Problems with new DIY OTG build

This Forum is about the Opentherm gateway (OTG) from Schelte

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Problems with new DIY OTG build

Postby tapgrove » Sat Feb 18, 2017 4:10 pm

Hi - hoping someone can help please with my issues..
I have built a new gateway, and am running through the diagnostics checks - between pins 5 and 14 of IC1 I am seeing around 6.9v though, instead of the 5v suggested. I can see this is reading off the 6.9 ish v between pins 2 and 3 of the 7805 voltage reg (IC3). IC3 shows very close to 24v on the input (pin1-2).
I have L7805CV as the IC3 part - having done a quick search I think there's some suggestions this may not be suitable? can anyone confirm this please? and let me know if there's anything else I can check to see where the issue lies.
I have double checked all the resistors, and did also check the diode's which all looked correct.

Thanks
JOnathan
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Re: Problems with new DIY OTG build

Postby tapgrove » Sat Feb 18, 2017 6:06 pm

I've now fixed this with a new 7805 and get 5v..but..
When I step further through the diagnostics, I get ok measurements for current and voltage on X1 in the first set of tests, but when I put in the OK1 and connect X1 to X2 I get about 26v on X2, and no change in this when I connect pin2 on IC1 to VDD as instructed - it just stays the same.

Any ideas anyone?
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Re: Problems with new DIY OTG build

Postby hvxl » Thu Feb 23, 2017 1:24 pm

There's something very wrong in the master interface of the OTGW. Check that diodes D5-D8 are placed in the correct orientation. Verify that Q1 is a PNP transistor (BC558 or equivalent). Measure the voltages across D9, D10, D11, R1, R2, and R3.
Schelte
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Re: Problems with new DIY OTG build

Postby tapgrove » Mon Feb 27, 2017 6:39 pm

Hi - Thanks for taking the time to reply. I've checked the diode orientation and all looks ok , as does q1 which is a bc558. I get a couple of mv across d9, 170mv across d10 and 340mv across d11 . I get nothing across any of the three resistors r1,r2,r3.
This is all with ok1 installed but ic1 removed.

Any ideas where I might focus investigations? Thanks Jonathan
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Re: Problems with new DIY OTG build

Postby hvxl » Mon Feb 27, 2017 11:58 pm

So, you have 26V on X2, but (close to) nothing across D10 + R3. Then there must be a problem with or near D5-D8. Try swapping the wires to X2. So if you had X1-1 to X2-1 and X1-2 to X2-2 (which uses D6 and D7), try X1-1 to X2-2 and X1-2 to X2-1 (uses D5 and D8).

If that doesn't help, power down the gateway and using the schematic to check the connectivity between the components of the master interface. So check that X2-1 connects to the anode of D8. Then the cathode of D8 to R3, the other side of R3 to the cathode of D10, the anode of D10 to the anode of D5, and the cathode of D5 to X2-2. Somewhere along that path you should find a broken connection.
Schelte
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Re: Problems with new DIY OTG build

Postby tapgrove » Tue Feb 28, 2017 9:21 pm

Appreciate the help with this.
I've stepped through the circuit schematic and as you suggested there was a break - the cathode's of D5/D6 appear to not have been connected through to the cathodes of D10/D11. I've bridged these together and all the checks work out fine now from what I can see, and all the voltages are within the ranges spec'd in the troubleshooting guide. Not had chance to plug this into my heating circuit yet but will give it a go in the next few days and hopefully it will work out fine.

Thanks again for the help.
Jonathan
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Re: Problems with new DIY OTG build

Postby tapgrove » Thu Mar 02, 2017 9:33 pm

Just to report back that I hooked this up earlier to a raspberry pi and all working good..guess it's onto the next bit of my project which I may need to come back for help with at some point!
The reason I wanted to set this up was to try and diagnose and get working my OPentherm setup with a Valiant boiler and a Nest thermostat.
All works well for heating in this setup with opentherm enabled between these devices, but the system doesn't work for hot water unfortunately.
What appears to happen is that the Nest triggers a change to the DHW enable setting via. opentherm, and sets the DHW temperature correctly, but the boiler never fires..
In my setup the boiler is expecting the control set point - i.e. the same flow temperature used for heating control via opentherm, to be set for hot water since there's only one circuit (and the relevant CH zone and HW is then controlled off this via a set of valves).
So what I'm looking to do is everytime the HW enabled status is changed, I'd like to change the control point to a fixed value - e.g. 65 degrees, and then when the HW status goes back to disabled, let the control point drop back to control via. the Nest to whatever it would have been otherwise.
I'm thinking I could do this via. a cronjob, which simply sets the control point temperature to 65 degrees at the same times I've set the Nest to schedule HW to come on, and having tested this it looks like it would work, but this doesn't seem to robust, and wouldn't work if I did a manual / override of the HW.
Would there be a way of doing this sort of control internally within the opentherm gateway perhaps somehow?
I've read the manuals on the gateway, and these seem to be suggesting I'd have to do the control within an external program on the PC the g/w was interconnected to?
I guess another way of setting the logic statement would be that I could set the heating temp set point to e.g. 70 degrees, and leave the max htg control point at less than this - e.g. 68 degrees, and then have a logic statement such as e.g. IF HW set point > HTG control point, then HTG control point = HW control point which was regularly checked and this would seem to work for all scenarios I can think of?

Jonathan
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