Impedance

Frank, Smitty, or Inga... can you explain impedance to me? I know it goes up at the end of battery life but don't understand what it is. My report today says 6-9 months battery life left but the tech said it'll be more like 2-4 mos since the impedance jumped from 2 to 6 this check. I go back in Jan and plan to ask to have it replaced at that time (Jan is not as busy as March and April, lol)

5 Comments

Impedance

by SMITTY - 2009-11-11 08:11:32

Tracey,

Webster's defines impedance as "something that impedes or makes an action more difficult." In your case it looks like the resistance (or impedance) to electrical flow on one or more of your leads has increased. This means your pacemaker is having to use more voltage, or more power if you wish, to get the impulse to your heart. This of course places additional load on the battery, which means it should play out sooner.

In your case look at the 6 to 9 months of expected remaining battery life and an impedance that has increased from 2 to 4. Now while I don't think impedance and battery life is a straight line function, if you double the impedance, then it stands to reason the battery life would be shorter than the stated remaining life expectancy of the battery because its additional work load .

Now don't take what I have said as absolute because I'm not that well versed in electronics and I do know there are many factors to be considered. One thing is as a battery gets weaker, it is unable to put out as strong a "punch" as it was so to perform the same amount of work it has to try harder and as it tries harder, it uses more of its remaining power. The snowball effect.

I see you have a St. Jude and when they were trying to sell me on a St. Jude to replace my Medtronic a few weeks ago one of the selling points was that the St. Jude would never "leave me on a hill" like my Medtronic did when the battery got weak. I have to say I got a chuckle out of the emphasis put on that point. Here I am 80 years old, with an expected battery life of 6 to 9 years and I find it hard convince myself I'll ever use up this battery.

Maybe someone can give you a better answer. I'll be watching.

Good luck,

Smitty

Battery Impedance

by ElectricFrank - 2009-11-12 11:11:42

It's probably easier to explain the effects of impedance than to get into the electronic definition of it. That used to come about half way though the semester when I taught electronics.

With batteries the effect of impedance is to cause the battery voltage to drop under load. If you have the headlights on your car turned on while running the starter you will see the lights dim a bit. This is the voltage drop from the internal impedance of the battery. As a battery ages the impedance rises due to chemical changes. So if your car battery is getting old you would notice the lights dimming more noticeably when using the starter.

The other thing that happens with age is that the actual voltage with no load also drops. So the battery life estimate in the pacer is based upon a complex calculation using both voltage and impedance.

The impedance is a better indicator though. I've been plotting my battery impedance and voltage since I was implanted. At implant the impedance was 100 ohms and the voltage was 2.79 volts. At my last checkup the impedance was 1935 ohms and the voltage was 2.68 volts. As you can see the impedance has gone way up, but voltage only dropped a small amount. Looking at how fast the impedance is rising, I don't have much longer.

Hope this answers it,

frank

numbers smumbers

by Tracey_E - 2009-11-13 05:11:43

Thanks Frank and Smitty! Frank, I still don't get what it is and I doubt I could make it through a semester in your class, but I can read the writing on the wall... no way will it make it until spring break. Either she was talking about something else or I misunderstood the numbers (was gabbing with her about our kids and forgot to ask for a copy of the report) because 2.something and 6.something don't sound like impedance.

It's going to be interesting getting through girl scout cookie sales without lifting. And a camping trip- me, 15 girls and one as-yet-unidentified other adult. I need to get on the ball finding another adult LOL, and kick myself just once for volunteering my troop for tents to free up cabin space for a younger troop on the waiting list. And the school band's rummage sale is in there. The timing sucks this time, but I won't complain because all of my other batteries have been kind enough to wait until summer break to go so I've been able to ship the kids to mom, and it's a dead time of year for my work and volunteering. Oh well! At least I should be good to ski by spring break :o)

Frank, how's your battery doing?
Smitty, you all recovered from your replacement now?

cookies

by Tracey_E - 2009-11-13 06:11:48

Patch, thank you SO much for clearing that up!! I'm taking the scouts camping next weekend, smores makings are the only food I bought so far. Wish I'd know all this impedance stuff before I found the hershey bars on sale buy one get one free.

Clearing up the numbers

by ElectricFrank - 2009-11-13 11:11:30

In electronics we commonly use the letter K to indicate 1000's. So where I mentioned 1935 ohms in my answer, some might correctly call it 1.935K or round it off to 2K or maybe just the the number 2. So when she said the impedance jumped from 2 to 6 she was saying that it went from 2000 to 6000 ohms.

This fits your comment of "it's a dead time of year". G(:

pace gently and be nice to your battery!!!

frank

You know you're wired when...

You have a $50,000 chest.

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