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Custom uninterrupted power supply

  1. Jun 20, 2013 #1

    I am wanting to build an uninterrupted power supply for a certain device that has multiple electronic devices working together.

    It will need to run about 1.5k Watts for about 15-30 minutes without an external power source.

    There will be a few moving parts such as wheels to move it from place to place, and quite a few electronic components.

    I was wondering what would be the most efficient way to build or buy something to satisfy my needs. I see people building custom UPS's with car batteries and things of that like, but I am afraid of it blowing up or being extremely inefficient.
  2. jcsd
  3. Jun 20, 2013 #2


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    Welcome to the PF.

    Given your level of expertise, I would recommend buying one. Can you post links to commercial versions that meet your needs?
  4. Jun 21, 2013 #3


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    Hi Jetach, Uninterruptible Power Supply (UPS) technology has come a long way since days. Now you can buy most any size/capacity UPS that has great efficiency for a reasonable price.

    One convenient place for beginners to start is the Wiki entry:

    Once you've decided on your requirements then Google search for suppliers, vendors, and manufacturers. More than likely there is a unit that will suit your needs. Note, please, the term used by the industry is "uninterruptible" and not "uninterrupted".
  5. Jun 21, 2013 #4
    Thanks for the responses.

    I've found that Lead-Acid batteries are the cheapest, and modding out an old UPS with car batteries appear to be the cheapest and easiest way.

    However, after some more research, I've found that lithium ion batteries are much smaller and efficient, although the cost is much higher.

    I am also wondering if building my own UPS by connecting AC/DC and DC/AC with a battery and a transformer or so for safety. Was also wondering if there were schematics available for online UPS or line interactive UPS.
  6. Jun 21, 2013 #5


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    In the UPS industry the item to be protected is called the “critical load”. Once you know its power requirements and decide the time you want to sustain that load during a power failure, then the selection of the batteries is based on several criteria. Ampere-hours is only one: there is cost, maintenance, battery lifetime, temperature requirements, and more to consider. If you select lead-acid batteries, for instance, know that their efficiency drops drastically with increasing temperature. So you may require air conditioning. What keeps that A/C operating in a power failure?

    Consider the criticality of your protected load. What happens if power is lost? Is it a hospital life-support system? Will there be a financial loss? Arrange to test your UPS under a full load for the required time.
    Since you are proposing constructing your own UPS as a “do it yourself” (DIY) project consider that a homemade UPS will not, in general, be as reliable as a commercially built UPS, so the risk to your load will be that much greater.

    You probably will not find UPS schematics and parts lists publicized on the internet. After all, those companies that design, build, and test UPSs are in business to sell their products, and not to help DIY UPS makers.
    Depending on the criticality of the load, it may be best to pay for a professional UPS consultant to assess the project and recommend a commercial UPS for purchase.
  7. Jun 21, 2013 #6

    jim hardy

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    Look into the devices that you are powering.
    Often the first thing electronic devices do with line frequency power is turn it back into DC.

    If your loads could run directly from a convenient battery voltage,,,


    think about it.

    old jim
  8. Jun 21, 2013 #7
    There will be multiple loads connected to various PCB boards and motors to keep the device functional.

    It is a device in development so I do not want to give too much information, but I want to have a safe, cost-effective, and efficient UPS able to deliver about 2kW.

    I've been leaning towards VRLA batteries with some sort of safety casing over it, but even then outputting 2kW of power can make it extremely hot, therefore losing efficiency...
  9. Jun 21, 2013 #8


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  10. Jun 21, 2013 #9
    Thanks for that link it is very helpful.

    Quick question, what are the pros and cons of a deep cycle battery for a UPS?

    From what I am able to gather, it is able to provide longer durations of power, however the overall life of the battery is shortened due to the depth of discharge.
  11. Jun 21, 2013 #10


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    Since you are doing product development, which safety agency will be doing your safety approvals? UL? Or some other agency? If UL, what UL safety standard does it fall under? Medical Equipment? Office Equipment? The batteries you choose may depend on the safety standard that you are going to be qualifying your product to.
  12. Jun 21, 2013 #11
    It is medical equipment, and I will ask the head engineers about which agency it will be under. Can I ask what the acronym UL stands for?
  13. Jun 21, 2013 #12


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    Jetach, UL stands for Underwriter's Laboratory. Google that. You may have great abilities and a strong potential to become a competent engineer in future. But since you did not know what UL means I imagine your level of expertise to be "not too experienced yet".

    It suddenly becomes apparent that one of our rules here on Physics Forums prohibits members from contributing to any dangerous activity. Your project has the potential to become dangerous, so it may just be prudent close and lock this thread.

    Damage to hardware and fires are possible because of mistakes and, worse yet, there is the potential for injury to people. You need a professional certified consultant for this project, either from within your company or from the outside.
  14. Jun 24, 2013 #13

    Yes, I have just finished my third year in a 5-year program for ECE, so I am somewhat inexperienced.

    However, I was still wondering if there were efficient ways to accomplish this.

    I've researched a bit more and in terms of cost-effective, I've found that taking apart an old ups and running two batteries (agm or gel cell) in either parallel or series to match the ups requirements for voltage to be the best way to get what I want which is 2kWh.

    I am wondering if I would need an extra voltage regulator as this would be drawing lots of power, or would it be overkill to have a UPS attached to another regulator.
  15. Jun 24, 2013 #14


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    The pertinant UL standard for Medical Equipment is UL544, although there may be some other standards that pertain to batteries used in medical equipment. I know that sealed lead-acid gel cells are used in some portable X-ray carts, but beyond that I'm not of much help.

    I agree that you need to find an experienced EE with medical equipment background, in order to get some help on this. This thread is closed.
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