Dead head regarding fans? 1

[MechEng92]

Please could someone explain to me how dead heading relates to centrifugal fans in simple terms? I'm struggling to get my head around it.

Thanks

 

[MechEng92]

Morning all,

It's a fixed control signal, we send the voltage signal to the fans. When we set it to 10V and the fan speeds up, it's cutting out at around 9.4V due to overheating on the motor from high current.

We're going to get the supplier in to take a look soon and give us their insight. I would have thought if the pressure resistance is on the low side that would suggest the fan motor is oversized would it not?

 

[LittleInch]

Mech eng92.

So the 10V is a control/ speed signal?

What's the power of the actual fan?

But no, if pressure resistance is less than the fan was designed for then it will flow more air at possibly a lower efficiency and hence need more power.

Hence why you need to look at and post the fan curves and data sheet.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MechEng92]

Sorry I wasn't available over the weekend hence why I'm responding this morning.

And I've already stated a lot of this work is confidential and IP so I can't share specifics like data sheets.

 

[LittleInch]

Without pump curve and knowledge of the motor power is difficult to say any more.

We're not asking for details of the whole thing, just the fan.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[HVAC-Novice]

"this work is confidential and IP"

LOL, no one is trying to steal the design of a system that doesn't appear to be working.

You should hire an HVAC engineer to look at that. You probably should provide them with more information than here.

 

[LittleInch]

So if you can't share even the fan curve then we're a bit stuck. i struggle to see how that is confidential or has some sort of IP.

It still sounds like you are running the fan beyond its maximum flow and the motor was not designed to do that. Does that make sense?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Rputvin]

We usually see overcurrent issues on EC fans when the driving signal has a parameter mismatch within the fan. For example, we had a fan that for some reason was setup for 2-10V control, but with an internal scale setup for 2-8v, so when 10v was applied the fan was attempting above-nameplate operation and internally cutting itself off. This has been an issue with parameters set by the user, and by the factory - we had a batch with the wrong configuration from the factory that just needed to be updated to the correct settings. I've also seen similar behavior from a fan programmed for 480v, but receiving 230v with double the amps - as long as the control power is generated the fan doesn't know the incoming voltage, only current.

I would recommend all of the fan settings and parameters are verified to the motor nameplate and the method you're attempting to use for control.

Is the motor *actually* overheating at 9.4V, or is the fan detecting "overcurrent" from its max setting and giving you an overheat error since that's just the designated fault for that condition? No way to tell without checking the actual current draw and comparing to the settings in the fan.

 

[MechEng92]

I'll check tomorrow if the control signal can be checked but thank you very much this has probably been the most helpful response so far. We do have the fan supplier coming in soon to check what the issue could be also.

 

[HVAC-Novice]

Rpuitn has a good point. There is 0-10V, 2-10V, and I also have used ECM that used 1-5V. I don't know if going above 5V would have meant the motor going over 100% or if it is internally capped.... unfortunately this all isn't standardized and you need to know exactly what the control signals are.

And we still don't know if that fan gets controlled based on anything. Is it just used a constant speed fan? in that case the ECM manufacturer usually has a potentiometer attached to the fan. but if OP isn't able to provide any information on the system, someone local has to look at that

Should hire an engineer anyway, since we are just some ID10Ts on the internet. and if all relevant data are a secret, we can just guess.

 

[MechEng92]

It's just a fixed fan speed, this scenario has happened on end of line test where the fans are manually set to 10V, as it has ramped up towards 10V (max. fan speed) it's shut down due to overheating at around 9.4V

 

[Rputvin]

All 6 fans behaved the same?

First step is verify the actual current draw and check against nameplate. It's very possible your vendor gave you overloading fans. I've never seen it, and it would be really dumb, but the EC fan space went from <5 suppliers a few years ago to 20+ now. Lots of that I imagine are copycat products without the engineering to back anything up.

If you're not pulling over nameplate I would put a healthy bet on there being a parameter out of place.

 

[MechEng92]

Unsure if all fans are behaving the same but certainly more than one of them. I'll ask them to check the measurements against the name plate. Thank you

 

[IanVG]

Just putting in my two cents here. If your system resistance is too low for a given fan or pump, you can "ride off the end" of the fan or pump curve. There are regions of fan and pump curves that you want to avoid, hence the need for a good calculation of overall system drop. If you notice, the brake horse power (the actual power being delivered by the fan or pump to the fluid), increases as flow increases. Ideally, as someone mentioned, the manufacturer should be selecting a motor that can handle the entire fan curve, not just the duty point. I'm attaching a little curve I drew a few years ago to help myself understand where and why to select a fan (and in part, its motor). If you notice a note of mine states: "Minimum S.P. [Static Pressure] for operating fan at minimum CFM." This means that if you don't have enough static pressure in the system to resist flow, your fan will overflow and correspondingly, draw more amps from the motor. That is my best understanding. It does seem that tracking down control problems with the input volt signal to the motor is a good first step. Mechanically, my instinct is to assume that the controls are fine and that something needs to be double-checked from a pressure-flow perspective!

 

[Heaviside1925]

This thread was a good read. I remember when EC motors first came on the market and my initial thought was electronics in the motor housing in heavy industrial use = no bueno. For this application among others, I can see where they would be a good choice until you're trying to troubleshoot one. I am hoping OP will be back with the answer to his problem.

 

[MechEng92]

Unfortunately no answer as to why it's behaving this way. It seems that the design team are going to limit the fan to a maximum control voltage based on the installation to get around it. So instead of 100% fan speed being the maximum it'll be more like 90%