Hot water thermostats - double - triple pole ?

[Dave B]

Hi gang,

  I will be heating water direct with my mill and want to switch to a dump load in the event of overheating the water. Should be easy with the mechanical snap disk type thermostats but I have searched and cannot locate double or possibly triple pole thermostats that I could replace the standard thermostat(s) with. This so if the water exceeeds the temp setting it will switch over to another load other than just open and shut off. Is anyone doing this or have a resource for this type of thermostat ? I appreciate the help,  Dave B.

[robl]

DaveB

Have not seen disc-type 3-phase. I expect this is hard to do mechanically. If you want to stick with disc units my recommendation is to use a single-phase disc unit to control a three-pole relay (dc up to 24V, AC coils from there on up). P&B, Omron, Guardian all make multiple pole/dpdt relays. Temp rise, disc kicks out, relay kicks in....gives you a fail safe transfer mode.

Regards

Rob

[TomW]

Dave;

Maybe you could use a standard thermo to drive a double pole double throw relay?

Seems that might get what you want?

Just a first thought.

Cheers;

TomW

[Dave B]

Thanks for the ideas. I want to keep it as simple as possible and avoid having to power the relays for switching. I know I can tap into the generated power to do this and solid state relays etc. etc. but it just seems to me so simple using the mechanical thermostat itself, that's what it does anyway. There are (on) at temp and (off) at temp snap disks available, maybe I'll look into these as seperate options to a manufactured thermostat to get it done. Any other ideas are always welcome, thanks.  Dave B.

[Nando]

HOT HEATER TANK BY PASS

For those interested in having a power transfer to another load.

This is what has been done in some systems.

The water heater does need a thermostat to open the current to the water heater resistive load and upon opening of the thermostat, a relay is turned ON to connect the power to another load.

The relay needed needs to have the same voltage than the resistive loads receive.

Place the RELAY winding IN parallel with the thermostat contacts, so when it opens, the relay is turned ON connecting the secondary load.

One needs to recognize that in this case the water heater is the main load and the Relay activate load is the secondary one.

So if the voltage is AC and high voltage, the relay is AC and high voltage.

In some cases with AC capabilities a transformer has been used to bring the voltage down to a lower voltage and sometimes rectified to be used with DC relays.

If a schematic is needed, let me know.

Nando

[Nando]

Dave:

Normally, a single thermostat is used to disconnect a 3 phase load, so the relay, that can be placed in parallel with the thermostat, should be a 3 pole Relay.

The use of three thermostats (one per phase, is not warranted or desired).

In some cases, there are 2 thermostats in series for added protection and in this case the relay should be in parallel with both thermostats,

Nando

[vawtman]

Hi Dave

 Why not have a large storage area with little or no chance of overheating?

 Just a preheater to your current system.

 My thoughts and plans.

[Dave B]

Size limitations and I'm thinking the pre-heat tank will become my main tank when the old one bites the dust. With my hot water consumption and inconsistent winds I want to utilize any pre-heated water soon after heated. Possibly a 50-80 gallon electric hot water tank used as a pre-heat tank in series with my main tank should work out about right for now, I can bypass it all together and shut the mill down besides if I'll be gone for a while and don't want to think about it. I think I also have the thermostat issue solved. Most tanks already have a spdt snap disk thermostat running the upper element that switches power to the lower element, I'll just switch an external load on instead. Fun stuff, thanks for your replies.  Dave B.  

[vawtman]

Dave

 The reason i mention a large tank(say fuel tank size)is that when hot water is used the water comes into the tank at around 55 degrees or so.If you had a large supply of even 80 degree water to feed it.Lots of savings.

 There would be times of no winds during winter months but the water would preheat from ambient air temp.But if slightly warmer would warm the house.

 You could insulate during summer months.

 Mark

[Ungrounded Lightning Rod]

I really like that "relay across the thermostat" approach, Nando.  Simple, does the right thing in all cases, no parasitic loads (except when you have power you need to dump), etc.

[Nando]

Dave B:

Have you calculated or estimated the water volume you may need ?.

Have estimated the daily watts the wind mill may produce ?.

One should do some calculations to make sure that the hot water volume exists even if the wind mill may be down for lack of wind for several hours or one or two days.

If you do not have the way to calculate the water volume, let me know to assist you.

I do not remember what is the capacity of your wind mill or the generated voltage at peak wind velocity.

Can you repeat them ?.

Nando

[Dave B]

Thanks for everyone's comments and suggestions. The spdt mechanical snap disk thermostat is the answer for me to switch on another dump load after a max water temp is reached. No relay coils, power or backup batteries needed for the control circuit to fail when you need it most (when high winds knock out the grid) been there done that. Time for action, need to wire the panel, purchase and plumb the tank, paint the tower, weld up a high stop on the tail,  and start to disassemble the alternator and blades from the test tower to be moved over to the tower top of the 85'. Then it's bolt it back together, wire it up and pull er up. Progress updates and photos to follow. Thanks again,  Dave B.  

[domwild]

Hi,

Have noticed that microwave ovens have an overtemp cutout switch attached to the cooking "case". I do not know at which temp they trip open, that may be a problem. On the other hand, getting three of them (one per phase) whould not be too much of a hassle.