# In Rush Current Limiter

Discussion in 'General Electronics Discussion' started by mbyamukama, Apr 5, 2011.

1. ### mbyamukama

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Apr 5, 2011
Can I use an in-rush Current Limiter in a DC circuit? I have a 12V car battery and i dont want the current to the load to go beyond 7A. I have a 7A current limiter from Ametherm available. Is this possible?
If not, what alternative doi I have?

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
What is your load? Can your load draw more than 7A? Normally? or in fault conditions? A fuse is often the device used to limit fault current.

3. ### mbyamukama

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Apr 5, 2011
The load should not draw more than 7A. I agree that I should use a fuse, and hence would like to know if there are special fuses for DC in this case. The spec should be a 7A trip voltage and it should operate at 12V. Please take note that it will be on a PCB so size is a very big issue. Thanks.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
7A is a current not a voltage -- do you mean 7A trip current?

What do you want it to do? Limit the current, or act like a re-settable fuse?

If you want to limit the current then you could well end up dissipating 84 Watts if the output is short circuited. This would require a pretty large heatsink.

The other option is for it to cut the power if 7A is exceeded. This is easier and would not involve devices dissipating huge amounts of power.

5. ### mbyamukama

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Apr 5, 2011
Oh, sorry I mean current, not voltage. In short, steve, how do I protect my DC system, running a nominal current of 7A, from a short circuit?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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The traditional method is a fuse. Probably something between 10 and 15 amps.

7. ### mbyamukama

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Apr 5, 2011
Just any fuse? Will I not need a DC fuse...? Can you reccomend from RS or farnell or any of the major providers? Thanks!

8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Except for some quite exotic uses (really huge currents), it doesn't matter a great deal if you're breaking AC or DC.

The voltage rating is important, and you'll generally find that 12V is going to be OK for almost any fuse.

There are many types, your choice depends on factors like the space you have available, whether you want the end user to be able to change it, the speed at which it has to blow, etc., etc.

Reasonable options range from an in-line or board mounted 3AG fuse, to small surface mount fuses. In some cases, you could even use a very thin trace on your PCB (although that would not be my recommendation).