Frequently Asked Questions - Wireless
It is surprisingly hard to do. The big problem is the battery terminal voltage is heavily influenced by how the battery has been discharged in the past. If it has been run down slowly with power gradually pulled out say over a 24 hour period, the relationship between remaining battery capacity and terminal voltage is fairly well defined. If the battery has been discharged heavily, say by a Lectro UM250, the relationship is not so clear. Basically the battery bounces back to a high voltage and can look like it is still pretty fresh. Under either a light or heavy load it will run down quite rapidly. The problem is, the battery tester has no way of knowing the past history of that particular battery.
As a demonstration, if a fresh 9 Volt is accidentally shorted out with a piece of metal for 1 minute, you will get very odd results. The battery will get moderately warm. If the battery then sits unused for 8 hours, the terminal voltage will then measure pretty close to a new battery even under a brief load, but it will only run a transmitter for 5 minutes or so and then die almost instantly. In fact, if you then let it sit for a while again, the voltage will come back up again and die again in a transmitter in just a few minutes. I agree that this is an extreme case but it does demonstrate the problem of prior history.
Even when you know the history you can get bit. Recently we have been running battery tests on different brand batteries and we have found that some alkaline batteries tend to die very rapidly at the end of their life but other brands continue to run with lots of warning before they finally die. What's worse, different batteries from the same manufacturer may act differently. The reason we did the test is that we were getting complaints that the UCR201 was not giving sufficient warning with batteries made by XXXX brand, a major manufacturer. We tested the batteries and found that Evereadys gave 34 minutes of operation after the battery indicator started flashing its warning and the XXXX brand were giving about 3 (!) minutes of warning. We found this to be consistent with XXXX from 3 different parts of the country. Since so many of our dealers sell XXXX, we aren't sure what to do other than recommend Eveready as the standard. The XXXX brand is a perfectly good battery but it has a slightly different chemistry that is optimised for things other than high current drain.
The safest answer is that a low voltage reading will always indicate that a battery is weak but a normal or high reading may not necessarily mean that a battery is good. This is why so many pros that absolutely depend on their equipment, put in a fresh battery at the beginning of a job or whenever there is the slightest doubt that the battery will "last long enough"
This information was gathered for a question on the RAMPS newsgroup for a UM200 transmitter but should be proportionally the same for other transmitters.
(See also FAQ #009-WIRELESS)
For newer tests on the iPower LiPoly rechargeable 9 Volt See (FAQ #086-WIRELESS)
Here's some more battery information as I promised a few days ago. It took a while to run all the batteries down. Here is what we did: we used the same transmitter, a Lectro UM200 for all the testing. This is a 100 mW UHF belt pack transmitter. This particular unit pulled 75 mA. We ran four different kinds of batteries to a final voltage of both 7.0 and 6.6 Volts. 7.0 Volts is where the LED is pretty dim and where two of our receivers with battery readouts start indicating low battery and 6.6 Volts is the very low battery indication. The transmitter is getting close to completely dying at 6.6 Volts but will usually run to 6.4 Volts or less. The LED goes out totally at 6.8 Volts. I'd put all this in a table but I don't think it would survive the news readers' formatting. So I'll list the type of battery and then the very dim LED point (7.0 Volts) and then the maximum use (6.6 Volts). Your mileage may vary.
- Ultralife Lithium 16.0 hours and 17.2 hours
- Duracell Ultra Alkaline 6.5 hours and 8.25 hours
- Eveready Alkaline 4.75 hours and 6.75 hours
- Varta NiMh rechargeable 2.5 hours and 2.5 (!) hours
- Varta after 2 months of sitting around is the same as above, 2.5 hours.
Here's my conclusions: Assuming that a sound mixer with good common sense would toss a battery when the LED is very dim (or sooner) and using an standard alkaline as a reference, you'll get 3 times the life with a lithium, about 40% more life with an Ultra alkaline and about one half the life with a top quality nickel-metal hydride (NiMh) battery. (Though the Varta NiMh claims only 150 mAh, they start out at more than 180 mAh.) Also, the NiMh batteries don't self discharge as quickly as NiCad batteries since the battery after sitting for two months was still at close to full capacity.
Disclaimer section: These were fresh, new batteries at room temperature. This was just one test, performed on just one transmitter.
Anti-disclaimer section: Most brands of alkaline batteries are about the same, alkalines and lithiums have a long shelf life, and our transmitters are pretty consistent. We have found the Eveready batteries to give the longest life for a standard alkaline battery. In any case, the ratios of battery life should be good numbers. You guys know what kind of battery life you are getting now, and the ratios should be informative.
Here's the total and long winded story on Lectro low end frequency response. Once upon a time, all the transmitters were set up to be flat (1 dB down)to 50 Hz. Some UM195 users were having problems with low frequency rumble driving the bass compander and causing rumble modulated breathing in the system. We did 3 different fixes in the system, one of which was to roll off the input at 70 to 90 Hz. We picked this number cause that's what Vega was using and they were the Big Dogs at that time and we figured, correctly, that they knew what they were doing. This improved the operation of the systems and all seemed well except that Jerry Bruck (the Schoeps importer) wanted response down to 50 Hz. So for a while we did a Jerry Bruck modification that was basically back to the original input reponse. Jerry knew what he was doing and could handle the room rumble and wind noise in other ways. Then a lazy engineer (me) decided this was too much paperwork to track all his orders and redesigned the UM series transmitters to have a variable rolloff. That way Jerry could have his cake and we didn't have to build bake a special. You can hear the rolloff on voice if the rolloff is set to maximum (185 Hz). If you set it for 100 Hz or lower, it leaves voice alone.
The UH195 and UH200 plug on series were never rolled off since most pro microphones have a low end roll off anyway or have switchable filters. Or they have extended bass reponse and the user has selected the mic for that bass reponse. In any case, we left the UH's alone and they are flat to below 50 Hz.
Here's the answer I posted on RAMPS about 9 Volt battery life:
Here's the last of the 9 Volt battery tests. This is a similar test to what we did in a previous post but with a high power transmitter. (See also FAQ #005-WIRELESS) For newer tests on the iPower LiPoly rechargeable 9 Volt (See FAQ #086-WIRELESS) Here is what we did this time: we used a 250mW transmitter, a Lectro UM250 in the testing. This is a 250 mW UHF belt pack transmitter that eats 9 Volts like they were potato chips. This particular unit pulled 105 mA. We ran three different kinds of batteries to a final voltage of both 7.0 and 6.6 Volts. 7.0 Volts is where the LED is pretty dim and where two of our receivers with battery readouts start indicating low battery and 6.6 Volts is the very low battery indication. The transmitter is getting close to completely dying at 6.6 Volts but will usually run to 6.4 Volts or less. The LED goes out totally at 6.8 Volts. I'll list the type of battery and then the very dim LED point (7.0 Volts) and then the maximum use (6.6 Volts). Your mileage may vary.
- Ultralife Lithium 5.5 hours and 6.6 hours
- Duracell Ultra Alkaline 2.6 hours and 2.8 hours
- Eveready Alkaline 1.8 hours and 3.2 hours (!)
- Varta NiMh rechargeable 1.0 hours and 1.25 hours
These are interesting results. If you saw the earlier post with a similar table, you will notice that the Ultra alkaline has the same 50% advantage to 7 Volts but when run to 6.6 Volts, has instead, a 13% LOSS. This is not the same as for a 100 mW transmitter. There the Ultra was 50% ahead at either end point voltage. The Ultra fell like a rock when the voltage got to 6.6 Volts. In fairness to the battery manufacturer, these 1/4 watt units are very hard on batteries. Same disclaimer as before: These were fresh, new batteries at room temperature. This was one test, performed on one transmitter. And same anti-disclaimer: Most brands of alkaline batteries are about the same, alkalines and lithiums have a long shelf life, and our transmitters are pretty consistent. In any case, the ratios of battery life should be good numbers. You guys and gals know what kind of battery life you are getting now, and the ratios should be informative. We have found Eveready to be the most consistent general purpose alkaline.
On to other projects. I've seen enough battery strip charts for a while.
The 185 series has diodes to the power supply to protect the output from 48 Volt phantom power or other high DC voltages on the output jack. If the voltage on the output line exceeds 12 Volts, the diodes turn on and shunt the excess voltage. Since the diodes are now conducting, they also shunt (kill) the audio. The solution is to remove the 48 Volts. Some years after the first 185 design, we ran into mixing boards (poorly designed IMHO), where the 48 Volt was on all the mics or none of the mics. We redesigned the protection to either include non polar capacitors or shunt resistors to ground as well as the diodes. The newer designs prevent the audio from being shunted. This is what you will find on all receivers after the 185 series. It is possible to change the output on your 185, but I recommend just removing the 48 Phantom power when necessary.