What would you like to see in evohome? (have your say)

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  • DIY2
    Automated Home Jr Member
    • Mar 2019
    • 16

    Originally posted by DorrisMancer View Post
    Because a forward conducting silicon diode will drop about 700mV whereas the voltage drop across a resistor is subject to Ohm's law and will vary with current (and resistance, of course)
    Exactly - so when the motor wants to pull more current, you dont want the resistor droping more volts and resucing the power further.

    Comment

    • DIY2
      Automated Home Jr Member
      • Mar 2019
      • 16

      Hi, Many thanks, I have not really done a video for this stuff before but if a lot of interest is shown I might try and put something together to show how easy it is. cheers

      Comment

      • gordonb3
        Automated Home Ninja
        • Dec 2016
        • 273

        Originally posted by DIY2 View Post
        Exactly - so when the motor wants to pull more current, you dont want the resistor droping more volts and resucing the power further.
        I believe that will actually work the other way around because the motor's internal resistance (impedance) is practically zero in rest. The impedance increases when the motor speeds up because of the magnetic flux created. Thus in theory a serial resistor would make it harder for the motor to start up but have a very reduced effect on the final speed of the motor. I think if you place the resistor in parallel this would not hinder the motor starting but it will reduce it's maximum speed as the current will favour the resistor over the increasing motor impedance more and more. One should be aware though that the resistor might become quite hot, depending on the value required to achieve the desired behaviour, and it will probably consume batteries like crazy.

        Just a thought: instead of regular diodes you could also use LEDs (light emitting diodes). By using two different colours you can make it visible whether the valve is opening or closing.

        Comment

        • DorrisMancer
          Automated Home Guru
          • Nov 2017
          • 129

          Sorry, the resistor suggestion just doesn't make sense. Also, the forward voltage of an LED is significantly more than a silicon diode so what sounds like an attractive idea would not work. The OP's suggestion of a couple of back-back 1N4001s is the way to reduce the voltage across the motor ... but whether that would allow the motor to generate enough torque to operate the valve, especially with an ageing battery or after a summer lay-off, is an open question. The "correct" way to reduce the noise is to improve the mechanics or acoustic damping, but this is rather more difficult.

          Comment

          • blowlamp
            Automated Home Sr Member
            • Apr 2017
            • 98

            Would fitting these diodes result in an increase in battery life by any chance?

            Comment

            • DIY2
              Automated Home Jr Member
              • Mar 2019
              • 16

              Originally posted by blowlamp View Post
              Would fitting these diodes result in an increase in battery life by any chance?
              Unfortunately not, the motor runs slower so also needs to run longer so it will balance out. Not sure at what speed the motor has maximum efficiency but even if it runs slighlty more efficiently it wont make a noticable difference. cheers

              Comment

              • gordonb3
                Automated Home Ninja
                • Dec 2016
                • 273

                Indeed. Don't know what I was thinking. LEDs do in fact have a voltage drop of around 2V (depending on the colour) so that would leave very little to spin the motor.

                @DIY2: so did you try simply replacing the batteries with rechargeable ones? That will also give you the 0.6V drop. Of course in that case this lower voltage would also apply to the electronics and an additional problem is that they don't gradually deteriorate but sort of instantly die, so when (if even) the controller shows you the low battery warning it will already have gone offline.

                Comment

                • DIY2
                  Automated Home Jr Member
                  • Mar 2019
                  • 16

                  Originally posted by gordonb3 View Post
                  Indeed. Don't know what I was thinking. LEDs do in fact have a voltage drop of around 2V (depending on the colour) so that would leave very little to spin the motor.

                  @DIY2: so did you try simply replacing the batteries with rechargeable ones? That will also give you the 0.6V drop. Of course in that case this lower voltage would also apply to the electronics and an additional problem is that they don't gradually deteriorate but sort of instantly die, so when (if even) the controller shows you the low battery warning it will already have gone offline.
                  Hi, no I didnt try that but switching the batteries would work too. I didnt want that route for the reason you have stated plus they dont last the same and I have 11 Rads so dont want the hassle. Also as one of the previous posters has mentioned, by reducing the voltage hence drive power, there is a risk that on a stickier valve operation then you run out of power. They are also correct that if your right on the limit then as the battery voltage drops further near the end of its life, again you might run out of power, although that would be unlucky.
                  With that in mind I wanted to try the current solution and see how it runs - I can always pick different diodes or qty with different voltage drops to tweek it later - but for now seems fine. If I had the time I would drive the motor directly with batteries out, and vary it to characterise where its performance drops off. Im snowed under at the moment so have not been scientific about it so far.

                  If someone else has the time - perhaps they could give it a go?

                  Wish Honeywell had just picked a better motor/gearbox combination.

                  Cheers

                  Comment

                  • DBMandrake
                    Automated Home Legend
                    • Sep 2014
                    • 2361

                    Originally posted by DIY2 View Post
                    Unfortunately not, the motor runs slower so also needs to run longer so it will balance out. Not sure at what speed the motor has maximum efficiency but even if it runs slighlty more efficiently it wont make a noticable difference. cheers
                    I would say battery life would be reduced as it takes (roughly) the same total amount of energy (Joules) to operate the valve whether you do it quickly or slowly, and the voltage drop of the diodes represents power dissipation as heat. Power spent heating up the diodes is power not contributing to operating the valve.

                    How much effect it would have on battery life depends on how much of the total battery consumption is actually turning the motor (vs long term wireless comms, etc) and what proportion of the supply voltage that would normally power the motor is being consumed by the 0.7v drop of the diode...

                    Comment

                    • gordonb3
                      Automated Home Ninja
                      • Dec 2016
                      • 273

                      Originally posted by DBMandrake View Post
                      I would say battery life would be reduced as it takes (roughly) the same total amount of energy (Joules) to operate the valve whether you do it quickly or slowly, and the voltage drop of the diodes represents power dissipation as heat. Power spent heating up the diodes is power not contributing to operating the valve.

                      How much effect it would have on battery life depends on how much of the total battery consumption is actually turning the motor (vs long term wireless comms, etc) and what proportion of the supply voltage that would normally power the motor is being consumed by the 0.7v drop of the diode...
                      That's quite simple: it's V*I. The main question here is: how do the curves for `I` relate to each other when you feed the motor with 3V versus 2.3V?

                      Comment

                      • DBMandrake
                        Automated Home Legend
                        • Sep 2014
                        • 2361

                        Originally posted by gordonb3 View Post
                        That's quite simple: it's V*I. The main question here is: how do the curves for `I` relate to each other when you feed the motor with 3V versus 2.3V?
                        So do we know that the motor is normally driven at 3 volts ? Has anyone measured it ? In stroke 1 or stroke 0 mode ?

                        There is a clearly audible difference in motor turning speed between the two stroke modes so the voltage must differ between the two. If we take 3 volts as the nominal voltage then 23% of the power supplied for the motor would be consumed by the diodes due to the 0.7v drop.

                        This could have a significant effect on battery life, however the thing that is completely unknown (and which some of us have speculated about before) is what proportion of the total battery consumption of these units is the brief bursts of operating the motor and what proportion is the wireless comms and standby power of the circuitry... although the motor uses orders of magnitude more current when turning, it's duty cycle across a day is also vanishingly small.

                        Comment

                        • Sentry1
                          Automated Home Jr Member
                          • Oct 2016
                          • 43

                          This is great! Going to give it a go. Thanks DIY1.

                          Honeywell should be a little red faced if this works.

                          I’ll let you know. (It won’t be anytime soon though).

                          Originally posted by DIY2 View Post
                          Like others I have noisy HR92s that I cant have in the bedrooms so I have done a quick hack that so far has solved the problem for me without any problems, so thought I would share it.

                          The bad news is you need a soldering iron (but it’s an easy job).

                          However do this at your own risk –and it will definitely invalidate any HR92 warranty.


                          The design flaw is that the motors/gears turn unnecessarily fast and generate the noise. I have purchased alternatives from China and might give them a go at some point but in the meantime put in a hack that works for me.

                          To slow the motors and reduce the noise I reduced the voltage to them - crudely using 2x 1N4001 diodes. (Zeners would be slightly better but I had these already and they worked fine). Note I have not done any voltage or current measurements to refine the diode selection – might do at some point.

                          NOTE: in slowing the motors, the motor power will decrease, so if you have hard to operate valve pins this might not work –ie not enough power to operate them and the HR92 will show error E2. If this happens you could try different diodes with less voltage drop than the 1N4001, but less voltage drop equals faster motor equals more noise.

                          This took me 15mins but may take up to half an hour of faffing first time. Lots of text for completeness but it’s a pretty easy DIY job.

                          You will need:
                          1. Soldering iron
                          2. 2x Diodes -I used 1N4001 (12pk on ebay for £1)
                          3. Insulation sleeve – again cheap on ebay
                          4. Small jewellers type of screwdriver

                          Steps:
                          1. Remove HR92 Cap and batteries
                          2. Remove plastic insert by removing the screw and using the small (jewellers) screwdriver bend the 3 retaining tabs GENTLY IN TURN while exerting slight lifting pressure on the insert (fingers in the battery compartment). Be careful not to over bend them or they will break, bend just enough so that they release in turn as you lift the insert gently. This sounds difficult but is actually easy if you take your time and be gentle.

                          You will now see the motor.

                          3. Unsolder the Red motor wire (doesn’t actually matter which one). Note the wire insulation is cheap stuff so melts easily, so don’t be too crude – you can re insulate with a sleeve if you melt it a bit.
                          4. Take the two diodes and twist their legs to attach them in parallel together pointing in different directions, ie with the stripe on them at different ends – see picture (if you don’t you will get an E2 error from the HR92 as motor will only turn in 1 direction)
                          5. Solder one end of the diode legs to the Red wire and the other to the motor. Use an insulation sleeve to avoid the diode legs shorting to the motor metal cover (and to cover any melted insulation on the Red wire). I don’t recommend using insulation tape – but hey it’s your HR92. Note: Its important to mount the diodes neatly – flat to the back of the motor and in a place that the plastic insert wont foul when you put it back on – I suggest place in the picture.
                          6. Refit plastic insert – you may need to bend out one of the tabs again gently. Don’t force it down –if it doesn’t seat right its probably fouling on the diodes, so don’t force it and re-mount the diodes.
                          7. Refit the insert screw, add the batteries and cap.
                          Your ready to try it.
                          Note if you do this to a spare HR92 and want to fit it to an existing zone –then follow the unbind procedure otherwise you will get a Comms fault on your controller – I just deleted the zone and added it again and hit bind on the modified HR92 to be sure.


                          [ATTACH=CONFIG]1443[/ATTACH]

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                          • DIY2
                            Automated Home Jr Member
                            • Mar 2019
                            • 16

                            Happy to help. Cheers.

                            Comment

                            • Evohome User
                              Automated Home Lurker
                              • Oct 2019
                              • 2

                              Originally posted by Sentry1 View Post
                              This is great! Going to give it a go. Thanks DIY1.

                              Honeywell should be a little red faced if this works.

                              I’ll let you know. (It won’t be anytime soon though).
                              Originally posted by DIY2 View Post
                              Happy to help. Cheers.
                              Did you ever get around to doing this MoD? I am going to buy some of the diodes this week and was wondering if any new developments!

                              Comment

                              • DIY2
                                Automated Home Jr Member
                                • Mar 2019
                                • 16

                                Hi, I modified 3 units. One for each bedroom. All have worked perfectly for the last 5 months. Batteries are still going strong. One is noisier than the rest but it was even noisier than the others to begin with and is about a third of the noise it was, so happy enough with it. The other two I barely notice even when I'm awake which a BIG difference. Cheers

                                Comment

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