reef-pi :: An opensource reef tank controller based on Raspberry Pi.

theatrus · May 10, 2019

Bigtrout said:
Yes, to put these in an apex and expect the end user to be able to know what types of loads to use is a bit much. Even electrical engineers missed this in designs when PLCs first started using triac outputs.

And to trust an SSR with no datasheet available from china, no thanks.

While im not a fan of the Songle relays used in the ADJ power board and most of the 8 channel relays we use in our builds, the relays are UL listed, and have a datasheet available, they just lack the usable life of a better branded relay, so they work safely just not as long as better quality relays can when switching heavier loads. Then again an 8 channel board can be had for the price of one good relay and base, and are fine for alot of the small equiment used in the average aquarium.

In industrial machinery control panels with tons of relays in them, the vast majority are still electromechanical relays, with SSR relays used for very specific uses and in uses that have been designed by an engineer, and its even more rare to see an SSR deployed in the most important use of all, in safety circuits like emergency stop circuits, etc.

Those Songle/Ningbo relays are a treat in cheap. $0.20 in quantity and this is marketed for the US market (would be cheaper locally).

https://lcsc.com/product-detail/Relays_SRD-12VDC-SL-C_C30431.html The UL file number is real as well. (https://iq.ulprospector.com/en/profile?e=89469)

But I'd much rather buy an Omron relay for anything high power :)

b4tn · May 10, 2019

Very good info, thanks @Bigtrout . I was just getting ready to ask what about the commercial controllers that use SSR's but @theatrus nailed it. I am still in the planning stage of my power strip rebuild and think I will go back to the plan of mechanical relays for everything except for the heater which will be a zero cross 40 amp SSR.

I do have a couple questions regarding my concerns. My wavemakers are DC Gyres that sit on each side of the tank and alternate. Each wave maker is switched on 12 times and off 12 times in a 24 our period. I really wanted to put those on an SSR for extended life but will stick with mechanical. are there any pre made, opto isolated, boards for the high end relays?

I would really like to use PWM to control the Gyres but I really dont want to spend $250 for a pair of interface controllers and I am not smart enough to design my own. Any other ideas for switching them without a mechanical relay? Maybe a mosfet on the DC side? If I recall the power supply is 24 volt 3 amp.

Bigtrout · May 10, 2019

I think a power mosfet would be fine to pwm those...

Dont take my caution wrong, my warning was about indiscriminate use in AC applications with mains power being switched.

Ranjib · May 10, 2019

Bigtrout said:
I think a power mosfet would be fine to pwm those...

Dont take my caution wrong, my warning was about indiscriminate use in AC applications with mains power being switched.

These power heads dont need BLDC/BEMF style drivers? I am very curious which one can work where. I use power mosfets in 12V single led strips only. I know meanwell drivers are popular for constant current usage (like LEDs) , but if I understand correctly we can use power Mosfets as well. I really want to know what the pros and cons of using these interchangeably. In terms of efficiency, safety, heating and convenience (sink/source types).

ps. I am very fortunate to have folks like you, @theatrus here in this thread to guide us through. Thank you again.

b4tn · May 10, 2019

@Ranjib you are correct they need BLDC drivers. Right now I just switch the control box on and off via the AC power supply. What I was talking about was using a mosfet on the DC power side of the controller to turn it on and off.

Bigtrout · May 11, 2019

b4tn said:
@Ranjib you are correct they need BLDC drivers. Right now I just switch the control box on and off via the AC power supply. What I was talking about was using a mosfet on the DC power side of the controller to turn it on and off.

Seek and ye shall find...here is a bldc driver that works from 6 to 50 volts and uses a 0 to 5v pwm signal as input
https://www.amazon.com/gp/aw/d/B072JTB4R8/ref=ox_sc_act_image_1?smid=A2PMIWMSUTAYGS&psc=1

bishoptf · May 11, 2019

Bigtrout said:
Seek and ye shall find...here is a bldc driver that works from 6 to 50 volts and uses a 0 to 5v pwm signal as input

Missing link? eh Nevermind ;)

Bigtrout · May 11, 2019

Tom Bishop said:
Missing link?

:)

Posted before morning coffee kicked in, thumb hit send before link was pasted...fixed!

b4tn · May 11, 2019

Interesting. I will have to look into it. There is another thread

https://www.reef2reef.com/threads/diy-gyre-controller-idea.295784/

I’m curious if this is the same chip from the eBay board in that thread. I’m just knowledgeable enough with electronics to be dangerous (very basic lol) from what I understand they will work and drive the motors but need tuning to be fully efficient. Thanks for the link.

bishoptf · May 11, 2019

Bigtrout said:
Posted before morning coffee kicked in, thumb hit send before link was pasted...fixed!

Understand, btw thats a massive heat sink on that board, wow! 50v, thats starting to get to where you really need to be more careful.

:)

That Crusso Kid · May 11, 2019

Tom Bishop said:
Understand, btw thats a massive heat sink on that board, wow! 50v, thats starting to get to where you really need to be more careful.

:)

Nahhh... only if you stick your tongue on it! It's not the volts but the amps. ;)

dmolavi · May 11, 2019

I've noticed some weirdness in how Adafruit IO displays the ATO "on time". Instead of being in seconds, their graphing engine appears to do some sort of division, so that a 5 or 10 second on time equates to some fraction. It's not consistent, either.

The attached shots show that a 40 second run time got cut down to 1.333 on IO....

Anyone else seeing this, and if so, how can I correct it?

bishoptf · May 11, 2019

crusso1993 said:
Nahhh... only if you stick your tongue on it! It's not the volts but the amps. ;)

Its really both, since our skin normally has a very high resistance, dry skin for the most part, but that is where voltage comes into play. Lower the resistance and increase the voltage and you have a very bad combination. Doesn't take much of either under the right conditions ( ~100ma will stop the heart) but that is why they consider 50V starting to be considered higher voltage.

I found this at some point in time and I think its a very eye opening read - https://www.dribin.org/dave/blog/archives/2003/12/29/amps_vs_volts/

ooh I forgot this one also - https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html

and this one - https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/ohms-law-again/

That Crusso Kid · May 11, 2019

Tom Bishop said:
Its really both, since our skin normally has a very high resistance, dry skin for the most part, but that is where voltage comes into play. Lower the resistance and increase the voltage and you have a very bad combination. Doesn't take much of either under the right conditions ( ~100ma will stop the heart) but that is why they consider 50V starting to be considered higher voltage.

I found this at some point in time and I think its a very eye opening read - https://www.dribin.org/dave/blog/archives/2003/12/29/amps_vs_volts/

ooh I forgot this one also - https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html

:)