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Forum Index : Electronics : making a big dummy load
| Author | Message | ||||
| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
I would like to build a big dummy load . I have a few large electric elements that could be handy , but before I start hacking into them ,would like some opinions on what is best . (this hair-brain idea of mine came about by having 3 Kw of solar and wanting to check its performance easily???. ) I've a 2 Kw wind genie dummy load -3 phase , so maybe its simply a matter of using it ? any past experience or clues ? Thanks Bruce Bushboy |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1387 |
I have had good experience with my approx. 1 Ohm resistor in a bucket of water. 3 6 foot lengths of 0.8mm stainless MIG welding wire around a bit of pine board under water can take 3KW easily. 1 Ohm could be inappropriate for your application. I used the resistor in development and testing of the mppt controller and it was about right since I wanted something like 45 to 55 Volts at 45 Amps so that means a resistance of 1 to 1.3 Ohms. wronger than a phone book full of wrong phone numbers |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Poida. I think years ago there was a list of postings on a similar dummy load , plus Phill M had a hand in designing a dummy load that was lowered and raised in oil ???. I,m wanting mine to check my new MPPT controller ,well, the solar panels really, to see what they are producing during different Sky conditions,4 Kw of them ,stand alone. I,ll rollout some mig wire and twist them together,don,t know about that, cause they are not insulated. ??? Any clues????. Thanks again, Bruce Bushboy |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Bruce, a fixed load will not tell you very much. During dismal cloudy weather it would pull the voltage down too far. In clear blue sky direct sun, there may be insufficient load to do the panels full justice. You really need to be able to continuously adjust the loading over a wide range, and then read max power at the optimum loading, which will always be pretty close to the panels rated output voltage. Cheers, Tony. |
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| poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1387 |
I agree Warpspeed. A fixed load is not very useful. And that is why I have the simple code driving the mppt board which is used for testing inductor saturation. The code can be used to pull power from a source to see what max power can be drawn from that source. The attached code is for the mppt project of mine. I can draw anything from 0 to 3000W, controlled by the pot. (the 3kW limit is based on 105V input and the 1.3 Ohm resistor on the output) The hardware used is a mppt brainboard and the powerboard which has it's output connected to the 1 Ohm resistor. Once you calibrate input and output Volts and amps, you get a quite useful output power reading on the LCD. Add about 5% to that and then it's the input power. buck_converter_nics_1_b4_nano_pwmserial_bb.ino.zip I have to say that twisting a pot to make it consume 3000W from 0W start point is really something. for me at least. To hear the resistor immediately start making small bubbles on the wire as power increases past 1700W, then get louder and louder as you get to 3kW.. wronger than a phone book full of wrong phone numbers |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It sounds like you are making a witches cauldron there Peter. Do you have to mutter the secret incantation, or is that already written into the code ? Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I built a Dummy load accidentally years ago while mucking round building a Hydrogen generator. I got some all thread rod and welded some metal plates to it, a positive and negative side and put them in a large piece of capped PVC Pipe. The rods went though a cap on the end but that is not needed in this case as not trying to capture the gas. I put a soloution of Koh ( caustic Soda) in the pipe as an electrolyte but you could also use salt, just watch out for Chlorine gas but it won't make much. I think Baking soda could be used as well. You just want something to get the conductivity of the water up. Only thing of course is not to let the plates touch but they can be close or distant as suits. This will sink huge loads but it does act like a kettle and the water will heat up. If you used say a 25L Drum, You could weld on plenty of plates ( more surface area, more conductivity) and it would give a decent run time before it got too hot. Put a fan over the top to extend run time if you wanted by evap cooling. For a variable load, all one would need to do would be raise or lower the level in the tank of the electrolyte OR, raise and lower the plates in and out which would do the same thing. This way it's completely tunable to the power level you want to sink or test. This is really cheap and easy and will take a ship load of power if you need it to. If you wanted to run all day, use a bigger drum and larger plates and then you can back off the concentration of electrolyte ( pool salt is cheap though) and have your run time. With a 200L Drum you could sink 3KW for about 4 hours in a 200L drum and take the water from 25 to 80C and that's if you don't loose any heat. Again, put a fan or two on that surface area and use a bit of evap cooling and it will last all day. Just like is used for thermosyphoning lister and other stationary engines. You can sink a lot of power into a small container for a short time anyway. I found this really useful for testing I was doing with car alternators because it's pretty much irrelevant as to what voltage you use. You can bump the concentrate of the electrolyte to get pretty much any amount of power sinking at any Voltage you want. Just lift the plates if you want to back it down from there or drain off some of the electrolyte. |
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| poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1387 |
nothing of the sort. Just have a goodly sized glass of home made vodka handy and there's no risk of rending the space time continuum. wronger than a phone book full of wrong phone numbers |
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Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 427 |
Well that conversation made me chuckle! on this cold dull winter morning. Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| dangraham Newbie  Joined: 07/10/2020 Location: ThailandPosts: 17 |
I use H4 car headlight bulbs, specifically the 100w/90w versions that can be bought locally for a couple of dollars. Using an old scrap piece of Alu sheet metal and making a matrix of 30x bulbs, this allows altering the series parallel connections to give the required resistance and voltage. I have used this bulb array for high current discharge testing of cells at +200A. Also for testing the output of inverters etc from 70v-24V. It is very convenient and provides a consistent response. It costs a little to set it up but once built proves to be very useful. There may be other bulbs that are more suitable for your application but the H4 has been used in many different vehicles so can usually be found very cheap and good supply. The Bosch 100/90 I have found to be very reliable I only poped one so far and probably because I dropped it. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Beware of naked flames around that stuff. Farts can cause absolute devastation. Cheers, Tony. |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 990 |
Naked old flames can be even more trouble...... If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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