some EE, Ham or electronic whiz must have some knowledge on diy remote?

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Forum topic by REO posted 03-06-2013 04:11 PM 1083 views 0 times favorited 12 replies Add to Favorites Watch
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928 posts in 2102 days

03-06-2013 04:11 PM

Topic tags/keywords: resource question diy remote dc switch auto dc switch

I have seen several posts on those who want an automatic or remote start for their DC. There must be someone electronic savy that can come up with a diy circuit for sensing the load on a line and using that for a switch to turn on the dc. A post run timer should be a breeze as well. I have seen a GFI outlet conversion but it is not for someone who knows little about electrical components and it was manufacturer model specific. Come on you electron smart folks what are the options?

12 replies so far

View Ripthorn's profile


1458 posts in 3013 days

#1 posted 03-06-2013 04:38 PM

For someone good with electronics and MCU that is programmed the right way could easily do just about everything. Of course, you would have to make sure you have the proper protections, and load (current) sensing inherently means you have to be in the circuit, so some design considerations have to be taken in to account there. For someone with the development board and an MCU, etc. it would be relatively inexpensive, but to buy the stuff to get up and started would not be super cheap.

Remote start is really easy, especially if just a one button remote for on/off. Again, requires the use of an MCU and infrared transceiver set.

-- Brian T. - Exact science is not an exact science

View Mosquito's profile


9355 posts in 2320 days

#2 posted 03-06-2013 04:45 PM

View Dan Lyke's profile

Dan Lyke

1520 posts in 4153 days

#3 posted 03-06-2013 05:05 PM

I haven’t done this, but… I’d consider a current transformer (ie: a couple of turns of wire around one leg of your power circuit) through a resistor. Measure the voltage drop across that resistor (or pair of resistors), I’d use a microcontroller ‘cause I’m a software guy, switch a transistor which drives a 20A relay (or buy someone’s TTL to 20A relay board).

Heck, thinking about this a little further…

Current transformer using a couple of turns through a current limiting resistor. Use a zener diode and a small resistor to limit voltage across the rest of the circuit, and in parallel run the other leg through the feed which switches the relay.

You could do all of the calculations yourself, or you could break out the parts box and a volt meter and just start playing. Be careful, you probably won’t generate a lot of current with that current transformer, but you could generate a lot of voltage. I’d start with like 2 or 3 turns around your feed leg, a 1k Ohm resistor, see what voltage you get with some known load (a 100 watt incandescent? 2 of ‘em?). Then scale up (or down) that resistor appropriately. If you can’t draw enough current to switch the relay, increase the number of turns and re-adjust any resistors.

-- Dan Lyke, Petaluma California,

View Hammerthumb's profile


2853 posts in 2003 days

#4 posted 03-06-2013 10:12 PM

Dan Lyke – I think you are on the right track with the system you described, but I think I would use the signal voltage developed by the current transformer to bias a transistor that is in series with a relay coil. I think this would be more effective than trying to use the signal voltage off the current transformer.


-- Paul, Las Vegas

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Dan Lyke

1520 posts in 4153 days

#5 posted 03-06-2013 10:21 PM

Yes, I think I mis-typed: You probably don’t want to drive the relay directly, you want a signal boost in there somewhere. Requires an external power supply, but easier for us software geeks to wire together.

-- Dan Lyke, Petaluma California,

View Hammerthumb's profile


2853 posts in 2003 days

#6 posted 03-06-2013 10:30 PM

I’ve built similar circuits for RF sensing. I don’t think it would be a problem with a few diodes, resistors, and a small transistor that is capable of handling the curent to run the relay.

-- Paul, Las Vegas

View REO's profile


928 posts in 2102 days

#7 posted 03-06-2013 11:04 PM

silid state relays are easy to find and cheap. what kind of simple down and dirty circuit does it take to turn one on.
Mosquito: these are not cheap over 50.00 plus shipping to start for something less than 1 hp. most DC systems are at least 2 hp. so it would require an additional relay anyway an additional 90+ to purchase from the same company.
Dan I think your on the right track. CT’s can create some terrifically high voltage though.

View woodbutcherbynight's profile


4883 posts in 2437 days

#8 posted 03-06-2013 11:07 PM

I think I will just turn the shop vac on by the switch and be happy about it. (laughing)

-- Live to tell the stories, they sound better that way.

View Dan Lyke's profile

Dan Lyke

1520 posts in 4153 days

#9 posted 03-06-2013 11:26 PM

A quick search reveals that other people have already figured out the current transformer thing: DigiKey has a whole bunch of current sensor options.

As REO points out there are any number of solid state relays out there, although you probably want to switch a reasonable amount of current which may put you back into mechanical relay plus a resistor, transistor and diode (to keep the inductive kick from the relay coil from blowing out the transistor) territory.

I’m a wuss, so I’d use a microcontroller like one of the Atmel AVR devices to measure the output of the current sensor on an A/D pin and make a decision on turning on or off the relay, but a little thinking should be able to come up with a solution that switches the whole thing through analog circuitry.

-- Dan Lyke, Petaluma California,

View KyleU's profile


2 posts in 2091 days

#10 posted 03-07-2013 02:15 AM

I used a Christmas light remote control unit that I bought for a couple of dollars in an after Christmas clearance sale. It is the type that switches a unit that plugs into an outlet. I wired a single pole relay into the switched outlet, and used the relay to start the DC. Less than $20 for the remote and the relay. The remote came with 3 of the switchable outlets so I have 2 left over for another project.

Works great from anywhere in my shop (24×32 ft). I attached it to a small clip so I can hang it on a belt loop and always have it handy.

View Craftsman70's profile


244 posts in 2153 days

#11 posted 03-07-2013 02:50 AM

I’ll second the Christmas light remote. I picked one up at Lowes in December for about $10. You have to watch because HD and Lowes both had them but one was rated 9amp and the other 14amp. Might as well go with the 14.

View kizerpea's profile


774 posts in 2395 days

#12 posted 03-07-2013 02:38 PM

thats what i did ..lowes bought the remote for a ceiling fan $20….220 volt contactor with a 110 volt coil from the electrical supply house..$30..the remote operates the 110 volt coil that closes the 220 volt contact..easy pezy…


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