question

miya avatar image

DC Loads Increase - with high Multiplus charge rate

Hi All

I wonder if anyone can explain a strange issue I am seeing on my system...

Set up - 3x Lithium (3x 200A), VE.Bus BMS, Venus GX, BMV712 and Multiplus (EasyPlus 12/1600/70 - set to 70A charge current max).

Example of situation / what I am seeing -

  • I leave the boat for a few days
  • with a constant load of about 1.5A on batteries
  • I arrive back at boat - and BMV says state of charge is 90%
  • all good so far

I plug shore power in - and switch Multi on - and do NOT switch on anything else -

  • it goes straight to Bulk - good.
  • If I look in Venus at the Multiplus - it says it is generating 70A - good.
  • I look at the BMV - and it says it has about 60A going in to batteries - strange
  • I expect the current going in to batteries to be about 68.5A (charge current - loads)
  • where are the other 10A going / being lost ?
  • I look on VRM and see DC Power showing my DC loads are pulling about 10A
  • but this is not true - the loads / devices are only about 1.5A
  • I have not switched any other loads on

This false high DC loads figure (about 10A) stays while charging Amp are high (in bulk). When multi goes to absorption - the false high DC loads (10A) reduces in line with the drop of charging Amps. I watch the 10A loads reading slowly drop to 1.5A as the multi reduces its charge current from 70A to almost nothing. Then - in float - the DC loads read accurately - 1.5A.

Any thoughts on what the issue is ?

Thanks

Tim

MultiPlus Quattro Inverter Chargerchargerdc system
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4 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

I've seen the same thing and similar when the inverter is supplying high power to the AC loads.

The number provided for the DC System is calculated from other values so my guess is that those other values don't add up at the instance the values are sampled.

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miya avatar image
miya answered ·

Interesting... I will test my inverter under high power AC loads and see if it does the same.

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pwfarnell avatar image
pwfarnell answered ·

The current measurement by the BMV is likely to be more accurate than the current measurement on the output of the Multiplus. The BMV uses a more accurate sensor and is probably the correct figure. In your case it may be that the Multiplus is reading about 10% high. Therefore, the GX device then allocates the difference as a DC load. This is why the DC load decreases as the current falls, the 10% error is also reducing.

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Thanks - that makes sense.

jw1971 avatar image
jw1971 answered ·

I believe it is the conversion loss being reported as DC load. Whenever my Multi is on, even if not inverting, I see these DC loads go up, and when inverting or charging it is worse.

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Thanks - on reading the Multiplus manual - I see the 'efficiency' is quoted as 92%. So I assume the 8% loss is being reported as DC loads.