HighTechLab
AKA Dexter - CTO of Current Connected, LLC
- Joined
- Sep 23, 2019
- Messages
- 1,685
Looking for electronics expert...
Recently I've acquired 2x HP/Agilent 6671A System Power Supplies. Their output is 220a @ 8v each. Let's come back to this...
Currently, I am successfully using HP 6031A 20v120a 1kw bench power supply, tasks including top-balancing and capacity testing, then recharging. It works well because the power supply can also be used to charge the batteries when they are setup in a 12v configuration as well as 3.65v thanks to 20v max limit of power supply.
The user manuals for the power supplies specifically state the following:
Quote
To accomplish this with my current setup, I have a 200a stud-type diode screwed into a heatsink with a small fan. Heat dissipation is minimal, because I'm dealing with only 120a & .7v forward voltage, so around 80 watts of heat, no big deal. I then provide voltage sense leads after the diode, connected directly to the batteries being charged and things work great.
Now that I have the two new power supplies, I can theoretically connect them in parallel, and charge 3.6v @ 440a, and due to the 8v limit if I wanted to charge at 12v, I would need to connect them in series (16v max limit). What an improvement to the speed that I can work, right?
Trouble is, the new power supplies need diodes also. If we calculate 220a of current @ .7v forward voltage of a diode per supply, I now have ~300w of heat to do something with. Where I previously had a tiny computer fan and a heat sink from a power inverter that was in the scrap bin, this new setup will require much more heat dissipation if I'm going to take the same approach of using a diode. Not that power usage of the system is a huge concern, I'm not the biggest fan of having a new 300w heater in the lab.
So I guess the question is, how can I build a more ideal diode here? I've heard that you can use PFETs (or perhaps NFETs) to provide a better solution here, but I am clueless...My area of expertise is batteries not FETs. Any guidance in the right direction is very much appreciated!
Recently I've acquired 2x HP/Agilent 6671A System Power Supplies. Their output is 220a @ 8v each. Let's come back to this...
Currently, I am successfully using HP 6031A 20v120a 1kw bench power supply, tasks including top-balancing and capacity testing, then recharging. It works well because the power supply can also be used to charge the batteries when they are setup in a 12v configuration as well as 3.65v thanks to 20v max limit of power supply.
The user manuals for the power supplies specifically state the following:
Quote
Battery Charging
The power supply's OVP circuit has a downprogrammer FET that discharges the power supply output whenever OVP trips. If a battery (or other external voltage source) is connected across the output and the OVP is inadvertently triggered or the output is programmed below the battery voltage, the power supply will sink current from the battery. To avoid this, insert a reverse blocking diode in series with the output of the supply. Connect the diode cathode to the + battery terminal and the diode anode to the supply + output terminal. The diode will require a heat sink.
To accomplish this with my current setup, I have a 200a stud-type diode screwed into a heatsink with a small fan. Heat dissipation is minimal, because I'm dealing with only 120a & .7v forward voltage, so around 80 watts of heat, no big deal. I then provide voltage sense leads after the diode, connected directly to the batteries being charged and things work great.
Now that I have the two new power supplies, I can theoretically connect them in parallel, and charge 3.6v @ 440a, and due to the 8v limit if I wanted to charge at 12v, I would need to connect them in series (16v max limit). What an improvement to the speed that I can work, right?
Trouble is, the new power supplies need diodes also. If we calculate 220a of current @ .7v forward voltage of a diode per supply, I now have ~300w of heat to do something with. Where I previously had a tiny computer fan and a heat sink from a power inverter that was in the scrap bin, this new setup will require much more heat dissipation if I'm going to take the same approach of using a diode. Not that power usage of the system is a huge concern, I'm not the biggest fan of having a new 300w heater in the lab.
So I guess the question is, how can I build a more ideal diode here? I've heard that you can use PFETs (or perhaps NFETs) to provide a better solution here, but I am clueless...My area of expertise is batteries not FETs. Any guidance in the right direction is very much appreciated!