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I am looking for an alternative RC remote on/off switch

PostPosted: Tue Mar 18, 2014 5:34 pm
by leo-rcc
Hi everyone,

Over the years in RC robotics I've used many different RC on/off switches to remotely switch solenoid valves. The best known is the Robbe 1-8445. However, after a while all these have broken down, all due to the relays getting stuck or cracked under the strain of hard landings. I am now looking for a new rc on/off swith, preferably without mechanical relays but something fet based for instance.

This is one of the boards I normally use:
Image

For regular use like in boats or trucks this works fine. But inside our robots even with proper shockmounting they normally don't last more than a year. We normally push 10S lipo @ 5A through that little relay, and they do not like that.

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Fri Mar 21, 2014 7:42 pm
by Ray Perry
Leo,
Those relays appear to be Single Pole Double Throw.
Do they do "Work" in both directions?
If so, you may be able to replace them with an H-Bridge. Perhaps a motor controller chip.

Do you have the part number for the Relays? Maybe there are some more robust replacements.

Ray

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Sat Mar 22, 2014 8:26 pm
by leo-rcc
Hello Ray,

The relays are indeed SPDT, but there are no markings on them. I use them to open and close 2 solenoid valves that in turn work as a pilot for a bigger pneumatic valve. 1 is open when the other is closed and vice versa, so there is no reversal of electrical flow necessary, just 1 fet open 1 fet close.

Best regards,
Leo van Miert

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Sun Mar 23, 2014 12:28 am
by Ray Perry
Leo,
When you have one of these boards fail, do you replace the relays or replace the whole board?
Can you measure the resistance of the larger solenoid valves and tell me what voltage drives them.

Ray

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Sun Mar 23, 2014 9:02 am
by leo-rcc
Ray,

I replace the whole board. I have to check the resistance but the solenoid valves are 36V DC that we power on 10S lipo 37v nominal.

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Mon Mar 24, 2014 9:12 am
by leo-rcc
The resistance of the solenoid is 57 Ohm.

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Tue Mar 25, 2014 2:02 am
by Ray Perry
Leo,
After looking at the info you have sent, and looking at the user's data sheet from Robbe, I've concluded that you are well within the current limits.

37V/57ohms = .65A

However, you are exceeding the voltage rating of 24v.
What is probably getting you is the INDUCTIVE KICKBACK when the relay "OPENS", (i.e., the voltage from the solenoid coil is removed.)
This is easily taken care of by placing a DIODE across the solenoid coil so that the arrow of the diode points toward the POSITIVE voltage applied to the relay.

Without the diode, the voltage can easily reach thousands of volts when power is removed from the solenoid. The diode will limit it to about -38 volts peak.

You would want to pick a diode with at least a 1 amp rating and at least 60v reverse breakdown.

Good luck,

Ray

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Tue Mar 25, 2014 7:48 am
by leo-rcc
Ray,

Thank you for your input on this. I'll give it a shot, those diode's are not that expensive.

Re: I am looking for an alternative RC remote on/off switch

PostPosted: Tue Mar 25, 2014 1:41 pm
by Ray Perry
I forgot to mention that the diode should be fairly fast not just 1N1004.
Look for a shottky diode.

You can mount it on the solenoid or the relay. Because you have screw terms on the relay, I'd put it there.
Just put a volt meter across the relay to determine the polarity (for sure). Things can get ugly if you put it in backward.
Arrow points toward plus (+)

Ray