# 110v 400w Current limiter

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#### Cameron_Toews

##### New Member
I have an inverter inside my pickup truck. It is rated at 110v ac and 400w. I want to be able to charge my batteries for my tools, but the inverters built-in protection cuts it off every time i plug the charger in. The charger only pulls 2.1A but it obviously has an inrush current which sends the inverter into protection. I'm looking to build a small device that would basically act as a current limiter, to minimize the inrush of the charger first trying to crank on. I'm picturing a standard plug that has male and female on it, acting as an inline device to limit current.

I figure i could use an ntc thermistor but my knowledge of these is very limited, i am an electrician by trade but have done some electronics work over the years but it has been sparse at best.

#### Colin

##### Active Member
Get a 1.2 amp-hr battery and put it on the output socket. Wait 1 min and now plug in the charger.

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#### Colin

##### Active Member
I was thinking the inverter would not start-up.

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#### MikeMl

##### Well-Known Member
Cameron_Toews and I were thinking of putting the CL in the 120V side of the inverter; not the 12V side...

Let's say you use a SL15 40004. It has a cold resistance of 40Ω, and a hot resistance of less than 1Ω. We dont know how much the inrush current to his charger is, but we do know that the steady-state current is about 2A. If the charger looked like a short, then the initial current would limited only by the 40Ω, so would be 120V/40Ω = 3A. Once the CL heats up and changes state, at the final charger current the voltage dropped across the CL is 1Ω*2.1A = 2.1V, which he can live with.

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#### ronsimpson

##### Well-Known Member
It has a cold resistance of 40Ω, and a hot resistance of less than 1Ω.
I have designed power supplies with these "inrush limiters".
Then the CL is hot it takes 48 seconds to cool off. (data sheet) From my experiance it takes longer. You have a load, unplug, wait 1 minute, plug in. It you don't wait the problem is not solved.

.

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#### MikeMl

##### Well-Known Member
I have designed power supplies with these "inrush limiters".
Then the CL is hot it takes 48 seconds to cool off. (data sheet) From my experiance it takes longer. You have a load, unplug, wait 1 minute, plug in. It you don't wait the problem is not solved.
The worst thing that will happen is that the inverter will shut down as it does now. Waiting for the CL to cool occasionally might be a bit inconvenient, but still better than never being able to charge the batteries...

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