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Building a discharge resistance load

Old 11-25-2016, 07:57 PM
  #1  
Topher
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Default Building a discharge resistance load

I'm looking at building a resistance load to discharge at a high current. Thinking about a 800 to 1000 watt discharge to mimic working load and use a computer to analyze the voltage drop.. I'm using my icharger to do this.. any market for such a resistor or interest...
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Old 11-27-2016, 02:11 AM
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There is a battery analyzer that will do all this if my memory is still working right. (I'm 68 so who knows)

I found it !!!

https://www.google.com/url?sa=t&rct=...iRAZ55KViV9x0Q
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Old 11-27-2016, 03:29 AM
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Not enough load.. I'm sitting around 800 to 1000 at the moment.. looks like that is 150watts or 40 amps..
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Old 11-27-2016, 04:19 AM
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For most people the discharge load of such would be provided by a tethered model.

General discharge of battery's to storage by either their intelligent charger or such as the MyRCMart 3in1 discharger rated at 150w.

One of the main reasons for this approach is the high risk of over-discharge with manual discharge systems. Using the model utilises the ESC capability to protect against over-discharge.

If you wish to go the resistive load path - it will be a matter of fabricating a safety cut-out to prevent damage to the battery. An ESC cannot provide as it needs the pulses of a motor for feedback.

Second the heat of such resistive load would be significant.


Nigel
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Old 11-27-2016, 04:21 AM
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I use my icharger to limit the load.. the load resistor has a fan and works great.. I was more wondering if there is any kinda market for such device..
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Old 11-27-2016, 04:27 AM
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Originally Posted by Topher View Post
I use my icharger to limit the load.. the load resistor has a fan and works great.. I was more wondering if there is any kinda market for such device..
There are already a number of solutions on market and most would be looking for moderate rate discharge to not stress their battery packs.
High discharge rates do more damage than charging.

Most peoples call for measuring high discharge rate is when they tether model and measure motor demand. Then its down to a Wattmeter in line and done.

If a real advantage could be shown - maybe a market, but I think not.

Nigel
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Old 11-27-2016, 04:33 AM
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It's nice to put the real flight load on your batteries and use a laptop to monitor the discharge of each cell and capacity and voltage drop off point.. I have tested my batteries and it's very clear that you can spot the weak points and health of your battery and is safer then to run your model up in your house.. once I get this made I'll put a video on YouTube and see what reaction I get. People have told me you can buy 1500 watt resistors that require no cooling but watching my setup it's hard to believe..
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Old 11-27-2016, 05:40 AM
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There is no way a resistor will not heat up ... its the reason an electric fire works ! At 1kw as you talk about - you can heat a room !!

I agree that watching cells on PC is good . But most people don't even use the iR function of their chargers to check resistance of cells let alone under load.

And judging by questions on various forums - a lot of people don't even know arse from elbow when it comes to battery's !!

I am not poo-pooing your idea, just looking at it from practical view point.

Nigel
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Old 11-27-2016, 05:43 AM
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Thanks for the info
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Old 11-30-2016, 02:25 AM
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Default Completed and sample video

https://youtu.be/LSdNktrquO8
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Old 11-30-2016, 04:27 AM
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Originally Posted by Topher View Post
I'm looking at building a resistance load to discharge at a high current. Thinking about a 800 to 1000 watt discharge to mimic working load and use a computer to analyze the voltage drop.. I'm using my icharger to do this.. any market for such a resistor or interest...
Go to www.digikey.com and search for:

"FSE1000" This search will give a list of 1000 Watt resistors whose resistance varies from 0.25 to several Ohms.

Ar a reminder, Amps = Volts divided by Ohms.

So, a 4 cell LiPo would pull about 4 cells times 3.5 V per cell fivided by 0.25 Ohms.That calculates out to 56 Amps.

Power is Volts times Amps, 14 Volts times 56 Amps, or 784 Watts.

Hope that helps.

FYI, these resistors can easily handle brief power levels way above their ratings. But they are ceramic. Don't drop them!
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Old 11-30-2016, 04:33 AM
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I'm not understanding your point.. I already know this.
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Old 11-30-2016, 05:51 AM
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I use a modified hairdryer to do exactly what you are looking for. It discharges at 1000W:
This is mine:


The important thing is you must re-wind the hairdryer to achieve (for the 4010 Duo) 1 Ohm resistance

I've seen others do the same thing with a bank of high power wire wound resistors on a large heatsink but overall i prefer the hairdyer because it's very compact and it runs cool. The resistors get scorching hot and are potentially a fire/burn risk.
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Old 11-30-2016, 06:08 AM
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Originally Posted by Topher View Post
I'm not understanding your point.. I already know this.
OK
Sometimes it's difficult to determine how knowledgeable a person is that posts in these websites.

At any rate, 1KW and even 2.5KW resistors are available. At a stiff price.
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Old 11-30-2016, 12:45 PM
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I'm using the same hairdryer motor but I checked it before taking it apart and it was running on 12v low and 24v on high. I think the voltage that you are at is over driving the motor unless you have a regulator on it.. being a machinist I decided to fancy it up a bit and also wound my own nichrome wire.. I did get my idea from your video but did my own version of it. If I could find another motor that could handle the voltage I could go higher wattage too. But yes it stayes cool...
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Old 11-30-2016, 06:20 PM
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You just tap the motor supply wire in part way down the resistance element windings so that you can get whatever voltage you want depending on how far along the element you go... Simple!
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Old 11-30-2016, 07:39 PM
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But what happens when you want to discharge a 10s then go to a 3s.. your motor won't even be spinning.
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Old 11-30-2016, 08:54 PM
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Originally Posted by Topher View Post
But what happens when you want to discharge a 10s then go to a 3s.. your motor won't even be spinning.
I very rarely discharge anything other than 6s. On the couple of occasions that I've done lower voltage it was not a problem because the discharge power is much less so the fan doesnt need to spin as fast. Higher voltage also isn't an issue because you can set a maximum voltage for the discharge channel.
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Old 12-04-2016, 04:23 AM
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Your idea already exist and any hobby charger can do it including your iCharger. With iCharger you have to use Discharge Plus mode along with a Ballast Resistor to take the heat off the charger.

As an electrical engineer, unless you have some really good Code writing skills and electronic design background building Constant Power or Constant Current dummy loads best to stick with manufactured device.

It is not a matter of just finding the right power resistor. That resistor has to be a Smart Resistor having the ability to change resistance for any given voltage at a specified current.

Say you wanted a constant Current 10-Amp dummy load for a 3S battery. The resistance required to draw 10 amps completely depends on the voltage being applied. So the resistance ranges from 1 to 1.26 Ohms. As the battery discharges the voltage decays, so resistance has to change.

Oh you need to do that on 4S? That means a different range of resistance. What you want to do can be done, and if one has the skills is really pretty simpleI just think it is as simple as you think it is.

Besides you already an iCharger and can do exactly what you want. Only catch is you need Ballast Resistors. To determine the Resistance is easy, you just use the Spread Sheet made for iChargers. Just enter end voltage and maximum current. You are going to get an answer of a 100 watt power resistor.
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Old 12-04-2016, 04:58 AM
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Isn't this the old case of a different Mouse Trap ?

We all come up with variations on existing ... nothing wrong with it.

I spent ages playing with car headlamp bulbs making and remaking dischargers. I arrived at a pretty good one that catered for up to 5S packs .. but then saw the 3in1 online and that was it ... simplicity !

Nigel
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Old 12-04-2016, 05:48 AM
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Originally Posted by dereckbc View Post

electronic design background building Constant Power or Constant Current dummy loads best to stick with manufactured device.
Years ago, I tried building up a 5 Amp constant current dummy electronic load using MosFets. And, succeeded in building a very good high power, 100 Kilohertz oscillator!

And, of course, that blew out MosFets at a regular rate. Finally got it to work with power transistors rather than MosFets. Still got that thing somewhere. The units microcontroller displayed current, voltage, and recorded MilliAmpere Hours on its LCD display.

It's been replaced with my Western Mountain CBA battery analyzer, orders of magnitude better than what I designed.
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Old 12-09-2016, 11:55 PM
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This one works great.. it puts a nice load on the other port of the 4010 duo and let's you set everything thru the charger that you want to do.. bleeds off heat very good and it's in a aluminum case If something bad were to happen..
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Old 12-11-2016, 09:01 AM
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Originally Posted by dereckbc View Post
Your idea already exist and any hobby charger can do it including your iCharger. With iCharger you have to use Discharge Plus mode along with a Ballast Resistor to take the heat off the charger.
The one in my video works different to the conventional ballast resistor. In my video the charger doesnt take any of the discharge load at all. It just controls the discharge. All the actual energy dissipation is done in the added resistive load (the hairdryer in my case). It's similar to regenerative discharge where you discharge into a lead acid battery, but instead of the a lead acid battery the hairdryer is used. The hairdryer discharges at 1000W which is more than any other discharger that I'm aware of.
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Old 12-11-2016, 03:55 PM
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Mine works the exact same way yours does..
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