What's Wrong With My Power Supply?

[HRTKD]

I have a Long Wei DC Power Supply PS-3010DF. With a setting of 3.40 volts (no current setting) and with 14 awg cable, banana plugs on one end and crimped ring terminals on the other end (battery) it works fine. The screen shows Constant Voltage of 3.41 volts and variable current of about 2.67 amps. Voltage measured at the terminals (not the busbar) is 3.32 volts.

If I add beefier cables (6 awg) with appropriately sized ring terminals on both ends, the power supply immediately changes to constant current. I don't understand this.

To complicate matters, any Constant Voltage setting over 3.49 volts causes the power supply to switch Constant Current no matter what cables are used.

I don't recall having these issues when I used the power supply a few years ago to top balance 8p 280Ah cells. This time it's 9p 280Ah cells, which is the first set of 18 cells to be charged.

No, I don't want to charge the cells using the BMS. I prefer to do the old school Top Balance.

 

[Bob B]

What is the current from the power supply when it switches to constant current?

Mine has both voltage and current settings, and when the current reaches the max output of the power supply it has that same behavior.

I don't know if it's that it can no longer maintain the set voltage .... or that it has reached max current that causes it to switch.

 

[niktak11]

That sounds like it's working correctly. It will operate in constant current mode until the voltage is at the set voltage. Use the larger gauge wire to prevent it from switching to constant voltage too early.

 

[LakeHouse]

With a setting of 3.40 volts (no current setting) and with 14 awg cable, banana plugs on one end and crimped ring terminals on the other end (battery) it works fine. The screen shows Constant Voltage of 3.41 volts and variable current of about 2.67 amps. Voltage measured at the terminals (not the busbar) is 3.32 volts.

How are you setting your voltage? If you set to 3.40 correctly, you should not see 3.41V, regardless of current. You need to have an open circuit (i.e., connected to nothing) to set the voltage. Once you've done that, then you can connect to your battery, but don't adjust the voltage knobs again. Leave them as they are.
To set maximum current, you short the connections and adjust the current knobs, but for that power supply you probably don't need to worry about limiting current and can just go flat out.

If I add beefier cables (6 awg) with appropriately sized ring terminals on both ends, the power supply immediately changes to constant current. I don't understand this.

This makes sense if your current knobs aren't dialed all the way up... With smaller wire, the power supply is reaching your voltage set point and only able to push some limited amount of current because there's resistance in the wires and connections. Like you said, 3.41V at the power supply, 3.32V at the battery - the rest of that voltage is being 'lost' from resistance in the wire and connections. If you switch to bigger wire, now you don't have as much loss and so the power supply is trying to get to the voltage setting, but can't because it ends up limited by the current setting.

 

[sunshine_eggo]

If I add beefier cables (6 awg) with appropriately sized ring terminals on both ends, the power supply immediately changes to constant current. I don't understand this.

You've reduced cable resistance and thus reduced the voltage drop enough for the power supply to supply max current.

To complicate matters, any Constant Voltage setting over 3.49 volts causes the power supply to switch Constant Current no matter what cables are used.

By setting a higher voltage, you've allowed more margin for voltage drop, so you've overcome the resistance in the higher resistance wires and are allowing max current.

 

[Zwy]

I have a Long Wei DC Power Supply PS-3010DF. With a setting of 3.40 volts (no current setting) and with 14 awg cable, banana plugs on one end and crimped ring terminals on the other end (battery) it works fine. The screen shows Constant Voltage of 3.41 volts and variable current of about 2.67 amps. Voltage measured at the terminals (not the busbar) is 3.32 volts.

If I add beefier cables (6 awg) with appropriately sized ring terminals on both ends, the power supply immediately changes to constant current. I don't understand this.

Less resistance so more current will flow.

No finger on the end of a water hose, water flows freely and more flow than when you cover one half of the hose end with your finger creating resistance.

To complicate matters, any Constant Voltage setting over 3.49 volts causes the power supply to switch Constant Current no matter what cables are used.

Working as it should, power supply will run in CC until the CV voltage setting is reached.

I don't recall having these issues when I used the power supply a few years ago to top balance 8p 280Ah cells. This time it's 9p 280Ah cells, which is the first set of 18 cells to be charged.

You're just getting forgetful.

No, I don't want to charge the cells using the BMS. I prefer to do the old school Top Balance.

I use a combination of both. I run the cells up to around 3.6V using a BMS, then parallel them. Finish at 3.65V until close to 0A. Only takes a few hours once I pull the BMS off.

 

[HRTKD]

How are you setting your voltage? If you set to 3.40 correctly, you should not see 3.41V, regardless of current. You need to have an open circuit (i.e., connected to nothing) to set the voltage. Once you've done that, then you can connect to your battery, but don't adjust the voltage knobs again. Leave them as they are.
To set maximum current, you short the connections and adjust the current knobs, but for that power supply you probably don't need to worry about limiting current and can just go flat out.

I set the voltage exactly as you've recommended. No leads connected, set voltage. Turn off power supply, connect leads. It sort of does its own thing as far as what it displays for the voltage reading. Sometimes it's 3.40, sometimes 3.31 and as stated in the first post, sometimes 3.41 even though the no load setting is 3.40.

I use a combination of both. I run the cells up to around 3.6V using a BMS, then parallel them. Finish at 3.65V until close to 0A. Only takes a few hours once I pull the BMS off.

I understand. But what I'm seeing is that if I did that, setting my power supply to 3.65 volts, it would immediately switch to constant current.

I don't know if it's that it can no longer maintain the set voltage .... or that it has reached max current that causes it to switch.

I'll have to go back and put the larger wires back on and see what the current was. The power supply is rated for 30volts/10amps.

To everyone else that responded, I do understand that larger wires means less resistance. I was hoping to bring up the amps to get the top balancing done a bit faster. In top balancing, constant voltage is what we want. Constant current would have bad results, right? I've never let it run constant current, so I don't know what the end result would be.

 

[Bob B]

I set the voltage exactly as you've recommended. No leads connected, set voltage. Turn off power supply, connect leads. It sort of does its own thing as far as what it displays for the voltage reading. Sometimes it's 3.40, sometimes 3.31 and as stated in the first post, sometimes 3.41 even though the no load setting is 3.40.



I understand. But what I'm seeing is that if I did that, setting my power supply to 3.65 volts, it would immediately switch to constant current.



I'll have to go back and put the larger wires back on and see what the current was. The power supply is rated for 30volts/10amps.

To everyone else that responded, I do understand that larger wires means less resistance. I was hoping to bring up the amps to get the top balancing done a bit faster. In top balancing, constant voltage is what we want. Constant current would have bad results, right? I've never let it run constant current, so I don't know what the end result would be.

It should switch to constant voltage once the battery voltage gets close to the setpoint.

 

[HRTKD]

It should switch to constant voltage once the battery voltage gets close to the setpoint.

I'm thinking of putting the big cables back on and using a constant voltage of 3.40 volts. However, since I'm not sitting there watching it, I'm a bit reluctant. Like I said before, this isn't how it worked last time, but I may not have used larger cables that time.

 

[niktak11]

I'm thinking of putting the big cables back on and using a constant voltage of 3.40 volts. However, since I'm not sitting there watching it, I'm a bit reluctant. Like I said before, this isn't how it worked last time, but I may not have used larger cables that time.

That means you used smaller gauge wires and/or had a poor connection last time. The charger should remain in constant current until the cell voltage is close to the set point or something is wrong.

 

[HRTKD]

I put the bigger wires back on, keeping the same voltage setting of 3.45. The amps were at only 2.85. If it had gone to 10 amps I could see that the power supply was doing all it could until it got closer to the constant voltage. But that doesn't seem to be the case. I switched back to the smaller wires so it was in constant voltage mode.

When I have time to keep a closer eye on it I'll put the bigger wires on and let it run for a while.

 

[niktak11]

If you set the voltage correctly then turn the amps all the way up and leave it on. Even at 10A it will take a long ass time unless the cells are nearly full.