Turbine Dump Load Question

TassietigTassietig Registered Users Posts: 1
I have a 600W 3 phase wind turbine and needed a dump load to protect the controller and turbine. I decided
to go with an 800W Load as explained below.
I have made up a dump load consisting of 8 x 15 Amp fuses protecting 8 x 100Watt headlight globes.
An electrical components supplier said to use an 8 fuse block unit, fed by the positive of the load feed, and
to connect the globes to a common negative plate, connected to the negative of the load feed, as per the
diagram below :-

Attachment not found.
I have read however, that this is basically putting these globes(resistors) in parallel, and won’t in fact give
me the 800 Watt dump load I’m looking to create.
Can anyone advise me if I have an effective load setup or if I’ve got it totally wrong ?
Regards,

Comments

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Turbine Dump Load Question

    This will indeed give you a total load of 8 times 100 watts = 800 watts - - if supplied with 12 volts.
    The idea however that a fuse will protect the load is not correct. Fuses protect the wiring supplying the load, but not the load. In fact, the resistance of the load restricts current flow, and in doing so protects the fuse from blowing. If a short circuit develops across the load, then the limiting factor if any will be the turbine output, and if it can supply enough current, then the fuse will blow, and in doing so protect the wiring from overheating.
    Do you have a make and model of the turbine? Reason asking, many / most / all "800 watt" wind turbines are promoted with VASTLY exaggerated and hyped output claims to increase sales. Been there, done that and the only time my 800 watt turbine ever produced any usable amount of power was during tropical storms / hurricanes that came up the East Coast in the Fall of the year. It was also during these times the turbine verged on self destructing and possibly initiating a military response from the USA as it's blades streaked through the sky and across the border on their way to New York.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Turbine Dump Load Question

    Welcome to the forum.

    You've got it right: paralleling loads increases the amount of current they draw. So 8 * 100 Watts in parallel is 800 Watts. If you put them in series it would reduce the the load to approximately 12.5 Watts.

    Now let's look at some other issues. You have a 3-phase turbine. I take it that is internally 3-phase and its actual output is rectified DC? Normally such output would be fed directly to the battery and the charge controller input would be connected there to 'bleed off' excess power at the Voltage set points, feeding it to the dump (diversion) load.

    Then there are the fuses. Fuses are a good idea, except on a diversion load. If they give up (and they can fail from fatigue) then your load reduces and so you don't have a load anymore or at least not a full one. Likewise car headlights can burn out. This is why resistive heat loads are what people usually use, and without any over-current protection. In theory there can never be too much current in this circuit because it is designed to handle the maximum output of the charge controller. That means the controller fries first. Some would argue that there should be one fuse or breaker on the controller's output, but there again if it pops you have no load and the turbine free spins into oblivion.

    The NEC requires redundant diversion loads and controllers to take care of such an eventuality: if one system fails the backup will prevent the turbine from over-speeding. In a way I think your idea is better; larger than necessary load with individual protection. However I would size the charge controller 2X necessary and use two diversion loads of a resistive type (not light bulbs) each capable of the full power and each with its own circuit protection.

    Others will have their own ideas and this is something that can be argued endlessly (it seems everything is these days).

    On the other hand I don't know exactly what turbine & controller you have, and they may specify quite a different wiring arrangement.
  • pleppikpleppik Solar Expert Posts: 62 ✭✭✭✭
    Re: Turbine Dump Load Question

    Doesn't this design create the possibility for a cascading failure?

    If you get into a situation where you're trying to absorb close to the maximum amount of power and one of the eight headlights (or its fuse) blows, then you immediately require the remaining seven to each take on extra power, which is likely to blow another headlight, and so forth until the whole string has gone. At this point whatever Bad Things the dump load is supposed to prevent will happen.

    That's probably why Cariboocoot recommended using power resistors and no fuses. You don't want the dump load going off-line when it's needed.
  • BB.BB. Super Moderators, Administrators Posts: 32,220 admin
    Re: Turbine Dump Load Question

    Each of your parallel dump loads should be designed to be "self limiting" within the design parameters (such as 15.5 VDC maximum, or whatever).

    So, if you "lose" one of the 100 Watt loads, then you still have 700 Watts of load bank remaining.

    You can get into how much redundancy do you want... There is a common scheme called N+1 redundancy. Put in 900 Watts of loads, and then if one fails, you still have your 800 Watt of load bank.

    Or you could also do a 2x redundancy. Two controllers, two "relays", two strings of 800 Watt loads. If any one of the pieces fails, you will still have an operational system.

    Then you get into more complexity... A 2x redundant system--You need a way to know when one of the parallel dump paths has failed--Say one controller fails and there is no warning (controller simply fails to "turn on" the dump loads)--You are now back to a single fault will take out the entire dump load system.

    And a 2x redundant system--Has 2x more components/failure points--So, in theory, it is even less reliable than the 1x original system. This is not an easy task to accomplish... You have to look at the cost of "failure" (batteries outside in their own box--Loss of batteries. Batteries in the basement of the home up against a wood load bearing wall--Possible loss of entire home and people inside).

    Personally, I will still argue for the load+fuse configuration... If you use wiring sized for your ~10 amp loads to each lamp. And if one of the headlamps fails shorted (I have had 120 VAC 100 Watt flood lamps fail and trip the 60 amp main service to the home--And leave the 15 branch circuit breaker still "on"???).

    You don't want the one head lamp shorted overheating and possibly starting a fire in your 10 amp wiring.

    You could wire, large enough cable (~8x10=) to carry 80 amps to all of the lamps (no 10 cable)--this will cost more and could (worst case example) cause a shorted 12 volt lamp to have sustained current that would break the bulb and start an arc fault with the bulb connectors and drop hot metal/sparks from a bulb short failure.

    The above is a worst case example--Would it happen--Pretty unlikely at 12 VDC (12 volts is about the low voltage limit to sustain an arc)--But at higher voltages (24 volts and more)--Actually very possible.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Turbine Dump Load Question

    In all my years I've never seen a light bulb short out.

    Seen it happen with plenty of wiring to light bulbs, but not the bulbs themselves. They are rather like fuses in their construction. We are of course talking about incandescent bulbs here.
  • BB.BB. Super Moderators, Administrators Posts: 32,220 admin
    Re: Turbine Dump Load Question

    Yep--"Blew" my mind.

    Came home and the house was in darkness. Reset the main 60 breaker for the home and then the 15 circuit tripped (or flood light was just out, no obvious melting/shattered globe--Was a couple decades ago, don't remember the details). Replaced the bulb and all was fine.

    All I can say is I was very happy it failed when I was away from the house for a few hours and not on a two week vacation and come back to find all the food in the freezer had spoiled.

    Anyway--That is why I really like separate protection for each critical circuit--In general, a single fault will not disable the rest of your home power system.

    Of course, now using LED bulbs (and some CFLs still left) now. Most of my CFL's die when the ballast electronics fail (burned ballast case, smoke, and sometimes even a little "death scream" as the failing capacitor vents???).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Turbine Dump Load Question
    In all my years I've never seen a light bulb short out.

    Seen it happen with plenty of wiring to light bulbs, but not the bulbs themselves. They are rather like fuses in their construction. We are of course talking about incandescent bulbs here.

    Heavy light bulbs with thick filaments, like the 150-300W PAR lamps have a tendency to arc momentarily as the filament vaporizes when they burn out.
    The result is that they will surely burn out 300-600W SCR dimmers and might even blow a 10A or larger fuse.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Turbine Dump Load Question
    inetdog wrote: »
    Heavy light bulbs with thick filaments, like the 150-300W PAR lamps have a tendency to arc momentarily as the filament vaporizes when they burn out.
    The result is that they will surely burn out 300-600W SCR dimmers and might even blow a 10A or larger fuse.

    And is that what Bill is talking about?
  • BB.BB. Super Moderators, Administrators Posts: 32,220 admin
    Re: Turbine Dump Load Question

    Yep--Originally 150 Watt PAR of some sort--But they kept dropping the wattage to 120 and 100 in the name of energy efficiency.... It was a couple decades ago. I don't remember the details now.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Turbine Dump Load Question

    The big differences between this behavior and a true short circuit are:
    1. It is self limiting; it will stop in a few cycles even if no overcurrent device intervenes.
    2. It is confined inside the envelope of the bulb and does not have any associated fire risks (outside of the electrical fire risks for connected equipment like lighting controllers.
    SMA SB 3000, old BP panels.
  • mike95490mike95490 Solar Expert Posts: 9,462 ✭✭✭✭✭
    Re: Turbine Dump Load Question

    I'd say no fuses on your dump load. Use wire from the turbine that is oversized and can't be burned. If it's a 12V system, use 24V headlights. You want a dump load that is reliable, not going to start a zipper/cascade failure when 13V hits the 12V bulbs for 12 hours in a windstorm. If the dump load fails, then the overspeed turbine will surely fail shortly afterwards. Blades and housing all over, or even a blade in your house.

    And the dump load is on the turbine, not the battery bank.
    Light bulb suggestions - halagen fog lamps, truck lights, aircraft landing lights

    You have 800watts of heat, and have to put it somewhere, and not have it BBQ anything. I've seen nichrome wire load boxes with blower fans in them, and they still fail.
    So I like the idea of 24V lamps on a 12V system. Even beefy 100w load resistors need massive heat sinks and cooling fans for multi hour run times.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

Sign In or Register to comment.