CCS vs. ICAS ratings

[stevef]

I need some clarification on CCS meaning as it relates to operating mode.

1.   If a choke is rated at 500mA CCS, does this mean that the choke can easily handle 500mA steady current "forever" without heating and failing? (I assume this equates to 100% duty cycle)

2.  If I use the same choke in a power supply for CW assuming a 50% duty cycle, does this mean the choke is good for 1 Amp ?  What happens if I am tuning a CW amp for 5 seconds key-down?   I assume this is okay at 500mA, but what about at 750mA or 1 Amp?   Is this enough time at 100% duty cycle to kill the choke?
 
3.  How about SSB assuming a 25% duty cycle?   4 Amps?

4.  And of course, how about AM with 100% modulation?

Thanks ahead for the education,

Steve KK7UV

[KE6DF]

Well here is my 2 cents worth.

First of all, the power dissipated in the DC resistance is equal to I (current) squared time R (DC resistance). So if you doubled the current, you would multiply the heating due to DC resistance by 4.

So doubling the CCS rating is probably too much.

But, of course, there is also heating in the core of the choke and I'm not sure how that increases with current.

One way to get a handle on this is to look in old transformer catalogs where both a CCS and an ICAS rating is given.

Usually the ICAS is from 20% to 50% higher than the CCS rating.

AM puts a lot more strain on power supplies than SSB. Plus it depends on how long you talk. If you tend to run on for 1/2 hr at a time, then you probably should figure on CCS ratings or close to it. If you never talk for more than a couple minutes, then use ICAS ratings.

Some linear amplifier supplier skimp on power supplies figuring the amps will be used for SSB and be used to only short duty cycles. Of course, those same amps may blow a power transformer if used for AM if the op is long winded...

Personally, I try to design things (both tube ratings and power supply ratings) to stay within CCS specs.

I'd rather scrounge a bit longer, or pay it bit more, for a bigger transformer or choke that push everything to the max.

[WA1GFZ]

Also, The choke inductance is rated at the CCS current 100% duty cycle.
As you incerase current the inductance will drop as you approach cor saturation at some current above 500ma. Most designers shoot for best performance at CCS with DC resistance and core configuration. The only way to find out where your choke rolls off is to bias the winding with DC current and measure the reactance at that current.

[stevef]

Here's is what I am after:

I have a GPT-750 power transformer.  Rating is 230 primary and 2800vdc @ 750mA CCS.  I'm assuming with 240vac the output is 2920vdc.  I measured the open circuit voltage from each end of the secondary to center tap at 3500vac with 240vac on the primary.

I'd like to build a new power supply for my CW/SSB amplifier (three 813's) which in typical operation I bias just at cutoff (ZSAC=0, Class B?) for CW work, and ZSAC at 90mA for AB2 SSB.   99% of the time is on CW though.

I bought a Raytheon choke from John K5PRO which is 12H at 500mA - also a CCS rating.

Using the Duncan PSU Designer software (choke input and 47uF cap), it appears I need a HUGE amount of bleeder current to bring the voltage drop to within 5% regulation.

I can model 2920vdc at 750mA but the current through the choke is 766mA.
To keep the key-up voltage within 5% (3075v), I need a bleeder 13k and 236mA = 725watts!!!

For 3250v key-up (10% regulation), I need 17.5k at 185mA bleeder = 599 watts!!!

So, how do I make this work?

A bigger choke?

For 25 Henries and 10% regulation, the bleeder is 35k at 93mA = 300watts.  That's more like it.
For 30 Henries and 10% regulation, the bleeder is 42k at 77mA = 249watts.
and so forth...

The point is....It does not look like I am going to get what I want with a 12H/500mA CCS choke.

[KA2DZT]

A big swinging choke would work better along with the choke you have.  Use a two stage filter LCLC and don't use a big cap off the first choke.  This may work out better.  If you had a input choke that can handle more current you can put some bleeder off the first choke.  You need to keep a load on the xfmr.  Only other thing I can think of is to load down the secondary of the xfmr before the choke.

You really shouldn't run more current through the choke than it's rated for.  Some chokes will begin to fall apart even before their rated current.

Fred

[W7TFO]

Key the primary, don't use grid block or cathode circuit.

That way the load stays constant, does the work and keeps the voltage stable without a huge bleeder load.

Plus, you get that satisfying kerchunk....

73DG

[WA1GFZ]

I would give it a try. 3 813s at 2900 X 500 ma is going to make them dance.
The tubes won't handle the CCS power of almost 1500 watts. Heck you only have 375 watts of disspation.

[WA1GFZ]

Don't worry about a little voltage swing unless you need a room heater

[Opcom]

There is nothing wrong with a heavy bleed as long as you have the current to spare.

An old home brew TX here uses two 8H 400mA chokes in parallel so it is 4H/800mA. The plate transformer is good for an amp.

The bleeder is running about 95mA at 3500V, so there's 330W dissipation.

I key the B+, so I don't need the bleeder for keying reasons but I prefer it for regulation improvements during modulation when the load is variable.

The 4-1000 output stage running from that supply can only draw about 650mA. - -but it is never operated on the air like that so such "QRO" operations that might push the power supply are few.

I'd guess the Raytheon choke could be pushed +20% for short periods on AM but why risk more?

[KA2DZT]

Read the OP's opening statement.  He is using the supply for CW and SSB.  I don't think he mentioned anything about AM.

Fred

[KX5JT]

Read the OP's opening statement.  He is using the supply for CW and SSB.  I don't think he mentioned anything about AM.

Fred

Uhm Fred??

4.  And of course, how about AM with 100% modulation?

Thanks ahead for the education,

Steve KK7UV

He sure did mention AM! 

All I know is when I finally get around to building my first plate modulated AM rig,  I'm going with CCS ratings on everything if possible.  That way no worries about keydown time.

Overbuild and underdrive!  HEADROOM BABY!

Thanks to these forums for teaching me this!

73 !! From the the land between the swamp, marshes and Gulf

de KX5JT
 
 

 

[WA1GFZ]

How about a 4-400 in the final and use the 813s as modulators.
You are not going to destroy the choke the inductance will drop on current peaks.  I think the GPT-750 ran a pair of 4-400s.

[KA2DZT]

Read the OP's opening statement.  He is using the supply for CW and SSB.  I don't think he mentioned anything about AM.

Fred

Uhm Fred??

4.  And of course, how about AM with 100% modulation?

Thanks ahead for the education,

Steve KK7UV

He sure did mention AM!  

All I know is when I finally get around to building my first plate modulated AM rig,  I'm going with CCS ratings on everything if possible.  That way no worries about keydown time.

Overbuild and underdrive!  HEADROOM BABY!

Thanks to these forums for teaching me this!

73 !! From the the land between the swamp, marshes and Gulf

de KX5JT
 
 

 

John,

You're right, he did mention AM in his first post.  But in his second post he said the PS was just for CW and SSB.  I guess I remembered the second post and didn't reread the 1st post, which is what I told everyone else to do.  

Fred

[KM1H]

There is commecial grade CCS and ham grade CCS. Roughly translated one is for 24/7 and the other for contest or RTTY duty.

Most of the old line transformer companies had a least 2 grades and sometimes an economy grade for the real cheap ham.... Dont make long AM transmissions

Mil Spec is hard to catergorize but is generally above commercial grade for excess current capacity

Carl

[Jim, W5JO]

ICAS = Intermittent Commercial Amateur Service.  CCS = Continous Commercial Service.  You can tailor parameters anywhere between the two to suit your needs.  One is 100% duty cycle at stated ratings and the other will stand about 50% duty cycle. 

If you have the money and patience build to CCS then cool it.  Insulation voltage is about the same.  If you build to ICAS follow the cooling specifications and operate in the manner the specifications describe.

[WA1GFZ]

or use the parts you have but leave room in the box for bigger parts when you find them.