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mzfly avatar image
mzfly asked

Phoenix inverter 12/250 in overload at only 60W

I'm trying to supply a electric blanket with a nominal load of 60W at my Phoenix 12/250 inverter.

The blanket has 3 power steps selectable by a switch. Step 1 = 20W, step 2 = 40W and step 3 = 60W.


The inverter is connected via a bluetooth dongle with the Vitron app.

The app is showing the load of the inverter in all the steps of the blanket switch correct.

In steps 1 and 2 the inverter works ok, but in step 3 (60W also showen in the app) the inverter goes into overload after 1sec.

The app never showes more than 60W power in the app.

The DC current is at 5,5A measured at the battery

The blanket is working normal at a 230V wall outlet.


DC 100ah battery is full and new, inverter is connected with 10mm2 cable with aprox. 1m length.

DC level in the app and measured with voltmeter is always over 12V.


I don't understand where the problem is, becauce the blanket is drawing much less the the 200W allowed.


I tried the inverter with an electric drilling maschine up to 250W load. The inverter is working ok and also the app shows everything correct. DC current goes up to 20A as expected


Can you please help me to solve this miracle.


Thanks in advance mzfly


Phoenix Inverter
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mzfly avatar image mzfly commented ·

I did a little more of investigation. It seems that the electric blanket is only drawing power at one sine halfwave.

The blanket is working with a triac which does phase shift, but only at the positive sine half wave.

The negative half wave is not used to produce heat energy in the blanket, but is suppressed by a diode and is used to detect shortcuts in the blanket.


The function and protection unit of the blanket is descriped in an patent for more detail see: https://patents.google.com/patent/DE4315488C2/de


Can it be that this asymmetrical power usage is the cause that the inverter is going into overload at only 60W??

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mzfly avatar image
mzfly answered ·

Since nobody is coming up with a solution, I think I need to solve my problem myself :-))

I did some more research and this is the best technical explanation why the 200W inverter is going in overload at only 60W


Since my electric blanket is only using the positive sine half wave, it is working like a half wave rectifier.

A half wave rectifier only draws uni-directional current. This causes the magnetisation in the output core of the transformator in the inverter to get a DC bias, which shifts the mid point of the magnetisation curve away from zero.

The effect of this is that a high saturation current pulse is additional flowing, as well as the normal load current. The sum of this two currents are bringing the inverter into overload.


There are calculation formulas for transformators with half wave rectifiers in the internet, that say that a transformator needs to be 3 times oversized compared to transormators with symmetrical load.


So my 60W asymmetrical load x 3 is about the 200W max power the inverter can handle.


It is sad to say but I think that my electric blanket is the worst load for the inverter to handle.

And this is a problem for me, because this was the main usage case for me.

So my two girls will stay cold in the night in my camper :-((

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Paul B avatar image Paul B commented ·

O well looks like its time to look at a different Blanket

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ripper avatar image
ripper answered ·

Have you tried the blanket at a wall socket? Maybe it is malfunctioning. If you havent, assume it is broken while testing and be careful. Sounds like the third step - probably a third individual circuit- is shorted somewhere. Maybe it warms up something in the junction box and shorts out after a second.

As a resistive load there is no reason for the inverter to go to overload. It is the least demanding of loads.


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mzfly avatar image mzfly commented ·

Hallo ripper,

thanks for your reply.

As I already wrote in my first post the blanket is working without any problem at a wall socket. And the blanket is drawing only 60W in that one second before the inverter goes into overload.

But I did some more research. Please have a look to my comment at my first post.

Perhaps you can bring some light into the dark.

Thanks in advance mzfly

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Paul B avatar image
Paul B answered ·

Have a look at the voltage outputs that go directly to the Blanket, These maybe say 12 Volts DC


and if so you could directly power the blanket from the Battery.


I would suspect for safety reason that the blanket would not have hi voltage going into it ie 120 or 220 volts AC


Direct DC should be ok as its a restive load,

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mzfly avatar image mzfly commented ·

Thanks for the hint, but the electric blanket wir running on 230V.

The controlling unit looks like this:

The red marked resistor R33 is the heating resistor with 100W.

And it is directly driven bei 230V over a phase shift triac T1.


As explained in the blanket with R33 there is also a diode, so only the positive sine half wave is used, and this results in the asymetrical load at the transformator of the inverter.

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elblanket.jpg (114.8 KiB)
moe avatar image
moe answered ·

Hi Mzfly,

thank you for your research! I have a similar problem. In my case it es a Vidabelle electrical blanket (60W) for my rooftoptent, and the Victron Phoenix 12/500 in my car. The behavior is the same, the blanket starts, the victron connect app shows a low usage (much less than 60W), and after a second the inverter stops with "overload".

If my blanket is also only using the positive sine half wave and I have to multiply the power with 3, I get 180W, my 12/500 should handle that. Why it doesnt work?

I have also a Suaoki G500, a mobile power station with a "300W pure sine wave ac". If I connect the blanket to this box, it works.

So I have a workaround, but ist would be nice, if it would also work with the Victron Phoenix. Any ideas?

Greetings from Germany

Maurice

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k-k avatar image k-k commented ·
@moe @mzfly just as idea: place a MP-condenser in line, just before the heating resistor. If you have an oszi look for the pulseform to get a good fit - i have no clue to calc a dimension üF or mF.

Or, just for testing: put a (de: waschmaschinen anlaufkondensator einfach in reihe zur ganzen schaltung um dc abzublocken)


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