Essential Hospital Equipment – Reviews & Information


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Power Management Systems for Mobile Medical Carts

Tue, 12/10/2013 – 2:21pm by Michael J. Mardis, Technical Sales, Hoffman Engineered Systems


Mobile medical computer carts and workstations are critical to the efficiency of today’s healthcare systems. They have been in use for more than 20 years to keep electronic health records (EHR) and to verify and administer medication at patient bedsides.

Most mobile carts feature onboard power systems equipped with single or multiple batteries intended to provide enough energy to run computers, displays, scanners and other devices for extended periods of time without recharging. Power systems run the gamut from simple battery chargers to sophisticated software-driven systems. Sophisticated systems can prove highly economical for both the manufacturer and end user over the life of the cart because of their adaptability to future changes in technology and their ability to optimize the performance of onboard batteries. These systems ensure that cart peripherals are safely and efficiently powered while properly managing batteries to reduce premature failures or costly battery replacements.

Computer carts with unsophisticated power systems are notorious for their high lifecycle costs for both the cart manufacturer and the end user. For end users, poor battery charging results in disappointingly abbreviated run times and fleeting battery life cycles. Because low end systems do not charge batteries to manufacturer requirements, battery replacement is an ongoing logistical problem and expense for the healthcare provider. End users have adapted to this poor performance by leaving carts plugged in, which reduces their work efficiency and increases operating costs.

For mobile cart manufacturers, warrantee service costs of failed power systems can escalate very quickly and eat into the profit from the cart’s original sale. Replacement of batteries under warrantee is another ongoing manufacturer expense.

As the technology needs of EHR systems grow and change, manufacturers must service the cart to build platforms that accommodate the new equipment. Additional equipment means that power systems must be redesigned to provide the energy needed for equipment to run reliably. This lack of adaptability presents challenges and results in unanticipated costs for both the cart manufacturer and end user.

If the cart’s power system does not meet current and anticipated workflow requirements, the hospital or healthcare facility’s huge investment in mobile EHR workstations is compromised. End users must decide whether to add onto the existing system at significant expense to the healthcare facility, or scrap the cart and shop for more advanced mobile equipment. Cart manufacturers can easily remedy these long-term problems by specifying flexible, adaptable power management systems into their carts to allow for advancements in peripheral technology and battery chemistries.

Battery Chemistry

Current battery technologies provide five distinct chemistries for point-of-care mobile applications:

  1. Nickel Cadmium NiCd
  2. Nickel-Metal Hydride NiMH
  3. Lithium-Ion Li-Ion
  4. Sealed Lead Acid Pb-Acid or SLA
  5. Lithium-Ion Phosphate LiFePO4

Each chemistry choice has characteristics providing advantages in specific applications however; none is optimum in all categories.

The following is a comparison and quantitative ranking of the five battery chemistries.

The data presented was obtained from a variety of academic/scholarly sources and Internet

sites. Unfortunately, not all sources agree in all regards. Because the data changes rapidly as technology develops, please note that the information presented is general in its context and not meant to provide precise measure.

Application requirements should dictate the most appropriate battery chemistry. While no chemistry is fully-compliant with all of an application’s specific requirements, there is typically one, however, that is more acceptable than the others. The user must decide the priority based on the application and, in response, prepare a requirement that dictates the overall system performance resulting in the preferred battery chemistry.

For example, using Mobile Hospital Carts, the priority of requirements might be as follows:

  1. Safety
  2. Price
  3. Cycle Life
  4. Shelf Life
  5. Load Current
  6. Charge Capability
  7. Toxicity
  8. Energy Density

This priority list is highly subjective. The following arguments are the basis of the above list:

  • Safety is considered to be paramount in a hospital environment while price, cycle life and shelf life reflect the total lifecycle cost of the battery.
  • The load current determines how many devices might be powered from the battery; this might be an advantage but not necessarily a hard “requirement”.
  • The charge capability can be managed through the choice of a superior charging system and, although affecting price, it typically is more of a nuisance as it may require longer charge duration.
  • The toxicity is relevant in that it either is or isn’t toxic and since all are in some way toxic, they all have concerns.
  • The ability to discard without undue problems would be an advantage but not of premium importance.
  • The energy density seems to be the least important in that as long as the mobile cart is not unreasonably heavy and difficult to move, it is not a significant issue.

Sealed Lead-Acid battery chemistry is an appropriate choice for a cost-conscience medical environment. Lithium-Ion Phosphate Batteries are the superior choice for health care organizations desiring improved performance, density, and safety.