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Old 08-16-13, 07:29 PM   #21
Mikesolar
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Hallowell is gone, partly because they made modifications to the comps that were not supported by Bristol and they had big warranty issus.

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Old 08-18-13, 05:52 AM   #22
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Default Controllers

As I now have 3 heat pumps I needed to design and build a control system for them.

After much brainstorming I decided to build a controller for each unit that is autonomous but connected to a central controller. This allows the individual unit to perform its own defrost if necessary. The main controller can send commands to the unit to switch them on and off and to force a defrost cycle if necessary (well why not!). Also each unit can be interrogated to report its status back to the main controller. Each unit has it's own address so can be individually controlled.

Each controller also has a manual override just in case! Also the units save their last operating mode (on or off) so will re-start in event of a power failure.

The control is implemented on an RS485 bus, this allows all the units to be connected to the same two wires and for each to listen for commands from the main controller. It also means the units will not conflict with each other when transmitting data as they are in a high impedance state when not actively transmitting.

I've built one of the controllers (pictures below before mounting in the machine) and am working on the main controller.

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Old 08-18-13, 03:19 PM   #23
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Quote:
Originally Posted by Acuario View Post
...I decided to build a controller for each unit that is autonomous but connected to a central controller. This allows the individual unit to perform its own defrost if necessary. The main controller can send commands to the unit to switch them on and off and to force a defrost cycle if necessary (well why not!). Also each unit can be interrogated to report its status back to the main controller. Each unit has it's own address so can be individually controlled...
Acuario, this is very interesting stuff...

Have you built your own custon controller? Are you using some kind of Arduino-ish controller that you have programmed?

Could you share more details? I have a heat pump (non-inverter) that will be needing something just like what you have here.

* * *

Also, did you ever triumph over the inverter unit that you were trying to crack?

I was hoping that you'd be successful.

Best,

-AC
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Old 08-18-13, 04:56 PM   #24
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It's a totally custom controller. The individual machine controller uses a pic 16F628A built on a pcb that I designed and the main controller has a 16F877 built on a pic board I bought off ebay. I'll upload schematics etc. when everything is finished. I currently have the controller and main controller talking to each other successfully over RS485, I now need to finish off the main controller and decide on its functions then install everything.

The inverter is on hold at the moment. I'm keen to move it forward but I'm still trying to decide what pic platform to use and how to move forward. It's not an abandoned project, just a delayed one. Necessity dictates the path at the moment as I need to be prepared for winter so it's a matter of the path of least resistance.

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Old 08-19-13, 09:32 PM   #25
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It's a totally custom controller. The individual machine controller uses a pic 16F628A built on a pcb that I designed and the main controller has a 16F877 built on a pic board I bought off ebay.
It uses a PIC..? I'm not so familiar with that, it is somehow comparable to the Arduino?

Also, I'm curious about how you contend with defrost? I would guess that you have a thermistor situated in the coils somewhere near the place where you have observed frost forming, and when it gets to some level that would indicate that frost is actually forming, your PIC executes a routine wherein it changes the state of the reversing valve, thus effectively reversing the positions of evaporator and condenser, and directs hot refrigerant into the frosted evaporator for a duration of maybe a minute, after which it restores the state of the reversing valve, and re-commences normal operation... did I get close?

Also, since my ASHP's mystery controller card is totally holding me up, could I persuade you to sell me one of your cards?

By the way, I did find someone who is working on a Panasonic mini-split and they posted some code HERE, possibly it could be useful to you in your quest to slay the Inverter Dragon.

Best,

-AC
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Old 08-20-13, 12:03 AM   #26
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I guess you could call PICs and Arduinos cousins - they are both widely used by hobbyists as they are cheap and the development tools are not expensive. Microchip Technology Inc is where you'll find the info.

The pic I'm using (PIC 16F628A) doesn't have an ADC input so I'm using a Dallas DS18B20 1-wire digital thermometer. The plan being to use the same method as on the defrost circuit I designed previously; i.e. the thermometer is positioned on the back of the machine next to the evaporator and monitors the temperature. When the temperature falls to around zero it triggers a defrost cycle turning of/on compressor and reversing valve as necessary.

There's a bit of fine tuning to be done to the defrost cycle, my biggest problem is the lack of days when the temperature falls sufficiently low to be able to test - I think last winter it was only 2 or 3 mornings at most. I have to test by putting the thermometer in the freezer. It does work fine but I prefer live testing.

When the card is fully debugged I'd be happy to sell you one. As you only have a single unit o control you could use it with an RS232 interface instead of an RS485 although both are readily available on ebay. If I remember correctly, doesn't your unit have a crank case heater as well? I guess you'd need to control this too.

Thanks for the link to the Panasonic control but they are simulating a remote control rather than controlling the machine directly.

Acuario

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Old 08-20-13, 09:08 PM   #27
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PIC is far more diverse than Arduino. You can get them in little 6 pin packages the size of ants to 100+pin 32 bit processors. The trade off is that they're much more difficult to work with than the Arduino so I wouldn't exactly recommend them for absolute beginners.
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Old 08-21-13, 01:24 AM   #28
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The trade off is that they're much more difficult to work with than the Arduino so I wouldn't exactly recommend them for absolute beginners.
Not sure I would agree - I think the range of the family of pics is amazing as you say. Microchip provide a free development ide for assembler or C and other companies produce BASIC compilers for those who don't fancy assembler or C.

There are tutorials for both processors and many examples on the web. I've never used an Arduino but from what I see it seems to be more expensive than pics and there is a lack of ICE tools for debugging.

I'll stick with the pics.
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Old 08-23-13, 01:11 PM   #29
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Here are pictures of the twin controller for the two units and the master controller for the whole system.

The controllers have several functions all operated by sending serial commands to the individual controller. The controllers also report back their status when any event occurs (such as temperature change or going into defrost) and this is then displayed on the master controller.

The functions allow for the unit to be switched on and off, set to operate in cool or heat, force a defrost cycle and interrogate the unit status. Each one also has an override switch that will force the unit into heating mode (whilst retaining the defrost cycle if required).

All the commands are sent from the master controller. The temperature of the water tank is displayed on the top line (after the time), followed by the unit that is being sent commands (the number in brackets).

Each unit (1,2,3) displays its status (on/off) mode C(ool)/H(eat) and the temperature of the evaporator.

Next job - install the controllers in the external unit, fit a decent keyboard and build the master controller into its box.
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Old 08-23-13, 07:50 PM   #30
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Not sure I would agree - I think the range of the family of pics is amazing as you say. Microchip provide a free development ide for assembler or C and other companies produce BASIC compilers for those who don't fancy assembler or C.

There are tutorials for both processors and many examples on the web. I've never used an Arduino but from what I see it seems to be more expensive than pics and there is a lack of ICE tools for debugging.

I'll stick with the pics.
If you're good with PIC, stick with it. What Arduino is good at is simplifying the initialization of various peripherals. Rather than write to individual registers, just load a library and the registers are taken care of behind the scenes.

MPLABX is great. It's just quite a bit slower and more complex than the Arduino IDE, but that's not surprising once you consider how many more devices it has to support.

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