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fans bad for inverters?


Dex_

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Hi,

just a really simple question I guess, are fans bad for inverters? I am particularly referring to fans with speed settings and running them at 1/3 speed for example.

Or is it not that simple, is it only when actually inverting and when using grid or PV it is fine etc?

TIA

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Hi Dex

I don’t think a fan is bad for an inverter.

I do know that a fan might not like a certain type of inverter. If I run my fan on a square sine wave inverter it makes a noise like it is struggling. On my pure sine wave inverter, it runs perfectly. 

Describe your situation in a bit more detail..

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1 hour ago, Solaris said:

Hi Dex

I don’t think a fan is bad for an inverter.

I do know that a fan might not like a certain type of inverter. If I run my fan on a square sine wave inverter it makes a noise like it is struggling. On my pure sine wave inverter, it runs perfectly. 

Describe your situation in a bit more detail..

from a recent post somewhere (I can't find it) it was mentioned that when a diode rectifier is used it causes power only to be drawn every second cycle etc and can cause damage inside the inverter.

This is more just for understanding rather than an actual current issue I have.

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On 2019/09/23 at 4:39 PM, Dex_ said:

running them at 1/3 speed for example.

I believe that 3-speed fans should be fine; they have separate windings that can be switched in to generate a different load, but still a normal load.

Really cheap 2-speed fans might use the diode trick, that that could be bad for the inverter. I would certainly avoid those on any inverter where the grid isn't in parallel with the load.

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4 hours ago, Coulomb said:

I believe that 3-speed fans should be fine; they have separate windings that can be switched in to generate a different load, but still a normal load.

Really cheap 2-speed fans might use the diode trick, that that could be bad for the inverter. I would certainly avoid those on any inverter where the grid isn't in parallel with the load.

do you perhaps know the mechanics behind this? It seems like a chance to learn sommin :)

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4 hours ago, Coulomb said:

I believe that 3-speed fans should be fine; they have separate windings that can be switched in to generate a different load, but still a normal load.

Really cheap 2-speed fans might use the diode trick, that that could be bad for the inverter. I would certainly avoid those on any inverter where the grid isn't in parallel with the load.

Do you know how one could tell? is it primarily when there are 2 speed settings?

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18 hours ago, Dex_ said:

is it primarily when there are 2 speed settings?

Well, yeah. The diode is good for only one setting: half power. You can't do thirds or any other fraction with a diode. It also needs a "cheapness and nastiness" factor 😮

The proper thing would be to use a current probe on a DSO, but not many of us have one of those lying around. (I used to have access to one or two where I worked).

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On 2019/09/24 at 10:53 AM, Dex_ said:

from a recent post somewhere (I can't find it) it was mentioned that when a diode rectifier is used it causes power only to be drawn every second cycle etc and can cause damage inside the inverter.

Some devices (most common are Hair dryers and heat guns) use a diode rectifier for the low speed setting. Basically what this does is allow the device to only draw current during one half of the AC cycle, so the average voltage that the device gets is halved. The problem with this approach is that it is actually drawing current with a DC average. (This is different to things like light dimmers that draw current for a small portion of each half-cycle and so the average is still 0). Having a DC average on the AC current is bad for transformers, it will cause them to saturate and draw very large currents from the inverter which could damage the inverter if it's protection isn't good enough. I have tested an SMA sunny Island with a heat gun on half speed and it didn't even seem to care, but they do have a hall-effect sensor on the low voltage side of the transformer, so I suspect they are doing something very clever like adding a DC offset to their PWM to counteract the DC average of the output current. Most other inverters will either make a terrible noise, or trip or blow up.

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42 minutes ago, Stanley said:

Some devices (most common are Hair dryers and heat guns) use a diode rectifier for the low speed setting. Basically what this does is allow the device to only draw current during one half of the AC cycle, so the average voltage that the device gets is halved. The problem with this approach is that it is actually drawing current with a DC average. (This is different to things like light dimmers that draw current for a small portion of each half-cycle and so the average is still 0). Having a DC average on the AC current is bad for transformers, it will cause them to saturate and draw very large currents from the inverter which could damage the inverter if it's protection isn't good enough. I have tested an SMA sunny Island with a heat gun on half speed and it didn't even seem to care, but they do have a hall-effect sensor on the low voltage side of the transformer, so I suspect they are doing something very clever like adding a DC offset to their PWM to counteract the DC average of the output current. Most other inverters will either make a terrible noise, or trip or blow up.

I think your initial post was the one I was looking for :)

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