Charger 101

[GallenH]

Thinking about B2B chargers made me realize that I know very little about them. I've seen discussion that most (except for the very $$$) rely on a timed algorithm to take you through the stages of boost-absorb-float. But how does this work? How does a charger tell the difference between a 100AH battery that is at 75% capacity vs. 50%. It must have to adjust the time when it only has to provide 25% vs. 50%. Or am I missing something?

[booster]

Originally Posted by GallenH

Thinking about B2B chargers made me realize that I know very little about them. I've seen discussion that most (except for the very $$$) rely on a timed algorithm to take you through the stages of boost-absorb-float. But how does this work? How does a charger tell the difference between a 100AH battery that is at 75% capacity vs. 50%. It must have to adjust the time when it only has to provide 25% vs. 50%. Or am I missing something?

You aren't missing anything at all. Mostly what it is about is that almost all, if not all, will not charge accurately on lead acid batteries if you are looking at them charging to the battery manufacturer's definition of "fully charged" which is usually and amps to the batteries that is a % of capacity. Some chargers have you set the size of the battery bank so at least they know that, and you usually tell them what type of battery it is. What it doesn't know is how far discharged it is, how old it is, or how much of the charge current is going to places other than the batteries. They do an algorithm determination of what they thing the battery needs. In general, of the ones I have seen or seen data on, they tend to leave the batteries undercharged somewhere between 5 and 20%. This is less damaging and slower damage than over charging, so it is probably intentional.

[markopolo]

The 20A/40A/60A Renogy units might have IUoU battery charging -> https://www.classbforum.com/forums/f...tml#post126653 <- so time or current can initiate the transition to float. It would be nice to know what that amperage trigger is if they have that type of charging.

As Booster notes, an undercharge would still be expected because the amperage trigger is likely set higher than you'd set to get an actual 100% recharge.

[hbn7hj]

As for the Kisae unit you are missing the fact that every five minutes or so it stops charging, takes some readings, and goes back at it. I don’t know what it does during the pause but it does get to 100% on a 210AH battery pack. There is no way (?) for it to know if your your battery bank is larger so that may well be undercharged.

I think the charging specs can be custom set but I haven’t done it. It also has a lithium setting. I think it cuts off at 14.3 volts for lithium.

The definition for charged is 2 amps at 14.4 volts for a 100AH battery, 4 amps for 200AH. The Kisae does indeed reach 14.4 volts and it seems to cut off at 2 amps regardless of bank size which would overcharge a larger battery bank. I watch it on the monitor but if I’m not around I don’t worry about it.

[booster]

Originally Posted by hbn7hj

As for the Kisae unit you are missing the fact that every five minutes or so it stops charging, takes some readings, and goes back at it. I don’t know what it does during the pause but it does get to 100% on a 210AH battery pack. There is no way (?) for it to know if your your battery bank is larger so that may well be undercharged.

I think the charging specs can be custom set but I haven’t done it. It also has a lithium setting. I think it cuts off at 14.3 volts for lithium.

The definition for charged is 2 amps at 14.4 volts for a 100AH battery, 4 amps for 200AH. The Kisae does indeed reach 14.4 volts and it seems to cut off at 2 amps regardless of bank size which would overcharge a larger battery bank. I watch it on the monitor but if I’m not around I don’t worry about it.

Like we have discussed lots of times, many systems and chargers say they are fully charged, 100% charged, etc but we rarely know how that is determined. Even battery monitors are very inaccurate if the settings aren't set properly. Very, very, few users actually get there batteries to true full without over or under charging in the real world. It does shorten life of the batteries, but for lots of folks that is OK because of the high cost and space requirements for equipment that can charge reliably to full.

[markopolo]

Originally Posted by hbn7hj

As for the Kisae unit you are missing the fact that every five minutes or so it stops charging, takes some readings, and goes back at it. I don’t know what it does during the pause but it does get to 100% on a 210AH battery pack. There is no way (?) for it to know if your your battery bank is larger so that may well be undercharged.

I think the charging specs can be custom set but I haven’t done it. It also has a lithium setting. I think it cuts off at 14.3 volts for lithium.

The definition for charged is 2 amps at 14.4 volts for a 100AH battery, 4 amps for 200AH. The Kisae does indeed reach 14.4 volts and it seems to cut off at 2 amps regardless of bank size which would overcharge a larger battery bank. I watch it on the monitor but if I’m not around I don’t worry about it.

I'd forgotten that the Kisae unit's have programmable Absorption to Float settings. I had to look up one of my old posts & I had posted about the Kisae 40A where the Absorption to Float could be set to 2A or 4A or 8A back then. It's still a bit of a guess as to what to choose if factoring in persistent or transient loads that would affect the switch over & maybe prevent it unless they also have the often used time limitation which would directly affect the switch over. I haven't looked through the manual.

[GallenH]

Thanks everyone for your replies.

[reilym]

Originally Posted by GallenH

Thinking about B2B chargers made me realize that I know very little about them. I've seen discussion that most (except for the very $$$) rely on a timed algorithm to take you through the stages of boost-absorb-float. But how does this work? How does a charger tell the difference between a 100AH battery that is at 75% capacity vs. 50%. It must have to adjust the time when it only has to provide 25% vs. 50%. Or am I missing something?

This is the first profile I recorded on our trip south from Michigan using a 60 amp Renogy feeding two 100 Ah LiFePO4 batteries from a 200 amp alternator. Ambient temperature was 42-46 degrees F and the alternator case was between 65 and 77 degrees F.