Hello,
I’m working on a home automation project with the K8055.
I can control it the way I want, but how do I connect a 5V solid state relay to it?
It should work with 5V 20mA, do I just connect it to
O1 and gnd,
O1 -Clamp and gnd???
i Would prefer to connect it trough digital outputs, do i need resistors??
, or do i have to connect it to the analog DAC1 and GND
[quote]It should work with 5V 20mA, do I just connect it to
O1 and gnd,[/quote]Yes, and use low enough pull-up resistor to get the 20mA from the external supply.
[quote]or do i have to connect it to the analog DAC1 and GND[/quote]No, the DAC output is too “weak”. It can output about 3mA max.
[quote=“VEL255”][quote]It should work with 5V 20mA, do I just connect it to
O1 and gnd,[/quote]Yes, and use low enough pull-up resistor to get the 20mA from the external supply.
So if I understand correctly, I have to use an external power source?
What parts do I need?
How do I connect it?
[quote]So if I understand correctly, I have to use an external power source?[/quote]Yes, the digital outputs of the K8055 are open collector outputs. There is no voltage coming out from these outputs.
Connect the digital output of the K8055 to the control input of the relay.
Connect a pull-up resistor between the control input of the relay and the external power supply positive pole.
By doing this you get proper voltage and current to the control input of the relay.
Please see also: viewtopic.php?f=12&t=6032
This is [color=#0000FF]a good document from Vishay[/color], describing how to properly select an input resistor for a solid state relay…
Indeed, you can also connect the solid state relay in series with the pull-up resistor as described in the Vishay’s document.
Connect the solid state relay similar way as the normal relay is connected in this drawing, but put a series resistor with it.
Looking at using a SSR with my K8055, is the series resistor needed, or just recommended?
If so what value resistor, and should it go between the output and - side of the SRR OR on the + side of the SSR and the clamp +
Cheers
It has little to do with the type of load (solid state or not). That only affects if you really need to connect CLAMP or not. What matters is the circuit voltage, the resistance of the relay control (coil for regular relays) and how many (or what else) the K8055(N) will have to turn on at once.
The K8055(N) uses a ULN2803 Darlington transistor array as the final stage for the 8 digital open collector outputs. While that thing can switch quite a lot per individual output, they also add up and the chip cannot dissipate the heat, that would be created if all outputs were maxed out all at once. This is a well documented and known design limit (not flaw) of that particular transistor array. Each channel can handle a lot of load. If you turn them on at that load all at once, the chip will overheat.
Using an open collector in its natural configuration, as in the image in VEL255’s previous post, is the preferred way. In that configuration the open collector of the K8055 acts like a “small” relay itself, connecting/disconnecting the load to/from ground. In that diagram the voltage from the battery (+) goes through the relay coil to O5 of the K8055 and when active, through the ULN2803 to GND where it meets the other side of the battery (-). In other words, in that configuration the K8055 acts like a switch/relay, that you can close and open using your computer. A small relay controlling a larger relay, so to speak.
Putting the voltage and resistance of your load (relay or not) into Ohm’s law and comparing the result with the ULN2803 data sheet will quickly tell you if you are good to go or if that load would exceed, what the ULN2803 can do.
If it does exceed those limits, then you have to add some support circuitry like extra (power) transistors. Which simplified boils down to slightly bigger relays controlling the larger ones. Wheels within wheels in a spiral array …
Regards,
Jan
Hi Jan,
Thanks for the reply, at the moment I’d be using using 1 of the outputs, hooked up to an SSR that would switch the 240VAC side of a 12VDC power supply (powering garden led lights).
Check the data sheet of your relay. It will tell what the control voltage range is and what a typical input current at a voltage within that range is.
If that input current does not exceed 50mA, you would connect the relay just like a mechanical one to the K8055. The + of the SSD’s control input to a power source within the control voltage range, the - of the SSD’s control input to a K8055 output and the GND of the K8055 to the GND of the power source.
Regards,
Jan
Thanks the SSR specs are below.
Load Current: 40A
Load Voltage: 24-480V AC
Control Voltage: 3-32V DC
Control Current: 3-25mA DC
On Voltage: ≤1.5VDC
Off Leakage Current: ≤2mA
On-off Time: ≤10mS
Dielectric Strength: 2500VAC
Insulation Resistance : 1000M ohm/500VDC
Ambient Temperature.: -30℃～75℃
Working indicators: LED
Certification: CE
SSR of course (just noticed I wrote SSD all over that post …).
Looks good to me. The K8055 should have no problem controlling that SSR. Connect it like you would connect a mechanical relay. Just mind the polarity of the control inputs. A mechanical relay doesn’t have polarity on the coil, but an SSR obviously has that on the control input since it is usually implemented as an opto-coupler or FET based circuit.
With the SSR only needing that little current, you should be able to drive at least one from the +5V USB power available on the K8055 itself.
No worries I knew what you meant.
I’m thinking for future use where I may use more then one SSR, I’ll supply 12vDC to the clamp terminal and hook the + side of the SSR to that with a 1K resistor between.
Was playing around with it yesterday, the screw down terminal on the GND near the CLAMP is buggered, it wont open or close. Can I use any of the other GND points on the board instead? If not I may just solder a wire to the board where the broken GND screw terminal is.
Cheers
[quote]Can I use any of the other GND points on the board instead?[/quote]Yes, you can. All GND terminals are internally connected together.
Perfect thanks!
