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Equalization with SCM and PSC55-12 charger

PostPosted: Tue Apr 24, 2012 8:35 pm
by Chorl
Is it possible to user the Smart Charge Manager current limits to perform equalization? I have a PSC55-12 charger with a SCM charging a bank of 2 8D's (of 276AH each). Can I just install a shunt and connect the sides of it to SHC and SHG on the SCM, set the S1 DIP switch for the appropriate amount of current and then assert LIM1 and ABS?

I'm calculating the equalization current required as follows:

The required current for equalization at 5% of the bank's 20 hour capacity = (275A * 2) * 0.05 = 27.5A

Therefore the required output of the charger will be = (27.5A/55A) * 100 = 50%

...and S1 should be set for the current limit of 50% by setting switches 5-7 off and 8 to on.

I'm not certain if asserting the ABS input will drive the SCM to the LIM1 setting if the battery is fully charged. If not, is there a way to tell the SCM to drive the charger up to the set current limit while I monitor the battery voltage to see if it reaches my equalization target?

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Wed Apr 25, 2012 4:33 pm
by Coulomb
True equalization isn't possible because the power supply unit may not be able to reach the voltage necessary.

If you know what a diode is, and which way it conducts, you can put a couple diodes in series with the sense line to make the charger think the batteries are low. Then with current limiting operating, the charger will put out a higher voltage.

Be sure to monitor this closely. The risk of overcharge is high unless you are very watchful!!!!

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Thu Apr 26, 2012 12:25 pm
by Chorl
Do I need to set the ABS input to something (5V - the documentation doesn't say)? The description for the ABS input is "a positive true input signal that holds the SCM in the absorption state" and the description for the absorption charge signal says, "Absorption Charge - The voltage is held at the absorption voltage and continues for a time dependent on battery chemistry." Will setting the ABS signal drive the output to the current limit (LIM1) or is it voltage limited by settings internal to the SCM?

I guess that I could try the diode idea. Have you done this at Ample Power? I'd need to monitor the voltage and current during equalization anyway.

I was hoping to figure out a more automated way to control the charger and set it up for equalization so that I could essentially just flip a switch or two and then monitor the battery. I realize that I can do this with my V3 alternator regulator but ...performing equalization while underway is impractical and not safe and running the boat's engine several hours just to perform battery equalization is not good for diesels (or the sanity of neighbors). It seems odd that there appears to be no AC chargers available on the market that have a proper adjustable equalization function built in. It would almost be just as easy to attach a separate portable charger for equalization although this still seems like an unnecessary fuss.

Do you have any other suggestions for a shore power equalization system?

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Wed May 02, 2012 9:32 am
by Chorl
Is there no followup on questions on this forum? Do I need to post a new topic each time?

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Wed May 02, 2012 10:44 am
by Coulomb
Positive true indicates the polarity required to activate the function. The battery positive, 12/24V is appropriate.

Current from a charge source depends on the battery state-of-charge. It could be at the limit, or something less.

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Wed May 02, 2012 8:49 pm
by Chorl
OK, I was just wondering if the SCM is locked in the absorption state if it will limit the voltage to something around 14V so the charger will never reach 15 to 16 volts for equalization.

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Thu May 03, 2012 3:22 pm
by Coulomb
It locks it at the ABS set point, as the manual indicates. That's why you need the diodes.

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Sun May 06, 2012 12:42 pm
by Chorl
So basically I need:

Target Equalization Voltage - Total Diode Voltage Drop < Absorption Set Point Voltage

I'm still not certain what the exact Absorption Set Point is on the SCM when it's set for "Thick Plate Liquid" batteries. Is this approximately 14.4V at 25 degrees C? Voltages don't seem to be listed in the SCM operating instructions.

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Mon May 07, 2012 10:40 am
by Coulomb
I don't have the number, but you can put that on the dip switches and find out. Disconnect the temperature senser.

Re: Equalization with SCM and PSC55-12 charger

PostPosted: Mon Sep 16, 2013 5:59 am
by igor
I used 2 diodes in series for 1.4 V drop inthe sense line, while the Temp sensor was disconnected, also disconnected the EMON, set the Limit at 5% C, and it worked: 15.6 V equalization from the chargers on the genset. Thanks!