5kW variable resistor for UAV project

[Reloadron]

Thanks very much for the help guys, I really appreciate it. If I'm correct I could use the following element:

Strip Heaters

Using 5 of the 'HCS-237' elements I would have a total power rating of 5kW. As far as I'm aware, as long as these elements dissipate the required amount of power (and I can use a potentiometer in series to control the load more precisely), I can go for the cheapest combination. I'm not sure if these heaters require fans or not, though.

What do you think?

If you go with the flat design I would use some fans and mount them on a chunk of steel. Unless they have a way to dissipate the heat they will self destruct but as long as they are mounted they should work fine.

Ron

 

[breakshift]

What kind of fans are we talking about? Something pretty powerful or just anything that will keep air flowing over the heaters?

Also, I'm not sure how I'd connect the pot (say a 3Ohm pot like you suggested). I'm assuming I'd connect the elements in series to act as a load bank - and connect the pot up in series with the 5th element (the one connected to ground at one end). But if the pot goes in before the 5th element, I'm short circuiting the element, and if the pot goes in after the element, I'm either short circuiting the pot itself or simply adding its resistance to the series chain (the two extremes of the pot configurations).

I've only used pots to control voltage before, so how can I use it to control load?

 

[Reloadron]

Just to keep an airflow removing heat. Nothing special. Mount the heaters on a chunk of steel (or aluminum) to serve as a heat sink to sink heat away from the heaters and then have good airflow over things to remove the heat. If you were to just apply 240 VAC to one of those elements it would just burn itself up. They need to be mounted and the generated heat removed.

Ron

 

[Gary B]

(and I can use a potentiometer in series to control the load more precisely)

Just be careful about the amount of power dissipated in the potentiometer. I would use a high power rheostat in series since the lower its resistance, the more power is being dissipated over a smaller portion of the winding.

 

[Reloadron]

You would want to configure things similar to the attached drawing. As Gary B points out you want a heater load in series with the potentiometer. Remember also the pot needs to have a very high wattage rating. Placing a smaller load heater in series with the pot will protect the pot and allow you to trim the load a little. If we have 1000 watt elements running on 240 VAC the load current would be about 1000 / 240 = 4.17 amps so you want switching that can easily handle a 10 amp load to allow a nice margin in there. Also, you will find pots rated for 1 KW are expensive, as in very expensive. Ohmite makes a 50 ohm and 100 ohm pot rated at 1 KW. Make sure the pot will handle the current and then some.

Make sure you use wire with a gauge to easily handle the current also. Here in the US I would likely use AWG 10 or larger which open air will handle 30 amps.

In reality you could likely use a lower rated pot but then make sure other loads are switched in before using or switching in the variable load.

Hope that helps a little...

Ron

 

[breakshift]

Okay I thought I'd connect the elements in series and have switches to allow the generators +v to connect in at the appropriate point. I suppose the parallel configuration would be better as the current would be divided between each branch.

How resistive are these heating elements likely to be? Around 50-100 Ohms? I have no idea.

 

[Reloadron]

Okay I thought I'd connect the elements in series and have switches to allow the generators +v to connect in at the appropriate point. I suppose the parallel configuration would be better as the current would be divided between each branch.

How resistive are these heating elements likely to be? Around 50-100 Ohms? I have no idea.

1500 Watt Element @ 240 VAC would be about 38.4Ω
1000 Watt Element @ 240 VAC would be about 57.6Ω
500 Watt Element @ 240 VAC would be about 115.2Ω

That would be about it. I typically use 1.5 KW, 3.0 KW and 6.0 KW elements in large heating arrays. Somewhere around here I have a few strip heaters but have no idea what they are buried under.

Yes, in a load bank you would set things up pretty much like the diagram I provided. You place loads in parallel and switch them into the circuit as shown. Loads like this are purely resistive in nature.

Ron

 

[kinarfi]

Here is another possibility for you, Allied Electronics has a triac that is good for 40 amps for $11.40 US. https://www.alliedelec.com/search/productdetail.aspx?SKU=2480310, Then go to your local stove repair place and get some used oven elements and hook them up to the triac and vary your load using a simple pot. You'll also need a really good heat sink.
Here's the spec sheet https://www.electro-tech-online.com...ECTRONICS_ACTIVES-AND-PASSIVES_2480310PDF.pdf
Using a triac would only require about 50ma of current to control the triac.
Attached is a schematic for a triac circuit, you just need to scale up for the 40 amp triac.


The fans you would need if use heater elements would just be the regular oscillating desk fan, just something to keep the air moving.

 

[jturn1bu]

Load Bank

We supply equipment to test UAV engines with alternators/starter generators up to 5KW but use semiconductor approach rather than resistive. The advantage of this approach is that you can provide a continuously variable load without the 'stepped' effect that you will get with banks of wirewound resistors. The resistive method is cheaper though and the designs knocking around in the industry tend to use fixed high wattage ceramic resistors in banks with contactors to switch them in or out as required hence the 'stepped' load effect. One thing to be carefull of if you use an off the shelf commercial electronic load bank is that most are for lab work and will suffer under long runs of say 300 - 400 hours for a duration test. Also if your generator does not have its own internal voltage regulation then you could see outputs ranging from 16 - 130 odd volts and higher for S/G systems. Upshot of this is most alternator test requirements demand a fixed load to be applied in Watts and to remain steady as engine RPM is varied. If you have an unregulated generator the voltage output will obviously then change with engine RPM so you would need a load bank that could adjust its load to suit. Again the benifit of semiconductor route is that this can be implemented in a PID controller.

Hope this gives some ideas,

Jack

 

[gary350]

This is what you need.

**broken link removed**

**broken link removed**

**broken link removed**

**broken link removed**

 

[bryan1]

I tested high power audio amplifiers into a very powerful speaker and nearly broke all the windows.

Ummmmm windows comes in two states NOT Broken or Broken so using the term nearly broken is like saying a glass of water is 1/2 full or 1/2 empty........ completly POINTLESS......................

 

[audioguru]

Ummmmm windows comes in two states NOT Broken or Broken so using the term nearly broken is like saying a glass of water is 1/2 full or 1/2 empty........ completly POINTLESS......................

The windows were vibrating vigorously. A little more power with a little more vibration would have broken the windows. Therefore the windows were nearly broken. The amplifier produced 1400 real Watts into 4 ohms because it was a bridged stereo amp with 400W into 4 ohms per channel. It was overloaded but was very stong and performed fine. The speaker had two 15" 8 ohms woofers in parallel.