# Capacitor Power Bank 12V for 2 DC motors and other eletronics

#### Kevin Mitchell

Joined Aug 19, 2015
9
Hello,

first of all, i want to say i am a big noob in eletronics, i learn my best in the internet and try to apply it in real world, i have had nasty experience of going into pratical without knowing the theory first in eletronics, and i paid the price burning my hand. So i quite want to have the theory first before even thinking to do anything.

ok, so, i have a 80 watt solar panel, and i want to drive 2 eletric DC Linear actuators, to move a heavy thing. details on this is not necessary as for i need help is in the capacitors.

so each motor is as estimated a low RPM DC motor with high torque, which these ones give out around 1200N of force in the mechanical geared actuator. these two motors consume 3 amps, at a voltage of 12V. multiplying it gives 36W each, so both would consume 72 watts when operating at the same time. Besides this, i also have an arduino, a 4 channel relay, and a few LDRs and switches. and a 4A thermoeletric Peltier module, with a heat sensor, and other sensors too, i have an arduino Uno, i am thinking in getting a multiplexer for the analog inputs but it seems very complicated, i think i will aquire a Arduino Mega. (Sainsmart has a cheap and very good one).

for the record, i am studying renewable energies.

and by far when you grabbed your mental calculator, you pretty much see the solar panel i have wont suffice for my needs right?
yep, that's when the Capacitor banks i read so much about, and saw so many videos about, even a rail gun.
so, i know so far that the capacitors have a very different use from a battery, like for one of those dozens of videos i saw, i can actually turn a small AC current into a DC current using just capacitors and a few diodes.

so, the idea of replacing a large battery here, is to prevent a deep charge or use of expensive controllers to take care of the batteries, and also the actuators wont be constantly running. they are for positioning accurately, so i dont need to run them constantly. only a few times per hour. making the calculations, without the two motors running at the same time it will give me around 55 to 65 watts of usage. and i forgot, i will use 2 small Dc water pumps, like those in aquariums. so i have then 15 watts of energy left for use. what i have now is a car baterry and its not fullfiling my needs.

so this is my idea:

to have a capacitor bank, that can power 72 watts of both motors for around 10 minutes. and be recharged fast with the 15 watts i have left to use from power from the solar panel, and then, capable of powering a single arduino in sleep mode, for 36 hours.
i heard avout the super capacitors and ultra capacitors, i went to check some prices, and well... my budget is not that big. so as cheap as possible is what i'm aiming at. Also capacitor bank volumes is not a problem. not weight.

How many Farads i would need? in parallel? or in series?

and thank you so much for taking your precious time to read this. i really apreciate it alot. and if help me, even more!
i'm just another DIY-er with super enthusiasm both in renewable energies and eletronics, although picked eletronics road,
as my family used to say, " a road is just one lane, a highway has more lanes". pretty inspiring to me to get into the multitasking world too. will you help me slowly getting into the eletronics world with this?

Joined Jul 18, 2013
19,958
How many Farads i would need?
Farads would be a correct term!
Max.

#### tcmtech

Joined Nov 4, 2013
2,868
Have you calculated out your total available watt/time numbers for your source Vs the total watt/time consumption for all the loads combined and assuming that the load number is less than the supply number how big of capacitor bank you would need to hold it and what that would cost?

#### Kevin Mitchell

Joined Aug 19, 2015
9
Basically assuming loads for one hour, it's 65Wh with the arduino, thermoelectric module and other sensors, plus the 72 watts for the motors, that is 137 watts load needed, since the solar panel can't power that at the same time, I want to use the 15 watts left the Solar panel is producing to store energy and then when the arduino requests the motor to function, they will using the stored energy in the capacitors for around 10 minutes, each motors takes 1 minute and 20 second to fully expand and/or retract it's piston, the 5 minutes are for allowing small adjustments a few times summing both motors, I was now thinking if it was easier to only function one motor and a time?

#### tcmtech

Joined Nov 4, 2013
2,868
Assuming a starting voltage of 15 volts and an ending voltage of 10 volts to hold 72 W/H of energy in capacitors would require a 15+ volt ~25,000 Farad bank. Recharge time with 15 W/h input would be at close to 5 hours.

Sure. You only need about 300 3000 F 2.7 volt ultracapacitors for that to work. Got a spare ~$11,000 laying around? Or maybe$200 for a good heavy deep cycle battery and a good charge controller instead?

#### Kevin Mitchell

Joined Aug 19, 2015
9
oh well...
what if i use only one motor at a time? for just 2 minutes
what would be my options ? i can program the arduino to move only one motor at a time, but that depends on how fast i would have my energy stored

#### tcmtech

Joined Nov 4, 2013
2,868
Just use a good battery and a proper charge controller for it.

#### Kevin Mitchell

Joined Aug 19, 2015
9
i have a 12V 7Ah lead acid battery, will this suffice for the work?

#### andrewmm

Joined Feb 25, 2011
158
Battery is the best option.

but do you have the watts ?

just because the panels pump out X watts ( Ah ) , does not mean the mattery would store X watts. the charger circuitery and the battery chemistry is not 100 efficient.

same for driving the motors, not 100 % efficient.

I'd tend to have two supplies,
one driving the arduino , and logic,
and one driving the motors,

that way the motors will not kill / reset the arduino and stuff.

Motors can run on spiky voltages, arduinos etc tend to like nice voltages.

#### Kevin Mitchell

Joined Aug 19, 2015
9
i can get those 9v small book size epoxy encapsulated solar panels just to power an arduino, but i would need to use a DC-DC buck converter to regulate and make the voltage stable for the arduino, in fact i have one, that i am using to convert 12V into 9v to the arduind DC jack. so separating the power sources is the better option then?
but what kind of battery? will the one i have laying around will do the work? or i need a bigger battery? or a better one?
which Ah are we talking about?
i've been also thinking, i can cut the Peltier thermoeletric chip power for 2 minutes, having my consequences, i would need to get lots and lots of insulation tape to prevent to loose heat, but for 2 minutes the peltier chip will loose all its temperature and when turned off will result in the logic of thermodynamics law, the hot side will tend to transfer heat to the cold side, since there is no insulation separating the sides, just the chip. i will try to find a way to prevent loose heat for 2 minutes. doing this of turning on and off the peltier, is like PWM but with longer periods. it will affect me critically.
what if i get another 7Ah battery? the charge controller(CC), i have a PWM CC i bought on ebay, but it doesnt really charge the battery that well, i've been looking for a few ones, i thought getting an MPPT CC, but its expensive, and its only recomended for really high loads because they were designed for higher loads like 3kW or even 10kW PV systems, also these CC takes temperature into the PPT equation and it can be very sensitive. is there a fairly low cost PWM CC you can recomend for Lead acid batteries?

btw, i apreciate the help you are all giving me, a lot

#### Alec_t

Joined Sep 17, 2013
10,892
Multiply the Watts by the number of seconds per day that each item is used to calculate the total number of Watt-seconds of energy used per day.
i have a 12V 7Ah lead acid battery, will this suffice for the work?
That will power a 7A load (84W) for 1 hour in theory, but total discharge of a battery will quickly kill it so in reality you'd be safer driving that sort of load for not much more than half an hour before re-charging the battery.