[Amps] Using switch mode power supply for heater power

[Randall, Randy]

Look here:‎

http://www.ametherm.com/inrush-current/megasurge-inrush-current-limiters.html

They supply units up to 50A and have free samples available, but @ $6.20 qty 1 ‎for the 50A part at Digikey why bother?‎
‎  ‎
Ametherm's MegaSurge Inrush Current Limiter is Rugged. Specially designed to ‎withstand up to 50 Amps of Steady State Current and 900 joules of input ‎energy.‎

Example:‎

Electrical Specifications
Resistance: 0.5 ± 25%‎
Max Steady State Current up to 25°c 50 A Max Recommended Energy 900 J Actual ‎Energy Failure 0 J Max Capacitance @ 120 VAC: 62000 µ Max Capacitance @ 240 ‎VAC: 15629 µ Max Capacitance @ 480 VAC: 3612 µ Max Capacitance @ 680 VAC: 1800 ‎‎µ Resistance @ 100% Max Current: 0.01 ohm Resistance @ 50% Max Current: 0.02 ‎ohm BodyTemperature @ Max Current 215°c Dissipation Constant: 78 mw/°c Thermal ‎Time Constant: 240 mw/s Material Type (for Beta and Curve) B  ‎



Randy.‎

Randy E. Randall AB9GO
Network Engineer
UC Health
Randy.Randall at UCHealth.com
Phone 513-585-7146
Fax 513-585-7159


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On Behalf Of Dr. David Kirkby
Sent: Tuesday, June 28, 2011 8:58 AM
To: 'AMPS'
Subject: [Amps] Using switch mode power supply for heater power

I'm looking at building a 4CX1000A amp, which I want to make as small/light as
practical. Using an SMPS for the heater would go some way to this, whilst
offering regulation, since my own supply varies by more than +/-5% and a
generator would vary even more.

The 4CX1000A needs 6.0 V at 9 A, but of course when cold it will be a very low
resistance. I thought of using a 7.5 V 13.5 A switch-mode supply, with a 0.17
Ohm series resistor to drop 1.5 V. But I'm concerned the heater will never get
hot, as the cold resistance of the tube will draw too much current, causing the
SMPS to shut down.

If I bought one rated 12 V at 18 A or more, then dropping 6 V across a 0.67 Ohm
series resistor would mean the current would never exceed 18 A, even if the
heater is a dead short when cold. But that's a lot of wasted power, and an
over-specified (i.e. expensive, heavy) power supply.

Another option might be a NTC inrush current limiter. I've not looked at what's
available, but I do know device exist for this sort of task.

Does anyone have any ideas on the best way to use an SMPS for a heater supply?
--
A: Because it messes up the order in which people normally read text.
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