20-11-2018, 03:38 PM
Andy, I left something out of my previous post that will be important to you if you build something using these valves in a series heater chain.
In a parallel heater chain, all valves receive the same heater voltage at switch on, irrespective of how long they take for the heater to reach its operating temperature. Because the resistance is initially lower at switch on, the current will be higher than specified, but the manufacturer will have factored this into the valve design so that no surge limiting is required.
In a series heater chain, however, it is the voltage, rather than the current that is split between the valves, so there may be just one valve that gets to its operating temperature quickly and several that take much longer.
Because these slower valves have, in total, a much lower resistance, the voltage drop will be much lower so that the fast heat-up valve(s) get a much higher share of the voltage drop than is good for them.
To negate this problem, a thermistor is placed in series with the valves which slows down the process because its initial high resistance allows only a small current to flow but, as it gets hot, its resistance reduces and continues to do so until it has reached its final operating temperature. This causes the heating up process to be slowed down and slowly speeded up which makes all of the valves much friendlier to their neighbours.
I hope that makes sense to you.
In a parallel heater chain, all valves receive the same heater voltage at switch on, irrespective of how long they take for the heater to reach its operating temperature. Because the resistance is initially lower at switch on, the current will be higher than specified, but the manufacturer will have factored this into the valve design so that no surge limiting is required.
In a series heater chain, however, it is the voltage, rather than the current that is split between the valves, so there may be just one valve that gets to its operating temperature quickly and several that take much longer.
Because these slower valves have, in total, a much lower resistance, the voltage drop will be much lower so that the fast heat-up valve(s) get a much higher share of the voltage drop than is good for them.
To negate this problem, a thermistor is placed in series with the valves which slows down the process because its initial high resistance allows only a small current to flow but, as it gets hot, its resistance reduces and continues to do so until it has reached its final operating temperature. This causes the heating up process to be slowed down and slowly speeded up which makes all of the valves much friendlier to their neighbours.
I hope that makes sense to you.
