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Virtual Battery Supply

post #1 of 17
Thread Starter 
Hello,

I have been researching on this topic for a few days now.

So far, I found nothing but chargers schematics. Please drop me some info's

Tomo
post #2 of 17
re: ppl's post? I think that's exactly what he was referring to... a linear charger circuit that can supply the batteries with charge while they power the load, all during a constant charging... which is why switching is a no-no... heat notwithstanding.

Maybe there is more to it than that, but I'm like you in the searching... that is, I can't find anything related to it online.
post #3 of 17
Jeff Rowland Design Group uses this Kinda Supply Thay have an Ap Note on this in the Technical Papers section of there web site www.jeffrowland.com. I think you will fing this non Overly technical Paper.
post #4 of 17
Thread Starter 
Ppl -

It's a little too general for me except the part about SLC. Regulation, Current Control, and Ripple Control. Many documents say that.

What I would like to know is how I can constantly charging while in use. It seems like it is impossible without blowing the batteries ...

Tomo
post #5 of 17
One of the general articles on the site talks about it, but operation still depends on how long the battery charge lasts. With the design used for one of the models, it could only be operated for 8 hours max, then has to be put into Standby mode so it can charge for 4-12 hours before using again. The article also warns against completely unplugging the system and letting it run from batteries only, to prevent deep cycling? or draining of the batteries, which they say shortens the life ot the batteries.

So this leads me to believe that with Rowland's method, the battery isn't kept at full life while in use, only that it's slightly charged. Not quite what I was hoping for.
post #6 of 17
The Jeff Rowland concept is regarding High Power Loudspeaker amps. When using a Lowpowered Device like a preamp and Headphone amps then the Concept comes in real handy because the batteries can be charged at a rate slightly over the Quesencet Current Drain of the Device. A IC type charger can be used like the Max712 so as to stop Charging the Batteries when thay are full.
post #7 of 17
How does noise from the power supply used for the charger come into play in the rest of an amp? The basic picture I see is a charger connected to the terminals of a battery, with those terminals also connected to the amp circuit.
post #8 of 17
One Artical stated that Removing the Charging Circuit improved the Noise about 40 dB but it was still lower than without the Virtual battery Supply. Ni-Mh and Ni-Cad's have an extreamly low impedance and also make a good shunt regulator. Sure Batteries have Noise But Less than a Typical Zener Diode. IC Regs like the LM-337/LM-317 Degrade every Audio Circuit that thay are used in If Regulation is Needed then a Complex Discreet component Reg. employing a preregulator is what is required. Most all the Three Termanal regs are series pass type and have been Foiund By some folks like Myself to sound worse than a shunt regulator. The Series pass three term. regs have Limited bandwidth can be unstable unless tricks not found in the data sheet are used like small resistors in series with the Input and output of the Reg. This is to Kill the Q of the L/C circuit that is formed when the regulator turns inductive. In fact i think a simple series pass transistor Biased with a Zener or Better yet a string of LED's make alot better Regulator than those Three Term IC Regulators. In light of this it is no wonder that Virtual battery Supplys are finding sutch wide use in High End Audio. I noticed when i Last visited the Technics Site that they are well into Virtual battery supplys. as is Jeff Rowland. I have seen at leist one DIY Preamp that uses this also so if your interested let me Kow i can email you the Docs to that.
post #9 of 17
Thread Starter 
Hey, Ppl,

I am very interested in reading that article. Can you send it to me?

Tomo
post #10 of 17
I have been in the Process of Upgraging my old BUF-634 Portable amp. This amp uses what could be called a Virtual battery supply since the Batteries are being Charged by a constant Current source when ever the amp is conected to the wall wart. Since i have been buzzy with other amps this unit sat Pluged in to the adaptor for almost a year. the charge rate is 1/10 c. When i first removed the amp the case felt warm from the battery heat. But a run time test showed thae Ni-MH 16 AAA cell pack to still exceed it's rated Mah ratingand i noted what it was when new on a posteit notpad stuck to the bottom. What this proves i cant say but use the info presented hear as Needed.
post #11 of 17
How does battery charging work? Do you only need a current source, or a certain voltage source too?
post #12 of 17
Ni-Mh and Ni-Cad's require Constant Current See the battery data Sheet for Recomended Charging Currents for your batteries. The Pannasonic battery site has great info on this. Basicly the Voltage is limited by the battery to 1.2-1.4 Volts per Cell and any attemt to apply more voltage will just cause more Current to flow. (Like A Zener Diode). The most simplest of battery chargers use a resistor as the Current souce But i use a real Active Current source Like Jfets ar a Bipolar Curent source. A one way Diode is also placed on the Charger's output to Keep Current from flowing out of the bvattery into the Charger. The Max unloaded voltage of the charger at the battery Termanals should be 1.9 volts per Cell so as to allow a full Charge as when Charging the batteries will reach a Voltage Peak just prior to Being Fully Charged.

visit the Maxium site and download the Data sheet to the MAX-712 Charger Ic This has a Complete Data on Battery Charging. This IC is what i now use since it can quick charge the Batteries (Except 9 volts) In addition many Charge protection Scheems are available like thermal and Other charge termanation methods are available. If not using a Charger IC then Do not Charge at more than the 1/10 c or one tenth the MAh capacity of the battery continiously or overcharging will result. This would be like 50 MA of charge current for a 500MAh Battery. Again the Max-712 will automaticly trickel charge when a full charge is reached. I would recomend this circuit for Fool Proof Plug in and forget Charging and let the IC do the Battery HouseKeeping. You can Charge up to 16 Celles in series with this IC and a Pass transistor. Heatsinking will be rrequired for Quick Charging at the 1 Hour Full Charge rate. I use 5 Hour Full Charge rate.

If Charge IC's are not your thing then a somple resistor and Diode with the Current set at 1 tenth the battery capacity will work. BTW if your Current is less than about 30 Ma an LED can be used in place of the Diode.
post #13 of 17
Would it be stressing the battery too much through charging if I'm use 3 9V NiMH (160-170 mAH) rather than, say, 16 AAA's (650 mAH)? The current drain of the intended amp is probably ~60-70 mA (50 mA alone for a nice bright lamp ). I found a circuit using the MAX712 that will fast charge a battery until it's full, and then switch to trickle charging it. Should I expect the batteries to eventually die where they won't have any life?
post #14 of 17
Yes it would. Why do you need 50 Ma for the Indicator light? Is this Lamp Then used as a Nite Light? If not you only Need 2 MA using a supper-Bright LED as an Indicator lamp To see in evean Bright Ambient Light. So if your Current requirements are in the 50 MA range the 650 MAh is the Min. you need for a virtual supply and still not Overtax the batteries. I gess you want them to last longer than a year. Yes use the IC Charger Circuit for battery Housekeeping. While not an absolute requirement The IC will allow the battery to be Fully Charged, but not overCharged if Programed Correctly.
post #15 of 17
Yeah hmm, the lamp was the only reasonably priced non-colored LED (do you know how hard it is to find the right blue LED?) that I found and Radio Shack and happened to fit in a lens and LED-mounting setup that was made for T1 3/4 LEDs. I suppose if I order parts elsewhere, I should find a proper clear LED rather than this flashlight-type lamp It really is quite nice to look at behind the blue lens; not your typical LED appearance.

I'll have to build the courage to spend ~$40 for 16 AAA NiMH's instead of ~25 for 3 9V's, but it will happen (hey, it did with headphones and amp parts ).
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