# VFD Output Filtering



## Susquatch (Oct 12, 2022)

I was looking at my VFD Output Voltage Characteristics on an oscilloscope recently and noticed some very high harmonic spikes. The spikes are not surprising - in fact expected given the square wave characteristics of the VFD output voltage. But I didn't expect voltage level spikes over 2000 volts. 

So I sent an Email to TECO - the manufacturer of my VFD to ask about it. Rather than reply to my email, they called me. 

The fellow said such spikes were typical of short cable runs between the VFD and the motor and especially in higher quality motors such as inverter ready motors like I have because they don't dampen the spikes and instead are designed to tolerate them. I'm not really surprised by any of that either. It's really just the very high voltage levels that surprised me. 

But what he said next totally caught me off gaurd. He recommended 3 phase *OUTPUT* filtering! At first, I was stunned. I have always assumed that the VFD measures current flow and back EMF from the motor and uses that information to set output parameters to optimize motor performance. He didn't disagree. However, he said that designing a filter with a cutoff frequency at least twice the carrier frequency would kill the spikes but still allow the current flow at the carrier frequency voltage to reach the analytical portion of the sensorless vector circuitry in the VFD. 

So that's what I plan to do. I guess we will see how well that works. 

I'm also curious to know if anyone else has had similar experiences or has tried output filtering. Please note that this is not input filtering on the single phase input circuit which is very common and in fact I am already doing that. This is output filtering on the 3 phase power from the VFD to the motor.


----------



## Darren (Oct 12, 2022)

You probably want to look at 'line reactors'.  As i understand it, they are a 1:1 transformer. Drive setup is done before installing the line reactor, to set motor parameters. 

I was going to install one on my 10hp lathe due to some cogging issues i was having, but i was able to tune them out.  I have a big input filter due to burning out light bulbs in my house whenever i'd use the lathe.


----------



## Susquatch (Oct 12, 2022)

Darren said:


> You probably want to look at 'line reactors'.  As i understand it, they are a 1:1 transformer. Drive setup is done before installing the line reactor, to set motor parameters.
> 
> I was going to install one on my 10hp lathe due to some cogging issues i was having, but i was able to tune them out.  I have a big input filter due to burning out light bulbs in my house whenever i'd use the lathe.



Yes, I have a good input filter too. There is nothing on the input circuits at all. 

That's a very good comment about letting the VFD set the motor parameters before installing anything into the output. I would not have thought to do that. 

I will look into line reactors. I'm guessing they are basically a simple transformer that would no doubt kill the harmonic spikes. But I would be worried that they might also kill the carrier frequency. I suspect they are mostly meant to be used in standard voltage/frequency control mode or in sensor feedback mode rather than in sensorless vector mode. They might even be intended for use in a non-frequency speed control mode where the VFD is only used to create 3phase output but doesn't change the frequency to change speed. I'll let you know what I find.


----------



## Darren (Oct 12, 2022)

I was going off memory before and made a mistake. Line reactors go before the vfd, LOAD reactors go between VFD and motor.



			https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjOyK_n9tr6AhXoLzQIHfBHAxcQFnoECAkQAw&url=https%3A%2F%2Facim.nidec.com%2Fdrives%2Fkbelectronics%2F-%2Fmedia%2Fkbelectronics%2Fdocuments%2Fwhite-papers%2Fapplications-of-line-and-load-reactors-with-variable-frequency-drives.ashx%3Fla%3Den&usg=AOvVaw2t8IaK4sGNY3TZqoCU7_Pn


----------



## PeterT (Oct 12, 2022)

Not sure if this is related or not, I'm practically VFD illiterate.


----------



## Susquatch (Oct 12, 2022)

Darren said:


> Line reactors go before the vfd, LOAD reactors go between VFD and motor.



OK, my read of that article goes like this.

Said load reactor is the same thing as the output filter I described earlier. 

However, the article suggests that the need for output filtering doesn't arise until output wiring lengths exceed 100 ft for non-vfd ready motors and 300 ft for vfd ready motors. 

The TECO guy specifically said that my spikes were the result of short wiring. Mine is about 6 ft. On the other hand, the article suggests that it is reflections on long wires that cause the spikes and harmonic noise. 

I suppose it's possible that my VFD Ready motor doesn't filter spikes and just reflects them instead and it's also possible that I am just concerned about nothing. 

Nothing in the article mentions the VFD control mode. I had thought perhaps it is an old publication, but although the article is not dated, it references other documents as recent as 2017. I do not know when sensor less vector control technology was developed. I'd guess at 2010 or so, but perhaps much earlier. Nonetheless, it strikes me as very odd that the article doesn't mention it or its implications. 

It turns out that the filter that TECO recommended is also called a "Line/Load Reactor". Apparently the one device handles both input and output. But it is $250 without a cabinet. I don't think that's in the cards. 

It doesn't appear to be a high enough low frequency cutoff to serve as an effective sensorless vector device either. I'd rather try and make one first. Who knows, that might become even more expensive.

Thanks for the info Darren. I'll keep this thread up to date with anything else I find or do.


----------



## Susquatch (Oct 12, 2022)

PeterT said:


> Not sure if this is related or not, I'm practically VFD illiterate.



It's related, but he is filtering the input not the output. I've already done that.


----------



## David_R8 (Oct 12, 2022)

Help educate us; what problem does the output filtering solve?


----------



## Darren (Oct 12, 2022)

If he's seeing 2000v spikes, the concern would probably be potential damage/breakdown of the motor insulation and possible damage to the drive.


----------



## jcdammeyer (Oct 12, 2022)

David_R8 said:


> Help educate us; what problem does the output filtering solve?


The high voltage spikes but don't follow what the idiot cough42 says.  "We're not going to wrap them around just run them through the cores".    

Oh but do click on my links because I get paid when you do that.  And I make these very long and boring because I get paid more if they are long.

Take a look at TECO's data sheet for their filters.


			https://www.tecowestinghouse.ca/wp-content/uploads/RL-Selection-Tables.pdf
		


The reason the cores are as large as they are is because if the current that generates the magnetic field is too high then the core saturates and the inductance created by the winding drops to near zero and then the filtering effect drops to zero.  So for example running the motor on the bench with no load is not an indication of the noise under full load. (Another reason why that video is silly)

I had to experiment with coil sizes back in the 90's when I designed this Sequential Fuel Injection and capacitive Ignition system for Honda 1.5L Engines modified with a belt drive to serve on Home Built EIA aircraft and Hovercraft.  






In this case there are two toroids, stacked with, IIRC, 88 turns of wire to handle at least 10A at 8V without saturating with enough inductance so when the current stopped the capacitor would charge up to almost 300V.  I went through multiple toroid combinations until I found something that was not too heavy but also met the specifications.

If you find an old transformer with a current rating of your motor and remove the windings you can create something like the ones you see in the above tagged PDF.


My two cents...


----------



## Susquatch (Oct 12, 2022)

Yes @Darren .  That plus I just don't like the idea of spikes that high. I was shocked to see that. 

TECO didn't seem overly concerned or surprised about it though.


----------



## Susquatch (Oct 12, 2022)

jcdammeyer said:


> The high voltage spikes but don't follow what the idiot cough42 says.  "We're not going to wrap them around just run them through the cores".
> 
> Oh but do click on my links because I get paid when you do that.  And I make these very long and boring because I get paid more if they are long.
> 
> ...



Might only be 2 cents from your perspective but totally spot on.

I had thought about using three transformers directly, but it requires testing like you describe to determine their real world performance for the range of loads my VFD and motor might see. I think it's prolly better to do some analysis and calculate the required parameters and then just buy that. It's either that or spend the money on the OEM filters.

I guess my hesitance is driven by the fact that there has to be thousands of similar systems to mine out there and they probably have the same problem but nobody even knows it because they don't have an oscilloscope.

Perhaps as @David_R8 might be implying, I'm just being a worry wart for nothing.


----------



## jcdammeyer (Oct 12, 2022)

Oh and if you are going to roll your own note the comment that a 5% filter is reduced to 3% if the current is 60% of the rated current.
Here's a schematic of the basic filter.  








						EMI / RFI / EMC Filter manufacturer
					

EMI / RFI / EMC filter manufacturer from India, with over 30 years of expertise in EMI Filter and EMC consultancy.



					emitech.co.in


----------



## jcdammeyer (Oct 12, 2022)

As I said it's been a few decades since I did the ignition.  I've forgotten how to do all the calculations but I'm sure the information is out there.  I'd tear down a surplus transformer like one out of a microwave.  If it is the classic E Type transformer core




Then just wind say 10 turns on each vertical leg like that RL50003 photo in the Teco data sheet.  I'm not sure you need the capacitors but I'd connect the frame to earth.


----------



## jcdammeyer (Oct 12, 2022)

@Susquatch Here's an example of a simple circuit to measure inductor current and coil saturation.  You have a scope.  If you don't have any sort of pulse generator here's a perfect little project for an Arduino to tickle the transistor to turn on the current.









						How to measure Inductor maximum current?
					

I have an inductor and seller claims that inductor supports a maximum of 5A current and he asked me to test it myself. Can someone help how to test that how much this inductor can support/ draw max...




					electronics.stackexchange.com


----------



## Susquatch (Oct 12, 2022)

jcdammeyer said:


> Oh and if you are going to roll your own note the comment that a 5% filter is reduced to 3% if the current is 60% of the rated current.
> Here's a schematic of the basic filter.
> 
> 
> ...



I guess my only problem with the filter in your suggestion is the low frequency cut-off of 60 Hz. I would think it needs to be more like 16KHz to allow the carrier frequency to get through even if it is a bit rounded. Perhaps 60KHz would be better to maintain more of the square wave structure. I didn't really look at how fast those high voltage spikes were but they were definitely well above the carrier frequency as they were just spikes sitting on the edges of the carrier square wave - perhaps something like 100KHz or even faster with a tiny bit of ringing.


----------



## jcdammeyer (Oct 12, 2022)

With a bit of experimenting with a transformer wound the way I suggested you can determine e the inductance znd therefore the reactance at 16 kHz.


----------



## Susquatch (Oct 12, 2022)

Agreed.


----------



## jcdammeyer (Oct 12, 2022)

Some quick math.  Assuming you want a bit of room above yhe 16khz frequency I used this web page for a pi filter





						Simple LC Low Pass Filter Circuit Design & Calculations » Electronics Notes
					

Design considerations, circuit and formulas for a constant-k 3 pole LC low pass filter for RF applications.




					www.electronics-notes.com
				




So freq is 18khz and I guessed at an inductor with value 0.000050 Henrys or 50uH.
That works out to impedance of 2.83 ohms. 
Using that value then gives me 0.00000625 Farads or 6.25uF.
A 6.3uF 900V cap runs about $5.86 at Digikey. C4AQOBU4630M11J

Ferrite cores aren't that expensive but single coils won't work as well as all three on the same core. Hence winding on a transformer core. 

I think that's shy you want to make one like a common mode choke but for thee phase. 

Been a long time since I did anything with this sort of stuff.


----------



## Susquatch (Oct 12, 2022)

jcdammeyer said:


> But single coils won't work as well as all three on the same core. Hence winding on a transformer core.



You lost me on that one. Why do you say that? 

Do the phases feed on each other in some way that's not obvious to me?


----------



## jcdammeyer (Oct 12, 2022)

It takes an entire book to explain the details.  The electrical noise may come frome one driver but is magnetically coupled and electrically induced into the other lines.
Winding the inductors on the same core reduces the interference.
Search common mode interference




__





						Loading…
					





					www.tdk.com


----------



## Dabbler (Oct 13, 2022)

You can get stalled on tying to go for the perfect solution here, but I'm not that guy.

How about getting some torroid material and winding some 12ga wire for 4- 6 loops, and then checking the difference with a scope?  sort of a 10$ test, and anything is better than nothing.

Really it doesn't matter if the core saturates, as it is the leading edge of the spike that you are modifying. (yes it is better to do it right, but you have to start somewhere)

edit:  I'd try 3 of these to start:





__





						Loading…
					





					www.digikey.ca


----------



## Susquatch (Oct 13, 2022)

jcdammeyer said:


> It takes an entire book to explain the details.  The electrical noise may come frome one driver but is magnetically coupled and electrically induced into the other lines.
> Winding the inductors on the same core reduces the interference.
> Search common mode interference
> 
> ...



Ah, I see. I apologize for not mentioning that I am using special VFD cable. The wires in this cable are individually shielded from each other with individual grounds to reduce common mode interference. Think a bit like twisted pair but ignore the differential floating voltage. Part of me suspects that cable is the problem LOL. Maybe I didn't terminate it properly. I might try some regular 4 wire cable at some point just for shi*s and giggles. 

The scope I used is a 400MHz 4 channel Tektronics 2465B. I did not see any common mode noise at all on any of the three outputs and I was looking for it.

I also have a 2 channel Digital 150MHz 2430A that I could try, but I have very high confidence in what the analog 2465 is telling me.

@Dabbler - you are always pragmatic - almost to a fault. I think I will do just that. It cannot hurt. Besides, I will know immediately if the VFD Output is compromised because I can watch it on the scope.

I'll have to order a few of those cores from Digikey first. No rush on my end.

You are also right about the silliness of chasing perfection. If I didn't have a nice DRO on my mill I prolly wouldn't worry about it. But I've seen what high amplitude noise can do to sensitive equipment. I don't like the thought of damaging the DRO and then in hindsight wishing I had looked after the spikes on the VFD. In this case, I think I'm better off safe than sorry.


----------



## YotaBota (Oct 13, 2022)

I was looking into this when I installed my VFD and came across these for those who would prefer a not cheap engineered solution. I didn't buy one yet but still thinking about it.








						EMC Output Filter for VFD, 6A/20A/80A/150A/300A to 1000A
					

Good quality EMC output filter for sale, designed for VFD load side to reduce the common-mode noise, protect the load and extend service life, 3-phase VFD output filter with rated voltage 250/440VAC 50/60Hz, current rating from 6 Amps to 1000 Amps, threaded stud or quick connect, high...




					www.ato.com
				



If this was a real issue mechanically I would think TECO would have done something about it. 


Susquatch said:


> spikes were typical of short cable runs between the VFD and the motor


Did the tech define "short" cable runs? 1 foot, 2 foot, 6 foot?


----------



## jcdammeyer (Oct 13, 2022)

Why reduce the noise spikes on the output? 

Ask how you might solve the problem of moving the carriage on your lathe to a specific position via the DRO and 1 out of 19 times it's wrong.  Not predictable. But it screws up the cut.  

The electrical noise not captured by the individual shielded wires that escapes can play havoc with other electronics.  Maybe that cut is screwed up when the tool hits the work during an interrupted cut and the load temporarily increases.

My book on electrical interference stresses the importance of removing or reducing the noise at the source rather than trying to stop it where it's picked up somewhere else.


----------



## Susquatch (Oct 13, 2022)

YotaBota said:


> Did the tech define "short" cable runs? 1 foot, 2 foot, 6 foot?



Yes, he did. Short is anything less than 50ft!   LOL!

But he also said that shorter is better not worse.

To your point, he didn't think my spikes were anything to worry about. He took the view that he had never had anyone put a lab grade scope on the wires......

As per what I told @Dabbler, I think he is probably right. I have not had any problems, but I don't like the idea of wishing I had done something about it AFTER I fry my DRO.....

The only reason I even looked at it and noticed it was curiosity.


----------



## YotaBota (Oct 13, 2022)

@jcdammeyer - I know the harm EMI can do with electronics but @Darren mentions possible damage to the motor and that's more what I was thinking about.


Susquatch said:


> Short is anything less than 50ft!


That's what she said! LOL
The only electronics I'm running is the vfd itself and the tach so EMI isn't a big issue in my use but it's still interesting watch and learn.


----------



## thestelster (Oct 13, 2022)

These are power my set -ups for the mill and surface grinder.  I also have for the lathe.  Don't ask me too much  cause I haven't a clue how they work.  I told the sales rep of the supplier of my VFD's what I had and he had his tech people tell me what I needed.  Main power into the safety switch, then into the line reactor, then into the VFD, then into the load reactor, then into the motor.


----------



## Susquatch (Oct 13, 2022)

thestelster said:


> These are power my set -ups for the mill and surface grinder.  I also have for the lathe.  Don't ask me too much  cause I haven't a clue how they work.  I told the sales rep of the supplier of my VFD's what I had and he had his tech people tell me what I needed.  Main power into the safety switch, then into the line reactor, then into the VFD, then into the load reactor, then into the motor.



Don't know why I didn't notice all that when I was at your place. But very pro looking.


----------



## thestelster (Oct 13, 2022)

Susquatch said:


> Don't know why I didn't notice all that when I was at your place. But very pro looking.


Ha....I must of scrapped 50' of conduit trying to learn how to bend that stuff!


----------



## Susquatch (Oct 13, 2022)

thestelster said:


> Ha....I must of scrapped 50' of conduit trying to learn how to bend that stuff!



They sell a really nice manual pipe/tube bender at Home Depot. I don't have one but my neighbour does. He borrows enough of my stuff that I never hesitate to borrow his!


----------



## thestelster (Oct 13, 2022)

Susquatch said:


> They sell a really nice manual pipe/tube bender at Home Depot. I don't have one but my neighbour does. He borrows enough of my stuff that I never hesitate to borrow his!


I have both 3/8" and 1/2" EMT benders, but, it's figuring out were to put the bends/off-sets and by how much.  I finally found an App which helped immensely, but of course after almost all was done.


----------



## jcdammeyer (Nov 2, 2022)

I was loaned a 1/3HP 3 phase motor to test the Baldor 3 phase drives I picked up.  First one worked nicely.  A bit of whine up in the higher speeds.  But with the pot I can make it turn 60 RPM and it appears to have decent torque.






I'll do some testing and see what sort of electrical noise it generates and then make up some inductors to see if I can suppress it a bit.


----------



## Susquatch (Nov 3, 2022)

jcdammeyer said:


> I'll do some testing and see what sort of electrical noise it generates and then make up some inductors to see if I can suppress it a bit.



Based on all the stuff I see you do, I know you must have some very good instrumentation. Just wondering what kind of scope you have to do this with? Which reminds me that I have to get some better scope probes for this kind of work...... 

Also wondering if you have ever tried one of those computer enabled USB digital scopes that have no screen of their own. Hantek seems to be quite popular these days and are even available on Amazon at decent prices.





__





						Products - Hantek Electronic & Your testing solution provider
					





					hantek.com


----------



## Susquatch (Nov 3, 2022)

jcdammeyer said:


> My book on electrical interference stresses the importance of removing or reducing the noise at the source rather than trying to stop it where it's picked up somewhere else.



I don't know how I missed this post, but I did. Sorry about that. 

I agree completely. It's not always possible though - especially when the source is out of your control - for example the guy arc welding next door..... LOL

It's easy to forget that though, and also easy to fall into the trap of dealing with symptoms instead of cause. 

Good reminder for me and prolly others too John.


----------



## jcdammeyer (Nov 3, 2022)

I have one of these that I bought specifically to be able to decode the alternating bit levels of RS232 and translate into the communication bytes.  It allowed me to see the timing differences between specific characters because a Pan & Tilt system wasn't talking 'friendly'.








						Analog Discovery 2: 100MS/s USB Oscilloscope, Logic Analyzer and Variable Power Supply
					

The Analog Discovery 2 is a USB oscilloscope, logic analyzer, and multi-function instrument that allows users to measure, visualize, generate, record, and control mixed-signal circuits of all kinds.




					digilent.com
				



I also have the BNC breakout board for it along with scope probes and the adapter for the digital side of things.
Essentially it's an "_Oscilloscope, Waveform Generator, Power Supply, Voltmeter, Data Logger, Logic Analyzer, Pattern Generator, Static I/O, Spectrum Analyzer, Network Analyzer, Impedance Analyzer, and Protocol Analyzer_". I like it but haven't used it in several years.

The reason for buying it was it was half the price of the serial decoder module for my Tektronics MSO3034 scope which is 4 channel, 300 MHz with 16 logic analyzer channels and has the 2 modules for decoding Automotive CAN bus, and also SPI, I2C.  Those modules are $1200 each hence the USB type scope for a PC.   This scope has been discontinued.




__





						Loading…
					





					ca-en.alliedelec.com
				




I also have two pieces of Agilent equipment.  A 6.5 digit meter, the 34410A which is also now discontinued.




__





						34410A Digital Multimeter, 6½ Digit [Obsolete]
					

The 34410A DMM will be discontinued December 1, 2016 and is replaced by next-generation 34465A Truevolt Series DMM.




					www.keysight.com
				




And the Agilent 33220A Function and Arbitrary Waveform Generator also discontinued.




__





						33220A Function / Arbitrary Waveform Generator, 20 MHz [Obsolete]
					

The 33220A function / arbitrary waveform generator will be discontinued December 1, 2016 and is replaced by next-generation 33500 Series Trueform waveform generators.




					www.keysight.com
				




For RF work I have a R&S FSH3 portable spectrum analyzer also discontinued along with the VSWR Bridge for it.




__





						Loading…
					





					www.aaatesters.com
				




So all my stuff other than the Digilent is old.  Like me.  But it still works.  I see on EBAY the FSH3 sells for as low as $895.  I believe I paid $15K for the kit including the carry bag.

I hesitate to dive in and figure out what it would cost to update all of the above.   Likely the price of a small car.


----------



## John 345 (Nov 3, 2022)

Susquatch said:


> It's related, but he is filtering the input not the output. I've already done that.


Not sure if this comment in the right place as it's my first.I started playing with vfd a few years ago ,had noise  problem affecting my blue tooth sound system so I just use shielded cable on vfd output to lathe motor have not checked with any fancy gear but solved my noise problem apparently as blue tooth NC  headphones work fine . Can't explain technically the reasoning  though.


----------



## Degen (Nov 3, 2022)

@jcdammeyer I have 2 VNA, HP8753C calibrated recently to 3GHz and a AEA Bravo2500 handheld, which also has Spectrum Analyzer and FDR built in.  Difference between the 2 sensitivity the HP while significantly older is still at the top end.  My main Spectrum Analyzer is a HP141T (18Ghz).


----------



## jcdammeyer (Nov 3, 2022)

@Degen There's nothing wrong with the old stuff.   Although my FSH3 was originally bought to work with the WORMs I also used it for my CANRF modules. Because my FSH3 has extra code features also for short circuit detection in long cables.  That came in handy for finding 'mistakes' in the cables for the YVR Olympic Rings.


----------



## jcdammeyer (Nov 3, 2022)

John 345 said:


> Not sure if this comment in the right place as it's my first.I started playing with vfd a few years ago ,had noise  problem affecting my blue tooth sound system so I just use shielded cable on vfd output to lathe motor have not checked with any fancy gear but solved my noise problem apparently as blue tooth NC  headphones work fine . Can't explain technically the reasoning  though.


Sure it's the right place.  Often just the right type of shielding will prevent the noise from going too far if at all.


----------



## Susquatch (Nov 3, 2022)

jcdammeyer said:


> I hesitate to dive in and figure out what it would cost to update all of the above. Likely the price of a small car.



Your lab is better equipped than mine by a wide margin even if it is old. The newest piece of electronics test equipment I have is a 150MHz 2 channel Tectronix 2430A Digital Storage Scope. I also have a 400MHz 4 channel 2465B Analog.

I do have a few signal generators but they are home made.

I'd love to have a few of the toys you have (especially the Discovery 2 multi function) but the truth is that I'd prolly never use it. I just don't do things like that anymore. Old age keeps relentlessly slowing me down.

I love reading your posts though. They make me laugh and remember days gone by with a big huge smile.


----------



## jcdammeyer (Nov 3, 2022)

I forgot to mention I also have a 300 MHz Tektronix TDS3032 but it saves screen captures to floppies.   And those are getting harder and harder to read even with new floppy readers.  The probe plastic is also disintegrating.  But it sits at the other workstation and/or gets dragged into the shop to look at encoder signals etc on the CNC stuff.

And then there's my analog 30MHz Gould 2 channel scope.  Haven't powered that one up in a couple of decades.  It's what moved me from being a sales guy for Cardinal and Bowtek into going back to school but taking Comp. Sci.  I used it to develop a wire wrapped 48K dynamic memory board for my S100 computer.  Back when all the EE's were telling me that you can't wire wrap dynamic memory boards.

Oh and I have one of these that I used to capture CAN bus data streams and decode into CAN bus messages.  That was before scopes could do this.  And I why I prefer integrated test gear rather than something with a PC based user interface.  I have a prom/pal programmer where support stopped working when WIN-95 showed up.  Cost me $1K back in 1994.  Became useless with WIN-95 and WIN98.
As did this after WIN-XP and the vanishing parallel port.








						NCI Gologic logic analyzer with parallel 25 pin interface  | eBay
					

Find many great new & used options and get the best deals for NCI Gologic logic analyzer with parallel 25 pin interface at the best online prices at eBay! Free shipping for many products!



					www.ebay.com


----------



## Susquatch (Nov 3, 2022)

jcdammeyer said:


> And I why I prefer integrated test gear rather than something with a PC based user interface.



Damn good point John. I keep a few old computers around for certain software. As you may recall, I wish I had kept my S100 System. 

An old boss of mine used to say that "Many the impossible thing has been done by someone who didn't know it couldn't be done.". 

But ya, I never wire wrapped a dynamic memory board either. In fact, I hated that tool so I seldom wire wrapped anything.


----------



## jcdammeyer (Nov 3, 2022)

The secrets to a 48K dynamic ram board for S100 are:
1.  Use a Z80 not 8080 because the Z80 provides the refresh signal for the rams.
2. Use 22g stranded wire for the +/-5 +12 voltages instead of 30g kynar WW wire.

As for old computers.  Pretty well a requirement.  The processor that runs my foundry was programmed with a specific Kanda dongle.  There is still the company resurrected from the original but they for some reason never bothered upgrading support for it and now it only works on WIN-98 machines.  Luckily I have a laptop with that software and OS.  Not functional on batteries but boots well enough that if I wanted to make a change to the code I could.

Likely what I'll do is make a new board that uses something more current or programmable.  The code is in C.  Pretty simple.  Runs spark plug, fan, gas solenoid and can interface to a flame detector and air flow sensor.  Just never added the flame and air flow stuff so the code has #ifdefs around that.


----------



## Dabbler (Nov 3, 2022)

I only wire wrapped small projects.  When I bought all my S100 stuff, it was on double sided PCBs.  I never got around to designing any S100 boards, so no wire wrapping them...  I still have a tube or 2  of 2101 dynamic memory chips for making a 4KX12 S100 memory board.  Oh the memories!


----------



## Degen (Nov 3, 2022)

jcdammeyer said:


> The secrets to a 48K dynamic ram board for S100 are:
> 1.  Use a Z80 not 8080 because the Z80 provides the refresh signal for the rams.
> 2. Use 22g stranded wire for the +/-5 +12 voltages instead of 30g kynar WW wire.
> 
> ...


Reminds me of building my first memory expansion on a KIM from 1K to to 2k


----------



## cjmac (Nov 3, 2022)

Susquatch said:


> Your lab is better equipped than mine by a wide margin even if it is old. The newest piece of electronics test equipment I have is a 150MHz 2 channel Tectronix 2430A Digital Storage Scope. I also have a 400MHz 4 channel 2465B Analog.
> 
> I do have a few signal generators but they are home made.
> 
> ...


I have a 2465A in working order, but I also have a 2445A that need that U800 chip and a 2430A that has power supply problems. The 2430A could be potential parts if something fails in yours. I don't envision ever trying to do anything with it myself. Also have a 1240 logic analyzer and a bunch of S-100 stuff like John.

Chris


----------



## whydontu (Nov 3, 2022)

Jeez. You guys are all old as me. 2102 chips, wire wrapped, to bump my RCA COSMAC from 256 bytes of RAM to a whopping 1.2kb! Built from plans published in Pop Tronics.

Used the COSMAC to drive R2R D/A converter for an analog modular synthesizer. Checked waveforms on my 10MHz Eico scope. 

Hated my Hantek scope. PITA to have a scope that needs a PC. Too many wires.

 For quick-n-dirty I have a couple of pocket DSOs
DSO213 4-channel 
DSO211 single-channel
For $100 if I fry them it’s not too painful.

I tried a touch-screen DSO FNIRSI 1013D, ok but touch-screen isn’t intuitive for someone who grew up with Tek gear

I don’t do critical stuff, just need to see if the signal exists and how much noise. mostly audio. My current real(ish) scope is a Siglent SDS1052, a decent compromise between price and usefulness.


----------



## Susquatch (Nov 4, 2022)

cjmac said:


> The 2430A could be potential parts if something fails in yours. I don't envision ever trying to do anything with it myself.



THANK YOU! 

I have book marked this thread. You never know how the story might evolve......


----------

