Bimetal multi stage dump load idea

[zvizdic]

I have that idea for same time and I am going to test-it in a coming days.
But before I do, like to hear some comments or ideas from you guys .

Idea is to use clothing iron bimetal switch (bimetal reversed to turn on additional load) in multi stage.
Each bimetal is capable of 10A switching , I think. So if I am right in my case 10' windmill I could build a air heather which would start at 500W and bimetal would turn on paralleled resistance of a next 500W and so on to total of 1500W or more for a bigger  machine.

My system is 48V making a 10A bimetal wary useful and Yes 10' windmill need 1500W dump load .
Couple days ago I  had a gail winds and catch it at 26A and voltage spike up to 65V tail fully folded.
I added  extra load and it brought under control so 800W load is not enough.     

Why you ask I like to use air heater and multi stage and answer is, it is portable inside for a winter time ,garage for a sumer .
 Only one load controller (bimetal is chipper ) and less stress on a batteries at lower winds .
 I think multi stage would be better in over all heath coming out performance then one big resistor .

But again I might be wrong so any input would be appreciated .

[SparWeb]

It will be like any mechanical switch, the number of cycles it can go from one state to another is limited.  Maybe a million times, maybe 100,000 times....  how much is enough?   Contacts could suffer quickly if it's switching lots of DC amps every time, too.  A hard-working turbine may cause your thermal switch to trip once per minute, cool down, trip again...  After a year it could be used up.

On the other hand a PWM circuit switches hundreds or even thousands of times per second, and will last for decades....  Billions or trillions of cycles.

[zvizdic]

In my experience about 80% or more of dumping would be handled by small load and how many of those big wind days is in a year 10-20 (1/3 I shut down mill for safety ).
So you are locking at a hundreds of cycles a year and a ironing bimetal cycles a lot in original application .
In each stage it would switch 6 to 7A so not to much and if it fails it would stay connected and provide necessary load.
And yes it all comes from PWM GHurd controller .
I could use second Ghurd controller but that kills mobility from garage to house for a need of 4 wires and use of a standard 2 wire plug .

[OperaHouse]

If you are switching AC it will work.  If DC you will eventually have an interesting experience.  I made the mistake 30 years ago using a relay switching DC.  Contacts opened, there was an arc and it never stopped till power was removed.  You are absolutely wrong.  The failure mode happens when the contacts open.  Rememver an arc welder operates on less thn 40V.

[dave ames]

Hey zvizdic,

Some interesting ideas here..however you may be trying to solve a problem that you don't have?

When we dig deeper into the workings of these PWM controllers they will reveal that changing the amount of load they have hooked to them does not change the amount dumped. WHAT??

If we have a dump load of 1000 watts at our set point voltage and the battery bank is receiving 500 watts too much, the controller will PWM an equivalent of 500 watts to the dump...it will be running at a 50% duty cycle.

If we have a dump load of 2000 watts at our set point voltage and the battery bank is receiving 500 watts too much, the controller will PWM an equivalent of 500 watts to the dump....it will be running at a 25% duty cycle.

If we are looking to move the dump heat inside the house in the winter from a battery some distance away you could do the ghurd controller->
timer board->inverter->AC heater method?

Fun stuff, dave

Edited to add: of course we always need to have at least enough to dump our maximum charging abilities plus headroom...the dump load size is then limited to the controller/component ratings. 

[zvizdic]

Opera House
I get that it is different to switch DC but it is pulsed DC so closer to AC then DC I think.
 
And Dave it is driven by GHurd controller so no duty cycle. As I understand workings of controller it is voltage that controls length and time of switching not frequency and duty cycle.

The reason for second stage is to be more efficient as a heater and retain dumping but with less stress on a batteries.
This is area of my concern. I am going to achieve better heating efficiency or not .
 
Thanks for inputs

[OperaHouse]

Rectified three phase for all practical purposes is DC.

Wisdom comes from knowledge.
Knowledge comes from experience.
Experience comes from bad decisions.