Author Topic: Constant load to increase efficiency  (Read 7309 times)

jzeeff

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Constant load to increase efficiency
« on: June 16, 2008, 03:35:49 AM »

An engine can be best optimized for efficiency if it will always operates at the same load and rpm.    Are there any charge controllers that keep the load on the generator constant?  Ie, any unused capacity is always used to charge batteries?  Once the batteries are fully charged it could turn off the engine and run on inverter only.

Ie, I'm looking for a battery charger that will always draw 2KW.



Doug

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Re: Constant load to increase efficiency
« Reply #1 on: June 16, 2008, 03:44:35 AM »
Good question....

You could probably make a regulator for a large Alternator that responded to rack possition as well as bus voltage......

Very good idea!
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Stan

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Re: Constant load to increase efficiency
« Reply #2 on: June 16, 2008, 04:50:45 AM »
What you want is a "shunt regulator" that is commonly used in solar chargers.  They can be set to charge batteries and then when a preset voltage is reached, the power is shunted over to another purpose such as charging another bank of batteries, operating a water pump etc. to keep a consistent wattage draw.   Since the amount of power coming out of a solar panel is consistent, at least when the sun is shining directly on it if you have a "sun seeking array", this would equate to a consistent rpm motor.

At least that is what I think you mean.
Stan

Tom

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Re: Constant load to increase efficiency
« Reply #3 on: June 16, 2008, 05:14:16 AM »
A Xantrex inverter will do exactly that when charging. It will also reverse and draw from the batteries if the load exceeds the available current from the generator. The Outback inverters I have will not. I can set the max amp draw from the generator and the inverters will reduce the charge rate as the load increases. However any load above the max just over loads the generator. I was real disappointed to find this out on my new system.   
Tom
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jzeeff

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Re: Constant load to increase efficiency
« Reply #4 on: June 16, 2008, 03:24:41 PM »

Ideally, there would be an ammeter on the line from the generator and  I could run lights, etc and this would be subtracted from the amount put into the batteries.  I assume that batteries can handle this type of "constant rate" charging.  I'll look into the Xantrex.

With this in place, tuned intake and exhausts (pumping losses) should be easy and % friction losses are minimized.


Tom

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Re: Constant load to increase efficiency
« Reply #5 on: June 16, 2008, 05:18:13 PM »
All the necessary metering is built into the Xantrex. Now let me qualify. I have a SW2512 and that is the way it works. I am not sure that the newer models do. I made the mistake of assuming the Outbacks did and I wouldn't want to lead you to possibly make the same mistake.
Tom
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ronmar

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Re: Constant load to increase efficiency
« Reply #6 on: June 16, 2008, 08:21:19 PM »
From what I have read, batteries like 3 stage charging.  So what do you do with the excess power when you are not at the highest rate/stage?  What if it is in the middle of the day and you don't need lights or some other electrical load to be powered?  I agree that there is a peak efficiency point for the genertor, but keeping it loaded at this point can be difficult on a small scale. 

Ron
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Tom

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Re: Constant load to increase efficiency
« Reply #7 on: June 16, 2008, 08:48:20 PM »
Well naturally when the batteries are full it will drop the load, however If you really wanted to you could have a dump load like an electric water heater to keep the load on the engine.
Tom
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biobill

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Re: Constant load to increase efficiency
« Reply #8 on: June 17, 2008, 02:13:32 AM »
  My Trace(Xantrax) c-40 charge controller can be configured as a diversion controller so it can be used with wind generators - some of which need a constant load so they don't over rev. I'd think that the dump load would have to be resistive, like a space or water heating element and, since the DC current would vary with the battery S.O.C., it would be hard to put it too any other use. 
   Seems like an electronically savvy guy could design a controller that would be in line between the generator and the charger - taking a constant 2kw from the  gen, sending the charger what it needed and the balance of the 2kw to a resistive load of appropriate size.  ???
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jzeeff

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Re: Constant load to increase efficiency
« Reply #9 on: June 17, 2008, 02:44:40 AM »
As I see it, if you don't have a good use for the excess power, shut the engine down and run off batteries for awhile.  The batteries will run down, then there will be a good use for the power.

I guess this is similar to a hybrid car.

rbodell

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Re: Constant load to increase efficiency
« Reply #10 on: June 17, 2008, 03:22:53 AM »
Ie, I'm looking for a battery charger that will always draw 2KW.

I run an automotive alternator with a manuel regulator. It has a full load whenever the engine is running
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Doug

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Re: Constant load to increase efficiency
« Reply #11 on: June 17, 2008, 03:59:52 AM »
Easy to do with a big Chrysler alternator from the 70s.

Had my best charging system at the camp built from a Chrysler and factory mechanical regulator, easy to adjust but required constant tinkering.
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ronmar

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Re: Constant load to increase efficiency
« Reply #12 on: June 17, 2008, 04:42:57 AM »
Too bad auto alternator efficiency is so low, they are pretty controllable.  I wonder how efficient a 3 phase generator re-configured to make DC, controlled with an alternator regulator(only excited enough to produce 12, 24, or 48VDC) would be as a battery charger?

Back to system efficiency, how will short cycling your batteries effect their lifespan?  An efficient generator regime might not seem so efficient if it shortens your battery life by a year...  Now if you used a hot water type heating system, and had a well insulated storage tank, and could find a source for assorted wattage heating elements...  I am sure a controller could be programmed to switch them on/off in particular combinations to keep a constant load on the generator for a full battery charge cycle.  Then the heat energy would at least set for a while in storage to perhaps be used to maintain house or domestic hot water temperature.  For that matter the waste heat from the cooling system could go this route as well.  This might keep a gas fired waterheater from cycling as often.  You are burning the fuel, might as well use as many of those BTU as possible.

This would seem like a good match for a solar electric and solar hot water system.  When the sun is available, the electric and heat energy is provided by these systems.  When it isn't available, you burn some of that liquid sunshine to put energy into these systems
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