PD Converters and Water Usage
For Dry Campers Only No secret I've been a fan of PD converters for 15 yrs or more, and for more than one reason. The PD maintains my batteries every day of the year, except for the 4-5 months that...
Forum Discussion
No, fan isn't the problem. What you see is the signature characteristic of all PD converters. It's a design flaw. As you see it's operating open loop. There's no current regulation, nor is there any voltage regulation. You can improve charging results if the charging cable resistance is reduced and/or if battery resistance is reduced (like AGM), but the signature remains.
All converters have:
1. a peak charge circuit (diode & capacitor) front end that converts ac to 170Vpeak dc.
2. a transformer that drops the 170Vdc to usable levels.
3. a pwm controller (and power fets) that controls transformer switching to achieve the desired output voltage.
4. diodes & inductor/capacitor filter at transformer output to convert pwm waveform to a dc level.
The regulated output voltage is:
Vout = Vpc * Np/Ns * pwm
Where:
Vpc is the peak charge voltage
Np is the number of primary turns on the transformer
Ns are the turns on the secondary
pwm is the percent duty cycle of the controller
Under high loads (in other words in boost mode), the front end peak charge Vpc drops. This is typical for that type of circuit. As Vpc drops, pwm gets bigger to keep Vout constant. So what's the problem? Vpc drops so much that pwm goes to 100% and can't maintain regulation. It's now operating open loop. The design flaw is that the transformer turns ration is incorrect. The secondary doesn't have enough turns.
Here's another plot. Same characteristics. The PD is at 14.1V while outputting 50A. Its regulation point is 14.4V. That's where it should be at (or in current limit). But it can't get there.
All converters have:
1. a peak charge circuit (diode & capacitor) front end that converts ac to 170Vpeak dc.
2. a transformer that drops the 170Vdc to usable levels.
3. a pwm controller (and power fets) that controls transformer switching to achieve the desired output voltage.
4. diodes & inductor/capacitor filter at transformer output to convert pwm waveform to a dc level.
The regulated output voltage is:
Vout = Vpc * Np/Ns * pwm
Where:
Vpc is the peak charge voltage
Np is the number of primary turns on the transformer
Ns are the turns on the secondary
pwm is the percent duty cycle of the controller
Under high loads (in other words in boost mode), the front end peak charge Vpc drops. This is typical for that type of circuit. As Vpc drops, pwm gets bigger to keep Vout constant. So what's the problem? Vpc drops so much that pwm goes to 100% and can't maintain regulation. It's now operating open loop. The design flaw is that the transformer turns ration is incorrect. The secondary doesn't have enough turns.
Here's another plot. Same characteristics. The PD is at 14.1V while outputting 50A. Its regulation point is 14.4V. That's where it should be at (or in current limit). But it can't get there.
DrewE wrote:Salvo wrote:
If you don't know what you got then you're in the dark.
Here's a 60A PD that only outputs 24A and declines from there. It takes the PD about 100 minutes for it to get to 14.4V.
I wonder if the fan in the converter was not working properly or it otherwise had inadequate cooling. It starts out at 44A or so, but after a very short time (a minute or two, maybe?) is much lower. The curves do suggest that it's neither being voltage nor current limited.
