have been working some 18 hour days but got some time now to bug you all with more questions.
The simulations you depicted above the circuit, a couple of questions please cause I don't think I am reading it correctly.
The plot shows the resistance of the thermistor rising to 14.4k at this point the relay switches of, when the resistance drops to 14k then the relay come back on. So discount the lag in the heating element to get back up to speed the circuit is responding to a swing of about -0°C to +0.6°C. Would you concur with this?
Finally with the thermostat cycling much faster now is is difficult to get the transistor to drive a SCR or suitable device rather than the relay which audibly clicks on and off. Could you point me in the right direction?
could something like this work, it is from Light dimmer circuits.
The variable resistor VR1 controls the dimming, just need to find a way to get the pot substituted for the thermistor. The problem with the thermistor is that the operating range is between 20 to 26k for the the desired temperature range.
Is this kind of circuit a good starting point?
hi Andrew,So how is this for a thought.
a) Complete "chemelec's" 12 to 220V inverter and make it handle ~500W.
b) Make the control circuitry all 220V and instead of using the 12V element only use the 220V element and drive this through the inverter.
Doing the above allows me to run with the freezer as well and will allow for a stop over without the engine running of ~ 90 to 120 minutes. Total element wattage is 335W and assumed 30% losses.
The question is, will the "dirty supply" from the inverter mess with the control circuit?
I can do either to power the circuit, from the battery makes the circuit a little easier?
I guess from this the 'control' circuit will be the therm and comps, OK.
No too sure I follow what you mean?
I was just confirming that we are talking about the same unit.The question is, will the "dirty supply" from the inverter mess with the control circuit?
been out the office for a while. Thanks for all the help once again. OK let me clear my thoughts now, we have been through a few iterations and thought processes and before I get totally confused a few questions please.
a) In order to reduce the element hysteresis do you agree that we employ some form of PWM? If I understand it correctly, no matter how good the comparitor is we will never get more accurate unless we manage to remove the inherent hysteresis in the element. Or am I missing the boat here?
With PWM in order switch 'after' the zero crossing of the phase so that the triac can be triggered anywhere over almost a complete half cycle, some form of ZCD will be required in order to sync the PWM.
b) If yes to a) then would that ASCI circuit I posted be acceptable as a starting point?
I would suggest that the lamp dimmer circuit is not the best option.
c) If yes to b) then you mentioned that the value range of the thermistor would not be a problem. Just as I was getting my head around comparitors a new technology LOL.
Providing the thermistor gives a measurable change of resistance over the tempr ranges you want to cover, I cannot see any problem in using that one.
Just to get some clairity and direction on the next step. Gotta get as much info before you fly out.
hi Andrew,Hi Eric,
So we still get to use the comparitor but instead of the LM393A driving the transistor and in turn the Relay we now effectively insert the MOC3081 and the S102S02 ZCD triacs in place of the tranny and relay? The reason for zero crossing is to avoid nasty transient voltages?
It is so frustrating not understanding electronics, I run a business with three factories, on different sites, emplying 240 people and I swear that is 100X easier than trying to understand electronics. My aptitude is mechanical.
If my assumption above is correct then will have a go at the new schematic.
I have downloaded PSpice in the hope that it will be of some assistance, is it easy to use? (for me that is)