NextStep2 regulator bulk charge issue

[jackt]

Originally Posted by StuM

Actually Amp hours is like volume. Amps is a flow rate like gallons per minute.

A better (but still imperfect) way to think about it is pumping water into a sealed tank which is initially full of air. As you pump more water (Amp hours) in, the air is compressed in the top of the tank, the pressure of the compressed air (battery resistance) opposes the pump pressure (Volts) so the rate of flow decreases (Amps). Once their is sufficient water in the tank (Amp hours) to compress the air so that it's pressure (resistance) is the same as the pump pressure (Volts), you can't put any more water (Amp hours) into the tank. If you increase the pressure (Volts) to try to squeeze a bit more water (Amp hours) into the tank the pressure can damage the tank.

As 2nd ed (1996) of Calder's bible (Chapter 1, Verse p20) shows, the water tank analogy is accurate, esp. if you include divisions to represent the inner plates versus the surface plates:

[jackt]

Originally Posted by Maine Sail

The real question is why you are charging, what I gather from your OP, ppis a bank of 6V golf cart batteries at such a low absorption voltage and for such a short absorption duration?

I can say why the low abs voltage:

Beginning mid-2000s on, I followed Calder's 1996 bible (and learned much from it). As you can see from the below pic (Chapter 1 Verse p23), it implies an absorption of around 14.25V would suit me...because my alternator current is quite low - only around 60A (with a max of about 70A with a 90A Bosch alternator).

With a 440 Ah bank as he writes at the end of the paragraph:

14.2V at 10% rate of charge = 44A (10% of 440)
rising to...
14.4V at 25% rate of charge = 110A (I can't get 110A)

So, given this range, 44 to 110A (14.2 to 14.4V) my 60A lies proportionately at about 14.25V. That's why my abs was set at around 14.3V.

What do you think?

[john61ct]

The voltage setpoints and other variables in the algorithm used should come strictly from the vendor. Sometimes tech support staff or trusted experts like MS may override what's in the documentation, but overall generalizations are well too general, each battery type - and more every year - has its own requirements.

Originally Posted by jackt

As 2nd ed (1996) of Calder's bible (Chapter 1, Verse p20) shows, the water tank analogy is accurate, esp. if you include divisions to represent the inner plates versus the surface plates:

Yes but still a simplification. First, when filling a tank it is very clear when the tank is full, and trying to overfill simply results in liquid being spilled without any damage to the tank. Second, using up the liquid until the tank is completely empty may be inconvenient, but again that does not damage the tank, even if the tank remains empty for a long time. Thirdly, filling the tank slowly or fast, whether the weather is hot or cold, or whether one is starting from a nearly-empty or nearly-full tank, does not affect the eventual amount of liquid in the tank. Finally, a tank’s capacity does not vary over time.

credit Ralph Hiesey

[jackt]

I also don't understand why on my previous batt bank of 440 Ah, I would recharge each 24hrs from around -50 Ah. This involved say 20 mins of bulk at 60 A to 14.3V and then another 1 hour of absorption at 14.3 V. In that time, my Link10 battery monitor would count back the amp hrs dutifully:
-50...-40...-30...-20...-10...-9...-8...-5...-1...0.
Also, the CURRENT would drop during absorption as expected:
60A...50...40...30...20...10...9...8...7...5...2.
at that point the monitor's algorithm indicated batt was full (algorithm: over 10% total Ah must be drained (>44 Ah) and current must drop to < 2% of declared batt capacity (8.8 A) for 5 mins).
Now it may well be according to your comments I was not running abs for long enough (only 1 hr) and batts were in fact woefully undercharged even though batt monitor said Ah were replaced AND CURRENT WAS < 2%. So were they undercharged or not after 1 hour? Since current acceptance was low - it was < 9 A and went as low as 2 or 3 does it mean they were in fact charged...or instead that the batts were not fully charged and simply could not accept more current because they were damaged? Sulfation? So the amps dropped (due to the regulator algorithm or the batt chemistry??) because they could not be "pumped in"??

[john61ct]

Accurately measuring SoC is a challenge, most AH counting monitors do drift.

But amps dropping low is an indication the batt is pretty full. If you think it might help to recover a bit from (past PSOC) sulphation, after current is at 2%, boost V a bit and keep pushing see how long it takes to get to 1%.

Or follow mfg "conditioning" protocol.

But once most lead has lost capacity it ain't coming back, and taking longer to finish Abs is a sign of that.

[mitiempo]

Originally Posted by john61ct

Accurately measuring SoC is a challenge, most AH counting monitors do drift.

But amps dropping low is an indication the batt is pretty full. If you think it might help to recover a bit from (past PSOC) sulphation, after current is at 2%, boost V a bit and keep pushing see how long it takes to get to 1%.

I agree. The problem is voltage. With a absorption voltage too low (not to mention a much too short absorption time) the batteries will accept less current. To make it worse the early drop to float voltage means the batteries accept even less current at the lower voltage.

GC batteries need to have an absorption voltage of 14.6 to 14.8 volts. And an absorption time of several hours. They will last longer treated this way.

[jackt]

Originally Posted by john61ct

But amps dropping low is an indication the batt is pretty full.

That's what was puzzling (with the old batts). The amps dropped as expected (<5 a) but the batts after 5-6 yrs did not hold charge.

If you think it might help to recover a bit from (past PSOC) sulphation, after current is at 2%, boost V a bit and keep pushing see how long it takes to get to 1%.

Or follow mfg "conditioning" protocol.

But once most lead has lost capacity it ain't coming back, and taking longer to finish Abs is a sign of that.

I now have new ones. I will increase V and increase abs time.

Why would Calder have recommended such a low abs voltage range (my previous post)? -

With a 440 Ah bank as he writes at the end of the paragraph:

14.2V at 10% rate of charge = 44A (10% of 440)
rising to...
14.4V at 25% rate of charge = 110A (I can't get 110A)

So, given this range, 44 to 110A (14.2 to 14.4V) my 60A lies proportionately at about 14.25V. That's why my abs was set at around 14.3V.

The page I posted earlier has the elusive answer, esp. in the last sentences.

My Q is WHY? Why does he imply that I can use 14.25 at low charge rate? Everyone here says voltage should be much higher (and abs time too).

He writes (see prior post of page) that at low charge rate amps, but with a longer charge time, battery can be charged more fully since it has time for the charge to percolate into the inner plates etc etc. Okay, so only 1 hour absorption sounds like it may not have been enough time, y'all say, but note, as I said previously, my bat monitor actually showed amps were dropping to <2%! So it seemed charge was being accepted as expected and bat was full. And...
|
"When fast charging a higher absorption voltage is needed......so at lower rates of charge [MY CASE] the point at which bulk charge is terminated CAN BE LOWER than at high rates of charge".

He also seems to base his case on below graph (from his previous page, p22, 2nd ed). Believe me, I've tried to understand this for 10 years!

[lateral]

Quote:
With a 440 Ah bank as he writes at the end of the paragraph:

14.2V at 10% rate of charge = 44A (10% of 440)
rising to...
14.4V at 25% rate of charge = 110A (I can't get 110A)

So, given this range, 44 to 110A (14.2 to 14.4V) my 60A lies proportionately at about 14.25V. That's why my abs was set at around 14.3V.



I don't see it that way. Your Abs voltage will be what you set it to.
Current will be what the battery SOC allows owing to its increasing internal resistance with increasing SOC. Your charger will be the current limiting device, to its spec. Depending on charging device regulation.
I don't see that the relationship above between current and voltage is correct.
M2CW.

[jackt]

Originally Posted by lateral

Quote:
With a 440 Ah bank as he writes at the end of the paragraph:

14.2V at 10% rate of charge = 44A (10% of 440)
rising to...
14.4V at 25% rate of charge = 110A (I can't get 110A)

So, given this range, 44 to 110A (14.2 to 14.4V) my 60A lies proportionately at about 14.25V. That's why my abs was set at around 14.3V.



I don't see it that way. Your Abs voltage will be what you set it to.
Current will be what the battery SOC allows owing to its increasing internal resistance with increasing SOC. Your charger will be the current limiting device, to its spec. Depending on charging device regulation.
I don't see that the relationship above between current and voltage is correct.
M2CW.

Not sure how you read it but don't be confused by his word "rising to" if that's what you disagree with. It's not that voltage "rises", I know. He wrote that to imply a "range" of set-point voltages that you choose. He's saying choose 14.2V if your alternator puts out 10% of bat capacity amps (C10) and other values up to 25% (C25). As he says a max would be 40% of bat capacity amps but few can get that.

I agree with you, and also think it's confusing, but I understand it that he's based it on the idea of high rate of charge amps for short time and higher volts (surface charge) or low rate of charge amps for very long time plus lower volts (inner plate charge), and need of finding a compromise. See his words:

[john61ct]

Originally Posted by jackt

Why would Calder have recommended such a low abs voltage range (my previous post)?

Lower is safer than higher if you need to generalize.

To high will damage Gel for example.

Also it's only in recent years so many have gone to AGM, and even more recently people have learned higher really does themgood for longevity.

If a normal charge (under .2C) to 100% full usually takes say six hours, then dropping voltage means it will take longer.

And old batteries take much longer!

One hour barely gets things started with lead.

The amps were dropping because the old banks resistance was so high.

Takes big amps and higher voltages to try to break through.

Some AGM now state .4C as a **minimum** charge rate, so a 600AH bank starting investment charger is 240A.

And some want nearly 15V, may need to isolate sensitive loads during charging.

Bottom line get the spec details from the vendor before buying, make sure charge sources match.

If you can't get the data, don't give them your money.

[jackt]

Thanks Lateral. Especially...

Originally Posted by john61ct

The amps were dropping because the old banks resistance was so high.

Takes big amps and higher voltages to try to break through.

That's the confirmation I needed! I suspected sulfation resistance meant amps would not go in, and the amp meter's amps dropped because batts would not ACCEPT any more. I guess it's like a line to get into a night club (they tell me!) and doorman says..."We have no more seats - they broke them!"...so the line waiting to get in just gets fed up, dwindles in numbers, and goes home.

True, I should have got the spec sheets for the batts myself before deciding on charging parameters (the vendor just said use 14.4 but no consideration of alternator amps to change the plan). But as my alternator is small so how should voltage change? According to Calder it should be lower and longer?

I earlier in thread gave the link to pdf of US Batts 2200 specs:

Quoting SPEC sheet pdf:



"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)"
[So for my x4 batt bank of 464 Ah:
Constant current 46.4 A (10% of 464) to 14.7 V (7.35 x 2)
]

I think I miscalculated in above - I missed the 10% OF C20:

"Constant current @~10% of C/20 Ah in amps to..."

10% of C20?? C20 is 20% of bat size (464 Ah), right? That's 92. 10% of 92 = 9.2. But 3 cells so 9.2 x 3 = 36.6. Then x2 since 2 series, 2 parallel = 36.6 x 2 = 73.2 AMPS.

So they are saying to charge at 73.2 A. Is this correct?

[mitiempo]

Originally Posted by jackt

I earlier in thread gave the link to pdf of US Batts 2200 specs:

Quoting SPEC sheet pdf:

Attachment 147644

"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)"
[So for my x4 batt bank of 464 Ah:
Constant current 46.4 A (10% of 464) to 14.7 V (7.35 x 2)
]

I think I miscalculated in above - I missed the 10% OF C20:

"Constant current @~10% of C/20 Ah in amps to..."

10% of C20?? C20 is 20% of bat size (464 Ah), right? That's 92. 10% of 92 = 9.2. But 3 cells so 9.2 x 3 = 36.6. Then x2 since 2 series, 2 parallel = 36.6 x 2 = 73.2 AMPS.

So they are saying to charge at 73.2 A. Is this correct?

No. What they are saying is to charge at 10% of the battery bank's capacity at the 20 hour rate. This is a minimum and is what most flooded battery manufacturers suggest. There is no maximum as at a given voltage the batteries determine the current they accept.

The reason the vendor stated 14.4 volts is the same reason virtually every AC charger and solar controller is set at 14.4 absorption. It is safe. Not best but safe.

14.7 is the absorption voltage for your batteries. Battery manufacturers know what your batteries need. Charger manufacturers just play it safe.

[jackt]

Originally Posted by mitiempo

No. What they are saying is to charge at 10% of the battery bank's capacity at the 20 hour rate.

So then, be explicit, what are your numbers?? It makes no sense without example numbers.

"charge at 10% of the battery bank's capacity..."
What's that value then?

I showed this calc initially = 46.4 A (10% of 464)
- but I think I was wrong as they actually stated:
"~10% of C/20 Ah in amps to..."

"OF" !!

"...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??

Remember their specs is PER CELL:

"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)"

Each of four 6 V 232 Ah batt has THREE cells.

What are your numbers?

[jackt]

Originally Posted by mitiempo

No. What they are saying is to charge at 10% of the battery bank's capacity at the 20 hour rate.

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??

[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.