Grid Tie Inverter Dump Load Revisited

Discussion in 'Connecting to the Grid' started by jagged, Feb 20, 2012.

  1. I have almost finished my cheapy home built dump load system and I have a few questions. I am going to use a battery as the initial dump load from my grid tie inverter. The battery is then protected by another dump load controller, which will energize a solenoid and then dump the load into my 720W light array. Keeping any current spikes from damaging expensive parts. Will this work? Is there a way I could utilize the battery to power the Grid tie inverter for awhile when there is no wind? Here's a couple of pics to give you an idea. Wiring isn't finished yet.
    IMG_0379 (640x480).jpg IMG_0381 (640x480).jpg
  2. Minnesota

    Minnesota WindyNation Engineer

    I'm assume you have a turbine driving a 500w 10v-30v GTI, and when the GTI goes to overvolt you intend the power to flow to the battery through the dump port. If the battery is directly attached to the dump port, then the there will be an inrush of current back into the GTI likely with bad results. It would work if you added a high current diode (50A), or several smaller ones in parallel, and a large power resistor (or set of lights) in series with the battery. The diode prevents backflow and the resistors/lights act as resistors to drop the voltage from the 30V+ seen at the dump port to the 12V of the battery.
  3. Yes, I do have a 60 amp diode installed on the + feed from the dump port to the battery, sorry I didn't mention it. I read somewhere that a large deep cycle battery can absorbe the 30+ volts with no problem. Any clues on my second question using the charged battery to power the inverter when there's no wind?

  4. Minnesota

    Minnesota WindyNation Engineer

    Yes, you can drive a GTI with a battery, but if the GTI is a 10.8V type then it will drain the battery down to that level which is far too low. You'd need a way to cut it off at 11.5V or so for Lead Acid type batteries (a low voltage disconnect circuit).

    Back to the dump load issue ... the battery will top out under 15V and you only have one diode drop (0.7V) above it so the voltage at the dump port will immediately drop to 15.7V shutting off the dump port. The resistor I mentioned allows the dump port to stay open until the turbine voltage falls back below 30V.
  5. I built the light bank to get away from buying an expensive power resistor. I'm not going to build a second light bank. So I might just as well lose the battery idea and just use the lights as my dump load. I thought the dump load circuit built into the GTI was driven not by the voltage below, but the voltage from the turbine. So regardless of what voltage the battery was at, it will still dump. The battery starts to dump into the lights at 13.7V, so it would never reach 15.7 anyways. Where can I get the schematics of a low voltage disconnect circuit?
  6. Minnesota

    Minnesota WindyNation Engineer

    You can use the Windy Nation resistors ... they are a good value. See their article on dump load resistors for GTIs. They are more reliable than light bulbs as bulbs are not designed to see rapid voltage changes which are common with wind turbines.

    There are also lots of LVD choices around if you still plan to use your battery; such as THIS ONE.
  7. Windy Nation Resistors might be a good value for Americans, if you think $21.98 X 2 = $43.96 to give you 600W is a good value, then if you add on the 38 buck shipping charge to Canada = $81.98 , you will see what I'm talking about. I'm trying to build this system cheaply, and hopefully some of my ideas will help other people. I've got just over 25 bucks invested in my 720W resistor so far. The only way I will see how it works, is to try it. Thanx for the link to the LVD. I've read all the articles on using lights as resistors, and I know the drawbacks, that's why I'm trying to iron out any problems that might cause voltage surges. Using the smaller 30 amp rated dump load controller from the battery to just energize the 300 amp starter solenoid to light er' up will help. The only thing that's going to experience the voltage spikes is the battery and it's worthless.

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