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5v power dc supply from variable source

Spezzer

New Member
I've included some context - feel free to cut to the chase in last paragraph!

I've been working on a model railway fpv camera and looking at alternatives. My first attempt was a wagon mounted cam with LiPo battery. Couple of problems, the 155mah battery only lasts a short amount of time and have little room for anything bigger. The battery drained to <1v and seems my charger will only charge from 3v - not sure what thats all about - must be a LiPo thing?

So, plan B - I mount the camera in a motorised chassis and pull off the 12v supply. The image is the i) drone cam ii) motorised chassis iii) 3d printed first attempt - hopefully puts into some sort of context. So my question - what circuit do i need to pull power from the chassis which can range from 0v to 12v depending on the speed. I also want to store some power (capacitor?) so the cam can operate for a few minutes if the chassis stops. The cam requires a 3v-5v feed but not sure how many milliamps minimum - it works (just) with 3.7v 150mah lipo so hopefully is a gauge of what feed is needed.

To summarise - I have a 0-12v supply to the train chassis and need a circuit to maintain power to the cam - input spec is 220mA~400mA @ 3v~5v.

Thanks in advance

Edit - this is part of what I want but also need storage https://www.instructables.com/id/Convert-12V-DC-to-5V-DC/
Edit - this resistor solution looks better as needs less space (which is limited) - http://www.learningaboutelectronics.com/Articles/How-to-reduce-voltage-with-resistors.php
Edit - it looks like I am talking about a Step up / Step down regulator - https://www.pololu.com/category/133/step-up-step-down-voltage-regulators - the only missing part is the requirement to keep it powered when the feed in interrupted - anything from micro-seconds to seconds)
 

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Pommie

Well-Known Member
Most Helpful Member
How long did the 155mAh battery last? A simple solution maybe a lipo charge/protection circuit powered from the track.

Mike.
 

Spezzer

New Member
LiPo lasts about 15 mins. I was just looking at a 5v UPS using super-capacitors here:-


So figured i could use a combo of regulator and mini UPS.

I like the sound of LiPo charge/protection using existing battery - would the feed keep the battery charged and then use that to power the cam?
 

gophert

Well-Known Member
Most Helpful Member
If you have a Tomex power pack with continuous Lighting, the problem can be solved easily.
Do you have a DC power pack or DCC? Is the power pack variable voltage or PWM (pulse width modulated) to control speed.

remember, any circuit you add has to accommodate reversing the voltage to back up your train so you'll need a bridge rectifier.
 

alec_t

Well-Known Member
Most Helpful Member
The battery drained to <1v and seems my charger will only charge from 3v - not sure what thats all about - must be a LiPo thing?
Lithium cells can be dangerous if not charged/discharged properly and should have a protection circuit. Draining it to below 1V is not good for the cell, and your charger correctly prevented charging from that voltage, as a safety measure.
 

Spezzer

New Member
If you have a Tomex power pack with continuous Lighting, the problem can be solved easily.
Do you have a DC power pack or DCC? Is the power pack variable voltage or PWM (pulse width modulated) to control speed.

remember, any circuit you add has to accommodate reversing the voltage to back up your train so you'll need a bridge rectifier.
The power to the track is via a couple of cheap components -a speed controller and reversing switch - using a 12v 1.5a power supply.

(The N gauge layout is just a simple loop to see how much of the layout i can 3d print& develop a model with fpv)
 

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Spezzer

New Member
How long did the 155mAh battery last? A simple solution maybe a lipo charge/protection circuit powered from the track.

Mike.
So I'm still entertaining your idea and googled it - this guy is on another level -

Is this the type of thing you were thinking? I love the idea of designing my own board and having it manufactured!

cheers
 

gophert

Well-Known Member
Most Helpful Member
So I'm still entertaining your idea and googled it - this guy is on another level -

Is this the type of thing you were thinking? I love the idea of designing my own board and having it manufactured!

cheers
Yes but these boards are available on eBay/Amazon/alibaba for very low prices. No need to make your own.
 

Spezzer

New Member
Yes but these boards are available on eBay/Amazon/alibaba for very low prices. No need to make your own.
OK that's worth knowing. That example is only part of the solution though. I decided to invest in the Pololu board, that will give the the regulator I need and it is tiny.

Cheers
 

gophert

Well-Known Member
Most Helpful Member
OK that's worth knowing. That example is only part of the solution though. I decided to invest in the Pololu board, that will give the the regulator I need and it is tiny.

Cheers
for future reference, Digikey carries many of the Pololu parts and then you have access to millions of other parts in the same order without additional shipping costs.
 

Spezzer

New Member
for future reference, Digikey carries many of the Pololu parts and then you have access to millions of other parts in the same order without additional shipping costs.
Thanks - the Pololu p&p is huge so went to CoolComponents. I'll keep Digikey in mind.
Cheers
 

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