Electric interference from inverter.

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Riwi
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Electric interference from inverter.

Post by Riwi »

Hi!

Got my nissan leaf motor and inverter installed in the boat. All works fine except that Im getting electric interference on the boats 12V system when the inverter is running/switching. I first noticed that the Oled display to the ennoid BMS started to "drop pixels" when I put the motor in fwd or rev.

BMS and Inverter share the same 12V. The Oled display is directly coupled to the BMS board and it runs of 3.3V.

I have routed the HV cables close to each other to minimize magnetic fields, but I have not put any ferrite-cores or filters into the system.
Any tips/ideas?

Any tips?

BR

Rikard
Reid0102
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Re: Electric interference from inverter.

Post by Reid0102 »

Riwi wrote: Thu May 05, 2022 12:32 pm Hi!

Got my nissan leaf motor and inverter installed in the boat. All works fine except that Im getting electric interference on the boats 12V system when the inverter is running/switching. I first noticed that the Oled display to the ennoid BMS started to "drop pixels" when I put the motor in fwd or rev.

BMS and Inverter share the same 12V. The Oled display is directly coupled to the BMS board and it runs of 3.3V.

I have routed the HV cables close to each other to minimize magnetic fields, but I have not put any ferrite-cores or filters into the system.
Any tips/ideas?

Any tips?

BR

Rikard
here are just some random thoughts.

Have you grounded the hull or have some sort of dump load for the static build up from the hull touching and running through the water? this should be so small it shouldn't be a problem.

are you using shielded cables? they are more expensive, but can also help with this.

some filters could help and if it is inboard then you can line the compartment too, but this is extreme and probably not necessary.

* after thought water can magnify magnetic fields if you have a metal hull then that can cause interference or the static buildup can increase noise in the system. fiberglass hulls less likely, but can still build up static charge which can damage sensitive electronics.
Riwi
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Re: Electric interference from inverter.

Post by Riwi »

Hi!
The hull is mahogany, and it has not touched the water yet.
Cables between battery and inverter are unshielded, so that might be an issue to look into.
Im thinking that the interference comes from the actual switching done by the inverter. If this is the case, it should show up as ripple on the 12V dc line.
I ordered an oscilloscope so that I can look at the 12v when the inverter is in opmode run and compare.
Reid0102
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Re: Electric interference from inverter.

Post by Reid0102 »

Riwi wrote: Thu May 05, 2022 4:19 pm Hi!
The hull is mahogany, and it has not touched the water yet.
Cables between battery and inverter are unshielded, so that might be an issue to look into.
Im thinking that the interference comes from the actual switching done by the inverter. If this is the case, it should show up as ripple on the 12V dc line.
I ordered an oscilloscope so that I can look at the 12v when the inverter is in opmode run and compare.
okay, just some more random thoughts. So probably not much issue from the hull then. try shielded HV cables and that should help some and you can also shield all HV junction points. and then If the problem still presets then get proper size for power and ground and have them be a twisted pair and then shield them, use thick aluminum foil for testing that runs the full length and roll them and tape them. Another thing you can do is shield the LV loom and then ground the loom itself. That should take care of most of the issues for noise. the cables and junction points are prime things that will cause a lot of noise. and then if all else fails then you can shield the inverter itself and motor if it is outboard then may be a little more difficult or you can line the motor compartment if its inboard.
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celeron55
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Re: Electric interference from inverter.

Post by celeron55 »

One thing that's not usually done but which could help is coupling HV+ and HV- to ground via capacitors near the inverter terminals. I think this should have a considerable effect on reducing interference from the inverter to the BMS, but haven't tried it myself.

Some kind of low capacitance high frequency capacitors should be used for this application, but I'm not sure exactly what.

The definite first thing to do is making sure the inverter to motor cables are shielded, but I'm thinking you already have that done.

It's often difficult to figure out the source of interference using an oscilloscope, don't expect it to be the magic bullet. The solution usually is to try to think through the system, figuring out what components are most prone to interference, are they wired appropriately and which wires are most prone to causing the interference.

Every component has its own tolerance for voltage spikes, and every switched wire will capacitively couple to other wires according to the switched voltage, and inductively based on the switched current. I think an inverter generally causes capacitive interference, not much inductive.

In addition to this, the inverter can create a high frequency voltage through the battery pack, via the wires themselves, because they are long, have inductance and thus conduct high frequency currents poorly. This causes high frequency voltages between cell terminals (according to the cell-to-cell interconnect wire length) and can mess up BMS communication if the BMS cannot tolerate this between cells or modules. The solution is to design the cell interconnect wire lengths according to what the BMS supports, and possibly to add high frequency capacitors to the inverter terminals - possibly to ground, like I mentioned at first, to get some extra benefit.
Reid0102
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Re: Electric interference from inverter.

Post by Reid0102 »

celeron55 wrote: Thu May 05, 2022 5:22 pm One thing that's not usually done but which could help is coupling HV+ and HV- to ground via capacitors near the inverter terminals. I think this should have a considerable effect on reducing interference from the inverter to the BMS, but haven't tried it myself.

Some kind of low capacitance high frequency capacitors should be used for this application, but I'm not sure exactly what.

The definite first thing to do is making sure the inverter to motor cables are shielded, but I'm thinking you already have that done.

It's often difficult to figure out the source of interference using an oscilloscope, don't expect it to be the magic bullet. The solution usually is to try to think through the system, figuring out what components are most prone to interference, are they wired appropriately and which wires are most prone to causing the interference.

Every component has its own tolerance for voltage spikes, and every switched wire will capacitively couple to other wires according to the switched voltage, and inductively based on the switched current. I think an inverter generally causes capacitive interference, not much inductive.

In addition to this, the inverter can create a high frequency voltage through the battery pack, via the wires themselves, because they are long, have inductance and thus conduct high frequency currents poorly. This causes high frequency voltages between cell terminals (according to the cell-to-cell interconnect wire length) and can mess up BMS communication if the BMS cannot tolerate this between cells or modules. The solution is to design the cell interconnect wire lengths according to what the BMS supports, and possibly to add high frequency capacitors to the inverter terminals - possibly to ground, like I mentioned at first, to get some extra benefit.
Great advice
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Re: Electric interference from inverter.

Post by arber333 »

Riwi wrote: Thu May 05, 2022 12:32 pm Hi!

Got my nissan leaf motor and inverter installed in the boat. All works fine except that Im getting electric interference on the boats 12V system when the inverter is running/switching. I first noticed that the Oled display to the ennoid BMS started to "drop pixels" when I put the motor in fwd or rev.

BMS and Inverter share the same 12V. The Oled display is directly coupled to the BMS board and it runs of 3.3V.

I have routed the HV cables close to each other to minimize magnetic fields, but I have not put any ferrite-cores or filters into the system.
Any tips/ideas?

Any tips?

BR

Rikard
Everything should share the same GND with exception of HV DC wires.
1. If you can twist your DC cables so you get twisted pair = differential wiring.
2. Shielding is not usefull if you do not have somewhere to ground it. So connect inverter case and motor via a good short 16mm2 cable so both are on the same potential. Then try to connect your 12V battery negative pole to either motor or inverter so that you create direct route for EMI to flow to.
3. Try to enclose motor/inverter into a steel box/mesh which would be connected to 12V minus... Attention holes in a mesh need to be smaller than weave length of inverter frequency.
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Re: Electric interference from inverter.

Post by johu »

I'm assuming we're talking a Gen2 inverter, so no wire between motor and inverter?
I never shielded DC cables but it does cause issues. I had to reroute the CAN cables further away from the power cables.

It may be cheaper to shield the 12V wires instead of shielding the DC wires.

OEM systems have super tight shielding. The full Faraday cage from battery box to inverter and motor.
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Reid0102
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Re: Electric interference from inverter.

Post by Reid0102 »

johu wrote: Thu May 05, 2022 5:56 pm I'm assuming we're talking a Gen2 inverter, so no wire between motor and inverter?
I never shielded DC cables but it does cause issues. I had to reroute the CAN cables further away from the power cables.

It may be cheaper to shield the 12V wires instead of shielding the DC wires.

OEM systems have super tight shielding. The full Faraday cage from battery box to inverter and motor.

Overall that is what I was thinking that the OEMs have to meet a certain THD so the shielding is pretty decent overall. I would also think it would be cheaper to shield LV cables.

If he is getting a scope that is capable of THD then couldn't they use that feature to see if what they are doing is effective or not?
Riwi
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Re: Electric interference from inverter.

Post by Riwi »

Gen2 is correct, not wires between inv and motor.

Can is OK (tc-charger <- ennoid bms). But if I remember correctly can is isolated on the ennoid bms.

I cant remeber if i have a connection between the chassi of the inv/motor and 12v gnd. I need to check that.
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celeron55
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Re: Electric interference from inverter.

Post by celeron55 »

The motor and inverter castings are basically shields also and should be connected to cable shields, so they need to be grounded. Also, don't skimp on the ground wire thickness. I'd use something like 16mm2 minimum.

That's really the easy part. If you shield everything, then the entire HV system is invisible to the 12V system. The hard part is interference within the battery pack, where the HV and BMS wires meet both physically and electrically. Similar issues are possible in DC charge ports also altough I'm not sure I've actually heard of any.
Riwi
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Re: Electric interference from inverter.

Post by Riwi »

celeron55 wrote: Fri May 06, 2022 10:31 am The motor and inverter castings are basically shields also and should be connected to cable shields, so they need to be grounded. Also, don't skimp on the ground wire thickness. I'd use something like 16mm2 minimum.

That's really the easy part. If you shield everything, then the entire HV system is invisible to the 12V system. The hard part is interference within the battery pack, where the HV and BMS wires meet both physically and electrically. Similar issues are possible in DC charge ports also altough I'm not sure I've actually heard of any.
The BMS I use, Ennoid LV 36s, is not isolated so "hv-ish" and 12v share the same ground.
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Re: Electric interference from inverter.

Post by celeron55 »

In that case you probably have to use a star configuration for your grounds. Don't connect the ground of any processor boards or displays to the opposite ends of the high power ground. And route those processor grounds far from the high power ground.
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Re: Electric interference from inverter.

Post by johnspark »

You can use large cables for the earth shielding, this helps reduce inductance and greater transference of electrical noise to the ground.
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