Components for Converting AC->DC + voltage step-down + reversing of polarity

[whytwo]

Hi all,

First, I really appreciate anyone taking time to read through this and provide feedback.

I’m working on a unique HVAC application where I have handful of problem statements and I’m trying to figure out what the most ideal components are. Additionally, I’d like to be as minimal as possible! For example, if there were a single device/PLC/relay that could do it all (even if pricey), that’s OK.

My preference would be to take off-the-shelf component(s), if possible.

Here is what I’m working with:

-My HVAC Zone Controller outputs 24vac designed to Open/Close Dampers (a typical HVAC actuator is 24vac).

-My Damper Actuator motors are 9vdc (mine are NOT typical).

-My HVAC Zone Controller has three 24vac outputs to Open/Close Dampers: 1) Common 2) Open, and 3) Close. (so common is always used, but the Open/Close terminals are used for their respective actions)

-My Damper Actuators have two wire inputs to Open/Close these Dampers. Since this is a DC motor Actuator, you simply reverse the polarity to Open/Close the Dampers.

So, when my HVAC Controller wants to Open a damper, it outputs 24vac to Common/Open terminals, and when it wants to Close a damper, it outputs 24vac to Common/Closed terminals.

I have a multimeter watching those outputs and it’s working as expected.

I am looking to Convert from AC -> DC, as well as step-down from 24v to 9v, as well as reverse the polarity of 3 wires to 2.

I believe I’ve identified components that could do everything… i.e. a Voltage Rectifier (to go from AC->DC), a transformer to go from 24vdc->9vdc, and then a Dual Pole Dual Throw Relay (DPDT) to reverse polarity of the DC motor…

Question is: Can any recommend the “cleanest” way to do this?

Another note, I have about 8 DC actuator Damper Motos per floor (3 floors total), so if there were some sort of DIN-mounted PLC/Relay/Rectifier module(s) that could take a number of inputs and outputs, that would be brilliant!

Some additional details:
-DC Damper Actuator motors draw 250mA.
-Zone Controller's AC Output is 2.5Amp max
-There is a use-case where multiple DC Damper Actuator motors may be connected to a single Zone Controller Output. (i.e. Zone Controller Open/Closed circuits could control up-to 3 Dampers)

Please let me know if you have any questions and thank you again!!

 

[Diver300]

I would arrange a separate 9 V dc supply, probably 120 Vac input, but you could power it from anything you want, and you could run as many actuators from one power supply as you want, just bearing in mind that the voltage drop at 9 V needs to be considered on building-sized wire runs, and making sure that the power supply can supply enough current for all the actuators you connect to it.

Then you need two 24 Vac single pole changeover relays for each actuator. Connect the coil of one relay to the 24Vac common and open terminals of the HVAC controller output. Connect the coil of the other relay to the 24Vac common and close terminal of the HVAC controller output.

At this point you can check that one relay operates when the controller is trying to close the vent and the other operates when it is trying to open the vent.

Now connect the NC connections of both relays to -ve of the 9 V supply. Connect the NO connections of both relays to the +ve of the 9 V supply. Connect the actuator between the Common connections of the two relays. Swap these two over if the actuator runs the wrong way.

It doesn't matter if both relays operate at the same time, the actuator will just stop, as it would when neither relay operates.

You need relays with 24 V ac coils. The ones with 24 V dc coils may not work on ac, and relays with 24 V dc coils are far more common. If a 24 V relay doesn't say if it's ac or dc, it's going to be dc. Something like this:-
https://www.newark.com/omron-indust...-ac24-s/relay-dpdt-250vac-30vdc-5a/dp/08J0973 would work and you can get a socket for it that mounts on DIN rail.

There may be much cheaper relays that are just as good for you.

Here is a the only 9V, DIN rail power supply that Newark have in stock:-
https://www.newark.com/xp-power/ece40us09-sd/ac-dc-converter-din-rail-1-o-p/dp/24T5140
but it wouldn't be too difficult to bolt any power supply onto DIN rail.

My guess is that one power supply and 16 relays per floor would be a good way to go, but I don't know what the arrangement is and whether you have enclosures with DIN rail on each floor.

Two relays per actuator is almost certainly not the cheapest way of doing it, but it seems that you want to use DIN rail mount, and stuff that any competent electrician can wire up once the circuit has been drawn up, and get parts for it in future, so that is what I would do.

I don't know if you need two functions per actuator (open - close) or three functions (open - do nothing - close). Two relays gives you all three functions. If you only need open or close and can leave the actuators powered one way all the time, you only need one relay per actuator. Wire the coil between open and common on the 24 V ac output of the controller. Connect the -ve of the 9V supply to the NO of one pole and the NC of the other pole. Connect the +ve of the 9 V supply to the remaining NC and NO contacts. Connect the actuator between the two common connectors, and swap those if it goes the wrong way.

 

[whytwo]

Diver300, thank you so much -- everything this all makes a lot of sense!

I really like the idea of a separate 9vdc power supply that is simply triggered by relays.

Some more information:

My DC Damper Actuators are considered "Floating" Dampers... i.e. there is a 20 second Open time and 20 second Close time... if you stop applying current at 10 seconds (in either direction), the Damper Actuator would "stop" at the halfway point... (essentially)

I cannot continue applying current continuously. My Zone Controller is programmed to deliver 250mA @ 24vac for the Open Command via 1 wire, and then 25 seconds of 250mA @ 24vac for the Close Command via another one. (25 seconds being a bit more than 20 seconds to ensure the Dampers are fully opened or fully closed). Additionally, during "start-up" or during Heating/Cooling, any Zone that doesn't require demand, the Zone Controller applies 2min 30 seconds of Close to "reset" the damper to zero, essentially... (I'm trying to get the manufacturer to make this configuration as I'd be applying current for over 2 mins longer than I want....)

Again, I cannot continuously apply current to the Dampers, only during Open/Close commands. (to ensure maximum life)

Traditionally, most Dampers are AC and have 3 wire (vs. 2) Common, Open, and Closed and are setup for "Spring Closed" or "Spring Opened" (i.e. once current stops, they mechanically "spring" to either the Open or Closed position to avoid continuous current...

I'm happy enough with the time-based Floating Schema, but I need to be able to trigger +9vdc Open (for a short period until the 24vac output stops), or -9vdc Closed (for a short period until the 24vac output stops. But when the Zone Controller is NOT either Opening or Closing a damper, I need NO current going to the Damper Actuator motor.

And, as you saw, the additional challenge of DC is polarity switching is a necessity here! A typical 24vac Damper Actuator has 3 Inputs (Open/Close/Common) just like the Zone Controller's output...

Couple questions: Above, you noted "two 24 Vac single pole changeover", but looking at the link to the OMRON it seems to maybe be a DPDT. Can you clarify??

When looking at DPDT, I kept coming across them being able to be used for polarity reversing.

I am totally fine with 16 relays per 8 dampers, but if it were possible to use a DPDT relay to reverse the DC polarity on a single relay, that would be great too!

Thank you again for everything, I am now much closer putting together a solution.

 

[Diver300]

Couple questions: Above, you noted "two 24 Vac single pole changeover", but looking at the link to the OMRON it seems to maybe be a DPDT. Can you clarify??

The relay that I linked to was just about the first 24V ac one I found, and it happened to be a DPDT.

When looking at DPDT, I kept coming across them being able to be used for polarity reversing.

I am totally fine with 16 relays per 8 dampers, but if it were possible to use a DPDT relay to reverse the DC polarity on a single relay, that would be great too!

You can use a DPDT relay to reverse polarity, but a single relay can have two conditions, so forward and reverse but he actuators would be powered all the time.

I'm happy enough with the time-based Floating Schema, but I need to be able to trigger +9vdc Open (for a short period until the 24vac output stops), or -9vdc Closed (for a short period until the 24vac output stops. But when the Zone Controller is NOT either Opening or Closing a damper, I need NO current going to the Damper Actuator motor.

If you need some way to only power the actuators when the 24V ac is turned on, then you will need two relays per actuator.

As I understand it, the HVAC controller only puts out 24V ac when the dampers are either opening or closing, in which case the actuators will be turned off most of the time if you connect up the way that I suggested for two relays.

If the "Close" output turns on for 2 minutes 30 seconds and you don't think that the actuators will survive that, it could be quite a problem. If you have a spare zone that isn't used, but the "Close" output operates at start-up, you could use that output to turn off the 9 V supply to everything each whenever it operates.

Other solutions would involve timers and it would all get complicated quite quickly.

 

[whytwo]

Diver300,

OK, I think I got it... thanks for your clarification on the Single Pole vs. Dual -- agree that it makes sense since I also need a Not Opening and/or Not Closing State.

To complete my POC (hopefully), I went ahead and ordered the following:

• 2 x https://www.newark.com/omron-indust...c-10a/dp/08J0953?CMP=e-email-sys-orderack-GLB (Single Pole 24vac coil powered Relays)
• 2 x https://www.newark.com/omron-indust...-1-b/dp/48AC2024?CMP=e-email-sys-orderack-GLB (Relay socket adapter for DIN)
• 1 x https://www.newark.com/omron-indust...n/din-mounting-rail-35mm-aluminium/dp/93B2043 (DIN Rail)
  
  
• 1 x https://www.newark.com/xp-power/ece...1-o-p/dp/24T5140?CMP=e-email-sys-orderack-GLB (DIN Rail mountable 9vDC Power Supply)

If you see anything that doesn't make sense, please let me know. Otherwise, I'll follow-up soon.

Thank you again for your guidance here!

 

[whytwo]

BTW, here is the DC Motor that is installed on all of the HVAC Supply Damper Actuators:

I wouldn't anticipate anyone would know much about the device, but this was all I could dig up.

I tried reaching manufacturer and have not had a response.

Any opinion on whether this would be the type of device I should be worried about my equipment applying current when either full opened or full closed?? (for a short period of time, hopefully)...

The way the Damper Actuator works is there is a tang that "bottoms out" in both directions to "stop" it from rotating... (so assuming the motor is still under load and can't move when applying current and it's in its respective maximum position).

I'm trying to get a 25+ Year solution put together here...

Thanks again!

 

[whytwo]

Just following up here... got my 24vac coil relays and 9Vdc power supply.

Good news and Bad news....... good news first!

The SPST Omron Relays with XP Power 120vac->9vdc power supply recommended by Diver300 worked PERFECTLY! (almost)

(please ignore the lack of soldering... I'm still waiting on my relay Sockets... ha)

But wired as described by Diver300 it worked exactly as expected.... putting the DC motor +and- across the COM (center terminals) provided +9vdc when the 24vac for Open was output from the thermostat as well as -9vdc when the 24vac for Close was output from the thermostat.

Stepping back for a moment, the DC motors on my Damper Actuators are supposed to be adjusted MANUALLY using the following tool from the manufacturer:

https://www.greenheck.com/shop/accessories/damper-accessories/893199

This is 9vdc battery powered....and connects via RJ11 plug into wall jack. You simply Open and Close the dampers with the tool...

There are some LED/lights on the product to indicate when full Open or full Close... I did wonder how they were indicating Full Open or Full Closed since there is only 2 wires...not a Status wire from the DC motor. I'm thinking I may now know...

So back to my issue.... These are 20 seconds Dampers, but this test actuator was in the half-way position when I had my Relay power +9vdc to "Open" my test Damper.... so about 10 seconds later, when the damper got to Full Open, (mechanical limit) I could hear the motor REALLY working (and not really slowing down)...and it basically broke the center plastic tang...ugh... (you can see a crack in the plastic where the motor wanted to keep spinning the metal shaft while the plastic stopper was pushed up against the metal frame...

The Tool does NOT seem to do this..... so maybe the Tool must be sensing current spike and then switching current off?... (was wondering how the LED lights were lighting up since there is not a "status" from the DC motor, just an Open or Close..)

So, it sounds like the tool has some more advanced sensing circuits than I thought.

When I measure the DC motor, it draws 255mA, which is essentially what is spec'd by the manufacturer...

So maybe there is a circuit in the tool that detects a spike over 255mA which shuts off current (and then illuminates an LED/Light indicator Open or Closed)...

Never Easy!

Anyone familiar with any off-the-shelf plug-in style components that would allow me to switch off/away current if/when draw exceeds 255mA?! (this could also solve the 2min 30 second Damper Close command the Zone Controller does upon Startup to "reset" the position...)

Thank you again

 

[whytwo]

Just thinking out loud here a bit... but I may also be able to re-purpose the Tool's circuitry itself... hmmm

I may be able to remove the board, wire this direct to 9vdc power supply and use relays to essentially "close" the Open/Close contacts on the board....

EDIT: looks like it's insanely simple actually...could this possibly have the current shut-off circuit or am I losing it?.. Maybe when resistance gets high enough, the current goes to the LED instead of motor output??

But since there are ~8 Dampers per floor that could be Opened or Closed at the same time, I may need one of these boards for each Damper?... Crazy idea or no?

 

[Diver300]

Is the 255 mA current measured with the motor running?

On the tester board, F1 is a resettable fuse. With that, and the relatively high internal resistance of the 9 V battery, there won't be much current available to the damper motors.

When the motor is running, and it is only taking a bit of current, there will not be much voltage drop across the fuse and so the LED will light up. When the motor stalls, the current will increase and the fuse will get hot. Its resistance will increase, and the voltage across it will increase, leaving only a couple of volts across the motor and the LED, so the motor won't do much and the LED will go out.

When the buttons are released, the fuse will cool down so that it's working normally when the tester is used again.

I've got to say that I'm impressed by the simplicity of the design.

You can simply add a resettable fuse in series with each damper. All you have to do is work out the rating.

I am not sure but I think that the fuse is one of these:- https://uk.farnell.com/bel-fuse-cir...ff2e/fuse-resettable-ptc-6vdc-0-5a/dp/2834926

However, different manufacturers have different trip currents for the same marking.

If you can, connect the fuse to a variable current source, slowly increase the current and measure the current which it trips at. Just about any resettable fuse with about the trip current will be do. You can buy resettable fuses in a variety of styles.

 

[whytwo]

Hi Diver300,

I did some more testing of the current with a multimeter... actually created a short video to demonstrate what I'm seeing. Unfortunately, I don't have a variable current source...

Looks like the motor actually uses ~.65mA when rotating... Would be great if you could review the following video to see if you can understand what's happening here...

New video by true

photos.app.goo.gl

Reposting the DC Motor specs:

I'm wondering if maybe the Resettable Fuse is tuned for Greater than or Equal to 260mA?...

And when the motor is mechanically stopped, maybe it spikes up to 260mA so quick I don't hear/see any movement when it's bottomed out?

I don't know why I see ~70mA when the motor is bottomed out, which is arguably more than when it's rotated...but I don't hear the motor buzzing/trying to turn, etc..

Additionally, I found this company that makes the resettable fuses:

Low Resistance PTCs - POLY-FUSE&reg Resettable PTCs - Littelfuse

www.littelfuse.com

It looks (visually) like this could be it as they are labeled/marked with a letter..

My Board (closeup):

Would the specs here make sense? (this is Datasheet for the Littelfuse PolySwitch® Resettable PPTCs)

If the N Marked specs would make sense -- I guess I could try finding a similar device with Leads that I can simply run in-line (serial) on the Relay Leads??..

BTW, I'm scratching my head a bit if the Fuse is tripped due to current, why am I seeing any current when holding Open or Closed when the motor is "bottomed out"?...

Thank you again!!

 

[Diver300]

The meter display is a bit confusing. It has got to be displaying Amps, as fractions of a mA wouldn't be enough to turn a motor like that, but 0.7 A seems too much.

Everything in the video is consistent with a resettable fuse in series with the motor.

The motor takes about the same current when running and when stalled against the end stop when it is supplied by the control box. When the motor is running, there is little load, and like all DC motors, it takes little current with no load even though it is being supplied with the full voltage. When the motor is stalled, the resettable fuse trips and limits the current to about the same value. The voltage across the motor is small, so the LEDs in the control box are turned off.

The current displayed by the meter never gets to a high value. That is because the meter only takes about 3 readings a second. That tiny motor will accelerate in something like 0.05 seconds and once it is at full speed the current is much less, so the maximum current doesn't last long enough for the meter to show it. The fuse it tiny, so it will heat up and reduce the current very fast, also too fast for the meter to see the maximum

The resettable fuse doesn't stop the current completely. That is a feature of resettable fuses. They reset when they cool down, so as soon as they start to cool down the current would increase. The result is that they have to stay hot the whole time that they are tripped, and they need power to stay hot. In the data sheet for the resettable fuses, there is a figure of about 0.6 W for Pd. That is the power needed to keep the fuse hot. That is about 70 mA with a 9 V supply, which I think is what you are seeing. A normal fuse would trip to zero current, but you would be needing to replace that every time the motor hit the end stop.

I think if you just get hold of resettable fuses with wires (https://www.littelfuse.com/products/polyswitch-resettable-pptcs/radial-leaded.aspx) of the same rating, and test them, you could just put one in series with each motor.

Do the yellow and black wires connect to anything? I would have thought that there might be a switch of some sort.

 

[whytwo]

Agree my multimeter display is a bit confusing.... I wasn't questioning it before, but maybe it's 600mA - 700mA instead of 60mA - 70mA...

The specs on the N Littlefuse .75A (guessing that's 750mA, so maybe it does make sense?).

However, the specs on my DC motor show Rated Current at <= 260mA... which I assume means Less Than 260 mA.... so back to wondering again... hmm.

I did go ahead and order a few RF3379-000 from: https://www.littelfuse.com/media?re...=littelfuse-ptc-radial-leaded-rusbf-datasheet

Couple notes notes... it looks like both the Surface Mount and Radian Lead devices are actually 6vdc.... the one on my "Tool", if N is right is also 6vdc....

Maybe the 4990 is a 500Ohm resister in-line to bring the voltage down??

Would I maybe need a Resister + the RF3379-000 Radial Lead Resettable Fuse?

While the Hold for both of these is .75 (which is nice), the Maximum is 1.5A vs. 1.3A (guessing this is the Trip Amperage)... so slightly Lower, but I'm guessing this should also be fine. Time to Trip looks like .2 vs. .4 seconds for the Radial Lead... and the Max Current... probably still OK.

Regarding the Black and Yellow wires....I don't seem the going anywhere, no....

Also found an install document for the motor:

Again, not showing/explaining the Black and Yellow works.... wonder if it's just using a more "standard" RJ11 jack that had 4 wires...

So anyway, I did order some RF3379-000 (the Radial from LittleFuse with very close specs) -- wondering if those specs are "close enough" -- and maybe more importantly, any chance I need a Resister to step down from 9vdc->6vdc as well??

Thank you again so much... I'm really happy how quickly I've been able to iterate in the last few days, really appreciate it!

 

[Diver300]

A resistor won't bring the voltage down in the way you want it to.

If you've ordered 6 V resettable fuses and you run them at 9 V they might burn out, they might not but they should tell you if you are on the right lines. You should get the higher voltage ones for any permanent installations.

 

[whytwo]

OK, in this product line, it looks like there are only 6vdc Max and 16vdc max... for the "lowest" Hold and Trip current 16vdc one, it's notable higher than the 6vdc one, so hopefully the 6vdc holds up (again, that's what the factory "tool" ships with... (I will do some testing, etc..)

One more question on the Resistor .... do you suspect they have a 4990 Resistor in the circuit JUST for the LED , and completely unrelated to the Resettable Fuse??

**EDIT** I also ended up ordering some Bel Fuse Resettable Fuses:

https://www.newark.com/bel-fuse/0zrr0010ff1e/ptc-resettable-fuse-0-1a-60vdc/dp/67AC9834

This model has a Hold Current of 100mA (which my motor specs as 100mA as no load current and think I'm getting ~65mA which makes sense).

My motor also says 260mA Rated current and I never saw it get that high unless it was getting buried mechanically without the Reset Fuse from the Tool...so seems like this might be more optimal and is up-to 60v DC (vs. 6vdc)...

Thanks!!

 

[Diver300]

One more question on the Resistor .... do you suspect they have a 4990 Resistor in the circuit JUST for the LED , and completely unrelated to the Resettable Fuse??

The resistor are certainly only there to limit the current that the LED takes. If you were to remove the LEDs and resistors, the control box would behave exactly the same other than the LEDs not working.

The resistors are 499 Ohms. Like many resistors, the last digit of the marking is the number of zeros on the end. That makes it possible to have high value resistors and still have space to mark the values.

"4990" is 499 Ohms
"4993" would be 499000 Ohms

 

[Diver300]

Again, not showing/explaining the Black and Yellow works.... wonder if it's just using a more "standard" RJ11 jack that had 4 wires...

I think they have just used a standard RJ11 jack along with a standard junction box on the end of it.

 

[whytwo]

Just thinking out loud here a bit as I wait for my Resettable Fuses...

I've been trying to find some specifications on "cycles", "maximum resets", "lifetime", etc...

I haven't been able to find a whole lot on that topic, but did dug up comments from manufacturers like:

These Polymer PTC (PPTC) devices are intended for protection against occasional overcurrent/overtemperature fault conditions and may not be suitable for use in applications where repeated and/or prolonged fault conditions are anticipated.

When using the manufacturer's tool to adjust these Damper Motors, the typical use-case occurs maybe just a couple times a year. For example, when you switch a building from Hot to Cold or Cold to Hot, you may adjust dampers slightly for airflow purposes, etc..

My plan is to setup a proper HVAC Zone Controller to automatically Open/Close these HVAC Duct Damper actuators dynamically based on Heating/Cooling demands of my building (the Dampers are already installed and in the "walls" behind finished insulation, drywall, etc.. i.e. so they are NOT accessible...).

As I noted above, when testing my DC power supply directly (i.e. not using the Tool which has the overcurrent protection build in), the 9vDC essentially twisted and broke the plastic that is fused to the actuator motor's shaft so it no longer stops at Open/Close. So, I am quite concerned about possibly "breaking" the Damper Actuators that are inaccessible in the walls...

So, I've been wondering -- should a Resettable Fuse be expected to be a solid "enterprise"-style solution that can be tripped 20+ times a day for 50 years?? Or, is this use-case just too aggressive for a Resettable Fuse??

Couple questions:

Does anybody know if these Resettable Fuses "blew", would they blow "open"?? i.e. limit the current always vs. unlimited current always? I could not seem to dig this up...

I have also just come across an "eFuse IC".... this is obviously more complex of a potential solution, however, would this be more of a "lifetime" way of limiting DC current with less risks???

Lastly, I did some temperature testing using my Thermal Imaging Camera and found the existing Fuse in the tool reached a max of 136F degrees after holding current for 3+ minutes.... It still works after that, but it really did heat up!! (which was cool to see it work, obviously too)

Any feedback always appreciated!

 

[Diver300]

136°F does not seem that hot. Lots of electronics runs a lot hotter than that. Where I have seen problems with temperatures in that range is where either electrolytic capacitors degrade over time, or plastics go brittle, but both of those take a long time with continual exposure, not 20 times a day for a few seconds.

Glue guns are heated by what are basically big thermal fuses, and they can run continually, but they take a long time to heat up compared to the fuses you may be using.

I don't know what the failure mode is for those fuses, but I guess they would fail open-circuit.

There are all sorts of solutions you could use but they are all more complicated or less effective. You could just add a resistor in series with the actuator. You would need around 50 Ohms, but some trial and error would be needed. If the resistance is too high, the actuator won't start, and having it too low would risk breakage.

The power rating should be 2 W or more. Having a larger power resistor of the same resistance will make the resistor run cooler, probably be more reliable, but will make the resistor larger and more expensive.

As the actuators take several seconds to complete their travel, you could start them with just the resettable fuse in series, and then add a resistor in series after a few seconds. The resettable fuse would prevent damage if the actuator didn't start of it if gets to the end stop before expected, but the resistor would normally limit the current at the end of travel.

The circuit arrangement would be that the resistor would be permanently in series, but some relay contact would short it out when not wanted at the start of operation.

That could be done with a timer relay or a with additional output from the HVAC controller if you have them and if they can be programmed like that.

 

[whytwo]

I added the following Resettable Fuse in-serial (I think):

https://www.mouser.com/ProductDetail/530-0ZRR0010FF1E

This was supposed to be 100mA "hold" and 200mA "trip"...

I simple added it in-line my multimeter leads... is there a polarity on the Resettable Fuse?

Unfortunately, it did not seem to work as I was expecting/hoping as the DC motor kept running for the full 23 second Actuator Travel time... even though the actuator was "in the middle" when the Open Damper began....

Example Video:

New video by true

photos.app.goo.gl

Still scratching my head a bit on the Klein display.. maybe the motors are using 600mA, which might align more with what the tool's "N" fuse is... Could a standard rectangle 9v battery even deliver between 600ma - 1.5Amps??? (what the tool uses)

Even if this Resettable Fuse is largely undersized, I would assume it would pop or get hot, etc.. nothing seemed to happen. Also, I think max trip time was 4 seconds, and it seemed to be over 200mA (or 2A) for over 4 seconds....

Is this an acceptable way to add it in-line?

Still waiting on my Relay sockets so have a bit of a mess, but seemed like it could/should have worked...

I am still waiting for: https://www.digikey.com/en/products/detail/littelfuse-inc/RUSBF075/5029811

Which is 750mA Hold and 1.3A Trip (which is more like my "guess" at what N Littlefuse Chip "might be.. (750mA Hold, 1.5A Trip @ 6v...)

Any ideas if I'm hooking something up incorrectly and/or why it seemed to not work??

Thank you,

 

[Nigel Goodwin]

I think you're rather optimistic how fast fuses blow, and I presume resettable ones are no different? - generally you need a massive overload to blow it quickly, something like 10A through a 5A fuse could well take minutes before it blows, if it even blows at all.