The Fantastic (and Painful) Portable Power Supply Hunt

Posted: January 27, 2012 in General SSL Commentary
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In an effort to create the highest possible performance in a portable lighting product, assembling the right combination of components is essential. Obviously the process begins with an efficient LED suited to the lighting effect desired. The LED must then be matched with an efficient driver. Finally, the driver must be fed power from an efficient power supply that converts incoming AC line voltage to clean DC power. Efficiency is generally found in matching the load of the LED to a driver designed for that load with no necessary over-capacity. Then, mating the driver to an efficient power supply matched in size to the driver’s operating load is necessary to produce the highest combined efficiency.

In addition to these core efficiencies are two additional factors; Power Factor and Off -State Power Consumption.

Power factor reflects the ratio of the real watts and the actual current presented by the product on the building electrical system. PF also reflects how much actual energy is required from the utility to operate the product. A power fact of 0.5 indicates that the real power in watts represents only 50% of the actual volt-amps, or current that is required to support the product. a PF of .90 means that the watts represents 90% of the current. While it is easy to set this aside when looking at one or two small loads, the effect adds up. For example, a 20A, 120V circuit can support 87 20W fixtures with a PF of .90, but only 64 with a PF of .50.

Off-State Power Consumption is the amount of energy a product consumes in the power supply circuit when the product is turned off. This applies mainly to task and portable products that have switches or controls separate of the mains voltage control. Depending on the type of power supply employed, the off-state power consumption can be insignificant, less than 3/10ths of a watt. In others, it can be high. This is energy consumed with no lighting benefit in lighting produced.

It is interesting to note at this point that dimming has a significant impact on all of these factors. As the dimmed load drops, power supply fixed power losses become a greater portion of the total energy consumed, so efficiency drops. If the approach to power factor is passive (fixed low cost design), as the load drops, the power factor correction becomes less effective, and the PF drops. It is not uncommon to see a driver/power supply combination start at 100% load / 85% efficiency / .90PF – drop to 45% efficiency / .40PF at a 40% dimmer setting. The same applies to power supplies that are larger than the connected load. In many cases a power supply with 83% efficiency will drop significantly with loads less than 80% of full rated load. Passive PF correction will have a similar response. For this reason, to avoid every individual product requiring a power supplies need to be designed with a unique power supply to fit the connected load, power supplies need to be designed to remain efficient over a load range for application to dimmed products as well as a range of LED loads. This will likely demand use of active PF correction strategies, to avoid the PF failing to meet requirements for loads less than 100% of nameplate rating. These power supplies also need to be rated for continuous duty at the connected load, which often demands a load less than maximum, where the peak efficiency and PF is measured for standard products today.

Now to the problem:

For portable products  less than 20W that use remote power supplies there is a significant issue in assembling the components required to attain high performance in all of these areas. Bottom line – there are no high power factor, high efficiency remote DC power supplies available on the market, none… nada. The vast majority of OTS (Off The Shelf) AC/DC power supplies are designed around electronic component use, under UL60950-1. While these are technically Class 2 by NEC definition and  considered Class 2 by UL – Energy Star requires “UL1310” Class 2 power supplies, with a PF of .90, ES Level V efficiency for any remote power supply used in portable lighting. Level V efficiency is primarily targeted at attaining an off-state consumption of <0.3W.

The following table shows a summary of tests accomplished on several driver/power supply combinations to illustrate what can be expected from products currently available to product manufacturers (Tasca product development results).

As can be seen here, while attaining a high efficiency can be accomplished with the careful selection of a power supply and driver well matched to the LED load, attaining a high power factor is not attainable.

Note that in the combination labeled “RT”, a high power factor was attained, but the design significantly reduced efficiency, and increased off-state power consumption. This is due to the design of the product, which utilizes a large coil wound transformer, which reduces sine wave interference that cuts into PF results.

The following illustrates the trade-offs involved in selecting the components when using current OTS components available today.

Based on testing of existing power supplies available, one can achieve one leg of this triangle with some ease. However, there are no .90PF power supplies available in power supplies under 100W, so anyone attempting to attain Energy Star for portable products using remote AC/DC adapters is out of luck. This leaves the Off-State power and Efficiency leg as the only available options, which can be found from several producers. However, all high efficiency, level V (>.3W off-state) products are UL60950-1 listed, which is not compliant with the ES demand for UL1310 listing, again leaving portable manufacturers out of luck

Ideally, a power supply with a high efficiency to support strong lumen/W efficacy, combined with high power factor, and low off-state power consumption would enhance any portable lighting product. Even considering the low actual loads involved, in facilities that use a large number of portable task lights would benefit from these performance levels.

For the near term, if Energy Star is interested in seeing portable lighting products in compliance, a reduction in the PF requirement is called for. otherwise, it is unlikely there will be any broad participation in this class of product.

No Current  Solution

As noted, there are no power supplies available that meet the requirements set by Energy Star. Development of such a source is an expensive proposition on all levels. First, a custom power supply that can attain all of the desired performance results mentioned here costs in excess of $25,000 in design, prototype, pre-production development and tooling. UL listing, and compliance testing will add another $12,000 minimum, plus the cost of first inventories, production setup, etc… By the time a power supply is created that can satisfy the efficiency necessary to produce desirable product efficacy, meet Energy Star efficacy, PF, Level V, and UL1310 listing, a sum of around $50,000 will be spent. To complicate matters, the costs of power factor correction circuits are such that designing the power supply for a very narrow load range is necessary to utilize a passive circuit design. Active circuits to support a wide range power supply (load range from 14W to 20W for example) adds significantly to the total cost of the power supply. In the end, while one can obtain power supplies with UL60950-1 listing, with efficiencies of >80% (.60PF) for $18, the cost of a custom made, a UL1310 high PF (.90) with passive circuit  is roughly $25, while a wide range power supply with high PF will run on the order of $30. While all of this may seem inconsequential to a massive corporation, it has a significant damping effect on the larger number of product producers who will simply do nothing until this can be solved without this level of cost and expense. even for manufacturers who have obtained a customized power supply, Lumenique tests have shown that there are none that have attained the requisite .90PF, few that have attained the UL1310 Class2 listing, and not one portable task lighting product has attained Energy Star (based on 1/12/2011 ES product listing). The lack of a viable Class 2 power supply is likely a significant factor in this.

To illustrate how frustrating this can be, the following is a compliance status for TASCA showing how all necessary issues have been addressed, save those associated with the power supply. Black results are those we attain regardless of power supply, based on the products design and driver selection. Green are results we attain with our current power supply, and red indicates results we are in need of improvement in order to attain Energy Star performance.

Call for Action

This is an open appeal to those who produce power supplies. The portable lighting market is a $1B+ market segment and a perfect match to LED technology. The reason a remote AC/DC adapter is so compelling in this product segment is that it supports the scale of product well, and is far less problematic for UL listing of the finished product.  Using a small driver, or LED board integrated driver, with a remote voltage conversion also creates produces that can be internationally marketed far more easily than carrying line voltage into the fixture itself. The UL1310 Class 2, combined with high efficiency, .90 PF, and <.3W off-state are good standards, that should be attainable. The power range to suit the vast majority of products could be attained in two power supplies; a 7-14W unit, and a 15W to 20W unit. The demand for both will be high, as there will be a need for small semi-decorative products for home and small office use, and high output products for commercial and industrial applications.  At TASCA, we use a 15W power supply today, with a need for 20W in the near future. We are not alone, with a very large number of portable lighting manufacturers, and potential start ups in this segment, that would all respond positively to availability of a product that would facilitate them attaining Energy Star compliance for their efforts. We can now attain the LED efficacy and optical efficiencies necessary, and meet all other criteria to hit this target – All that is holding us back is the availability of a viable power supply.

I am asked by electronic and SSL providers where there are opportunities to fill product needs in the market. Well, here is a product need that in nearly 2 years of trying I have not been successful finding a partner to provide a solution. While I do have an option to create a custom solution, I hesitate, as I know that this is a larger market need, that when filled by a mass produced solution will make anything I do on a custom level obsolete. All that is needed are two power supplies, either in a thin desktop or compact plug-in configuration, that meet the criteria outlined by Energy Star, including UL1310, and UL8750 compliance, that manufacturers can include in their own UL product efforts, that will facilitate ES compliance.

If you or anyone you know is able to produce an efficient, high PF 24VDC power supply meeting these requirements, please help, or ask them to help! I will gladly share specifications we have collected for the power supply we need at Tasca. If I find anything that will solve this problem, I will buy the product and post everything about it here, make a big deal about its discovery, offer them for sale at the Lumenique Product Center – and be eternally grateful, as will many others jammed up by this problem.  Failing that, is there anyone interested in working with us, either financially, or as a joint venture, to pursue developing a unique product we can market against all other available power supplies in the portable lighting market? Since many LED task lights now short of ES compliance will be able to attain the performance required with only a change in power supply, it appears a latent demand worth pursuing.

  1. Kate Reifers says:

    Terrific discussion and topic. Still absorbing it =)

  2. Bruce Taylor says:

    Yes I believe we have a solution that is the next generation of charging technolgy that will address your needs and many others. The development has been completed along with prototypes. Please see basic description below.

    The Lighting Product is a self regenerating LED lighting systems that can maintain charge and function for up to 8 + consecutive hours of operation. Once the lighting units power has been depleted or has been turned off the unit will begin to regenerate and be ready for the next day of operation. The unit does not require any external AC, sunlight or external power source while it regenerates.

    The base technology incorporated in the units described below can be used for a variety of other lighting market applications for broader market appeal and penetration.

    Please contact me for further information

    • kwillmorth says:

      While I appreciate what you are offering, it has no relevance to what I am looking for. However, I do like the idea of considering an off-grid power source, there is a greater market need for cord connected product.

      • Bruce Taylor says:

        The design can be of grid or on grid. The circuitry for example in a 2×4 commercial application would replace the balast and the floresent tubes with the charging circuitry and LED’s the system would run for 8-12 hours off grid then switch to the grid. This would also maintain lighting during apower outage.

      • kwillmorth says:

        I am not doing grid products or fluorescent retrofit. I am looking for cord mounted, high efficiency, high PF power supplies at ~24VDC to power a constant current driver located in the head of a portable lighting product. This has been outlined in some detail on the blog entry.

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