a PMOS, should handle the current but may run hot as Jeremy pointed out. i will do that, thanksdnmun wrote:what is the 4905? will it handle the current?
you could just use a resistor to precharge the caps, then make the connection.
i'd love to use RFID in the future. for now i will settle down on FETSJeremy Harris wrote: If you take a look at the way I switched the power with a soft start on my RFID ebike switch, here: viewtopic.php?f=2&t=39589&hilit=RFID#p578778 you can see that I used a bank of parallel IRFB4110 FETs, not to get better current handling, but just to reduce the Rdson and so get low losses. My ebike runs at up to 30 A through those 4 FETs and they barely get warm, as the total power dissipation is only about 1 W at 30 A, or about 0.25 W per FET.
This is more efficient circuit and I don't need to use a power switch. I can use a simple switch that can be mounted on the handle bar. ThanksJeremy Harris wrote:You could use the same switch circuit as I have, just connect a switch in series with the gate resistor to the FETs. I've drawn a quick and dirty circuit diagram to show how this works, below. The capacitor across the 10k resistor does the soft start, by turning the FET on (and off) slowly enough to avoid any appreciable surge current.
The risk of damage is really only to the switch or connectors, rather than anything else. This can be quite severe on a big controller, I've had an Anderson get ruined in just a few connections from the spark.Confab wrote:Does a precharge circuit only prevent the sparking or does it actually prevent current inrush damage?
I've built a spare one you can have. It's got counterfeit IRB4110s, but the other two that I built with the same ones work perfectly and don't even get warm at 20 amps.Diamondback wrote:Hi all.
any chance that someone here would be interested in building one of these (either switched or RFID) for a fee ?
i would love to have one on my trike, but i truly suck at these kinds of projects.
i would love to have an RFID switch with the soft start feature....
id happily pay just about any reasonable fee.
the trike is 20A 12S2P lipo. (20A constant, around 35A peaks)
Being a minimalist, I just used resistor selection as the way to limit the gate voltage to a safe level, but you're right, clamping it with a zener would remove the need to fit the right value resistor.fechter wrote:I'd suggest adding a 12v zener diode from gate to source on the FETs just to reduce the chances of blowing them up if the voltage is out of range. With a zener, both resistors could be something like 1M, and you could run anywhere from 24v to over 100v with the same components.
Some kind of heat sink on the FETs would be a good idea at higher current levels. I generally rate the 4110s at 20 amps each with minimal heat sinking.
We think alike.Jeremy Harris wrote: Being a minimalist, I just used resistor selection as the way to limit the gate voltage to a safe level, but you're right, clamping it with a zener would remove the need to fit the right value resistor.
Different countries, different prices! We seem to pay more for everything over here......................fechter wrote:We think alike.
The cost of a zener from Mouser is about $.05ea. About the same cost as a resistor.
Sure, but this was just a dirt simple switch, that emulates a mechanical switch, but without the spark. It could be a heck of a lot more complex and sophisticated, but I threw that circuit together in about a minute simply to fix the primary problem with the original design in the first post, the high on resistance of the P channel FET. It's just the power end of the switch in the RFID switch on my bike.fechter wrote:It should also be possible to tie in the LVC from a cell level monitoring system like Methods' or CellLogs to kill the power in the event a cell goes low if this is desired. Personally, I like to just pull the throttle line down, but in the case of forgetting to turn off the power for a long time, it would cut power to the controller and draw only about 1uA per volt of battery voltage.
Yes, it would be OK. The maximum gate voltage allowed is 20V,and the gate needs at least about 8 to 10V to ensure the FETs are hard on, so the different resistor values were just my simple way to gate the drive voltage in the right range for each battery voltage.Diamondback wrote:Should R1 still be 22k for 12S lipo ? That's just over 50V fresh off the charger.
You can pretty much ignore the FET power dissipation in the datasheet, as it's misleading and can rarely ever be achieved, because the FET can't get rid of heat through any real heatsink at a rate that would allow that dissipation figure to be reached.mvly wrote:humm looking at the datasheet. Max current is 180A @10V but max power dissipation is 370W So if we have 4, wouldn't that theoretically limit you to 370*4 = 1480W?
But if use the 120A @10V, then we have theoretical max dissipation is 1200W per FET? so 4 is 4800W?
I am a bit confused on the Specs in the data sheet
Don't increase the resistors to 1M, it's far too high a value to get a zener to turn on reliably (they need around 1 mA to get to the start of the turn on knee) and it would also increase the FET turn on/off time to a point where the FETs might well start to complain. The range of turn on times (and turn off times) I selected was intended to keep the FETs in the safe area, even when using a controller with a lot of capacitance (like the big Kelly's).shinyballs wrote:Wow, awesome contribution from Jeremy and Fechter's improvements! This should be standard equipment for every ebike.
To use the switch for higher voltages up to 150v, is IRFB4115 a good choice? and by replacing the 2 resistors to 1m, and a zener on each fet, it can be used for a much wider voltage range, right?
Regarding using the switch on a Kelly controller, they stated that to avoid damaging the controller, the Battery -V has to be connected 1st before applying power. On your diagram, can the power wires be reversed, meaning the gate connection comes from the Battery's -V, and fet source from Battery +V ?
Fire away, anything I put on here is just open source doodling, for anyone to use or mod as they see fit.shinyballs wrote:Thank you for the very thorough explanation. Based on your input, do you mind if I show the changes I made to your Soft Power switch diagram for your perusal?