System Of Relays for DumpLoad Control - Will it work?

[romekgm]

Hi
I have a 48V Wind Turbine system connected to a Battery and a DumpLoad
I'm trying to build ,  a secondary system ,that will take the output from Midnite Controller(48V,1500W max) , and will PWM it to a dump load(48V ,1800W heater) , to a capicity I want (the battery is not envolved)
for example ,if I have 1000W of power to spend , and I want only to spend 500W ,the PWM will transfer only 500 and the rest will accelarate the turbine.
My idia ,is to use 2 relays, one mechanical ,that is attached between the battery and the Midnite , and will disconect/connect them by  a command from my controller, and a second one Solid State Relay, that is connected between the Midnite and the Dump Load ,will be on/off by a PWM signal I'll send from my controller(not from the AUX of the Midnite!), so by suitable software(LabView) , I can control the power delievered , and compare my algorithms to Midnite performance.
I know it sound a little confusing, so I made a sketch with all system componets and conections, and attached it to the post.
The upper part, is the system I have now, usual Wind Turbine control hookup
The lower part, is a computer system ,atached to programmable controller (Nationa Instrument) , that controls the two Relays.
I know its better to use it in AC form as it go from the Turbine , but I want to have the electrical losses that the Midnite have , so I can compare the systems
I would be glad to hear your opinion if it can work
thank you

[mike90045]

I'd use a sold state relay for both.  High amp mech relays worry me.  A  Contactor  http://en.wikipedia.org/wiki/Contactor would be my choice instead of a relay.


And I don't understand using DC power to accelerate the turbine ?

[Halfcrazy]

It is hard for me to follow but it sure looks to me like you want to move the battery side of the classic away from the battery? This will not work.

[dgd]

This circuit does not make sense. The Classic will not function as expected when disconnected from the battery.
Looks like an MN Clipper would do all you need as you could experiment with feeding the Clipper your own PWM signal to adjust power burned off over the Clippers resistor bank.
As you reduce this then as expected the turbine would speed up.

Although why you would want to do this has me confused. Unless the turbine's mechanical braking/furling is good then you could have a runaway and burnt out turbine.

dgd

[romekgm]

thank you for your all replies

mike90045

And I don't understand using DC power to accelerate the turbine ?

when you use less power than the turbine provide(RPM*Torque), that power have to go somewhere, the the Torque on the blades, accelerate the blades, it also works in the opposite way , when you overload it.

I'll check what these "Contactor" is , my knowledge in electronics is limited...

dgd

Although why you would want to do this has me confused

The turbine is used for educational and academic porpoises only , so I want to have control over its parameters, and use other type of loads\algorithms beside the one in Midnite,and compare them to Midnite performance

Looks like an MN Clipper would do all you need

Your are right but a Clipper costs alot of money and time (convincing the University to buy it ,ordering threw University department, delivering its oversea to Israel,its all very slow here...) , and I its much more fun to do it yourself 

Halfcrazy

you want to move the battery side of the classic away from the battery? This will not work.

Can't I cheat Midnite controller  to work as a transformer(high DC voltage to low DC voltage)  even when the battery disconnected?
I want to have both ,a system with a battery and a system without

[zoneblue]

Can't I cheat Midnite controller  to work as a transformer(high DC voltage to low DC voltage)  even when the battery disconnected?
I want to have both ,a system with a battery and a system without

No, the controller requires a battery attached at all times. Its how they work.

[TomW]

Can't I cheat Midnite controller  to work as a transformer(high DC voltage to low DC voltage)  even when the battery disconnected?

This has been discussed before.

There is just no way to use the Classic without a battery.

Might get away with a small battery but it will need one just to power up.

Sorry but it is what it is.

Tom

[dgd]

dgd

Although why you would want to do this has me confused

The turbine is used for educational and academic porpoises only , so I want to have control over its parameters, and use other type of loads\algorithms beside the one in Midnite,and compare them to Midnite performance

ok, I would suggest instead of trying to divert the Classic output to a resistor, instead of battery, which won't work anyway, why not have resistor before input to Classic and pwm'ed into circuit with SSR and your pwm generator. You just need to place a power diode between resistor and Classic to prevent reverse current flow from Classic input to resistor.
Using various shunts you could test current at different pwm settings and compare system efficiency and Classic efficiency.
However, this would all be a purely academic exercise unless you are planning to reinvent the Classic firmware that deals with WIND input.

dgd

[romekgm]

dgd

why not have resistor before input to Classic

ye, Its a good idia,I  read some articles about similar setups(only with diffrent resistors , no one used pwm as load control), but I hoped to use the Midnite transformer and logging system as part of the expirment ,but if I won't find a solution , thats the way I'll go.
Anyway I'll keep you all posted about my progess or failure...
thanks for your help and opinions

[RossW]

I hoped to use the Midnite transformer and logging system as part of the expirment

The Midnight is not a transformer in any sense of the word.
It is a sophisticated computer-controlled device, and like all computers requires a good connection to a reliable power supply.