50 amp+ thermistor

Anyone know of a manufacturer of high current thermistors? Say 50+ Amps at

120V?
Reply to
Ztag
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Hello,

I assume you are talking PTC type thermistor used for current limiting. I have not seen any rated for more than about 10 amps or so.

Andy

Reply to
Andy Pichotta

On Tue, 17 Feb 2004 19:48:27 GMT, "Ztag" Gave us:

Bwuahahahahahaha... What do you have that will have such inrush abatement needs?

Reply to
DarkMatter

On Tue, 17 Feb 2004 19:48:27 GMT, "Ztag" Gave us:

For choosing one, you could refer to these notes and aides.

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for selection, there are many. None at 50 that I found, however.

36 A was the most I saw.

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Plenty more. Did a google on "thermistor inrush" and got 2000 hits.

Reply to
DarkMatter

I'm attempting to build something to squash the noise generated by the capacitor charge circuit for a very large camera strobe pack. The environment has 40 of these flashing at once. Very nasty.

Reply to
Ztag

There is 1.25" diameter surge current limiter (SG405) which is rated at 30 amps - but its cold resistance is 1 ohm - so it can still pass

120 amps at 120VDC. If your 50 amp surge is only temporaray at less than a few seconds and if your steady state current is less than 15 amps, you could use one SG405.

If your steady state current is 50 amps, you will have to parallel at least 3 SG405 units if you don't want them to smoke! The inrush current will also triple to 360 amps maximum with 3 paralleled SG405's.

To reduce inrush current back down to say 120 amps, then you have to use three paralleled SG405's in series (total 9 SG405's).

SG26 is rated at 12 amps maximum but it is 5 ohms when cold, so it will limit current to 24 amps at 120VDC. You can use the same parallel/series combination to arrive at optimized inrush current limit for a particular steady-state current.

Inrush current limiters rated for 1 to 30 amps can be found at:

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Good luck & happy current limiting !!!

Reply to
Nam Paik

On Wed, 18 Feb 2004 06:48:50 GMT, "Ztag" Gave us:

You mean the audible singing as it charges prior to firing?

Forget it. It is an inseparable parasitic of the strobe unit.

Reply to
DarkMatter

Not talking about the audible noise. I'm talking about the inrush spike that is created after the caps have been discharged and start to charge.

Reply to
Ztag

This might just work. I still have to fully characterize the inrush with a current probe, but that won't be for a few days as I am still waiting for my test pack to arrive. Maybe I will get lucky and the inrush isn't as high as I think it is. I'll post more in a few days.

Thanks Nam!

Reply to
Ztag

On Wed, 18 Feb 2004 21:47:07 GMT, "Ztag" Gave us:

If you abating a single spike, you should snub it. Those inrush limiters are made for inrush that is continuous if one compares your momentary spike to what they are designed to quench.

Put a small snubber on each strobe or a small, cheap thermistor on each.

Probably do a much better job placed locally, and on each unit.

You could also place a large cap on each one. That would allow for a huge energy storage at each device which would not spike the main supply as each fired. They would call on the stored energy in the caps first, and the caps would exhibit less inrush demand on the main supply rail.

A large electrolytic cap and an inrush NTC on each device.

There ya go man... be as cool as you can...

Reply to
DarkMatter

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