Relay Switch or PWM?

Zakarume

If money was an issue and could not afford a MPPT controller for a wind turbine. But you had a choose between a Relay switch or PWM what would you get and why?

BB.

A relay based dump load controller vs a PWM dump load controller is the question?

In general, relays are mechancial devices and have a limited cycle life. So, I would pick a dump load controller with a relay unless I knew the cycle life (i.e., 100,000 cycles) and the how often the controller turns on/off the relay (say 10 seconds per cycle):

• 100,000 cycle life * 10 seconds per cycle * 1/3,600 seconds per hour = ~278 hours of cycling life

Next question is how many hours a month/year does your controller "cycle" while the wind is blowing (cycling, I assume, happens only when the battery is in absorb or float phase and the wind turbine is generating enough current to cause the controller to "dump" during absorb and float stage)... 1 hour per month? 10 hours/100 hours per month? I have no idea.

Also, if they have extended cycle time--(say not 1 or 10 seconds but 1+ minute per cycle)--The battery bank is subjected to larger swings in charging/discharging cycles (possibly higher charging voltages if delayed off cycle, deeper "micro cycling" between charging "hits", etc.).

On the other hand, with an electronic Transistor has no cycling life issues (they do have temperature / aging life issues--Assume ~10 years is a "good life" for a PWM controller). Down side, if you have inductive issues, possible lightning strikes, etc. -- Transistors can be easier to damage vs a relay.

Which gets back to the fundamentals of a "safe" Wind Turbine/Dump Load system design... I believe (read from somebody else) that such a system requires to independent systems to limit charging to the battery bank to prevent overcharging/unsafe battery operation. This could be a pair of identical dump controller + loads, or it could be a dump controller + loads and a second limiting method (automatic braking system, relay across the turbine output, etc.)

Anyway--That is how I would look at the question.

-Bill

Zakarume

So overall a PWM type controller would be better but not much

inetdog

A relay switch would be simply on/off with one voltage set point, and it would have to be electronically driven with hysteresis.
A PWM controller would give you varying voltage set points for different stages of charging. Otherwise you would have to set the relay to the float voltage and limit the current during lower SOC by limiting panel or turbine power.
A PWM controller feeding the battery would not by itself provide a safety dump load for a wind or water turbine. Same with an MPPT CC.

You will probably end up needing both a CC and a dump controller for good performance.

Zakarume

Attachment not found. Something like this

BB.

I worry that a mechanical relay would not last very long.

-Bill