Issue with DC power supply? please help

[x4dow]

hey guys, using a dc power supply (small 30v10A one) to top my lf280Ah and im a bit confused. I've used this power supply on little diy projects before, always worked fine. on its own the voltage is spot on, etc.

now the issue i have.
I got eve 280ah cells all hooked in parallel. set the dc supply to 3.6V, and when i connect it to the batteries , the dc power supply instead of staying on 3.6v and shooting out X amps, it displays the batteries voltage ( 3.32v) and apparently is sending out 1.5Amps. (batteries on their own measure 3.31).
now.. i may be wrong, but shouldnt the display stick to whatever i set it and measuring the busbars while connected should say 3.6 right?

adjusting the voltage knob doesnt change the voltage/amperage while connected, but as i disconnect the voltage goes to whatever its set.

seems like the current is going backwards?

 

[Bud Martin]

The Voltage display on the power supply will drop down and it will rise back up when the battery is full charge.
Are you using 10 gauge wires and ring lugs for wiring? What did you set the CC setting too?
What is the Vdrops shown on the wires?
I would not do full 10A current pull on these low cost power supply, I would set the max current limit to 8A (80%)

 

[x4dow]

The Voltage display on the power supply will drop down and it will rise back up when the battery is full charge.
Are you using 10 gauge wires and ring lugs for wiring? What did you set the CC setting too?
What is the Vdrops shown on the wires?
I would not do full 10A current pull on these low cost power supply, I would set the max current limit to 8A (80%)

tried higher gauge cables and have the same issue.
my problem is not the 1.5A, these power supplied dont shoot a lot of amps at low voltage.

what i think is not right is the voltage not moving when i try to adjust while connected/on. it just displays the battery voltage. even if i turn the knob to the max (30V), the display remains on 3.32V 1.5A, the moment i disconnect 1 end, goes up to whatever voltage (30 for example). Surely the voltage/amps would go up if i gone up to 4V for example, but isnt doing that

All videos i see on top charging, the dc power supplied shows the voltage you SET, not the voltage of the batteries you're connected to. if you connected to a 12v battery and set it to 14.4, the display shows 14.4, not 12.

 

[Bud Martin]

Can we see the power supply?
If is rated at 10A it should be able to do 10A easily from 1V ~30V, 30V 10A power supply is 300W power supply.
How big is the wire gauge?
Can we see you setup?
Do you get the same result using resistor (large wattage) as the load?

 

[x4dow]

Can we see the power supply?
If is rated at 10A it should be able to do 10A easily from 1V ~30V, 30V 10A power supply is 300W power supply.
How big is the wire gauge?
Can we see you setup?
Do you get the same result using resistor (large wattage) as the load?

atm I'm using a 1 footlong 12Awg cable,
its a cheap Chinese one, thats probably the issue (photo below)

all the videos i see on top balancing (like here:

) the moment the supply is plugged to the battery, for example set to 3.6, the value stays on 3.6 on the display, on mine, the moment the connector touches the battery, drops down and shows the voltage of the cell instead and adjusting the voltage knob does nothing. CC/A is set to max.

Again, my problem isnt how many amps its outputing, but the fact that the unit just reads the battery's voltage instead of outputing whatever voltage i set on it.

 

[Bud Martin]

As you know power supply has output impedance (Zs), the really good power supply will have very very low impedance.
If the load has very low impedance, lower than the output impedance of the power supply, when you hook that load to it the power supply at the out put will drop. For example you set the output of the power supply to 2V, then you connect the load to it (disregard the cable resistance for now) then you see the power supply meter only shows 1V, it means that there is 1V Vdrops internally inside the power supply due to the power supply has internal impedance same as the load. If you at the Z (Ir) of battery as printed on the label, it is < 1 milliOhms (my LIESHEN 280Ah shows 0.13 milliOhms, so when I connect my power supply the Voltage on the display drops down from the setting of 3.60V (open circuit)), the Zs of your power supply is higher than that. Does your power supply spe sheet show Output Z value? It is also why it is important to use large wire gauge.

Output impedance - Wikipedia

en.wikipedia.org

 

[x4dow]

As you know power supply has output impedance (Zs), the really good power supply will have very very low impedance.
If the load has very low impedance, lower than the output impedance of the power supply, when you hook that load to it the power supply at the out put will drop. For example you set the output of the power supply to 2V, then you connect the load to it (disregard the cable resistance for now) then you see the power supply meter only shows 1V, it means that there is 1V Vdrops internally inside the power supply due to the power supply has internal impedance same as the load. If you at the Z (Ir) of battery as printed on the label, it is < 1 milliOhms (my LIESHEN 280Ah shows 0.13 milliOhms, so when I connect my power supply the Voltage on the display drops down from the setting of 3.60V (open circuit)), the Zs of your power supply is higher than that. Does your power supply spe sheet show Output Z value? It is also why it is important to use large wire gauge.

Output impedance - Wikipedia

en.wikipedia.org

so in short when i set the power supply to 3.6 and plug it to a 3.31 cell and the power supply display shows 3.33 1.5A, it is charging it right? (at roughly 5w~ in this case)

I might wire the cells in 8S (24V) with the BMS and charge them series at ~28V first as I will get all the cells closer to 95~%+ capacity faster

 

[Bud Martin]

so in short when i set the power supply to 3.6 and plug it to a 3.31 cell and the power supply display shows 3.33 1.5A, it is charging it right? (at roughly 5w~ in this case)

I might wire the cells in 8S (24V) with the BMS and charge them series at ~28V first as I will get all the cells closer to 95~%+ capacity faster

if it shows current draw it means it is being charged it, but like I said, 1.5A is very low charging current, something is limiting it, I.E. wiring, contact resistance, etc. What is the Voltage drops on the wire?
Do you have Solar charger controller yet? Is it charger controller with built-in AC-DC charger? if it is you can use that to charge the whole series pack (with BMS), or just use your 30V10A power supply to charge the series pack. (with BMS).

 

[x4dow]

if it shows current draw it means it is being charged it, but like I said, 1.5A is very low charging current, something is limiting it, I.E. wiring, contact resistance, etc. What is the Voltage drops on the wire?
Do you have Solar charger controller yet? Is it charger controller with built-in AC-DC charger? if it is you can use that to charge the whole series pack (with BMS), or just use your 30V10A power supply to charge the series pack. (with BMS).

well a eve 280ah at 3.32 (jumped 0.01V now) is technically already at 90%+ capacity, so that might be a factor too. Voltage at power supply and terminals on the battery is the exact same.

I have a hybrid inverter capable of AC charging at up to 60A or 80A (not sure now), but was aiming at only hooking the battery to it after sorting all the top balancing/etc, but might charge it on it (with BMS ofc) up to 27-28~V or when BMS shuts it down (my bms i can monitor each cells voltage) and then top balance the cells to 3.6 on parallel as by then they will be on very high 90s% anyway

thank you for the help

 

[Bud Martin]

Sounds good, what ever you do, keep an eye on them while charging.

 

[x4dow]

Sounds good, what ever you do, keep an eye on them while charging.

absolutely. even though its charging slowly at 3.33, i look at it every 5min. I wouldnt go to sleep and leave it hooked up. I even made little "+" and "-" out of eletrical red/black tape to put near the terminals so i dont do any stupid mistakes

 

[Bud Martin]

I put big Red dot on my battery, I do not understand why the Chinese battery makers decide to use Black as the Positive terminal for the battery, they cannot find Red plastic?

 

[x4dow]

I put big Red dot on my battery, I do not understand why the Chinese battery makers decide to use Black as the Positive terminal for the battery, they cannot find Red plastic?

yeah main reason why I did put red pluses. don't want to get confused.

 

[x4dow]

power supply is proving to be a P.O.S. wired them in series (8S) with the BMS, into the power supply set to 28.8V and its displaying 26.33v/0.52A, so its charging at like 14 watts

 

[tjoiner1986]

The Voltage display on the power supply will drop down and it will rise back up when the battery is full charge.
Are you using 10 gauge wires and ring lugs for wiring? What did you set the CC setting too?
What is the Vdrops shown on the wires?
I would not do full 10A current pull on these low cost power supply, I would set the max current limit to 8A (80%)

Just so I'm clear before I toast a lot of expensive stuff...

Setting the voltage on the power supply to 3.65V and then watching it drop to around 3.45V once connected to the LFP battery bank is normal?

I'm sitting here at work right now, about to start top balancing since I don't have anywhere else to do it. I've got my 4 cells in parallel, 30V/10A Amazon power supply set to max current and 3.65V BEFORE connecting to the battery, 15" long 4 AWG cables between power supply and battery. I started top balancing but flipped everything off when I saw the voltage readout on the power supply drop. I wasn't sure if that was normal.

The display doesn't show current until it's connected to the battery. I've read about shorting out the supply -- connect the (+) and (-) leads from the power supply? -- but I'm overly cautious and don't want to do anything until I know for sure I'm doing it correctly.

 

[Bud Martin]

Just so I'm clear before I toast a lot of expensive stuff...

Setting the voltage on the power supply to 3.65V and then watching it drop to around 3.45V once connected to the LFP battery bank is normal?

I'm sitting here at work right now, about to start top balancing since I don't have anywhere else to do it. I've got my 4 cells in parallel, 30V/10A Amazon power supply set to max current and 3.65V BEFORE connecting to the battery, 15" long 4 AWG cables between power supply and battery. I started top balancing but flipped everything off when I saw the voltage readout on the power supply drop. I wasn't sure if that was normal.

The display doesn't show current until it's connected to the battery. I've read about shorting out the supply -- connect the (+) and (-) leads from the power supply? -- but I'm overly cautious and don't want to do anything until I know for sure I'm doing it correctly.

That is normal, the power supp;y is on constant current right now so the Voltage will drop down.
If there is no load (in this case, the battery is the load) is connected to the power supply then there will be no current flow so meter will show no current flow.
So what is shown on the Amp meter of the power supply when it is all connected?
Pictures of you setup?

 

[tjoiner1986]

That is normal, the power supp;y is on constant current right now so the Voltage will drop down.
If there is no load (in this case, the battery is the load) is connected to the power supply then there will be no current flow so meter will show no current flow.
So what is shown on the Amp meter of the power supply when it is all connected?
Pictures of you setup?

These were taken at around 11:15 this morning. Admittedly, I posted this question in another thread and got the answer there as well. But hey, better to have the answer all over so that it turns up readily in search results, right?

 

[John Frum]

Admittedly, I posted this question in another thread and got the answer there as well.

Cross-posting is generally frowned upon.

 

[Bud Martin]

Looks good!
Are your batteries 280Ah? If they are and they were at 50% SOC, so 280Ah x 4 = 1120Ah, 50% SOC = 560Ah, charging at 10A it will take 560Ah/10A = 56 Hours. You will have to be patient and keep an eye of them in case something goes wrong with your power supply.
BTW, as you can see, the CC LED is on indicating CC mode, in CC mode the power supply Voltage is varied to maintain constant flowing through the Load.
Are those M6 Wing-nuts? Do you have the source where you get them from?

 

[tjoiner1986]

Cross-posting is generally frowned upon.

I'm aware. This isn't my first forum membership. By the way, so are replies unrelated to the topic. ?

Looks good!
Are your batteries 280Ah? If they are and they were at 50% SOC, so 280Ah x 4 = 1120Ah, 50% SOC = 560Ah, charging at 10A it will take 560Ah/10A = 56 Hours. You will have to be patient and keep an eye of them in case something goes wrong with your power supply.
BTW, as you can see, the CC LED is on indicating CC mode, in CC mode the power supply Voltage is varied to maintain constant flowing through the Load.

Yeah, I did the math and figured 56 hours. I have this set up at my office since I don't have constant 120V access outside of work (currently in van life mode). I wasn't about to let this run overnight and risk burning the building down so I powered off the charger before I left and will resume in the morning when I return. At 9 hours a day, that's 6.22 days.