Harmonics and interference issues

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Thejake

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Residential Electrician
I did some searches and didn’t find an exact answer to the question I had so I figured I’d start a thread about harmonics and interference.
Here is the problem I’m having at a clients house: 5th floor condo unit, new Bosch heat pump installed on the roof (happens to be the roof of the unit), the heat pump uses an electronic inverter. When the heat pump kicks on it causes multiple banks of lights to flicker and strobe. All the lights effected are LED bulbs on Maestro dimmers. When I bypass the dimmer the problem stops. Only issue with that is; one the customer wants the dimmers, two it is also effecting the lights in the hood and a plug in heat blanket. The heat blanket has a small digital display and won’t work. This is a 208 system. I’ve checked the voltage with the system running and it’s still 208. The other interesting thing is the owner owns 2 units (501 and 502) both had new heat pumps and both are having the same issues. I checked the heat pump connections and everything is tight. I haven’t checked the main lugs in the panel but they appear fine, wire looks slightly snug and there is now discoloration or sign of heat damage on the wire. Let me know your thoughts
 
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Yeah, definitely a problem with the heat pumps. You or the HVAC installer needs to get with Bosch on this. Don't waste your time otherwise. I think the HVAC guy would have more clout but you know what's going on. Good luck with this one. Probably need a rep to come look at it unless it's a known problem.

-Hal
 
These sound more like EMI/RFI issues, and that is often a result of poor grounding practices on the equipment. When inverters are involved, you cannot rely upon grounding via conduits etc., you need a well connected ground wire from the inverter to the ground system, as well as from the motor direct to the inverter. Someone may have taken an NEC acceptable shortcut, but the NEC is not concerned with Common Mode noise and EMI/FRI issues, only safety.

That's the cheap / easy thing to check first. If you don't find anything, another option is to use a shielded isolation transformer ahead of the inverter, again with solid grounding of the transformer shielding / case.
 
hbiss said:
Yeah, definitely a problem with the heat pumps. You or the HVAC installer needs to get with Bosch on this. Don't waste your time otherwise. I think the HVAC guy would have more clout but you know what's going on. Good luck with this one. Probably need a rep to come look at it unless it's a known problem.

-Hal
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I have contacted Bosch and so has the HVAC company. They blew us off basically. Which sucks but now it’s my job to try and figure it out.
 
Thejake said:
I have contacted Bosch and so has the HVAC company. They blew us off basically. Which sucks but now it’s my job to try and figure it out.
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Well, no. The customer bought them from and had it installed by the HVAC company. So it's their responsibility to make it right. What's your involvement here? Were you asked to run power for them or were you asked to just look into the problem? Nothing like making their problem your problem.

So when "the you know what hits the fan" and the HVAC contractor ends up in court because the customer wants their money back plus damages you don't want any part of that to have your name on it. You need to put in writing that you checked the lights, dimmers, voltage, etc and nothing abnormal was found.

If the HVAC contractor can't get any satisfaction from Bosch that's their problem. They probably have legal recourse against their supplier and Bosch.

-Hal
 
Thejake said:
I have contacted Bosch and so has the HVAC company. They blew us off basically. Which sucks but now it’s my job to try and figure it out.
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hbiss said:
Well, no. The customer bought them from and had it installed by the HVAC company. So it's their responsibility to make it right. What's your involvement here?
..You need to put in writing that you checked the lights, dimmers, voltage, etc and nothing abnormal was found.
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If sparky wants to be a hero, let him try EMI filter kit or HF chokes in rooftop heat-pump disconnect enclosure.

If it works, and he gets paid for trouble, its all good. If other tenants install same heat pump, who they gona call?

Modern GFCI receptacles / GFCI SPA disconnects also have some degree of EMI filtering built in, for cord & plug appliances w/ switch-mode HE motors.
 
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Jraef said:
These sound more like EMI/RFI issues, and that is often a result of poor grounding practices on the equipment. When inverters are involved, you cannot rely upon grounding via conduits etc., you need a well connected ground wire from the inverter to the ground system, as well as from the motor direct to the inverter. Someone may have taken an NEC acceptable shortcut, but the NEC is not concerned with Common Mode noise and EMI/FRI issues, only safety.

That's the cheap / easy thing to check first. If you don't find anything, another option is to use a shielded isolation transformer ahead of the inverter, again with solid grounding of the transformer shielding / case.
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The unit does have a dedicated ground wire but the sub panel in each unit uses the conduit as it’s means of grounding.
ramsy said:
If sparky wants to be a hero, let him try EMI filter kit or HF chokes in rooftop heat-pump disconnect enclosure.

If it works, and he gets paid for trouble, its all good. If other tenants install same heat pump, who they gona call?

Modern GFCI receptacles / GFCI SPA disconnects also have some degree of EMI filtering built in, for cord & plug appliances w/ switch-mode HE motors.
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I’m being hired by the HVAC company to try and resolve. Originally all I did was reconnect the units, old unit was the same amperage. Bosch said they can’t replicate the problem and have only heard of this happening one other time. So currently the easiest, simplest and cheapest thing to do is to pay me to try and figure it out. That’s what I’m trying to do.

The conduit is being used as the ground, I’ll see if a bonding bushing helps. Another user messaged me about Ferrit chokes being a potential option that could help.
 
ramsy said:
If sparky wants to be a hero, let him try EMI filter kit or HF chokes in rooftop heat-pump disconnect enclosure.
Click to expand...

And who is going to pay for the materials and labor when that doesn't work? Is he just going to eat it and chalk it up to being a nice guy? Is sparky some kind of EE who knows anything about EMI filtering or HF chokes or even what's going on here?

No offense, but if Bosch can't figure it out you think you can?

Thejake said:
Bosch said they can’t replicate the problem and have only heard of this happening one other time.
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Yeah, well now you have three so get your engineers *** over and look at them!! The problem happens all the damn time!

Personally, I'm sick of garbage products starting with LEDs, AFCIs, A/C s and pool pumps that we think we are supposed fix when some engineer hasn't done their job and left beta testing to their customers.

-Hal
 
electrofelon said:
I gotta say, I am skeptical Jraef.....
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I agree. JRaef keeps claiming this everywhere with zero proof.

As a counter example,



The trouble with conduit as ground is that as far as engineering goes, it’s a very messy situation. It’s just not that easy to calculate. The above research is very enlightening though.
 
Jraef said:
These sound more like EMI/RFI issues, and that is often a result of poor grounding..
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If grounding path is not broken or high impedance, how much current is expected to flow from switch-mode electronics to the bonded frame?
 
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If you really want to solve this from an engineering point of view then you'd use a spectrum analyzer with a relatively wideband current probe to monitor the conducted interference from the inverter unit. That way you could identify the frequency range where the interference predominates, and then purchase or design an appropriate filter targeted to those frequencies.
Short of that you'd be limited to trial and error with ferrite chokes or LC filters.
A shielded isolation transformer like Jraef mentioned would likely be effective, but would also probably be the highest cost option for material only.
I'll let others consider the business issues of the situation.
 
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