excess power

[artv]

Hi all ...........not quite sure if this is the right spot for this question,.....I don't really understand dump loads when the battery bank is full you dump the excess???Once your bank is full why not just send the extra to a hot water tank ,store it in the form of hot water,...then everybody could run a 48volt system.This dosen't make any sense it's about conserving energy not dumping it, when you guys talk about dumping it where does it go ,I know some talk about water heaters,but some just seem to get rid of it..............totaly confused............artv

[Flux]

With wind you get long periods of little power and other periods with a great deal. When power is short you have to conserve then when the wind comes your priority is to get the batteries back up as soon as possible.

With a small installation you will have excess power when the battery is charged, best to plan your life stile to use as much as possible on these days. If you don't use it all you need to dump it unless you can shut the mill down.

For small machines this extra will not contribute a great deal to water heating but it may still be useful. A few peaks of 500W is a lot to get rid if in a dump resistor but it would make very little difference to a water tank. As it is primarily a means of protecting the battery then many just waste it in a dump heater.

For larger machines then you will have some really useful heat available on windy days when the batteries are charged and then it does become worth the effort of dumping to the hot water system.

Those that live off grid and understand their set up will manage their load use to make best use if the wind available but not everyone understands or is prepared to devote the time and effort to these things so a system that looks after the battery but doesn't use the extra energy satisfies their needs.

Heat is the lowest form of energy and you need a lot of watts to make it very useful so it is far better to use as many other loads on windy days as you can rather than be permanently dumping. Do your drilling, grinding, sawing and water pumping on windy days and there is not so much need to be dumping.

Flux

[ghurd]

"then everybody could run a 48V system"?

To me, 48V does not make sense in a small system.
Lots of batteries and balance issues, expensive and larger equipment (like inverters), special switches and fuses, etc.

Heating water with a small system does not make a lot of sense to me.
Lets say you have a couple hundred watts of solar and a 100~200W wind turbine.
If the power is being used effectively, then there is not a lot of power to heat water on a regular basis.
The cost of the water pre-heater, elements, a decent controller able to deal with the amps the element draws, etc, is a lot of money for something that does not do much.
That money would be better used for more solar or wind or something.

Watts are directly convertable to BTUs.
Going through some simple math will show how a small system heating water with the dump load is almost pointless (IMHO).  There is just not enough excess power to do any real good.
G-

[artv]

Hi ...could you charge capacitors with this excess??...and could you hook a capcitor in reverse to catch the back emf.............artv

[ghurd]

Why would you want to?

Caps hold very little usable power, almost 'nothing' compared to a very small 12V battery.
When the cap is charged (almost instantly), it again leaves the battery overcharging and needs a dump load.
Adding a very large amount of capacitance will be much more expensive than adding a little more battery capacity, with no practical gain from the caps.

Your next thought will be "Why doesn't everyone just use a battery so big they do not need a dump load?"
Because batteries have self discharge.  The act of keeping them charged, even when not loaded, takes power.
Because batteries are expensive and do not last forever.
If a system is 100W of solar and an Ametek windmill, it does not make any sense to have a $5,000 battery because all the power will go to keeping it charged from self discharge losses.
If a system is 100W of solar and an Ametek windmill, it does not make any sense to have a $30 7AH 12V SLA because the battery will not hold enough of the power made to use worth a darn.
The system needs to be balanced for most days and conditions, and for days with excessive power production there must be a (sensable and cost effective) way to deal with the excess power.

"catch the back emf"?
Not sure I follow what you are thinking, but there is almost less than no power in the inductive spikes in the power resistors.  Flyback diodes basically only absorb amps to keep the voltage very low, which protects the semiconductors.
It still comes back to caps holding very little power.

G-

[fabricator]

Short answer is in a battery charging system you HAVE to dump power when the loads are not calling for power and the turbine is making lots of power, if you don't you'll boil the electrolyte out of your batteries and destroy them, the easy ways are direct air heating or heating water, the way I do it is to use a controller with a relay that turns on a dedicated inverter that powers a heating element in my hydronic heating system, this way you make actual hot wate. Using DC elements with large conductors and line losses you never get much actual hot water.

[artv]

Thanxs for the replies...could you design the turbine just as a dump load and create as much heat as possible,.....seems alot of effort goes to fighting heat , why not just go for straight heat??.......artv

[artv]

Sorry I forgot to ask ....if the stator was encased in water would the water get hot??.............artv

[fabricator]

Thanxs for the replies...could you design the turbine just as a dump load and create as much heat as possible,.....seems alot of effort goes to fighting heat , why not just go for straight heat??.......artv

Yes you can build a water or air heating turbine, you are not "fighting heat" you are keeping your battries from being over charged, the power that would be over charging your batteries can be used for something else like heating water or air.

[ghurd]

could you design the turbine just as a dump load and create as much heat as possible,.....seems alot of effort goes to fighting heat , why not just go for straight heat?

I said "Watts are directly convertable to BTUs."?
Heat and watts are the same.

"create as much heat as possible".
That means create as much power as possible.
Which means create as many watts as possible.
That is the whole point of everything.

"seems alot of effort goes to fighting heat"
No.
A lot of effort goes into fighting wasted watts being wasted and disapated in the wrong place, such as wated power in the stator in the form of I^2R.

"could you design the turbine just as a dump load ".
No.  It would make no power compared to what it would make as a battery charging turbine.
I think you mean 'could you design the turbine to ONLY power a dump load'.
Yes.
The problem is the controller.  It needs to be a high voltage dynamic smart MPPT to match the load power with the available power.  That sounds simple enough.  It is anything but simple.

"if the stator was encased in water would the water get hot??"
Of course.
If something using watts is put in water, the heat from whatever is using watts goes into the water.
When the water (in liquid form away from the freezing and boiling points at that pressure to mostly avoid complications from Dalton's Laws) and stator reach equilibrium temperatuters, a watt hour disapated in the stator will travel to the water as 3.41214 BTU/H.

I do not believe you are following the basic math...
1 btu = 1055.05585 joules
1 joule/second = 1W
1 Newton = 1 Joule/Meter
746W = 1HP
1 BTU = 251.5 calories
1 BTU = 780 foot-pound-force

Just like Ohm's Law, you can not argue with it.  It is what it is.
Just like Ohm's Law, if your measurements or calculations do not come out the same, you did not do it right.

[WindriderNM]

I am working on a pump to pump water from my well into a 300 gal. tank on a tower to dump extra power.
When the battery are charged the pump will come on when the tank is full the extra water will go into a drip watering for the garden and trees. If i have to much water i will plant more trees.

[birdhouse]

wind rider-
doesn't someone on here use their dump function to pump water to a tank on a hill, to later release the tank to a hydro turbine for a short battery boost?  or am i completely mistaken? 

sounds like a good idea, if tank height was pretty high, lets say 20 foot, and tank size was over 1,000 gallons.  that's got to be good for a few watt hours???

adam

[ghurd]

Not nearly as much as it seems.
1000 gallons 20' high at 60% efficient at 10 gallons per second, 1360W for 100 seconds, 37Watt-Hours.  (if I did that right)
That's an 11W CFL for 3 hours.

The cost of a 1000 gallon tank spent on a solar panel would make more power per day.
The solar panel would do it many days instead of just when there was extra power.

Another way to think about it?
An efficient pump does not use a lot of power to pump 1000 gallons up 20'.
The pump has a lot of losses, even if it is extra power.

The generator has a lot of losses.
There are other losses too.  Friction, rectifiers, etc.
The rest of the power is there to be harvested.

Build a pond, which increases taxes?  Might be feasable if excess power were enough to cover the pump and hydro costs.  I have a feeling if there were enough extra power to cover the costs there would be no need to harvest the excess power from the hydro system.
I can not imagine a normal situation where that would work out as a good idea.
G-

[artv]

Hi Ghurd, I have an artiesen well in my yard and my well line that comes out of the ground continually pumps water out by itself. If I hold the water line (1-1/4")  18 inches above the ground level the water keeps pumping out by itself. If I go 2feet above ground level it seems to just hold at hte 18" mark inside the pipe. Could this be put to a practical use? I've often thought of some form of water turbine system since my wind situation is not good.I have estimated that at a foot above ground level I get ~1 gal/min.......thanx  for any ideas.      ..artv

[hayfarmer]

Hi,I have a 48 volt system at my home and my major concern is keeping my battery strings (3) "warm & fuzzy" close to 77 degree as possible,how ever in a outdoor power shed with great insulation  and insulated battery box its a fight in the winter time so the ceramic resister heater dump load is helping the fight,winter winds and winter cold temps .seems like a good use of dump load in the winter,but summer is another fight, I just exhaust the heat outside.with a 48 volt fan controlled by thermostat.

[Ungrounded Lightning Rod]

Lead-acid batteries do better if you mostly keep them fully charged.  Also you'd like to keep your batteries charged to maximize the amount of stored power you have available when the wind dies and the sun goes down or behind clouds.

That means you want more charging capacity than load.  And it also means that, once the batteries are fully charged, you have an embarrassment of extra power.  You don't want to shove it into the already full batteries because it will damage them.  (Flooded lead acids will "boil off" - electrolyze into explosive gas - much of their water, just for starters.  Lots of other bad stuff can happen.)

But while you can easily shut down solar panels by either unhooking them or shorting them (upstream of the blocking diode), unhooking a wind machine from its load means it may run away and self-destruct.  And shorting it MAY shut it down, or MAY cause it to burn up.

So it's easier (and for a mill, safer) to just leave the sources hooked to the battery and get rid of any excess power.  You can "throw it away" by burning it into heat in resistors.  Or you can use it for something useful but too power consuming to be done all the time.  (Heating is a good example of something that takes a LOT of power for a little benefit.)

Think of:
 - The battery as a reservoir behind a dam.
 - The stored water in the reservoir as stored power.
 - The generator and solar panels as rivers running into the reservoir.
 - The loads as pipes taking pressurized water out to users.
 - The "dump load(s)" as spillways, allowing extra water to run away (like downstream benefiting nothing but maybe fishes in the delta or off to irrigate some fields) once the reservoir is full.  This keeps the dam from breaking.
Then you'll have a good understanding of a battery/charging/dump-load system.

You need a (set of) dump load(s) that can consume at least the maximum sustained generation your sources will provide.  If you burn too much power they'll shut down when they've pulled a bit off the battery.  If they burn too little you're still OK if you get a sudden burst (which they can burn off over a little extra time) but a sustained excess will get ahead of them and you're back to overcharging and maybe damaging or destroying your batteries (followed maybe by other components of the system).

[Ungrounded Lightning Rod]

Lead-acid batteries do better if you mostly keep them fully charged.  Also you'd like to keep your batteries charged to maximize the amount of stored power you have available when the wind dies and the sun goes down or behind clouds.

That means you want more charging capacity than load.  And it also means that, once the batteries are fully charged, you have an embarrassment of extra power.  You don't want to shove it into the already full batteries because it will damage them.  (Flooded lead acids will "boil off" - electrolyze into explosive gas - much of their water, just for starters.  Lots of other bad stuff can happen.)

But while you can easily shut down solar panels by either unhooking them or shorting them (upstream of the blocking diode), unhooking a wind machine from its load means it may run away and self-destruct.  And shorting it MAY shut it down, or MAY cause it to burn up.

So it's easier (and for a mill, safer) to just leave the sources hooked to the battery and get rid of any excess power.  You can "throw it away" by burning it into heat in resistors.  Or you can use it for something useful but too power consuming to be done all the time.  (Heating is a good example of something that takes a LOT of power for a little benefit.  You usually don't put in a generation system just to make heat, because there are cheaper ways to get what you need.  But when you've got extra power you MUST get rid of NOW you can often turn it into useful "free" heat and use less of some cheap but not free fuel.)

Think of:
 - The battery as a reservoir behind a dam.
 - The stored water in the reservoir as stored power.
 - The generator and solar panels as rivers running into the reservoir.
 - The loads as pipes taking pressurized water out to users.
 - The "dump load(s)" as spillways, allowing extra water to run away (like downstream benefiting nothing but maybe fishes in the delta or off to irrigate some fields) once the reservoir is full.  This keeps the dam from breaking.
Then you'll have a good understanding of a battery/charging/dump-load system.

You need a (set of) dump load(s) that can consume at least the maximum sustained generation your sources will provide.  If you burn too much power they'll shut down when they've pulled a bit off the battery.  If they burn too little you're still OK if you get a sudden burst (which they can burn off over a little extra time) but a sustained excess will get ahead of them and you're back to overcharging and maybe damaging or destroying your batteries (followed maybe by other components of the system).

[thirteen]

if you have the water won't a ram pump work for temp storage of water in a tank. Unless it freezes it would be good for a temp  power boost a couple of times a day. ?? Mybe??

[ghurd]

Hi Ghurd, I have an artiesen well in my yard and my well line that comes out of the ground continually pumps water out by itself. If I hold the water line (1-1/4")  18 inches above the ground level the water keeps pumping out by itself. If I go 2feet above ground level it seems to just hold at hte 18" mark inside the pipe. Could this be put to a practical use? I've often thought of some form of water turbine system since my wind situation is not good.I have estimated that at a foot above ground level I get ~1 gal/min.......thanx  for any ideas.      ..artv

About 0.4 meter head, about 0.058 liters per second, with a 100% efficient turbine, is 0 watts.

http://www.reuk.co.uk/Calculation-of-Hydro-Power.htm

G-

[Ungrounded Lightning Rod]

Hi Ghurd, I have an artiesen well in my yard and my well line that comes out of the ground continually pumps water out by itself. If I hold the water line (1-1/4")  18 inches above the ground level the water keeps pumping out by itself. If I go 2feet above ground level it seems to just hold at hte 18" mark inside the pipe. Could this be put to a practical use? I've often thought of some form of water turbine system since my wind situation is not good.I have estimated that at a foot above ground level I get ~1 gal/min.......thanx  for any ideas.      ..artv

About 0.4 meter head, about 0.058 liters per second, with a 100% efficient turbine, is 0 watts.

http://www.reuk.co.uk/Calculation-of-Hydro-Power.htm

G-

Rounded down from 227.6 milliwatts.