Home-brew battery measuring station

[BrianG]

Actually, this project is probably permanently on hold. I don't think it will have enough use to justify its cost to assemble - at least for what I originally planned. Who knows, I may revisit this later on, but let's just say it's not on my immediate "to-do" list.

That doesn't surprise me really. A 1500w heating element running on 120v means the core has a resistance of 9.6 ohms. A 4s battery will only draw 1.54A with that resistance.

You could go with some dummy loads. Depending on how much current you want to draw, you have to arrange a bunch in parallel and make sure the power rating for each one can handle the heat. And the power dissipated will obviously change depending on what voltage you are testing. If you are looking to only test ~10A on 2s, that's easy enough since the power is only ~75w. Eight 4 ohm 20w resistors in parallel to get a 0.5 ohm load will get you there, and then you use the ESC to regulate that amount. Don't forget, the ESC will only reduce the current (via voltage switching) to any given load, so make up a resistor bank that will have the lowest resistance you will ever want to test. Wiring again depends on test current. For ~10A, 12-16GA is adequate. As you go up, gauge has to go up as well.

This test system becomes rather complex as you start getting into the higher test currents. If you want to draw 100A @ 2s, you really need to make sure the resistors can handle the heat, there is minimal wire/contact resistance, and shedding the heat can become a problem.

If you want, I still have a bunch of 3 ohm 50w resistors that I'm not using. I got over 200 of them via ebay, but it was cheaper buying this many even though I won't need near that amount rather than getting the exact amount I needed. Their 50w rating is only good if properly heatsinked. Some CPU heatsinks can work if there is a fan blowing on the fins.

[sikeston34m]

Originally Posted by BrianG

Actually, this project is probably permanently on hold. I don't think it will have enough use to justify its cost to assemble - at least for what I originally planned. Who knows, I may revisit this later on, but let's just say it's not on my immediate "to-do" list.

Well that's too bad. You know your stuff when it comes to this kinda thing. I was looking forward to seeing the end result of your creation.

If you don't mind, I'll go ahead and pursue it. I may call on your expertise from time to time in figuring things out.

That doesn't surprise me really. A 1500w heating element running on 120v means the core has a resistance of 9.6 ohms. A 4s battery will only draw 1.54A with that resistance.

You could go with some dummy loads. Depending on how much current you want to draw, you have to arrange a bunch in parallel and make sure the power rating for each one can handle the heat. And the power dissipated will obviously change depending on what voltage you are testing. If you are looking to only test ~10A on 2s, that's easy enough since the power is only ~75w. Eight 4 ohm 20w resistors in parallel to get a 0.5 ohm load will get you there, and then you use the ESC to regulate that amount. Don't forget, the ESC will only reduce the current (via voltage switching) to any given load, so make up a resistor bank that will have the lowest resistance you will ever want to test. Wiring again depends on test current. For ~10A, 12-16GA is adequate. As you go up, gauge has to go up as well.

I'm looking at two options for the load.

#1. Create an Large Electromagnet using High Temperature Motor Winding Wire. Using multiple strands to step up to the 100+ Amp Load Rating, this should be one heck of a Magnet.

#2. In the Cold Storage Environment, (my work) They install heaters everywhere inside the equipment. There is one type in particular that is 24 volts and puts out about 200 watts of heat.

Wire 6 or 7 of these parallel and strap them to a heat sink assembly with a blower.

This test system becomes rather complex as you start getting into the higher test currents. If you want to draw 100A @ 2s, you really need to make sure the resistors can handle the heat, there is minimal wire/contact resistance, and shedding the heat can become a problem.

If you want, I still have a bunch of 3 ohm 50w resistors that I'm not using. I got over 200 of them via ebay, but it was cheaper buying this many even though I won't need near that amount rather than getting the exact amount I needed. Their 50w rating is only good if properly heatsinked. Some CPU heatsinks can work if there is a fan blowing on the fins.

I'll start out with a 100 amp continous discharge goal on 6S. 2500 watts.

Perfect this setup, then step up to bigger if needed.

I appreciate your input Brian. Thanks.