A 150 Ws homebrew monolight

This flash unit was designed in winter 2004-2005. Click any image for a full view.
Some short points:

This monolight is intended as a complementary flash unit to be used together with a more powerful flash system. It will be used primarily as an accent or background light. The flash energy and recycling times were selected to modest values.

The unit is housed in an enclosure fashioned from 110mm plastic drainpipe tubing, and homemade aluminium parts. All controls are on the back panel, and the housing has holes on the top and bottom for cooling. The reflector shown in this picture was fashioned from a regular lamp fixture (IKEA).

The flash tube is from the european electronics distributor Conrad. It has a low price and is rated for 500Ws. The modelling light is a small 40W E27 bulb. This low wattage was chosen in order to maintain proportionality with more powerful units.

The flash circuit is separated into a high voltage part and an isolated low voltage part. The flash capacitor bank is 2 x 1600 uF, 330V. The charging circuit uses a triac for switching, and a 150 ohm / 50 W power resistor on a heatsink for setting the charge current. The modelling light is adjusted by a simple triac dimmer circuit.

The controls on the back of the unit are A: modelling light power, B: flash energy, C: power switch, D: modelling light on/off E: photocell on/off, F: photodiode: G: sync cable connector, H: charge ready indicator, I flash test button. (The panel was not labeled when this photo was taken). This unit is not intended to be used with diffusers such as umbrellas or softboxes, but it needs some kind of lightformers such as honeycomb grids or barn doors. Such accessories are to be added in the future.

Warning! Flash circuits are very, very dangerous! Never attempt a project similar to this one if you do not have the right experience and equipment. If you just want to get a flash unit at low cost, there are plenty on the second-hand market.

(c) Marcus Gunnarsson 2005

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