Panel Voltage Readings

[nornaj]

Hi, Guys
Insight appreciated - as always.
Recently we installed 2 x Blue Seas P12s for an aggregate shore power max charge of 80 amps.
(House bank is c 700ah, starter 110ah, thruster/windlass 110ah.)
Cold up here in BC (about -2/0 degrees C today).
When the chargers powered up (in bulk) today they gave 15.0v.
Understandably, the panel alarms for an overcharge (usually starter, sometimes house).
I guess the question is as follows:
+ the P12s compensate for temperature.
+ does the panel?
If the panel doesn't compensate then (presumably) everything is fine.
If it does, then we need to run some diagnostics.
NornaJ

[dbostrom]

By any chance are you trying to parallel the output of these chargers?

[rene460]

Hi nornaj,

May I suggest that the first step is to consult the manual to check what voltages are expected.

My non-floating caravan has a "Projecta Intelligent Charger" which has seven different charging steps.  Depending on the battery chemistry selected, some of these steps run up to 16 V, though only for a short time.  However it would not normally be expected to reach this stage on first connection, especially if the batteries were a bit down when the Chargers were first connected.

I am not sure that parallel operation would be much of an issue.  After all most of us have a solar charger connected, usually in parallel with either shore power or the engine alternator.  However this can easily be checked by switching off one charger.  It is surprising how little information seems to be around on parallel operation of chargers.  I have only seen one C-Tek document, and ithe context was not necessarily applicable to other equipment.

rene460

[dbostrom]

The concern over parallel charging* is that one of the key parameters used by a charger to determine present charging stage and hence voltage/current is the terminal voltage of the battery and what happens to that voltage in the presence of current delivered to the battery. Two chargers stirring that broth will end up becoming confused; without any explicit arrangement for cooperation (paralleling) there's no way for either charger to discriminate between actual battery terminal voltage versus the influence of the other charger on voltage, as each charger attempts to establish a charging regimen.

Stages of charge are established and tracked by using the charger's measurements of voltage and current and --indirectly-- battery resistance. Unless a charger is explicitly told that available amperage into the battery is doubled and that some other agency (the other charger) is also influencing battery terminal voltage, the assumptions employed by the charger will yield incorrect results. Reading this useful description and then thinking about two chargers working in ignorance of one another makes it easier to understand the problem.

Different designs of chargers will misbehave differently in a blind parallel situation depending on their implementation details. Ideally they'd throw an error and shut off in the face of confusion over battery behavior.

*With "smart" chargers. "Dumb" chargers can be paralleled.

[nornaj]

Thanks, guys
The P12s have now been operational for several months. We had some initial concerns about how they would behave in a parallel arrangement, but BlueSeas and the marine electrician were certain that there would not be an issue providing they were programmed identically. So far they co-operate well and one them shuts down whenever >40 amps is no longer required.
As far as I can tell, the only issue is some slight overcharging of the starter bank, but that is most likely due to a five-year old deteriorating Gp31 battery which should be replaced fairly soon.
The P12s correct for temperature. So an initial 15v is not unexpected at 0 degrees C. The question was whether the original voltage meter in the panel corrects for temperature. There is no documentation that I can find on that. I am assuming that it doesn't, in which case this is really a non-issue and I'll just silence the alarms (if I am on board).
NornaJ

[dbostrom]

...one them shuts down whenever >40 amps is no longer required.

Ah, so! I stand corrected. Bulk charge done by both, absorption by just one. That stands to reason in a way because bulk charge is sort a brute-force affair, although how the priority between chargers is established is a little puzzling. As well, does the dormant charger go back into bulk mode if the battery is depleted again (he wonders aloud) by a stiff load prior to completion of absorption (he wonders aloud)?

I suppose it's the sort of thing needing checking on a case-by-case basis.

--> Actually, having done some more reading on this I think you need to ask Blue Sea exactly how a parallel configuration works, in detail, and I wouldn't turn off your alarm until you have a plausible answer. Perhaps there's some kind of software magic going on but extraordinary claims need extraordinary evidence and given the limited information available to a charger at its output terminals, knowing there's another charger in the picture is an extraordinary claim. Most charger manufacturers seem to be silent on this topic but the few items I've found that refer to paralleling smart chargers are rather discouraging. For example this, which is pretty much typical of cautions on using parallel smart chargers (and explains why there needs to be cooperation between chargers):

"While smart chargers deliver clear charging benefits, multi-charger applications can present challenges to chargers with built-in smart charge control technology. In this case, the charge controller manages the individual charger when the purpose of the series or parallel configuration is for the chargers to work together for total increased output voltage or increased amps. Chargers with built-in controllers can interfere with each other in their various charge stages of bulk, absorption, float, and equalization and the batteries may not reach full charge. In operations where auxiliary battery power is mission critical, chargers with built-in controllers can contribute to decreased battery performance and battery life."

[nornaj]

Interesting stuff and food for thought, thank you.

Let's see if I have this right.
The default temperature correction on the P12s is 30mV per 1 degree C below 25C.
The default absorb and float voltages are 14.5V and 13.5V respectively.
At 0 degrees C the voltage correction is 0.75V.
At 12 degrees C the voltage correction is 0.39V.
The LinkLite reading on bulk charge was 15.0V at 0 degrees C, which is equivalent to 14.25V at 25C.
The Linklite reading on float charge was 14.0V at 12 degrees C, which is equivalent to 13.6V at 25C.
The differences between the Linklite, Panel voltmeter and the P12 readings were never greater than 0.1V.

This suggests that the P12s are behaving as per manual.

And, therefore, the alarm issue at the OEM panel is probably due to there being no temperature correction on that function. (Afterall, with the 39i we are talking about a boat designed primarily for the tropical/summer charter markets.)

Other than the panel alarm, the P12s are doing everything we had hoped for (and expected) when they were chosen and installed. We like 'em.

My choice seems to be to either to ignore the alarm or adjust the temperature correction on the P12s. In the absence of any information that the OEM panel alarm is temperature corrected, think I'll go with the first option.

NornaJ

[dbostrom]

Sure, that makes sense nornaj. Might nonetheless be worth casting an eye on the battery producing the alarm. 

I did some more digging into this because it's something related to work I do. From what I can tell, parallel connections of 3-stage/"smart"/[brand name here] chargers not equipped or intended for the purpose tends to end up with subject batteries not reaching full charge. This stands to reason as either/both chargers will be increasing what other the charger sees as actual battery terminal voltage. The upshot is that absorption is terminated prematurely.

Undercharging is arguably better than the other possibility with all of its exothermic baggage.

[As long as the question of charger smarts is in play it's worth noting also that online battery maintenance is a bit different to standby charging; ongoing DC load during charging can confuse a charger. These are online chargers I've found to be quite good at handling a bank under load without becoming deranged.]