NextStep2 regulator bulk charge issue

[john61ct]

Originally Posted by jackt

"charge at 10% of the battery bank's capacity..."
What's that value then?
...
"...at the 20 hour rate"
What does that mean? "Rate" is amps.

What is the "20 hour rate" - C20 of 46.4?? What's that??

The number of AH a battery holds varies depending on how fast you draw it down from 100-0%.

The standard used to compare batteries is the 20-hour rate or "C/20", and you say yours is 460AH. They got that number by drawing down at a 23A rate, to 0% SoC over 20 hours.

So the minimum size charger at .1C (1/10th of 460, rounded up) you should use is 50A.

Lower than that will likely shorten their lifespan, and certainly make charging from 50% back to full take a very long time, say ten hours.

Better to get a 100A charger, then maybe 6 hours will be enough time.

Charge at 14.7A, until "full", meaning current drop to say 10A, only then go to Float. If your charger doesn't allow this, measure manually to calibrate Abs time. Default to longer rather than shorter, gassing's no problem with FLA, just replenish more often.

Ideally hit this Full level every cycle. Missing that more than occasionally will reduce lifespan. Same with going below 50%.

Equalize/condition according to vendor specs, ideally manually, supervising in person.

[StuM]

Originally Posted by jackt

20 hr rate, C20 = 20% 464 = 93A. I believe typical recommendations are an alternator sized to be C25 or C20.

10% of bat cap 464 = 46.4.

That's 46.4A at 93A. Huh? Your statement is confusing. Please use numbers.
---

I think they mean this:

"Constant current @~10% of C/20 Ah in amps to 2.45+/-0.05 volts per cell
(e.g. 7.35 volts +/-0.15 volts per 6 volt battery)"

Looking at their example PER BATTERY...
"(e.g. 7.35 volts +/-0.15 volts per 6 volt battery)"

7.35 = 2.45 x 3 cells per batt. For 2 batts = 2 x 7.35 = 14.7V bulk/abs voltage. Fine.

But what is the AMPS - the rate?

10% of C20?? C20 is 20% of bat size (464 Ah), right? That's 93A. 10% of 93 = 9.3. But 3 cells so 9.3 x 3 = 36.9A. Then x2 since 2 series, 2 parallel = 36.9 x 2 = 73.8 AMPS.

So they are saying to charge at 73.8 A.

Is this correct folks??

No. C20 (20 hour rate) is the number of Amp hours that the battery (or bank) will deliver if fully discharged over 20 hours. That is the most commonly quoted battery capacity. In this case it is 464 Amp hours.

(And the C20 rate would be achieved with an average current of 23.2 Amps 464/20. If you draw less than 23.2 Amps on average, your batteries would deliver more than 464 Ah, if you draw more than 23.2 Amps on average, they would deliver less than 464 Ah).

10% of the C20 Amp hour rating in Amps means 10% of 464 = 46.4 Amps.

So they are saying that for the initial bulk charging phase, keep the charge current at 46.4 Amps until the charging voltage climbs to 14.7V. (Your charger does this by starting at whatever voltage is needed to push that 46.4 Amps and steadily increasing the voltage to keep the current steady at 46.4A. Once the charger has ramped up to 14.7 Volts to achieve the 46.4 Amps, it holds the voltage steady at that level and the system enters the absorption phase where the voltage is maintained and the Amps that the battery can accept decreases steadily)

[StuM]

Originally Posted by lateral

So they are saying to charge at 73.8 A.

You're not listening. You don't dictate the amperage you charge at you dictate the V set / time. The battery state dictates the current, to the limit your charger will supply.

Not quite. During bulk charging, the charger determines the voltage required to deliver the correct current. If you stuck a huge charger on a small battery bank and just let it hammer away at 14.7V right from the start, you would probably cook the batteries

[StuM]

Originally Posted by john61ct

So the minimum size charger at .1C (1/10th of 460, rounded up) you should use is 50A.

Lower than that will likely shorten their lifespan, and certainly make charging from 50% back to full take a very long time, say ten hours.

Better to get a 100A charger, then maybe 6 hours will be enough time.

Careful. The manufacturers recommendation, apparently, was to charge at 10% of C20, not at a minimum of 10%. You are recommending charging at twice the manufacturers recommended rate.

[john61ct]

No, the charger only "offers", delivery is as much current as the battery can pull, up to the chargers' max. No mobile charger has a "46.4 amps" setting!

A 320A alternator going full bore in an 18-wheeler doesn't do a small lead battery any harm at all.

A too-small power supply without overcurrent protection will get fried by a big depleted bank though.

[StuM]

Originally Posted by john61ct

No, the charger only "offers", delivery is as much current as the battery can pull, up to the chargers' max. No mobile charger has a "46.4 amps" setting!

A 320A alternator going full bore in an 18-wheeler doesn't do a small lead battery any harm at all.

A too-small power supply without overcurrent protection will get fried by a big depleted bank though.

Ever seen a 320A alternator "going full bore" with no load other than a partially depleted battery and pushing 320A into it? (Regulators are part of the system for a reason)

Pushing 4.5kW into a small FLA battery would fry it.


"bigger alternators do not give bigger charging currents but they can supply bigger resistive loads"

[lateral]

Originally Posted by StuM

Not quite. During bulk charging, the charger determines the voltage required to deliver the correct current. If you stuck a huge charger on a small battery bank and just let it hammer away at 14.7V right from the start, you would probably cook the batteries

I am aware of increasing Voltage to Vset/constant current in bulk phase, but JackT's posts harked back to somehow setting current in absorb, which made no sense to me.
All good stuff though.
I wonder if all bat manufacturers give their capacities in terms of C20?

[StuM]

Originally Posted by lateral

I wonder if all bat manufacturers give their capacities in terms of C20?

Nope, you will also see batteries displaying their C100 capacity, especially common for land based "off grid" solar systems.

[john61ct]

Originally Posted by StuM

Ever seen a 320A alternator "going full bore" with no load other than a partially depleted battery and pushing 320A into it? (Regulators are part of the system for a reason)

Pushing 4.5kW into a small FLA battery would fry it.


"bigger alternators do not give bigger charging currents but they can supply bigger resistive loads"

Sorry you are wrong.

The regulator regulates current, only indirectly, via attempting to keep voltage constant.

It doesn't, can't "push" current into a battery above what the battery's resistance permits. In effect wrt current the alt, just like a solar panel, is self-regulating, the battery is "pulling", determining the amps flow, not the regulator.

I used to think like you, but have been convinced by others that know far more than me, including Maine Sail.

The "maximum rate" some AGMs specify apparently is just CYA, because wiring infrastructure may overheat.

But we're talking FLA, and bottom line is wrt your charge source, no such thing as "too many amps", just wasting money, not harming the battery.

LFP is completely different, 2-3C, even 5C, depends on the mfg, low resistance does make this an issue.

But not lead.

http://www.sailnet.com/forums/showthread.php?t=277761

[john61ct]

Originally Posted by lateral

I wonder if all bat manufacturers give their capacities in terms of C20?

Normally yes.

This guy selling Chinese LFP out of Arkhangelsk Oblast

http://www.ebay.com/itm/162418302716

sent me a chart showing 2C discharge, 100-0% in 30min!

[StuM]

Originally Posted by john61ct

Sorry you are wrong.

The regulator regulates current, only indirectly, via attempting to keep voltage constant.

Agreed, but directly or indirectly - that's what it does in effect.

A truck alternator will generally be regulated to around 14.2-14.4V. Since the current is dependent on the potential difference between the charging voltage and the battery voltage in conjunction with the battery internal resistance , limiting the voltage keeps the current down, especially given how quickly the surface voltage on the battery plates would rise given a high inrush current.

It doesn't, can't "push" current into a battery above what the battery's resistance permits. In effect wrt current the alt, just like a solar panel, is self-regulating, the battery is "pulling", determining the amps flow, not the regulator.

Guess it depends on how you look at it.

Your first sentence is correct. As for the second sentence: a battery doesn't have a "tendency" or "imperative" to charge itself. The battery doesn't "pull" anything. It will accept whatever energy is thrown at it adn convert it into either chemical store energy or heat. The higher the charging voltage is above the battery voltage, the more current it will accept, but it can only convert that energy to stored chemical energy so fast. If it is fed several hundred amps (which is quite possible if the charging voltage is high enough), all sorts of nasty things are going to happen to the battery (assuming that you don't have an appropriate fuse or fusible link somewhere that should blow well before those several hundred amps did any damage)

By regulating the voltage difference between the battery and the charging source, the regulator limits the amount of current that can be pushed against the battery's internal resistance.

I used to think like you, but have been convinced by others that know far more than me, including Maine Sail.

The "maximum rate" some AGMs specify apparently is just CYA, because wiring infrastructure may overheat.

But we're talking FLA, and bottom line is wrt your charge source, no such thing as "too many amps", just wasting money, not harming the battery.

LFP is completely different, 2-3C, even 5C, depends on the mfg, low resistance does make this an issue.

But not lead.

Batt. charger and Amp hr. - SailNet Community

I'm not sure what point you are trying to make with your link.

A "maximum charge rate" is primarily a function of how much the battery will heat up with a high charging current and battery manufacturers give it for that reason.

Ask Maine Sail what would happen if you allowed voltage to get high enough to send those 320A into a "small lead battery." for any length of time.

[mitiempo]

Originally Posted by StuM

Not quite. During bulk charging, the charger determines the voltage required to deliver the correct current. If you stuck a huge charger on a small battery bank and just let it hammer away at 14.7V right from the start, you would probably cook the batteries

Not true. The manufacturer recommends a minimum of 10% of C20, in this case 46.4 (round that to 50) amp charger as a minimum for good battery life. There is no maximum. For a given voltage (14.7 in this case) the batteries will accept what they will accept based on internal resistance. This is about 20% of capacity in AH. A bank of 464 AH will accept a maximum of about 90 amps for a short time at the beginning of bulk and this will start dropping quickly for Fla batteries. This makes no difference whether the battery charger is 100 amp or 1000 amp output. The only way to cook (overcharge) a battery is to increase the voltage beyond the manufacturers recommendation. This can happen with a 10 amp charger at too high a voltage but not with a large or very large charger at the correct voltage.

Given the above there is no logic in using a charger that is larger than the batteries acceptance plus any house loads. A charger of 60 amps or so would be a good choice and an alternator of 80 to 100 amps.

[mitiempo]

Originally Posted by StuM

Ever seen a 320A alternator "going full bore" with no load other than a partially depleted battery and pushing 320A into it? (Regulators are part of the system for a reason)

Pushing 4.5kW into a small FLA battery would fry it.


"bigger alternators do not give bigger charging currents but they can supply bigger resistive loads"

All a regulator does is set the voltage - it has nothing to do with current - the battery decides that.

[mitiempo]

Originally Posted by StuM

By regulating the voltage difference between the battery and the charging source, the regulator limits the amount of current that can be pushed against the battery's internal resistance.

Ask Maine Sail what would happen if you allowed voltage to get high enough to send those 320A into a "small lead battery." for any length of time.

Allowing the voltage get high enough to send 320A into a small battery is hardly the issue. Wouldn't happen unless the charger was totally unregulated.

The regulator does not "regulate the voltage difference between the battery and the charging source". It has a set absorption voltage. The battery takes the current it can until that voltage is reached. It stays at that voltage for a period of time, set too short on most chargers as previously stated by Mainesail. 3 to 4 hours is much better than 1 hour. The charger then goes into float voltage at about 13.4 to 13.6 volts with the last few percent of charge going in slowly. This assumes a 3 stage charger. An alternator that has internal regulation is considered to have "dumb" regulation and has a single voltage setting, typically 14.4 when cold. As the alt heats up this voltage will drop.

A charger can be too small but not too large. The battery determines current.

[jackt]

Originally Posted by lateral

So they are saying to charge at 73.8 A.

You're not listening. You don't dictate the amperage you charge at you dictate the V set / time. The battery state dictates the current, to the limit your charger will supply.
Ideally you charge with a charger capable of 10-20% of capacity when SOC allows.
How I understand it anyway.
Bat manufacturers are always going with conservative spec's.
Safe and sells more bats.

Maybe you're not listening! I understand their SPECS as stating the ideal amps to get an alternator to put out. That would make perfect sense - you need a decent alternator with decent amps - they are recommending a value! What's the problem with that interpret. Regardless, it's utterly opaque and difficult to convert specs PER CELL to a specific case.

What does Maine Sail say? Isn't he the guru?