The normal way to do this is with a MOSFET with feedback. (MOSFETs are natural current sinks, but feedback makes them a lot more accurate.) Check out these options:rg12 wrote: ↑Oct 15 2018 11:25amI know that for different loads I can play with different resistors with different ohm ratings and using them in parallel or in series.
* Not looking for adjustable bulb load or whatever, just resistors.
I was told it's impossible to control the current with a pot as the pot needs to carry the whole load, BUT I was just discharging a few cells with my Turnigy balancer that can go up to 5A Discharge at 8S and I can digitally select the desired amperage in 0.1A increments.
How does that work?
Do you know a way how to calculate how many and which fets for my requirements?fechter wrote: ↑Oct 16 2018 10:03amThe FET ratings will let you calculate how many you need in parallel. You need to stay under the continuous current rating and the dissipation rating. Also good to have about 2x or more headroom in the specs.
The real trick is keeping them from burning up. You need a massively large heat sink and good thermal coupling. For very short durations, just a big block of aluminum will do. For longer runs, you need big fins and a fan.
You understand that an incandescent light bulb is exactly a resistor, right? Even when it's used at lower than its intended voltage and thus doesn't emit light.
Yes I guess you are right but I rather not go with lots of bulbs...Chalo wrote: ↑Oct 17 2018 1:33pmYou understand that an incandescent light bulb is exactly a resistor, right? Even when it's used at lower than its intended voltage and thus doesn't emit light.
It seems to me that no matter what you use as a resistive load, you could use a DC brushed motor controller to PWM whatever current you like, up to the amount that the load will accept. A big fat capacitor for smoothing would probably help make the current smoother and more measurable between the cap and the load.
You can see a single big transistor on a heat sink with a fan. Says maximum continuous 60W. So imagine using 10 of these or 10 FETs on a much bigger heat sink with a fan and you could run 600W.Discharge current: 0.20-9.99A stepper 0.1A or 0.01A
Discharge Current Maximum Error: 0.7% -0.01A
The Maximum Capacity Test Error: 0.5A 2.5%, 2A 1.5%, 5A and above 1.2%
Offline ( termination ) Voltage Range: 1.0-25.0V stepping 1V or 0.1V
Discharge Voltage: 1.00-30.00V
The Maximum Voltage Measurement Error: 1% + - 0.02V
Maximum Power: 60W super power automatically limits the maximum current (for example, up to 60W when it can open 9.99A 6V and 20V maximum at the only open 3.00A)
That's a pretty tall order. I don't think transistors are going to be an economic solution at that level. You need a giant resistor.
These are 120v rated, so will be slightly less power at 100VCat# TH34268
Add. info: 14" U Shaped
Yep. You'll need a very large resistor bank. Light bulbs also work but have a high inrush current which can hose things up a bit.rg12 wrote: ↑Oct 18 2018 12:48pmI need this for discharging packs and also for stress tests so it will need to be able to run very high amps at very high voltages for periods of 30 seconds or so.
Talking around 100V and 180A for maybe 10 seconds and 100V 100A for 30 seconds.
Constant will be around 1500W
Because the FETs are either fully on or fully off and never asked to dissipate much. When you run a transistor in the linear region, the heat dissipation gets crazy.