I'm getting a great deal on a Sennheiser kit including bodypack transmitter, lav mic, and handheld mic. The only problem is that the receiver runs on a DC adapter, and I would need at least part of the time to be mobile.

The EW300 receiver is listed at 10.5 – 16 V DC, nominal voltage 12 V DC. I have a portable mixer that runs at the same voltage and also off 2 X 9v batteries, and I was wondering whether I can just make a battery pack that plugs into the DC input, or is it more complicated than that?

I did a Google search but there does not seem to be a battery pack accessory for that receiver.


J.

I ran a quick search on the Sennheiser website, and I'm a bit confused. They seem to use the model number EW300 for several different systems, including an IEM system.

I did not find a specific receiver with the model number EW300. If you can provide a different, more specific model number for the receiver, I will try to research it.

Aside from that, as a general rule, I would think you could easily power your receiver from a battery pack, especially because the specs you quote seem to indicate a fairly wide voltage range.

Of course you need to be sure you're providing the correct polarity at the connector. You may want to provide a bit of decoupling from the battery, and perhaps an RF bypass capacitor. The power pack should be fused at the battery end, to protect you in case the end connector is accidentally shorted.

You should ascertain the receiver's DC current draw, and be sure your battery pack has adequate amp-hour capacity to keep the receiver running for an adequate length of time. In general, the small 9V batteries have pretty low amp-hour ratings, so you may end up using a bank of 10 or 12 AA cells (assuming you want to use rechargeables, which are ~ 1.2 volts each). But of course in that case you'll need a charger that can recharge all of them, if turnaround time is important.

Alternatively you might consider a 12 volt gel cell, which will have a great deal more capacity, but will be heavier and less portable in the trade.

If you find a specific model number for the receiver, I'll try to provide a more specific answer.

Thanks Greg. The receiver model is EM 300 G2. The AC adapter is listed at 12v, 300 mA. I have several rechargeable 9v batteries at home that are rated at 280 and 300 mA (the biggest I could find), but I also thought of using AA batteries since the ones I buy are rated at 2200--2800 mA.

J.

Hello again Greg, I just purchased this on ebay. It's cheaper than making my own. :-)

Portable 12V Li-ion Rechargeable Battery Pack 6500mAh - eBay (item 110615719782 end time Mar-23-11 23:30:51 PDT) (http://cgi.ebay.com/Portable-12V-Li-ion-Rechargeable-Battery-Pack-6500mAh-/110615719782?pt=US_Batteries&hash=item19c135ef66)

J.

Hi Jacques,

If the adapter is rated at 300mA, then as a worst case the receiver needs that much current. That's fairly reasonable.

Personally, I would avoid 9V batteries for this application. One battery won't provide enough voltage for the receiver's 10.5V minimum. Two in series would provide too much voltage for the receiver's 16V maximum. Sure, you could jury-rig some sort of voltage regulator to lower 18 volts to 12, but any sort of regulator will be less than 100% efficient, so you will just eat up some of your run time.

Ten NiCd or NiMH cells in series would give you about 12V as a starting point. The best brand of NiMH are the Sanyo Eneloop cells, the AA size is rated at 2,000 mA-hrs, so a pack of those would give you better than six hours of run time. (Maybe more, if the receiver actually draws less than 300 mA.) A battery pack like that could be fairly portable and light. As I said, though, you'd need a way to recharge ten cells, if turnaround time is important. And you'd want to get a charger that charges each cell individually! If you try charging them in series (even in series pairs, as many cheap chargers do) you will end up with unevenly charged cells, lower voltage, shorter runtime. You must always charge and monitor each cell individually.

If you go with NiMH, I urge you to consider the Eneloop brand cells. They have a much better shelf life than other brands. (NiMH cells self-discharge just sitting on the shelf, so if you haven't recharged them the night before you need them, they may be seriously discharged when you grab them. Thus, most NiMH cells are not a good choice for "go kits" that might sit around for a few weeks and then be needed on short notice. Eneloops will largely avoid that problem.)

However, the current model Eneloop charger charges cells in pairs, so it's not a good investment. You'd need to go with a brand like Maha, and get a few of their 8-cell chargers if you need to charge 10 cells at once (e.g. overnight). Ideally you want a charge rate of about 1/10 of the cell's capacity; in other words, if it's a 2,000 mA-hr cell, you want to charge at around 200 or 250 mA, so fully charging will take about 8-10 hours. A low charge rate like that will prolong the life of the cells. If possible, avoid fast chargers.

Or, as I said, if you want a lot more runtime, a simpler charging scenario, but more weight, go with gelled lead-acid chemistry. You can get one 12V, 7 A-hr battery, such as is frequently used in UPS power supplies, and one charger for it, and be done. That battery would give you well over 20 hrs of runtime (with a 300 mA load).

If you're not the DIY type, you may well find some commercial 12V battery packs, already made up, and marketed with appropriate chargers.

As I mentioned before, if you construct any sort of external battery pack, be sure it includes a fuse right at the battery, to protect you from any potential short circuit in the cable or connector.

The EM receivers can be run easily on battery power. I have a rack of 4 mics and 4 IEMs that is powered by an Anton Bauer 90W brick, runs most of the day.

The receivers don't require a lot of current, but I don't think it will run very long on 2x9V, besides thats really outside of the required voltage. Radio Shack used to sell a battery holder than held 8 "AA" size batts, wired with the right power plug would give you 12V and run one receiver for more than a few hours.

Another option is to just get a portable receiver on the same freq range as your transmitters. The EK100/G2/G2 and EK500/G2/G3 are all compatible with your 300 series transmitters. It is much smaller for your camera, but will also have reduced range compared to the EM receiver.

@Greg, the EW prefix is used for complete packages. Individual components use EM for rack receivers, EK for portable receivers, SK for body packs, SKM for handheld mics, SKP for plug on transmitter, and SR for the IEM transmitters.

Radio Shack used to sell a battery holder than held 8 "AA" size batts, wired with the right power plug would give you 12V and run one receiver for more than a few hours.

Eight non-rechargeable cells (typically 1.56 volts per cell) would give you 12 volts.

But eight rechargeable cells (typically around 1.2 to 1.25 volts per cell) would give you under 10 volts total, and that's when the batteries are fully charged and fresh.

So, unfortunately, if you want to use rechargeable cells, an 8-cell holder wouldn't provide the specified 10.5V minimum. IMHO you're better to start with ten cells, 12 volts, and have a little room for voltage droop as the cells discharge before then hit 10.5 volts.

Of course, you could just give this "great deal" a gigantic swerve and just go for a fully mobile system to start with, and save all this buggering about.

It ain't cheap if it costs you a heap and all the hassle of running a system in "limp mode".

I never cease to be amazed what normally sensible people will spend to get systems "cheap" when it's going to cost 4 times the money and sheer bloody murder to make work and keep it running down the track.

Avoid at all costs is my answer, but I guess you already spent the money?

Bit late to ask after the event, guess you're stuck with that turkey.


CS

Bit late to ask after the event, guess you're stuck with that turkey.

I wasn't asking permission to buy the unit, Chris. I was asking about running the receiver off a battery.

I found a rechargeable 12v, 6400 mA battery pack (with charger) for $25 on ebay. So the "turkey" (em 300 receiver, sk 500 beltpack lavalier, skw 500 handheld mic and rechargeable battery pack) ended up costing me $400, all inclusive. Perfect working condition.

@ Jacques:

I just saw, this morning, that you had bought a Li-ion pack. I started my (long) comment early yesterday, was interrupted, and didn't finish it until evening. Apparently you posted during that period so I missed it.

Well, that pack certainly should have enough capacity to run your mixer. Li-ion batteries have very high energy density. They have suffered from some manufacturing defects in the past; perhaps you recall the self-igniting laptop computers (Sony, I believe). The construction of the cells makes them also somewhat susceptible to physical damage resulting in an internal short circuit, excessive internal current, overheating, etc. I believe I recently heard that some airlines have banned transportation of Li-ion cells for this reason.

Also, Li-ion cells need to be charged quite carefully. Laptop computers that use them have internal charging and protection circuitry that is specific to the particular cell for that model.

Hopefully the charger you purchased is appropriate and safe for that particular battery pack.

By all means, protect that coaxial power connector from accidental shorts!


@ Chris Soucy

Contrary to your comment, I doubt that any animals are involved in Jacques's setup.

Some people like to throw a wad of money at the "latest and greatest" offerings from the marketing department. Manufacturers and retailers love these folks.

Others prefer to adapt, modify, and learn in the process. IMHO a thorough understanding of theory, often obtained as a result of thinking things through and spending some time working in the shop, is a very valuable resource which keeps one flexible and functional in unexpected situations. I'm frankly surprised that anyone in this forum would deride another member for trying to get some extra functionality from his equipment, while learning something in the process. (I call this attitude "pride in ignorance.")

At one end of the spectrum, there are appliance users. At the other end, engineers. To each his own.

Jacques -

I bought a 12v model, similar to the one you purchased off EBay for my wireless receiver and it works fine. After a year, mine still works very well.

I know a couple other people using them to power everything from receivers to monitors and haven't heard any horror stories.

@Greg: the battery pack is a bit of a test. If I see that I do need to use the receiver running off batteries a lot, I may buy a better-suited NiMH pack. But given that I'm doing a lot more corporate videos and less roaming events, I may be running it off the AC more than I had anticipated.

@Tom: That's very good toknow. I've often thought of setting up rechargeable batteries in a belt pack to power assorted equipment. The "pro" belt packs are prohibitively expensive, but this may prove to be perfectly suitable alternative.

J.

@ Jacques:

The battery pack you bought, in theory, should be fine. I just wanted to post a few precautions, to be on the safe side. Pack it carefully when transporting it.

By the way, since it isn't clear whether that is a "smart charger" that will reduce current or turn off when it senses the battery is fully charged, I would advise you to disconnect everything after a reasonable length of time for a charging cycle. Typical chargers are designed to charge in about 10 hours, but that one might be a bit different.

To be really scientific, we might need to get out a multimeter. Let me know if you want to go that far, and I'll try to provide some more helpful info. Otherwise... carry on!

Hi Greg, I received the battery pack today (the only drawback to ordering from China is the long transit time, but hey free shipping!).

I was worried about the size of the barrel connector, so the first thing I did was plug it into my ew 300 receiver. Not only is the connector a perfect fit, but the battery came pre-charged and powered on the receiver right away (see pic).

2011-04-05 12.21.16 | Flickr - Photo Sharing! (http://www.flickr.com/photos/11588302@N03/5592747842/)

At 6500 mA, the battery should run the receiver (300 mA) for longer than I'll ever need it. I'll run some tests, and if they're successful I'll get more battery packs for my other devices.

I've also thought about using the pack to run my laptop, which I sometimes use to capture video directly. I have to run tests, but in theory when the battery pack runs out, the laptop's battery should take over, affording me continuous power. If I get several battery packs, I can run my laptop indefinitely.

J.