Author Topic: dump load? (Read 7053 times)

greenkarson · « **on:** February 12, 2012, 06:54:06 PM »

I've been using a hot water element for a dump load for my 100watt turbine. It is 240v/3000watt so about 12.5 amps plenty for the turbine. But i added another 10amps or 150watts of solar sharing the c40 controller with the turbine. so when the batterys hit full the heater element could not use the extra amps fast enough so i had to turn on all my lights in the cabin to keep it undercontrol.

So i guess i will have to add another element. So that got me thinking (And here is where i show how stupid i am) could i not just use a piece of round steel rod with cooling fins on it for a dump load. For my 12v 250watt system?

dave ames · « **Reply #1 on:** February 12, 2012, 08:10:31 PM »

Hey Karson,

We are coming up short on the dump load

...only dumping about 10 watts at ~14.5 volts with that water heating element.

240v*240v/3000w =19.2 Ohm

14.5v/19.2 Ohm =0.75 Amps

.75A*14.5v = ~10 watts dumped

Won't cost crazy money to get some proper power resistors...In a pinch some folks have had good luck with a 12 volt car heater?

Cheers, dave

greenkarson · « **Reply #2 on:** February 12, 2012, 08:57:16 PM »

The ohm thing is still a mystery world to me. I thought i read somewhere on here that i needed 1 ohm for every 14 watts i needed to burn. That brings up another bunch of questions. If its only burning 10watts of electricity why hasent my battery bank over charged before with just the turbine? It puts out a hundred watts for about four months in the winter with out a break.

But back to my original question. I know there are cheap options but im just curious. Why wouldn't a peice of steel with cooling fins work as a dump load? Isnt the point just to keep a load on the turbine with out the dumpload over heating?

windy · « **Reply #3 on:** February 12, 2012, 11:20:04 PM »

greenkarson,

Not sure if this would work, but you could try an old stove top element. They are rated for 240 volt. I'm sure you could find used ones from an appliance store that recycles old stoves. Just keep adding elements in parallel until you get the right sized dump load.
I found 10-120volt, 1500 watt elements for my dump load on my 48 volt system and after tying them all together in parallel, am able to dump up to 60 amps.
As far as using a steel rod, I think it would show as a dead short.

windy

Flux · « **Reply #4 on:** February 13, 2012, 03:25:32 AM »

Yes you can use a steel rod, but to keep it to reasonable length it will have to be thin ( we then call it a wire) but the idea is the same. Steel fencing wire can be used. You will not need fins as you will need such a length that the cooling area will be great enough. Steel is not the best material as it rusts and corrodes when hot so you need more of it to keep the temperature low but it will work. Stainless steel works better.

If you use a fine wire you would need the cooling but the fin needs to be electrically insulated, not very practical for home construction but you can buy commercial resistors with an aluminium cooling fin and they are fairly cheap.

You can use more immersion heaters, but the high voltage ones will not take much power at 12v and you are not using them effectively. At 100w the heat is not going to be useful so a big power resistore or a few smaller ones in parallel may be simpler. If you can do it safely without fire risk the steel fencing wire will work absolutely fine.

Flux

greenkarson · « **Reply #5 on:** February 13, 2012, 06:43:36 AM »

Thanks for the info. Any guess as to how long the wire should be?

ghurd · « **Reply #6 on:** February 13, 2012, 07:37:54 AM »

Quote from: greenkarson on February 13, 2012, 06:43:36 AM

Thanks for the info. Any guess as to how long the wire should be?

It depends on the diameter, and metal composition.

The next problem, in my opinion, is getting reliable electrical connections to the SS wire. Same goes for Nichrome wire.

Someone had inductive issues with a coil of wire as a dump load, resulting in a smoked or very confused controller. I can't recall what brand the controller was.

Just a thought: If you decide its not worth the effort to make your own dump load, it's not expensive to buy and ship enough of my resistors to Canada (bit under $25? total).
G-

electrondady1 · « **Reply #7 on:** February 13, 2012, 08:45:20 AM »

i've been saving old toasters with the idea of using them as a dump loads.
the one on my counter is 1400 watts@120volts

four separate banks of nicrome heating ribbon.
if i take off the crumb tray i could put a fan on it.

Bruce S · « **Reply #8 on:** February 13, 2012, 10:22:57 AM »

You could always grab one of those 12V car interior/defroster units they have at Canadian Tire / Harbor Freight.
I prefer the ones with the fan as they work a lot nicer at pushing the heat off the Ni-chrome wire. Which is similar to what ED1 is proposing.
The $15.00 ones at HF have served me well for a few years now.
I figure 12Vdc with the 15A fuse means they're good for 60A continuous with the fan running flat out.

Hope that helps... a little
Bruce S

birdhouse · « **Reply #9 on:** February 13, 2012, 11:27:00 AM »

karson-

Quote

If its only burning 10watts of electricity why hasent my battery bank over charged before with just the turbine? It puts out a hundred watts for about four months in the winter with out a break.

are you using flooded lead acid batteries? do you keep a close eye on the voltage when it's really windy out? i'm wondering if your turbine has trouble keeping your battery bank totally full, then when it is full, you're accidentially putting it through an equalize charge until that 10w of dump slowly brings the bank voltage back down?

the beauty of 12v systems, is you can use almost anything for a dump load. especially if your only dumping 250w. light bulbs, water pumps, car heaters, resistors, basically anything you can plug into a cigarette lighter.

if it were me, i'd use cheap items like mentioned above. however, i'd use enough of them to nearly max out the 40A rating of your controller. this way, if one of the "cheap not well made" items breaks/fails, you still have well above your 250w dump requirement.

just because your dump is way larger than you need does not mean you'll be dumping/wasting power. the controller will handle this via PWM to the dump load. it will only dump what is needed with varying quick bursts to the dump load.

or you could just order the correct sized resistor from Ghurd and call it done.

adam

greenkarson · « **Reply #10 on:** February 13, 2012, 06:03:50 PM »

Sorry i guess i forgot to mention that its a hydro turbine. I have two 8d cell batterys agm's. There is a princess auto(canadian version of harbor freight) a few mins from my work they have all sorts of cheap 12v heaters i will have to take a look.

But im still curious. What i think your saying is the charge controller can sence the difference between a load and a plain shorted out piece of steel? So in theory if the steel was to thick it would not be able to turn the electricity into either heat or movement so it would be a short. But if the steel was thin enough it could turn the electricity into heat and could be made to work in theory.

birdhouse · « **Reply #11 on:** February 13, 2012, 09:46:19 PM »

karson-
yes, to an extent. if the steel was too thick/short, a few things could happen, one it would dump over 40 amps, and fry your controller, or two- your controller may have protective measures against this and go into "fault" mode thinking it was a dead short. i'm not super familiar with the c40's so don't know. but i wouldn't try using a railroad spike as a dump load

thin/long steel: this is a fine line. if too thin, it will melt. that's where ohms law comes in.

or you could do it like i did, without any math at all. i took nichrome wire out of old electric cadet heaters. hooked one end to an amp meter and used an alligator clip at various distances to see where the wire turned orange, and noted how many amps were drawn.

i found a point where the length i used was just below turning orange (made me feel safer about it) i think it was pulling five amps. then used 10 lengths of the same wire to my desired 50 amp dump load. wired them all up between two busses off the controller and put them in a steel box with fans wired into the same busses.

now when my dump kicks on, the wire burns off the heat, and the fans carry it away.

adam

wooferhound · « **Reply #12 on:** February 14, 2012, 06:22:09 PM »

I have heard of people using small Threaded Rod for a dump resister. Just put wire on one end of the rod between 2 nuts, and adjust the distance to the other wire until you have the right resistance.

dinges · « **Reply #13 on:** February 14, 2012, 07:29:03 PM »

I've used stainless steel welding wire (0.8mm diameter) a few times when I needed to load a power supply.

The MIG-welding wire (not flux-core) had a resistance of 0.8 ohm/meter, IIRC. At the time I needed 1 ohm resistance, so used 1.25 m of that wire.

It can dissipate quite a bit of power, I recall mine getting red, then yellow.... Not saying you should push it so far, but you might be able to find a bit of stainless steel wire and turn that into a dummy load. You can put lengths in series and/or parallel to get the resistance and power rating that you need.

Just a thought.

Nothing simpler than converting electricity into heat - the only energy conversion process that's 100% efficient.....

dave ames · « **Reply #14 on:** February 17, 2012, 03:07:14 AM »

Quote from: greenkarson on February 12, 2012, 08:57:16 PM

That brings up another bunch of questions. If its only burning 10watts of electricity why hasent my battery bank over charged before with just the turbine? It puts out a hundred watts for about four months in the winter with out a break.

This is the BIG question here..you sure would have noticed if you were over charging by now! That hydro turbine must be self regulating somehow?

Scouting around in your past posts, looks like you have an aquair/UW-100? wondering now if that rectifier box mounted by the stream is the factory unit called an E1B or perhaps an E3B? those two add on options from the company are a combination rectifier/controller...it brings the turbine on line at a battery voltage of 13.6v and goes open circuit at 14v...then every tenth cycle it runs up to 14.4v before it disconnects.

If that's the case and it's working fine for you (seems so) that would free up the C40 to run as a series solar controller

Wishing I had that hydro set-up...
Good stuff. Cheers, Dave

It feels good to be unbanned

http://www.ampair.com/downloads/Aquair_100_manual_rev_Feb_2007.pdf
<- 3 minute download with dial up....see page 15

frackers · « **Reply #15 on:** February 17, 2012, 05:51:25 AM »

Quote from: windy on February 12, 2012, 11:20:04 PM

greenkarson,

Not sure if this would work, but you could try an old stove top element. They are rated for 240 volt. I'm sure you could find used ones from an appliance store that recycles old stoves. Just keep adding elements in parallel until you get the right sized dump load.
I found 10-120volt, 1500 watt elements for my dump load on my 48 volt system and after tying them all together in parallel, am able to dump up to 60 amps.
As far as using a steel rod, I think it would show as a dead short.

windy

I've used the ideas from page 2/3 of this article to make a 25amp and a 50amp dump loads, both rated at 2000w (which it will never hit!!) for a 24v system

http://www.thebackshed.com/windmill/articles/BuildingEncapsulatedResistors.asp

whythehecknot · « **Reply #16 on:** March 13, 2012, 08:48:35 PM »

The welding wire .035 in US measurement is what I used and of course it was not the flux core type. And I used it with the C40 that was also hooked to a water turbine producing curiously enough around 100 watts, just like yours. The length I used was like three ft and I doubled up the wire as it got too hot using only a single strand. I wound the wire around a pencil real tight and then fastened between two L-brackets, cheap and easy. The C40 uses PWM so you can hear it humm when it begins to dump.

TimS · « **Reply #17 on:** March 13, 2012, 09:01:53 PM »

When the Bergey boys visited, they told me that when they build a house, they put a round of copper wire in the foundation in case a dump load is needed at a later time- I thought it was a great idea. Not really going to heat up the slab too much, but it won't resonate like the coils do. Mine whines quite a bit when I'm diverting my load, but I kinda like it- lets me know I've got excess power.

roosaw · « **Reply #18 on:** March 16, 2012, 12:31:26 PM »

I think we have some confusion here. I know I'm confused
What voltage does the water heater load dump operate at? 220 or 12 or something else?

As to how much wire do you need, that is pretty simple to calculate but you have to know the following
Power = volts times amps P=IV
Voltage = Current times Resistance V=IR

example
you wish to dissipate 1000 watts (power) using a voltage of 14.4 ---> P=IV or reordering I=P/V=1000/14.4=69.4 amps
and since we now know V and I (amps) we can determine the wire resistance --> V=IR, reordering R=V/I=14.4/69.4=0.207 ohms.
Most wire will come with a spec of "ohms/thousand feet" and max amp capacity or you can just get a long length of the stuff and measure the resistance. 22 AWG (American wire gauge) wire has a resistance of 16.14 ohms/thouand feet. we know that we only need 0.207 ohms though so --> feet needed = ohms/resistance /thousand feet = 0.207/16.14=0.0128 thousand feet or just 12.8 feet. Unfortunately the maximum amp capacity of 22 AWG is less than 14 amps.
If we go to wiki at http://en.wikipedia.org/wiki/American_wire_gauge we find that the minimum gauge to pass that 69 amps is a 4 gauge wire with 0.2485 ohms / k feet
Plugging this back in you get 0.207/0.2485=0.833 thousand feet or just 833 ft
If you use steel or stainless you don't need as much as the resistance /foot is much higher.

ghurd · « **Reply #19 on:** March 17, 2012, 08:45:37 PM »

That's why I recommend power resistors.
G-

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Author Topic: dump load? (Read 7053 times)