mppt charging question

[Minimoose]

Is an mppt charger a "smart" charger? If it doesn't need a 2 hour boost mode will it automatically switch to float or does it just back down the amperage until the 2 hour set point has passed? I just notice that all things being equal that one of my battery banks will be in float mode before the other.

 

[MisterSandals]

Is an mppt charger a "smart" charger?

MPPT and smart are 2 different concepts. MPPT refers to how the SCC manages the array and turning that energy into charging current.
Smart (as i believe you are using it) refers to the charge profile, charge stages and the likes.

Searching for an analogy, i come up with:
Is a diesel a turbo engine?
These are 2 different concepts. A diesel can have a turbo, or not. A turbo can be on a diesel or other engine.

 

[FilterGuy]

Is an mppt charger a "smart" charger? If it doesn't need a 2 hour boost mode will it automatically switch to float or does it just back down the amperage until the 2 hour set point has passed?

I am not sure how you define 'smart' so I can't really answer that......

Each make/model of MPPT charger will have it's own charging algorithm. Some of the chargers will let you adjust various parameters of the algorithm, some won't.

• The simplest chargers will just charge to the target voltage and stop... no accumulation phase.
• Slightly more advanced will hold the target voltage for a preset or configurable time to allow for an accumulation phase.
• The most advanced chargers will hold the target voltage till the current drops to some preset or configurable level. (These are not very common)

 

[fratermus]

Is an mppt charger a "smart" charger?

Smart typically means multistage, and MPPT tend to be multistage chargers. Smart doesn't neccesarily equal knows what is exactly correct for the battery bank.

If it doesn't need a 2 hour boost mode will it automatically switch to float or does it just back down the amperage until the 2 hour set point has passed?

The transition between Absorption and Float varies between chargers and configurations of chargers.

* timer - start a timer after absorption voltage has been attained. Drop to float when the configured or (hard-coded) duration is up.
* trailing amps (end amps, acceptance, etc) - watch for controller output to drop to a certain level of current then drop to float.

The timer is far simpler/cheaper but takes observation/adjustment on the part of the owner. Uneven charging current (as from solar-only charging) can make this tricky. Unfortunately many inexpensive controllers (like mine) have a max Absorp duration of 3 hours or less, which can be deadly for lead-chemistry batts IMO.

one of my battery banks will be in float mode before the other.

Separate systems?

For lithium chemistries I think it's a non-issue if you are hitting your state of charge targets.

For lead chemistries it's more important when they are fully charged than when they drop to float. In theory "dropping to float" = "fully charged" but all too often "dropping to float" is not contingent on being fully charged. Hence lead-acid battery murder. IMO, of course.

 

[John Frum]

How are your batteries paralleled?

 

[Minimoose]

I have 4 100ah for the house 3000 watt inverter and 2 200ah for the 4000 watt well inverter. Parallel 12 volts. I have noticed that the controller drops the amps down to about .5 amps after it is in boost mode for a while and holds that in float too. I'm assuming it senses only what it needs, My worry was overcharge, but the algorithm seems to be similar to a standard battery charger. It backs off on amperage when it needs to.

 

[John Frum]

I have 4 100ah for the house 3000 watt inverter and 2 200ah for the 4000 watt well inverter. Parallel 12 volts. I have noticed that the controller drops the amps down to about .5 amps after it is in boost mode for a while and holds that in float too. I'm assuming it senses only what it needs, My worry was overcharge, but the algorithm seems to be similar to a standard battery charger. It backs off on amperage when it needs to.

You should watch this.

 

[Minimoose]

I have my 4 parallel charging from opposite ends and the inverter hooked up on the other opposite ends. should be a good balance. I'm not having problems, but was just curious. The well draws a big surge at 12 volts, but works good. Would lifepo be better or worse for a big sudden surge than AGM? 200 ah batteries

 

[John Frum]

I have my 4 parallel charging from opposite ends and the inverter hooked up on the other opposite ends. should be a good balance. I'm not having problems, but was just curious. The well draws a big surge at 12 volts, but works good. Would lifepo be better or worse for a big sudden surge than AGM? 200 ah batteries

Sounds like a good question for @sunshine_eggo as he has lots of experience with lead acid and lfp.

 

[sunshine_eggo]

Sounds like a good question for @sunshine_eggo as he has lots of experience with lead acid and lfp.

HAH!

LFP has lower total resistance, so there will be a small reduction in surge due to the lower resistance, but the issue is the pump itself. They tend to have a 5X surge compared to run current.

LFP may actually be problematic if the surge is significantly higher and longer than the BMS can tolerate.

 

[Minimoose]

Thanks! That's what I was thinking. I'll just stick with LA batteries for now. The prices keep dropping on lithium and it makes it tempting. My AGM batteries are doing fine.