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jangeja avatar image
jangeja asked

Multiplus 12/3000/120 showing voltage across even when disconnected

I’m seeing something very interesting.


When I disconnect my multiplus from my 12v battery, I see 13.2 volts across the BAT - and +.

The multiplus BAT + is connected to a bus bar that my dc loads are connected to as well. When I flip the breaker for my dc loads, the voltage drops to 4.8 volts. No dc loads are running except for a few control panel LEDS which can’t be more than 50 mA.

Is it possible a capacitor is tied to the positive terminal of my multiplus and it’s getting the voltage from that?

MultiPlus Quattro Inverter Charger
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Justin Cook avatar image
Justin Cook answered ·

@Jangeja, when first disconnecting the MultiPlus from the battery, it's fairly common to see residual voltage at the Multi's BAT connections because its capacitors do indeed store energy for some time. I expect this to drop fairly rapidly, though... I just tested this on my test-bench MultiPlus setup and observed that the voltage across the BAT connections dropped to ~5v within 15 seconds (under no load other than the multimeter) and continued to drop.

Does your observed 13.2v persist, or does it immediately start to drop off? Also, have you tested whether there's any actual current behind that voltage? Ie, if you connect a small load to the MultiPlus BAT terminals, will it power that load, or does the voltage immediately fall away without powering the load?

You may have answered the question in a way, but I'm not sure which way you were flipping the breaker when you say that "when I flip the breaker for my DC loads, the voltage drops to 4.8v".

As a side note, depending on the busbar that you're using and the nominal voltage of your system, I'd pretty strongly recommend connecting the Multi directly to the battery bank (after appropriate fusing and battery switch, of course) since many busbars are only rated to 250A and a MultiPlus 12/3kVA can easily pull well in excess of that (inrush current at 516A for ~13ms, potentially over 300A continuous under heavy load).

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jangeja avatar image jangeja commented ·

Hi @Justin Cook

Thanks for replying! Here are a couple of things to answer your questions.

The 13.2 volts persists for some time after I turn off my battery switch. I haven’t tested exactly, but I’ve seen it for an hour or longer.

When I said “flip my DC breaker” I’m essentially connecting the positive of my DC fuse panel to the positive bus bar, which the multiplus is connected to. I have 0 DC loads running, except for a DC control panel with rocker switches with LEDs. The LEDs in the rocker switch are lit up, but again, no actual big DC load. The few rocker switch LEDs drop the voltage to 4.3, but the LEDs are still lit. Once I disconnect my DC breaker, effectively turning off the rocker switch LEDs, the voltage climbs back to 13.2

As far as my bus bar goes, I use to have a 250A bus bar, and connected the multiplus to the battery fuse. I didn’t like this because it out unnecessary strain on the fuse holder. So I purchased a 600 A blue sea systems bus bar. This bus bar is protected with a 400 A fuse.

Im not too worried about the voltage reading in the positive BAT on the multiplus. I just wanted to confirm that this was normal. Thanks for testing it and validating what I was seeing!


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Justin Cook avatar image Justin Cook ♦♦ jangeja commented ·

Ahhh okay, @Jangeja, I see... you definitely have the right busbar and fusing, that's good to see. As for the persistent voltage from the Multi, though... that's definitely persisting longer -and with more current behind it, if it'll run those little LEDs- than I would expect. Yes, to be fair, the LEDs are in the mA range I'm sure, but that still sounds like more than just residual power from the Multi's capacitors, particularly because, if the battery is truly disconnected, the capacitors will invariably drain, they won't "bounce back" when you remove the loads. When you say the voltage comes back to ~13.2 when you flip your DC breaker back off, that's "bounce back" behavior, which means it's not just the Multi's caps.

Are you running the Multi off a battery switch that's maybe allowing vBatt through even when in the "off" position, or something like that? How are you disconnecting the Multi?

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