Here is a picture (not balanced F5)!
Almost a year, I am using 2SK1529/J200 without thermistor & current limiter, I like them better than Fairchild mosfets!
Biased at 1.75A and 8oC-10oC (kapton isolators) difference between heatsink and mosfets!
An externally hosted image should be here but it was not working when we last tested it.
Inrush calculation check
I posted a form of this question on the PS forum, but didn't get any answers.
I'm accustomed to the NTC (CL-60) that NP uses for the F5 PS. In looking at a PS for the Balanced F5, I could not tell if a different NTC was appropriate. I've read through the various calculations, the one area I couldn't really understand was Cmax.
I was considering two 500VA toroids with 120V primaries and 15V secondaries.
I used the Ametherm website and tried to fill in the blanks.
On Imax, they suggest 120V input (170Vmax) and I thought I'd be OK with 10A max yielding a 17 ohm NTC.
Many of the NTCs list a Cmax of around 300-5000uf. If I have 108,000uf in filter caps, how many joules do I need to worry about? Is it simply Joules=.5*(.108)*20^2? Or about 21 joules? That seems quite small.
Finally, if I use 500VA toroids, is the calculation of maximum constant current as simple as =500/120*.9 (efficiency) or ~4.6A?
In conclusion, an NTC with 17ohm resistance, able to handle 21J, and 4.6A steady state is proper?
I posted a form of this question on the PS forum, but didn't get any answers.
I'm accustomed to the NTC (CL-60) that NP uses for the F5 PS. In looking at a PS for the Balanced F5, I could not tell if a different NTC was appropriate. I've read through the various calculations, the one area I couldn't really understand was Cmax.
I was considering two 500VA toroids with 120V primaries and 15V secondaries.
I used the Ametherm website and tried to fill in the blanks.
On Imax, they suggest 120V input (170Vmax) and I thought I'd be OK with 10A max yielding a 17 ohm NTC.
Many of the NTCs list a Cmax of around 300-5000uf. If I have 108,000uf in filter caps, how many joules do I need to worry about? Is it simply Joules=.5*(.108)*20^2? Or about 21 joules? That seems quite small.
Finally, if I use 500VA toroids, is the calculation of maximum constant current as simple as =500/120*.9 (efficiency) or ~4.6A?
In conclusion, an NTC with 17ohm resistance, able to handle 21J, and 4.6A steady state is proper?
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NP, thanks for the input.
The CL-30 is 2.5 ohms. Do you use them in series?
The CL-30 is 2.5 ohms. Do you use them in series?
I would use one for each transformer.
I'm pretty casual about the calculations on the thermistors -
with FW I use one CL60 with 240V operation and one for
each winding on the parallel 120V primaries.
For larger products, we use CL30's.
Thanks Andrew, yeah I figured lowering the rails slightly might be a consideration due to the smaller pad, its an advantage one way WRT capacitance and likely bandwidth, but as you say cannot lose as much heat.
but if that is the only thing I need to worry about I can cope with that, I will build as specified and measure temp, if there is a very small issue I will lower the rails and bias current, if there is more than a minor reduction needed then I will simply replace with K1530/J201.
I built a 1.2kva balanced power supply using a toroid.
To start the toroid, I bought a Microprocessor controlled soft start relay. It allows the power to ramp up from 0V to full voltage over one second. It's a bit expensive at $100, but I sleep well at night.
It is made by crydom, and is in their MCS series. I got it from mouser.
No. We have a switch/breaker with a large surge capacity.
On the higher power units we don't want the losses of a
higher thermistor value.
Pictures please
Only a true DIY'er can get excited about pictures of a transformer...
My transformers probably won't show up for a couple more days over here on the west coast, so yes pictures please...
Attachments
Wow--you mean, you even got a stack of $1 bills, with your transformers? Nice.....
If you are in Western New York state, I'm guessing you'll have a LOT of time to build the amp, before you get your Spring Thaw!
Nice tranformer!
Yeah! The dollar is so weak the Canadians use it for packing
Be thankful your not from Zimbabwe, their currency is used for heating
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