Running 12v DC equipment on 120v AC (indoors)

Discussion in 'General Information' started by mixerbd699, Aug 30, 2010.

  1. timmy

    timmy Member

    i hadn't thought of a sequencer. the biggest problem with using a sequencer is that the way federal signal wired the lightbar(s) only allows you to feed power to one spot; the distribution after that is hard wired (soldered) under the tray and power goes to both items (lights and motor) at the same time. i would have to re-wire the bar to use a sequencer. a sequencer would be a great idea if you had one BIG power supply and wanted to run several lightbars at the same time off of it. you could start the bars up one at a time and avoid getting all the startup surges at once as the bars came on at the same time.

    i tried the approach of paralleling two of my 30amp 12vdc power supplies to run the bar. i still get about a five second delay as the two power supplies work through the surge before the motor starts. my guess is that the bulbs are slowly warming up and at some point the resistance is low enough to let the motor start. with one of the 30amp 12vdc power supplies the lightbar sometimes starts but after a lot longer delay. i tried this with both of the model 22/4 rotar bars i have and got the same result so i don't think i have a component issue with just one bar - they just take a lot of power to get going.


  2. shues

    shues Gold Level Member

    The motor's draw is negligible, as compared to the start up current required by all of the bulbs.
  3. stansdds

    stansdds Veteran Member

    I always allow 1 amp for each motor, that is usually more than enough. But a motor that is old or a mechanism that no longer moves smoothly is going to increase the amperage required for the motor.
  4. Henry455

    Henry455 Member

    Anybody looking for a 25-30 amp power supply might check out 12 VDC 29A 348W Regulated Switching Power Supply 320-315 , they are on sale for a few more weeks. Mouser has the exact same model for $97.00. Here is the spec sheet Meanwell Power Supply Products . In regards to ATX computer power supply conversions, the one I converted showed 12.3 volts under no load but dropped to 11.7 volts under a 10 amp load (specs showed a 27 amp 12 volt rail). My understanding is the ATX PS industry specs allow 5% voltage variation on all rails. If that does not present a problem then a ATX PS conversion is a good economical way to achieve "12 volts".
    Last edited by a moderator: Feb 3, 2013
  5. shues

    shues Gold Level Member

    Have you had any trouble with noisy power? I have had problems with switched-mode power supplies over the years, especially in audio amplification. I prefer linear power supplies for this reason.
  6. timmy

    timmy Member sells the same unit (several sources) for a lot less money. I have had great luck with these.

    $29 12v Dc 30a 360w Regulated Switching Power Supply Silver: Electronics

    If you are an Amazon Prime member there is no shipping cost and depending on where you live no sales tax.


  7. Henry455

    Henry455 Member

    I will know more in about a week. If you can believe the customer reviews on the Parts Express website, none mentioned any noise problem. Hopefully this will replace my trusty linear supply I threw together about 25 years ago. Its been reliable and steady as a rock but weighs 20 pounds, has filter caps the size of soda cans and only has a 10 amp output.
  8. Henry455

    Henry455 Member

    That's a good find but has a slightly different model number. Meanwell no longer shows that model number listed on its website.
  9. timmy

    timmy Member

    i have bought them from several different vendors from

    they are all the same basic unit with cosmetic differences.

    somewhere in china is a factory (or sweat shop) that makes these for hundreds of different retailers. they are all the same except for stickers and minor cosmetic things.

    you can spend more if you want a specific part number but they are the same.


  10. Henry455

    Henry455 Member

    Found the data sheet for the S-350 model, there are a few minor differences in the specs. compared to the SE-350 one being the SE model is 9% more efficient and has a 2 year warranty compared to the S's 1 year warranty, S model uses 25Khz switching freq. and the SE uses 90Khz. I am assuming the SE series replaced the S series, still a heck of a bargain for a 350 watt PS.

    Just an update: Received the SE-350 and used it to demo a couple of my vintage electronic sirens and noticed no PS noise. Mine came with the input voltage set at 220 volts, had been warned to flip the power selector switch to 120 before powering up.
    Last edited by a moderator: Feb 8, 2013
  11. FCV96

    FCV96 Junior Member

    After reading through the contents of this thread multiple times, I believe I am beginning to start to grasp the matter at hand. With that said, I have a relatively noob-ish question in regards to power supplies.

    I am looking at this 12amp at 13.8v Pyramid Power Supply in order to power a siren. The siren requires 12amps at 13.6v so I believe that is in order. I want to know if it would be alright to directly attach the siren's power and ground cables [from its wiring harness] to the power supply, or if I need to extend those cables first.
  12. JohnMarcson

    JohnMarcson Site Founder Administrator

    Admin Post
    The supply you linked is cutting it close. I go 150% (and round up) of what I want to power when choosing a supply. When devices first start up they often have a spike in amp draw. Power supplies are rated by constant and surge. For example that power supply provides 12 AMP Constant 14 AMP Surge. Your siren needs 12 AMP constant and up to 20 AMP surge from my experience (it can vary depending on the condition of components). At the very very minimum I'd get a 15 AMP constant supply to run sirens, 18 or 20 would be better. There is a 20 amp on Amazon for $95, and they go on ebay for about the same.
  13. toon80

    toon80 Veteran Member

    I'd also suggest spending a few more bucks for bigger amp capacity and be sure it will do the job, instead of having to eventually buy another power supply. You might also want to power up something more powerful in the future.That extra margin will become handy then.
  14. Kent@MoveOverOutfitters

    Kent@MoveOverOutfitters Established Member

    Check out powermax inverters on amazon. 55 amp for around 100 and a 100 amp for around 175. These are awesome
  15. LRGJr72

    LRGJr72 Premium Member

    Is there any reason one of these things wouldn't work? Massive amperage for 12v at a pretty low price. Keep in mind I'm almost electrically illiterate. 


  16. EVT

    EVT Member

    I've seen guys use them to bench test stuff. I guess you'd just want to make sure you're fusing the lights if it's more then a few seconds. That's a lotta amps.
    Last edited by a moderator: Sep 9, 2015
  17. Jarred J.

    Jarred J. Archive Expert Silver Level Member

    did you read this thread?

    thats not really a lot of amps... because its that many amps for a few seconds...

    theres usually an 18 amp /hour 12v battery in those things...

    what are you wanting to run off it?
  18. TheCrownie

    TheCrownie Registered Member

  19. bluestinger90

    bluestinger90 Member

    Wall warts are ok. Just make sure it's kept away from flammable materials. They have a tendency to get hot if you run it near the maximum amperage rating.
  20. Skulldigger

    Skulldigger Site Veteran

    I have been running mine off of a Stanley Professional Power Station.  It is basically a sealed car battery with a built in re-charger. I can simultaneously run 18 - 30w lights and 5 - 1.5 w motors off of it at one time.  (Two light bars and 3 beacons) You will run it down pretty quick doing that but it will run two 4 bulb lightbars for about an hour at 18amps an hour.  This single 12v battery shouldn't put out more than a vehicle with a battery and an alternator which provides about 14 - 15 volts under load.  My little Ford Ranger with a 4.0 V6 uses a 650 cranking amp battery so if I had a beacon on top, that is what it would have powering it.  I can imagine a large 12v Truck or other loaded rig will have quite a few amps pumping out of their charging systems.  Do you install a down step for your lights in a 24 volt system?

    I have amp tested all of my lights and they only pull what they use. You should not have an issue with power spikes from a simple battery with no other equipment connected to it like an alternator as it is always under draw.  I would not leave my charger connected or on when running lights to prevent a spike.

    You can buy the sealed 12 volt battery that is used in the Power Station and other jump starters for only about $35.  No fumes !  You can use any car battery charger with it. 

    Hoff likes this.
  21. Jarred J.

    Jarred J. Archive Expert Silver Level Member

    uhhhh you have to use a AGM charger  on AGM batteries.....  a wet cell charger wont cut it, and will hurt the battery in the long run
    Skulldigger likes this.
  22. LRGJr72

    LRGJr72 Premium Member

    Very interesting. Super information. Thanks, SkullDigger!!
  23. Skulldigger

    Skulldigger Site Veteran

    I would post a pic of my setup but it would give the techies chest pains.. Lol..
  24. Straypuft

    Straypuft Registered Member

    According to the Federal Signal Vector Manual for the SV series, I think it needs 8 amps per light, but 2 of the pods on mine have 3 lights inside of them, Does that mean I need a 55 amp power supply/converter or should I go higher to 75 amp?

    Someone mentioned a powermax supply, So would this get the job done?:
  25. Skulldigger

    Skulldigger Site Veteran

    8 amps for an individual light would be a lot. That would be a 96 watt light bulb.
    Count up your lights by wattage. If you have 30 w bulbs, your 6 lights would be 6x30= 180 watts.
    Watts / volts = Amps
    180 / 12 = 15 amps
    Add 1.5 amps each for any motors
    As long as your amps exceeds your needs you are good.
  26. gtpts27

    gtpts27 Registered Member

    Does this mean you shouldn't use a switching supply w halogen/rotator bars? I vaguely remember reading that somewhere else but don't understand why it would be the case.

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