DIY 360 VDC Power Supply for Vivitar 365 head

Discussion in 'Lighting Equipment' started by Aoresteen, Sep 4, 2013.

  1. I like to build a 360 VDC power supply for my Vivitar 365 Flash heads. I'd like to get the full power recycle times down to 6 seconds. Anyone know of an AC power supply that can deliver 360 VDC? Or pland to build such a puppy?
    The Vivitar ac adapter SB-5 does deliver 360 VDC but the recyle times are 50 seconds plus (not the 14 secs listed in the Vivitar manual - it's an error per Vivitar).
    Thanks all!
  2. I think you could build one out of a boost regulator, transformer and caps from an old PC supply. You could probably reuse the transformer too. Check Linear Technology for their free circuit simulator and start designing!
  3. You probably don't need much of a circuit for this, but it depends on what your local mains supply voltage is. If it's 240 volts (AC), then simply full-wave rectifying the mains will get you close to 340 volts DC. Best bet is to find a little auto-transformer with multiple mains tappings. To get 360v rectified DC out, you'd need an AC input of 255v.
    According to one thread I found the 365 has a storage capacitor of 1800uF. So assuming it gets charged to 360v, that's a flash power of almost 120 Joules, and to charge it to 360 volts in 6 seconds would require an average current of just over 55 milliamps. You'll have to limit the current to prevent any possibility of blowing the mains when the flash is fired, and a suitable resistor should be placed in series with the supply. If you limit the maximum charging current to 100mA, I don't think you'll be far off your target charging time. The limiting resistor should be a wirewound type with a rated wattage of around 20 watts and a value of 3K6 ohms. Voltage rating should be 400v, obviously.
    20 watts is a lot of power to dissipate, so expect the resistor to get quite hot and make sure it's not touching any insulation or plastic casing.
    You shouldn't need any smoothing capacitors in the supply, since the flash storage capacitor will do that job on its own.
    Below is a quick sketch of what should be a suitable CCT. However please check it out thoroughly for yourself, no responsibility taken for use or misuse, no money returned, YMMV, etc, etc.
    BTW, I'm assuming you have some electrical/electronics knowledge. If not, please don't even attempt to make something like this!
  4. OOops! I just realised that the charging cct above is only going to be 50% efficient, and as much power gets dissipated in the limiting resistor as gets put into the storage capacitor. Therefore the resistor value needs to be dropped to 1K8 ohms or under to reach the required charging time of 6 seconds. Sorry!
    To improve the efficiency would require a much more complex circuit. So I think you'll have to live with a rather 'sweaty' supply if you want that rapid charge time.
  5. I wouldn't use an auto transformer for this. A fully isolated transformer would be better.
  6. I agree Steve, but where are you going to find one with such a close step-up ratio? Maybe splitting the limiting resistor between the pos and neg outputs would be a safer idea.
    Edit. Just remembered that small shaver socket transformers sometimes have multiple voltage taps. It's worth investigating.
  7. Danger, danger, danger!
    On further thought an auto transformer isn't a good idea at all. We don't know what Vivitar have done with the connections to their flash capacitor, and an autotransformer may well indirectly route the mains to the trigger lead of the flash.
    Don't use the above circuit as it stands. Use an isolating transformer - if you can find one that's suitable.
    In fact if anyone moderates this forum, could they please remove that circuit diagram.
  8. Don't know if it could be of assistance but here's a Vivitar patent for a high voltage battery pack anno 1986.
    Perhaps one could use a similar circuit but do DC/DC step up from rectified 110V (from an isolation transformer).
  9. Unless your old PC is some 20+ years old, you will not find any parts in the switching power supply that would be usable for building line AC-to-360 VDC converter, except possibly the power supply box.
    PC switching supply produces 5 VDC and 12 VDC, and does not have any high voltage transformer that you may need for your design, and for circuit separation/isolation.
  10. I agree Steve, but where are you going to find one with such a close step-up ratio?​
    Well, here in the UK I could use the transformer from an isolated shaver outlet for a bathroom at 240 volts. Perhaps in the US, two such units in series.
    Or the HT winding for a valve (tube) circuit. UK electronic supplier RS has such a transformer as well as 30 - 0 - 30 centre tapped transformers - two of which could also be wired in series.
    EDIT: Believe it or not, I only read this part of your reply after I made my post!
    Just remembered that small shaver socket transformers sometimes have multiple voltage taps. It's worth investigating.​
    Such transformers here usually have a 115 volt output for US visitors. Do yours have a 230/240 volt output?
  11. I think a voltage doubler circuit from 120VAC would be sufficient. It has the advantage of droping the voltage when under high load thus when the capacitor is empty it won't supply too much current.
  12. Steve, I'm in the UK too.
    BeBu, a simple diode-capacitor "cockcroft" multiplier would have the same drawback as that circuit I embarrassingly posted (without sufficient thought I admit). It would allow the mains supply a direct path to the flashgun. Of course you could add a transformer at the front end to isolate it, but then if you're using a transformer, what would be the point of a multiplier circuit?
    Matt: If you're checking this please save my face from getting any redder, and possibly save someone else from injury by eradicating the circuit I posted earlier.
  13. Thanks guys! I came up with another idea. The LV-1 power pack has 8 C cells for 12VDC. It then bumps it up to 360 VDC for the flash.
    I just need to make an external conncetor for the 12 VDC where the batteries feed in. Then connect it to one of my 20 amp 13.8 VDC power supplies from my ham radios.
  14. Steve, I'm in the UK too.​
    Sorry. I automatically assume that everyone else is American!
  15. 20 amps will fry the LVP-1. In testing ,I found that a 12 volt 5 amp SLA battery will deliver 3-3.5 second recycle times. Figure out where to stick a connector and you're good to go.
  16. "20 amps will fry the LVP-1"

    - Not necessarily, or even likely.
    Just because a voltage source is capable of delivering 20 Amps, that doesn't mean the circuit connected to it has to draw 20A.

    A gel lead-acid battery will easily deliver 20 amps into a low resistance circuit. So if a 12V (13.8v O/C fully-charged) SLA battery doesn't 'fry' an LVP-1, then why would a 20A capable PSU?

    BTW. This thread is now nearly 5 years old. It's likely the OP has finished with or moved on from the project by now!
    PapaTango likes this.
  17. Joe! What size of capacitor do you think such a flash has? Or a typical flash?
  18. The Vivitar 285/365 that I took apart had a 350v 1000uF capacitor in it. I doubt that the capacitor is charged to its rated voltage though. It probably holds a charge of something like 55 Joules (Watt-seconds).

    This compares with 350v 1400uF in a Nikon SB-800, 900, 910 etc. Similar values in Minolta and Canon's top line speedlights too. Their charge is around 75 Joules - meaning about 50% more light output than the Vivitar.

    Cheap flashes by Cobra, Hanimex and other off-brands usually have a 360v 600uF capacitor that holds a charge of only ~ 35 Joules. Consequently they're a stop less powerful than a top line speedlight. As are the likes of the SB-600, 700 etc.

    So while the Vivitar 285/385 is a slight cut above cheap low end flashes, it's not as powerful as a good camera-brand flash. Together with the lack of head swivel and built-in power control; the continued popularity of Vivitar flashes totally baffles me.
    Their cheaply produced PCB and 1970s electronic design is pretty low-end as well.
    Last edited: May 26, 2018
  19. I have some servo motor power supply that can charge 10,000uF in a fraction of a second. I thought of using it.

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