Fan Control and Trans Control Cct Discussion

[NITROPIXIE]

Just looking at the motor controller http://www.jaycarelectronics.co.uk/prod ... ?ID=KC5225 I can't tell if it sinks 12v to ground, ie controls the motor by grounding, or supplies the motor with 12V. Do you have the instructions to literate on this??

Also it might be advantageous to remotely mount the MOSFETS on a heat sink with their own parallel power supply just to protect the board and the MOSFETS from over heating. Just an air on the side of caution. I wouldn't like to see 20 Amps going thorugh those tracks. You could possibly sink more than 20 Amp with multiples of the MOSFET's if needed.

[NITROPIXIE]

Right the second part of the circuit.

I think i have designed this right. It's been a while since i played around with rc timing circuits but what i have tried to do is to de-complicate the circuit a bit.
Basically what this circuit will do is operate the fan and pump when above 98 deg or over the desired PSI and keep them going for an adjustable set amount of time.

When over 98 deg or set PSI the change over relay (RL1) will switch to its Normally Open (NO) position where there is a regulated voltage. This will do 2 things, firstly charge the capacitor (C1) and second, operate the NPN transistor Q1. Q1 will then in turn operate the relays to control the fan and pump.

Once it is no longer over the 98/psi, RL1 will switch to it's Normally Closed (NC) position. This will complete the RC circuit and this circuit will then keep Q1 closed. In the RC circuit there is a Variable Resistor (VR1) which can be adjusted to change the amount of time the RC circuit takes to discharge and therefore keep the fan and pump operating. The capacitor, once fully charged, of the RC circuit will discharge at a set rate according to the resistance of VR1. Q1 requires a voltage of 0.7V to close/conduct. The time base of the RC circuit to reach 1% of its total value is 5 x resistance x capacitance.

There are some sites if your google RC timing circuits such as http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=31 that are quite helpful.

This circuit will no longer start timing when it fall sbelow 95 degrees but i can't see that being a problem, unless you can.

[37Pickup]

Hi

That makes sense. As you suggest the controller has a similar network to adjust the speed manually, so the two combined would give the required result.
I wasn't sure what was better O/C the O/P of the controller (eg C/O relay) or earthing the O/P (the controller uses Mosfet and O/Ps earth).

The next two O/Ps I have redrawn in relay langauge again and attached, I believe this would work if diodes were not a problem, but an electronic solution could be a little sweeter.

Rob

B always operates first, when b operates it prepares the trigger, and the o/p relay self locks via the timer. When b drops off the timer is trigered and at the end of the timing period breaks the cct to the o/p relay.

If it gets hot enough O/P C operates and also locks via the timer. The fan relay will not release until o/p B drops off.

The diodes prevent the MJLJ from trying to drive the Fan and Pump, the extra diode in the B cct prvents the relay lock up earth from holding up the trigger relay.

[37Pickup]

Whoops just saw your second post. I'll go off and study this.

Rob

[37Pickup]

Hi

The reason I was using 95 and 98 was after searching for some info on electric water pumps extra, I found that the pumps are usually put to full speed 3C before calling for the fan. I guess to reduce noise and the fan may not be needed. So looking at your cct I can't see a problem with having a couple on the board , one for each relay, and using two MJLJ o/ps.

So I will investigate the components and give it a go.

Thanks heaps
Rob

[NITROPIXIE]

Hey Rob

Glad you like the circuits and i hope they help.

For the RL1 Change over relays you could almost use someting like this http://maplin.co.uk/Search.aspx?menuno=12454 as they are mountable onto a pcb along with the rest of the circuit components, which can be very handy and can then power the pump/fan relays. Just for consideration.

[37Pickup]

Thanks again will keep you updated.

Working on some other aspects for the next few weeks then onto this, I'll collect the bits in the meantime.

Regards
Rob