Alternator: Voltage or current limited with high load?

[Nicholson58]

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.

Voltage regulated. If you connect to a very large battery bank using an alternator that is not rated for continuous full load duty you might burn it up. We did. We now use a small alternator with a Balmar external regulator set to 80% of rated output. It will runs long time and the engine load motor sailing is greatly reduced.

[sailcrazy]

following, or trying to.

[sailcrazy]

Nicholson58...what alternator and extnl reg do you use? What type batts, and how do you have the reg set? Our "stock" Hitatchi 80 amp altnr, on our Yanmar 4JH-TE, does not seem to be recharging our 6 T-105s (LA) like it should, although it is outputing a little.

[Nicholson58]

Originally Posted by sailcrazy

Nicholson58...what alternator and extnl reg do you use? What type batts, and how do you have the reg set? Our "stock" Hitatchi 80 amp altnr, on our Yanmar 4JH-TE, does not seem to be recharging our 6 T-105s (LA) like it should, although it is outputing a little.

We replaced our smoked 2.5 kw 24 volt P Type externally regulated alternator with a 24 volt 35 amp alternator. We moved the two belt pulley to the new alternator and removed the factory internal regulator. The Balmar 624 controls this easily as a multi-stage Charger at 80%. Battery primary bank #1 is Firefly 6 X 4 volt = 24 volts, 450 AH. The charge rate on these made the batteries look like a short to the old alternator. We experience frequent overheating with the old alternator as well since the engine was working extra hard to drive the alternator. We motor sail if to weather for hours at a time so the small alternator along with 660 watts of solar is no problem. I think any standard alternator can be made externally regulated. If you are not able, take it to an alternator shop to be done.

[john61ct]

Originally Posted by sailcrazy

following, or trying to.

http://www.cruisersforum.com/forums/....php?p=2941411

Maine Sail is Da Man #1

https://marinehowto.com, see the alternator articles, eventually try to work through all of it, great stuff

[Jlp0217]

I quit reading half way through the first page, as there was a lot of confusing and incorrect information. Alternator controllers, whether intermal or external are voltage regulators, not current regulators. They either full field the alternator to produce whatever current the alternator is capable of, or the reduce the field to limit the voltage output. The battery is the current limiter when the system is in absorbtion mode, not the alternator/regulator. Internal regulators may include a temp sensor, which cuts output to protect the alternator, not just external regulators, but that is a voltage limit, not current limit, as are Balmer's belt saver, small engine mode and battery and alternator temp compensation.

[nilespf]

The battery is the current limiter when the system is in absorbtion mode, not the alternator/regulator.

Depends upon the smarts built into the regulator. The typical older style small frame alternators with simple internal regulators will have a single voltage set point. Since the regulator is the simple internal regulator the output voltage of the alternator will be the voltage set point with no differentiation between bulk-absorption-float voltage. The user tweaks the voltage set point to achieve a suitable value consistent with battery requirements.



A regulator with some smarts like a Balmar MC-612 will alter the output current delivered to the battery by changing the field current. Alternator output current absorbed by the battery is a function of the battery terminal voltage set by the alternator and the SOC of the battery. Bulk vs. Absorption vs. float charging state (to the alternator) is nothing but a change in voltage output accomplished by the smart regulator.

[rgleason]

Originally Posted by transmitterdan
Some regulators can be set manually so the alternator will produce less than maximum current (belt manager) but there is no knowledge of the actually current charging the batteries.

Originally Posted by rgleason

---
I believe the Balmar Belt Manager limits the max field current in incremental steps, based on the programmed setting, thus limiting the maximum current.

I could have been clearer, but please notice that I never said the alternator limited the current output. The subject of the sentence was "max field current", that is what gets limited (not alternator output current) the result is that the alternator output voltage is reduced.

[sailinglegend]

Originally Posted by rgleason

I could have been clearer, but please notice that I never said the alternator limited the current output.....

A lot of confusion still here I think.

The Belt Manager limits the alternator output current about 10% each setting by limiting the field voltage and hence the field current.

The small engine mode also limits the alternator output current by 50% with a click of a switch. This does not change the alternator output voltage by 50%!!!!

[Maine Sail]

Originally Posted by sailinglegend

The small engine mode also limits the alternator output current by 50% with a click of a switch. This does not change the alternator output voltage by 50%!!!!

Small Engine Mode cuts the field potential in half...

[sailinglegend]

Originally Posted by Maine Sail

Small Engine Mode cuts the field potential in half...

Sorry Rod but is that a correction to my post or just a clarification. I thought I had implied this in my post?

More confusion - for me anyway?

[rgleason]

Ok, so again, regulator changes in field windings voltage, affect the amount of current in the winding and thus change the magnetic force and the output.

Yes, I did have that wrong. So sorry.

[Maine Sail]

Originally Posted by sailinglegend

Sorry Rod but is that a correction to my post or just a clarification. I thought I had implied this in my post?

More confusion - for me anyway?

Originally Posted by sailinglegend

The small engine mode also limits the alternator output current by 50% with a click of a switch. This does not change the alternator output voltage by 50%!!!!

My point is that the field potential cut is not necessarily taking a 100A alternator and making it a 50A alternator. Lots of folks assume this is what happens though. In other words a 50% cut in field potential does not always directly translate to the alternator output amperage being cut by 50%.

The Wakespeed WS500 regulator, when used with the shunt option, can be set to deliver a desired alternator output current from the alternator. The Balmar's are not sensing alternator output current, so a field potential change is not necessarily a direct correlation to output amperage changes.


Certainly confusing for sure...

[transmitterdan]

There are a couple of old “sayings” that help me remember these concepts:

1) you cannot control that which you do not measure.

2) you can’t get blood from a turnip

Likewise, a regulator cannot control alternator current if it does not measure current. It can control voltage because it measures voltage.

And a regulator cannot elicit more current from an alternator than its designers intended. So the voltage will be below the set point until current is less than the maximum for the field current and RPM.

[nilespf]

Originally Posted by Maine Sail

My point is that the field potential cut is not necessarily taking a 100A alternator and making it a 50A alternator. Lots of folks assume this is what happens though. In other words a 50% cut in field potential does not always directly translate to the alternator output amperage being cut by 50%.

The Wakespeed WS500 regulator, when used with the shunt option, can be set to deliver a desired alternator output current from the alternator. The Balmar's are not sensing alternator output current, so a field potential change is not necessarily a direct correlation to output amperage changes.


Certainly confusing for sure...

That's the consequence (and for the case of batteries) of having a non linear load. The battery is both a time variant load and simple resistance. The engineer can actually make the alternator behave as a variable current source as long as the output voltage is within the voltage range of the battery.



High end bench power supplies can have programmable output currents regardless of the output voltage providing the total power output remains constrained. Generally speaking in the lab environments one wants current limiting at a voltage not max current regardless of voltage. These are non trivial design challenges. In the case of alternators, if a battery load is behaving correctly, all the engineer has to do is vary the voltage at the terminals of the battery and they can take the alternator through it's entire range of current capability assuming of course one stays within the constraints of the battery.



Then the engineer merely produces an alternator capable of sourcing X number of watts dictated by physical constraints of the installation. If they put some smarts in the regulator we have a variable cheap current source. One can argue both ways but only because we are dealing with batteries.