How does the Meanwell 2400 rsp charger potentiometer work with sbms

[jedics]

It says it adjusts voltage but on the sbms120 it adjusts the amps, how is this so?

I ask because the potentiometer broke, and was sending the full 100amps to the sbms.

took it to get fixed but it no longer adjusted the amps when I got it back so technician re tested it and said it is adjusting the voltage.

So he is confused as to how I was using it to adjust the amps as am I. 

[Dacian Todea (electrodacus)]

The Mean Well  RSP-2400 is a constant current limited power supply.

There is no potentiometer unless you installed one and you can adjust current or voltage. So not sure what potentiometer you had installed.

If 2400W is to much for your battery then you will want to limit the current that is user adjustable and not the voltage.

Voltage adjust range is 22 to 28V and you should just have that at 28V

Then current range is 0 to 100A and you should adjust to whatever your battery is comfortable with.

Then SBMS120 should control it ON/OFF unless you connected the power supply to the PV input of the SBMS120.

You may have used voltage adjustment to limit the current but that is very imprecise way to do it and not the best choice.  Say battery voltage is 26.5V and you set the voltage on the power supply at 27V then the current will be set by the voltage delta of 0.5V and the wire resistance connecting the supply to the battery and the battery internal resistance. But then as battery voltage increases the current will decrease so not the best way to do that.

Best to set the voltage to max 28V in this case and then set a current limit. That way the current will be the same no matter the battery state of charge.

Likely you controlled the voltage and that is the reason the potentiometer failed as you need to always adjust the voltage.

So in the example above say your wires resistance plus battery internal resistance is a total of 10mOhm = 0.01Ohm then you set the voltage to 27V and battery voltage is 26.5V you will get 27V - 26.5V = 0.5V and 0.5V/0.01Ohm = 50A but as the battery charges and battery voltage increases the current decreases (not constant). That is likely what you where doing instead of setting a fixed 28V output and using the potentiometer to control current limit then current will have been constant to whatever you set and not dependent on battery voltage.

[jedics]

The potentiometer came with the Meanwell and when I first got it I was able to use it to adjust it down from 100a to about 60a.

"Set a current limit" in the sbms? In advanced parameter setting "over current chg".

[Dacian Todea (electrodacus)]

Maybe you got that second hand and someone installed a potentiometer for voltage control.

Current needs to be limited by the charger the SBMS can not do that. The overcurrent limit is a protection limit like a circuit breaker.

Like I mentioned you can adjust the current by adjusting the voltage but that is not the way it should be used.

Please take a photo so I can see where exactly the potentiometer is connected so I know what it is doing. If it controls voltage that is not what you want.

You want to setup power supply so that current is limited to 60A.

This is the manual for it https://www.meanwell.com/Upload/PDF/RSP-2400/RSP-2400-SPEC.PDF

You need to setup remote ON/OFF as shown on page 5 Example 3.2C and connect to EXT IO4 set as type 1  (not needed if you are not using PV1 or PV2 to connect the MeanWell to the SBMS120)  

Page 7  You need to remove the factory shorting connector so like Fig. 5.2

I just noticed this model dose not have the PC pin to allow for user current limit control externally like most of the other MeanWell RSP models.

The SBMS120 will not like 100A trough PV1 or PV2 input as I asumme you have it connected and voltage control to reduce current is a bad option.

So unless there is some internal potentiometer not mentioned in the manual to adjust the current down to around 60A it is just not usable.

I see a photo of a similar unit and has two internal potentiometers. There is a good chance one of those can be used to set a lower current than 100A

[jedics]

Bought the meanwell new so highly doubt it was added after, also I talked to the reps in Australia and they knew about the potentiometer.
Remote on/off is set up. I am not knowledgeable enough to understand why using voltage to reduce the amps going in is bad which is how I was using it for years. Cant give you a photo because the repairer has it. I have a 9kw battery set up so they should be ok with getting 100a and the sbms is rated for it, why is it bad? 

[Dacian Todea (electrodacus)]

As far as I can see the external potentiometer is not included with a new MeanWell so if you got one it was an option that was added at your request or maybe someone that originally ordered that and canceled the order.

It is not important if you have or not that option as you just set the potentiometer to max value so that power supply outputs 28V. So having the potentiometer is not a problem.

The SBMS120 max input current for either PV1 or PV2 is 75A with the combined total PV1+ PV2 being 120A see manual page 4 https://electrodacus.com/SBMS120/manual/SBMSmanual.pdf

So you can not leave the MeanWell set at the default 100A and connect it to PV1 or PV2 as that will damage the SBMS120

Reducing voltage is just not a reliable way to reduce current.

I will try to explain using the earlier example.

Assuming your battery internal resistance + the resistance of the cables you connected between the MeanWell and the battery is 10 mOhm = 0.01Ohm

a) If battery voltage is 26.5V and you set the MeanWell voltage at 26.5V or less the charge current will be zero.

b) If battery voltage is 26.5V and you set the MeanWell voltage to 27V then charge current will be 27V - 26.5V = 0.5V and 0.5V / 0.01 Ohm = 50A 

c) If battery voltage is 26.5V and you set the MeanWell voltage to 28V then charge current could be 28V - 26.5V = 1.5V and 1.5V / 0.01Ohm = 150A but because of the current limiting it will be at 100A in reality.

d)  If battery voltage is 26V and you set the MeanWell voltage to 27V  (same as case b) then charge current will be 27V - 26V = 1V and 1V / 0.01 Ohm =  100A 

So because battery voltage changes and resistance is basically constant no matter what voltahe you set at the MeanWell you will still get the max 100A sometimes.

You did not need remote ON/OFF control if you connected the MeanWell to PV1 or PV2 input.   But if you have remote ON/OFF setup you can connect the output of the meanwell directly to battery and then there are no problems as long as your battery can handle 100A (meaning your battery is in good enough condition with low enough internal resistance to handle 100A).

So all that broke on your MeanWell was the potentiometer ? Is that because you used it everiday to set some current limit based on battery voltage or do you live in a corrosive environment and the potentiometer corroded.

If you decide to connect the MeanWell directly to battery and have the SBMS120 EXT IO4 set as type 1 remote ON/OFF the MeanWell then you do not even need the potentiometer. Even with a defective or removed potentiometer it will still work.

If the repairer has experience with this he can likely set for you a lower current limit using the internal potentiometer.  Hope you will not be charged to much for a defective potentiometer that you did not even needed.