need help selecting a solid state relay to connect to my BS2 stamp

damage31

I'm looking to connect a SSR to my BS2 stamp to control a small 120v pump (a Tom Aquatics Aqua-Lifter Dosing Pump specifically). I have a saltwater tank and would like to build an auto top off controller that will replenish the freshwater in the tank as it evaporates.

The specs on the Toms pump I have found on the web indicate it is has a 3watt rating, and uses 34mA from what I can tell. I assume this pump presents an inductive load.

So, I'm wondering if the Sharp 8A Solid State Relay is a good choice for this application? If it isn't, can someone help point me in a better direction?

Part of my concerns at the moment are what appears to be the small current draw of the pump, which I believe could possibly cause the relay to not turn off? Also it appears that this SSR does not include any internal protection within it, thus I'll need to also build a "snubber" circuit (of which I am not familliar at the moment)?

Any thoughts and advise on this matter are appreciated.

coldsprings

If you are looking for simplicity I would recommend a pump that plugs into wall power and then get a SSR that actuates off of 3 to 5 volts dc and can handle up to 110 or 220 VAC.

Mike Green

The easiest thing to do would be to use a standard (electromechanical) relay with contacts rated for 120VAC and 1A or more. You can get them with coil voltages of 5V. You'll need a switching transistor, diode, and a resistor. See Nuts and Volts Volumn #1 Column #6 for schematics and parts suggestions. Everything you'd need is available at RadioShack (here's one relay that would work).

damage31

Thanks Mike, I'll follow that posting you mentioned. Seems simple enough and I can test it tonight.

I was thinking of using solid state relay to keep the parts count down, and also maybe gain long term reliability. I have a bit of a concern about the mechanical relay soldering itself shut in the on position. Although, I have heard that solid state relays also can fail in the on position so I guess that point is mute.

Side note: I'm still interested in experimenting with a solid state relay. Any suggestions on selecting/implementing one are still welcome.

wiresalot

Hello damage31,

I use SSR's on my BS2 to controll 120v, I like the fact there optically isolated.
I use these ones,

http://www.mouser.com/ProductDetail/Crouzet/DROAC/?qs=MufAK3yimRPUAEKcTMTGeA%3D%3D

They require 18ma on the load side, to work but it seems your pump draws more. They come with a 5 amp fuse also (replaceable).

3.7-32 VDC input
12-280VAC output 5Amp


wiresalot

robertsjg1000

Digikey has a huge selection of ssr. I just bought 100 myself. Gonna control the hell out of the Christmas lights.

Try this one for a start. You should stick with the zero cross ones and don't forget the snubber circuit for motor use. The 8A on the Parallax is overkill for your small load (I have 10 of these too, ha, never too much control!).

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=425-2365-5-ND

$WMc%

damage31 wrote: »

Thanks Mike, I'll follow that posting you mentioned. Seems simple enough and I can test it tonight.

I was thinking of using solid state relay to keep the parts count down, and also maybe gain long term reliability. I have a bit of a concern about the mechanical relay soldering itself shut in the on position. Although, I have heard that solid state relays also can fail in the on position so I guess that point is mute.

Side note: I'm still interested in experimenting with a solid state relay. Any suggestions on selecting/implementing one are still welcome.

'
Take a look in the Parallax store for this Item code400-00053 also this Item code27113

damage31

robertsjg1000 thanks for the link, I might try a few of those as they seem super cheap, and if I blow a few up learning its not a big loss. They appear that they might be able to cover what I am looking to do, so long as I can handle the pumps startup and shutdown. My next step is to learn more about snubber circuits.

damage31

Just a quick status update: Thanks to everyone for the assistance, I am now 95% complete on my little project with your help.

For anyone with a saltwater fish tank, my little project is to replicate the Tunze 3155 auto top off device. If I had purchased this off the shelf ATO device that uses the same general process I am using, the cost is normally right at $200+ tax locally. Now, I suppose I could have gone that route...heck, considering my time, it was cheaper. But whats the fun in just buying something when you can build it yourself, as well as learn a ton of stuff about practical application of electronics in the process?

I am building this device to help control the salinity of my little 8 gallon saltwater fish tank. As water evaporates, the switch will detect the loss after a very small level drop, and the stamp will then run the relay to activate the aqua-lifter pump to slowly fill the tank with freshwater to replace the evaporation. Combine this switch with two additional float switches (one for overfill detection as a safety backup cutoff switch, as well as one for low reservoir level detection so i dont run the pump dry) and I've automated a task that would otherwise need to be done manually every day by hand. Now, all I need to do is keep the reservoir level filled up, and I'll be good for a month or more after each refill.

I am in the final stages of the project. Almost ready for a wet test after I do a bit more thinking in one area to make sure I have not overlooked anything.

FYI, I purchased the radio-shack 1 amp relay, and have just now assembled and begun testing of my little aqua-lifter pump controller. So far all is well, and this has been a very enjoyable time for me thus far. So far, my little DIY auto top off has cost ~$80 in parts, and about 8 hours of thinking/assembly/googling. Also, I get to use the basic stamp I had laying around for 10+ years that was doing nothing.

In case anyone is interested, I am using an Anderson Dwyer OLS-12 optical level switch that I bought of of eBay. This switch is the same general style/type of switch that Tunze uses on their 3155 auto top off device for the most part (which is what I am replicating for my personal use DIY style) and this style switch allows for very precise control of a fluid level. This switch needs a minimum of 10volts, so I am using a LM317T to power the switch, and using a 7805 to power the relay coil + stamp.


What's cool is that I can still use the stamp for other things tank related later on as I get time. Temperature control is next on my list of to-do items, as my tank swings +-5 degrees each day, which makes it impossible for me to keep any corals that are sensitive to temperature swings. After I finish this project, my next step is to start reading the PID industrial control process from one of the stamp manuals I know i saw a while ago.