hot water

[capta]

In my research on wind generators it seems a dump or shunt is needed, for when the batteries are full.
I can not imagine putting a big honking resistor in the engine room to absorb this excess energy and heat everything up.
What about connecting it to the hot water heater element? I have the Raritan 1125 ohm element for 110 volts A/C. I have seen 12 volt elements to use in this way for sale on the web, but is it really necessary to have a 12 volt element? Isn't it just a big honking resistor and even if it didn't get as hot as a 12 volt element, it should consume the excess energy and give some heating?
Thoughts? Thanks.

 

[MrUnix]

Are you sure it's 1125 ohms and not 1125 watts? Most typical heating elements are less than 15 ohms..

Since wattage = Voltage squared / resistance in ohms

110^2 / 1125 = only a little more than 10 watts which I don't think is going to get you much hot water

However, if it's a 1125 watt element, then you are looking at right around 10 ohms and about 10 amps, which sounds much more reasonable.

Now, if instead of 110, you put 12v through that 10 ohm element, you get
12^2 / 10 which works out to about 14 watts and would require a little more than an amp to do so.

I don't have the exact numbers, but I'm pretty sure that your water heater loses more heat than what 14 watts would be able to maintain.

Cheers,
Brad

 

[alexco38]

I heard Some wind gen just short out the coil to prevent the blade from turning when the battery is full or excessive wind. Check the user manual.

Dump electric into resistor won't slow down the blade especially in high wind.

 

[Kordie]

My wind turbine stops turning when batteries are full. In stronger wind it will turn slowly and silently.

One useful spinoff is that when you are on watch at night with the auto helm on you can tell how the batteries are going by the wind turbine activity.

 

[John Nantz]

Water Heater load diversion

One of the things on my wish list is a 12v (or 24v) & 120v hot water heater element and this would be a good load diverter, at least for awhile. Just do a search and you'll find some hits. We all like hot water when we're on our boats.

For my wind generator I've got a pendant hanging from the end of it's rudder and when I want to stop the blades from turning I grab it and pull the rudder into the wind until it stops then just tie the lower blade off (Rutland 6-blade) and around the mast. From there on the blades are stationary but the unit can still swivel around the mast. I suspect the brushes last longer too and with less carboning of the slip-rings.

 

[Don12364]

And when the water boils - what then?

I know it seems unlikely but you still need to cater for this for a long lasting gale.

 

[Rich Stidger]

My Air-X has a built-in regulator that starts charging at 12.7 volts and stops at 13.4V. It can't over-charge the batteries but will keep them fully topped off.

If the wind blows harder than about 40mph, the controller in the generator shorts the output and the blades slow to a crawl. This device is rated for 100mph winds.

Maybe other wind generators have a similar control system?

 

[capta]

Mr Unix
You are absolutely correct, I meant watts not ohms. Either it's "old timer's disease" or my blonde (white) hair.
It's really not about the hot water, but about absorbing the excess energy with out heating the engine room pointlessly.
With a 600 watt windgen and 500+ watts of solar, until I get 12 volt refrigeration, I believe I'll have a lot of excess energy.
The windgen will be mounted 30' up the mizzen, a bit too high to deal with strings and the one I'm considering (a SILENT ONE, but that's another thread) needs a load dump.
"And when the water boils - what then?
I know it seems unlikely but you still need to cater for this for a long lasting gale. "
We'll take lots and lots of HOT showers!

 

[Don12364]

Hot Tank??

My hot tank contains 6 US gallons. It reaches 60°C under engine or immersion heater and then, after 10 hours it cools down to 30°C. This means that, on average, it looses the equivalent of 77 watts constantly. Yours is probably similar.
Your wind generator can produce far more energy than this so it will boil your tank.
Something MUST give. Either the safety pressure relief valve will vent boiling water into your bilge continuously or the tank or any of the boat's piping will burst.
This might occur more quickly than you expect if you have just come in after motoring for an hour or more.
If you intend to dump waste energy into the hot tank you MUST have means of turning it off or diverting this energy before it causes damage to the boat.

Edited missed the '0' off as above. Now reads 77 watts. Apologies if I mislead anyone.

 

[capta]

Donalex
All joking aside; your answer is why I posted the question. Thank you.
Is there a difference between the 12 volt element and a 120 volt element or is it just a way to sell the same element more expensively? Isn't the temp controlled by the thermostat unit?
Wouldn't it take roughly 10 times longer to heat the 12 gallons of water with 12 volts over 120 using the same element? I doubt that I could use the 120 volt A/C thermostat w/ the 12 volt D/C, but could one be purchased, do you think? Raritan has nothing that I know of, yet.
I have the Raritan 12 gal w/ engine heating as well as electric, I believe similar to yours.

 

[Don12364]

Capta

A 1Kw immersion heater at 120 volts would only draw 10watts when run off 12 volts. i.e. 0.83 amps.
This would hardly load your wind generator so would not prevent it overspeeding, whilst, at the same time, hardly heating the water because the cooling rate will be over 7 times greater - so neither problem will be solved.
If you can buy a 12 volt immersion heater to fit in the same hole - or an additional hole then things might be more realistic.
Also you need you understand that the thermostat only controls the temperature by TURNING OFF the heater. This is not what the generator maker wants to prevent runaway in gale force winds.