| T O P I C R E V I E W |
| ll81 |
Posted - 26/08/2007 : 15:36:57
I ended up with this through a series of unexpected occurrences. After my first linear dump I decided I needed to go switch mode to keep transistor dissipation down. I then used a sensor circuit to feed a Velleman DC-PWM kit. Whilst operating I noticed that the sensor would go from a high-low output due to a capacitor on the input taking time to dischage and charge.
I wonder what happens if I ditch the Velleman kit and run the FET direct off the oscillating sensor I thought. Scoping shows a relativly clean pulsed output that keeps transistor dissipation minimal. A small heatsink is all that is needed on the transistor.
The load must be large enough to put enough current drain on the batteries that there is some voltage drop upon operation for the circuit to oscillate.
This can be built cheaply and easily by absolute begginers with a good soldering iron, the necessary components and a piece of vero board (strips of copper on a piece of board with lines of holes in it). Just adjust the potentiometer to start the load dump at the required voltage.
I have actually got this very circuit as the load dump on my turbine I finished constructing yesterday.
woo-hoo |
| 15 L A T E S T R E P L I E S (Newest First) |
| ghurd |
Posted - 25/09/2007 : 19:26:37
Best N.A. deal I found so far (sorry UK guys) is Digikey, 5 ohm 50W, 10 for $34, 25 for $76.50. #HLB-5.0-ND.
G- |
| BushWhacker |
Posted - 25/09/2007 : 04:12:35
Thanks Ghurd,
So my best bet is to find a 12 Volt electric heater of some sort?
BTW these block heaters are made to plug into 110 AC power supply. Still that wouldn't be nearly enough.
Back to the drawing board...:-(
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| ghurd |
Posted - 24/09/2007 : 15:13:44
Warning:
Lets say that is 480W. It is certainly not made for 12V.
So 480W / 240V = 2A, and 240V / 2A = 120 ohms.
And a 12V system dumping at 14V, into 120 ohms? 14V / 120 ohms = 0.1167A.
And 0.1167A X 14V = 1.6W.
That is awful expensive for the equivalent power of a 2W resistor.
G- |
| BushWhacker |
Posted - 24/09/2007 : 03:23:59
Usually block heaters are in the 400 to 1000 watt range. You can also get circulating water heaters up to 1500 watts. The circulating water heater operates something like a coffee percolator, heating up small amounts of water and then circulating that into the system many times. This is the system I prefer on a vehicle, but think a block heater is better for the dump load application I'm thinking about.
Here's a pic of a block heater. The element sits inside the engine block submerged in coolant, the O ring provides the seal, and the screw above the electrical plug holds the block heater in the frost plug hole.
 http://z.about.com/d/autorepair/1/0/3/W/block_heater.gif
I hope that helps,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| fungus |
Posted - 23/09/2007 : 20:29:37
I see BushWhacker; not too familiar with them obviously :) Do you know what power they're rated at? |
| BushWhacker |
Posted - 23/09/2007 : 19:53:01
Actually Fungus the block heater element is located in the "water jacket" of an engine and is submerged in coolant during normal operation. They usually last about 3000 hours of full power (500 to 1000 watt) use.
I guess you have to live in a colder climate to be exposed to these things. ;)
So I'll need a dump load controller, and then hook a load such as a block heater up to it. I think I've got it now, Thanks!
The reason I would like about 20 liters of coolant is the thermal mass will help regulate the rate that the porch/green house heats and cools.
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| fungus |
Posted - 23/09/2007 : 14:41:20
BushWhacker- a dumpload controller redirects electricity to another load such as a heater when the batteries are full; this is what ghurd's circuit does. An automotive heater block could be pretty good; although I wouldnt put it in water or antifreeze as I think they are conductive? Mineral oil like the stuff from oil filled heaters could be better to put it in I think as it isnt conductive and wont corrode the heater block with the electricity. |
| BushWhacker |
Posted - 23/09/2007 : 08:24:23
Time for an electronically challenged question. Most of the above discussion went right over my head. By load dump are you talking about the components that redirects excess electricity to a component (light bulb or resistors) or the component it's self?
What I would like to use the excess electricity for is "free heat".
I propose using an automotive block heater installed in the side of a large cooking pot filled with water or antifreeze solution. I don't think that a block heater cares if the power supply is AC or DC, please correct me if I am wrong.
This heat supply would be set in a porch, fall through spring, and in a green house during late spring through summer. The part I don't understand is the electronics needed to detect when the batteries are fully charged and divert the excess electricity to the load dump (block heater in my example).
Please use little words as I have no background in electronics.
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| Del |
Posted - 22/09/2007 : 11:51:53
Hi Ghurd,
That sounds excellent. I'll send you a private message (you'll see it in the top right hand corner of the Gotwind page) to firm up the details.
Thanks again.
Del. |
| ghurd |
Posted - 20/09/2007 : 23:23:42
Hi Del,
Ben received a pre-production "prototype" version of the kit.
All the parts should be there, but it is hard to say for certain. Things change.
The instructions still 100% totally suck. Most people didn't get any instructions at all and did fine building a working circuit.
The cost is US$12.50 for each kit, plus US$3 per order shipping and handling.
US$15.50 total for 1 kit. US$28 for 2 kits. 3 kits may cost more for S&H.
UK, Europe, Asia, etc, will receive instructions via email. (reduces the shipping costs)
PayPal is fine. I still do not know what they charge.
Honestly, I don't understand how these boards work.
Please do not expect me to see a reply to this message. I try.
I seem to be old and not very computer savvy. :-(
email to yahoo for ghurd1
|
| Del |
Posted - 20/09/2007 : 20:14:10
Hi Ghurd,
From the posts and conversations on the "solar panel" thread I see Mr Ben now has one of your dump load circuits. Are you now ready to make these generally available to all of us and if so what's the price. I seem to recall ben suggested £10 ($20) and that would cover your costs inc those naughty paypal fees. Just let me know and I'll order a couple from you.
Cheers
Del. |
| fungus |
Posted - 07/09/2007 : 13:19:58
I used to use 4 50w resistors in series for 2A (28w) dumping current, on a heatsink, could reconfigure for 100w... now I'm using a 150w ceramic car heater, can get them from maplin for £15.
I still have the old resistor panel if anyone wants it? Could chuck in the old 'ghurd controller' on perfboard.. Picture of it below in the top right:
 |
| gotwind |
Posted - 06/09/2007 : 21:30:44
Ok thats fine Glenn.
Please let us know when a fixed price is available.
I suspect there are at least 10 members that would be interested in receiving such a kit here.
No rush.
Ben.
The Futures Green - Getwind of it. |
| ghurd |
Posted - 06/09/2007 : 21:08:57
I got tired of spending what seemed like forever building dump load resistors that were, uh, crappy when I was done. The 100W are less stressful, about £32 for 10.
Ben, I didn't consider paypal fees. I'll have to look into that. The cost of the silly little bubble-ope is what irks me.
1st class mail goes on the plane right after some of the fancier mail. If the weight stays to 2 kits, it's just as fast as air mail, but a lot cheaper.
G- |
| ll81 |
Posted - 06/09/2007 : 19:43:10
Them resistors are a bit pricey. I have a 4ohm 400 watt dummy load I use for testing my amplifier projects that works well. It didn't cost alot to make and was made of 40x 0r1 10 watt power resitors soldered in series. 20 woulld make a good load dump for 100 watt turbine.
The flyback diode is connected between the Drain and Source terminals of the FET with it's Cathode to Drain and Anode to Source. This way it is forward biased until any back EMF causes a potentail of more than -0.6v across the FET and therefore shunting it away and protecting the device.
woo-hoo |
