Stumped by a 2CH RF relay

[vu2nan]

Hi Yeoman,

Looks like you don't need to add anything after all!

- Nandu.

 

[Yeoman]

Hi Yeoman,

Looks like you don't need to add anything after all!

- Nandu.

Actually, I can’t say that yet. Recall this module is prewired with +/- wire set for each Chanel. Looking at your drawing, if my module was set up as such, I should be able to connect each of the grounds to the motor and cause + current to flow from one of the channels activating the motor, without utilizing the + lead of either channel, but that doesn’t work. Each of my + feeds carries current when its respective channel is activated, but the other + lead does not become a ground when that occurs, hence my problem in running the motor forward and reverse.

 

[Diver300]

Vu2nan’s circuit is what you want, with K1 as one relay and K2 as the other. Wire the coils to the two outputs of the receiver.

Energising one relay will make the motor go forwards. Energising the other will make it go backwards. Energising both together, or neither, will short the motor out, which makes it slow down faster than disconnecting it. Energising both together, or neither, will mean that no current is taken from the supply.

 

[Yeoman]

Vu2nan’s circuit is what you want, with K1 as one relay and K2 as the other. Wire the coils to the two outputs of the receiver.

Energising one relay will make the motor go forwards. Energising the other will make it go backwards. Energising both together, or neither, will short the motor out, which makes it slow down faster than disconnecting it. Energising both together, or neither, will mean that no current is taken from the supply.

Ha, yeah, that’s what I want, but what I have is a hardwired 2CH module, and so far haven’t figured out what’s happening internally. Don’t know if you read all of the descriptions above. Thanks for trying. I have a “free hand” module on the way to set this up, just stumped as to how this prewired module is wired.

 

[Pommie]

Your module probably has MOSFETs doing the switching as that's the easiest (and cheapest) way to do it. Two relays looks like the simplist solution.

Mike.

 

[vu2nan]

Hi Yeoman,

Your unit would be wired like this.

Hence the external relays K1 & K2 would be required. Their coils would need to be connected between Brown & Yellow and Green & Blue. Freewheeling diodes would be required across the coils.

- Nandu.

 

[Nigel Goodwin]

Freewheeling diodes would be required across the coils.

Probably not, the diodes are to protect the driver transistor - as this is driven by relay contacts there shouldn't be any issue requiring the diodes - and they aren't normally fitted across relays switched by smaller relays.

 

[rjenkinsgb]

Probably not, the diodes are to protect the driver transistor

They also prevent contact arcing, burning and RF interference!
They should always be used.

 

[Yeoman]

Hi Yeoman,

Your unit would be wired like this.

View attachment 124479

Hence the external relays K1 & K2 would be required. Their coils would need to be connected between Brown & Yellow and Green & Blue. Freewheeling diodes would be required across the coils.

- Nandu.

I believe you’ve nailed it Nandu! My customizable 2CH module arrives tomorrow. I will wire it up as per your “two negatives to motor feeds” above, and store your last schematic with this module for use another day. Got your beverage of choice on credit.
Thank you.

 

[vu2nan]

Anytime, Yeoman.

Have fun!

- Nandu.

 

[Diver300]

They also prevent contact arcing, burning and RF interference!
They should always be used.

There is a downside to freewheel diodes. They slow down the de-energising of the relay and can therefore increase the arcing of the relay contacts. Some car manufacturers won't allow freewheel diodes for that reason.

There are alternatives.

1) A resistor, about 10 times the resistance of the coil. It keeps the voltage surge down to about 10 times the supply voltage, which should be manageable, at the expense of 10% extra power. Does not matter which way round it is fitted. Many relays have these fitted internally.
2) A resistor and a diode. No extra power, but has to be fitted the right way round.
3) A varistor. Needs to be bi-directional, or has to be fitted with a diode. The surge voltage is well defined, and is constant(ish) so the relay current reduces linearly, not exponentially, so probably the best performance but highest price.

 

[rjenkinsgb]

There are alternatives.

100% agree, we use diodes, R-C snubbers, varistors etc. as appropriate.
I was just trying to keep it brief and avoid topic drift