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Lionel SEYDOUX avatar image
Lionel SEYDOUX asked

Overload L1 on VE bus system

I often have that alarm cleared about 30s later. Last time yesterday at 18:47, maybe at the starting time of my washing machine, but not sure. Does not alarm me but I woul like to understand! My setup:

- Off grid, 2kWp on my roof + 23kWh lead batteries.

- 2 solar MPPT 150/65, 1 multiplus 24/5000/230

- BMV712, CCGX

Around the time of alert, exact time to be checked I am normally on my local sun time (UT+28m) but VRM may have some other tim:

  • 17:39: -0.40
  • 17:48: -121.00
  • 18:06 -7.07
  • 18:24 -24.90
  • 18:33 -5.90
  • 18:51 -3.60
  • 19:10 -6.7
  • 19:19 -124.60
  • 19:37 -128.00
  • 19:55 -8.10

Any idea?

offgridVE.Busovervoltagelead-acid
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Alexandra avatar image Alexandra ♦ commented ·

@Lionel SEYDOUX

If you are receiving overloads then that is what is happening.

A 5kva will run 4000w at 25°C. If it is hotter where you are then this goes down. At 230v this is 17 or so Amps on the AC side but on the dc side it is 166A. That's quite a draw. Are your battery cables the recommended size?

You can have a pump or motor with not so great power factor also trigger an overload because it is drawing greater amperage than your system is designed for.

https://www.google.com/url?q=https://m.youtube.com/watch%3Fv%3D4SXtGIx0x5w&sa=U&ved=2ahUKEwj0kIet6obqAhXjlFwKHcvpDA0QtwIwAHoECAYQAQ&usg=AOvVaw21DZGyfhJjoM-XvgN7M2sJ

This is a great webinar on diagnosing overloads, if you have the time.

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Lionel SEYDOUX avatar image
Lionel SEYDOUX answered ·

Thanks for that anqwer.

Just checked Amps on VRM: it went down to,-128A several times but very short probably when starting my washing machine. My Multiplus 24/5000 is supposed to give 5kVA 230V that is 21.7A. I was on a clear overload but only for one second or so...

A lazy reader of the manuals...


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ejrossouw avatar image ejrossouw commented ·

It only delivers 17A (4000W) at 25 degrees and 3700W at 40 degrees. Overloads are only warnings as it can handle short bursts up to 10000W e.g. for washing machine startup. Washing at high temp also does aggravate things.

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Lionel SEYDOUX avatar image
Lionel SEYDOUX answered ·

Lionel Seydoux back:

A new alert this afternoon at 15:47, cleared at 15:47.

As the sun is bright amps around that time are +5.6 to +5.8. No machine working, except a CD reader and ampli which I started again at 18.31 with no alert whatsoever

I could try to record at hi frequency the amps out of L1 (easylog WiFi) but a bit expensive for suche a "small" incident!

I do not understand that. Any idea?

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Alexandra avatar image Alexandra ♦ commented ·

Isloating the cause is difficult not knowing your site first hand. Overloads can also be caused by wiring shorts as well. Bad light switches as well.

Maybe others with more install experience will have other ideas?

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tojohn avatar image
tojohn answered ·

I have a similar problem: multiplus is alarming at every short-duration spike in power over whatever the overload threshold is (what IS the overload threshold value on these units anyway?). There should be an adjustable overload threshold warning, e.g. overload past 80% rated capacity over 30 sec triggers alarm. Every time I start a motor in my shop the multiplus generates an alarm, even though most of the motors are rated at 50% or less of the rated inverter capacity. Better logging and messaging would help isolate overload problems, e.g. "overload with 3800w for 0.5 seconds on L1."

Are these short-duration overloads even harmful to the inverter? If not, then they need to be much less frequent.

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Alexandra avatar image Alexandra ♦ commented ·

@Tojohn

The threshold is VA divided by voltage.

So 5000va / 230v = 21.7A on AC

Watts and VA are two different measurements. As watts are what the system sees as being used but VA is the actual power used and the difference is caused by power factor. We usually work with an 80% average power factor so a 5kva will be rated for about 4000w depending on the components of your system.

Motors usually have poor power factor unless there is a system put in place to correct it. So a 500w motor can draw anything up to and over 3000VA.

I have seen a 1500W lawnmower overload a 10kVa inverter.

If system battery voltage it is

5000va / 24v = 208A

5000va / 48v = 104A some batteries cannot handle the Amp draw so siszing so there is no voltage collapse is important.

Of course this is very simplistic working as it does not account for temperature derating and cable or other resistance and heat losses.

Sustained overload causes overheating and system shutdown. Short bursts should be ok if you know what is causing it. But if you are overloading frequently then you system is a bit undersized.

For motors like pumps there are easy start controls you can use to prevent the heavy amp draw and bad power factor. Capacitors on motors like grinders may need to be checked as they are a simple from of power factor correction and if they are not well then you will also see overloads.

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