question

axisential avatar image
axisential asked

Low voltage error only on the DC Bus

This is an EasySolar 24/3000 with a BMV700. LPG gas hot water was switched on (DC ignition, about 5A nominal draw) and a low voltage alarm was triggered momentarily. VRM shows a momentary spike down to about 18V (!) on the DC Bus chart only, where the plain Battery Voltage and Current chart doesn't show this. Any ideas - is this just a spurious error? What's the difference between the 'voltage' part of these two charts?

EasySolar All-in-One
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3 Answers
JohnC avatar image
JohnC answered ·

Hi Ax. Your 2 graphs are a little different because they're getting their info from 2 different sources. The first, note the Device Instance [258], is likely your BMV and will be the most accurate. The second, the VE.Bus, is your inverter.

The spike, whether logged or not, will be a function of when the data is taken. It doesn't all happen at the same time, and for the graph purposes they're sampled and reported as often as the set timespan defines and are not 'integrated'. You'll see the effect of the 'rotating' sampling on your CCGX screen - the flows never balance..

So your spike, if only for a few seconds, was (by luck) picked up by one device and not the other. The alarm you received is likely from a genuine low V, and won't wait for the graphs.

That's actually a helluva spike from 5A dc @ 24V. Sorta like something a dead-short would do, and perhaps worth further investigation.

Spurious is always possible too, maybe a crook contact somewhere?


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Rob Fijn avatar image
Rob Fijn answered ·

Hello,

This could be just because the sample rate of the logging.

The low voltage could be real.


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axisential avatar image
axisential answered ·

Thanks Rob and John - got to the bottom of it this morning when I asked my son (7) to show me exactly what he'd done when he switched the HW on. Turns out he'd fiddled with the isolator that's in the same cabinet, effectively isolating the inverter for an instant (then getting freaked out by the alarm, letting the isolator go and restoring power!) So that explains perfectly why the BMV shows normal voltage while the inverter recorded the drop. Whew!

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JohnC avatar image JohnC ♦ commented ·

Yeh, ha. Definitely fits the spurious category. I had actually wondered about the Battery Current spiking to zero. Hope the young fella learnt his lesson, and he now knows that Dad is watching him via VRM. :)

Please congratulate him for being honest. A lot of kids would deny it cold..

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