The ground of the separate supply will need to go to ground of the circuit as well (Source of the NFET)

Thanks Ronv, that does the trick and stops the pulsing. However, I need to figure a way to use the same power supply as the circuit as there's no room for 2 power supplies. Should I run two sets of wires from the 2 battery packs one set for the circuit and one set for the receiver?

Any other thoughts appreciated.

Kind regards
Nick

 

What are you using as the +-3V supply? It sounds like the coil current may be pulling the voltage down too far for the circuit to work as designed. What is the coil current (or resistance)?

Hi Alec_t, been experimenting this evening and the current drain appears to be 3.5 amps, tricky to measure though. Ronv suggested I try it with a separate power supply for the receiver which appears to work without pulsing. I just need to figure a way to use the same power source (2 x battery holders each with 2 AAA batteries) for both the circuit and receiver and we're good.

Any further thoughts from you guys greatly appreciated.

Many thanks
Nick

 

Hi Alec_t, been experimenting this evening and the current drain appears to be 3.5 amps, tricky to measure though. Ronv suggested I try it with a separate power supply for the receiver which appears to work without pulsing. I just need to figure a way to use the same power source (2 x battery holders each with 2 AAA batteries) for both the circuit and receiver and we're good.

Any further thoughts from you guys greatly appreciated.

Many thanks
Nick

I'm back to the original thought that the coil resistance is to low for the small batteries.
I think I saw where you said it was 28awg wire, but I didn't see how many inches of feet (meters) of it there are.
If you know the total length we can figure out the resistance or you could try to measure it. But my guess is it may be to low a resistance to measure very accurately.

 

I think 3.5A will drag the volts down significantly if using only AAA cells. You could try decoupling the receiver supply with a diode and capacitor, like this :-

 

I think 3.5A will drag the volts down significantly if using only AAA cells. You could try decoupling the receiver supply with a diode and capacitor, like this :-
View attachment 116617

Hi Alec_t

Just got round to giving this a go as per your schema. Same result unfortunately, when I press and hold the transmitter button the coil pulses in short bursts which counters the reversing effect. If I can just get it to deliver a constant current when pressed and held, job done. Either that or I could look at using two button cells to power the receiver separately I guess, just starts getting a bit complex. Any other thoughts welcomed.

Kind regards
Nick