PD or Iota for my upgrade?
I'm thinking about a converter and battery upgrade. The batteries will be wet cell lead acid 6 volt Possible T-105s or the 230AH, EGC2 from Sam's club. I'll probably go for four. (Does nayone have...
Forum Discussion
I don't know why, but my last post seems to have disappeared.
The voltage feedback circuit uses an optoisolator, and I looked it up. It's actually a precision optically isolated error amplifier. That's why the UC3846 is connected with unity gain - they aren't using it as the error amp. It's just the input from the FOD2741 optically isolated error amplifier.
I've also considered the gain issue. The UC3846 keeps increasing duty cycle and current (and voltage) until the signal from the current monitor matches the error voltage signal. Increasing the error voltage signal would give more current, but so would decreasing the current signal. It turns out that the PD has a (crudely) adjustable setting for the current signal. It has multiple resistors in parallel and by removing one or more, one can increase the resistance and increase the voltage produced at any given current level.
And, surprise, the PD has one of those resistors removed to adjust the signal. This produces the same effect as changing the voltage error signal amplifier gain, except for one thing. There's a current limit resistor bridge that sets the maximum allowed current. That bridge would need to be adjusted for the new voltage that corresponds to 80A.
Still, that seems to be how the circuit was designed for adjustment. Adding a resistor in the current sense circuit to replace the missing one will cause the UC3846 to send more current for any given voltage error signal. It should send up to the current limit (which needs to be readjusted) until it matches the voltage error (difference between the output voltage and the target voltage of 14.8VDC)
The voltage feedback circuit uses an optoisolator, and I looked it up. It's actually a precision optically isolated error amplifier. That's why the UC3846 is connected with unity gain - they aren't using it as the error amp. It's just the input from the FOD2741 optically isolated error amplifier.
I've also considered the gain issue. The UC3846 keeps increasing duty cycle and current (and voltage) until the signal from the current monitor matches the error voltage signal. Increasing the error voltage signal would give more current, but so would decreasing the current signal. It turns out that the PD has a (crudely) adjustable setting for the current signal. It has multiple resistors in parallel and by removing one or more, one can increase the resistance and increase the voltage produced at any given current level.
And, surprise, the PD has one of those resistors removed to adjust the signal. This produces the same effect as changing the voltage error signal amplifier gain, except for one thing. There's a current limit resistor bridge that sets the maximum allowed current. That bridge would need to be adjusted for the new voltage that corresponds to 80A.
Still, that seems to be how the circuit was designed for adjustment. Adding a resistor in the current sense circuit to replace the missing one will cause the UC3846 to send more current for any given voltage error signal. It should send up to the current limit (which needs to be readjusted) until it matches the voltage error (difference between the output voltage and the target voltage of 14.8VDC)
