9V rechargeable batteries and chargers?

Yep, I shall try not to forget to do that :-)

Probably more than 1/2 year though because you can't tell a premature battery capacity drop before that. I neither believe nor expect the 1000 cycles most marketeers claim. If we get 100-200 out of them I'll be happy. Capacity and the reliability to accumulate a true full charge is much more important to us.

A typical 9V-shaped NiMH rechagable outputs a nominal 7.2V

there may be some brands constructed with 7 pancake cells in them, but AIUI mut use 6 AAA cells.

eg:

If they will run off those rechargables Li-poly will be an improvemenr.

Nowadays they are pretty much all 8.4V except for some Maha/Powerex and maybe other brands with 9.6V.

Those are really sub-par these days and our mikes do not run on 7.2V NiMH batteries. Must be at least 8.4V. There are some 9.6V versions as well.

I'd love LiPoly because of the mAh but afraid someone will screw up with those but putting them in a standard charger. We even had people throw NiMH away because they thought they were primary cells.

Joerg,

It seems many of the problems are caused by the manufacturer's choice of battery style. He needs ~8 volts to operate the mike, but the required current will quickly drain the battery. So you are faced with an expensive battery that has a short operating life and minimal number of recharges before it has to be discarded.

How about using a clip-on microphone with the cable going to a belt- mounted transmitter. The battery could be an external package mounted on the belt with an extension cord to the transmitter.

That way you could enlarge the battery pack to whatever is needed, and use whatever battery type gave the best performance for the money. This would allow you to use much less expensive batteries that will stand up to the heavy use.

Perhaps you could use a battery that has a simple method of monitoring the state of charge. For example, I believe that a sealed lead-acid shows the state of charge by simply measuring the voltage at the terminals. But I don't know if SLA is available in the small size needed.

I went to a recent LTspice seminar by Mike Engelhardt. He used a similar arrangement with a belt transmitter, but I didn't think to enquire what kind of microphone he used. His speaking tours cover a lot of countries in a very short time, so he doesn't have much chance to keep the batteries charged. Maybe you could ask him what kind of setup he uses and see if that would help fit your needs.

Mike

That's what we have. Shure and Sennheiser belt packs plus lapel microphones. Also two handhelds of same technology.

Under a pastor's robe that would be a major bulge. Unless the pastor is a heavy-set guy (ours isn't) people could think he's got a concealed-carry gun :-)

Usually speakers like him use the setup provided by the hotel or other event venue. For example, you cannot legally use most US systems in Europe and vice versa.

The new Sennheiser belt packs are much better because they (finally!) figured out that AA cells are much more efficient. The new series can offers over 6h or uptime. However, those things are expensive and we can't just toss >$2k worth of gear. The new charger is only $40, much better deal. If that together with 8.4V/300mAh batteries still won't be good enough we'll try the LiPoly variety that Martin suggested. But only after major training so nobody ever plugs these into a regular NiMH charger.

Then just get a 9V battery clip and bring it out to your own battery pack, mounted on the same belt. Your choice of AA, C, D, etc.

No, he has his own system, including a Class D amplifier and speaker. I asked if he had any problems going through airport security. I believe he said the only problem was when he used his own amplifer, they always questioned it. But that stopped when he got a small commercial unit.

The seminars last from about 8:00 am until I think 3:00 pm or so. Then he has to catch a plane to go to the next city. He arrives late, so he barely has time to check in and get some sleep, then back at it again the next morning. A terrible, grueling schedule. I asked him how on earth does he manage to keep his energy up. His answer was medical grade caffein!

A 9V battery clip with a sold shell cost very little on eBay. I got some

- they are very good quality. You can hook them up to anything you like.

I would recommend coating the contacts with a light film of petroleum jelly (Vaseline). This removes any surface oxidation and leaves a thin film that lubricates the contact and prevents grime and oxidation from forming. It reduces the contact resistance by a factor of ten and stabilizes it. I have measured the results and can confirm it works. It's an old radio engineer's trick from the 1930's, taught to me by the engineers at radio station CFRB in Toronto, Canada. Works great on all kinds of electrical connections - SATA, memory, flashlights, toys, etc.

Mike

Just for confirmation, here is a picture I took while he was setting up for a seminar. You can see the overhead projector is turned on, and I think he is extending the legs on a stand for the notes. As you might imagine, he has done this many times, so it is very smooth and there is no wasted motion. He can do it in his sleep.

I only wish I had taken more pictures. He is a fantastic individual, and he has done an incredible job getting SPICE to new users. Along with Helmut, these two are my vote for the most influential engineers of the century.

Mike

Oh, our pastor and others would hate that. Plus it'll wreck the whip antenna on the belt pack in no time. They have to wear the pack inside a pocket. Also, there are no battery clips, it's a nifty slide-in bay with a sturdy metal latch.

Well, I guess where there is no plaintiff there will be no judge. Don't let the French equivalent of the FCC hear that :-)

Yikes! That's an almost perfect recipe to work yourself up towards a heart attack. And at Mike young age those are often fatal.

And I agree, Mike ought to be given a Nobel prize or something. He has done more for electronics engineering than nearly anyone else.

Even the Chinese know. The cheap meters I got for the road all had that on the wiper contacts. Probably Confucius told them :-)

I'm sure he was joking. I used to travel a great deal on business, and the adrenaline can keep you going for a while. But his tours are unbelievable.

Amen

Mike

One way to deal with that is to throw out every NiMH charger

Of course we'd do that. However, you know how it goes. Someone swaps a battery during a bible study and puts the other in his shirt pocket. Drives home, darn, should have stuck this into the church charger. When the family gets there next Sunday it'll be too late. Oh wait, the teenagers have some sort of charger up there and that has those 9V battery contacts ... *POOF*

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charger.

If you add LiPoly to the mix, please be sure to use a very different connector. It will help reduce oopsies.

?-)

And that's the problem, it is impossible to do so. It must be the regular 9V battery contacts or they won't fit the mikes.

Or 'The burning bush'. :)

Oh yea of NO faith!