NextStep2 regulator bulk charge issue

[jackt]

Originally Posted by StuM

14.7 What? Certainly not the 14.7A he stated.

So much wrong with this:
1. Bulk charging doesn't have a voltage. It starts somewhere above the existing battery voltage and increases steadily until absorption voltage is reached (So in a way it does have a maximum voltage.)

When you start bulk charging a battery at , say, 50% of SOC, the charging voltage will be regulated to limit current. It could well be below float voltage initially to avoid pushing too high a current and overheating the battery. As the SOC increases, the current is kept constant by steadily increasing voltage up to the absorption voltage. (That steady current should be in accordance with the manufacturer's recommended charge rate(s). Exceeding the recommendation is likely to overheat and damage the battery).

14.7V is the charging voltage, not the battery voltage.

The charger in bulk will bring the charging voltage up to 14.7 while still maintaining the bulk current limit.

Once it can no longer deliver the set bulk current at 14.7, it will go into absorption mode by holding the charging voltage steady at 14.7 and the current being pushed into the battery will decrease as the battery internal voltage continues to increase towards 14.7V and the potential difference between the charging source and the battery's internal voltage decreases.

Once the internal voltage (actually surface charge) of the battery gets "up to 14.7V", no further charging can take place. That's when absorption ends, not when it starts. (Actually, a bit before that, when the battery voltage is slightly below 14.7 and some small amount of current is still flowing).

"The charger in bulk will bring the charging voltage up to 14.7 while still maintaining the bulk current limit.
Once it can no longer deliver the set bulk current at 14.7, it will go into absorption mode by holding the charging voltage steady at 14.7 and the current being pushed into the battery will decrease as the battery internal voltage continues to increase towards 14.7V "

Is this the reason why my (newish/4 yo) batts are seeing the NS2 switching EARLY (say, at 14.15V) to abs before the batt monitor shows 14.3V (my absorbtion set pt). Is it that the charger voltage (14.3) is not the same as the BATTERY voltage at the point in time when the switch from bulk to abs occurs? And so I should not worry if the switch to bulk "appears" to be early. It's just what it's programmed to do?
But by definition, I thought bulk (increasing volts at constant current) occurs up until the abs set point (voltage of batt) is reached - at which time it switches to abs. But you seem to be saying the abs voltage will not even be approached by the batts until the END of abs! Wow.

Hence the early switch????

[lateral]

Absb Vset should =14.7V....mine is 14.8
Bulk = increasing voltage to vset ....max current
Absb= constant Voltage at Vset......decreasing current to timeout or 0.015C current flow.
*Charger voltage after bulk should remain at 14.7 until end of absorb.
But you seem to be saying the abs voltage will not be approached by the batts until the END of abs!
Not me.......but yes. Turn off the charger and it will blow back reasonably quickly to 12.8V (24hrs) or quicker with loads. Mine does.

Dunno why your NS1 was doing that ...maybe it was dying and reading incorrect current. Or loose connections..did you cover that?

[jackt]

Originally Posted by lateral

Absb Vset should =14.7V....mine is 14.8
Bulk = increasing voltage to vset ....max current
Absb= constant Voltage at Vset......decreasing current to timeout or 0.015C current flow.
*Charger voltage after bulk should remain at 14.7 until end of absorb.
But you seem to be saying the abs voltage will not be approached by the batts until the END of abs!
Not me.......but yes. Turn off the charger and it will blow back reasonably quickly to 12.8V (24hrs) or quicker with loads. Mine does.

Dunno why your NS1 was doing that ...maybe it was dying and reading incorrect current. Or loose connections..did you cover that?

Correct, not you, StuM posted the piece I quoted.
To the rest you wrote: Sure. Connections? Yes, that was raised.

You sent a second message that I only read on the email notification:
"Sorry busy right now but....You have a 95A bosch with NS2, right? Four hrs motor run is excessive..." etc. Do you want me to re-post it here or do you??

[mitiempo]

Originally Posted by jackt

They got that number by drawing down at a 23A rate, to 0% SoC over 20 hours."

No. not to 0% SOC. Batteries are considered dead at 10.5 volts. That is the low voltage used in a 20 hour test.

[mitiempo]

Originally Posted by jackt

It

Good. all understood now. But what if I was to let alternator at normal (happy, low-ish) engine revs charge at 60A?? It's a Bosch 90A and does no more than about 60-70 happily.

Until it warms up a bit and the current drops.

[jackt]

Originally Posted by mitiempo

Until it warms up a bit and the current drops.

Yes, at start of bulk I see it at about 70A (at medium+ idle-at-anchor revs). Within 1 or 2 mins it's down to 65. After 3 or 4 mins, depending on SOC, it's happily at about 60A and working up to abs set poit, maybe showing 13.7...13.8V...

[StuM]

Originally Posted by jackt

Is this the reason why my (newish/4 yo) batts are seeing the NS2 switching EARLY (say, at 14.15V) to abs before the batt monitor shows 14.3V (my absorbtion set pt).

No, if it's switching early there is a problem somewhere.

Note that a "battery" (so called) monitor during charging is not measuring the internal voltage of the battery. It is measuring the voltage between the battery terminals. If your charging source is at 14.3V, then that is what you "battery" monitor will show.

...
But by definition, I thought bulk (increasing volts at constant current) occurs up until the abs set point (voltage of batt) is reached - at which time it switches to abs. But you seem to be saying the abs voltage will not even be approached by the batts until the END of abs! Wow.

The surface charge on the cells of a battery may reach 14.3V but that's not the "open circuit voltage" of that battery once it is disconnected from the charge source. As lateral correctly points out,disconnect the charger and the "battery voltage" steadily drops back to it's real "Open Circuit" voltage.

This is why using voltage to estimate SOC is so fraught with difficulty. The voltage across the terminals will be lower that the OCV (the better indication of SOC) when a load is on (or has recently been on) the battery and will be higher when it is charging (or has just been charged). That's why just about everyone recommends that a battery needs to "rest" for 4 hours before trying to use terminal voltage as a SOC indicator.

If you are interested, there is a good semi-technical explanation of why this happens here:
http://www.mpoweruk.com/chargers.htm#rates

[john61ct]

Yes, you can't use voltage as an accurate State of Charge.

The Merlin SmartGauge is IMO the best, re-branded and supported by Balmar in the states. Within 2% accurate with bank at rest, maybe around 4% while charging or heavy loads.

All the rest use a shunt to measure AH in and out once you tell it the bank is full, give a (bit less) accurate estimate off that, need periodic attention, recalibrating. Since SG only shows SoC and voltage, many who want to see AH logged use both together.

Best in this group IMO is Bogart's Trimetric, but for the marine market seems Victron BMV-702 is the way to go.

I'm sure Vanner, Magnum, BEP and Sterling's are also good

Used to hear a lot about Xantrex Link line, these days not so much

[jackt]

Originally Posted by john61ct

Yes, you can't use voltage as an accurate State of Charge.

The Merlin SmartGauge is IMO the best, re-branded and supported by Balmar in the states. Within 2% accurate with bank at rest, maybe around 4% while charging or heavy loads.

All the rest use a shunt to measure AH in and out once you tell it the bank is full, give a (bit less) accurate estimate off that, need periodic attention, recalibrating. Since SG only shows SoC and voltage, many who want to see AH logged use both together.

Best in this group IMO is Bogart's Trimetric, but for the marine market seems Victron BMV-702 is the way to go.

I'm sure Vanner, Magnum, BEP and Sterling's are also good

Used to hear a lot about Xantrex Link line, these days not so much

Thanks,
So you can use volts to (accurately?) measure SOC and I realise you need to rest the batt or put a small load to get a better reading. I have the Link10 and looks like this (Heart Interface version, not Xantrex).

[jackt]

This discussion has been extremely helpful to me and even the disagreements are comforting as it shows that it's not just me who is not clear on what's happening and why! Admittedly, your quibbles are at a finer level of detail than I could have initiated but I do understand what you are debating...so thanks to all.

My original post actually was two Qs. To paraphrase:

1. Why, with my new Nextstep2 reg and new batts (464 Ah), at the end of my constant voltage (14.3V) absorption phase (too short at only 1 hour I now know!), was current still around 20A whereas with my old NS1, after also 1 hour abs, current had dropped to < 5A as expected.

I think Q1 can be put to bed (bunk?) as solved. Thanks.
---

2. Why is bulk phase apparently sometimes switching "early" to absorption - before set point of 14.3 is reached, like at around 14.1 or 14.2 earlier in some tests (eg, after Christmas when I got a new 50A 3-stage smart external charger, charged them up real good at dock, went off cruising, and at anchor seem to have seen it switch early, even at 14.0). Also some recent tests in last few months.
See earlier posts on this thread on Page 2 that I recently updated with tests:

Page 2: NextStep2 regulator bulk charge issue

eg, My comment, #18.

Earlier in thread around P2 there were suggestions as to why - wiring etc.

As for Q2. Next time I'm at dock, maybe I should charge with external smart charger (50A, 14.7), get them full, and check NS2 again, with abs time at 2 hours and abs volt at 14.7V.

Or rather, FIRST do a test with the boat engine charging - NS2 (abs set to 14.7V and 4 hours?) and engine alternator (60A max is my usual) while they are NOT fully charged??

Suggestions?

[jackt]

eg, as initially in #20...

I did various checks. Note, this was a few weeks ago before the recent set of answers regarding the high float. The high float issue is solved, leaving the early switch issue:

I noticed that it tends to switch early from BULK to ABSORPTION phase at around 14.15 or 14.2V which is .1V - .15V less than set point of 14.3V - even with a temp sensor OFF.
I would expect with temp sensor off that it would get closer to set point rather than switch earlier (as was suggested to try by sales rep/technician) - as expected by the temp compensation logic: to avoid boiling batts with increased voltage acceptance of chemicals as temp of batts increases, switch earlier. But temp sens wire was disconnected and still early switch. Ambient temp is around 20 deg C. A volt meter test shows voltage on batt monitor is same as at terminals of batt so batt monitor seems accurate enough.

Also puzzling is the float stage voltage - float voltage is also higher by .1 or .15 V above set point of 13.4V.

Here is an example:

I had left something on and when I returned to boat at dock, there was -65 Ah. I was a bit horrified as I never do that! I decided to charge with motor and alternator. I recorded times and everything. Two tests - that afternoon (temp off) and next morning (temp on). Ambient temp around 20 (68) deg. An early switch to absorption??

[jackt]

Originally Posted by Maine Sail

You still seem to have a volt sense issue which can also lead to an inadequate absorption cycle..

Maine Sail, Please see my recent post with a table of values during charging. Does this data help clarify? Also, in the meantime, the absorption/float voltage issue was well-addressed and debated (!) by others...

[jackt]

Going back to review Page 1 of my thread, and now understanding much more due to all the great help from you all, I re-read the NS2 regulator manual about time staying in bulk. Is it to be expected the early switch from bulk - before abs set point is reached - if alternator not capable? But it is sized okay - 60 A. See table of my tests.
System:
464 Ah batts (4 x US 2200 - 232 Ah)
Bosch 90A alt puts out 60A


https://www.amplepower.com/manuals/ns2/ns2.pdf

"The regulator will not stay in bulk charge mode long if the batteries are full, or the alternator can produce more than the batteries will accept.
The regulator cannot drive the battery voltage to any specific level
if the alternator is not capable of producing enough current to
satisfy battery acceptance capability, which varies with state–of–
charge.
Alternators don’t produce maximum output unless they are rotating
at 6000 to 7000 RPM, so don’t expect high current unless the alternator is rotating fast. If the batteries won’t accept high current, the voltage will quickly rise to the absorption setpoint and hold atthat voltage. The regulator hasn’t skipped the bulk charge step, just
moved through it rapidly because the batteries don’t accept much
current."

[john61ct]

They also don't accept as much as they get older.

Set up a good 100+A shore charger to compare.

You got a new bank right?

Are you still seeing problems?

[jackt]

Originally Posted by john61ct

They also don't accept as much as they get older.

Set up a good 100+A shore charger to compare.

You got a new bank right?

Are you still seeing problems?

Not new, newish - almost 4 yrs old but not heavily used or many many discharge cycles (boat stays at marina, not liveaboard anymore). Only got a good shore charger later last year (50A, 14.7V). (100A?? - I'd be dreamin'!). So before that they could have been a bit undercharged. But when I put new charger on last year, they seemed to come up well and hold charge just fine, similar to when they were new (ok, perhaps a little less so). I hope they are not sulfated too much!

I have not been back yet to check - this w/e...

Do you think I should immediately bring up to full with shore charger, or try alternator with longer abs? Did you see my table of tests?