I’m looking for a rotary incremental switch. It has to be mechanical since a power supply is not available.
The switch would work like this:
Pos 0: Open
Pos 1: Contact 1 closed
Pos 2: Contacts 1 & 2 closed
Pos 3: Contacts 1, 2 & 3 closed.
The switch should not open the circuit whiile switching between positions 1 and 2 (optional 2 and 3).
The application is to build and EVSE emulator (= EV charging station emulator). The pilot signal comes from +12V DC in series with 1KOhm. With the switch we need to connect different resistors to lower the signal to 9 and then 6 VDC (optional to 3V DC). Important is that there should be no interruptions on the line. i.e. a normal rotary switch will break before making contact and then the signal would jump momentarily back to 12V (open circuit). The switch we need should first close contact 1, then while keeping contact 1 closed all the time, also close contact 2.
Is there such a switch?
Welcome to the forum.
Assuming you don’t want to buy 10,000 pieces, you’ll probably need to buy a 3 pole, 4 position, make before break (shorting), rotary switch and wire it up for your function.
This is the least expensive one I found in stock:
Hi Paul, thanks for jumping in!
I did look at “shorting” rotary switches but these won’t work in this case. See, we need to have smooth transitions from 12V → 9V → 6V, without peaks or dips. What I’m really looking for is an “incremental” rotary switch that will connect Pos 0, then Pos 1, then Pos 1+2.
I’ve attached the J1772 signaling circuit for EV (electric vehicle) charging to show what I need to emulate:
Let’s see if I get your idea correctly:
On Pos 0, it will be an open circuit. I have 12VDC on the anode of D1 (the input to the car)
On Pos 1, we would have 2.7K. The voltage divider between R1 (1K) and 2.7K will give me 9V. Check.
On Pos 2, we would have 2.7K || 1.3K, and the voltage divider with R1 will give me 6V. Check.
The problem I see is that if I use a non-shorting rotary switch the line will jump momentarily to 12V while changing from 9V–> 6V.
And if I use a shorting switch then I would have a dip when changing from 9V → 6V because I will have 2.7K || 2.7K || 1.3K for a brief moment.
Neither a peak nor a dip on the signal will be acceptable because voltage comparators on the EV and the charging station will go bananas.
Do you know if there is a rotary switch like the one Iḿ proposing?
OK I think I’ve got a better understanding of what you’re looking for. You want a system that can smoothly transition between 12, 9, & 6V.
I can’t think of any easy and obvious to me way to do that. It would take learning a lot more technical details of the target application and a good deal of design time to come up with a solution and it could be substantially more complicated than just a basic switch and resistors. If this was a one off situation for a business I’d probably just buy a piece of off the shelf test gear that can perform the task for a few thousand dollars. If many copies were needed I’d spend up to 100 hours learning about the application and designing an inexpensive solution (up to $20k NRE charge).
I think that type of rotary switch would likely be a custom design. Could you use three toggle switches rather than one rotary switch? You would have to be careful to switch them in the correct order, which adds a human error element, but would be fairly simple to implement.
Alternatively, one could use a standard rotary switch connected to a programmed microcontroller, which, in turn, controls relays or MOSFETs to perform the desired function. You would have to get someone to design that circuit and write the code, but it should be a relatively simple design. Probably much cheaper than a custom switch.
I’m not familiar with the standard or the nuances of it’s prescriptions, but a standard 3-position switch with an RC filter with a fairly long time constant might be a plausible option.
Hi all, thanks for taking time to think about this! Much appreciated
- Yes, I had the same considerations about NRE costs. The product won’t justify them.
- We have a solution in place with a uC and relays. Works really well. But that would need a power supply which is not desired.
- A long RC is an idea. We’ll have to experiment to see how it works in practice. Will reply if it works.