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Requires 70 Volts AC

Discussion in 'Troubleshooting and Repair' started by Last_Mavrik, Jul 8, 2013.

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  1. Last_Mavrik


    Nov 15, 2012
    Hello again everyone!

    Been a little while. Haven't had any real curve-ball's thrown my way I couldn't handle until this last week.

    I'm repairing a set of 4 camera's, pipe/sewer inspection cameras to be precise. Each one has had assorted issues, but nothing major that couldn't be fixed. They all had in common that they needed new control/power apparatus' made as their original equipment was very out-of-date.

    The problem is, each camera has a 512Hz transmitter to locate it with above ground, and while 90% of manufacturers use a 12vDC transmitter, these 4 use 70vAC. In the control boxes I've assembled I have available 12vDC and 120vAC (wall voltage) to work with, and limited space.

    So my dilemma is this: I need to find someplace I can purchase 4 relatively small transformers that will drop 120vAC to 70vAC, or a set of equally small power inverters that can produce 70vAC from 12vDC.

    I've searched the web for a couple days now and called/e-mailed several companies to no avail. Most of what I find in searches are 70v audio equipment, all DC. I need AC, and have approximately 5"x4"x4" (LxWxH) worth of hidden space to work with per box.

    If anyone knows where I can find something that'll fit the bill, great! If necessary I can mount said transformer on the side of the box if it can't fit beneath the control panel, so long as it has some form of weather-resistant housing.
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    How much power (or current) do you need?

    Where are you located? (There's a place for this in your profile settings. It can be helpful to other users.)
  3. duke37


    Jan 9, 2011
    If you cannot find a 70V transformer, you could perhaps find two 36V (18-0-18)transformers which could be connected in series. Or three 24V (12-0-12) in series.
  4. KJ6EAD


    Aug 13, 2011
    Last edited: Jul 9, 2013
  5. Last_Mavrik


    Nov 15, 2012
    - Updated my location.

    @ KrisBlueNZ
    As for the power requirements, the manufacturer didn't give me those details. Only 70 volts AC. I asked a week or so ago, just haven't received a reply yet. I'll be calling them up this afternoon to see if they've got any information for me and I'll update you here.

    @ KJ6EAD
    Those look promising. Once I know power requirements I may buy one, but I don't want to purchase more than I need. It's 1 small transmitter per unit, and is only meant to reach about 20ft.

    Speaking of Power requirements, correct me if I'm wrong, but I was taught that even if current is higher than necessary, any electrical device will try to draw only as much current as it needs, while in most cases more than about 0.5 volts higher than specified could potentially fry it.
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    For all but the most critical applications, +/- 10% is typically safe. For example USB is specified as 4.5 to 5.5V (nominally 5V). The same goes for TTL which is notorious for requiring 5V.

    In your case +/- 7V would *probably* be acceptable. Remember that mains voltages are typically specified to +6%/-10%, so applications running from the mains need to be capable of handling this as a minimum.
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    You're right that a load will only draw as much current as it needs. So you could in fact power a 12V, 2W light bulb (which draws 0.167 amps) from a transformer that's rated to supply up to 1000 amps!

    OTOH, many voltage sources have poor load regulation, so they may provide more voltage if the load (in terms of current or power) is too light. Older DC adapters were bad for this: an adapter specified for 12VDC 1A might produce as much as 18~20VDC with a very light load (or no load). Modern adapters use proper regulated switching supplies and have tight load regulation.

    Transformers by themselves have reasonably good regulation; it depends on the characteristics of the transformer. Others on these forums know a lot more about this than I do.

    Yes, circuitry can be damaged by overvoltage. Usually the tolerance for input voltage is viewed as a percentage. An overvoltage of 0.5V will turn a Pentium with a 1.5V core into grilled cheese on toast, but on a 70VAC supply, it would be insignificant.
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