Renard wrote: I've managed to get the file about consumption and efficiency displayed:
Nothing is showing up. I see the URLs when I click reply, but my browser can't load the images. Maybe try jpg files instead of png?
jonescg wrote: You might need to provide some context first, and then walk me through it. Which contactor is this? For the heater? For the traction pack? DC/DC is affecting precharge?
4Springs wrote:How much current is required to drive that optocoupler? I've not had much to do with optocouplers myself:
The equations at the top of the diagram state that at 29V (1.4mA) the opto is off, and at 370V (10-15mA) the opto is on. I'm not sure exactly when it switches though. I had a look at the datasheet (6N139), but couldn't work this out. I suppose a variable resistor in this part of the circuit could allow for adjustment.
If this was not accurate enough, I suppose that zener diodes could be used on the input to pass current at an exact voltage.
Why have the op-amp and the transistor? Wouldn't the transistor be sufficient?
Could there possibly be an optocoupler that would sink enough current to drive a relay? In that case the circuit could be simplified greatly.
If I have understood correctly, the relay is powered to disable the contactor. Wouldn't it be better to reverse the logic, and require power to enable the contactor?
There is a relay in series with the traction pack contactor. The relay's normally closed terminals are in use, so that when we power the relay, we break the supply to the contactor.
Renard wrote: Can people see any problems with this circuit?
Ah, I see. I was treating the optocoupler as a discreet switch. So the level is set in the 12V section, not in the high voltage section like I was thinking. If I wanted an adjustable threshold then I'd make the 4.7k pullup resistor variable. That's why we need the 12V & 5.6V zeners (which was something else I was wondering about!).BigMouse wrote:The op-amp is there as a comparitor because the optocoupler does't "switch" discretely. It's a gradual increase. Renard is avoiding operation of the transistor in its linear range.
Shirker wrote: On the other side of the build vs. buy decision, you could send $55 to Ian for a ZEVA Smart Precharger, and get a couple of additional features... (I have not used one)
Hi all The CPC1968 I use in the higher voltage precharger is actually rated for 500VDC, so not much good for Chris's 700V race bike, but would probably be safe working up to say 400V nominal packs. It'd probably just need higher value power resistors and voltage sense resistor.jonescg wrote: The Zeva precharger utilises a solid state relay for switching precharge. It's tough to get them rated for voltages much higher than that. However your circuit above would avoid that problem.