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AC current limiter

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MaximRice

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I am powering a small inverter with a 12 volt battery. The output of the inverter is 120 VAC at 60 Hz. I need to limit the AC current to about 10 to 50 milliAmps, but the voltage and frequency must remain stable at 120 VAC and 60 Hz. Is there a simple way to use a capacitor to do this, or can you suggest another circuit that would work? Thanks.
 

alec_t

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Welcome to ETO!
A 1uF cap would limit the current to ~45mA.
As for voltage stability, are you referring to the voltage of the source or that across the load?
 

crutschow

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Most Helpful Member
Why do you need to limit the current?
What is the load?
 

spec

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Most Helpful Member
I am powering a small inverter with a 12 volt battery. The output of the inverter is 120 VAC at 60 Hz. I need to limit the AC current to about 10 to 50 milliAmps, but the voltage and frequency must remain stable at 120 VAC and 60 Hz. Is there a simple way to use a capacitor to do this, or can you suggest another circuit that would work? Thanks.
Hy MR,

Could you post a schematic of your inverter.

A simple way to limit the output current from a 12V to 120V AC inverter would be to limit the input DC current, but this is just off the top of my head without seeing a schematic.

spec
 

Les Jones

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You say that you want limit the current drawn by the load but you also say that you do not want to reduce the output voltage of the inverter. Without allowing the inverter to drop it's output voltage then it has no way to control the current through the load. If the output voltage remains at 120 volts then the current is only determined be the reactance of the load. Giving more details of what you ar trying to achive would be a great help in trying to solve your problem. What is the nature of the load on the inverter and is there only the one load ? If there are multiple loads on the inverter and you only want to limit the current through one load without effecting all the other loads then it should be possible to deisign something to do this but it will have to reduce the voltage to the load whose current you want to limit.

Les.
 

MaximRice

New Member
Thanks for the suggestions. Let me give you more detail.
I have a solar array fed into an inverter (120 VAC output) that in turn goes to standard loads AND charges a 10 kWh battery bank. The main inverter is of the grid-tied type, which means that if it does not sense 120 VAC 60 Hz from the grid, it shuts down. I want to use the PV array and inverter OFF GRID, so there is no grid voltage to keep the inverter on. Since I cannot afford to replace the inverter ($2000+) with a non-grid tied model, I am trying to fool the inverter by connecting a very small (inexpensive) inverter (powered by a small 12 VDC gel cell) to the main inverter so it thinks it is connected to the grid. But I need to keep the current from the small inverter low so that when the sun goes down the main inverter does not draw down the little 12 volt battery, which would quickly shut down the system. I also need to keep the current flow between the two inverters very low so that the small inverter is not damaged by back flow from the main inverter.
So I'm trying to limit current flow both ways between the two inverters to maybe 10mA, but keep the voltage at 120 VAC and 60 Hz.
Many thanks to all the great minds tackling this problem!
 

tcmtech

Banned
Most Helpful Member
It won't work. GTI units are smart and safe enough to not fall for that trick once you put a load on it assuming it would stay connected to begin with.

Buy a dedicated power inverter and be done with it unless you want to run the high risk of doing damage to your expensive GTI unit.

Also, $2000 for a dedicated power inverter seems pretty high unless its some sort of high-end 10+ KW capable unit that has to run off some nonstandard input voltage.

What is the load you want to run off your battery bank and what does the battery bank do for the system now?
 
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