragraph above indicating that it's okay for a certain size but not for another size (although it seems intuitive that the larger inverter the larger surge; but then you'd also use a larger BP).

But I'm actually wondering if this is an OPPOSITE misprint in Victron's manual (it's in the SmallBMS manual, btw). Everything else I have read - including here from Victron - has said this is an absolute no-no, and will damage the BP because of the surge. And whereas they say you can't use a Cyrix or contactor in this same paragraph (shown above), I thought those were the acceptable alternatives (since you can't use a BP). So it seems backwards. But it would be handy to use a BP, so if it's fine, I'm all for it.

Here is a link to a thread that states this is an "expressly forbidden" use of a BP (connecting it between battery and inverter).

https://community.victronenergy.com/questions/63134/why-can-i-not-use-a-smart-battery-protect-between.html

Hence my wish to clarify the SmallBMS manual that I downloaded from Victron Energy today. Has something changed now? It's now okay? Maybe the BP's have been re-engineered? If so, is there a part number delineation?

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coaster coaster commented · Jan 21, 2022 at 11:02 PM

Just to tag @Justin Cook - Bay Marine Supply USA because he was involved in that other thread.

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Answer 2 · 2022-01-21T22:57:25Z

coaster answered · Jan 21, 2022 at 10:57 PM

Mike Dorsett,

I'm not sure if I did this right, but I responded to you in the form of a "Comment" to your post (because here it shows as an "answer" instead of nesting under yours as a reply.

I linked a thread in that "comment" that shows that Victron "expressly forbids" the battery/BP/inverter chain.

I hope Victron will also reply because I'm wondering if there is a mistake in the manual -- or if the BP's have been redesigned (and when did that happen so I can make sure I get current stock).

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Answer 3 · 2022-02-07T22:19:23Z

coaster answered · Feb 07, 2022 at 10:19 PM

Is there anyone from Victron who could address this? I got one reply who said "trust the manual," but I am reading completely opposite guidance from manuals and threads that did include Victron's input. (I linked one thread in my previous reply.)

In one place Victron says it's "expressly forbidden" to use a BP Smart to control an inverter (internal damage to BP will result from inrush as capacitors fill). In the Victron SmallBMS manual I screenshotted above, Victron specifically says you SHOULD use a BP for this, and not a contactor, Cyrix, etc.

These are two diametrically opposed positions so it seems that one of them may be completely wrong. I want to know before I buy parts and put them together. Which is it? (And if one is wrong perhaps the manual could be corrected.)

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klim8skeptic ♦ commented · Feb 08, 2022 at 12:51 AM

I think you have found an error in the Small BMS manual, thus you should ignore it.

Follow the schematic in the Small BMS manual for disconnecting (shutting down) the inverter.

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