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 Post subject: Another magnifier lamp coversion to LEDs
PostPosted: May Sat 25, 2019 2:38 am 

Joined: Nov Tue 14, 2017 5:09 am
Posts: 1915
Location: Austin, Texas
I put quite a bit of time into converting two magnifier lamps from fluorescent to LEDs but I wanted a lot of light and something reliable enough to pass on to my grandson. As with other conversions described on the forum, I used the 12V LED strips that are sold on reels. The strips for these conversions are warm white 5630 LEDs. The strips are in series to get a total near 100 volts and use a current limiter to power them directly from the 120VAC power line.

This first conversion is an all metal lamp with about a 40mm annular ring for the light source. Since the LED strips are 50mm long, they had to be mounted at an angle. They were cut through the connection pads on each end of the strips so the length was closer to 48mm as mounted. Having the edges of the copper exposed made it much easier to solder the strips to the PC board used to hold them.
18 Strip in Lamp.JPG
18 Strip in Lamp.JPG [ 430.47 KiB | Viewed 586 times ]

The PC board is divided into 18 segments and one of those segments is divided to separate the strips into a group of 9 for a positive voltage supply and 9 for a negative voltage supply. The large copper area provides a good heat sink for the LEDs and soldering them down at four points assures that they will stay in place.

The second lamp has a plastic housing with an annular ring of a bit over 50mm. The LED strips could be mounted in a radial pattern and 20 strips fit well with the mounting points on the plastic.
PCB in Lamp.JPG
PCB in Lamp.JPG [ 436.2 KiB | Viewed 586 times ]

Both lamps have a clear plastic safety cover over the PC boards.

The circuit used to power the LEDs provides two voltages near + and - 100VDC for the two strings of LED strips. The original 22 watt ballasts would have provided too much voltage and current to the LEDs but I had some 8 watt ballasts of identical size that produced the correct power level. The converted lamps actually use 7 to 8 watts of power. A 5 uF AC rated capacitor also worked OK for the power limiter but the inductive ballasts seemed like a better choice.
LED Magnifier Ckt.jpg
LED Magnifier Ckt.jpg [ 85.46 KiB | Viewed 586 times ]

The diodes and capacitors to convert the AC to DC are on the back of the PC board so the lamp wiring is nearly identical to the original except for the removal of the fluorescent lamp starting circuit.
Complete PCB Bottom.JPG
Complete PCB Bottom.JPG [ 113.81 KiB | Viewed 586 times ]

Cutting the PC board copper into segments was done on one of the low cost CNC machines but it was used in a manual mode.
Milling Slots 3.JPG
Milling Slots 3.JPG [ 372.69 KiB | Viewed 586 times ]

The converted lamps work very well and, in my opinion, are considerably improved over the fluorescent tube.

Using all new parts, the conversions would have cost around $17 each. The PC board stock is over half of that so the cost could be much lower if you have some on hand or get it at a swap meet.


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