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OVM-14 MkIII development (update)

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 24, 2024 10:08 am Post subject: OVM-14 MkIII development (update)

Haven't been ignoring you guys . . . fun projects got

kinda diluted with holiday festivities and frivolities

along with a few home maintenance items that could

not wait . . .



But in the mean time:



I've been fiddling with the etched circuit for the

prototype OVM-14 upgrade . . . due to the very compact

ecb layout I was interested in exploring solder reflow

assembly processes using joint-by-joint application

of solder paste.



The experiments were frustrating. The consistency

and makeup of the solder 'paste' is critical. Samples

I had on hand proved problematic in that they were

reluctant to 'stick' to the pad until the component

was placed. Seems this stuff has a shelf life too.



Finally did conquer the process but while working

with these cute little boards, it occurred to me

that it was a bit late in my career life cycle

to be spooling up in new manufacturing processes and

inventorying new products!



To my way of thinking, the optimized assembly

configuration would lend itself to offering

bare boards or even kits in addition to limited

sales of completed assemblies while striving

for compact assembly.



Thought I give this a try:



The attached figure is a snapshot of the present

configuration OVM-14 ECB. It's not terribly

larger than the legacy CBOVMs. I've not used

this assembly technique in more years than I

can recall . . . first observed it in the

fabrication of my first solid state pocket

radio. A Regency TR1 that cost me a pretty

penny in newspaper route earnings about 1958!



Note the resistors stand on end soldered into

pads with very close spacing. This offers

a tighter layout opportunity with another

benefit: The upper end of each resistor can

be oriented such that it attaches to an

interesting 'test node' on the board. An

oscilloscope or voltmeter probe can be clipped

to the lead wire for performance evaluation

and/or troubleshooting.



What, you may ask, is that 'thing' hanging

off the end of the board?  My short path

to low cost prototype boards is predicated

on a fixed 3.8 x 2.5 inch coupon. Hmmm . . .

what to do with that opportunity for a 'free'

ecb?



How about exploring a recently noticed LED

product that caters to night time drone

pilots? Red or green LEDs with built in

flashers. A bit slower than I'd like but

certainly bright enough. I've added a little

'parasite' board to the layout to proof an

idea for a precision low volts warning

annunciator with a very low parts count.



I'll publish drawings for the ECB

shortly with the notion of exploiting

any willing talents for proofing the

layout. I've got an order into Digikey

for thru-hole parts to assemble the prototypes

which should go VERY quickly.



This may not be the optimal route but I

think it's better than the rabbit hole

I dove into the first time. Let's see

what shakes out.

   Bob . . .



                    ////

                   (o o)

    ===========o00o=(_)=o00o=========

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

    =================================



    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

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merlewagner2

Joined: 01 Jun 2016
Posts: 18
Location: Spring Hill, FL

Posted: Thu Jan 25, 2024 3:57 am Post subject: Re: OVM-14 MkIII development (update)

Bob,



If you send me the schematic I can then make up a board with SMD and have it made by PCBway. They are very cost effective. 

As an example the photo is an RF/audio probe I just finished using SMD. I used 1206 sized SMD for this.

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_________________
KC1DNJ
General Radiotelephone
Commercial SEL
A & P
Building scale P51, rebuilding Tailwind W10

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 29, 2024 9:56 am Post subject: OVM-14 MkIII development (update)

At 05:57 AM 1/25/2024, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "merlewagner2" <wagnermerle(at)gmail.com>



 Bob,



 If you send me the schematic I can then make up a board with SMD and have it made by PCBway. They are very cost effective. 

 As an example the photo is an RF/audio probe I just finished using SMD. I used 1206 sized SMD for this. 	


   Thank you so much for the offer sir. BTW, nice

   looking assembly.  SMA connectors? What does it do?



   I did a surface mount ECB and already have the

   boards. However, while resolving some issues with

   solder paste dispensing I had an epiphany . . .

   I'm not at the stage of my 'career' to be

   launching a project to be manufactured in

   my shops.



   Decided to convert it to thru-hole so that

   I might offer kits . . . and perhaps get

   some local kids interested in learning how

   to put such things together. I've published

   the 'plan-b' details in another posting.  I'll

   comb it for errors one more time and get

   boards on order. Should be here Friday.

   I'll also get an order in to Digikey for

   parts compliment.



   If you'd care to proof the layout yourself,

   your input would be truly appreciated.

   It's a bit risky to proof one's personal

   work product . . . but then I'm probably

   not telling you anything you don't already

   know! 



   Yeah, about that 1206 footprint . . . that's

   been my favorite choice for hand assembly for

   the past 20 years or so!



 

 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 29, 2024 10:02 am Post subject: OVM-14 MkIII development (update)

I've published the ECB layout and assy data at



  https://tinyurl.com/ytdg9ehf 



 Any any assistance in proofing the layout to the

 schematic would be appreciated. Will order boards

 late tonight.



 Got an order about ready to ship to Digikey for

 parts.



 We might get this project into smoke-test yet!



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

pjc

Joined: 13 Jan 2021
Posts: 7

Posted: Mon Jan 29, 2024 11:04 am Post subject: OVM-14 MkIII development (update)

Bob,

Still interested in being a beta-tester.  With the through-hole redesign I can probably competently assemble it myself! Even better for my use case if the low voltage warning light/LED option is included.

Peter



 	  Quote: 	
		  On Jan 29, 2024, at 10:12â€¯AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:



ï»¿  I've published the ECB layout and assy data at



  https://tinyurl.com/ytdg9ehf 



 Any any assistance in proofing the layout to the

 schematic would be appreciated. Will order boards

 late tonight.



 Got an order about ready to ship to Digikey for

 parts.



 We might get this project into smoke-test yet!



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 29, 2024 12:01 pm Post subject: OVM-14 MkIII development (update)

At 01:03 PM 1/29/2024, you wrote:

  	  Quote: 	
		  Bob,

 Still interested in being a beta-tester.  With the through-hole redesign I can probably competently assemble it myself! Even better for my use case if the low voltage warning light/LED option is included.



 Peter

  	  Quote: 	
		  	
	
 

   You're at the top of the list. We'll assemble the

   first 'batch' here for testing. The lv warning

   board gets trimmed off . . . that's a separate

   project that's still under cultivation. But you

   can have one of those too once they're ready

   for prime time.



 

 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

merlewagner2

Joined: 01 Jun 2016
Posts: 18
Location: Spring Hill, FL

Posted: Mon Jan 29, 2024 1:16 pm Post subject: Re: OVM-14 MkIII development (update)

[quote="nuckolls.bob(at)aeroelect"]At 05:57 AM 1/25/2024, you wrote:

 [quote]--> AeroElectric-List message posted by: "merlewagner2" <wagnermerle>



 

   Thank you so much for the offer sir. BTW, nice

   looking assembly.  SMA connectors? What does it do?



 /quote]



Bob, The unit displayed is an RF/audio probe for signal tracing. this feeds an amplifier. Yes, SMA connectors. It makes a nice compact unit using RG 174 as a lead. The probe is powered from the amp.



I am not sure how this is going to get displayed as I rarely use quotes or even reply. 



Merle

_________________
KC1DNJ
General Radiotelephone
Commercial SEL
A & P
Building scale P51, rebuilding Tailwind W10

merlewagner2

Joined: 01 Jun 2016
Posts: 18
Location: Spring Hill, FL

Posted: Tue Jan 30, 2024 7:02 am Post subject: Re: OVM-14 MkIII development (update)

 	  nuckolls.bob(at)aeroelect wrote: 	
		  I've published the ECB layout and assy data at



  https://tinyurl.com/ytdg9ehf 



 Any any assistance in proofing the layout to the

 schematic would be appreciated. Will order boards

 late tonight.



 Got an order about ready to ship to Digikey for

 parts.

We might get this project into smoke-test yet!



 

   Bob . . .



  	




I looked at your layout and after finally figuring out the semantics it looks OK initially. It was confusing until I understood the numbering scheme for components.



For me it usually takes about 3 iterations to figure out what I forgot. At 82 I am finally recognizing a memory failure. 



Merle

_________________
KC1DNJ
General Radiotelephone
Commercial SEL
A & P
Building scale P51, rebuilding Tailwind W10

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 09, 2024 8:55 am Post subject: OVM-14 MkIII development (update)

Boards are on order . . . stared at that last

 iteration of the layout and finally succumbed

 to an instance of 'creative destruction'. I've

 re-laid the board to more conventional fabrication

 philosophies. Yeah, it got a bit bigger but will

 go together in minutes and 'look good'.



 The assembly is now 2.2 x 0.7 inches and will

 still 'house' nicely under a piece of heat

 shrink.



 Those interested in taking a peek can download

 the proof prints at:



  http://aeroelectric.com/DIY/OVM14%20mkII%20proof%20prints.pdf



 

 The boards will be solder masked and silk screened

 to facilitate kit-builders. Parts and boards will be

 on hand for 15 prototypes next Thursday.



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

1rv4

Joined: 11 Sep 2006
Posts: 24

Posted: Fri Feb 09, 2024 5:15 pm Post subject: OVM-14 MkIII development (update)

Hi BobVery interested in a kit or a completed and tested one.

Â Thanks

Â  Â  Chris

On Fri., Feb. 9, 2024, 9:10 a.m. Robert L. Nuckolls, III, <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    Boards are on order . . . stared at that last

 iteration of the layout and finally succumbed

 to an instance of 'creative destruction'. I've

 re-laid the board to more conventional fabrication

 philosophies. Yeah, it got a bit bigger but will

 go together in minutes and 'look good'.



 The assembly is now 2.2 x 0.7 inches and will

 still 'house' nicely under a piece of heat

 shrink.



 Those interested in taking a peek can download

 the proof prints at:



  http://aeroelectric.com/DIY/OVM14%20mkII%20proof%20prints.pdf



 

 The boards will be solder masked and silk screened

 to facilitate kit-builders. Parts and boards will be

 on hand for 15 prototypes next Thursday.



 

 Â  Bob . . .



 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  //// 

 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (o o) 

 Â Â  ===========o00o=(_)=o00o========= 

 Â Â  < Go ahead, make my day . . .Â Â  > 

 Â Â  < show me where I'm wrong.Â Â Â Â Â  > 

 Â Â  =================================

 Â 

 Â Â  In the interest of creative evolution

 Â Â  of the-best-we-know-how-to-do based

 Â Â  on physics and good practice.

pjc

Joined: 13 Jan 2021
Posts: 7

Posted: Wed May 29, 2024 9:52 pm Post subject: Re: OVM-14 MkIII development (update)

Bob (or others),

Iâ€™ve not been keeping up with the mailing list lately, and at some point there seemed to be a service outage, so apologies if I should know better., but â€¦



Has there been any further progress on the â€œnewâ€ OVM module?



PJC

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Mon Apr 07, 2025 6:32 pm Post subject: Re: OVM-14 MkIII development (update)

There haven't been any updates on Bob's OVM-14 Mk III overvoltage protection module since Feb 2024 so I took a look at it to see what I could do.  I found some minor things that might have been problems, so I made a few small changes:



1. Looking at the datasheet for the crowbar SCR... [https://tinyurl.com/yjvrdtfx] ...the specification for gate triggering current states that it could take as much as 15mA to trigger.  As configured in the last schematic that Bob posted... [https://tinyurl.com/3jeddsky] ...with the gate drive resistor (R14) of 2.49k ohms connected to the bus, 15mA gate current would not be achieved until the overvoltage exceeded 37V.



CHANGE: R14 reduced to 620 ohms and connected to the 10V supply rail instead of the bus.  This provides 16mA to trigger the SCR's gate, while preventing an overcurrent through the output of comparator U11.B (maximum 20mA).



2. At a bus voltage of 14V, current-limiting resistor R1 (392 ohms) would dissipate of about 1/3 watt, and would run hot.



CHANGE: R1 increased to 470 ohms and pass transistor Q17 added.  This provides a sturdy 10V supply rail for the circuit, including adequate gate current to trigger the SCR.  Continuous power dissipation in R1 will be reduced to 0.03W.  At the high end of its 1% tolerance (475 ohms), with bus voltage at 12V, R1 will provide 3mA to U3 and the base of Q17, more than double the minimum required for regulation.  At the low end of its tolerance (465 ohms), R1 will protect U3 against exceeding its absolute maximum current rating up to a ridiculous bus voltage of 81V.



3. The trip delay capacitor (C12) is a ceramic type, which may not be stable in a timing application due to the effects of DC bias, temperature and aging.



CHANGE: C12 changed to a 5% tolerance solid tantalum type.



-----



With that done, I created a board layout that's very similar to Bob's and is the same size (0.7" x 2.2").  It still uses all through-hole parts except the SCR, which is large for a surface mount component and is relatively easy to hand solder.  I moved the SCR to the top side of the board and added a 2-position 0.25" quick-connect terminal to make installation easy (wires can still be soldered directly to the board if preferred).  I also changed to a "piano key" style DIP switch to activate the maintenance mode, which makes the switch accessible at the end of the assembly after heat shrink is applied.



After building a prototype, I found that the resistors that set the trip voltages didn't quite work as calculated, so I tweaked them experimentally to find the values that provide a normal trip at 16.0V (R8 = 2.61k) and a maintenance test mode trip at 13.7V (R10 = 69.8k).  To ensure that maintenance test mode works correctly with all battery types, I bumped the test mode trip point up by 0.2V, from 13.5V to 13.7V.  This will accommodate the higher resting voltage of a fully charged LiFePO4 battery (typically 3.4V per cell, or 13.6V for a 4-cell battery).



Finally, I assembled four additional prototypes and tested all five.  In each case, the modules tripped at the desired voltage and in the desired time, blowing a 5 amp fuse with no discernable heating of the SCR.



Full documentation for the project is attached to this post.  You'll find links on page 7 to purchase circuit boards and components.

Nuckolls OVM-14 MkIII (Rev 1d).pdf

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user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Tue Apr 08, 2025 5:02 am Post subject: Re: OVM-14 MkIII development (update)

Wow Eric, you went to a lot of work to help out aircraft owners and builders.

Your excellent documentation will allow even a complete novice to build an 

overvoltage protection circuit.  I like the through hole design.  Expert soldering 

skills are not required.  I commend your efforts to help others.

_________________
Joe Gores

dj_theis

Joined: 28 Aug 2017
Posts: 68
Location: Minnesota

Posted: Tue Apr 08, 2025 6:12 am Post subject: Re: OVM-14 MkIII development (update)

Very nice.

I second Joeâ€™s recognition of your contribution to the group, Eric.



Dan T.

_________________
Dan Theis
Scratch building Sonex #1362
Revmaster Alternator problem solved.

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