Looking for some advice on making my first project. May be a little ambitious...

Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
Hey guys, I'm in the middle of creating / planning my first real project. I'm looking for some advice on the circuit to power all the components.

Overview :
I am making an RC charging station to charge LiPO batteries on the go. I made a 12v - 3s6p 18650 battery pack. My charger is 12v/8a Max. I also want to include 12 volt DC input in order to power the charger at home to charge up the 18650 pack. Along with the charger I want to include a Raspberry Pi and a Arduino Nano.

I'm going to use diodes for the dual-power inputs and charging the battery. I'm planning on using a voltage regulator IC in order to Step the voltage down for the Raspberry Pi and Arduino. Should I put the filtering before or after the voltage regulator? I was thinking of just using a simple LC filter.

I'm in the middle of making all this into a schematic to have for reference instead of just all in my head. I Pretty much understand how it all has to be done now I just need to put it all together. I'm going to build it outside of the case first.
RC_Charge_Case_v1.0_2.png
***the capacitor on the output of 5v voltage regulator is supposed to go from the 5v output and ground. Schematic app moves things on export ***


Thank you
 
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spinnaker

Joined Oct 29, 2009
7,837
Hey guys, I'm in the middle of creating / planning my first real project. I'm looking for some advice on the circuit to power all the components.

Overview :
I am making an RC charging station to charge LiPO batteries on the go. I made a 12v - 3s6p 18650 battery pack. My charger is 12v/8a Max. I also want to include 12 volt DC input in order to power the charger at home to charge up the 18650 pack. Along with the charger I want to include a Raspberry Pi and a Arduino Nano.

I'm going to use diodes for the dual-power inputs and charging the battery. I'm planning on using a voltage regulator IC in order to Step the voltage down for the Raspberry Pi and Arduino. Should I put the filtering before or after the voltage regulator? I was thinking of just using a simple LC filter.

I'm in the middle of making all this into a schematic to have for reference instead of just all in my head. I Pretty much understand how it all has to be done now I just need to put it all together. I'm going to build it outside of the case first.

I will upload a schematic tomorrow. Any advice would be greatly appreciated.

Thank you

Buy a proper Lipo battery charger and avoid burning yourself or burning your house down. Engineers with years of experience sometimes get design wrong and start fires. Doubtful someone with no experience is going to be able to do any better.

And you just don't apply a voltage to a Lipo and expect it to charge properly. There is a whole science in charging batteries.
 

MaxHeadRoom

Joined Jul 18, 2013
19,197
I got a beauty on Ebay, cheap, it monitors the charge voltage and regulates accordingly, can be set for a few battery technologies, it also can be used in the field from a 12v automotive lighter socket.
I could never build one for the cost.
Max.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
Hey guys thanks for all the replies. Maybe I didn't State my project be clearly I tried to make it short.

I already have a lipo charger. I am putting the lipo charger and a big battery in a case to charge batteries in the fields on the go. I'm using the big battery to power the charger so I can charge my RC batteries. But when I get home I want to be able to power the charger with a 12-volt adapter so I can charge the big battery that's in the case so it's ready for the next use. I'm not trying to charge the big battery with a circuit I'm trying to design. I am just creating a circuit so either the battery can power the charger or when I get home a 12 volt adapter can power the charger. I think for now I am going to manually plug the big battery into the charger to charge.,

I hope this makes a little more sense. I would never think of trying to balance charge a big battery like this from my own homemade designed circuit.

I should have the schematic uploaded some time tonight
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
Project details:
1. built in raspberry pi with 7in touch screen. which will play music, record video, run software to change paramaters for our racing/freestyle quadcopters, games etc... with speakers & camera built in to the cases lid.

2. built in 50,000mah diy 18650 battery to run a RC charger to charge our quadcopter lipo batteries

3. Battery Voltage LCD readout

4. USB ports to charge misc. electronics and batteries etc...

5. Built in amplifier and speakers

6. 15v DC input from wall adapter in order to charge internal 18650 battery* / power RC charger when mains voltage is avalable, with auto switching circuit using diodes.

7. RGB led strips underneath the Plexiglass inside the case to illuminate it. And change colors as the Battery voltage drops, as a easy battery voltage indicator.

* I AM NOT MAKING A DIY CHARGING CIRCUIT TO CHARGE THE INTERNAL 18650 BATTERY!!! (everyone is always assuming i am and warning me on the dangers of doing so incorrectly)
 

atferrari

Joined Jan 6, 2004
3,489
Project details:
1. built in raspberry pi with 7in touch screen. which will play music, record video, run software to change paramaters for our racing/freestyle quadcopters, games etc... with speakers & camera built in to the cases lid.

2. built in 50,000mah diy 18650 battery to run a RC charger to charge our quadcopter lipo batteries

3. Battery Voltage LCD readout

4. USB ports to charge misc. electronics and batteries etc...

5. Built in amplifier and speakers

6. 15v DC input from wall adapter in order to charge internal 18650 battery* / power RC charger when mains voltage is avalable, with auto switching circuit using diodes.

7. RGB led strips underneath the Plexiglass inside the case to illuminate it. And change colors as the Battery voltage drops, as a easy battery voltage indicator.

* I AM NOT MAKING A DIY CHARGING CIRCUIT TO CHARGE THE INTERNAL 18650 BATTERY!!! (everyone is always assuming i am and warning me on the dangers of doing so incorrectly)
You seem to be upset for the warnings. Do not feel bad and do not complain. All what warned you about, are doing the right thing. Your safety is a concern.

Use capital letters to ask for help in an emergency. Relax and move on.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
You seem to be upset for the warnings. Do not feel bad and do not complain. All what warned you about, are doing the right thing. Your safety is a concern.

Use capital letters to ask for help in an emergency. Relax and move on.
No. Not at all... I appreciate them. What if I didn't know any better. I had posted another thread and included the project details. I just copied and pasted them into here so it's clear on what I'm doing.

Sorry if it came off the wrong way.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
RC_Charge_Case_v1.0.jpg

Sorry. I thought I added the schematic the other day. Guess it didn't work.

This is just the 15v dc input & 12v battery input circuit. Want to make sure I have this correct before I draw up the entire circuit. (very time consuming which I didn't expect).

After I have this main input circuit correct, I will try to add another diode/s in order to charge the battery from the rc charger while plugged into the 15v dc power adapter.

Any advice, and critiques on the above circuit is welcome. This is my first circuit that I have designed from scratch.

Thx again
 

Norfindel

Joined Mar 6, 2008
326
Charging the batteries will take time, and the process isn't a 100% efficient, so isn't it better to just charge the required amount of rc batteries at home, and swap them when needed?
You can still build the raspberry pi thing, now with less batteries required. Still, the raspberry, screen and speakers will consume a considerable amount of energy.
By the way, that 5v regulator is switchmode, right?

The diodes will allow the supply with the higher voltage to be the one supplying the power, and won't interact with the other. Your schematic shows the output of the 5v regulator going into a 5v and a 3.3v supply pin on the raspberry. The raspberry is powered by USB, so i suppose that you're just connecting the 5v there, and let any regulator on the raspberry board to take care of the 3.3v? Connecting a 5v supply to an input labeled 3.3v isn't generally a good idea.
 
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Thread Starter

bigjoncoop

Joined Feb 1, 2019
40
Charging the batteries will take time, and the process isn't a 100% efficient, so isn't it better to just charge the required amount of rc batteries at home, and swap them when needed?
You can still build the raspberry pi thing, now with less batteries required. Still, the raspberry, screen and speakers will consume a considerable amount of energy.
By the way, that 5v regulator is switchmode, right?

The diodes will allow the supply with the higher voltage to be the one supplying the power, and won't interact with the other. Your schematic shows the output of the 5v regulator going into a 5v and a 3.3v supply pin on the raspberry. The raspberry is powered by USB, so i suppose that you're just connecting the 5v there, and let any regulator on the raspberry board to take care of the 3.3v? Connecting a 5v supply to an input labeled 3.3v isn't generally a good idea.

thx for the reply...
'
we charge our lipos like this all the time out in the field. with a parallel charging board i can charge 4- 3s 2200mah lipo battery's that are at 10.5v bringing them to 12.6v in about 1 hour, running the charger at 6amps. (less then 1c charging rate. Charger is 6amp max)

The 5v coming from regulator is only going to the 5v pin on raspberry pi. Just looks like its going to both pins. (first time making a schematic with that software)
The 5v regulator is a 7805 ic

so the circuit i've made should work just fine? should I add any Capacitors or anything else on the 12v line going to the charger? i have some 35v 1000uf & 470uf, low ESR capacitors... not sure if they are needed or not, before and after RC Charger.

Anything else I should add or do differently?

I will upload the complete schematic with all the circuits as soon as i can finish it. Didn't realize making a schematic would be so time consuming....

thx
 

Norfindel

Joined Mar 6, 2008
326
Well if that's ok for your use, then no problems at all. But take into account that if you have 50 Ah battery, used to power a charger that charges another battery, and if this charger is, say, 70% efficient, your 50 Ah battery will only be able to recharge a 35 Ah battery. That's still a lot, however, and if it suits your needs, then that's ok.

Also, the datasheet for the 7805 specifies that "a 0.33 μF or larger tantalum, mylar or other capacitor having low internal impedance at high frequencies should be chosen". So, if you want to use the 33 uF electrolytics, that's fine, but you should also add the recommended ones, as electrolytics aren't good at high frequencies.
The raspberry pi 3 can draw from 500 mA up to 1 A, and you're lowering the 12 or even 15v to 5v using a linear regulator, so the power dissipated by the regulator can be anywhere from 3.5 watts up to 10 watts, depending on the PSU voltage and current draw. That's quite some power dissipation, especially for a battery operated device. That would require a big heatsink, and will eat power form the batteries needlessly. You should consider using a switching dc-dc converter instead.

Other than that, if the connections are short from the batteries to the RC charger, i don't think that you will need additional capacitors.
 
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