Hot Topic: Manikin batteries! How to Replace An Overheating Medical Simulator Battery

12/06/2016

Blog post by SimGHOSTS President Scott Crawford, MD, CHSOS

Hot Topic: Manikin batteries! How to Replace An Overheating Medical Simulator Battery

Most high-fidelity manikins can be powered either directly from the wall, or with the use of an internal Ni-Cad, lead acid, or lithium-ion battery. When fully charged, these batteries can power the device for several hours or more. By manufacturer’s recommendation, the manikins that operate on Ni-Cad batteries from Gaumard should only be operated from the battery, not from the wall charger. This includes the Newborn Hal and Hal One Year Old manikins. Laerdal recommends unplugging their manikins when not being charged to preserve the battery. Batteries and charging systems work well in general across manufacturers. Sometimes batteries can fail as part of normal life expectancy (decreased storage capacity is an early sign of aging), or an internal short circuit can cause overheating and a sudden and complete absence of power. As the news would make us aware, no manufacturer is safe from potential battery failures. These rare, but potentially dramatic failures can lead to overheating and occasionally explosions. The most impressive failures come from lithium-ion batteries (currently in use on most Laerdal products). These batteries are known for causing explosive fires, most notably in e-cigarettes, hover boards and now the Samsung Note 7. Lead acid batteries can heat and swell, while Ni-Cad batteries are probably the safest overall.

This article will describe a lead acid battery failure, the steps for removal from the manikin, and what to consider when selecting a replacement product. Let’s start with a quick review of battery technology and power usage calculations.

Batteries:

Batteries have an anode and a cathode. The anode is the “-” side and the cathode is the “+” side. A battery exists by grouping one or more “cells” together. A cell is created when two different metals are placed adjacent to but separated from one another by an electrolyte solution (usually an acid). When a connection is made between these two metals, electrons flow from the anode to the cathode because of the relative affinity for these electrons between the two metals. The voltage of a battery is a physical characteristic of the two metals relative to one another. Putting these cells in series or parallel will either increase the voltage of a battery (series) or allow it to run longer before running out of power (parallel).

Power calculations:

This is true for electrical power of all types, including batteries and wall connectors.

Power (watts) = Current (Amps)*Voltage (V); often written as P = IV

Wattage is an instantaneous power output or demand and is often paired with time to determine the length of time a battery might be able to operate. There are many other formulas in electronics, but with this one alone you can determine most power requirements for household products.

The wall adapter for Gaumard’s Susie, for example, outputs 12 volts at 2 amps (written on the plug) for a total of 24 watts (obtained through the above calculation). To find a battery or power adapter to match this need requires use of this calculation to find a 24 watt power output. A lithium-ion battery pack for recharging phones and tablets via a USB port can output 5v at 2.1 amps (defined by the battery pack), for a total of 10.5 watts. Even if an adapter were used to increase the 5v output to 12v (commonly available for about $10), the total power output in watts by the plug is less than what might be consumed by the device (24 watts). If the voltage were increased, the amperage would be decreased as described by the equation above.). Trying to draw more power than can be output from a device can lead to overheating or device malfunction.

Our manikin, through no fault of the manufacturer, suffered a battery failure. Two of the internal cells likely short circuited, causing the battery to overheat and the plastic casing to swell. The device was immediately unplugged from the wall to stop any further attempts of charging the battery. This also stopped the overheating and eventually the smell.

The manikin was opened to give access to the battery compartment. All skin pieces, organs and electronics were carefully disconnected and connections catalogued (and photographed) to ease reassembly. The battery, in addition to being secured to the manikin frame with Velcro, had swelled, forming itself to the securing strap and battery compartment. We needed to physically pry the battery pack out using a hammer, screwdriver and the precision extraction techniques known to most jack hammer operators. As described previously, this extraction method would not be appropriate for lithium-ion batteries for fear of additional damage to internal cells and the resulting fiery chaos that would surely ensue. After the battery was extracted the specifications and model could be read from the side of the battery. It was a model PSH-1280 lead acid battery operating at 12v and with a capacity of 8.5 amp hours. This suggests that it could operate the manikin at full power requirements (based on the information from the wall adapter) for about 4 hours. A smaller or larger capacity (amp hour) battery could be used, which would only affect the duration between charges, but the voltage output must match (or be adapted to match). In the end, a similar battery, much like what would operate a back-up battery (Uninterruptible Power Supply (UPC)) device for temporary power outages, could be ordered from an office supply store or even picked up in stock from a local battery supply store.

To prevent any accidental disconnections once installed, the new battery was secured back into the manikin’s frame and the connections were soldered to the terminals of the battery. The terminals were also covered with heat-shrink tubing, as had been present previously, to prevent a short circuit inside of the manikin frame. Once correctly re-assembled, the manikin woke and began breathing again, at which point we all shouted, in the creepiest voice we could muster, “It’s alive!”