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Inrush current limiter... How to do it?

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Clarkdale44

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Hello...

I have an DC to AC inverter, which is capable of outputting 600 Watts at margin. I have a few inductive loads that causes the inverter to overload and restart (after restart the load works fine). Although it only takes 1 second approx but still it's annoying...

My inverter can run all the load without a problem when overall current the equipment are consuming is at normal.

I believe i need a NTC for this type of problem... But i don't know how to calculate which part i need and how to make it's connection.

my AC voltage is 230V 50Hz

I would really appreciate if someone could give me the basic idea.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks the link is quite helpful...


Its my old 20" CRT TV.
I would suggest fitting a switch on the deguass circuit of the TV, as the deguass circuit takes a large switch-on surge when the TV is turned on from cold.

You can easily check if this would help - plug the TV in normal mains, and turn it ON for a few minutes (until it's hot). Then disconnect the mains and immediately connect the inverter and see if it starts OK. If it does, then fitting a switch to the deguass circuit would cure your problem.
 

Clarkdale44

Member
plug the TV in normal mains, and turn it ON for a few minutes (until it's hot). Then disconnect the mains and immediately connect the inverter and see if it starts OK
Thanks but i have already tried this. No matter how long the TV runs on mains, if it's power source is suddenly switched to inverter, that still causes inverter to overload and restart.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks but i have already tried this. No matter how long the TV runs on mains, if it's power source is suddenly switched to inverter, that still causes inverter to overload and restart.
OK, it's not the deguass then.

There's usually some kind of surge limiter in the TV, in series with the bridge rectifier - either a wirewound resistor (4.7 ohm was common) or an NTC thermistor - replacing it with a higher value resistor might help your problem.

However, binning the antique and replacing it with something vaguely 'modern' is probably the way to go :D
 

ci139

Active Member
the CRT takes some 3x and maybe peaking +2x more of it's normal operational power at startup but i'd guess the 600W should be more than enough for all that . . .
. . . the http://energyusecalculator.com/electricity_lcdleddisplay.htm shows 90W (assume 270W (flash 540W) for few seconds at startup) (my 15' past millennium PHILIPS consumes 60W) ??? . . . if that is that flash to near 600W that causes the inverter to shut down then even a small limiting would be sufficient . . . i assume but i can't confirm
 

Clarkdale44

Member
However, binning the antique and replacing it with something vaguely 'modern' is probably the way to go :D
Yeah i know... but as i said it's an old TV which i just use it the way it is occasionally. Also opening it up is not an option for me. So i was looking for an external solution.

I was thinking of using an NTC thermistor but to do that i am gonna need to know the exact inrush current value, how do i measure that? I don't have the required equipment.
I had an old thermistor lying around at home NTC 5D 09(5 ohm 3 A), i tried using that and it wasn't making any difference. If i go for the higher value, it would only be trial and error.



the CRT takes some 3x and maybe peaking +2x more of it's normal operational power at startup but i'd guess the 600W should be more than enough for all that . . .
. . . the http://energyusecalculator.com/electricity_lcdleddisplay.htm shows 90W (assume 270W (flash 540W) for few seconds at startup) (my 15' past millennium PHILIPS consumes 60W) ??? . . . if that is that flash to near 600W that causes the inverter to shut down then even a small limiting would be sufficient . . . i assume but i can't confirm
Thanks... I tested with my clamp meter set at 20A, upon turning on the TV for a split second i saw my meter going over 20A mark on the clamp.... I am not sure if it's correct it is just my assumption.... But we can't be sure until i have the right equipment for the job.

I am currently using UNI-T UT210E and it doesn't have any inrush or min/max function. Should i consider buying a new one with this feature? Or is there any other way i could find peak current with my existing clamp?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Try fitting a big wirewound resistor externally - it's wattage depends on the value you find that you need.

As I mentioned before, 4.7 ohm was a common value inside a TV set, and was usually 7W.

If you could get a bunch of 4.7 ohm 7W resistors you could keep adding them in series with the feed to the TV until you get to a high enough value to make it work.
 
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