MPPT vs PWM test

[B and C]

Anything that uses end amps is better than a timer. Timers lead to chronic undercharging unless monitored closely. There are a lot of MPPT controllers that use end amps (best) to know when to go to float. Mine is a Midnight Kid with a WhizBang Jr. It uses a shunt to measure end amps. The WhizBang Jr. and shunt adds the end amp function to get rid of the timer. I took a quick look at the Victron, it just talked about time too, not end amps.

 

[John61CT]

Every FLA manufacturer I've used or referenced specifies holding Absorb until trailing amps spec is reached, and Float only for storage, non-cycling to counter self-discharge.

IOW no different from AGM.

You can look up the specs or contact tech support at Crown, U.S.Battery or Rolls to confirm they all use a similar type of protocol

Deka's is: Absorption End Point = Current change over 1 hour period of less than 0.1A

Trojan uses .01C for endAmps (.03C if Absorb goes over 4 hours) but then specs after that CC "finish charge" allowing voltage to **rise** until the electrolyte is bubbling so well mixed.

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I would not use Interstate since they are just a marketing relabeller, and their current FLA supplier JCI does not have a great rep.

Also their engineers are not made available for direct tech support, as the rest do.

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Finally, 6-7 years is to be expected from proper care, even 10-12 years is not unheard of starting with a top-notch FLA bank.

Of course, pushing much below the 80% SoH spec for scrapping a bank, it's possible to get there even with an ordinary one.

 

[John61CT]

> Is managed pwm better at absorption?

The Hold Absorb algorithm is independent of PWM vs MPPT, depends on each specific brand / model.

> I chose the Victron mppt because it manages absorption based on acceptance. The other mppt controllers all do it based on adjustable time.

Acceptance of the bank cannot be measured by the SC directly if there are consumer loads active.

That requires coordination with a coulomb-counting batt monitor based off a shunt at the bank.

Victrons do have the ability to communicate with their BMs. As does Blue Sky with IPN-Remote, Bogart's SCs and Midnight's Whiz Bang Jr.


> Iirc default was two hours

And that almost always is premature, as is the default for every charge source I've seen.

Better than the usual eggtimer is where the Hold Time is an adjustible multiple of the time spent in Bulk/CC, which an SC alone does have direct access to.

 

[DLTooley]

My speculation on pwm was that the pulse width modulation might allow for a longer absorb.

The ‘long tail’ approach works for me, my take away is that absorb voltage shortens the tail relative to float post ‘egg timer’ absorbtion.

The Victron load terminals allow for the measurement of trailing acceptance. (I’ve read three mppt manuals and no pwm manuals).

 

[John61CT]

> My speculation on pwm was that the pulse width modulation might allow for a longer absorb.

No, that factor is determined by the design of the output regulation control, especially user adjustability.

> The ‘long tail’ approach works for me

Not sure what you mean, it's not an "approach". I coined it to just refer to the objective fact that lead banks require that the (very lengthy) final declining (tiny) current stage be allowed to complete until the spec'd endAmps level is reached, in order to say the batts are fully charged.

> my take away is that absorb voltage shortens the tail relative to float post ‘egg timer’ absorbtion

There is no more Absorb at all once voltage has dropped to Float, unless a very high load drops voltage low enough to trigger a new cycle.

But yes the higher voltage is required in order to get to 100% Full.

> The Victron load terminals allow for the measurement of trailing acceptance.

So confused. You do know that means measuring declining **current** in amps, with an ammeter, right?

**Charging** current comes out the main charging ports, not the load terminals.

If you wanted for some reason to measure amps from the load terminals, that would only capture the current going to the loads fed from there.

A battery should not be attached there, that's what the charge output ports are for.

You can't just measure bank acceptance of trailing current via the **total** SC output at those ports if consumer loads are present, since they are pulling/diverting a portion of that output current, likely many times greater than the bank's amps acceptance.

That measurement (acceptance of trailing current) **must** be from a shunt at the bank, so you are only seeing that portion of the SC output current which is accepted by the batteries.

Finally, even if consumer loads are all off, resistance/voltage drop between the SC and the bank may skew your results. Again, measure at the bank.

 

[DLTooley]

Babble; everything that needed to be said is on the other thread on this topic.

I am still observing voltage drop at the panels during early charging at the higher acceptance rates.  Why is that so hard to understand?  It is exactly what my admittedly basic understanding of electrical theory would indicate.  You have some deeper issues at work here not related to solar, you need to spend some more time alone and outside the world of BS corporate office politics - if you don't mind my frankness.

My definition of the absorption state was wrong, however it is the case that the 'long tail' is completed via float in systems whose 'user adjustability is limited to setting the time for absorption.

I am also observing a discreet reduction of around 3 volts in that voltage drop at a time period roughly consistent with 'eggtimer' defaults.  I have used that time point successfully in two separate cases,  in applying daylight loads to my FLA system and with an AGM starter battery that was being recharged from solar after an alternator failure.  This second case was observed about a dozen times in the course of getting out of some pretty deep backcountry.

I've asked you not to respond any further on this sub-subject, I repeat that request.