Charging Project

[Demis]

Hey all. I am currently working on a university project involving charging a battery. First of all to say that I have very little knowledge of electronics in general (only the fundamentals).

So my situation is the following: I will be charging out a Lead acid battery of 6V or 12V and a capacity between 1.3Ah and 12Ah (I still haven't ordered it). I will need to charge this by using a basic motor configuration. I am not confident that I know for sure what to do to put this circuit together. I looked through other threads and forums and I collected some information already: I will need a diode to avoid the battery actually powering the motor in low RPM values (when motor output voltage less than battery voltage), my supervisor told me I MAY need a charging filter (could anyone please explain me the role of this and if necessary? ) and I also read about using a regulator which I suspect is similar to a 'charging filter' (I am not sure). It is also important to mention that the source of rotation of the motor is NOT STABLE and so there will be a varying motor RPM.

So what I have now in mind is that on the one end will be the rotating motor connected to the battery by wires and a diode between them to avoid power flowing backwards.

I will greatly appreciate your thoughts on the components I mentioned above as I am a bit lost about these things. And any additional help and components that I should use I would greatly appreciate it!!

THANKS A LOT,
Demetris

 

[ronv]

There are several ways to do it, but a little more info would help nail the best (good) method down. Do you know the output voltage and current of the motor?
Is charge time important to you? - Longer is easier but not a big deal. Curiosity, what drives the motor? Is it a brush motor?

 

[Demis]

well, I dont have direct access to the motor model yet but according to a datasheet of the company (https://www.electro-tech-online.com/custompdfs/2013/07/83.pdf) the nominal voltage of any model is no less than 18V. Assume for now that my motor is the 118797 model with 18V nominal voltage and 2.90A nominal current. Charge time is not crucial but it would be good if I could keep it down somehow. The motor I believe is a brush one (see datasheet). This project utilises the rotational motion of a gyroscope to rotate in turn the motor and hopefully charge the battery, which is the desired output of the project. So instead of using the gyroscope for stabilisation purposes as usually its rotational motion is harvested. But take in mind that the rotational speed of the gyroscope will not be constant (I sense this is a crucial part for the components required)!

My battery will be a lead acid one and I guess for charging purposes (from a motor) it is preferably to use one with low votlage to facilitate easier charging (to prevent flow of power from the battery to the motor). Am I right on this? So if I have a choice between a 12V and a 6V battery should I go for the 6V one?

I will greatly appreciate your help on this! Let me know for any further information required that may be of help.

 

[ronv]

Sounds like fun. I can't remember, but maybe it was old telephone backup that stored power in a big gyro and used it when power failed.

Is this just a demo or is it important that it be highly efficient, etc.?
Some things to consider:
The more power (bigger battery) the faster or heavier the gryo, so it might be good to try to match things up.
If you need to squeeze all the power out of the gryo the voltage could be boosted once it fell below 6 volts - but more complicated.
If efficiency is important you would want to charge the battery as quickly as possible to avoid wasted power in friction. -- also a bit more complicated.
The same is true. If efficiency is not important an analog charger would be simpler but a switch mode more efficient.
Any idea of the energy stored in the gryo?
Can you use purchased assemblies or must it all be home grown.

 

[Demis]

it is just a demo for now and the time i have is quite limited so I am not aiming for something extremely sophisticated for the time being. I am free to get whatever commercial components I want so this is not a problem. I have a budget of 300 pounds. The gyroscope is capable of producing between 0.8-13.9 W of power depending on its RPM which ranges approximately from 5000 to 20000 RPM.

The friction in the gyroscope is not a problem as this will be constantly be rotated (energy will not be actually stored in it from before) so assume an infinite rotation capability for the gyroscope without this stopping (ideally will only stop when the battery is fully charged).

Any suggestions then for the list of components I will be requiring??

Thanks a lot!

 

[alec_t]

The gyroscope is capable of producing between 0.8-13.9 W

For how long? How much energy can it store at 20k rpm?

 

[Demis]

for as long as I desire as the motion of the gyroscope will be induced by a moving bed for experimental purposes. so the energy does not need to be stored in the gyroscope. the only useful part of the gyroscope is its rotation in order to rotate the motor through a simple gear arrangement. The power that can be produced at 20000 RPM is 13.9W. this was roughly calculated by using the mass moment of Inertia of the gyroscope, angular velocity of the moving bed and RPM of the gyroscope. So what i need is start from the rotation of the gyroscope, connect this motion to the motor in order to rotate it and then connect the motor and battery through wires to charge the battery which is the desired outcome. I am in the process of designing this circuit and it would be really useful to get some help from someone experienced in this sort of configurations.

 

[alec_t]

the motion of the gyroscope will be induced by a moving bed

The mind boggles .
Seriously though, can we assume the motor plays no part in spinning-up the gyroscope and is being used solely as a dynamo?

 

[Demis]

maybe i wasn't very clear in my description probably a small motor will induce motion to the gyroscope and after this the gyroscope will keep rotating by the movement of the surface on which it is resting (an experimental bed). The main motor will be acting solely as a dynamo. NEVER as a motor. so we have: gyroscope --> motor (dynamo) --> battery. don't forget though that the gyroscope will not be running at fixed RPM due to the random variability of the bed movement during the experiment. hopefully now it is more clear )

 

[alec_t]

Unless you have very active bed occupants I doubt you'd get more than 1W of energy from them on average, and most of that is likely to be lost in the inefficiences of the mechanical linkages between bed and dynamo. Have you done the maths? Your battery is unlikely to get charged in a reasonable time .

 

[ronv]

Hmm. OK.
Here is what I would try:

6 volt 1.3 AH battery.

A little buck boost charger like this:

https://www.ebay.com/itm/LM2596-LM2...CV-Charging-/300878228425?hash=item460dbd6bc9

You can set the voltage to 6.81 volts and the current to .13 amps (battery capacity / 10)

It will charge a dead battery to about 75 80% 10 hours, maybe another 5 to 100%.

It should work down to about 4 volts from your motor and up to 18 without a problem.

It looks like it needs leds to be added for indicators and maybe a Chinese translator - but the price is right.