resitors how to?

[smidy]

hello!

i need some help here! i have a hot water storage tank at 2000 liters (in gallons??) wich is heated with woodfire and in emergency with comercial electricity by heater resistors at 6000 watts. now to my question when i installed this system i puted in one extra resistor "fore futher use" it is rated att 6 kw (3*2000watts) at 380v, i have no idea aboute what ohms its at, and now i´m want to feed the "for futher use" with some windpower from a not construkted windmill, so what to do? by a "turn key" is not an option :-). so is it diffikult to make an alternator for this? or shoud i go whit an comecial alternator and transmisson? can maybe be good to mention that its not nesesery to use all resistors or mayby even put them in series i just want to reduse the woodfire use and take care of mother earth!

tahnks smidy

(and yes my english spelling sucks)

[Putte]

Hi smidy

The simplest (cheap) way would be to use a ordinary induction motor as a generator with capacitors but then you need the gearing to get the right speed simple but not very efficient.

Then you can connect some capacitors on the generator and some on the heating element and therefore reduce the need for control device.

Like this but ad the some capacitors on the induction generator. you need a good furlig system or similar to stop it from runaway i think some max 100hz is a good max limit.

The right value for the capacitors is hard to say.

I have run this system with a pmg and done some experiment on induction motor / generator and it seams to work just fine.

I hope it to some help.

Putte.

[Nando]

Where are you located ?.

2000 liter/ 3.78 = 529 gallons

It seems that the "fore futher use" resistor is a set of 3 ( one for each phase), is that so ?

if 380 volts and 2000 watts the resistance is Resistance = V^2/power = 72.2 ohms for each phase.

Let's assume that the tank needs to have the temperature raise by 90 F = 50 Celsius.

KW = (Gallon * 8.34 lb/gallon * 1 BTU/lb*(F) *90 F ) / 3412 BTU/KW

KW = (529 * 8.34 * 90) / 3412 = 116.4 KW

So if the water needs to be heated in 6 hours the wind mill will need to produce 116.4 / 6 = 19.4 KW

Why 2000 liters ( small Sauna size pool)

Reduce the tank size.

Regards

Nando

[richhagen]

For the Ohms, I believe, that since voltage = current * resistance, and power = current * voltage, then substituting and rearranging, resistance = square of voltage divided by the power, which for you case means that you have essentially 3 72.2 Ohm resistors capable of handling 2000 watts.  

I am not certain, as I have never built one, but it seems to me that for an induction motor run as a generator, you would set it to run unloaded until the generator reaches speed, and then add the load.  It also seems like you would want the load to be matched to the generator reasonably closely to hold the operating voltage within a limited range.

What I might try, because I would be more familiar with what I had to do, would be to build a large (because a small mill would likely have negligable impact upon your water heating wood requirements) targeting an output of at least a minumum of 500 watts at my average wind speed.  At 120V rms from across your resistor, you should conduct a current equal to the square of the voltage divided by the resistance, or 199.45 watts per resistor, for a little shy of 600 watts across all three.  Above that voltage, you would need to be extra careful about arcing and moisture around your connections and wiring.  A mistake could be deadly.  I would look at the Nirvana machine built by Hugh Piggot on his website Scoraigwind.com

http://www.scoraigwind.com/nirvana/page1.htm

Your goal seems similar in voltage and power, and you are both planning to dump that power into heating elements.  You will need to make sure that you can sink the maximum power that your mill can produce even if that means an additional dump resistor bank for periods of high wind.  

Rich Hagen

[willib]

Thats a shame about the first nirvana..

btw can anyone see the pics of the second one? they dont seem to be there??

I am glad he posted that pic though , did ya notice that every coil in that particular phase is burnt.and the one next to it is also slightly burnt. the one next to that isnt burnt at all.

[smidy]

hello

i´m located on the aland island (small spot on map between sweden and finland)

yes it is one resistor for each fase.

the thank i 2ooo liters for storage so i dont have to fire up the wood burner (40kw)(dont know the real english word) so often and because the woodburner reqiers so big tank, and at resonble whether (over -5 degrees celcius) i only need to fire up every third day, so i dont think the mill have to be very big to reduse my "wood bill"

thank´s

smidy

[dinges]

120VRMS being the threshold of dangerous?

Over here we're a bit more conservative. Generally anything below 42V was considered low voltage and safe. That's why many welding machines have 42V as open circuit voltage (the transformer kind, inverters is a different story). I recall reading that it had been recently changed to 50V, (guess we humans have become more tolerant to volts?...)

It also has to do with AC vs. DC, DC being considered safer.

I'd say that anything above about 40V (including 48V? Perhaps that's a reason for choosing this strange voltage, it's just below 50V??) will require extra care.

On the other hand, I've gotten stung often enough by 230VAC and 310VDC (caps) and survived. Still, better safe than sorry, I don't go looking for danger. An extra layer of (good quality!) heatshrink tube over open pieces of metal that carry voltage never can hurt (though it can make troubleshooting harder: in my projects, I often have difficulty finding places where there's a piece of bare metal that carries the voltage I need to measure; I apply heatshrink as if my life depends on it (which it may one day?), LOL)

Just some thoughts.

Peter,

The Netherlands.

[smidy]

sounds great putte!!

so i dont need any control system, i mean the generator(motor) will always be conected to the resistors (and the capacitors)? my qustion i because of every capacitor motor/generator i read about they say "no load before speed up".

how big motor shoud i get? i asume it shoud be greater than 6kw if i run all three fase at the resistor, then it shud be "burn" safe with a proper furling system?

thank´s

smidy

[Putte]

I have done some experimenting on a induction generator and it seams to work pretty good i have not done it full scale with a induction generator but have run it on a pmg fore some time. You can do some testing on your load with a gas engine connected to the generator and see what value you need on the capacitors and so.

If you try to build on 5.5kw for one 6kw heating element you will have some limit before getting failure on the heating element.

I think that would be like a 5 meters turbine if you go for tsr 6 thats would be if you start generating power at some 4 m / s 4 * 6 * 60 / 15.7 then you have some 91rpm you will have to have a 4 poles induction motor and not more poles then that. A 4 poles deliver stable and good volt before the capacitors start to work. I would say that some 30Hz would be a good starting point 30hz * 30 = 900 / 91 then you need a gearing on 9.89 to 1 i think you would get max effect at some 9-10 m/s at some 70Hz then you want the wings to stall or furl out of the wind. You would need a runaway brake if some thing going bad.

I think you can have some 3-4kw at 10 m / s and some safety if the wings stalls it a bit later 12 m / s or so then you may have 5kw ( i am guessing) but you can always change something tsr or gearing ets. The hardest part is to find the right uf value for the capacitors but thats easy if you have groups of capacitors that you can switch on and of in different wind speed to find the right value.

http://www.flowtrack.com.au/

A nice machine to look at.

And have respect for the big loads big wind can put on wings and tower.I think an easy calculation is 50kg on every m / 2 thats some 785kg in a 5 meters turbine in hard weather

Now if i did get some numbers wrong i hope someone will correct me.

I hope it to some help.

Putte.

[richhagen]

I tend to think when your dealing with 6000 Watts, its going to have a few hazards no matter what.  The risk of electricution goes up with voltage I would think.  I believe you could electrocute yourself with 12 volts under the right circumstances though.  (stand in salt water on a hot sweaty day and get stuck to a conductor in the right location of your body and in such a way that you couldn't detach)  It is how many amps that get conducted through your organs that kill you. Rich

[Nando]

Why don't you tell us about the wind velocity ( Wind Regime ) and how you are located in reference to install a tower for a smaller wind mill, like 1.5 KW size.

This way you may have a good power assistance from the wind mill to heat up the water tank.

A fellow in UK, I have been helping him, acquired a Chinese 5 KW wind mill that produces 380 volts at 200 RPM, he is using it for the same purpose, the mill costs around 3400 Euros, I think, but not sure.

I am assisting him to set the PLC ( Programmable Logic Controller) to behave like a heater controller with MPPT capabilities -- from thinking that the mill did not work to say now that it is a good energy generator.

[dinges]

You have a point,

However, the 42V is taking into account the 'feet in a puddle' factor, IIRC.

12V isn't lethal, not even in the right place (ok, maybe if you insert two electrodes near the heart and put voltage on those). I used to check out 12V with my tongue (9V is nice; 12V is doable; 16V hurts; 24V and I think I would bite my tongue off). BTW, the last time I got bitten by 310VDC (capacitor) the only thing that did get hurt was my tongue.

As far as current goes, it's not so easy that more current is more dangerous. I'm no doctor, but the range between 100mA-1A seems to be the most deadly one, because the heart will start to fibrillate. Above 1A the chance of fibrillation gets less; the heart simply stops, and starts again when the current is removed. So, more current can actually improve your chance of survival. On the other hand, more current probably means you will suffer burn wounds (up to boiled limbs).

To get back to your point: not only the amount of amps matter (and more isn't necessarily worse), also the organs it goes throught; last time that 310VDC cap bit me, it went from left forefinger to right thumb (my right hand was in my pocket, where it should be; but when your thumb is on chassis and forefinger on capacitor: ouch. And my tongue almost got a bit shorter.)

As for the power; 6000W at 12 or 24V means some big currents; not necessarily danger of electrocution, but perhaps other problems (hot conductors/burns/sparks when (dis)connecting stuff, etc.) One of the nice tricks of my bike generator I consider to be the welding together of two wires Hefty sparks, even for such a little plaything.

Safe experimenting,

Peter.

[smidy]

well the wind blows about 7 m/s medium over a year over the aland island and normaly it can peak to around 35 m/s some times it can be over 35 m/s but thats not normal. I own the house and the land it standing on so it shoud not be any problem putting up a mill, and i think i have a pretty good windsite since there are 3 enercon 500 or 600kw lokated about 800-1000 meters from my house. where did you find the chinese mill? sounds pretty intresting for the money

thank´s

smidy

[Nando]

The site is in UK

http://www.navitron.org.uk/

The 5 KW comes with a tower, I believe 9 meters and, as well, tower anchor kit and it is around 3600 Pounds not Euros.

Since you up north, I would suggest to buy a spare set of blades.

The mill has a brake, hydraulic ??

If you buy one, make sure that you check the rotor spacing ( clearance) to the stator and the bearings are not LOOSE.

You need a heater controller capable of accepting up to 9 KW with at least 4 stages, one PWM, and 3 ON/OFF.

I would, as well, tape the leading edge of the blades.

Nando

[nanotech]

When I was in the US Navy, I worked on the NATO SeaSparrow missile system.  In the radar components is one cabinet called the SDP (Signal Data Processor) that takes all the incoming radar signals and processes them into computer-useable information.  To do this requires a WHOLE lot of cards.  All running at 5VDC.  In parallel.  

I think you can see where this is going.  The 5VDC power supplies (3 of them) were rated at 125 amps EACH!!  Yes, 375 amps at 5VDC.  That cabinet had one of the BIGGEST warning labels on it!!  

From what I managed to find out, some poor sap was doing the overvoltage check on the power supplies while the ship was at sea.  The ship rolled under him and he lost his balance.  He grabbed the cabinet (grounded) to steady himself at the exact same moment his other hand landed on the positive post.

The medical examiner's description was quite graphic (as you can imagine) as to how all of his organs were cooked as if they had been in a microwave oven for 30 minutes each.  The only outside indicators that something was wrong were the two burn marks on his hands (entry and exit wounds) and his eyes were bloodshot.  But there wasn't a single portion of the inside of his body that didn't have second if not third degree burns throughout.

Not a pleasant way to go, I wouldn't think......

Now, in one of the other cabinets is the radar transmitter.  2KW of 10GHz 10,000V energy.  I managed to short that to the cabinet from one hand to the other (some idiot had ignored the lockout/tagout and turned the system on anyways while I was working inside the cabinet.  He was court-martialed out of the Navy for it on a charge of attempted manslaughter).  I was checked out by base medical and there were no effects from it.

Now, the guy in the first instance had only 1,875 watts of power go through him.  I had a little over 2,000 watts (we always ran the radar slightly overdriven for better signal clarity).  Why the difference?  The amperage, and that he was attatched to DC for a while and I was thrown flying by A/C (and my own fear since I heard the system crank up the coolant pumps and was on my way out of the cabinet with a MAJOR quickness!!)

[hvirtane]

my question because of every capacitor motor/generator i read about they say "no load before speed up".

You can run an induction generator

always loaded, if you'll install

some permanent magnets

on the rotor or between the coils

to guarantee it will start generating.

With a three phase induction generator

you might try using three different size

loads, one for each phase, to be switched

on at predefined wind speeds? It seems to be

the case that in practice

induction generators are quite

happy with unbalanced loads.

- Hannu