Author Topic: Dump load options (Read 10305 times)

Miller Time · « **on:** March 25, 2009, 01:12:30 PM »

Hello Everyone,

I just have a quick question; which i'm sure there is no easy answer too. Came across an Wall Heater with these specs: 240Volt, 8.34Amps and 2000Watts.

Can this be used for the ten foot homebrew model wind turbine as dump load?? My friend and I are making it as a 24V using the 1x2x0.5inch magnets.

Also have 240V 1500watt water heating element. Is it possible to use both these together?? The more we get into this project money seems to become an issue. If we can save a few dollars with informative help then that is good for everyone. Thanks so much; waiting patiently!!!

ghurd · « **Reply #1 on:** March 25, 2009, 07:43:15 AM »

Easy answer!

Ohm's and Watt's Laws.

With 240V and 8.34A, thats 28.8 ohms.

Dump voltage on a 24V system is about 28.8V, so the 2000W heater will use 1A.

The 1500W element is 38.4 ohms, and will use 0.75A at 28.8V.

Together they will dump 50W.

In perspective, for $12 I will sell you enough power resistors to dump 165W.

Sometimes saving money gets expensive and time consuming.

G-

electronbaby · « **Reply #2 on:** March 25, 2009, 07:54:17 AM »

Using Ohms Law:

The 2000 watt heater has a resistance close to 28.77 Ohms. This would mean that it would draw .97A at 28v (24v nominal). This means that the heater would only be able to dump less than 28 watts of energy at 24v.

The 1500 watt heater would be even worse. The resistance of this heater would be 38.4 Ohms. This allows it to dump .73A which, at 24v nominal (28v) would be close to 20.44 Watts.

If you put them in parallel, you would have a resistance close to 16.447 Ohms. This will allow you to dump 1.702A which is approx 47.67 Watts at 28v.

Goahead · « **Reply #3 on:** March 25, 2009, 08:00:49 AM »

Hi Miller

Not a very guru person on this subject but:

V x 8.34A = 2kW
V x 8.34A = 200W

Resistance will also be lower.

So i believe you will only be able to dump 200W.

If its a 1kw turbine..then guess what will happen to the heater!

W / 240V = 6.25A
V x 6,25 = 150W

(i fill so stupid doing this calculations since i could just divide by 10

)

So... those 2 in parallel will give you 350W of dump load...

No enough even for a 500W turbine.

Regards

Goahead

imsmooth · « **Reply #4 on:** March 25, 2009, 10:19:53 AM »

You can purchase power resistors and string them in parallel, or you can run some low voltage lights in parallel to consume the watts.

jaskiainen · « **Reply #5 on:** March 25, 2009, 10:23:20 AM »

Hi Goahead

Your calculations would be right IF the heater element would take 8.34 amps.

But you forgot to calculate the element resistance first wich would decrease

the amperage quite a bit.

If you look posts before you then you should see where you got a bit off track.

Miller Time · « **Reply #6 on:** March 25, 2009, 12:38:28 PM »

Smooth,

lets say my turbine makes 1500W on strong wind for some reason (not furling). This would be max. Would the voltage be above lets say 28V? 1500w=28*I Thats 53.6Amps. The turbine is designed to cut in at about 140rpm. Probably a little over 24Volt right? And as the wind picks up so does the Voltage and Wattage.

These coil resistors, are they hooked up direct on a heat sink and is there more to it like insulators or fuses. I just want to dissapate power and heat to keep the genny under load. Nothing fancy for a dump.

Do I just calculate max Wattage or Amp to get resistance. w=I^2*R but this varies on the power curve of the turbine does'nt it??

I realize that unless I had 50 heaters in parrallel that system would burn out. Not a great idea but great time waster as stated. Thanks!

ghurd · « **Reply #7 on:** March 25, 2009, 01:22:38 PM »

I see how you are thinking.

Think in amps.

The battery voltage is THE voltage.

The dump load is connected to the battery. Not the turbine.

Turbine amps are not sent directly to the dump load.

The turbine continues to send amps to the battery.

When the battery is 'full' the controller sends battery amps to the dump load.

Something here may help,

http://www.fieldlines.com/story/2009/2/3/141346/1558

G-

Ungrounded Lightning Rod · « **Reply #8 on:** March 25, 2009, 05:59:40 PM »

However the dump load has to pull more amps than the output of the turbine in a high wind or the turbine will get ahead of it and fry the batteries.

(Note that we're not talking the peak-in-a-gust, but the over-several-minutes average at max output.)

Ungrounded Lightning Rod · « **Reply #9 on:** March 25, 2009, 06:02:44 PM »

If you want to build a dump load from 120V heaters, get a nichrome coil heater, not a glowbar or ceramic heater. You can shorten the coil to get the current up to make-it-glow-red and draw the original amperage at whatever lower voltage you want. (Or double-up the coils to draw twice the rated current, ...)

Or visit a truck stop and see what appliances they've got for lower voltages.

wooferhound · « **Reply #10 on:** March 25, 2009, 06:12:37 PM »

A dump load is hooked hooked up like this . . .

halfcrazy · « **Reply #11 on:** March 26, 2009, 04:37:11 AM »

Wooferhound that's a very good diagram.

halfcrazy · « **Reply #12 on:** March 26, 2009, 04:38:34 AM »

Ghurd whats the link to your site? i am in the process of needing to build a 1500-2000 watt dump load and wanted more specifics on the resistors.

ghurd · « **Reply #13 on:** March 26, 2009, 05:15:32 AM »

They are 10 ohm 25W 5% with standard 0.25" terminals. Each will dump about 1.4A or 20W on a 12V system.

Nice resistors for 4' or Ametek or treadmill windmills, but probably Not the perfect choice for 2000W!

Wiring up 75 or 100 resistors would be a PITA, though it has been done.

http://ghurd.info/

G-

Opera House · « **Reply #14 on:** March 26, 2009, 09:18:32 AM »

300W halogen lamps are cheap. I can't resist 300W 120V Harbor Freight lamps that are two for 99 cents. You can easily solder wires to the end tabs. 48 ohms at normal operating voltage but are only 4 ohms cold. This is the reason many controllers warn against using lamps as a load. A good load of low voltage lamps would appear as a dead short due to the ten fold resistance change. These 300W lamps only go up to about 6 ohms at low voltages.

DamonHD · « **Reply #15 on:** March 26, 2009, 11:41:12 AM »

G, has your dozenaire status been dented in the current economic crisis? Has BO called to offer you 13-aire status yet?

Rgds

Damon

zap · « **Reply #16 on:** March 26, 2009, 11:47:16 AM »

LOL

G- is too humble... Even if King BO(hmmm... something smells) did call, I doubt G- would admit it.

Miller Time · « **Reply #17 on:** March 26, 2009, 06:21:31 PM »

Thanks for the info.

Woof I like your diagram also. It explains things well. I would just have to ask if at the points were the positive wires come together from various places ie: Inverter, Controller, Batteries and Power sources is that where you have a junction box?? Same for the negative side of the scematics to huh I guess??

Also, Gurd I was wondering if there is a controller or set up that allows me to dump resevoir power without draining the batteries.

It seems the dump load is fed from the batteries once they get above charged state by 0.1V lets say and then switch off once batteries drain down.

Is this correct??

I plan on buying a C60 Xantrex 3 stage power charge controller. Is this advisable (fast and efficient enough compared to say Tri-Star or Outback)

OperaHouse, I have seen a space heater made from halogen lights and a fan. It ran on 120V and was enclosed; very nice. Would love to make something of this sort for lower voltage.

Miller

ghurd · « **Reply #18 on:** March 26, 2009, 08:30:29 PM »

Decent controllers work very fast. The power they drain is tiny.

It is the only decent option, which is why almost all controllers do it that way.

There are multiple reports of the C60 having a slow reaction time. It can cause problems.

I believe most people like the TS-60 over the C60.

The Outback is different.

I may throw up a o-scope pic of my controller, if anyone is interested.

G-

wooferhound · « **Reply #19 on:** March 26, 2009, 08:30:49 PM »

Thanks Y'all for the compliments on the drawing. This is a very simple drawing and shouldn't really be considered complete, but it does introduce the newbie to the proper hookup for connections.

Your question about making the connections inside of a junction box, it's OK but not the safest. The best way to do it is to fuse anything that connects to the battery and make all of your connections to the battery through separate fuses.

Like This . . .

http://www.fieldlines.com/story/2008/6/7/21233/94327

ghurd · « **Reply #20 on:** March 26, 2009, 08:31:12 PM »

If BO called, he did not leave a message.

G-

zap · « **Reply #21 on:** March 26, 2009, 09:30:54 PM »

Woof... how much power are you getting from the perpetual motion device?

Can you post any pics???

DamonHD · « **Reply #22 on:** March 27, 2009, 12:55:12 AM »

Well, how rude of him not to try again: you're a busy man!

Rgds

Damon

DamonHD · « **Reply #23 on:** March 27, 2009, 12:57:35 AM »

BTW, there's a nice story how in a recent (UK) government the ministers were meeting with the Queen in "Privy Council" when one of the ministers' mobile phones rang. As the minister fumbled to silence the thing the Queen is reported to have said wryly "I do hope it wasn't anyone important."

Rgds

n

Damo

Madscientist267 · « **Reply #24 on:** March 27, 2009, 05:36:47 AM »

I'm interested too... We could save a lot of time and effort by just using that instead of solar and wind. My transmogrifying teleporter is depending on this technology. The dilithium crystals are running out, captian... can't drrriver anah faastah!

>X-D3

Steve

jaskiainen · « **Reply #25 on:** March 27, 2009, 08:30:16 AM »

I wouldn't use lamps for dump load at all.

Imagine what happens if they burn up? Yes there will be no dump load at all anymore.

Disaster for batterys...

TomW · « **Reply #26 on:** March 27, 2009, 08:50:06 AM »

jaskiainen;

Exactly my thoughts. OK for "testing" maybe but too fragile for dump load. Average resistance dump load will be totally unaffected by a short burst of excess amps / volts but a bulb will likely pop and fail open spelled no load.

Just from here.

Tom

ghurd · « **Reply #27 on:** March 27, 2009, 09:11:04 AM »

I had a big square car head light burn out in under 45 minutes.

It was running at a high frequency (for a light bulb), and I think that's what pops bulbs. Not sure.

I know I don't trust them.

G-

Opera House · « **Reply #28 on:** March 27, 2009, 09:28:29 AM »

By definition you have already exceeded the bulbs rated voltage when going into dump. Hundreds of thousands of dimable 12V halogen lamp modules work at high frequency without shortening lamp life. A lamp as a load should never be operated above 1/4 of the lamps rated voltage. For reliability you should never rely on a single resistance. Parallel many resistive loads in the event any one fails.

ghurd · « **Reply #29 on:** March 27, 2009, 12:16:02 PM »

So that's why he hung up on me. The bugger.

If I'd known they were together, I would have dialed Liz's mobile.

G-

PS- I have no idea who "BO" is.

TomW · « **Reply #30 on:** March 27, 2009, 12:52:18 PM »

G;

PS- I have no idea who "BO" is.

BO be the current President of the U.S.

Capiche?

Just cuz your a circuit magnate doesn't mean you shouldn't keep up on current slang.

Tom

ghurd · « **Reply #31 on:** March 27, 2009, 01:32:30 PM »

OHIO... remember?

Earlier I even googled "BO".

The #1 hit on google included Bo Duke of Hazzard County.

"Bo Duke, one of the main characters from The Dukes of Hazzard television ..."

Liz is going to laugh at me over this one.

The sircut magnet,

G-

wooferhound · « **Reply #32 on:** March 27, 2009, 04:18:02 PM »

If I give 'er any more Power

she's gonna Blow . . .

News:

Author Topic: Dump load options (Read 10305 times)