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I have this connected to a 7100 PID, and I just burned my finger accidentally touching the back metal plate. How hot are these supposed to get? Is mine defective, or is this normal behavior, and I should look into a heat sink?

Thanks.

Hot enough to melt it! You should have a heatsink installed with a SSR over 10A.

Good to know. There was no documentation with the SSR at all, so I didn't know.

I wish I did--I wouldn't have burned my finger!

Marco, this new forum member is the person with whom I'm working... and many other owners of our RV Trailer are interested in installing such a refrigerator control circuit (after we've figured out exactly how to do it). I just looked at the Fotek/Zenli documentation table; they indicate a voltage drop (and resulting heat generation) of about 3V ... which would be about 40 watts of heat generated on this DC-DC SSR, running about 10A of current.

Unfortunately, the voltage reduction also effects the heater output. So, I have a question: If he switches with from the "20A" model to the "40A" model, running it at only 1/4 maximum current, would the voltage drop (and generated heat) within the PID go down? Or is it a nearly constant voltage loss, at about 3VDC for any amount of current below the maximum capacity?

Thanks again! We're almost done

Actually you're talking two different things. The SSR and PID controller. The SSR always have a potential drop as it's built with a Triac, just like two SCR connect in opposite way for AC. The potential drop is not preventable. The PID controller output signal is always 8V (some may be 5V). Regardless which model of SSR you use, the drop is always there and it is constant, as I know

Some info about the SSR: http://en.wikipedia.org/wiki/Relay

In your case, may be a coil type Relay will works better as a coil type relay don't have potential drop at all. It's just On and Off, like a switch

My previous post was entirely about the SSR, and you have answered perfectly.

For our AC-powered refrigerant heater, 3V is perfectly OK. (The heater will still have 97% of it's original power, and the current is only about 1.6 watts). mposner has decided to implement AC only. For those of us with Solar panels, using DC in the middle of nowhere ( ) I will look for an appropriate 12VDC-controlled, 12VDC-load coil relay. That relay's control circuit will be the "load" connection on the current SSR.

All controller built in relay but the max. current handling is 3A only. If you need to control over 3A, you can use the internal relay to drive a bigger relay. The 7100 is just a single display version. All funtionality is the same as the 612.

By the way, when you said you guys in the nowhere when dealing with DC, whay is that?
What kind of heater/cooling do you need? I may have a solution for you folks.

FYI, we're enterering solar business and will carry UL certifed solar panel, power from single cell to 180Watt a piece. But the manufacturer need us to order one cargo which is almost half a million. Ding, it's a lot of money!! However, I do carry solar heater and it's much better than you can find in US market. It's vaccum tube with super heat transfer. So, no water in the glass tube. The efficience is over 74% compare to45% you find those applying on the roof. Also, the my solar can run without water and it will not blow off like the traditional solare heater than need water to be in all time. I'm not sure if RV need a lot of hot water or not. If it does, then may be I find a new market, with you folks help!

Moreover, I'll have my PWM power supply ready soon. It's ideal for motor control and good for HHO system. It can handle up to 120A and both frequency and duty cycle is controllable. It may be cool for solid state peltier(thermo junction). But I got to do more research on how to drive a peltier in better way.

I just came to the same conclusion, finding no coil relays which could be (1) controlled by only 5V and (2) handling load current of 10-12A.

In "recreation camping", using these trailers http://trailmanor.com, we are often far away from 120V "grid" electrical service. The refrigerator works in 3 different ways (propane gas, electrical DC heater, or electrical AC heater). This is NOT a normal refrigerator, built with a compressor. It uses the more primitive "Vapor-Absorption" technology, powered entirely by heat, with no motors or moving parts. (See http://en.wikipedia.org/wiki/Absorption_refrigerator for details.)

Our problem with the refrigerator is the lack of a QUALITY thermostat. There is a rotary dial control which spins from "warmer" to "colder", but it works in two dumb ways-- and neither way knows about the actual temperature inside the refrigerator. The dial is a timer for the two electrical modes- when you spin the dial to "colder", a higher percentage of time is spent with the corresponding electrical heater turned "on". The dial is also directly connected to a propane control needle valve: when propane is selected, gas runs through the valve, and "colder" has the valve more open. (More open = more heat.) Propane never actually turns off, you would have to re-light the burner. But the dial controls the size of flame, and the size is always the same when you have turned the dial to a particular spot.

And so, during the hottest part of the day, the beer and vodka gets too warm. Then, at night when less refrigeration power is needed, everything freezes. The 7100 PID will allow us to simply spin the dial to "maximum cold" whenever DC or AC is being used. On the "hot" wire into each of the heaters, the PID and SSRs disconnect will disconnect the circuit if the temperature ever falls to 34F (one degrees C), and they will close the circuits when the temperature reaches 40F (about 4C.) And in between, of course, the PID performs variable switching to keep the fridge close to our designated target: Right around 2C, maybe 3C.

Parts of the western USA desert have no people, no buildings, and hardly any roads for dozens of kilometers around. In such places, it would be great to use propane at a small flame size (small enough to avoid freezing the fridge contents at any time of the night), and then add 12V heat to "finish" heating the refrigerant coolant. Every bit of propane used saves electricity in the batteries, but the electrical is controllable. Using both, together, is best of all: perfect temperatures, and minimal electric consumption. In "campgrounds" with electrical service, of course, we just use the120VAC plug-in. No propane, no DC. An hour ago, mposner decided that this will be OK from him- he will not be using DC.

But I probably will do the "SSR relay drives the coil relay" on my installation. I'll simply use an un-switched 12VDC power source as the "Load" connection for the SSR, driving a high-power automotive relay. The current on the SSR will be vastly less than one watt, causing no thermal issues within the relay. Thanks!
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Now, for your solar-related questions. Our RV has propane-powered water heater, and (unlike the refrigerator) it has a good thermostat already built in. That will not be interesting to any of us for this purpose. It may be very interesting at our homes but we have no special interest for these RV camping trailers. (If it can withstand freezing on the roof, that would be fantastic!) Solar electrical panels are of great interest to many owners of Trailmanor- and fortunately for you, the factory "option" is too costly and also too small (only 80 watts). Many owners have installed solar, and at 180 watts, you would be exactly on the "sweet spot" for power versus cost and weight. For us, the efficiency would need to be high; unlike houses, surface area and weight from lower efficiency panels is unacceptable on Trailers. The biggest problem for you is: The business is cut-throat, EVERYBODY is trying to get into it, and so the profit margins are turning into sh%#. Shipping of large panels is also a new issue, compared to your current product line. But you know that, I am sure that you are more expert than I about solar electrical systems.

Our solar panel rated 150W to 200W each. The size is about 1mx2m (3.3ft x 6ft). Plus, we can get deep cycled battery as well. But the issue is that we need to order in a quantity lot or the manufacturers are not interested to deal with us. That really discouraged us from starting the solar business. If we don't handle it carefully, it may get us in finiancial problem, especailly nowaday when economic was down and slow.

The panel is we can get is high effecience type and UL certified. It's Monocrystalline. A lot of sellers out there selling same rating, non-UL approved panel but with 20% or less cheaper. But customer don't know that the difference between Monocrystalline silicon vs Polycrystalline & the non-crystal type. It end up that the power output is disappoointed. Well, at least I know that we can target solar to the RV home owner.

How much do they weigh? I'm not really in the market at this time -- we will always camp with AC for the foreseeable future, but nonetheless I like to know my options. I know I'm pushing the limit on weight for my setup, so every little bit of "optional" weight matters.

Thanks for all the other info! I think that by the end of next week I'll have the fridge set up nicely for my needs