Power supply voltage off ~0.1v?

memilanuk

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A few months ago, I picked up a 30v 10A bench top power supply (Rockseed RS310P, if that matters) and for the last few days I have had it chugging away charging a pack of four Gangfeng 277aH cells in parallel @ 3.50 vdc & 9.5 amps. The cells are bolted together using the vendor supplied bus bars, and I replaced the OEM banana plug / alligator clip leads for the PS with #10AWG and ring terminals, the + lead to one end of the positive bus bars, and the - lead to the opposite (diagonal) end of the negative bus.

I've been checking off and on, with my old warhorse Fluke 79 series III multimeter connected at the mid point of the + & - bus bars respectively... and it routinely reads 0.1 to 0.14v lower than the $99 power supply e.g. with the power supply finally reading 3.50 volts after days of charging... the Fluke reads ~3.37vdc.

I know which one I trust, based on long years of experience... but what to do about it is the question? I'm not seeing anything in the manual about any kind of zero calibration...
 

Horsefly

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Never, ever, ever trust the voltage displayed on the power supply. When you set up to top balance your cells, hopefully you adjusted the voltage with the power supply disconnected from the cells, measuring the voltage with the Fluke and adjusting it to the desired charge voltage. Ignore what the PS says.

While it is charging, hang on to your belief in Fluke. Don't touch the power supply dials.

Don't worry about calibrating the power supply. Doing so would make you trust it instead of the Fluke. TRUST THE FLUKE!
 

Bob B

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You should check the voltage right at the power supply terminals.

Even though you have improved the power supply leads, you will still be getting some voltage drop across the leads at close to 10A.
As the top balance nears completion, the current will drop off and the voltage drop across the loads will reduce.
So .... to know what voltage the power supply is actually providing, you will need to test the voltage right on the power supply terminals .... or remove the load and test on the end of the leads.
This is why it is recommended to adjust the power supply before connecting the leads because the load will change things.

You want the voltage adjusted for low or zero load since that is what you will have when the top balance finishes.
 

memilanuk

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Alright... even when I check right at the terminals on the PS, I'm not getting quite the same reading as what's on the display... although as it gets closer to final charge, the delta seems to tighten up a bit.

So if I'm going for (eventually) a 3.60 volt top balance, but the Fluke still says it's at 3.51 or 3.52 even after the PS voltage seems to have stabilized @ 3.50 and the current has dropped way off to 0.4xx amps... do I then dial up the PS to 3.65 or 3.7, so that the 'actual' voltage at the cells is @ 3.60?
Or better to call it close enough, assemble the battery in its final 4S config with the BMS and let the system charger do it's thing?
 

Horsefly

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Alright... even when I check right at the terminals on the PS, I'm not getting quite the same reading as what's on the display... although as it gets closer to final charge, the delta seems to tighten up a bit.

So if I'm going for (eventually) a 3.60 volt top balance, but the Fluke still says it's at 3.51 or 3.52 even after the PS voltage seems to have stabilized @ 3.50 and the current has dropped way off to 0.4xx amps... do I then dial up the PS to 3.65 or 3.7, so that the 'actual' voltage at the cells is @ 3.60?
Or better to call it close enough, assemble the battery in its final 4S config with the BMS and let the system charger do it's thing?
I'm still not sure if you are understanding what I said above. Based on the wording you just posted, I think you probably didn't understand. Let me itemize the points:
  1. Never trust the voltage being displayed on the PS
  2. Disconnect the PS from the batteries (or any other load), before adjusting the voltage on the PS
  3. Use a good meter (Fluke is good!) to measure the voltage of the PS with NO LOAD.
  4. Adjust the PS to the final voltage you want to balance at, with NO LOAD and READING ONLY THE FLUKE
  5. Hook up the PS to your parallel-connected cells.
  6. While there is much current at all going from the PS into the cells, there will be voltage drop in the wires, so seeing a lower voltage at the cells than at the PS is to be expected.
  7. The current will drop as the voltage at the cells rises to what the PS was adjusted to. You should not stop the top-balance until after you have seen the same voltage measured on the PS and the cells USING THE FLUKE on both sides.
 

Bob B

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Alright... even when I check right at the terminals on the PS, I'm not getting quite the same reading as what's on the display... although as it gets closer to final charge, the delta seems to tighten up a bit.

So if I'm going for (eventually) a 3.60 volt top balance, but the Fluke still says it's at 3.51 or 3.52 even after the PS voltage seems to have stabilized @ 3.50 and the current has dropped way off to 0.4xx amps... do I then dial up the PS to 3.65 or 3.7, so that the 'actual' voltage at the cells is @ 3.60?
Or better to call it close enough, assemble the battery in its final 4S config with the BMS and let the system charger do it's thing?

You never want to adjust the power supply while it is under load .... only when it is not connected to the cells.
 

memilanuk

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  1. Never trust the voltage being displayed on the PS
  2. Disconnect the PS from the batteries (or any other load), before adjusting the voltage on the PS
  3. Use a good meter (Fluke is good!) to measure the voltage of the PS with NO LOAD.
  4. Adjust the PS to the final voltage you want to balance at, with NO LOAD and READING ONLY THE FLUKE
  5. voltage measured on the PS and the cells USING THE FLUKE on both sides.

#3 is where I'm having some trouble. PS is set for 3.500 vdc, 9.80 amps. Disconnected the leads from the PS entirely. Press the small green button to activate the output. The voltage output light flashes green for a moment, then goes out, and the bottom line of the display goes from reading 'OFF' to 'O.U.P.' (or 'O.V.P.', hard to tell with a seven-segment LCD). Doesn't matter if I have the Fluke connected or not. If it is connected, the voltage briefly starts to rise, but just about as fast as that output light goes off... the voltage goes away.
 

Horsefly

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#3 is where I'm having some trouble. PS is set for 3.500 vdc, 9.80 amps. Disconnected the leads from the PS entirely. Press the small green button to activate the output. The voltage output light flashes green for a moment, then goes out, and the bottom line of the display goes from reading 'OFF' to 'O.U.P.' (or 'O.V.P.', hard to tell with a seven-segment LCD). Doesn't matter if I have the Fluke connected or not. If it is connected, the voltage briefly starts to rise, but just about as fast as that output light goes off... the voltage goes away.
I have no idea what is going on with this PS. Can you provide a link to where you bought it? A "small green button to activate the output"? I have several of these bench power supplies, and all of them have an ON/OFF switch, and if the switch is on the output is active.

I may be tired, but I have no idea what O.U.P. or O.V.P. could mean.
 

Hedges

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This supply appears to have "over voltage" and "over current" settings, in addition to voltage and current.
Look into adjusting those values.

I've used them (in my HP supplies) to protect against commanding excessive voltage. They also detect of circuit under test goes too high for some reason, and shut off. Turned out whatever setting also became the opposite-polarity limit, so if I set a supply for 17V and 0.5 above that 17.5 for over-voltage, then output pulled negative (two supplies to make +/-17V), when pulled below -0.5V it tripped. I used clamping diodes and set the over-voltage more than one diode drop.

 

memilanuk

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I have no idea what is going on with this PS. Can you provide a link to where you bought it?

Programmable 30V/10A DC Power Supply Variable, Adjustable Switching Regulated Power Supply with 4-Digit Large Display Alligator Leads, PC Software, USB Interface, 110V~60HZ, (310P)


A "small green button to activate the output"? I have several of these bench power supplies, and all of them have an ON/OFF switch, and if the switch is on the output is active.

41YiwJsTmRL._AC_SY580_.jpg




Big red button turns on the unit. Small green button next to it activates the output.
 

Hedges

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Check and adjust the over-voltage protection:

"14. "OVP" over-voltage setting key: Use a short press of the OVP button to enter edit mode of the over voltage protection feature. The top Voltage display (item 1) will now show “OUP” and the center Current display (item 2) labeled “A” will be enabled for entering the voltage as indicated by the flashing least significant digit. The 3rd Power/Time/Status Display (item 3) line of the display will show the On/OFF status of the over voltage protection feature, pressing the OVP button again will toggle this feature On and OFF. To enter the OVP value press the “B Lock” (item 9) key (see note below about the inactivity timeout). With the "OVP" feature turned “On” as indicated above, when the main ON/OFF power output button (item 4) is turned on then power is applied to the load. If the load encounters more voltage then the OVP setting then the OVP key briefly flashes, power to the load is turned off, and “O.U.P.” appears on the Power/Time/Status Display (item 3).

Note: there is a 5-second inactivity timeout in effect during editing mode. This means that if no front panel adjustments are made for a period of 5 seconds then the unit will time out and automatically enter the settings currently displayed and will then exit edit mode. Press the “OVP” button again to re-enter edit mode. "

 
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