I'm trying to finish a 13.8v dc linear PSU to run to 30A.
[This may sound strange but I'm now retired, and had most, if not all, the bits so got started.]
General circuit:
The Pass transistors are MJ11016 (30A each, 250w). There are four of them on two enormous fan-cooled Heat-sinks.
The transformer is a 7 inch C-core cube delivering about 28v. I've satisfactorily tested this to 50A load.
Mains is applied in two stages via a small relay and a series resistor.
The rectifier is a 50A rated device, well bolted to the chassis.
There's about 75000uF, 40-60v rating in smoothing.
Wiring is in thick wire (generally around 2.5mm (but it's all AWG sizes)).
The problem as experienced:
The regulator is a standard 723 Circuit (by GI3HXV in the RadCom Handbook); it can also be found in Fig 17 of the data sheet.
Using a car headlamp as a first-step test load (5.7A), I have noticed that the output voltage fell from 13.8 to 13.65v,
and I do not know why. If I have read the data sheet right, it should hold to within 15mV.
Careful checking of the circuit showed no apparent problems.
Can someone please give me a few pointers while the three test loads arrive from China ?
Or have I missed something important?
Photos of the story so far can be provided at need.
73
Dave
[This may sound strange but I'm now retired, and had most, if not all, the bits so got started.]
General circuit:
The Pass transistors are MJ11016 (30A each, 250w). There are four of them on two enormous fan-cooled Heat-sinks.
The transformer is a 7 inch C-core cube delivering about 28v. I've satisfactorily tested this to 50A load.
Mains is applied in two stages via a small relay and a series resistor.
The rectifier is a 50A rated device, well bolted to the chassis.
There's about 75000uF, 40-60v rating in smoothing.
Wiring is in thick wire (generally around 2.5mm (but it's all AWG sizes)).
The problem as experienced:
The regulator is a standard 723 Circuit (by GI3HXV in the RadCom Handbook); it can also be found in Fig 17 of the data sheet.
Using a car headlamp as a first-step test load (5.7A), I have noticed that the output voltage fell from 13.8 to 13.65v,
and I do not know why. If I have read the data sheet right, it should hold to within 15mV.
Careful checking of the circuit showed no apparent problems.
Can someone please give me a few pointers while the three test loads arrive from China ?
Or have I missed something important?
Photos of the story so far can be provided at need.
73
Dave