Overload Board

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Re: Overload Board

Postby K9ACT » Fri Oct 22, 2010 5:04 pm

This exercise with current zero and gain is getting me nowhere.

The only condition that produces 3v with key down, produces 2.5v with key up.

The only condition that produces near zero volts key up produces .8v key down.

Both conditions allow the transmitter to run at full power with full modulation with no faults or other problems.

Under both sets of conditions TP1 is 3v key down and TP3 is 3v key up

TP4 2.5v key up and 2.855 key down.

The only good news is that whatever was blowing fets seems to have gone away but I have no confidence in the Overload protection working.

Help!

js
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Re: Overload Board

Postby kf1z » Fri Oct 22, 2010 5:26 pm

Yes, odd....

I measured my pots... R706, R708

with power on, but in stand-by mode...

R706 reads 2.4 vdc ( same as my TP4 )
R708 reads 2.5vdc

This is from gnd to the wiper of each pot .

I do not know if "pre-setting" your pots to this value would get you anywhere or not.
(your R706 should probably be set to the same value as your TP4)

Might be worth a try.

Getting these two set can be "fun".

they work with ( against) each other, there is a sweet-spot if all components are correct etc.

Just double check that R706 is a 1k pot and R708 is a 100k.
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Re: Overload Board

Postby K9ACT » Fri Oct 22, 2010 10:56 pm

kf1z wrote:Yes, odd....

I measured my pots... R706, R708

with power on, but in stand-by mode...

R706 reads 2.4 vdc ( same as my TP4 )
R708 reads 2.5vdc

This is from gnd to the wiper of each pot .


Those are pretty close to the numbers I get but under these conditions, TP2 reads 2.5V. Note that this is the same as R708 wiper.

>Getting these two set can be "fun".

Maybe for the first few hours but it's not fun anymore

>Just double check that R706 is a 1k pot and R708 is a 100k.

They are as should be.

js
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Re: Overload Board

Postby K9ACT » Wed Oct 27, 2010 11:46 pm

I think it's time for Steve to get back in here. As mentioned back a message or so, there is no way that I can get current zero at no load and 3V under load. I give up; it is impossible as it sits.

There is either something wrong with the board or it's another aspect of running at 30 Volts.

The only good news is that if I key the transmitter with the VFO off, the needle on the current meter barely leaves the peg before it is shut down. That is the only way I have come up with for testing the overload but it's a pretty gross test.

Also, I still have not had any failures of any sort to exercise the board so whatever the problem was seems to have gone away but as long as I went to the trouble of building and hooking up the board it would be nice if it worked properly.

js
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Re: Overload Board

Postby steve_qix » Thu Oct 28, 2010 6:04 am

Hi - I did respond to the current sense setup, but I didn't hear any feedback about the results of what I suggested, so I figured you were still working on it and would report back!

Please check/do this:

Even though there is a 1k resistor and a capacitor to ground at both TP1 and TP2 - RF can STILL GET INTO THE OP AMPS if you have a lot of RF in the shack, or a radiating souce (like a coil) nearby. RF getting into the op-amps WILL completely skew your measurements, and they will be meaningless. Put a 10k resistor in series with TP1 and TP2 if there is any question about RF (which at this point, there is!). Solder the 10k resistors right into the TP holes, and have them simply stick out above the board. Makes a handy place for your meter probes, and keeps the RF out of the board. Note also, if you are using a meter like a Simpson 260, compensate for the small voltage drop across the resistors in your readings. EG you may lose .2 volts or whatever. Add the drop to your readings.

QUESTION: Are the additional recommended resistors in place? If so, what is the voltage drop across the resistors (measured with no RF present)?


The board can be adjusted to run with between about 5 and up to 10 amperes without modification. If you want to run MORE current, put a shunt across the high voltage modulated DC input and output on the overload board. I have used these overload boards with transmitters running 25 amperes at carrier using a shunt.


Settting the current zero and current gain pots to get the output you want (3V at TP2) involves a bit of pot balancing, but it is not overly complex. The idea is to get 0 volts at TP2 with no current, and about 3 volts (or slightly less) at TP2 with normal carrier level current. Both the current gain and current zero pots will effect the zero current output.


You set these pots experimentally, which is how I do it.

1) Set the current gain at about half way. Adjust the current zero for 0V at TP2. Make sure you have 0V at TP2 with no current.
QUESTION: Can you get 0 V at TP2 doing this?


2) Run current through the sensor (transmit at normal power) and measure the voltage at TP2. If it's at 3 V, buy a lottery ticket :D
QUESTION: what is the voltage at TP2 with current (assuming 0V with no current, as set above)?


3) Adjust the current gain one way or the other, kill the carrier, and re-zero the current zero - 0V at TP2 with no current. Transmit again. Did the output voltage at TP2 move in the direction you wanted (higher or lower, depending)? If so, and it's not where you want it, keep adjusting the current gain in the same direction, kill the carrier - re-zero, etc.. If the voltage moved in the wrong direction, adjust the current gain in the opposite direction, kill the carrier, re-zero, etc.
QUESTION: What Happens when you do this?

4) Keep balancing the current gain and current zero adjustments until you get it right. It usually only takes a few tries.


Regards,

Steve
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Re: Overload Board

Postby kf1z » Thu Oct 28, 2010 6:51 am

K9ACT wrote:\

There is either something wrong with the board or it's another aspect of running at 30 Volts.

\
js



I can say with certainty, the board as is, with the parts supplied, works fine at 20 volt carrier,
No extra parts needed.
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Re: Overload Board

Postby steve_qix » Thu Oct 28, 2010 8:24 am

kf1z wrote:I can say with certainty, the board as is, with the parts supplied, works fine at 20 volt carrier,
No extra parts needed.

This is a bit of a sidebar between myself and Bruce, and I don't want to distract from Jack's stuff - but this seems somewhat anomalous :D The section of U702 used for the voltage sense forms a unity gain amplifier. This is preceeded by an approximately 10:1 voltage divider - meaning that 20 volts can only yield 2 volts output at TP1 with the voltage cal (R702) set for maximum. So, will the board actually work with 2 volts at TP1 - well, yes - assuming you also have 2 volts at TP2 under normal operating conditions (and 0 volts with no current) - and that the vthresh pot (R720) is also set for 2 volts at TP3.

It is not ideal, but the circuit is very robust, and will allow for some rather wide variations in voltage levels, and will still work - if the variations are carried throughout (EG, everything operating at 2 volts instead of at 3 volts, etc.). Higher voltages will cause problems - op amps will start saturating under heavy modulation, etc., so any operation above 3 volts at TP1, TP2 and TP3 (at carrier) can cause problems.

Bruce, if you are able to get more than 2 volts at TP1 with 20 volts, something is amiss :P
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Re: Overload Board

Postby kf1z » Thu Oct 28, 2010 8:32 am

Oh so it's MY board that has a problem.....

Wow.... go figure... :D

With 20 volts input (carrier)
I can set TP1 to just over 4 volts!


So I've been steering Jack in the wrong direction all this time.
And caused him several days of headache!

He mentioned a while ago that he thought he should then set TP2 etc to 2 (point something) volts, and I said no, that wasn't correct.


Well...

Now I must appologize to Jack profusely....

And now I think I will refrain from commenting an anything else on the forum.. !
I obviously don't know what I'm talking about!

Sorry Jack!
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Re: Overload Board

Postby steve_qix » Thu Oct 28, 2010 8:54 am

kf1z wrote:Oh so it's MY board that has a problem.....
And now I think I will refrain from commenting an anything else on the forum.. !
I obviously don't know what I'm talking about!


You better NOT stop commenting in the forum - or the Class E On-Line University will lose one of its premier professors!! :) :o :D :P Heck, you answer more questions than I do - and we sure appreciate it!

You certainly DO know what you are talking about!! Think about this: You have probably built more class E rigs than anyone in the world, except possibly for myself - and I'm not even sure about that !!!

There is obviously something going on that is giving you the readings you're getting - it could be anything from RF getting in when you're making readings (do YOU have the 10k resistors at TP1 and TP2?) to a bad value series resistor (is it really 1 meg?) to who knows what!! This is the science of electronics, so everything that happens can be explained, once there is sufficient information.
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Re: Overload Board

Postby kf1z » Thu Oct 28, 2010 9:03 am

You better NOT stop commenting in the forum - or the Class E On-Line University will lose one of its premier professors!! :) :o :D :P Heck, you answer more questions than I do - and we sure appreciate it!

[/quote]

But....

What good is it if the questions are answered with FALSE information...?

None.



Problem in this case is...
I ASSUMED that my board, and my measurements were correct.
And, without looking at the schematic enough to know that MY setup is incorrect,
I ended up telling poor Jack that HIS board had a problem!

Not good! :oops:
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Re: Overload Board

Postby K9ACT » Thu Oct 28, 2010 9:09 am

steve_qix wrote:Hi - I did respond to the current sense setup, but I didn't hear any feedback about the results of what I suggested, so I figured you were still working on it and would report back!



Sorry. You may assume that I try suggestions before further comment. I did the resistor bit and it makes no difference.


>QUESTION: Are the additional recommended resistors in place? If so, what is the voltage drop across the resistors (measured with no RF present)?

They are in place and I just measured the voltage drop as about 3mv at both points with or without current flow.

>Settting the current zero and current gain pots to get the output you want (3V at TP2) involves a bit of pot balancing, but it is not overly complex. The idea is to get 0 volts at TP2 with no current, and about 3 volts (or slightly less) at TP2 with normal carrier level current. Both the current gain and current zero pots will effect the zero current output.

>QUESTION: Can you get 0 V at TP2 doing this?

Again I ask... does this mean tens of of mv or ground sort of zero? If the former the answer is yes but the pot is too touchy to ever get .000.


>QUESTION: what is the voltage at TP2 with current (assuming 0V with no current, as set above)?

I get about 0.8V


>3) Adjust the current gain one way or the other, kill the carrier, and re-zero the current zero - 0V at TP2 with no current. Transmit again. Did the output voltage at TP2 move in the direction you wanted (higher or lower, depending)? If so, and it's not where you want it, keep adjusting the current gain in the same direction, kill the carrier - re-zero, etc.. If the voltage moved in the wrong direction, adjust the current gain in the opposite direction, kill the carrier, re-zero, etc.
QUESTION: What Happens when you do this?

Always the same .8v approx depending on the exact level of "zero".

>4) Keep balancing the current gain and current zero adjustments until you get it right. It usually only takes a few tries.

I believe this but it's time to look beyond what is supposed to happen and what might be the cause of what is actually happening in my case.

Herewith from my previous post....


This exercise with current zero and gain is getting me nowhere.

The only condition that produces 3v with key down, produces 2.5v with key up.

The only condition that produces near zero volts key up produces .8v key down.

Both conditions allow the transmitter to run at full power with full modulation with no faults or other problems.

Under both sets of conditions TP1 is 3v key down and TP3 is 3v key up

TP4 2.5v key up and 2.855 key down.

js
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Re: Overload Board

Postby kf1z » Thu Oct 28, 2010 9:15 am

Found out why my board gave misleading readings....

My 1% tolerance, 1Meg resistor actually measures ...... 460 kohms!!!!
Checked it with 2 different meters...

Wow !

I don't think I've ever seen one THAT far off...
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Re: Overload Board

Postby K9ACT » Thu Oct 28, 2010 9:31 am

kf1z wrote:Oh so it's MY board that has a problem.....

>Now I must appologize to Jack profusely....


Don't you dare! Unless you send me an invoice you for the 101 good suggestions you had.

I never would have gotten to this point without your help. You can't catch them all and this advice is free.

Not that it needed to but it did increase my respect for Dan K9WEK who solved the riddle of the Voltage Follower op amp and came up with reducing the value of the 1M resistor before Steve got back with the same idea.

I learned a lot about op amps in the process and have the front end of the board in Spice now.

>And now I think I will refrain from commenting an anything else on the forum..

Be a very exciting board without you, ha ha.. don't you dare.

Aside from this issue, my current problem is getting the RF deck to work on 80M again. I had to modify the output transformer to work on 160 but now it won't work on 80 unless I go back to the original config. I am thinking of just building another RF deck but it would be nice just to be able to change filters.

Anyway, thanks for all your help and as said before, this is all a learning exorcise for me.

What the heck do I want with a boring solid state thing for when I have two wonderful tube transmitters?

js
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Re: Overload Board

Postby K9ACT » Thu Oct 28, 2010 9:39 am

kf1z wrote:Found out why my board gave misleading readings....

My 1% tolerance, 1Meg resistor actually measures ...... 460 kohms!!!!
Checked it with 2 different meters...

Wow !

I don't think I've ever seen one THAT far off...



That is a bit out of tolerance. Aint that sumpin. The good news is that mystery is solved.

AND you can blame a resistor instead of your brain for missing problem.

js
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Re: Overload Board

Postby steve_qix » Thu Oct 28, 2010 9:32 pm

This is very odd.... Ok, Jack - if you adjust the 100k current gain resistor, such that it is all the way at full resistance across the op-amp minus input and output (this will be maximum gain) - AND if you then adjust the current zero resistor so you have 0 volts at TP2 (or very close to it - you probably can't get it at perfect 0), what do you get at TP2 when you transmit - AND how much current are you running when you get whatever reading you get?

If you then put the current gain pot all the way to the other extreme - re-zero and transmit again, what do you get?

Once we know these numbers, I can advise further !

Let me know :?

Thanks and Regards, Steve
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