Did I undersize my Multiplus?

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ddrolett asked Jan 14, '19

Did I undersize my Multiplus?

Hi there, new Victon Multiplus user here. I own a Multiplus Compact 12/2000/80 120v and intend on installing it in my small camper. My inverter needs are simple as I will probably only be using about 250 Watts of continuous power when off grid. But, one requirement I had when I sized my inverter was that it had to run my coffee maker twice in the morning which is 1475 watts when heating (Keurig single cup model). I did the research and calculations before my purchase and was under the impression that a 2000VA inverter could handle that load assuming the coffee maker ran at a power factor near 1.0.

But when I start the brewing process, the entire unit shuts down with an alarm. I have the digital multi controller installed as well, and it does not show an overload, it shuts down with the Mulitplus.

I decided to mock up the setup before installation and give it a test. Here is my setup:

- Multiplus hooked to house mains (15A circuit with input limited to 15 amps)

- 100Ah 12V Lithium Battleborn battery connected with 2/0 gauge (9.27 mm) wire

- Standard outlet wired to the AC output of the Multiplus with 14/2 cable

Have I undersized? What should I be looking for to help me troubleshoot? What information can I provide? Thank you in advance for any advice or guidance.

Dave

MultiPlus Quattro Inverter Charger

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Answer 1 · 2019-01-14T03:03:17Z

dynaco1 answered · Jan 14, 2019 at 03:03 AM

Perhaps the 100Ah battery lacks enough discharge current to satisfy the first second of the inverter DC bus demand, when powering the coffee maker. Have you tried a smaller AC load?

We own the Victron 12/2000 inverter/charger and are able to power our Keurig, while on shore power or on battery. We use a single 12/200 Victron 200Ah battery.

When you are on shore power, the unit should detect AC "mains", switch to shore power and provide plenty of power the Keurig.

From Battleborn 100Ah O&M manual:

High Current The BMS will not allow a current that exceeds 100 (+/- 5%) Amps for 30s, or 200 (+/- 10%) Amps for 0.5s. Although these thresholds have been verified with a DC load bank, the 30 second high current threshold may be reduced from 200A to around 150A for certain highly variable loads through an inverter – like a microwave or space heater. After a high current disconnection, the battery will automatically reconnect after 5 seconds.

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ddrolett commented · Jan 14, 2019 at 03:12 AM

Thank you for your reply! I believe you are correct about the battery not handling the initial load. I placed a multimeter across the battery during the failure and based on the voltage drop and the way the Mulitplus is shutting down, I believe the battery is shutting down due to over current. The battery turns back on in 5 seconds just like the manufacturer is stating in the manual.

I did hook a 1200 watt toaster to the inverter to test another high load device and it worked fine. My solution will probably be to find a coffee maker with a much smaller load, of which there are many to choose from.

Thanks again,

Dave

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wkirby ♦♦ ddrolett commented · Jan 14, 2019 at 06:46 AM

In your search for a coffee machine, please continue to bear the power factor in mind. Some of them use induction heating and therefore may have a power factor of less than 1.0

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Answer 2 · 2019-01-14T05:33:01Z

Guy Stewart (Victron Community Manager) answered · Jan 14, 2019 at 05:33 AM

Your DC wire is WAY too small. Section 4.2 of the manual for your unit recommends 70sq mm -

https://www.victronenergy.com/upload/documents/Manual-MultiPlus-Compact-2000-120V-EN.pdf

You will get voltage drop, rising current and overcurrent issues.

9.27 sq mm wire is rated for about 70A.

Your 1500W load at 12V = 125A.

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wkirby ♦♦ commented · Jan 14, 2019 at 06:39 AM

They said that they used 2/0 cable which is actually 70mm2. I think the mm dimension that they stated in is the diameter.

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Guy Stewart (Victron Community Manager) ♦♦ wkirby ♦♦ commented · Jan 14, 2019 at 06:48 AM

Thanks for the clarification, I never did get the hang of the AWG units.

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Answer 3 · 2019-01-18T16:26:38Z

vantalk00 answered · Jan 18, 2019 at 04:26 PM

So I had a similar question about sizing of the battery cable. The surge rating of the Multiplus Compact 12/2000/80 120v is 4000W or 333A at 12v. The ABWC wiring standards indicate 2/0 can handle 280 A inside or 330 A outside and indicates a square mm size of 62.

Seems to me it would be prudent to go to 3/0 (81 sq mm and 327 A inside). Not sure how ABWC comes up with these as they don't relate to AWG tables, but the AWG tables don't automatically assume DC, and I'm guessing you have to account for that somehow. I assume ABWC has done that. I don't understand the square mm discrepancy.

From Battle Born,

"High Current The BMS will not allow a current that exceeds 100 (+/- 5%) Amps for 30s, or 200 (+/- 10%) Amps for 0.5s. Although these thresholds have been verified with a DC load bank, the 30 second high current threshold may be reduced from 200A to around 150A for certain highly variable loads through an inverter"

Clearly, surging your Multiplus from one battery is going to overload it at 4000 W. At 1475 W, the current is 122 A. I can't imagine a coffer maker with a power factor much lower than unity, and I can't imagine a high inrush either. I think the situation is that your coffee maker has a sustained current of 122 A for over 30 s, and that's the problem. You either need another battery or need to avoid appliances with sustained current over 100 A.

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