# Capacitor as backup to 12v train camera system power

Discussion in 'Power Electronics' started by mcates, Apr 3, 2019.

1. ### mcates

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0
Apr 3, 2019
Hello,
I am using a 12v step down that then outputs 2 USB 5v 2amp ports. I connect an HDMI 5v transmitter and a GoPro like a camera via USB 5v. I would like to put a capacitor in front of my 12v stepdown to ensure reliable power when the train is moving and sometimes may not have a solid connection to the tracks. I cannot seem to figure out what I need to do this. Looking for help on a simple capacitor backup to a 12volt system for a 1-3 second power loss. I have a Bridge Diode Rectifier before step down and I think I may need to add a Power Resistor and/or a Schottky diode. I am no electronics expert but I am learning... I just not understanding how to use capacitors as a momentary backup to this buck converter... Please, any help would be appreciated and I can share much more on what my situation is.

2. ### Alec_t

2,663
702
Jul 7, 2015
Welcome to EP!
To calculate the capacitor value you need to know :
1) How much current the transmitter draws,
2) How much current the GoPro draws,
3) How low the '12V' input to the 5V regulator (stepdown) can go before the 5V drops unacceptably.

My guess is that you'll need a pretty hefty capacitor.

mcates likes this.
3. ### BobK

7,609
1,648
Jan 5, 2010
If the current is 1 Amp and he needs it for 3 seconds, and the input can drop to 6V before the 5V is in trouble, here is the math:

dV / dt = I / C

6 / 3 = 1 / C
2 = 1 / C
2C = 1
C = 1/2 F

It's only a small supercapcitor!

Bob

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4. ### mcates

23
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Apr 3, 2019
Hello and thank you both, i have been working on this for some time and the this power capacitor issue is got me for a look. I have it working direct for the tacks and all is well but there are times the train rocks or comes off track and power is interuptted for 1-3 seconds and casuse the system to go out and requires a reset.

Here is what I know for what my draws are
Gopro 2.1 watts 1.5 amp max.
https://cam-do.com/pages/power-consumption-by-gopro-camera-model
Dimond Tranmitter 1.5 watts 1.0amps

Now my issue/question is: How do i wire the capacitor? I wont go into what I tried but here is what I beieve I need to do

power in from tracks (12-16 volts) to a rectifer diode -> schottky diode - (some kind of diode for charging?) - capacitors? (wired parallel or inline) - input of stepdown/booster - out to usb devices
I have the following capacitors (I just don't know how to lay it out )

Can you tell me out it should be wired in my example above?

https://www.amazon.com/gp/product/B000701BA6/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

2pcs Elna 6800uF 35V 30x40mm for Audio Electrolytic Capacitors-4393

https://www.amazon.com/gp/product/B07CF82HZM/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

2pcs Audio 63V 12000uf Filter HiFi Electrolytic Capacitor 3550mm for Circuit Control
https://www.amazon.com/gp/product/B07HG6LG64/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

6 pcs Panasonic FR Series Capacitors - 35V 2200uf Ultra Low ESR
https://www.amazon.com/gp/product/B072SSJQSK/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

5. ### BobK

7,609
1,648
Jan 5, 2010
A capacitor can simply be placed across the input to your DC to DC converter.

None of the listed capacitors will work, The 1F has enough capacitance to help, but it is only good for 5V, which is typical for supercaps. The others are orders of nagnitude too small.

Bob

Cannonball likes this.
6. ### mcates

23
0
Apr 3, 2019
Can you recommend a capacitor that would work? and/or a link please?

When you say placed between dc to dc converter, I do not understand.

power from tracks -> diodes -> cap -> booster/stepdown -> (2) usb usb 5v ports -> devices.
OR
power from tracks -> diodes -> booster/stepdown -> capacitor ->(2) usb usb 5v ports -> devices.

Thank you again.

One last thing as i ordered some of these I just don't know if I can use it? And then how to where and how to wire it in line to by booster/stepdown
TURNIGY VOLTAGE PROTECTOR 783333uf (3sec) STOP RC RECEIVER BROWN OUTS
https://hobbyking.com/en_us/turnigy-voltage-protector-783333uf-3sec.html

or I was looking at something like this
Shaluoman Farad Capacitor 2.7V 500F 35X60MM Super Capacitor With Protection Board

Last edited: Apr 3, 2019
7. ### BobK

7,609
1,648
Jan 5, 2010
No, because supercapacitors do not come in voltage high enough. You would need several in series with with additional circuitry to keep the voltages on them balanced as they charge.
Maybe that is because that is not what I said. I said across the DC to DC converter, meaning across the input lines to it. I should have been more explicit. But this is problematical also, because it will take some time to charge the capacitor. A 1F capacitor charging at 1A will take 1 second for each volt it is charged with.

Now we are getting somewhere. This might do it. It is basically supercapacitors in series adding up to 15V with the necessary circuitry.

Bob

8. ### Alec_t

2,663
702
Jul 7, 2015
Or not. The capacitance is advertised as '783333 uF'. Not only is that unbelievably precise, but even if true it is also about half what is needed if the current draw is actually 2.5A.

Edit: Rather than a cap, a 3S lithium battery pack might be a better bet. That would require a proper charger and a diode-or arrangement to isolate the pack from the '12V' supply.

Last edited: Apr 4, 2019
9. ### mcates

23
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Apr 3, 2019
Ok I agree that we need a set of capacitors in series I will do whatever is needed! I believe this would work I just don't know how to wire it in.

https://hobbyking.com/en_us/turnigy-voltage-protector-783333uf-3sec.html
The TURNIGY capacitor set helps prevent "brown outs" resetting your Rx if your servo amp draw spikes or you have an Rx glitch. It will also help reduced the load on your ESCs BEC and reduce the likelihood of glitching.

Operating Voltage: 3.2V - 11.1V (1s ~ 3s LiPo)
Capacitor voltage: 15v
Storage Capacity: 783333uf
Weight: 26.2g

Data on a 3A load spike typically seen when large retracts jam:
Supply 6v with a voltage drop to 4.7v over 0.88sec
Supply 6v with a voltage drop to 3.0v over 3.0sec

I just don't know how I could wire into my current situation. would I splice the wires on the turnigy then wires as follows (track power 12v) rectifer diode -> schottky diode then turnigy voltage proctector -> wire into buck step down converter -< 5v usb?

OR how would you wire that.

Then there is this which is very similar super capacitor

Shaluoman Farad Capacitor 2.7V 500F 35X60MM Super Capacitor With Protection Board it has 16.2 volts by 83.3 Farad.
https://www.amazon.com/gp/product/B0162NYWUW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

And if I need to wire to in parallel I can.

So would I wire this the same as above, I know where the + and - connections are so what resistor or diode do i need to add before or after for anything?

10. ### mcates

23
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Apr 3, 2019
Ok I agree that I need that
I was looking at that as well but here is how I see it set up.

power from tracks is connected directly to lipo charger/battery that feeds the camera and transmitter wired though relay so that when the relay detects power loss on the tracks that in a delayed 10secs it kills the power to the camera/transmitter. The reason is if it loses power for a second or two I do not want it to shut off power to the camera/transmitter. But at night when the system is shut off I will need it to shut off camera/transmitter as not to drain the battery every night. DOES this make sense?

So what relay do I need for this. I have no problem with setting it up I just am not sure of what I need and how to wire it correctly.

Any help would be appreciated I don't mind doing this at all.

11. ### Alec_t

2,663
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Jul 7, 2015
Do you have a Lipo charger which will accept a 12-15V input?
For disconnecting the battery a power MOSFET would be more compact than a relay.

12. ### dave9

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171
Mar 5, 2017
I would sooner use a 12V battery, so not only the step down board receives continuous power but so does the train (motor) itself, while a supercap array would be too massive and expensive to reasonably power both.

Whether to use lead acid, Li-Ion, or NiMH, is a different topic onto itself based on price, weight, available space, need for different charging circuits.

13. ### mcates

23
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Apr 3, 2019
Yes i have a battery and usb charger for it.

Can you please tell me how I would wire it I do have some of those here.
Bridgold 10pcs FQP27P06 P-Channel MOSFET, 60V, 27A, TO-220,3-Pin
https://www.amazon.com/gp/product/B07LG3X8KF/ref=oh_aui_search_asin_title?ie=UTF8&psc=1
will these work? and if so I should i wire it?

If these do not work can you please recommend one? and tell me how and where to wire it in?

Last edited: Apr 5, 2019
14. ### mcates

23
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Apr 3, 2019
Just to clarify, this is for a camera/transmitter system that is located in a car by it's self and is pickup on power from the tracks.

15. ### Alec_t

2,663
702
Jul 7, 2015
What gauge railway? This will limit battery size (hence possibly battery type).

16. ### mcates

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Apr 3, 2019
G-size
G size system. I have a unique setup but I have 12-18volts on my track and up to 5amps max.

Last edited: Apr 5, 2019
17. ### mcates

23
0
Apr 3, 2019
I know I have been confusing but I am looking for the easiest solution and I believed it to be the use of some supercaps to hold power for 1 to 3 seconds. incase the train loses its connection to the tracks. So I made some diagrams of what I am envisioning. I am no expert so please do not beat me up (lol) I am learning and have been tasked to making this work. So I have a train that has a camera on it with HDMI transmitter to broadcast to a tv so you see the train ride around. The train is 20 up on the wall and is not reachable easily. At night the power is turned off to the entire system. At times the train rocks and can lose its connection and it causes the transmitter or camera to go off and then requires an entire reset. If I leave the battery in the camera it will drain overnight and eventually go bad (so I take it out). The transmitter has no batter and is powered by micro USB power. So i need some sort of stable power incases of the brief power loss.
1. Supercaps for 1-3 seconds loss
2. A DELAYED relay or Mosfet (don't understand them) to monitor power on the track power and when the system is powered off it will cut power to camera and tranmitter after 1-10 seconds. Thus not draining the battery that is giving the camera and transmitter power. Once power is restored the next day, power is turn on to the tracks, the relay detects it and turns of the camera and transmitter

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18. ### mcates

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Apr 3, 2019
Thank you all I do appreciate all of your help!

19. ### Alec_t

2,663
702
Jul 7, 2015
A battery similar to one of these should suit. If fully charged before installation, a trickle charge from track power would probably suffice to keep it topped up.
Is that the AC RMS voltage?

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Oct 5, 2014