question

Edgargw22 avatar image

Hmmm, color monitor shows negative DC draw

Take a look at this picture. I had a hair dryer going and I see a negative draw on the “DC Power”. I thought the only time I would see a negative draw is when the engine alternator was running. I have a Gigavac merge solenoid that should prevent any draw from the chassis batteries. What am I missing? TIA...

BMV Battery Monitor
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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Edgargw22

read this:

https://www.victronenergy.com/live/ccgx:start

relevant text:

'has DC system'

Enable this for boats, vehicles and installations with DC loads and chargers - in addition to Multi and MPPT chargers. This won't be applicable to most off-grid installations; and any discrepancy between the DC current measured by the Multi, and by the BMV, will be attributed to a 'DC system'. This may be power-in from an alternator, or power-out from a pump, for example.

A positive value indicates consumption. A negative value indicates charging, for example by an alternator.

Note that the value shown will always be an approximation, and is affected by the variation in sample rate between elements of the system.

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Yes, my system does have "Has DC System" tunned ON because the engine altenator does help with some house battery charging while we are traveling (actually, the solar panels do a much better job of charging, but the engine helps a little).

I assume the "Note" above is my explination.... variation in sample rates may cause it to go negative...

Thank you.

correct, if one value is updated every second, and the other every 3 seconds for example. You can see some crazy values sometimes because of this.

But it's good for general use, to notice if there are DC loads pulling or alternators charging etc.