Inverter anomaly: Hair dryer causing overload (39 Viewers)

[offagen]

OP here. Just as a follow-up to my query and posts back in March of this year: I decided eventually to bite the bullet and take the MH to the great guys at Offgrid Power Solutions. There the pair of AGMs were replaced with a single 280Ah Fogstar Drift lithium battery. Everything was rewired, including the Victron 1200VA inverter, and a Victron Orion XS 50A DC-DC charger was added. All done to a very high standard.

Interestingly, this did not address the issue with the hairdrier. As before, the drier will run OK on the first setting but then when switching to the next, slightly hotter setting the inverter cuts out after a couple of seconds. I've since added a Bluetooth dongle to the inverter so I can monitor events in the Victron app. It indicates overload when the second heat setting is selected. The conclusion is that the hair drier manufacturer didn't give the full story when quoting wattage and current draw. However, the strange thing is that the drier only draws 39 amps on its lowest setting (which is quite warm rather than cool) so the next heat setting must draw a lot more current to trip the inverter - or the inverter is faulty*.

The good news is that the boss finds the first, fairly warm, setting of the drier to be quite adequate to dry her hair so I'm not going to fret over the lack of higher heat settings.

FWIW I am totally happy with the outcome of the work carried out by Offgrid regardless of hair drier performance.

* The inverter works fine with an electric kettle, a toaster and various battery chargers so doesn't appear to be faulty.

 

[Purrfecttune]

OP here. Just as a follow-up to my query and posts back in March of this year: I decided eventually to bite the bullet and take the MH to the great guys at Offgrid Power Solutions. There the pair of AGMs were replaced with a single 280Ah Fogstar Drift lithium battery. Everything was rewired, including the Victron 1200VA inverter, and a Victron Orion XS 50A DC-DC charger was added. All done to a very high standard.

Interestingly, this did not address the issue with the hairdrier. As before, the drier will run OK on the first setting but then when switching to the next, slightly hotter setting the inverter cuts out after a couple of seconds. I've since added a Bluetooth dongle to the inverter so I can monitor events in the Victron app. It indicates overload when the second heat setting is selected. The conclusion is that the hair drier manufacturer didn't give the full story when quoting wattage and current draw. However, the strange thing is that the drier only draws 39 amps on its lowest setting (which is quite warm rather than cool) so the next heat setting must draw a lot more current to trip the inverter - or the inverter is faulty*.

The good news is that the boss finds the first, fairly warm, setting of the drier to be quite adequate to dry her hair so I'm not going to fret over the lack of higher heat settings.

FWIW I am totally happy with the outcome of the work carried out by Offgrid regardless of hair drier performance.

* The inverter works fine with an electric kettle, a toaster and various battery chargers so doesn't appear to be faulty.

I had exactly the same fitted by Offgrid two days ago! (Plus a 185w solar panel to go with the already fitted 100w).

Tested today with kettle, toaster, microwave and hairdryer, all worked great

 

[Gromett]

There are a few possible explanations, all depending on how the hairdryer manufacturer actually reduces the load to achieve the lower setting.

Option 1

There aren't different resistance coils inside the hair drier for each power setting (in your case just two). Just a single 880W element, and then a switching circuit that cuts the power in and out. 1/2 of the cycle for 440W, full cycle for 880W.

The way to measure this is with a high frequency oscilloscope. Multimeters and the built in measurement of the inverter are not fast enough to see high currents for a fraction of a second (they will show the average over a cycle, or even multiple cycles, which are happening 50 times per second).

The overload circuit is fast enough to react to a potential overload though, which is what you're probably seeing on the lower setting.

Option 2

Sometimes, in order to reduce power on first stage, the hair dryer may use a simple diode to power the resistive element only by one side of the sine wave.

This could be very tricky for many inverters, because it is a very unbalanced load.

There might be other explanations that I’m not aware of.

In a nutshell, it all depends on how your dryer implements the lower setting. If it truly has two heating circuits and the switch switches on only one or both of them then the results are surprising.
If your dryer implements it using some “clever” electronics then the above explanation would hold.

One thing is clear though, on the higher “simple” draw the inverter is coping. So the inverter is providing enough for a 1000w dryer.

Most interesting. Thanks.

I hadn't considered manufacturers doing anything other than having 2 PTC elements. That is the simplest and easiest solution. Adding electronics adds to the cost of production and hits bottom line with practically no benefit that I can think of. Hence me not even considering those possibilities. Seems I was thinking like a business owner and not an engineer. That is something I find disappointing in myself

 

[Raul]

As RogerIvy explained it well, the modulation of the hair dryer is soooo crap, that it throws allot of harmonic distortion back into the inverter, and reactive power. The inverter protects itself from anything lower than 0.8 power factor.
Use the drier on its high setting, or look for a quality hair drier.
If anyone knows anymore more, please add.

 

[RogerIvy]

Most interesting. Thanks.

I hadn't considered manufacturers doing anything other than having 2 PTC elements. That is the simplest and easiest solution. Adding electronics adds to the cost of production and hits bottom line with practically no benefit that I can think of. Hence me not even considering those possibilities. Seems I was thinking like a business owner and not an engineer. That is something I find disappointing in myself

We had a very similar experience with a heat gun that has two settings. When using the lower setting the 2000va Multiplus made such a racket, when on the higher setting all was fine.

I suspect that it's cheaper to use a diode (not very complicated) than two heating coils. I suspect that would be the "standard" approach when an appliance has two settings. No evidence to back this up ... but it does make sense (to me anyway).

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[Gromett]

We had a very similar experience with a heat gun that has two settings. When using the lower setting the 2000va Multiplus made such a racket, when on the higher setting all was fine.

I suspect that it's cheaper to use a diode (not very complicated) than two heating coils. I suspect that would be the "standard" approach when an appliance has two settings. No evidence to back this up ... but it does make sense (to me anyway).

Interesting thoughts.
Not sure that a diode + switch would be cheaper than a double length of PTC wire? Although perhaps you need to keep the elements a minimal distance apart so the increased size of the ceramic mountings may add up?

I honestly don't know. Would have to get one of the ladies on here to open one up when it was end of life and take a few pictures for our entertainment and education.

But to be honest, your idea about it being a half wave rectifier completely explains why the inverter doesn't like low power but handle high power perfectly, so I suspect you are correct.
Just seems an awfully strange way to do it to my mind.

 

[Raul]

We had a very similar experience with a heat gun that has two settings. When using the lower setting the 2000va Multiplus made such a racket, when on the higher setting all was fine.

I suspect that it's cheaper to use a diode (not very complicated) than two heating coils. I suspect that would be the "standard" approach when an appliance has two settings. No evidence to back this up ... but it does make sense (to me anyway).

On small inverters this a problem, as I mentioned above, they don't like small power factor.
I have a screwfix Titan 3 heat modes running of 10kva multiplus, and all the loads in the house, not a problem as the inverter can cope with such poor loads. It's the balance of the reactive power from load to the apparent power of supply.

 

[Gromett]

On small inverters this a problem, as I mentioned above, they don't like small power factor.
I have a screwfix Titan 3 heat modes running of 10kva multiplus, and all the loads in the house, not a problem as the inverter can cope with such poor loads. It's the balance of the reactive power from load to the apparent power of supply.

That raises a question in my mind. A hair dryer even with a diode would surely still be a resistive load? This would indicate a unity power factor from memory (been a long time).
I believe you are correct on inverters not liking poor power factors. But I don't think that is the issue here? There is no inductance or capacitance in a hairdryer or hotair gun I wouldn't have thought?
And from memory power factor is only affected by an inductive or capacitive load putting the voltage and current out of phase with each other?

Been a very long time since I did my electronics engineering training/courses and my memory of the details are starting to fade over the last few years sadly.