Powering Nano from batteries best practise.

I am hacking an old RC Car handset, basically just taking out the old circuit board and replacing it with one powered by a nano.

The handset was powered with 8 AA batteries, so around 12V (I am getting 12.7V with brand new batteries) and wanted to ask what the best way was of using that power.

So the Nano needs 5V and I am also using a NRF24 which needs 3.3V. I have plenty of space to include additional voltage regulators.

So I believe I have a couple of options but I dont know what would be thought of as best practise.

Option 1. Connect the batteries directlly to VIN on the nano and let the internal regulator handle the 5V and also connect the 3.3V regulator to teh batteries. My concerns here would be both the regualtors overheating due to having to deal with the large dissipation.

Option 2. Have a seperate 5V regulator just to power the nano. Still have the 3.3V regulator connected directlly to teh batteries.

Option 3. Have the seperate 5V regulator use that to power the nano as well as powering the 3.3V regulator.

Option 4. Something else entirely that you would suggest.

So how would you do it?

Thanks.

I don't know about best practise but I would use 5V and 3.3V DC-DC converters connected to the main battery. NOT linear voltage regulators. So no problems with wasted power causing overheating.

Steve

I've looked into that but apparentlly buck converters cause RF interfearence so would be the best option to be used in a RC handset.

How much power does each of your components use? That would be my first question if I were doing this.

On the 5V side its just the Nano and two 5K pots, I've found a few posts elsewhere suggesting 200-300ma draw from the nano.

On the 3.3V side will be a NRF24L01+ PA LNA and I have found some posts showing a draw of between 20-140ma depending on transmitting or receiving.

Is there a way you could alter how the batteries are connected? If you could change it somehow so that 4 cells were connected in parallel with the other 4 cells, you would only have 5~6V instead of 12V

PaulRB:
Is there a way you could alter how the batteries are connected? If you could change it somehow so that 4 cells were connected in parallel with the other 4 cells, you would only have 5~6V instead of 12V

... or you might not need all 8 batteries, really. You could make the extra 4 slots for fresh battery storage.

From reading other Threads I get the impression that the nano's 3.3v pin cannot provide enough current for even the low power nRF24 (with PCB antenna).

...R
Simple nRF24L01+ Tutorial

Robin2:
From reading other Threads I get the impression that the nano's 3.3v pin cannot provide enough current for even the low power nRF24 (with PCB antenna).

...R
Simple nRF24L01+ Tutorial

I haven't tried that, but I recall that the ESP8266 will make the onboard regulator run really hot... probably close to or over the limit. It's definitely a concern.

GForce2010:
...connect the 3.3V regulator to teh batteries.

I don't think the OP is planning to run the NRF module from the 3.3V output of the Nano.

PaulRB:
I don't think the OP is planning to run the NRF module from the 3.3V output of the Nano.

...which is limited to the 50mA from the FT232RL.

PaulRB:
Is there a way you could alter how the batteries are connected? If you could change it somehow so that 4 cells were connected in parallel with the other 4 cells, you would only have 5~6V instead of 12V

aarg:
... or you might not need all 8 batteries, really. You could make the extra 4 slots for fresh battery storage.

That is a fair point that I did not think of. Although I dont think I would be able to get away with just 4 batteries would I? the 5-6v would be fine for the NRF24 through a 3.3V regulator but the nano really need 7v+ when using an unregulated supply. I know it can work down to 6V but standard AA batteries don't hold the voltage level for long. I could bypass 2 cells to give me around 9V.

Though if I am now loooking at modifying the battery tray it might just be easier to use a small 2s LIPO battery that gives a nice level 7.4V seeing as I already have chargers etc.

Will you be using only NiMH rechargeables? If so, 4 of them will give you around 5V. Bypass the Vin pin of the Nano and power it directly from the batteries through the 5V pin. This should give pretty good battery life, as the Nano will be fine down to 4.2V, and possibly lower. (Don't use non-rechargeables like this, the higher voltage could damage the Nano.)

Alternatively, use a 3.3V 8MHz Pro Mini. This will extend your battery life even further (no USB-serial chip to waste power). Power the Pro Mini via its Vin and you can probably use the 3.3V output to power the NRF module also.

"Option 1. Connect the batteries directlly to VIN on the nano and let the internal regulator handle the 5V and also connect the 3.3V regulator to teh batteries. My concerns here would be both the regualtors overheating due to having to deal with the large dissipation."

You should be able to check that out pretty quickly just connecting things up with some test leads. If there are some issues, then you can move to the next options. There are efficient 5v/6v UBEC voltage regulators on ebay for a couple of dollars that are made for RC systems. Getting efficient 3.3v might be a little more challenging.

PaulRB:
Will you be using only NiMH rechargeables? If so, 4 of them will give you around 5V. Bypass the Vin pin of the Nano and power it directly from the batteries through the 5V pin. This should give pretty good battery life, as the Nano will be fine down to 4.2V, and possibly lower. (Don't use non-rechargeables like this, the higher voltage could damage the Nano.)

Alternatively, use a 3.3V 8MHz Pro Mini. This will extend your battery life even further (no USB-serial chip to waste power). Power the Pro Mini via its Vin and you can probably use the 3.3V output to power the NRF module also.

Again, something else I didn't think of. I was planning on using a Nano because that was what I already had but using a 3.3V processor would simplify things by only having one voltage required. I think I still need an external regulator as I have found some spec showing the in internal regulator can only handle about 150ma.

So now I am looking at using only 4 AA batteries outputting somewhere between 4.8V-6V depending on using standard or rechargables with a single 3.3V regulator to provide power to both the NRF24 and a 3.3V pro mini. I already have some ST LD1117V33 regulators that can handle up to 800ma.

Thanks.

aarg:
...which is limited to the 50mA from the FT232RL.

Presuming it is a "genuine" Nano. :astonished:

Wrong board! The USB interface - whatever it is - on the Nano will waste current. A Pro Mini is more appropriate, also smaller, and you could indeed use a 3.3 V version. If you use a switchmode "buck" converter you can efficiently use any batteries - such as 12 V.

Paul__B:
If you use a switchmode "buck" converter you can efficiently use any batteries - such as 12 V.

From what I've read whilst researching this project Buck converters are fairly noisy and could cause problems with the NRF24. A linear regulator, although not as effiencent, doesn't cause any noise so would be the better option in this case.

Careful what you read! :roll_eyes:

The frequencies used by the switchmode converter and the NRF254 are very different. :astonished:

GForce2010:
From what I've read whilst researching this project Buck converters are fairly noisy and could cause problems with the NRF24.

I am creating some radio controlled 009 model railway locos. They are powered by a 1S LiPo in the tender. Also in the tender is a cheap Chinese voltage step-up board to give 5.5v for driving the motor. The Attiny84 is powered directly from the battery and I use a diode to drop the voltage for the nRF24.

Initially I had some trouble with slow response from the radios and it seems to be related to the step-up board. However the problem has gone away - I think because of more careful routing of the wires that connect the tender to the loco.

I realise I am using a step-up converter rather than a buck converter but I think their internal circuitry is very similar.

...R

GForce2010:
From what I've read whilst researching this project Buck converters are fairly noisy and could cause problems with the NRF24. A linear regulator, although not as effiencent, doesn't cause any noise so would be the better option in this case.

I've modded a couple of RC transmitters including DC-DC converters with no problems and used them in a few other RF projects. That's why I suggested them back in #1.

Steve