One controller or two?

[Bleemus]

Originally Posted by noelex 77

See post #26.

A slightly longer absorption time is better than too short, but I do not think this is a good idea, especially with more sensitive batteries like gel.

From the Victron manual . . .

When the charge current decreases below the Tail current, the battery is fully charged. The Absorption stage ends before the Absorption time has expired. The Tail current is 1A for models 100/20 and smaller; and 2A for larger models.

[john61ct]

Originally Posted by noelex 77

See post #26.

A slightly longer absorption time is better than too short, but I do not think this is a good idea, especially with more sensitive batteries like gel.

As long as the usage pattern, concurrent loads etc are consistent, keep extending Absorb Hold Time until trailing Amps is under the spec'd endAmps level before dropping to Float.

With low currents, this can easily take 4-6 hours after the CC-CV transition.

Reduce loads if necessary.

GEL needs to get to Full as much as any other lead, just ensure Absorb voltage isn't too high.

Sunset reduces likelihood of any significant overcharging.

[noelex 77]

Originally Posted by Bleemus

When the charge current decreases below the Tail current, the battery is fully charged. The Absorption stage ends before the Absorption time has expired. The Tail current is 1A for models 100/20 and smaller; and 2A for larger models.

Unfortunately “tail current” is not any use unless the loads are zero, or at least very low. Victron recommend attaching all the loads to the load terminals so the controller can allow for load current, but this is not practical on boat systems.

So the absorption timer, rather than tail current, is the method used to terminate the absorption cycle.

[noelex 77]

Originally Posted by john61ct

As long as the usage pattern, concurrent loads etc are consistent, keep extending Absorb Hold Time until trailing Amps is under the spec'd endAmps level before dropping to Float.

With low currents, this can easily take 4-6 hours after the CC-CV transition.

Low charging currents (relative to the battery size) need shorter, not longer, absorption times.

If the current is “low” the voltage will drop below the absorption voltage and the timer will stop. This is unless the SOC is very high in which case the absorption cycle should be close to ending.

Holding the battery for 4-6 hours at the absorption voltage (which is likely to be between 14.4-14.8v for a 12v system) is a long time. For most cycles this will overcharge the batteries. An absorption time of between 1-3 hours is used by most charge sources and is more appropriate.

Note: The absoption time is not just the time after the CC-CV transition. This is a common misconception that results in people imagining a very long absorption time is needed.

I agree looking at the battery return amps is the best method.

[john61ct]

Standard terminology is based purely on voltage level.

Bulk for CC stage, Absorb after CV transition.

Then drop to Float, only after endAmps shows SoC is at true 100% Full.

If you have a 500A source, Bulk may finish in twenty minutes, say 70% SoC. There will still be 4-5 hours left of Absorb time.

Dropping the rate to 200A may only add another 20min to Bulk, and the Absorb stage barely finishes any quicker.

But if solar-only, dropping to say a 20A rate, with a large bank that may mean just getting **to** Absorb takes 2-3 hours, and there are not enough sunny hours in the day to **ever** get to 100%.

In which case must run a dino-juice source in the morning to get to 80-85%, in order to get to Full.

And concurrent loads of course have a big impact.

My point is that 1-3 hours of Absorb is hardly ever enough. It is the user's job to keep increasing that Hold Time until endAmps is reached.

Actually setting Float=Absorb to see how long that takes is a good start.

Better SCs have an algorithm where you can set HAT as a ratio of time spent getting to Bulk, much better than a straight egg timer.

Most batts are fine holding Absorb until trailing amps is .005C, half an amp per 100AH.

[Bleemus]

Originally Posted by noelex 77

Unfortunately “tail current” is not any use unless the loads are zero, or at least very low. Victron recommend attaching all the loads to the load terminals so the controller can allow for load current, but this is not practical on boat systems.

So the absorption timer, rather than tail current, is the method used to terminate the absorption cycle.

Ok call me confused. The 100/30 units I have do not have load terminals like some models. The manual for this model outlines the ending of absorption with or without load.

What am I missing?

[john61ct]

Those defaults are determined, as with all SCs I have seen, to prevent overcharging.

Which means they usually result in what MS calls premature infloatulation.

They are just defaults, and usually require extending to get to 100% Full.

[Bleemus]

Originally Posted by john61ct

Those defaults are determined, as with all SCs I have seen, to prevent overcharging.

Which means they usually result in what MS calls premature infloatulation.

They are just defaults, and usually require extending to get to 100% Full.

John,
I do understand that part about the defaults but the part that confuses me is if I set a long custom absorption period I assume that the Victron will go to float when it reaches two amps no matter what. What are the dangers of setting a real long absorption since it appears it will automatically end at a tail of 2 amps?

I know I am missing something so please forgive me if I sound stupid.

[Bleemus]

Originally Posted by Bleemus

John,
I do understand that part about the defaults but the part that confuses me is if I set a long custom absorption period I assume that the Victron will go to float when it reaches two amps no matter what. What are the dangers of setting a real long absorption since it appears it will automatically end at a tail of 2 amps?

I know I am missing something so please forgive me if I sound stupid.

I think I figured out my confusion. If I have a 600Ah bank my target tail amps would be 3 (600x.005). So the time going from 3 amps to 2 amps (Victron default) is in fact overcharging.

If I am correct then maybe we can get Victron to add a custom target amps. Wishful thinking right?

[noelex 77]

Originally Posted by john61ct

If you have a 500A source, Bulk may finish in twenty minutes, say 70% SoC. There will still be 4-5 hours left of Absorb time.

Dropping the rate to 200A may only add another 20min to Bulk, and the Absorb stage barely finishes any quicker.

But if solar-only, dropping to say a 20A rate, with a large bank that may mean just getting **to** Absorb takes 2-3 hours, and there are not enough sunny hours in the day to **ever** get to 100%.

The absorption time will be shorter for the 20A charge rate than the 200A or 500A charge rate.

Originally Posted by john61ct

My point is that 1-3 hours of Absorb is hardly ever enough.

John, I disagree.

All solar regulators have a default absorption time of 1-3 hours. This is for a good reason. It is generally a sensible number. With low output solar charging you can end up with very short absorption times (using battery return amps) on occasions.

[noelex 77]

Originally Posted by Bleemus

Ok call me confused. The 100/30 units I have do not have load terminals like some models. The manual for this model outlines the ending of absorption with or without load.

What am I missing?



Attachment 167595

Nothing.

This is correct. The absorption timer does not use “tail current”.

[noelex 77]

Originally Posted by Bleemus

What are the dangers of setting a real long absorption since it appears it will automatically end at a tail of 2 amps?

I know I am missing something so please forgive me if I sound stupid.

The simple Victron (and most other) regulators cannot distinguish between the load current and the charging current.

So if there is a 2A load, the criteria for “tail current” will never be met.

[john61ct]

Yes, the Victron's default 2A override, or ANY settings based directly on tail amps are useless as long as there are larger loads pulling more than that.

Except for the ideal, which is when a BM tied to a shunt at the bank is controlling the charge cycle. I have only come across a half dozen of these, and of course adds to the cost. But if you want a good BM anyway, not so much more.

[john61ct]

Originally Posted by noelex 77

The absorption time will be shorter for the 20A charge rate than the 200A or 500A charge rate.

Sorry, that's just an insane assertion, either you have no basic maths, are not using the standard definitions I outlined, or are living in another alternative universe.

Originally Posted by noelex 77

John, I disagree.

All solar regulators have a default absorption time of 1-3 hours. This is for a good reason.

Yes, good for the companies' liability,

For getting to true 100% Full, hardly ever.

I'm done for now, hopefully Maine Sail will come & by straighten thing out.

[Bleemus]

Thank you John.