dump load through the inverter?

[libra]

I am working on my control board and have 3 3750 w 220v heating elements for a dump load. These would have to go through the inverter to be used but would this be putting undew stress on the inverter.

I haven't seem much written about control panels and would appreciate info and pictures if I could get them

tx  Libra

[electronbaby]

towards the end of this post it explains how i do what i think you mean.

http://www.fieldlines.com/story/2005/8/9/3443/28146

and something else i did as an alternative lol.

http://www.fieldlines.com/story/2006/3/26/19291/2011

Ive never had a problem with either design, but I dont like putting unnecessary stress on the inverters either.

[robl]

Libra

What is your mill voltage and what is your battery voltage? Going through the inverters should really be your last resort.

Rob

[libra]

It will be 24v system  (3 phase) with 24v batteries. About using water heater elements do they run off the wild ac or are they dc elements?

Another question is what kind of resistance can be used to load the genny so you don't have a slam and shock before you short out the kill or brake switch?

tx Libra

[robl]

Libra,

The beauty of using water heater elements is that they are practically pure resistance loads. Wild AC or DC makes very little difference. When I had my Dunlite up, I was running 120VDC through a dump into a 240VAC/3KW (AC) element with no problems except some relay-contact arcing. That was resolved with a rectifier and 300V/1uF capacitor.

What is is your anticipated maximum sustained current output at 24V/3PH (or rectified single phase DC), and what amperage will you be setting your fuses/breakers for?

Once that information is shared, it becomes easier to determine how best to absorb it. For example, if you have the power, you can even consider the option of stepping up the AC from the gennie to a higher AC voltage before rectifying and powering the heaters.  

Rob

[libra]

Hi Rob  It looks like there is more that I don't know than what I know!

This genny will be 24v, 3 phase with and average wind speed of 8-13 mph about 18 hours per day. Genny will be at 150'. The cable to the genny is about 250' of 00 3/8" solid copper.

What amps I get would be a guess so will have to play things by ear. I have 24v 300 ah batteries that are used but think that they will do until I can afford better ones and know more of what the genny is capable of. My ocntrol panel is under construction and so far have a 600 amp contactor as a kill switch, parallelled with a manual switch, again with heavy contacts. I also have a 100 amp 3 phase rectifier on a massive heat sink.

I would like to find a way to dump a load into a element or resistor to slow the genny down before slamming the kill switch. I have a time delay relay but don't have any resistive wire to make elments just yet. I figure about 2 ohms would work but have lots to learn. Also have 45 amp fuses but no breaker until later

Appreciate comments and suggestions

Libra

[robl]

Hi Libra

Yes, it's a never-ending learning experience for all of us!  I guess you'll have a better handle on the actual voltage & current once you've had the unit up for a bit.

In the mean-time consider these options. 24V into 2 ohms is around 12A/288W. Standard high voltage baseboards and immersion heaters are a much higher resistance, although you may find that when they are derated to 24V that they'll be fine. Certainly my 240V hot water element is a perfect match for my 48V dump load.

If you parallel a couple of high voltage units in a 5 gallon pail you'll probably be fine for the short period you are planning to use the system. I've also had good luck with several feet of steel banding strap wrapped around insulators in a zig-zag pattern.

You can also consider building a "softstart" circuit to ease the shock load. Some circuits use triacs and a control circuit (and can be found on the web, mostly in hifi forums) but, given your low voltage, you can also simply use a large wirewound resistor ahead of a sizeable capacitor. Start with a 100W 1 ohm resistor ( or 5 - 5 ohm/20W units in parallel) and about 20,000 Mf of capacitance ahead of the dump load. Lightbulbs for the resistance will immediately seem to be the solution, but I consider that to be too fragile an option.

HTH

Rob