While preparing to move I found my old Isotip
soldering iron, but the batteries were worn out:
Years ago I had added an SCR LED circuit to the base to indicate when the batteries were charging.
When the iron is first placed in the base, the red LED goes dark or dim when the iron makes proper contact.
Eventually the LED gets brighter when the batteries are drawing little current.
I happened to have a pair of Nimh 1.2 volt, 6000 mah tabbed rechargeable batteries so I replaced them
The large copper plate is pushed down to the + battery button on left to heat the tip and light a lamp.
The lamp gets positive voltage from the copper plate to the side through the bent down tab originally.
The button on left can be unscrewed using needle nosed pliers. I enlarged the + tab hole with a rotary tool.
After recharging the new batteries, I noticed how dull the lamp was compared to a 10 mm bright LED.
The lamp uses .27 amps or 270 milliamps while a simple coil Joule thief circuit uses .04 amps or 40 ma or less.
Problem is that the batteries need to deliver 3 volts, but both only give 2.5 volts max. Needs a Joule thief:
The 5252F chip and a 33 uH coil on right needs to be added to the soldering iron so I removed the button plate.
NiMH denotes the battery required, one or two 1.25 volt rechargeable or 1.5 volt regular batteries. Do NOT use regular batteries in rechargeable devices!
. Pin 1 is used for solar or low +DC charging voltage.
Chip pin 1
is unused and cut off. Pin 3
needs bent back and soldered to the negative bus on right first. Pin 4
and one end of the coil go to the + side of the lamp base as the bulb bottom is wired to negative bus. Pin2
goes to other end of the coil and plate. After straightening the lamp tab, the coil wire slid right in.
I didn't even solder the pin 4 coil wire to the plus button plate. It could also have been run to the plate screw.
I broke the old lamp and put a 10 mm white LED in the socket with anode to side and cathode to bottom.
Now I can actually see what I am doing 10 times better using one tenth of the soldering tip current to do so.