Robot Car Base for Experimenters - Power board

Posted by: @jbo

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Hi. I'm really enjoying Use a PS3 Controller with an ESP32. I know I'm late to the party; I didn't watch it at first, since I'm not a gamer, do not have a console, and just misunderstood the concept. I'm catching on. 🙂 

Even before the main project, I immediately liked the idea of a board for some common functions, and thought Bill's setup is great. I want to do something similar, though perhaps with a smaller scope.

So I'm looking at the video and article where it's talking about a third voltage for servos. The component seemed small in the video, compared to the LM2596. Bill didn't name it specifically, here, but I remember a section in a different power article, so I thought about that.

I came up with Positive voltage regulators L7806 (Amazon link). 

Sorry for long preface, but my question is this: did I get this right, would this be a reasonable choice to drop my 2x18650 (nominal 7.4V) batteries to 6V for a light duty servo? 

Thanks!

John

Yes, that is a 6V regulator. NOTE it is limited to 1.5A or 1,500 milliAmps. The VR can be used in parallel to double the current, but if you need much more than that a different VR is needed. Now I just use chatgpt to ask for 3 part number of 6VDC output Voltage regulators that can produce x Amps.

Hi Jbo,

You may have a problem with that regulator. It is rated for 8V and up on the input, and will not produce 6 volts with only 7.4 in. A low drop out (LDO) regulator would be a better choice.

See the article here:

https://www.ti.com/lit/ml/slup239a/slup239a.pdf?ts=1728429834609#:~:text=Low%20dropout%20regulators%20(LDOs)%20are,clear%20and%20easy%20to%20understand.

Mouser electronics has a good selection, just enter the voltage and current you need and pick a package type that works for you.'

https://www.mouser.com/c/semiconductors/power-management-ics/voltage-regulators-voltage-controllers/ldo-voltage-regulators/?output%20type=Fixed&output%20voltage=6%20V

Bob

@bbutcher85 @zander  Thanks Ron, Bob, for your answers. I will keep reading, and looking around for good choices. Thanks for the idea on ChatGPT. To gain confidence, I have only (so far) used ChatGPT and others for questions to which I already have the answers.

Ron, regarding voltage drop, I'm kind of embarrassed. In Bill's article I referenced, I only had to read a few more paragraphs to get the detail you mentioned:

Despite their age these regulators are still very much in use today and are good for line-powered designs. They are not as efficient as modern regulators however so for battery powered devices you’ll want to look at some of the other solutions presented here.

Oh well, still learning. A robot car definitely qualifies as battery powered. It's hard to remember all these factors at once - which is why I'm glad to have you guys! Thanks again, John

Here's my LM2596, mounted on perfboard using "stilts" of 18 AWG wire. I have no idea how other people use it. I am intending to use it to supply the 5.0V for the microcontroller, typically Arduino Nano. However, just for grins, I asked ChatGPT for 3 buck converters that would convert 7.4 to 6V, and would power two SG90 servos. It suggested LM2596, two different part numbers, plus a Mini-360. These were all in Bill's article, so that felt good. 

So I got to thinking. Never had a Mini-360, but maybe I could use one for a Nano (or ESP32), and use the LM2596 for the servos, since it can provide more current. Anyway, don't mind me, just rambling on. 😉 

Switching converters are a good choice, especially when your battery voltage is a lot higher than the load voltage, but they are larger, heavier, and usually a bit more expensive than linear regulators. For comparison if you used a linear regulator to drop 12 volts to 6 volts, you waste power. In that situation the linear regulator will turn the same amount of power the servo uses into heat (50% efficient). If the servo uses 0.5 Amp of current (I), the servo power (watts, V*I) would be 3 watts. The power wasted in the linear regulator would be [(Vin-Vout)*I] or 3 watts, likely requiring a heat sink. 

A good switching regulator can be closer to 90-95% efficient, prolonging battery life a bit. It probably will not save much power with the small difference in load vs battery voltage in your situation.

Switching regulators come in three varieties, buck, boost, and buck/boost. The buck regulator works only for battery voltage higher than the load voltage. The boost regulator works only for load voltage higher that the battery voltage. The buck/boost regulator will work for battery voltage higher, lower, or equal to the load voltage. The LM2596 is a buck regulator.

In your case I assume a LIPO battery which has a nominal voltage of 7.4 volts. In reality the battery voltage will be 8.4 volts when fully charged, and will drop to 6.54 volts when fully discharged. The battery should remain above 7.4 volts except for the last 10 % of battery charge, so this may not be a big problem. 

An LDO regulator will stop regulating if the minimum input voltage drops too low. It provides a simpler solution, but the drop out voltage (Vin-Vload) must be considered. For this application you would need a drop out voltage of less than 0.54 volts to be able to get regulation down to minimum battery voltage. This is considered an ultra LDO. If you don't try to get the last 10% out of the battery, the drop out voltage could be <= 1.4 volts.

The power loss would not be too bad for a linear regulator in this situation. If the servo uses 0.5 Amp of current, at full charge the voltage difference would be 8.4 - 6 = 2.4 volts times 0.5 A = 1.2 watts. at 10% charge, the voltage difference would be 7.4 - 6 = 1.4 times 0.5A = 0.7 watts. The average power loss over the full discharge cycle would be close to the average, 0.95 watts.

Bob

Posted by: @jbo

↑

Hi. I'm really enjoying Use a PS3 Controller with an ESP32. I know I'm late to the party; I didn't watch it at first, since I'm not a gamer, do not have a console, and just misunderstood the concept. I'm catching on. 🙂 

Even before the main project, I immediately liked the idea of a board for some common functions, and thought Bill's setup is great. I want to do something similar, though perhaps with a smaller scope.

So I'm looking at the video and article where it's talking about a third voltage for servos. The component seemed small in the video, compared to the LM2596. Bill didn't name it specifically, here, but I remember a section in a different power article, so I thought about that.

I came up with Positive voltage regulators L7806 (Amazon link). 

Sorry for long preface, but my question is this: did I get this right, would this be a reasonable choice to drop my 2x18650 (nominal 7.4V) batteries to 6V for a light duty servo? 

Thanks!

John

If you're using light-duty servos and the current is low (under 1A), the L7806 should work fine. Just be mindful of potential heat.

@bbutcher85  Thanks for that. I think that would work, at least in one scenario, similar to Bill's. He had just one servo; looked like an SG90. That could pan a sensor.

@bbutcher85  Thanks, Bob. I have heard some of this before, but repetition may help me retain it. I especially appreciate your tradeoffs between regulator vs. converter, in that "gray area" where there's a voltage difference, but not too much, and the difference decreases over time, with battery discharge.