SSR heat losses

[bagmaker]

so (again laymans thinking, be gentle) would it be the acceleration of electrons causing the heat as opposed to the flow?
Also, surely there isn't much voltage difference between a full battery and a charging panel? If so, why not reduce the voltage at that (final) stage of charging?

[jon_d]

You're delving into quantum physics.

Tradition theory is that electrons travel at the speed of light. However at the instant, the the electons have to travel up the wire. At this mirconic point in time, are they accelerating from zero current flow to full current flow?

Are the electrons being stretched in their little shell? For the point of the argument, I'd say there is no noticeable acceleration heat being generated.

[jon_d]

To Terry's question;

A FET can be considered variable resistor. In the off state, it should approach infinite resistance. In the on state, it should approach zero resistance.

In the middle, (not fully on and not fully off) it's just a resistance. Hence, why Jim's explanation is right.

FET's were and still are used in electronic instruments to switch in and out ranges. Very common in auto ranging voltmeters.

[TassyJim]

Tradition theory is that electrons travel at the speed of light.

The electrical field travels at close to the speed of light depending on the conductor layout but the poor little electrons are actually moving at walking pace.
On a downhill path, I could keep up with them!

If we want to get into the nitty-gritty of switching, the capacitance of the semiconductor has to be considered as well.
When the circuit is made open circuit, there is a flow of current that charges up the capacitor.

I have one of the el-cheapo ebay 'PWM' regulators rated at 30A
The size of the heatsink is laughable. If it really was a PWM controller, I wouldn't need to pack a toaster.
It actually switches on at approx 13 battery volts and hard off at approx 14V so a very slow PWM indeed.

Jim

[grizzzman]

So in reading all this, it appears that a "good" SSR that is over sized will pull less power then a traditional relay of the same rating while on at a steady state?

[bagmaker]

that all being the case then would it be a good ploy to turn on the HWS via a thermostat switch mounted on the SSR heatsink?
https://www.jaycar.com.au/normally-open ... s/p/ST3833
Theory being that the SSR puts out most heat whilst switching at the high end of charge. This heat turns on the HWS, lowering the SOC and SSR switching. As it cools the HWS would be turned off again.
Some positioning of the thermoswitch might be needed to make an accurate "on" point?

[T1 Terry]

that all being the case then would it be a good ploy to turn on the HWS via a thermostat switch mounted on the SSR heatsink?
https://www.jaycar.com.au/normally-open ... s/p/ST3833
Theory being that the SSR puts out most heat whilst switching at the high end of charge. This heat turns on the HWS, lowering the SOC and SSR switching. As it cools the HWS would be turned off again.
Some positioning of the thermoswitch might be needed to make an accurate "on" point?

Love it, why not use the load circuit on the solar regulator to drive the relay that powers the hot water element? Adjust the on voltage to around the end of boost stage voltage and off at say 13.6v, then the excess solar is used to heat the water and the rapid switching is avoided.
The SSR isn't too keen on temps much over 50*C so one of the Jaycar 50*C N/O thermostats mounted under the heatsink just above the SSR and a fan wired through the thermostat. Fan only cycles when the heat sink exceeds 50*C

T1 Terry

[TassyJim]

Cut out the middle-man.
Put a water cooled jacket on the SSR and use it to directly heat the hot water tank.

[T1 Terry]

Cut out the middle-man.
Put a water cooled jacket on the SSR and use it to directly heat the hot water tank.

Electrical cable is easier to run than water hose and a tad safer in the back of the electrical box, but if there was enough high speed switching using cheap SSR's then it would be well worth the added effort. 50*C is plenty warm enough for a shower use the kettle to heat the washing up water if it needs it. The basic idea was to use the excess solar to heat water rather than waste it.
You could make the whole system even more efficient. Run a heat exchanger matt under each solar panel and increase the panel efficiency while heating the water...... but it's getting a tad complex now with pumps and temperature differential flow switching etc, but it would be worth the effort on a house system.

T1 Terry