Low amperage NC Mosfet/SSR Solution?

[Bryant Tonkin]

Hi,

I'm finally getting around to connecting my SBMS0 to my Samlex 4024 inverter to disable charging/inverting. An earlier related post suggests that it's a good idea to use a normally closed relay on the Samlex input so charging/inverting is disabled by default in case there's an issue with the signal from the SBMS0. I think I essentially need a normally closed relay but that seems like overkill for the voltage and amperage used on the Samlex input. Do any of you have recommendations for an inexpensive and simple solution? Thanks!

[Dacian Todea]

Bryant,

A normal closed Solid State relay should work great. There is the CPC1705 but should be even smaller SSR if you want. https://www.digikey.com/en/products/detail/ixys-integrated-circuits-division/CPC1705Y/7776155

Output of that will connect directly to your switch and the input will be supplied trough a current limiting resistor say 470Ohm should be a good value with 24V.  So  Battery+ then 470Ohm resistor then EXT IO3+ then EXT IO3- connected to pin 2 of CPC1705 then pin 1 of the CPC1705 will connect to battery negative.

This will work to protect against over-discharge of the battery but it can not work for grid charging and for that you need something like a AC SSR on the AC input line controlled by the EXT IO4 set as type 1

Only the Victron Multiplus as far as I know has separate remote ON/OFF controls.

But I think you should not need to invert the signal on the Samlex 4024. Please check the manual to see what jumpers need to be set to make the Remote ON/OFF connection work properly for ON/OFF control and you should be able to connect the EXT IO3 directly there. The inverter should be OFF by default if you make the correct settings and should only start when the Remote pins are shorted.

  

[Dacian Todea]

Ignore my initial replay. I checked the Samlex 4024 manual and you do not need anything special see page 79 and  6.2.2 the switch type.

So inverter will be in the OFF position you should be able to turn ON the inverter by just shorting the two remote ON/OFF pins.  

[Bryant Tonkin]

Hi Dacian,

It does appear the remote ON/OFF for the inverter functionality can be controlled directly however it's slightly more complicated than just shorting the two ports. The remote on/off actually requires an external 12+ signal to operate.  I found the following post from someone who appears to have sorted most of it out. https://diysolarforum.com/threads/how-to-control-samlex-evo-with-electrodacus-sbms0.10885/ . The  built-in 12v power source is only on when the unit is powered up, but fortunately, when the Remote On/Off is set to switch mode, the stock remote panel can still be used to "jump start" the inverter which in turn activates the 12v output to sustain the on state through the SBMS0. One downside to using the remote on/off input is that the stock remote control panel no longer works to turn the invert off since the inverter is being kept on my the 12v source. A switch will need to be placed between the 12v power source and the remote on/off port to allow the inverter to shut off. It seems silly to have an extra switch just to turn the unit off but that appears to be the simplest option.

I still need to be able to disable charging since the inverter is always on when it's plugged in to AC power, regardless of what the remote on/off is set to. For that I still need a NC SSR to control the Stop input. Thanks for the hint on the CPC1705. It got me headed in the right direction. What do you think of the CPC1219Y? The CPC1219Y appears to accept a 5-12v input signal so it could be controlled using the same 12v power source provided by the inverter. 

If everything works according to plan I'll be able to get by with one switch and one NC SSR. 

[Dacian Todea]

Bryant,

I do not have an account on that forum so I can not see those diagrams but from what I can see it seems he has hacked the inverter internals and controls the internal charging relay directly.

As for inverter control I'm quite sure that remote ON/OFF work it just needs to be setup as switch type (not sure how that is done likely by setting a jumper). The inverter then should be OK and can be turned ON by shorting those two pins likely one of them provides the 12V or whatever voltage is needed for the second pin.

The CPC1705 can accept any voltage you want and all you need to do is limit the current to around 5 to 10mA using just a simple resistor calculated based on your available voltage can be 5 or 12 or even 24V

The CPC1219 is only capable of switching 200mA (may be insufficient to control a relay coil) and the just added a resistor internally on the input.

I will not recommend you modifying the inside of the inverter if you do not understand how the CPC SSR work and the required resistor to limit the current to an LED.