Ni-MH Voltage

Xzn

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At our theatre, we're tiring of using up almost a thousand AA batteries per run (about 4 weekends). We have 20 actors, all wearing Shure wireless behind the ear mics (we produce musicals).

PROBLEM is: The Shure mics detect how much capacity is left based on voltage of Alkalines. A freshly charged set of NiMH batteries would register about 50% full on my RF base station.

Is there a way around this? Are some NiMH cells higher in voltage than others? Seeing around a thousand AA's thrown away per month + the cost of Duracell Coppertops is staggering.
 

Mr Happy

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Some NiMH cells do maintain higher voltages than others. Sanyo Eneloops are notably good in this regard. A freshly charged Eneloop will start out over 1.4 volts, and will typically maintain above 1.2 volts almost to the end of its charge.

Alkaline cells decrease in voltage as they are used, starting out about 1.6 volts and dropping all the while until they are mostly discharged at 0.9 volts. Devices designed for alkaline cells ought to work reasonably well right down to 1.1 or 1.2 volts.

If you put Eneloops in one of your mikes, you might find they would register 50%, but remain that way for the whole time until they were empty. It is also possible that they might register 100%.

Since every device is different, it is hard to predict without testing. You could try buying a set of Eneloops and charger and doing the experiment with your particular microphones. Charge up the Eneloops before use because they will come out of the package with a lowish voltage.

In the digital camera world there are many variations in how well different makes and models behave, and some cameras will work perfectly on Eneloops but not work well on other brands.
 
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Marduke

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Sounds like it's worth spending $20 on a Eneloop Charger + 4AA's at WalMart (camera section) to find out if they will work for you.
 

SilverFox

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Hello Xzn,

You will have to run a few tests.

It may be that, while the initial indication is 50%, it may stay at 50% for an extended period of time. This means that you would loose some resolution on your indicator, but you still may get ample runtime.

Tom
 

Darkpower

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At our theatre, we're tiring of using up almost a thousand AA batteries per run (about 4 weekends). We have 20 actors, all wearing Shure wireless behind the ear mics (we produce musicals).

PROBLEM is: The Shure mics detect how much capacity is left based on voltage of Alkalines. A freshly charged set of NiMH batteries would register about 50% full on my RF base station.

Is there a way around this? Are some NiMH cells higher in voltage than others? Seeing around a thousand AA's thrown away per month + the cost of Duracell Coppertops is staggering.
You might consider RAMs (rechargeable alkaline manganese). I use those in devices that need the full voltage, long shelf life and are low drain. However, as far as cycles, you will only get 25 to 100 cycles if you deep discharge and much more up to 500 cycles if you shallow discharge.

If your microphones need one set of batteries every night, that might be too much discharge and you will ruin the RAMs. But if you get two or three uses out of each battery set (50% to 30% discharge), then RAMs may work for you but you will have to swap out the batteries after every show, and charge them.

The nice thing about RAMs is they have a very long shelf life.

http://store.sundancesolar.com/axlramrealba.html
 

NA8

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PROBLEM is: The Shure mics detect how much capacity is left based on voltage of Alkalines. A freshly charged set of NiMH batteries would register about 50% full on my RF base station.

Is there a way around this?

I have an old Palm OS PDA that had a code you can enter that would change the calibration of the battery level indicator for several different types of batteries. This wasn't in the owner's manual, I found the information in a palm users group forum. It's possible you can change the calibration of your mikes either with a software trick or through a resistor change. You might email Shure or do some snooping around the internet.
 

Xzn

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You might consider RAMs (rechargeable alkaline manganese). I use those in devices that need the full voltage, long shelf life and are low drain. However, as far as cycles, you will only get 25 to 100 cycles if you deep discharge and much more up to 500 cycles if you shallow discharge.

If your microphones need one set of batteries every night, that might be too much discharge and you will ruin the RAMs. But if you get two or three uses out of each battery set (50% to 30% discharge), then RAMs may work for you but you will have to swap out the batteries after every show, and charge them.

The nice thing about RAMs is they have a very long shelf life.

http://store.sundancesolar.com/axlramrealba.html

If we put in fresh batteries, they're about 60% at the end of a performance, so we throw them away for redundancy. SOMETIMES.. I sneak them into 2 performances but if any mics start cutting, i'm in hot water (people pay $30+ per ticket).

I'm mainly the lighting guy that knows sound.

P.S. Metal Halide moving lights rock :p
 
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Sub_Umbra

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This is interesting -- and sad. I'm another who wonders if there isn't some way to tell the mics that you're using NiMH cells. As a last resort, perhaps there is some way to do a firmware upgrade to make them play nice with NiMH cells.

At the club where my wife techs they bought some new body mics that seem to love rechargables of all flavors. I maintain a set of lowly AA 1000 mAH NiCD cells in a FIFO box (First In, First Out) and they have performed flawlessly -- astounding the sound techs that handle them. The mics must automagically sense the cell chemistry as the base gives no false readings on them.

If nothing else perhaps you could get a good dynamic cell analyzer, use it all the time and just blow off the indicators on the base station.
 
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Xzn

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How do you plan to deal with the logistics of charging 250 batteries every week?

Well if I can find a solution that works, I would not mind getting 6 Maha C801D's.

That's just the mics.. Our crew uses Telex wireless intercoms for communication. We have 12 Telex TR-800's ( http://www.bhphotovideo.com/c/product/334911-REG/Telex_71306B4R5_TR_800_2_Channel_UHF.html ) with PH-1 Headsets ( http://www.bhphotovideo.com/c/product/88539-REG/Telex_64438100_PH_1_Full_Cushion_Single.html ). Each uses 6AA batteries. Every 2 shows, we end up chucking out 72 batts.
 

Sub_Umbra

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Hi again,

I brought up this thread with Mrs Umbra this morning as we have hashed out some of these issues for a while. We know that all houses are different and what works in one may not work in another -- still, below are some points which will help in some situations, no matter what chemistry you end up with in your mics. You probably do some of these things already.
  • Date all primary cells before use.
  • If you power up mics 30 min before curtain consider changing power up time to 15 min before curtain.
  • Sometimes when you can't get 2 performances out of a given cell you may be able to safely get 1.5 out of it. While one sound tech can't change out the cells in 20 mics in a 20 min intermission, chances are that there is time to change out all the cells for the Chorus. They may often safely get 1.5 performances from their mics as they aren't used as much as the Principal's are.
  • By keeping topped off cells in a locked box right in the dressing room and only swapping out the Chorus cells this may become a doable intermission task.
  • The sound tech needs to literally chase down and haunt all miked performers immediately after each show to get those mics shut down and get the cells out of them ASAP. Every min that they are left on after a show is another min they can't be making money for you on stage.
  • While some dated alkys may have had too much use for even another 1/2 performance some of their cost may still be recouped by using them for rehearsals. Some of them, anyway.
We've found that each of these tactics may variously increase run-time of any mic by 6, 4, 3, or 2 percent. When it's all added up in your real world situation you may find that you gain enough run-time to get more out of the alkys you have to use or find some applications that your secondaries now have enough headroom for safe use during performances.

YMMV. Hope this helps.
 
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mdocod

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I would test out some eneloops during rehearsals and especially in your intercoms. keep track of how much runtime you are getting out of cells. Just to make sure they will make it through a performance without any possibility of failure (plenty of overhead).

I'm not sure how many cells go in those Shure mics..... I'm going to assume 2 per transmitter. I'm not sure how many shows you have in a day. Assuming 2 shows 3 nights a week? That would account for A lot of cells being tossed....

My personal method would be to plan on swapping the cells of every mic and intercom between every show and rehearsal. This way you would never be very worried about a cell you tried to get through an extra show with going dead on ya, and no guilt of waste either :) If I'm doing the math right, adding those intercoms into the equation, you need to have about 300 cells on hand. And the ability to charge as many as about 150 at a time. Does this sound right?

As far as the logistics of the battery level indicator, the test run during rehearsals might give some indication of what can be the expected behavior of the state of power indicator there. The way I see it, by always knowing that a freshly charged set of cells is going into every mic before every show, there wouldn't be any substantial need to even watch the battery indicator, one less thing to worry about during the show anyways, so might be well worth the investment.

Don't worry about the MAHA 808, nice charger, but it's going to take up too much space on the rack and cost too much to be worthwhile. If figure you need to be able to charge up to ~150 cells in a day. A large charging station will need to be set up with ~150 available charging bays... You could probably work out a deal on 20 MAHA 800S chargers for about $1000.. Which is probably overkill. But would definitely pay for itself... Are your "runs" back to back pretty much all year long or do they come and go? this may be the difference between whether a cheap charger investment or fancy charger investment should be considered. A rack of 20 800S chargers could be loaded up with yesterdays used cells when you come into work that night, and be done and ready to go part-way through the shift, which may be overkill...

In an effort to reduce initial costs, I would have to imagine that you could get by on a set of like 15-16 10 bay "cheap" chargers, like these: http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=518
With these you would have to make sure all the used cells are on the charging station before you leave at the end of the night, and they should all be topped up when you come in the next day. Total cost of 16 chargers (enough for 160 cells) would be ~$350..


So in theory, buying 300 eneloops should get you a bulk discount that's at least, sortof noteworthy, maybe $450-500? Plus a huge charging station, even if you build a charging station out of 800S, you're looking at ~$1500 total investment... based on my calculations, it would pay off in about 3 runs, sound around right to you?

Sorry if I can have way farther in depth than required here, I'm just thinking out loud about how I would deal with this situation...
 

TorchBoy

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You might consider RAMs (rechargeable alkaline manganese).
They have some advantages, but they lose capacity with every cycle so it wouldn't be long before they weren't lasting a full show.

Xzn, this is a fascinating thread. The rate at which you go through batteries is incredible. Until you get all those Eneloops and 8 or 10 slot chargers how about giving all the 40% used cells to the local Scout troop?

Sub_Umbra, would dating a thousand batteries every month-long run really be a good use of time?
 

UnknownVT

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eneloops and Uniross Hybrios are reputed to maintain higher voltages.

eneloop actually claims higher voltage maintenance on their Canadian site.

To see how this may actually affect things practically - specifically in my Pentax K100D dSLR - which is known to be very battery fussy - in comparison with another LSD - Kodak Pre-Charged (which also has good rep) - please see this thread -

eneloop vs. Kodak Pre-Charged Voltage Maintenance

Note this is higher operating voltage maintenance ie: under-load, as opposed to open-circuit - as seen in that thread the o-c voltage on the Kodak P-C were very respectable - yet it showed lower charge level on the dSLR than the eneloops, even though the eneloops were used more and actually had lower o-c voltage.

Other threads of relevance -

My Eneloops charge to and hold a higher voltage than other LSD's ...
in Post #15 Chevrofreak claims Uniross Hybrios maintain higher o-c voltage. But beware all Hybrios may not be equal -
When is a Hybrio not a Hybrio?

[Slightly OT] Cutoff voltage of cameras favors Low Self-Discharge batteries?

As others suggest - try some eneloops ($9.99/4 at Circuit City, I have also read HH Gregg had them for $7.99/4 - but NOT listed on their website) and a fast charger.....
 
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eebowler

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Hmmm.
Xzn said:
At our theatre, we're tiring of using up almost a thousand AA batteries per run (about 4 weekends).
Assume 1000 cells in 4 weekends (to make it easy). That's 250 cells a single weekend and approximately 125 cells per day... Does this sound about right?

Xzn said:
If we put in fresh batteries, they're about 60% at the end of a performance
Alkaline cells have a capacity of about 3000mAh. Assuming that this 60% figure is correct, each performance you use approximately 1200mAh.

A rechargeable cell of 2000mAh capacity (eneloop)should be more than enough to last a performance even with some delays.

An 8 bay charger such as This one would be suitable for your needs and are relatively cheap. (I've had one for over a year now and it hasn't given me any problems.)

If you do need to recharge 125 cells per night (day, or whatever period you are not performing) you'll need a maximum of 16 of these chargers. They charge at 750ma so theorhetically should take just under two hrs to recharge the 1200mAh removed from the batteries after a performance. If cost is an issue and someone does have the time, you can have half the number of chargers and some willing individual to remove the fully charged cells and put the rest of the uncharged cells to charge in time for the next performance. 16 chargers: recharge time = 2 hrs. 8 chargers: recharge time = 4 hrs.

Of course, some system must be kept in order to keep the used cells away from the fully charged cells. Recharging fully charged cells will damage them.
 
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Jarl

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Make sure you get a smart charger. That way, even if fully charged batteries do get put in to charge, they shouldn't be damaged.

A big bin that the performers drop their used batteries into at the end of the show should work (though batteries can be damaged if they're dropped too far), as long as you make sure people know to only put in used batteries- have them return unused batteries to you (for whatever reason they're unused).
 

eebowler

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Jarl: this happens with smart chargers. A NiMH cell has a slight drop in voltage (dV) when it's full. If you place a full cell to recharge, it will begin recharging and the charger will keep checking for the dV drop which would not happen since the battery is fully charged already. Maybe my explanation is incomplete and maybe the battery doesn't recharge indeffinately but it will be overcharged.
 

TorchBoy

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They recharge at 750mAh so theorhetically should take just under two hrs to recharge the 1200mAh removed from the batteries after a performance.
You mean they charge at 750 mA (or "750 mAh/h")?

What happens if someone forgets to charge any cells? Would it be a good idea to have an alkaline backup supply? (These should be dated, as per Sub_Umbra's suggestion earlier.)
 

Bones

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Trying to keep track of the charge status of a several dozen cells in this situation strikes me as an impossible task.

Accordingly, the only viable option may be to always use a standard .2C discharge to 1volt and a .1C timed charge of about 14 hours.

That way, you're never going to cook the cells by overcharging due to missed terminations, and it will also maximize available capacity.

As well, whenever you're in doubt about a cell's charge, you can just toss it in the charger with the only negative consequence being the loss of a single cycle.

I presume this option would also negate voltage depression.
 

mdocod

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here's a thought:

to insure that cells get cycled properly, order half eneloops and half hybrio cells that way they have a substantially different look to them, have hybrio days and eneloop days. alternate days, that way all you have to do to make sure everyone has charged cells is just make sure they are all using the right brand for that day.
 
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