CF325-TF-2-A-5  Temperature Controller  $55.00
TS665-TF-2-40-A  Thermistor		$14.80
CF325-TF-2-B-5  Temperature Controller  $55.00


For heating Aluminum Dewar top, used Heater Rope of 32 Ohm; ran ~25 Volts AC --> 625/32 Watts ~ 20 Watts, ~0.8 Amps
                                                   
So using ~40 Volts DC --> need R= V^2/Power = 1600/20 = 80 Ohm; 40 Watts --> 40 Ohms

15 June 04
Using TC wire I have 40V @ <2 amps, barely enough power for clear plastic top (R = 22 ohms)

Let's say we want 100Watts with 24V P.S.: need ~4 amps @ 6ohms. No Good: Resistance too low.

		100W with 48V p.s. need 2 amps 


8/8/04

We have a 48V (~38-54V adjustable), 5amp power supply.

ALS Standard heater ropes are 6' 30 ohms,
@ 50V, V=IR -> 5/3= 1.66 Amps

Heating Top of Dewer with TC wire of 54 ohms ==> ~ 1 amp

In parallel: 30 ohm + 55 ohm = ~20 ohm

(Heater inside supply Dewar is ~ 10 ohms ==> 5 amps! No.)

9/21

TC wire for heater top = 2 pieces in parallel, each ~ 6ft. long
~ 28 ohms each.  --> ~28/6 == = 4 2/3 ohm/ft.
The effective total resistance is 14 ohms
At ~44 V this gives I = 3.14 Amps; 138 Watts.

138 Watts/12 feet= 11 Watts/Ft.

Wire was looped and curled around top -- higher density near openings, particularly around sample pickup area, but also LN2 input line, and motor shaft piercing.
Heat is too high in some places (particularly over insulated dewar), a little too low in others. Over all it's OK!

10/14
Now want to try uninsulated NiChrome wire.  HOW? Here's what we've got:

NiChrome #10 2.7 Ohm/ft
NiChrome #12 4.4 Ohm/ft
NiChrome #15 6.7 Ohm/ft
Chromel  #10 ~4 Ohm/ft

Let's shoot for 120-140 Watts total 
Must minimize heating near the insulated trough.  
Note: After cooling down, the i.d. of the trough is  ~5" X 20"
      If we used 6 lengths 20" long we'd have wires every inch over LN2
      This gives 120" total length = 10 feet.

Assume 6 equal length wires;  R total = R/6 
V^2/R = Watts; R = 40^2/120 = 13 Ohm
Each wire needs to be 13 X 6 = 78 Ohm: forget it!
3 lengths: 13 X 3 = 39 Ohm; using #15 = 5.8 ft each; 17 ft. total
13 * 2 = 26 Ohms;
2 lengths; 13 X 2 = 24 Ohms; using #10 5.5 ft each = 11 ft total
This is just what we had before.  This time we'll use pins to carefully locate the wire -- worried that the heat around the motor and LN2 input may not be enough...


3-14-05
New aluminum top for luke/fifi combo
minco #5468 rubber heater 3" X 6" @ 46.1 ohm each
Part Number: HR5468R46.1L12A
---HR: Silicone rubber
---L12: 12" leads
---A:  No adhesive


@48 Volts these heaters produce ~50 Watts
which is ~ 3.3 Watts/sq.in.

3-17-05
tested lid with 6' long 30 ohm heater:
  worked fine with no LN2 flow, but got cold when gas was running