# Combining 3 renewable energy sources

Discussion in 'The Projects Forum' started by dannn, Nov 10, 2010.

1. ### dannn Thread Starter New Member

Nov 10, 2010
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Hi guys, I am working on a project to bring 3 different renewable energy sources (hydro, wind, and solar) into charging a single 12V 9 AH battery.
The wind will turn a 12V 3W DC motor.
The hydro will turn a 12V 8W DC motor.
And I have 3 solar panels rated 6V 6.5W each.

I think I have to connect them in parallel, but I have found out that connecting power sources of different voltage is finding trouble.
The voltage generated is naturally lower than the rated one.
What should I use/do to make the power generated stay at a voltage high enough to charge the battery?
On a note, I did not use a linear regulator because the efficiency is too low, and I am not very limited on money.

Nov 9, 2010
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I would say put 2 solar panels in series to make 12 volts, and maybe put the 3rd in parrallel to one of them (not sure what gain it would be). Then just use diodes to prevent any backfeed from the other sources, i believe.That way everything flows in the same direction, and nothing gets blown up.

3. ### dannn Thread Starter New Member

Nov 10, 2010
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Someone told me that if i parallel, say, 16V and 14V, no current will flow out from 14V source. Is that true?

If that is false, does it mean that if i parallel 16V and 14V, both will work to charge the battery?

4. ### wayneh Expert

Sep 9, 2010
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It's true that, if you're charging something and the battery's poles are at 16v, hooking up another power source that is delivering max 14v will not add to the charging. Without a blocking diode, current will flow from the 16v source into the 14v source.

That all said, the voltage actually at the battery poles may be less (eg. 13v) than the no-load voltage of the second source. In that case, the second source might contribute a small amount.

As you experiment, don't forget that a diode drops voltage ~0.7v as current passes thru it. You need to overcome that also, to get current moving into the battery.

5. ### thingmaker3 Retired Moderator

May 16, 2005
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I suggest reading up on the concept of the "DC to DC voltage converter." You will want three of them, one for each input.

6. ### themotorman Member

Jun 13, 2009
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Connect the solar panels in series. This will give an open circuit of 18 volts. Under load it will drop so as thingmaker says the best way is to use three DC-DC converters. The alternate approach especially since only one source will probably be useful at any time is to just use diodes to isolate them and connect the diode junction to a battery charger that has a DC input. One that works from a 12 volt input might be available , it would be a DC-DC converter itself.
Trying to use all three might be a real challenge especially at your very low power levels. The losses of conversion will eat away at the power you have available.

7. ### themotorman Member

Jun 13, 2009
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Just a thought .. unless you use a DC-DC converter ( flyback type ) that can convert low voltages to the voltage needed for charging ( max 14.4 V ) you will get no current until the motors are spinning fast enough to put out nearly 16 volts ( to allow for diode drop ). Can your motor/generators spin fast enough for this?

8. ### wayneh Expert

Sep 9, 2010
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You might also benefit from learning about a what a 3-phase full bridge rectifier looks like, since the 3 phases from a 3-phase generator are a little like 3 separate sources being combined to give a single DC out. Are your motors actually generating DC when turned? Or are they really alternators (more likely, IMHO)? Your solar panels of course are true DC.

9. ### iONic AAC Fanatic!

Nov 16, 2007
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Did anyone mention that a 12V source will not charge a 12V battery. If the charge voltage is not greater than the battery to be charged then you will not be charging the battery. Thus the suggestions of using DC-DC Converters is ideal as you can setup the output between 13.5V and 14.2V. Also, with all those sources operating at once you could charge the battery quickly, then begin to overcharge them. You might consider a means to stop charging altogether or to reduce the charge voltage and max current to a maintenance charge once the battery reaches it's fully charged state.

10. ### dannn Thread Starter New Member

Nov 10, 2010
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Many thanks to all who have posted.

I have with me a boost circuit(linked).

The wind turbine will generate a peak of 9V, but i think it is varying like this:

1) Should i regulate the varying input?
2) How much should i boost the input voltage to charge the battery? 2 times?
3) Will a switching regulator be useful? I read that it can produce a desire DC output with relatively high efficiency.

11. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
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A smoothing cap will bring you closer to 9V and that is an effficiency boots.
I think, however, that you might need some sort of charge controller that can accept various input voltages and currents.

12. ### wayneh Expert

Sep 9, 2010
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Not for mere battery charging. Ignoring for now that even the peak voltage is too low, under normal circumstances where it IS enough to do the job (eg. charging a 6v battery), the battery will only charge during the brief period at the top of the peak when the wind generator voltage exceeds the battery voltage. No amount of regulation will change that, and any manipulation will reduce efficiency. Regulation is used when the load can't tolerate ripple. A battery can.
More is better. I'm guessing your wind generator will spend a lot of its life making less than 5v, so tripling or quadrupling that would not be excessive. Being able to SWITCH the degree of boost would be great. Just remember that the power transfer efficiency can only go down when you convert one signal to another. BUT, raising the voltage will give you back some of the lost efficiency, since it will enable charging when you couldn't otherwise.
That's my understanding too. Is there any chance you could use the un-rectified AC power coming from the generator? If you could boost the AC voltage before it's rectified, you'd avoid the relatively huge loss you're currently seeing across the rectifier. A full wave rectifier loses ~2v under load, so when you're making only 5v DC out, the AC side is making 7v and you're losing 2v out of those 7. A lot of your power is lost as heat in the rectifier.

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13. ### dannn Thread Starter New Member

Nov 10, 2010
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Many many thanks for the useful opinions! I will give you a hug if i could, but i doubt you're in Singapore.

It is unlikely that i will be able to use/change other generator other than what i listed in the first post.
To my knowledge, there isn't a rectifier in this DC micro motor, correct me if i am wrong.

14. ### wayneh Expert

Sep 9, 2010
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True, it doesn't look like you can do much with that internally.

Are you confident that it will generate a useful voltage when you spin it at whatever speed you are planning? It's meant to function as a motor at high speed and may not be very good as a low rpm generator.