Hand Held medical device - power supply requirements

David Nicolson

Registered
Hello all,

First time posting on this forum, so thank you in advance for your comments and advice.

We've developed a Class II hand held device which is powered by a Lithium-ion rechargeable battery. The device will be supplied with a docking station that is connected to the mains supply. We're using a pogo-pin arrangement between the device and the station. The device cannot be used while docked.

My question is about the power supply that will be moulded into the docking station. Do we absolutely need to use an already certified 60601-1 power supply, or can we use a 60950-1 certified power supply (or other relevant standard) and have the docking station and embedded power supply tested to 60601-1 as an entire system? If the allowable leakage from the non-60601-1 certified power supply is too large, is our only option to move to a 60601-1 charger? Or can we incorporate our own isolation barriers into the design of the device / docking station that will be sufficient?

We're exploring all options as we're finding the cost of 60601-1 power supplies quite prohibitively expensive.

Thanks.
 

David Nicolson

Registered
Wondering if anyone has experienced a similar dilemma or found a definitive answer. Happy to provide more details if the details above are unclear?

Thanks.

David.
 

Peter Selvey

Leader
Super Moderator
I think the solution would be to treat the docking station as a separate "device" from the point of view of the regulations. If it's purpose made for your system, it's still technically a medical device (accessory) but since it doesn't contact the patient it can be assessed to other standards as appropriate for a normal battery charger. Take care though that sometimes those standards can be a bit obscure as well and can end up being expensive.
 

David Nicolson

Registered
Thanks for the reply Peter. Just to clarify, the device cannot be powered on while in the docking station, however, technically the patient can make contact with the applied part of the device while it’s docked and connected to the mains.
 

Peter Selvey

Leader
Super Moderator
Applied part is defined as having contact necessary for the intended use. So incidental contact is excluded. Someone could argue that it's not time related i.e. once an applied part always an applied part, but from first principles, applied parts have special rules based on the nature of contact which just don't apply in this case.
 

David Nicolson

Registered
Applied part is defined as having contact necessary for the intended use. So incidental contact is excluded. Someone could argue that it's not time related i.e. once an applied part always an applied part, but from first principles, applied parts have special rules based on the nature of contact which just don't apply in this case.
Appreciate again your input Peter. Further clarification from my side: when the device is charging, the charging base is like a cradle that the device is seated into. The applied part makes contact around the eye. Therefore, while docked, the device could in theory be lifted and the applied part placed on the eye. As mentioned before the device can not be turned on while charging. But the argument being made is that irrespective of the device being off, the device is connected to mains supply through it's connection with the docking station. The interaction to lift the device to the eye while docked would be very awkward and counter intuitive but I suppose possible. Can an argument be made that the intended use and design of the ME system make it highly unlikely (I concede not impossible) that the user will attempt to place the applied part on their eye while docked. It should also be noted that during normal operation, there is 90 second "start-up" phase after the user has powered on the device before it is operational.
 

Peter Selvey

Leader
Super Moderator
What you are describing is foreseeable misuse. By definition, an applied part does not take into account foreseeable misuse, incidental, accidental contact etc. An applied part is a part the contacts the patient during the intended use as described by the manufacturer. Obviously that does not include while the device is charging, which can be specified in the IFU and also protected against e.g. if power on is prevented by software/hardware while charging.

Misuse, incidental contact still needs to be taken into account, but it's a separate issue and the judgement is based on risk. In my opinion it's not an issue largely due to the nature of contact, it's just not a high risk type of contact that raises special concerns. Things like like ECG electrodes or catheters, infusion devices etc that make low impedance contact with the body over long periods, sometimes with small contact areas, sometimes for unconscious patients or patient's that cannot react; they need special consideration. None of those apply. And as you said, it would be fairly rare thing to do anyway, being awkward.

Keep in mind that:
(1) risk is based on the probability of harm, not the probability of contact or misuse
(2) the standard for battery chargers will still have excellent insulation, it's just not the super special high level we required for applied parts in medical devices, for the reasons given above (low impedance, long duration etc.).

It's not like someone will get electrocuted from the battery charger if they put it up on their eye ;)
 

David Nicolson

Registered
Thank Peter, the points you make are well considered and make perfect sense. I think my next step is to establish the potential harm that could be caused by misuse as described previously, while considering the short contact time and the fact that the user will be conscious and not attached to the device.
 

mehrnaz

Starting to get Involved
Applied part is defined as having contact necessary for the intended use. So incidental contact is excluded. Someone could argue that it's not time related i.e. once an applied part always an applied part, but from first principles, applied parts have special rules based on the nature of contact which just don't apply in this case.

Dear Mr. Selvey
Thanks for all your helpful points you always mention,
I have a question regarding a heating pad which has to be worn and has a handheld control which is directly connected to mains in order to supply and control the heating pad, Im sending its similar product image in the attachment,
according to clause 8.10.4.1 Cord-connected handheld parts are exposed to severe condition and for the worst case, where the enclosure of such a switch is broken, IEC60601-1 standard needs them to be supplied within the limits of clause 8.4.2.c, which is not exceeding 42.2v,
but on the other hand from the clause 4.10.2 Handheld devices can be supplied up to 250V,
would you please help me with this problem, whether this is allowed to supply this equipment directly to Mains supply?
 

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Peter Selvey

Leader
Super Moderator
It's not a case I have seen before. I think 4.10.2 is intended to cover the whole equipment, which may include a power supply part that is not hand held, while 8.10.4.1 covers the actual hand held part(s).

Either way, 8.10.4.1 would take priority and it makes sense. Mains voltages are dangerous and they are best confined in a small space in the power supply, it is best not to have them in cords and hand held controls where possible. This is not only the control but the heating pad itself, it would be a worry if this is directly mains. It can be done, but it needs a lot of insulation, plus endurance testing, environmental testing, waterproof testing etc etc to prove it is safe over the lifetime of the device. Much easier to use a SMPS and run everything of say 12V, 15V, or 24V at the most if high power is really needed.
 
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