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Old 11-21-2017, 10:57 AM   #1
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Does alternator regulator voltage depend of temperature?

OK, here is the explanation and question.
I am using an old alternator by Delco Remy 12V/50A without internal regulator and use an old external Motorcraft regulator. Everything works, but I have a small dilemma. When I just start the engine the voltage on the output is 14V and later when I cruise for some time, output decrease and stays at 13.8V. This is still valid voltage for this older setup, but I am not sure what is the main reason for voltage decrease from 14 to 13.8V. I can think of two scenarios:

1. Battery is emptier at the beginning because of cranking the engine and if not being connected to shore, so that charging current is higher making voltage a bit higher until the battery is not being charged to some level, but I think this process is not that slow and rather measured in seconds than 10-15 minutes.

2. Since the regulator is above the engine in the engine room where the temperature is higher, when the temperature increase, the regulator decrease the voltage or start switching it on and of (modulating the voltage to 13.8V).

Anyway, I have come up to these two scenarios by thinking for myself, but I would like to know what is really happening if anybody knows. Because I would like that voltage to be a little higher with newer generation of batteries (well up to 14.4V or at least above 14V). Although, this setup works OK for two years now.
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Old 11-21-2017, 12:09 PM   #2
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Who knows how old, fixed voltage regulators work as temperature or current demand changes.

I wouldn't worry at all about 0.2 V swing.

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Old 11-21-2017, 12:35 PM   #3
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I think your #1 is correct. Regulators regulate and that is dependent on the battery charge that they are pumping Volts into. If you want to change that, a smart regulator (Balmar etc.) will give you the option of setting up your own charging regimen
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Old 11-21-2017, 12:46 PM   #4
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Many regulators have a temperature sensing element. When cold, setpoint is higher. Once things heat up, it is assumed that the bulk phase is mostly done, and volts reduce. Not talking about a batt temp sensor, this is resident in the regulator itself.

On my ride, winter cold starts are about 14.3Vdc, summer cold starts starts are about 14.0. Both winter and summer after running a few hours it drops down to 13.8 and stays.

Cheap and easy way to get some semblance of a proper charge profile.
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Old 11-22-2017, 06:08 AM   #5
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Thank you all.

I think that my case is similar to Ski's.

Ski, do you have any problems with 13.8V being the dominant voltage, how long your batteries last? I use lead acid batteries for engine bank and AGM batteries for house bank, which are being paralleled together when charging (and at proper conditions) with smart relay (Victron Cyrix) which is considered to be OK since AGM and lead acid batteries have almost the same voltage levels. Anyway I have read somewhere that newer batteries and alternators are being designed for a bit higher voltages, but according to voltage levels 13.8V is still floating voltage level which prolongs the battery life long term, although a bit higher voltage does charge the battery a bit faster. Maybe the batteries are just more robust today than before so they can take bad conditions for longer period than before. I have even measured the voltage at new Hyundai car and it was 13.78V, too.

Anyone having longer experience with paralleling AGM and lead-acid, how did that show up?
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Old 11-22-2017, 07:35 AM   #6
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The hassle with car V regulators is how they charge.

Usually the start batt is almost full , so the V reg will not push hard.

A car V reg will usually only give 1/2 the amps missing , plus a little bit to push the amps in.

So a 50% discharged batt will only get 25% of full, added in the first hour , 12% the second hour and so on. 100% is a long wait!

This is why the 3-4 stage V regulators were created , an attempt to charge hard to 85% full where the charge rate always falls off with LA batts.

Brave folks in the past used a resistor as field voltage control , in an attempt for more rapid charging , but they boiled a lot of batts.
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Old 12-01-2017, 08:54 AM   #7
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To consistently hit 13.8 vs. 13.7,13.9,13,5... suggests it may be a function of the moto regulator and not the alternator.
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Old 12-01-2017, 09:12 AM   #8
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I don't have any problem with 13.8 as a final voltage. Over about 100hrs on a month long trip, batts don't need any water. I get at least 5yrs out of batts, but house bank I often run to near flat so I know I am killing it. About time for new house batts before next trip. Flooded grp 31's. Start batts still in good shape.

My regulator is adjustable, but not multi stage. Balmar alt (really just an Autolite) with Transpo regulator.

Engine alt volts: Cold start 14.3, decays to 13.8 then steady.
Charger volts: Bulk phase 14.4, after an hour 13.3.

Seems ok to me.
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Old 12-01-2017, 10:27 AM   #9
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Each regulator has its own logic or lack thereof.

Ones designed for keeping a Starter topped up are not suitable - if you are fussy - for replenishing large deep cycled banks.

If the alt can even handle that, separate issue.

The Balmar MC-614 is custom-programmable, the only one I'd use **if** my alt were capable **and if** it were sensible to use it as a significant charge source.
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Old 12-01-2017, 10:43 AM   #10
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Here is a good simple explanation: http://www.chargetek.com/assets/equal.pdf

Flooded lead acid cells are quite tolerant of significant, short term voltage excursions. And 0.2V hardly qualifies as an excursion!

Gel Cells, another matter altogether. Yes, I've turned some to stone with overvoltage.
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Old 12-01-2017, 11:22 AM   #11
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Yes, keeping volts down is the one thing stock VRs do well unless broken.

Problem is how they handle the alt (diodes) getting hot when any decent current level is being pulled for any length of time. You actually want V to be kept high and current to be dropped, and very few do that.

Higher the bank chemistry's CAR (acceptance), the bigger the problem.

Result is a big depleted bank never getting to full (murdering the bank if not corrected), or the charge taking 10x longer than needed if properly regulated.

Or in some cases (LFP) the alt getting fried.

FLA banks low CAR help reduce such problems, more self-limiting, charging very slowly.

Also, a DC-DC charger can often solve this too, if it's not possible or appropriate to upgrade the Alt/VR.
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Old 12-01-2017, 11:36 AM   #12
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Quote:
Originally Posted by djmarchand View Post
I wouldn't worry at all about 0.2 V swing.
:I agree:I see that kind of a swing in voltage all the time after I fire up the engines.
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Old 12-01-2017, 01:14 PM   #13
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Yes, keeping volts down is the one thing stock VRs do well unless broken.

Problem is how they handle the alt (diodes) getting hot when any decent current level is being pulled for any length of time. You actually want V to be kept high and current to be dropped, and very few do that.



Also, a DC-DC charger can often solve this too, if it's not possible or appropriate to upgrade the Alt/VR.

Of course, the typical charger in use has no idea temperature of diodes or cells; doesn’t even know current. So you are left with a constant voltage system that is current limited by the alternator magnetics.
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Old 12-01-2017, 01:40 PM   #14
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A better system like a Balmar, does have optional temp measurement points for both the batt and the alt. However, It's not clear what is being done with those values, other than throwing alarms and shutting down when they exceed a preset limit.
For flooded lead acid, the temperature effects are just not as critical as other technologies; listing Li-ion as the extreme case. Never charge when below freeqzing, never charge over 70 deg C, be very accurate with constant voltage systems, etc.
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Old 12-01-2017, 03:09 PM   #15
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Of course, the typical charger in use has no idea temperature of diodes or cells; doesn’t even know current. So you are left with a constant voltage system that is current limited by the alternator magnetics.
If by "charger" you mean voltage regulator, I agree about current.

But I did think many stock even automotive VRs have temp sensing, not for voltage compensating, but to protect the alt from getting fried. Unfortunately those that do basically drop voltage so in effect stop charging.

If not yours, then definitely get an ammeter and infrared temp gun to do some testing when hooking up a hungry high-CAR bank.
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Old 12-01-2017, 03:14 PM   #16
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A better system like a Balmar, does have optional temp measurement points for both the batt and the alt. However, It's not clear what is being done with those values, other than throwing alarms and shutting down when they exceed a preset limit.
The MC-614 manual is very clear, and available as PDF online.

That model has full temp compensation to auto adjust the voltage setpoint to optimize charging.

It also has automatic derating of **current** to protect an overheating alt, while maintaining the user-customizable voltage setpoint. As well as canned profiles for FLA GEL and AGM.

It has a "small engine" option where it won't even try to get past a user-defined current level.

And it has a "belt manager" feature that is similar but with finer granular levels of control.

An LFP system (OT here?) would still need BMS protection and more if you're getting into well-below-freezing conditions.
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Old 12-01-2017, 08:49 PM   #17
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That model has full temp compensation to auto adjust the voltage setpoint to optimize charging.

It also has automatic derating of **current** to protect an overheating alt, while maintaining the user-customizable voltage setpoint. As well as canned profiles for FLA GEL and AGM.
Just a point of elaboration on the Balmar; the temp compensation uses battery temp to adjust the voltage setpoints as John indicated, that compensation IS adjustable through a rather obscure setting indicated as "SLP" or slope. As a Balmar engineer explained, it's a pulse width modulation setting that determines mv to degree of temp ratio. It protects batteries for those of us who woefully have them located in the engine room. For For AGM's & particularly GEL batteries that are sensitive to overcharging and especially at higher temperatures, temp compensation is a lifesaver.

The SLP OEM setting is initially strong, significantly throttling voltage relative to battery temp, but can be adjusted for a specific battery profile. However, there's no chart or table that references the slope setting, so it's not a linear ratio to determine the correct setting. To tweak the setting, the best way is to find the manufacturer's voltage/temp profile and consult with Balmar to determine the optimum setting.

In application: I noticed that while underway float voltage was much lower than the battery profile for the corresponding temperature, despite having the float voltage (FLV) programmed per the battery profile. A call to Balmar and some discussion of the battery charging/temp profile led to a change in the slope setting and a more accurate charge voltage. For those interested, the OEM slope setting is ~3.7, mine was changed to 2.4. So a lower SLP setting means a lower mv/degree of correction and a higher voltage. After the correction, the float voltage now matches the manufacturer's temp/volt profile for the batteries.
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Old 12-06-2017, 09:37 AM   #18
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Wow, you really had many interesting comments after I stopped reading the conversation.

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Originally Posted by Ski in NC View Post
I don't have any problem with 13.8 as a final voltage. Over about 100hrs on a month long trip, batts don't need any water. I get at least 5yrs out of batts, but house bank I often run to near flat so I know I am killing it. About time for new house batts before next trip. Flooded grp 31's. Start batts still in good shape.

My regulator is adjustable, but not multi stage. Balmar alt (really just an Autolite) with Transpo regulator.

Engine alt volts: Cold start 14.3, decays to 13.8 then steady.
Charger volts: Bulk phase 14.4, after an hour 13.3.

Seems ok to me.
Good info from experience that I needed, thanks. Similar to my case, except that I will add solar panels and MTTP charger because of the compressor fridge which does empty house bank more than I want, but not flat, anyway it makes my cruising not relaxed.

About the temperature protection that you all have been talking about, actually, I believe it is fairly easy implemented in case of alternator, since the regulator controls the charging current indirectly by controlling the alternator field. Actually, the voltage is the result of charging current and feedback is used to set the charging current at which the voltage will be i.e. 13.8V. And in case of predefined extreme temperature, field current can be stopped (set to zero) which protects both the alternator and the battery. When I have seen this technique for the first time, I was delighted, since this is so elegant solution, you can control tremendous amounts of charging current with just a small field currents and if done right, no sparking, no peak transients, very smooth control. The best solutions are always simple solutions, but you have to get there, which is not an easy journey.
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Old 12-06-2017, 10:23 AM   #19
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Wow, you really had many interesting comments after I stopped reading the conversation.



When I have seen this technique for the first time, I was delighted, since this is so elegant solution, you can control tremendous amounts of charging current with just a small field currents and if done right, no sparking, no peak transients, very smooth control. The best solutions are always simple solutions, but you have to get there, which is not an easy journey.
look up Audion tube from 1906. This is the first control electronic piece of hardware that allows tiny currents to control very large currents.
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Old 12-06-2017, 10:46 AM   #20
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Yes, from tubes, BJTs, JFETs to MOSFETs and IGBTs, but this one in alternator is specific being magnetic control inside the generator where the power is being generated, you really control the source of power, not i.e. controlling the resistance of the conductor like in MOSFET conducting the current. Almost irrelevant heat dissipation in controller compared to produced currents through rectification diodes. Imagine controlling those diodes instead (it would have to be i.e. IGBTs, not diodes), that would be much more complicated. Controlling field is very elegant solution in alternator application.
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