Alternator: Voltage or current limited with high load?

[john61ct]

Originally Posted by Wotname

If this acceptance current at any one time is lower than the alternator's rated current output, the alternator will simply stay at it's regulated voltage point while the battery receives it's acceptance current. As the battery increases it's SOC, the acceptance decreases.

If the battery's acceptance current is higher than the alternator's rated current, then the voltage will decrease below the regulated point as the alternator struggles to supply the current the battery will accept.

This will continue until battery's SOC increases to a point where the acceptance current is again below the alternator's rated current. Then the voltage remains at the regulated point. Unless of course you burn up the alternator first .

That's it in a nutshell

Yes, the reason stock internal VRs do not regulate current output

or do so just by dropping voltage so low that effectively charging is halted

is that "normal" lead banks are of lower capacity and/or low-CAR chemistry.

The essence of the OP question is

"how do stock internal VRs handle (larger Ah and/or higher-CAR) banks that are demanding a higher current than the alternator can safely produce?"

The short answer is, very poorly.

It is the self-regulating nature of "normal" (small, lead) banks that allows manufacturers to by default supply cheap VRs that do not **effectively** limit current.

By effectively, I mean while maintaining a voltage high enough to optimize charging the bank.

In many scenarios, **after** the Absorb/CV stage has been reached, voltage is being capped, the current demanded by the bank is still much higher than the alternator can safely produce.

Many more modern stock internal VRs are now **better** at protecting their alternator against heat damage. But they do so by in effect drastically lengthening the charge cycle, even when the Absorb/CV setpoint has not yet been reached you still need to keep it much higher than they do, or SoC will not increase in a reasonable time.

This is how current-limiting B2B chargers like Sterling BBs, get **much** faster charging in these conditions, by keeping a (maybe not constant but) **higher** effective voltage going, even while at the same time, protecting the alternator from the overcurrent condition imposed by the too-thirst bank.

That is the also the key advantage of Balmar's MC-614 and those from Mark Grasser, Ample Power, Next Step, Sterling's Alt-to-batt series, etc. Yes higher cost but also **effectively** delivering a higher proportion of the alternator's rated current output, without parallel-stacking BB units.

The "normal" cases where the current demanded by the bank is **lower** than the safe continuous output capacity of the alternator, are irrelevant to the issues above, as a current-limiting mechanism is no longer required.

All this applies no matter the chemistry. The only difference LFP makes, is that overcurrent conditions occur with a much smaller Ah capacity bank, and continue for a much longer period of time, right up to 95% SoC.

With say, Lifeline AGMs, their max CAR of only say 0.85C is very short-lived, even when you get bank size up to say thousands of Ah, the chemistry is self-limiting, overcharging is not a risk from current, just overvoltage or holding Absorb too long.

While LFP will demand (accept) five times the current rate you would ever want to supply them for longevity.

In which case the current-limiting device (external VR or B2B charger) is **protecting the bank**, as well as the alternator.

[thomm225]

Originally Posted by ayates

I should have been able to figure this out myself, but...

If a high load (like a partially discharged large battery bank) is placed on an alternator (with a standard OEM regulator), will the alternator be voltage or current limited? That is, will the voltage stay at say 13.8V and the current be limited to the capacity of the alternator, or will the voltage drop?


Thanks,

Allan.

The voltage will stay constant just like on your vehicle's battery gauge when you start.

Now if you have the old current gauge you will notice the current being way high at first like your car used to do when you first started it with the old amp gauge and then come back to center into the normal range

The current will go to max allowed then come down as the battery bank charges up kinda like a regulated DC Power Supply

[john61ct]

Originally Posted by thomm225

The voltage will stay constant just like on your vehicle's battery gauge when you start.

Sorry but no. You are describing what happens with a regular battery, likely a Starter, small in size, high resistance, barely depleted.

With a large deep-cycling bank at low SoC, it may take hours of Bulk / CC (so-called) charging for voltage to rise up to the Absorb/CV setpoint.

What SoC the bank is when that happens, could be 75% or 95% depending on various factors, all independent of the gear regulating the charge cycle.

[a64pilot]

The voltage will stay at set point, only if the ability of the bank to accept charge is less than the current limit of the alternator, if the bank can accept more than the alternator can supply the voltage will drop until they equalize out.
Increasing voltage increase acceptance rate, decrease voltage decreases it. So the voltage will decrease until the current limit of the alternator matches the acceptance rate of the bank. This is also called Bulk charging, once the voltage set point is reached, your in absorption.

Thomm your describing absorption, which if the bank isn’t discharged deeply, or if the charge source is large enough can happen right away, you just skip bulk and go straight to absorption.

People with real small bank will skip bulk, just as cars do, unless they have a dead battery, and they may then as some cars have large alternators, I believe my Duramax Diesel had a 200 amp, but may well be wrong, that’s off memory

[Stu Jackson]

Originally Posted by john61ct

Yes, the reason stock internal VRs do not regulate current output

or do so just by dropping voltage so low that effectively charging is halted

is that "normal" lead banks are of lower capacity and/or low-CAR chemistry.>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>

NO simple vr known to man regulates current.

Dropping voltage, of course, reduces current flow from the AO (alternator output) to the bank.

What does a "..."normal" lead bank..." mean? And they are not of lower capacity.

This "introduction" of yours is meaningless and negates any of the further malarkey.

john, it's very simple:

A VR regulates voltage. All it does is set a MAXIMUM of volatge that the alternator can produce.

The CURRENT produced is either of two things:

1. The maximum current that the alternator can output based on the acceptance of the battery bank and its voltage which rises as the AO reaches it

2. Lower current later in the charging process because of the reduced acceptance of the bank as it gets fuller

All the rest are merely modifications to the basics, for equipment protection, i.e., temp compensation, belt manager, SEM, and do not modify the basic concepts in 1 & 2 in any way.

KISS.

For the OP,

50% house bank, engine starts, internal AND external regulators tell the alternator to pump amps.

Voltage rises from original battery bank V to set point of regulator while at the same time current is maxed to alternator capacity.

Once V set point is reached, current maintains (large bank w/ small AO for example) and then begins to drop as battery bank gets full.

Not so hard to describe for the OP.

[john61ct]

OMG. OK let's start with this

Originally Posted by Stu Jackson

NO vr known to man regulates current.

So what do you call it when the user has the option to set a ceiling on the alternator's current output?

**You** were the one pointed to documentation for Ample's and Balmar's among others.

Explain the advantages of Balmar's "Belt Load Manager" feature for example.

From my common-sense end-user POV, allowing the owner to reduce the output load demanded by the thirsty high-CAR bank, de-rating (reducing) max output current in small increments

maybe "inside the black box" by some theoretical EE circuit modeling equation, you say that's "not regulating current?"

Also their "Small Engine" mode.

Mark Grasser, Ample Power, Next Step, Sterling's Alt-to-batt series, etc all do the same, whatever spin you want to put on it, the ability to control the output current

are **critical** to the question the OP raises,

in many cases just as important as adjustable setpoints.

> What does a "..."normal" lead bank..." mean?

As stated many times, the scenario of a higher-CAR chemistry and/or higher capacities have been increasing in relatively recent times, and is what's been driving the development of these specialist regulators.

A 200Ah bank that demands 0.2C or 40A is still pretty standard for many boats.

When a 1200Ah bank that pulls 0.6C hits a stock alt/VR setup, that changes things, right?

Exactly the issue the OP asks about.

Now with even higher CAR, say a LI chemistry at 4-5C, even a 200Ah bank presents the same kind of issue.

How is that not obvious?

Yes, with the old school bank, these newer VRs aren't needed as critically for this current limiting functionality.

But say with an expensive GEL bank, just those VRs' ability to drop to a Float stage, user being able to tweak the voltage setpoint that alone may justify the VR conversion.

I'm sure you've read this article many times
https://marinehowto.com/automotive-a...cle-batteries/

Maybe re-visiting it will help.

And sure, if the "inside the black box" control mechanisms do not match the EE circuit modeling terminology for "current regulation", even if it's irrelevant to these real-world practicalities, I'd still appreciate your (or someone else) explaining the distinction, just to further my education on the theoretical side.

[john61ct]

Besides Balmar & Ample, the Wakespeed docs give plenty of parameters for current control

https://shop.marinehowto.com/product...ator-regulator

Their CAN comms documentation goes into more detail.

Also used with American Power HPI alternators, I know Bruce@OceanPlanet deals in those

_____
Nordkyn also is well respected

http://nordkyndesign.com/product/nor...nce-controller

____
Mark Grasser R230a line specifically feature current control

____
See also the new Integrel (inTEGrel) / Triskel systems Nigel Calder has been working on.

They can explicitly dial up/down the amps output "live" while underway, help limit the HP diverted away from engines' propulsion capacity

[Wotname]

Originally Posted by ayates

I should have been able to figure this out myself, but...

If a high load (like a partially discharged large battery bank) is placed on an alternator (with a standard OEM regulator), will the alternator be voltage or current limited? That is, will the voltage stay at say 13.8V and the current be limited to the capacity of the alternator, or will the voltage drop?


Thanks,

Allan.

Hey Allan, are you still around; if so, has your question been answered to your satisfaction?
If not, let us know and we will try again (still keeping it simple)!

[OceanPlanet]

Hi folks,

Although the MGDC R230a isn't available yet, setting a reduced field % (to keep alts from baking themselves when charging high CAR banks) is possible with the Balmar MC's, the Mastervolt Alpha Pro 3's, the Wakespeed WS500/AP500, etc.

Note that the AP500 is a slightly more advanced version of the WS500. Programming these units is something we do in house (not all that easy) however the level of adjustment is astounding. We've been working together with Wakespeed, Lithionics, and American Power to refine the capabilities of the CANbus communication between the AP500 and the Lithionics BMS.

The AP500 can get current info from the BMS, a shunt, or both, and the max charge current can be set as needed. Which for us is typically 400A continuous for each BMS.

This capability is important on applications with multiple powerful charging sources, for instance with two engines/alternators AND a generator with AC/DC chargers. If the combined power is >400A, and it's all running through one BMS, then the AP500(s) will cut back the alternators as needed to stay under the 400A ceiling.

[tanglewood]

The way a regulator actually works is that it monitors voltage, and commands current from the alternator. If the desired voltage isn't attained, it will be commanding max current from the alternator, which will be the rated output of the alternator. Once the desired voltage is attained, it adjusted the commanded current to maintain (regulate) the desired voltage.

[rgleason]

Although the MGDC R230a isn't available yet, setting a reduced field % (to keep alts from baking themselves when charging high CAR banks) is possible with the Balmar MC's, the Mastervolt Alpha Pro 3's, the Wakespeed WS500/AP500, etc.

Field Current % is a setting in Balmar parameters. I wish there were some rule of thumb chart for those settings, but Balmar simply advises not to touch that. As I understand it now, this setting is to protect the alternator, not the battery.

So, Adjusting Field Current % is not a good direct way of stopping alternator charging, particularly when trailing current gets to a certain point, which is the means currently used to protect certain types of batteries.

In a given system with the same conditions, could the "% field current limit" be set such that the alternator would stop charging right at the correct point in the battery resistance curve, or in other words at some "value for trailing amps"?

If so, how would this be accomplished without a lot of pain and adjustment?


--The Belt Manager basically reduces % field current by some amount (is it 20%) each step.


---Later: So I guess there is no means to detect % field current in the regulator's electronics? Thus there is no way to take regulation action at a certain % field current?


--- Perhaps someone clever could use %field current to eliminate those 2 shunts in the WS500, for example or is this a bad way to do it?


WS50 has ,TargetVolts, TargetAmps,

[Stu Jackson]

Originally Posted by john61ct

OMG. OK let's start with this

So what do you call it when the user has the option to set a ceiling on the alternator's current output?

**You** were the one pointed to documentation for Ample's and Balmar's among others.

Explain the advantages of Balmar's "Belt Load Manager" feature for example.

From my common-sense end-user POV, allowing the owner to reduce the output load demanded by the thirsty high-CAR bank, de-rating (reducing) max output current in small increments

maybe "inside the black box" by some theoretical EE circuit modeling equation, you say that's "not regulating current?"

Also their "Small Engine" mode.>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>


And sure, if the "inside the black box" control mechanisms do not match the EE circuit modeling terminology for "current regulation", even if it's irrelevant to these real-world practicalities, I'd still appreciate your (or someone else) explaining the distinction, just to further my education on the theoretical side.

OK, john, you can quit the OMG malarkey now. You know darned well that I am a proponent of the Small Engine Mode and have an MC-612 which I know how to use.


My comment

no vr known to man can regulate current

remains correct.


Why?


Because voltage regulators regulate VOLTAGE, not current.


You may consider this semantics, but as an engineer I don't. And I think it's important for others who read these kinds of detailed discussions to be able to understand the concepts and how they work.



ONLY by modifing the VOLTAGE can the end result of the PROCESS be the reduction of current. Less pressure, less flow, but the less pressure, i.e., VOLTAGE, comes first.



But VRs do NOT regulate current. Especially internal ones.



That's all. I have read and could cite from memory all the links you've provided and I know that you know that I do.

[john61ct]

Originally Posted by OceanPlanet

Note that the AP500 is a slightly more advanced version of the WS500. Programming these units is something we do in house (not all that easy) however the level of adjustment is astounding. We've been working together with Wakespeed, Lithionics, and American Power to refine the capabilities of the CANbus communication between the AP500 and the Lithionics BMS.

Great stuff Bruce thanks so much for checking in here, very interesting stuff!

And no, I haven't fired up your dad's DC genset yet, it's at a friend's boat shed and he's threatening to steal it

8-D

[john61ct]

Originally Posted by rgleason

Adjusting Field Current % is not a good direct way of stopping alternator charging

Well, completely **disabling** Field Current is a bog standard function, preferred way to ensure full engine HP is available for propulsion, via a switch from the helm.

It would be trivial to implement that under mcu control based on hitting your LFP's 100% Full stop-charge point.

And obviously that is the preferred mechanism to limit current output by all these feature-ful external VRs, whether proportionally like belt manager, or via a fixed amps cap.

_____
What has **not** been widely implemented is "live arbitrary variability" of current output (field current) by the captain, or as part of an intelligent control process.

Except (afaik uniquely) for the case od inTEGrel / Triskel's pioneering work, goal of maximizing alt output in line with the engine's efficiency/power curve vs propulsion power needs.

Back when Al Thomason's programmable Wakespeed/APS regulator was an open source "Very Smart Regulator" / "Smart Alternator Regulator" project*, Al commented that it could be adapted by someone with programming skills to do something similar.

You talk about the VR sensing bank acceptance. That can only be done by a sensor (usually a shunt) located right at the bank. Best practice is this is part of the BMS, or the BM responsible for SoC monitoring, which can then communicate back to the regulators of the various charge sources, as Bruce just described above. Many boats will have multiple sources feeding concurrently, they will need coordinating.

Victron has their comms protocols, but a non-proprietary one based on CAN would be more open.

So, when the endAmps point is reached the BM or BMS sends out a signal, or opens relays, whatever to terminate all charge sources together, or at least isolate that bank from the charge buss.

In normal conditions, wouldn't you want your sources to keep producing and carry active loads? Better IMO to just isolate the LFP bank, using Starters or a lead Reserve bank as output buffer.

But obviously depends on the source type, boat's system design, let's not derail this thread, go to another one for discussing that detail.

[a64pilot]

I sort of got lost in all of the verbiage as a lot of it is confusing.

But it’s important to know that Balmar doesn’t control or reduce alternator output current directly. It has no idea of output current, but what it can do is reduce the field current, that reduces the alternators output to protect it from overheating, you just derate the alternator is all, but you cannot reduce the current and leave voltage high, I see that said, but you can’t do that. You can leave the voltage setting the same, but if you reduce current on a bank under charge, the voltage drops with it.

Now for the question of being able to get the alternator to drop to float when the trailing current is correct, you can in theory, you can set the alternator to drop when its output reaches x percent, which could correspond to trailing current.
What kills that though is the alternator only knows total load, it can’t know how much is going into the bank and how much is used by the rest of the boats electrical system, I was convinced I could get it to do it. But gave up, the fridge cycling off, or the autopilot or running the water pump etc, kept it from being possible, so I just gave up and programmed it IAW Maine Sails directions.

It could be possible and I think that it should be able to be connected to a standard 500 amp / 50mv shunt and based on that shunt that is connected to the bank,drop to float at a set trailing amps into the bank point, unfortunately that’s not an option.
But make me king for a day and it would have that option.