9 replies to this topic

[Ted]

I have 400 watts of solar and two lithium 100 Ah batteries. When my Blue Sky monitor is in Battery Volt/Amp mode it reads 13.7 and -14.2 with no appliances or lights on. If I turn on the fridge it will then read 13.7 and -10.2. Why would the Amps read as a negative?

[Dadocut]

Yes, negative amps  is a thing.  If the current is negative it means the current is flowing in the opposite direction. 

 

It sounds as if the sensors on a current shunt are hooked up backwards giving you readings that are negative.  

 

Hope this helps

[Dadocut]

Current is measured by sensing the voltage drop across a shunt.  That is, the wire from the battery goes through a shunt (a low ohm resistor of a known fixed value).  On most RV's this shunt is on the ground wire to the battery. The shunt has a slight voltage drop that is proportional to the current.  Measuring the voltage drop across the shunt gives the current (since Volts=current*amps).  The two wires sensing this voltage drop are backwards so the current incorrectly reads as negative.

[Ted]

Thanks Dadocut. I will follow up on this with the manufacturer.

[Dadocut]

How one refers to current direction is arbitrary. yours is set up so Negative current means juice is leaving the battery. Positive current means the battery is charging. That's the way my system is set up too. There's really no reason to switch the polarity of your current sensing wires.

I should have mentioned that in the first place but got carried away by negative amps!

[pvstoy]

I have 400 watts of solar and two lithium 100 Ah batteries. When my Blue Sky monitor is in Battery Volt/Amp mode it reads 13.7 and -14.2 with no appliances or lights on. If I turn on the fridge it will then read 13.7 and -10.2. Why would the Amps read as a negative?

 

Yea I'm not understanding why you are seeing negative "-" 14.2 amps with nothing being drawn and turn on fridge reads negative "-" 10.2 amps.  

 

Did it read more normal or different in the past?  If so what has changed?

 

You have a three amp draw when you turned on the fridge.  My Victron shunt would show if I had zero amp draw as 0.00 amp.  If I created a draw like you with the 3 amp draw for fridge the meter would show a negative "-" 3.0 amp draw.  Display would show it as a negative draw.  Solar going in would show as a positive.

 

What does it show when your solar is putting in amps to the battery with nothing on?

Edited by pvstoy, 19 September 2023 - 11:59 PM.

[Vic Harder]

I have 400 watts of solar and two lithium 100 Ah batteries. When my Blue Sky monitor is in Battery Volt/Amp mode it reads 13.7 and -14.2 with no appliances or lights on. If I turn on the fridge it will then read 13.7 and -10.2. Why would the Amps read as a negative?

The important bit I see here is that the negative number gets smaller when you add MORE draw.  It should read bigger!  Does this monitor have a "Calibrate" function?  That is used to setup the shunt so it reads "0.0" amps when there really is nothing going in or out.... 

[Jon R]

Solar is supplying -14.2 amps, reading negative because of the direction the shunt was installed, then the fridge comes on and draws about 4 amps, hence the reduction in amps into the battery to -10.2?

[pvstoy]

Yea that all sounds reasonable, but Ted has had his Tiger for some time now and suddenly it's reading backwards?? Question is what has changed to make it this way.

Mice getting organized and rewiring his system?

[Vic Harder]

Solar is supplying -14.2 amps, reading negative because of the direction the shunt was installed, then the fridge comes on and draws about 4 amps, hence the reduction in amps into the battery to -10.2?

Possible, assuming the wires are backwards.  BUT, as Patrick pointed out, Ted has had this camper for a while.  Mice are creative, but not typically good at attaching wires in reverse....