Voltage Regulator

[dusty IV]

Receivers are designed for 5V nicads. I wonder how critical this is. WalMart is selling out the dis- continued Black and Decker 123 cells for $11 for two cells. These would make a great receiver pack for my Sail boat except the voltage is about 6.6V for 2 in series. What I really like about these Li-ion cells is almost zero self discharge. I can leave them in the boat house and don't have to worry about them being dead every time I want to go sailing.

Do I dare plug these directly into the rec and servo system? Probably need a voltage regulator. What would be the cheapest way to go for 5 V, 5 amps regulator? Trying to regulate 6.6 volts down to 5v is tricky.

[alexcmag]

The problem is not with the receiver itself, because it has a internal 3.3V regulator and so low current that will not complain with the voltage.

The problem is with servos, that would burn with the 7.4V of the two cells fully loaded.

You can use an UBEC or your can make your BEC using a linear regulator. I suggest using a LM1117-5.0 and a small electrolit capacitor (10uF x 10V is enough) in the output.

[thanhTran]

...WalMart is selling out the dis- continued Black and Decker 123 cells for $11 for two cells. ...

Is it an official announcement? I just bought a handheld vacumm cleaner from Black & Decker. Sure hope they don't discontinue making those cells...

Thanks

Thanh

[Dan Baldwin]

While the LM1117-5.0 is considered an LDO (low drop out) regulator, it's dropout is fairly high at about 1.2 volts. The current limit on that regulator is also a bit low at 800 MA. The L4940V5 is rated at 1.5 amps and has a typical drop out voltage of .5 volts at 1.5 amps. The mouser part number is 511-L4940V5.

There is a thread about using 2 A123 cells for the reciever pack in the Batteries and Chargers forum. http://www.rcgroups.com/forums/showthread.php?t=914941

Dan

[David T]

If you want the 5A you mention, the MIC29502 or cheaper clone like SPX29502 are good choices. 0.6v dropout.
David.

[Dan Baldwin]

If you want the 5A you mention, the MIC29502 or cheaper clone like SPX29502 are good choices. 0.6v dropout.
David.

OOPS :o

I missed the 5 amp requirement.
Sorry

Dan

[dusty IV]

Is it an official announcement? I just bought a handheld vacumm cleaner from Black & Decker. Sure hope they don't discontinue making those cells...

Thanks

Thanh
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There was a post on Batteries by someone who claimed he got an e-mail reply from DeWalt/Black and Decker saying the VPX line is being dropped because lack of sales. I have sent an E-mail to Corporate but no reply as yet and don't expect to get one.

There is a big patent suit on the chemistry that 123 uses. Every thing I read indicates they are in violation. There was an preliminary injunction ordering DeWalt and others to stop selling these cells it was claimed but I can find no court papers.

A very confused and convoluted mess with no official comment by anyone in volved. There is an official document that does detail the patent suit.

BAK China used to make the 123 cells but bailed when they were named in the patent suit.

I tend to believe that there is so much smoke here that there is a fire and DeWalt is/was out of the 123 Li-ion biz using 123 cells of any size. They don't need this hassle.

I also use some DeWalt tools using 123 cells but not to concerned as there are a lot of good Li-ion battery mfg out there and DeWalt will repackage packs. Not good PR to orphan tools me thinks. If you want a really nice hobby drill cheap,Walmart has the Black/Decker on sale for $60-$70 with batteries. I have one and for model making or light use is terrific. To weak for hard work like deck screws however.

I'm stocking up on the small 123 cells at $11 a pack. If the price drops to $5.00 I'll take them back to Walmart for return. Have 90 days to do this. On the big 123's I'm waiting as the price is still to high to stock up. My last buy recently was $125 delivered from ToolUp.

I no longer use anything but 123's in all my planes and since they don't wear out will last 5 years or so. By that time you won't believe what will be available for up to 3 times the ma, 1/3 the weight and half the cost. LG of Korea is the front runner on this and has the resources to pull it off for automotive use.

[Andrew0820]

The LM1084-5 (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=LM1084IT-5.0-ND) is a fixed 5v LDO regulator rated at 5A. Add a couple of 10uf tantalums and you're ready to go.

andrew

[dusty IV]

The LM1084-5 (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=LM1084IT-5.0-ND) is a fixed 5v LDO regulator rated at 5A. Add a couple of 10uf tantalums and you're ready to go.

andrew

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Good tip. I ordered 3 each from Digikey. Total delivered about $12. Think I will etch a small board to mount. VR part # was LM1084i7-5.0-ND and the caps were 478-1839-ND. I think I can get by with only one cap but will try to see what happens.

Thanks

[Dan Baldwin]

While the LM1047 is called an LDO regulator, at 1.3 volts typical drop out at 5 amps, it aint all that low. That means that at 5 amps your battery pack would have to be at least 6.3 volts under load to maintain a 5 volt output. Your actual current draw will probably be less than that most of the time, and the drop out voltage is probably less than 1.3 volts at lower currents, so it might work okay. Keep in mind that you will need a heat sink for that regulator.

I'm planning on using 3S lipos with a 10 amp switching regulator in my nitro plane, but I might use 2S 1100 A123 or K2 cells with a diode in series to drop the voltage a bit.

Dan

[dusty IV]

While the LM1047 is called an LDO regulator, at 1.3 volts typical drop out at 5 amps, it aint all that low. That means that at 5 amps your battery pack would have to be at least 6.3 volts under load to maintain a 5 volt output. Your actual current draw will probably be less than that most of the time, and the drop out voltage is probably less than 1.3 volts at lower currents, so it might work okay. Keep in mind that you will need a heat sink for that regulator.

I'm planning on using 3S lipos with a 10 amp switching regulator in my nitro plane, but I might use 2S 1100 A123 or K2 cells with a diode in series to drop the voltage a bit.

Dan

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Hi Dan, I'm aware of the higher VR drop on the 1084 and hoping the 5amp will minimize this problem. Can't imagine pulling anything close to 5 amps with normal servos full on. I bought them because that's all Digikey had, price was right and no minimum charge. If they don't work I'm out $12 ,no big deal. I also may want to use 3 mini 123's on a boat for more capacity, then the VR drop is not a worry.

I'm still confused on the regulator used on receivers. I have no idea what they are or how much dissipation they can stand. No free lunch as usual and overheat the small linear regulator they use will result in a crash. I'm using the Futaba Fasst 2.4Gig system. I doubt if Futaba will give you any info on max Voltage input or what regulator they are using. I assume you have seen the post on modifying the Spectrum Xmitter regulator to extend battery life. Using a switcher instead of the el cheapo linear.

Rule 101A- modifications always lead to grief. I never learn.

[ZAGNUT]

why fool around with regulators? a pair of A123 cells is just about identical voltage wise to a 5 cell nickel pack which every receiver and 99% of servos handle just fine.



dave