Author Topic: Multiple DC Generators  (Read 5226 times)

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Dave

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Multiple DC Generators
« on: September 18, 2014, 06:00:35 PM »
I'm a newbie and I've learned a ton from this forum. Thanks!

I'm wondering about connecting multiple DC generators to a single battery bank. The threads discussing this seem to all say “it's possible but not advised” and then they digress into a discussion of why you should just get one bigger turbine.

To avoid the rabbit trail of “just get one bigger turbine”, let's focus on the use case of one water wheel and one windmill. I'm going to end up with two different DC voltages from the two generators. So connecting them in parallel after the rectifiers will basically just mean that whichever is producing the higher voltage will be the only one that matters. (That sucks…) Connecting in series will eventually blow one of them up. A DC to DC voltage regulator seems like an viable option (according to the laws of physics) but google doesn't know of anything that will handle the input/output voltages that would be required.


Does anyone know how to harvest energy from multiple DC generators (likely producing different voltages) and pump it into one single battery bank? If I'm producing 500W and 300W, I'd like to be putting something pretty darn close to 800W into the batteries.

Thanks for any electrical engineering expertise you can offer!
Dave

lifer

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Re: Multiple DC Generators
« Reply #1 on: September 18, 2014, 06:41:09 PM »
You could always put two (three or as many) chargers in parallel on a single battery (bank). They're all acting like current generators so every single one will "participate" to battery charging.

Every charger has reverse current flow protection so there will be no sparks at all. Every single (small) generated current will go through the battery (or load).
« Last Edit: September 18, 2014, 06:45:19 PM by lifer »

Dave

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Re: Multiple DC Generators
« Reply #2 on: September 18, 2014, 06:48:21 PM »
Oh, what a simple solution. Thanks for the direction! I think this solves the problem.

As a side note, the charges are would essentially be voltage regulators. So, while i was on the right track, it seems i missed a crucial component  :)
Thanks again,
Dave

gww

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Re: Multiple DC Generators
« Reply #3 on: September 18, 2014, 09:04:56 PM »
Dave
Welcome.

Quote
As a side note, the charges are would essentially be voltage regulators. So, while i was on the right track, it seems i missed a crucial component 
Thanks again,


I don't understand what you mean by this comment.
Cheers
gww

lifer

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Re: Multiple DC Generators
« Reply #4 on: September 19, 2014, 12:56:34 AM »
The usual chargers are smart enough to act as a current/voltage regulators, depending on load (battery) status. Also, the battery itself acts like a variable load (variable internal resistance) depending on its charging state.


dgeneral02

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Re: Multiple DC Generators
« Reply #5 on: September 19, 2014, 03:47:49 AM »
500w and 300w from dc motors? Those motors will be huge then. What type of dc motors are you planning to use?
Peter Anongo

Flux

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Re: Multiple DC Generators
« Reply #6 on: September 19, 2014, 04:08:29 AM »
You can connect multiple dc generators in parallel to a battery and they will all contribute as long as the emf of each is above battery volts, Series connection is not useful.

The main reason not to use lots of small wind turbines is that you are duplicating expensive items such as propellers and towers and generally one decent size one costs less and performs better but sometimes 2 or 3 sited for various wind directions can be better on poor sites.

For wind and hydro, combining several sources makes perfect sense.

Don't worry about regulators unless the battery is fully charged, the battery will drag all sources down to the same voltage and current from each will be determined by their open circuit voltage, impedance and more probably the mechanical energy available to drive each. Hydro will be a steady contributor and wind will only contribute when there is enough energy in the wind, it may be the biggest contributor on a windy day. 

Flux   

Dave

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Re: Multiple DC Generators
« Reply #7 on: September 19, 2014, 10:57:57 AM »
I don't understand what you mean by this comment.

I typoed. Charges-->ChargeRs. Basically, I was just commenting the same thing that lifer said. That chargers will act as voltage and current regulators.

Flux, your point isn't one that I didn't think of. You're saying that the battery, itself, will keep the voltage consistent along the entire circuit. This makes sense to me. As an analogy, if you have a big air compressor and a small air compressor both hooked up to the same tank, they'll both show the same PSI on their gauges. (This will be the case as long as they're both able to pump to a higher pressure than the tank. If that's not the case, then one of the pumps will essentially act as a "leak" and start drawing air out of the tank. i.e. The generator needs a higher voltage than the battery (or a diode) or it will start spinning in reverse.) At any rate, in the analogy, both compressors continue pumping air and the tank's PSI will raise faster than if either one was pumping alone. So i completely get what you're saying. Thanks.

Thanks all for the help on this question.

Dave

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Re: Multiple DC Generators
« Reply #8 on: September 19, 2014, 11:03:34 AM »
500w and 300w from dc motors? Those motors will be huge then. What type of dc motors are you planning to use?

The small one is a 3/4 HP DC motor from Reliance electric. (I picked this up, used, for $50.) Haven't found a cheap/suitable bigger one yet.
Is that big? The size of the turbine is really not much of a factor as I have a process for making arbitrarily large blades (up to 10ft-->20ft diameter). I'll be posting about my blade plan shortly.
« Last Edit: September 19, 2014, 11:12:21 AM by Dave »

Dave

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Re: Multiple DC Generators
« Reply #9 on: September 19, 2014, 11:24:36 AM »
Flux, your point isn't one that I didn't think of.

Oops, I should be a better proof reader of my posts. I meant that your point IS one that I didn't think of. You gave me a new idea, and I'm thankful.  :)

gww

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Re: Multiple DC Generators
« Reply #10 on: September 19, 2014, 01:33:06 PM »
I have two turbines and one small aray of solar panels going strait to the 48 volt battery bank.  These are independent of the solar aray going through two charge controllers.

I find that lots of times when I type, what is in my mind, is not what ends up in type.

Good luck
gww

Mary B

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Re: Multiple DC Generators
« Reply #11 on: September 19, 2014, 07:52:25 PM »
Could put each on an MPPT charge controller and run them in parallel. My morningstar MPPT 45 can do that as can some others.

dgeneral02

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Re: Multiple DC Generators
« Reply #12 on: September 25, 2014, 10:43:21 AM »
500w and 300w from dc motors? Those motors will be huge then. What type of dc motors are you planning to use?

The small one is a 3/4 HP DC motor from Reliance electric. (I picked this up, used, for $50.) Haven't found a cheap/suitable bigger one yet.
Is that big? The size of the turbine is really not much of a factor as I have a process for making arbitrarily large blades (up to 10ft-->20ft diameter). I'll be posting about my blade plan shortly.

Never tried  a similar motor before but maybe you should look here http://www.windynation.com/jzv/inf/testimonials
I got the pictures from that website. The motor used is a 4HP pm dc motor.
Peter Anongo