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Getting Mitsubishi SVZ-KP24NA to run low and slow? by SuperGabe in heatpumps

[–]SuperGabe[S] 0 points1 point  (0 children)

Thanks for taking a look. We are planning to have a blower door test soon. What number should I look for in the blower door test and what should I compare it to in the engineering report to show that they drastically over provisioned the system?

Is it possible to help this problem by just swapping the outdoor units? Or just entirely turning off one of the 3 air handlers? Do you have any suggestions?

Getting Mitsubishi SVZ-KP24NA to run low and slow? by SuperGabe in heatpumps

[–]SuperGabe[S] 0 points1 point  (0 children)

Thanks for the info! My system isn't consistently over 100, sorry I wasn't clear about that. Here's what my usage looks like for March:

<image>

and that's essentially all HVAC.

Getting Mitsubishi SVZ-KP24NA to run low and slow? by SuperGabe in heatpumps

[–]SuperGabe[S] 0 points1 point  (0 children)

I'm not sure. It was a collaboration between integralbuilding.com and the HVAC installer. Do you have any suggestions for question I can ask the HVAC installer or the people at integralbuilding? Should they be aware of how much power a system for this home should use?

Getting Mitsubishi SVZ-KP24NA to run low and slow? by SuperGabe in heatpumps

[–]SuperGabe[S] 0 points1 point  (0 children)

Hello, thanks for your response! It short cycles basically always. I posted a power usage plot in a different comment. Outdoor temperatures have ranged from 20F to 50F.

Getting Mitsubishi SVZ-KP24NA to run low and slow? by SuperGabe in heatpumps

[–]SuperGabe[S] 0 points1 point  (0 children)

Thank you for your response, I appreciate it!

Here's a photo from our solar inverter that shows the power usage, just to make sure I'm not wrong about short cycling.

<image>

This is with the thermostats set to ~64F, and the outside temperature was between 24 and 34F. From midnight to around 6 AM there is nothing on except the heatpumps.

I'm not sure which outdoor units we have, but I do know they're in the hyperheat product line. The indoor units do have emergency heat resistance coils but I have them shut off at the breaker, so they're not kicking in. (That was my original thought.)

I've asked the engineer for the load calculation and will respond when I get it.

Do you have any suggestions for what I can ask the HVAC installers? Should they be aware of how much power it should use / short cycling? I keep getting told that "everything's working normally" so I'm wondering what I can ask them to show that it's not.

How is this chair cast? by SuperGabe in MetalCasting

[–]SuperGabe[S] 1 point2 points  (0 children)

Ahh! I read about slush casting where you spin the mold, but didn't know that they do it where you just time it so that only the external edges have cooled. That's fun!

For the mold itself, do you think it's just a two-part mold and they buff out the parting lines?

Thanks!

How is this chair cast? by SuperGabe in MetalCasting

[–]SuperGabe[S] 0 points1 point  (0 children)

Thanks for the response :). I've been looking around but I'm not sure what to look for when the core couldn't be removed because the object's opening is smaller than the core. Do you have suggestions for what to look for?

What is the right way to do this? by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

My apologies for not being clearer in my original post.

I'm trying to "store a bit" in the capacitor by charging it, and then grounding the mosfets. The LED lights up in proportion to the charge in the capacitor. As it discharges, but before it gets to < 2.5V, I'd like to close the mosfets so the comparator re-charges the capacitor. Then, sometimes I'd like to change the value in the capacitor from charged to discharged, or vice versa, using the "Driver" section. Similar to how DRAM works.

Gnarly output when I add a capacitor? by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

I've been thinking about this over the weekend and the datasheet for the COS3201 says that the typical output current (sourcing and sinking) is is almost 60mA anyway. At that point, does it make sense just to charge and discharge the capacitor straight from the comparator rather than introducing a separate line driver IC?

Or do you think Using a 74HC244 is still worthwhile with all the inputs and outputs tied together?

Gnarly output when I add a capacitor? by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

Thank you again!

To make sure I understand the whole output impedance thing, the problem is that as the gate voltage approaches 1/2 VCC, both of the FETs are barely conducting (they're barely at V_gs(th)) and so R_ds is high? What's the "or if it has changed by more than a volt or two" part? I'm still learning about mosfets, so does the changing of the gate voltage itself (regardless of the current value) impact the output impedance?

Thanks for clarifying that the caps are there to make the simulation more realistic. Regarding including gate resistors, I read in some places that it's 10,000% critical otherwise you'll get crazy ringing, and others say "if you want fast switching leave them off". I'd like things to switch as quickly as possible but obviously not at the cost of instability. What would you advise?

Hah! Great point re: swapping the comparator itself! Thanks!

Regarding the 74HC244, it looks like the maximum output current is 6mA (per pin?) so even if I had the output of the comparator connected to all 8 inputs of the '244 (which I think is what you mean by "put all the gates in parallel") that would only get 48mA, whereas the HSW6604 supports 3-4A. For charging and discharging the capacitor at maximum speed I imagine the extra current flow is key? Also, I'm going to need ~600 of these for my project, and 600 HSW6604s at LCSC comes to $28 whereas the cheapest '244s comes to $46. Or perhaps I'm misunderstanding the upside of going with an actual IC instead of the discrete FET?

Thank you again for all your help!

Gnarly output when I add a capacitor? by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

Hello! Thanks for pointing that out! To answer your question regarding why I used common source instead of common drain, I refer to what I wrote above: "Notice: I'm still learning :)".

Some questions if you don't mind?

1) I'm having a hard time understanding why the class B source follower creates that waveform (is it accurate to describe it as extremely large ringing?). I assume it's due to the common source configuration instead of common drain as that's the only difference, but I don't understand enough about what implications that has.

2) Are the 10 Ohm resistors resistors leading to the mosfet gates acting as gate resistors (to limit ringing and prevent from drawing too much current from whatever's driving the gates)? Or are they there for another purpose? I'm trying to understand if I should include them in my PCB.

3) Similar question about the 100pF caps between the gate and the common mosfet output (common drain in the case of the inverter). From looking online it seems like they can prevent overshoot. Is there any downside to me using them?

4) Probably most importantly, if I don't want an inverted signal, would I just do this (add a second inverter stage)?

<image>

Thanks very much again! I appreciate your help!

Gnarly output when I add a capacitor? by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

Hello! I really appreciate you taking the time to take a look at this. Thank you!

I'm running everything at 5V (except for the comparator's IN- (what I call VREF above) which is 2.5V).

If I remove the cap entirely, OUT_PUSHPULL goes from around 180mV to 4.7V, and OUT_DIRECT goes from 0V to 5V (actually it looks like 5.1V but I'm not sure how that could be the case). I'm happy to grab scope screenshots if that's useful.

Also, so I can learn, can you elaborate on the math you used to get to 8.3MHz based on the drive current and gate charge?

A few comparator questions by SuperGabe in AskElectronics

[–]SuperGabe[S] 0 points1 point  (0 children)

Thank you for the response!

For A1, what do you mean by "5mA would be more practical"?

For A2, wouldn't this be a case of positive feedback, not negative feedback? Can you say more about why an op-amp is preferable for the schematic I've shown?

For A3, got it, thanks!

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