# Differential controller



## woodsy (Oct 13, 2008)

After almost 5 years of trouble free use i think my solar water heater controller 
may have a blown fuse and can't find any instructions how to access 
it anywhere , including the owner manual. It did come with a spare under the cover. The fuse seems to be hidden behind the circuit board and not easily accessible .

Anyone have any experience in changing the fuse on a 
SunEarth Aeca TR 301 u model.

Do i really need a specialist to replace a fuse in this controller ? The manual
suggests i do, sheesh.

Oh, the back light is on but the pump won't run .


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## a'ightthen (Mar 17, 2012)

No experience but got curious while passing thru.

You mention replacing the fuse but not being able to locate it. Apparently Littelfuse
215.004 is a part number but figure 4.4.3 ( online manual) shows that perhaps it is a standard cartridge type fuse that should not be too hard to locate ( changing/accessing may be different).

Ye say that the back light is on but section 9 ( manual) says that if the display is blank, check the fuse. No schematic found so do not know if the lighting is pre or post fuse ... however, no mention is made differing blank from other colors that it may show ... keep reading the faults.

9.2 mentions testing the sensors but does not really say why. Apparently these are RTDs and require 1k resistors ... either which could be bad or have a loose connection.

Typically, one would expect these conditions to result in an "upscale burnout" condition ... when heating and they go out, heat is turned off ... I would suspect that this situation would warrant the pump running ( to prevent excess pressure and/or freezing) but who knows.

Anything else on the display? The lights being on leads me to think that ...
Perhaps a sensor/resistor has gone out or lost connectivity ... and the controller is simply "lost" due to poor configuration.

Could be that the light is wired ahead of the fuse ... but not really logical.

4.4.3 also shows a terminal labeled "R1" ... might be "relay 1" and that has gone bad.

9.2 shows typical resistance readings and that is where I would start. Anything else on the display? The manual seems to cover several possibilities


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## woodsy (Oct 13, 2008)

Display is normal, no short circuit symbol or warning display appears.

I found it wasn't working when i turned it on manually to circulate water 
through the wood stove. 

Tomorrow when the sun shines i will see if it works on auto for the solar side.

The pump symbol rotates on the screen when in the manual on position but the pump is not actually running.


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## woodsy (Oct 13, 2008)

Had a spare cartridge for the Taco 006 circulator pump so changed it out and
everything works now. Not what i would have expected but an easy fix.


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## a'ightthen (Mar 17, 2012)

Again, interesting. Did not sound like a blown fuse.

The other info "The pump symbol rotates on the screen when in the manual on position but the pump is not actually running." would have been helpful ... in knowing that the controller was functional but the pump was not running. Would bring it down to R1 ( controller output) being bad ... or the pump.

Would be interested in seeing a pic and the final issue ... specs of that pump ( "cartridge circulator") shows that it has both a capacitor that could have gone bad or a ceramic shaft that could have broken ( among other things).

Just thinking along the lines that a simple flow switch could have been incorporated into the system for better diagnostics .... "Hey, I have sent power to the pump motor but water ain't moving ... check the pump/filters". Seems logical enough for a better end user experience than that which ye have described.


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## Virgil (Sep 29, 2009)

Reading through the general operational description for this pump controller the 120 vac output to the water pump is fused... This is a single channel output system... The fuse is there to protected the 120 vac wiring which feeds power to the motor pump... It protects only the 120 vac side of circuit... 

With no available online schematic to view... it is assumed that the controller's single dc output signal operates the low voltage side of the coil within the relay... If the controller does use a mechanically operated relay for this purpose you might be able to hear a faint audio click as it is turned off and on by the controller... However, it is possible for the 120 vac output of a controller to be completely solid state using SCR devices... Those devices would be silent in operation... However, it seems not to be the situation in this case... Relay contacts are useable up to a predetermined current/horsepower rating... Never exceed those current ratings... 

The important point in this situation, as it seems, without any feedback loop indicating otherwise to the controller, it assumed the pump was energized and operating normally...It had done it's job as a differential temperature device... This is referred to as operating in the blind... That is why the controller showed a rotating water pump symbol on it's display... despite the fact the pump was not operating... This is not an unusual circuit design for lower priced controllers... 

To help in future troubleshooting a simple 120 vac low wattage (4 watts...etc..) plug in night light could be wired, via a 120vac receptacle, in parallel with the motor... Therefore, a lighted visual indication would at least verify that the controller is outputting voltage to the motor end of the circuit... I have an old analog 120 vac clock plugged into the motor end of my hot water solar system.... It shows at a glance not only that the circulator pump should be on when it is supposed to be, but also gives me the actual pump run time that I log down on each solar gain day.... 

Hope this FYI helps in the future... Virgil...


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## SolarGary (Sep 8, 2005)

woodsy said:


> After almost 5 years of trouble free use i think my solar water heater controller
> may have a blown fuse and can't find any instructions how to access
> it anywhere , including the owner manual. It did come with a spare under the cover. The fuse seems to be hidden behind the circuit board and not easily accessible .
> 
> ...


Hi Woodsy,
I think that the controller is a Steca (not an Aeca).
If you google for Steca 301U there are some downloadable operating manuals around.
Steca makes the controller and SunEarth adds their logo and sells them.

I had one just like it before the pump relay on it failed.

I'm looking at the defunct circuit board now:
- It does have a relay (on mine the relay stuck closed)
- There is no replaceable fuse on the circuit board. I did not save all the parts, so there may be one somewhere else, but I don't think so.

If you think you can use any of the left over parts from mine, just PM me and I'll send them.

If you conclude its not repairable, then I'd think about the sr208C -- this is a China import and is sold under several names -- googling sr208c brings up some of them.
Joe Hennesy at sun-pump.com is one of them.

They run about $100 with shipping. They have pretty much all the bells and whistles the Steca has.

I've got two of them and have no problems at all with them.

Edit: Oops! did not notice that you already fixed it.

Gary


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## woodsy (Oct 13, 2008)

Thanks for the input everyone. 
1st time i've had do do any troubleshooting on the system and am more mechanical 
than electronic minded. 

I learned some from the breakdown though the replies here so will be better equipped to deal with 
future issues maybe.

Thanks for the spare parts offer Gary , should be all set now.

Think I've become addicted to solar hot water over the past 5 years. 
Having it not working all of a sudden put me in panic mode.


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## Virgil (Sep 29, 2009)

SolarGary said:


> Steca makes the controller and SunEarth adds their logo and sells them.
> 
> I had one just like it before the pump relay on it failed.
> 
> ...


I am rather curious Gary about the failed pump relay on the PCB.... I assume it is a small relay box mounted directly on the circuit board... If so,,, that is a real bummer... I wonder if the manufacturer is using small signal relays with insufficient current rating for a motor circuit... Even a small universal motor can spike three or four times it's normal running current draw while starting under an static load... 

I don't know if it is possible on this forum,,,but could you post a picture of this relay...??? 

On the in-house differential temperature controllers I have made I always use plug in socket Potter Blumfield or equivalent relays for the final drivers to the motor/pump... Steady state running current draw for the brass Taco 009 on our small system is about 1.5 to 1.8 amperes... Our system is like yours... a fresh water full pump up with gravity drain back... Maximum head distance for us is about 22 feet... The current relay contact ratings are no less than 8 amperes... And have had no problem with that design thus far... About four years in operation... 

I have another question about the sensors used on these SunEarth controllers ...but,, I will put that on another posting... 

Virgil...


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## SolarGary (Sep 8, 2005)

Hi Virgil,

I put a picture of the controller board here: http://www.builditsolar.com/Tests/Steca.htm

It does use a circuit board mounted relay.

At the time the contacts were welded together, I was using a 15 watt DC pump that was plugged into a wallwart type of 12 VDC supply, which in turn was connected to the 120VAC contacts on the Steca for the pump. So, when the controller switched the pump contacts on via its relay, this powered up the wallwart which powered up the pump. 

This seems a bit of an odd arrangement, but it does give the advantage of very low pump power consumption, and the brushless DC motor used on the pump has a long life. I've since had to change to an AC pump because I increased the size of the collector to more than the DC pump could handle.

The explanation from Steca is that the switching type DC power supplies (like my wallwart) have very large starting spikes, and that the starting spike welded the contacts together. The solution was to change to a linear transformer style power supply.

My total differential controller history (on 3 separate solar thermal systems):

- Steca controller failed as described above after a few months (more my fault than theirs -- but a relay with more margin would have been nice)

- Caleffi controller replaced the Steca and has been fine on both DC and AC pumps for several years.

- A Goldline controller bought for the original Solar Shed system failed after about a year. Something internal on the circuit board.

- Two China import SR208C controllers now in use have worked fine -- I think the oldest is about 5 years old.

Gary






Gary


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## Virgil (Sep 29, 2009)

Thanks Gary for posting the picture.... Looking at it ...I think the Hahn labelled component with the the low volt/amp rating of .32 is the units low voltage transformer/rectifier modular in the upper left of the board...(with the visible lettering), Though, Hahn does manufacture a variety of electronic components... 

The small rectangle black box with no visible markings on the lower left side of the circuit board is perhaps,,, the sealed output relay component... If that is it...it's small with very low current handling capabilities... 

The silver metal item in the middle of the PCB was hard to identify as the single picture was taken from directly above.... (no other perceptive picture angles..) Did this unit have tel-communication capabilities...??? Maybe that is a R46 comm port or equivalent external connection point... Though, I may be wrong on that... 

In either case.... due mostly to their physical size none of the modular components visible on this side of board have much power handling capabilities....particularly for a motor starting circuit.... 

If I were to use this type of differential temperature controller I would use the on board output relay to trigger the low voltage coil circuit of an externally mounted mechanical or equivalent solid state relay only.... A protector diode would also be placed across any relay contacts subjected to the reverse voltage inductive kick associated with the sudden release of a DC voltage energized circuit.... This diode would need to be wired in the opposite polarity relative to that of the DC power supply... The point here... is to protect and isolate as much as possible the small on board low power relay from the actual motor starting circuit... 

Years ago a company called Grayhill... if I recall the name correctly... Was an excellent source for all solid state relays... Some of their product lines used optically isolated low voltage to high voltage triggering circuits... Whenever possible I used their relays to replace the older mechanical relays when I worked in industrial electronics and system controls... So that type of low to high voltage..(aka 120vac ) solid state relays would be another good choice in this application of low power motor circuit controls... 

And Grayhill than was American made.... Should Google that company to see if it is still in business... So much of the crap now is China made... smoke and throw away junk...

The company's reason for the welded relay contacts was plausible .... But,,, the relay modular has limited power/current handling capability to begin with... as you had indicated.... 

Added thought... If the DC relay coil terminals are accessible reverse voltage protector diode can be connected directly across these terminals... Which is a better place to hook up the diode,,,but not always feasible.... to help quell the voltage spike as the sudden lost of power and the collapsing DC current produces a magnetic field and resultant induced voltage in the opposite electrical direction... Thermistors,, sometimes referred to as MOV's are sometime useful on the AC side of the circuit to reduce line voltage spikes caused by such relay switching circuits... 

Virgil....


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## SolarGary (Sep 8, 2005)

Virgil said:


> Thanks Gary for posting the picture.... Looking at it ...I think the Hahn labelled component with the the low volt/amp rating of .32 is the units low voltage transformer/rectifier modular in the upper left of the board...(with the visible lettering), Though, Hahn does manufacture a variety of electronic components...
> 
> The small rectangle black box with no visible markings on the lower left side of the circuit board is perhaps,,, the sealed output relay component... If that is it...it's small with very low current handling capabilities...
> 
> ...


Hi Virgil,

I believe that the silver looking component in the middle of the picture is the relay -- it has contacts on the left end and a coil and core under the silver metal.

The manual says its rated for pumps up to 0.5 hp at 120VAC.
The manual also lists a Littlefuse 215.004 which is a 4 amp fuse.
http://www.steca.com/index.php?Stec...26/2610_0x0_Steca_TR0301_U_instruction_EN.pdf

Gary


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## Virgil (Sep 29, 2009)

If I were to use these types of differential temperature controllers at 200 bucks a pop I will stick to my method of isolating the small onboard relay contacts from the switching voltage spikes with an externally connected mechanical relay or solid state devices that I know is capable of handling the motor load current safely...!!!!


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## SolarGary (Sep 8, 2005)

Virgil said:


> If I were to use these types of differential temperature controllers at 200 bucks a pop I will stick to my method of isolating the small onboard relay contacts from the switching voltage spikes with an externally connected mechanical relay or solid state devices that I know is capable of handling the motor load current safely...!!!!


Probably a good way to go -- its funny they don't want to spend the small amount extra it would cost to put a real relay in.

Gary


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## Virgil (Sep 29, 2009)

Yes...Gary I agree wholeheartedly.... The manufacture knows that probably 99 percent of the application of these types of controllers are used for motor circuits... And the repetitive on/off opening of the contacts during current draw load conditions cause voltage spiking which results in arcing and corona carbon tracking across the contacts... 

And DC current circuits are usually worse in that regard... Generally speaking,,, never use AC rated only components such as wall switches on a DC system.... DC is a different animal...It does not want to let go unlike an AC sinusoidal wave form which is actually turning current flow off and on 60 times a second... There are a whole lot of SCR solid state components.... originally development I believe by GE that are referred to as zero voltage crossing devices... They are designed not to switch either on or off until the AC cycle is at the zero voltage point.... Cool devices... 

On a unrelated note... We viewed the video of the Lucy Deep Sand Solar Storage house that was built in Michigan several years ago...(On your Website)... It was very informative... I believe Dale Anderson was the tour guide... Alot of good info there and the techniques applied to that construction has sustained the test of time.... 

Virgil....


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## SolarGary (Sep 8, 2005)

For those who are curious about the video that Virgil mentioned, this is it:
https://www.youtube.com/watch?v=xJz4cKwddBs

Its a dandy. 
A solar home that uses an 8 ft deep sand bed to successfully store heat gathered by solar collectors in the summer and make use of it through a large part of the winter. The heat gathering starts in August and the stored heat lasts into February.

Gary


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