# EMI from Inverter interfering with current shunt.



## kennybobby (Aug 10, 2012)

Try using a shielded twisted pair for the shunt wires. The shield needs to be grounded at one end. 

How are you using the ferrite core (and why)? What is the frequency of the inverter noise? Do the shunt wires feed in to a differential op amp circuit or how are they used?


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## Ampster (Oct 6, 2012)

Thanks, I typed out a long response on my computer and now realize I did not send it to the thread. I am away from my computer but will try your suggestion and later will answer your other questions.


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## Ampster (Oct 6, 2012)

The noise has quieted down after I used shielded twisted pair wire to the shunt. I can still see the plot of current measurements vary from 20 Amps to 1 Amp but I am no longer getting error messages. It will take me a few more days to get the shunts and the rest of the battery cable in a metal box to shield the noise. 

The ferrite cores were just a guess on my part based on seeing them on the end of some computer cables. I don't know for sure but some people on the Outback Power forum have guessed that it is a 20 kHz. signal.


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## Ampster (Oct 6, 2012)

I now have all the DC cables in metal conduit and the shunt is in a junction box. I also replaced wires from the shunt to the BMS with sheilded twisted pair wires per Kennybobby's suggestion. All the errors have disappeared. I'm now getting consistent measurements of Amps going into and out of the pack. Problem is now solved.


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## jkirkebo (Jul 23, 2015)

Ampster said:


> I now have all the DC cables in metal conduit and the shunt is in a junction box. I also replaced wires from the shunt to the BMS with sheilded twisted pair wires per Kennybobby's suggestion. All the errors have disappeared. I'm now getting consistent measurements of Amps going into and out of the pack. Problem is now solved.


Thanks for the solution. I have the exacte same problem on my off-grid system, the shunt value jumps around on my Orion Jr. when the two Outback VFX3048E inverters are turned on. The 3 shunt values from my FN-DC is rock stable (yes, I have 4 shunts in my system...).

I have tried twisting the cables to no avail. Will get some STP and try that next. Metal conduit and junction box will be more problematic as I have an Outpack PS2 and not very much space to spare. I hope the STP fixes the problem...

My system is 14S lithium charged to 57V. 10P7S of Leaf modules for a total of 35kWh (of which I use approx. 24kWh). Outback FM80 CC connected to 8 SunPower 337W panels.


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## Ampster (Oct 6, 2012)

jkirkebo said:


> Thanks for the solution. I have the exacte same problem on my off-grid system, the shunt value jumps around on my Orion Jr. when the two Outback VFX3048E inverters are turned on. The 3 shunt values from my FN-DC is rock stable (yes, I have 4 shunts in my system...).
> ...........


Here is an update. The issues have become intermittent. I got no luck from the vendor of the BMS so I finally called Outback, since it was the their inverter that was causing the problem. The only thing they suggested was to bond the battery pack negative to ground. I did that and it helped a little. After a few hours or within a 24 hour cycle I still get unlogged error messages and my BMS goes into Error mode. Therefor the state of charge information was useless and the only value the Orion BMS gives me is the ability to see how well my 16 cells are balanced. At this point I have a $700 investment in something that cell logs or a VOM could give me the same information. It is still convenient to log onto the BMS with my PC to check on cell balancing.

In the meantime I invested in a Battery Monitor from Outback (FNDC) and have good input from the two shunts that respectively measure Charging Amps and Discharging Amps. I don't have enough cycles to see how good the SOC information is but this seems to be stable.

A week before i installed my FNDC Battery Monitor I set of the OPTICSRE account and I think it will give me everything that I need to monitor my system. I think I can set that up to send me texts or emails when SOC gets low or an event happens. 

I am thinking will ask my BMS vendor to escalate this to Orion (Ewart Energy) because I would think this is a problem they would want to solve. With the price of Lithium Batteries coming down the stationary market has to be a niche that they would want to be in.


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## kennybobby (Aug 10, 2012)

Do you have an oscilloscope in order to capture a time history to see if the disturbance is periodic or random, low or high frequency noise, etc.?

Some ideas: 
The low-voltage power supplies for the instrumentation circuits may need decoupling capacitors at the ICs.

May need to add some low-pass filtering of the sensor signals.


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## Ampster (Oct 6, 2012)

kennybobby said:


> Do you have an oscilloscope in order to capture a time history to see if the disturbance is periodic or random, low or high frequency noise, etc.?
> 
> Some ideas:
> The low-voltage power supplies for the instrumentation circuits may need decoupling capacitors at the ICs.
> ...


I don't have a scope but I can chart the amps in the BMS software and and see the disturbance only when the inverter is on. I am using a Meanwell switched power supply as my source for 12v DC for instrumentation. I guess I could try running them off an old 12v battery and see if that makes any diffference. fortunately every thing is put together with Andersons so connecting up to 12v battery is an easy thing to do.

NOTE: 11;30 AM I ran the BMS off a 12v battery and still the same disturbance. After reconnecting to the meanwell I disconnected the STP leads to the amp meter and disabled the Amp meter in software. Things have quieted down. We will see how long I go without errors. Now that I have a reliable measure of amps in and out of the pack with the Outback FNDC I don't need the amps measurement in the Orion.


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## jkirkebo (Jul 23, 2015)

Ampster said:


> NOTE: 11;30 AM I ran the BMS off a 12v battery and still the same disturbance. After reconnecting to the meanwell I disconnected the STP leads to the amp meter and disabled the Amp meter in software. Things have quieted down. We will see how long I go without errors. Now that I have a reliable measure of amps in and out of the pack with the Outback FNDC I don't need the amps measurement in the Orion.


I think the Orion needs the shunt input to calculate the cells internal resistance? It uses the voltage drop of the cells and the amps flowing through them as data points for making the calculaton I think. Erratic amp readings lead to erratic internal resistance calculations and thus erratic weak cell error messages.


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## Ampster (Oct 6, 2012)

jkirkebo said:


> I think the Orion needs the shunt input to calculate the cells internal resistance? It uses the voltage drop of the cells and the amps flowing through them as data points for making the calculaton I think. Erratic amp readings lead to erratic internal resistance calculations and thus erratic weak cell error messages.


Well it has been 24 hours and I don't have an error. By disconnecting the shunt on the Orion I probably have disabled 50% of the benefit of the Orion. I will get no internal resistance and I will get no SOC calculation or any over current calculations. It sounds like Canbus communication will be cripppled so no point in hooking up a CANbus charger. Essentially I will have a crippled Orion that can do cell balance and when connected to a PC will let me see individual cell voltages. My JDL 5740 will control power to my charger based on limits set in the JDL not in the BMS.


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