Battery Packs

[rockrobotics]

I have two 9.6V battery packs!  But the problem is that he's saying that you need a 6V battery pack for the $50 robot.  Will the fiveV regulator thing fix this problem to lower it to 6V?  Please help!  Thanks!

[Ryltar]

I believe the regulator will lower it to the required levels. The primary issue with this is that it will waste a lot of energy and heat. You also have to worry (though not too much I think) about burning out the regulator if it gets too hot.

Taken directly from the Advanced Electronics Tutorial page on the site:

A 20V battery can also be regulated down to 5V too. However to drop a voltage, current must be expended as heat. Inneffecient! Always try to have the smallest voltage change possible when using regulators. If you need a regulated 5V, use a 6V NiMH pack for example.

[Soeren]

Hi,

Use one of the switch mode replacements for 7805 and the loss will be smaller than the regular setup with 6Vin and 5Vout.

[rockrobotics]

Thanks Ryltar, and Soeren I know you're trying to help, but you sound too technical, and I'm a beginner!  Can you explain to me what you're talking about!  Thanks!

[rockrobotics]

Okay pleeeeease answer me....Will I have to buy the 6V NIMH pack or can i stick with the 9.6V NIMH pack?  I just want to know if the heat WILL be a problem!  I don't want to buy a another battery pack, but if it's a really good idea to then I will.  Thanks.

[little-c]

7805  < the regulator.

switching regulator, a regulator that is a lot more efficent at dropping higher voltages.

[SmAsH]

Well, it will work as long as the servos don't run off that battery directly.

[guru]

Yes, you will be better off finding an appropriate 6v battery pack if you dont have any requirements for 9v. If your servers can only handle 6v and servos combined take a lot of power, getting a switching supply wont save you any trouble. Having said that, if you really want to use the 9v battery you can find ready made switcher modules as easy to use as a 7805. DO NOT USE a 7805, it *will* get too hot for servo use. It would be ok to power a small PIC, Atmel IC, propeller IC, etc. (This is because the small IC only needs a little amount of power, so the power loss from 9v -> 5v would be small too, and it wouldnt get that hot either.) Even a heatsink on the 7805 probably isnt going to help you much. Plus the loss will consume about 1/3 of the battery, so your 1000mAh battery just became a 600mAh batt (the math isnt exact here, see datasheets if you want exact loss.)

Here is an example of a switched regulator thats plug compatible with 780x:
http://www.all-battery.com/1aswitchingvoltageregulatorseriesSW050.aspx

more at:
http://www.all-battery.com/search.aspx?find=switched+regulator

I just ordered from all-battery.com, great experience, really good support. I talked to the support guy with a few questions and he was really helpful and friendly.

If you want to make your own switching regulator circuit, they are pretty simple circuits. Finding the right diodes and coils are the toughest part usually (but not that hard at digikey or mouser). Download Linear Tech SwitcherCAD (LTSpice):
http://www.linear.com/designtools/software/

LTSpice has examples for every switcher IC they have, and the you can see how well they operate with different part substitutes. easy peasy to use.

[Soeren]

Hi,

If you want to make your own switching regulator circuit, they are pretty simple circuits.

Strange postulate here!
I can assure you that even seasoned engineers sometimes give up, as they relied on jigsaw puzzle assembly instead of math (of which there's a brimfull in even a simple switcher). A total noob should stay well away and stick to the drop in replacements for linears.

[guru]

I've made a number of them and I havent had any problems, but I suppose you're right there is a lot going on inside even a simple switcher. Notice I first gave links to ready made switcher circuits. For 15$ I dont think you could make your own as cheap given time and money.

With Linear's LTSpice they have lots of examples. I've often used those as a starting point. Then after sourcing the parts, I enter in all the part parameters including the impedance of the coil and caps.

Soeren: I know I dont need to tell you how a switching voltage regulator works, but for the rest of us:

A switching voltage regulator is a servo, not much different than the control theory in our RC servos. I like to use water as an example. The coil and capacitor are like a storage tank. There is a valve off the bucket leading to the system load. The valve will open/close as the requirements of the system load change, thus the speed at which the tank empties will vary. You, the controller, will continually fill the tank with more water, but only as fast as required to keep the level of water constant, if you overfill a little, you will back off some. If the water level drops quickly you will add more water quickly. However, there may be a point where you cant fill the tank as quickly as it is emptying...your ability is saturated and the system will break down. In this case, you are the servo controller.

In the switcher's case. It is servoing the voltage in the coil and capacitor. If it drops, it pumps more current into the coil, if it rises it backs off a little. It is pumping the coil with current via a PWM output gating a mosfet. The mosfet charges the coil which feeds the cap. The c ap is the source for the system load. The switcher controller will vary the PWM duty cycle to keep the voltage constant.

Every electrical system follows V=IR. In this case, the system R changes, the controller measures V, and changes C to keep V constant.

Hi,

If you want to make your own switching regulator circuit, they are pretty simple circuits.

Strange postulate here!
I can assure you that even seasoned engineers sometimes give up, as they relied on jigsaw puzzle assembly instead of math (of which there's a brimfull in even a simple switcher). A total noob should stay well away and stick to the drop in replacements for linears.

[Soeren]

Hi,

Notice I first gave links to ready made switcher circuits. For 15$ I dont think you could make your own as cheap given time and money.

Yes and they are the best option for a hobbyist.

Every electrical system follows V=IR. In this case, the system R changes, the controller measures V, and changes C to keep V constant.

That's a gross simplification when talking design of a switch mode power supply. Just the magnetics involved will give you pages (assuming pen and paper calc) of math, if you wanna do it right.
Then comes endless hours of measuring and tweaking.

Doubt me?  Then answer this: How many µm of gap do you use and what's the permeability and dielectric constant of whatever material fills this gap.

I don't think a hobbyist wanna go into this, when their main goal is making something besides a switcher.

There's quite a large difference between a good design with 90% to 98% efficiency and something thrown together after a now-it-does-produce-an-output approach, which can easily be as low as 50% (or even worse than a linear supply).

The drop-in replacements is the best way to go if you just want something that works.

[waltr]

Søren is completely correct about designing a switcher PS. They are not easy!

[guru]

The answer, of course, is "it depends". You make it sound like we shouldn't attempt anything because we are too dumb to handle math. Maybe I am oversimplifying things. I was trying to relate something that most people don't understand in a way that they can. Regardless of being simple, the metaphor works. I've done many things that were beyond me at the time, but I learned, because the journey is more important than the destination.

Hi,

Notice I first gave links to ready made switcher circuits. For 15$ I dont think you could make your own as cheap given time and money.

Yes and they are the best option for a hobbyist.

Every electrical system follows V=IR. In this case, the system R changes, the controller measures V, and changes C to keep V constant.

That's a gross simplification when talking design of a switch mode power supply. Just the magnetics involved will give you pages (assuming pen and paper calc) of math, if you wanna do it right.
Then comes endless hours of measuring and tweaking.

Doubt me?  Then answer this: How many µm of gap do you use and what's the permeability and dielectric constant of whatever material fills this gap.

I don't think a hobbyist wanna go into this, when their main goal is making something besides a switcher.

There's quite a large difference between a good design with 90% to 98% efficiency and something thrown together after a now-it-does-produce-an-output approach, which can easily be as low as 50% (or even worse than a linear supply).

The drop-in replacements is the best way to go if you just want something that works.