Can this very simple circuit be improved?

Thread Starter

Haverford West

Joined Feb 27, 2019
5
cjcbyS_Haverford West.jpg

I made this circuit for controlling a bunch of haunted house type effects. I simply pulled the circuit boards out of some cheap RC cars, removed the motors, and replaced them with the circuit above. The only other change was to replace the 3XAA battery holder from the cars, with a single 18650. Power for the effects comes from battery packs of 2 or 4 18640 batteries, and the relays have 3v coils and 2A contact current max.
At the time I made these, I had a really hard time finding relays with 3v coils or less, and never found anything with more than 2A contact current. now, I look on Ebay, and see dozens of listings for cheap relays with 10A contacts and 3v coils...dunno what changed there. But #1 Would it be better to use transistors, rather than relays? The noise of the clicking isn't really an issue, but I suppose it potentially could be. The main problem was that, after a short period, the relays would become intermittent and everything would get messed up as the batteries drained to where they could no longer operate the relays. That's why I switched to an 18650 I haven't tested, but it should be more than enough life for what I need, considering that the AAs weren't too far off.
So then I guess the real question is about the little circuit I made to operate a different relay (or none), depending on which way the current formerly meant for the motor, is flowing. Is there a better way? A more efficient way? Did I make some glaring mistake? I never got the idea from anywhere, it just made sense to me to do it that way, but I have virtually no experience in electronics
Edit: One sec. Can't find a free image hosting site that works here
 
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sghioto

Joined Dec 31, 2017
1,038
Is there a better way
Your circuit is OK if you like relays. Sometimes simpler is better.
Transistors or FETs will work and draw less current to switch the relay coils. Component selection determined by the current demands of what needs to be controlled.
SG
 
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AnalogKid

Joined Aug 1, 2013
8,134
On another EE site there is a voting system for questions. Yours would get a -1. There is zero information necessary to answer your question.

How does your system operate now? What comes from the RC board? What is it the relays are switching? Voltage, Current, how often, peak vs steady state power requirements? Also, do you need the isolation provided by relay contacts, or can the load and the control systems share a common ground? Does the control system power have to remain 3 V?

ak
 

Thread Starter

Haverford West

Joined Feb 27, 2019
5
From the board? Just what used to be the output to the drive motor and steering motor. DC at around or a little below the voltage of the power supply for the board. I replaced the drive motor with the circuit above, and did the same with the steering motor, so that a different one of three relays is switched on momentarily, depending on which of the buttons on the controller is depressed. (Forwards, backwards, left, or right) These relays were used to switch power to the effects on and off. The effects were powered by a 6v lead acid battery. Since the only relays I had, had a maximum contact current of 2A, I made sure the current drawn by the effects was below that. I say "effects", because they were all different. But 2 amps was always enough. Some effects using motors, briefly exceeded that by a small amount, but the duration was well under a second. 5A would be more than enough headroom. Not sure if the load and control systems can share a common ground. I don't know what could potentially be a problem with that. Also not entirely sure about control system voltage. I mean...like I said, it's the guts from a cheap RC car. It originally ran off 3Xaaa batteries. I don't know how much higher I could go. I chose 3v relays because it can barely close those with 5v coils. It doesn't have to be 3v. That's just approximately the voltage across where the motors would have been, when the board is powered by a source at approximately the voltage of 3Xaaa batteries
 

sghioto

Joined Dec 31, 2017
1,038
I would try running the entire circuit from the 6 volt battery. I don't see a problem with a common ground. To be safe you could add a 4.5 volt regulator off the 6 volt battery to power the RC electronics.
SG
 

KMoffett

Joined Dec 19, 2007
2,770
I played with tiny ZIPZAP RC cars' controls years ago. After Christmas they were dirt cheap. Some of my adventures might be of use to you.

Ken


ZipZapOutput3.gif ZipZap8ChTransmitters-Receiver.gif ZipZapOutputPicaxe18.gif
 

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