Author Topic: Do I need a dump load?  (Read 2980 times)

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(unknown)

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Do I need a dump load?
« on: January 26, 2010, 02:42:31 PM »
I will be producing lots of power 24/7 from hydro and hope I don't have to use batteries. Since I don't have batteries do I need a dump load? What I understand a dump load to be is a load so that when the batteries are full the energy still being produced needs to be used. Also how would I hook a dump load up with no batteries?
« Last Edit: January 26, 2010, 02:42:31 PM by (unknown) »

ghurd

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Re: Do I need a dump load?
« Reply #1 on: January 26, 2010, 08:41:24 PM »
I do not think anyone can answer that, because you do not have the system nailed down.


Not sure how you came up with 3KW of generation.


Imagine: Cold night out, so you get a blanket and watch a DVD (25W DVD, 100W TV). OK.

Furnace kicks on (1/4HP with a 420W draw, 1700W surge).  Still OK.

Grab a beer from the fridge (40W bulb).  Fine.

Flush.  Well pump, and surge.  Uh oh.  Getting pretty close.

And then the fridge thermostat realizes it is time to kick on (1500W surge).

Not OK.


Hydro is great, and 3KW 24/7 is a whole lot of power.

But 3KW max limit at any time is not much at all.


If it was me, I'd have some battery.  Or grid tie.


If I could actually get 3KW 24/7, I'd probably be off grid.

Unless they made grid tie much more appealing than it was last I checked, which I think they did.


Grid tie would probably be worth looking at adding some solar since most of the expensive stuff would already be dealt with.  Then solar is gravy?


Other things to consider for nailing down the system.


Heat.  A battery with a 3KW dump load sounds like a pain?  3KW heats a lot of water.  Those old electric space heaters are like 1500W, and 2 of them running all night would be a lot of heat.


'Car alternators' insinuates 12V.  3000W at 12V is 215A?  #000 copper is rated about 240A.  

And the wire losses would be high.  #000 (#3/0) carrying 215A 500' loses 5700W, nearly double what you want to make.

Even #0000 (#4/0) copper running 50' with 215A wastes 2265W, or 75% of what you want to make.


Watts is Watts, and 746W is 1HP.  HP can be converted to torque, and torque ruins bearings.

A 250A car alternator at 14V is 3500W, 4.7HP of output.

The force on the bearings is 4.7HP, plus losses whatever they are, but I expect it's less than (way less than) 50% efficient at 3500W, so those little bearings are being subjected, 24/7, to 10HP or more.


If you can get 3KW 24/7,

you probably want to go 48V with a battery system,

more for a grid tie.


G-

« Last Edit: January 26, 2010, 08:41:24 PM by ghurd »
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Dave B

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Re: Do I need a dump load?
« Reply #2 on: January 26, 2010, 10:29:58 PM »
Subman,


  2190 KWH per month. If you have the grid now I would be off the grid in a heartbeat and in no way would I ever consider grid tie. Come and pull my meter.


  That power here in Western NY would cost me (at the current "total" rate .21 cents / kwh. Grand total, $459.90 per month, $5518.80 per year !!


  I'd have many standard large electric hot water tanks and heat hundreds of gallons of water for your home heat and domestic hot water for starters. I'd purchase the largest battery bank and inverter I could afford then I would kick back and enjoy life.


  If you still generate more than you use then sell extra to your neighbors for a discounted rate or heat your sidewalk, garage floor or hot tub and pool.


  Man, I hope you are correct with your figures and can make it work. Keep us posted of your hydro system and specifics as you progress.


 Dave B.  

« Last Edit: January 26, 2010, 10:29:58 PM by Dave B »
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Flux

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Re: Do I need a dump load?
« Reply #3 on: January 27, 2010, 12:54:35 AM »
I don't know anything about your intended set up but it is unlikely to be as simple as you hope.


To use power directly you need constant volts and constant frequency. For constant frequency you will need a turbine with good speed governors. For precise volts you will need a well regulated alternator. Neither of which normally comes within the realms of small hydro unless you have a lot of water and a lot of money.


For simple direct loading of small hydro when there is plenty of water most schemes use a controller that maintains constant load on the turbine so the frequency and volts stay constant.


This is in fact a special dump load specifically designed for this duty. So normally you will need either batteries and a dump load or a hydro controller with no battery.


Much depends on the constant supply of water and the peak demand you need and also the type of load and how critical it is on volts and frequency.


Flux

« Last Edit: January 27, 2010, 12:54:35 AM by Flux »

Subman

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Need to be more clear
« Reply #4 on: January 27, 2010, 05:27:03 AM »
Sorry I should have been more clear. I have a 3kW inverter, that's why I say 3kW. I will be running a 200 amp car alt to start. If that doesn't last long I will make a diy one. I hope to connect the car alt directly to the 3kW inverter. What I am asking is if I don't use 3kW all the time will it hurt the inverter?
« Last Edit: January 27, 2010, 05:27:03 AM by Subman »

Flux

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Re: Need to be more clear
« Reply #5 on: January 27, 2010, 06:46:30 AM »
You will still have the same voltage regulation problems using the inverter without a battery. As the load changes you will go out of the inverter input voltage band. You will probably need some monster capacitors anyway to deal with the peak currents.


You should be able to get away with a fairly small and perhaps indifferent battery and if the load is constant and you are prepared to baby sit it you may not need a regulator if your hydro is very controllable. Otherwise a simple dump controller would make life much easier.


You don't need an elaborate and costly controller, one of Ghurd's would be more than adequate and would add little to the system cost and simplify life a great deal.


Flux

« Last Edit: January 27, 2010, 06:46:30 AM by Flux »