Your Vehicles voltage regulator

[SternWake]

The voltage  that a Vehicle's voltage regulator allows, plays a huge huge part in both starting battery longevity, but even more so, house battery longevity when the alternator is to be the majority, perhaps only charging source.

Voltage is electrical pressure, so the higher the pressure between source and load, the more amps can flow

Older vehicles, from about '88 and earlier had external voltage regulators on the firewall, set to a constant voltage, like 14 or 14.2v.
Some alternators have the voltage regulator internal to them.

Some other vehicles have the voltage regulator inside the engine computer.

My 89 dodge b250 is such a vehicle, and I swear its voltage regulator is bat crap crazy. it will choose either 13.7v, or 14.9v, and very rarely 13.9 or 14.

I have never discerned any logic as to why  or when it chooses these voltages when it does.

Needless to say it is frustrating when it holds 14.9v, and I know for a fact my battery is 100% full, and does not need to be held at 14.9v.
It is also frustrating when my battery is depleted and the VR decides 13.7v is just  fine and dandy.  Well, 12 peasley amps might be required to hold the battery at 13.7v, but if the VR were seeking 14.9v, then  50 amps or more might be required.  Fine and Dandy my ass.

If I am driving for 20 minutes with a depleted battery, I want 50 amps, not 12, But I could not control this and the ECM chose, poorly, more often than not.
If I am driving for hours, with an already fully charged battery, I want 13.7v, not 14.9v, But I could not previously  control this, and the ecm chose poorly, more often than not.



Note the past tense.

Now wiring up an external voltage regulator is not rocket science. There are a few kits out there which allow one to bypass the internal voltage regulator on Dodges with internal to the ECM VR's, without causing the Check engine light to illuminate.:

http://store.alternatorparts.com/er...gulator-conversion-field-replacement-kit.aspx

I bought their 'field replacement module'.  for way too much money with shipping.
 It is just a 50 watt 10 OHM resistor one can get on Ebay for under 3$.

http://www.ebay.com/itm/2pcs-10-Ohm...129131?hash=item3a9254b92b:g:~IIAAOSwoQ1TobUr

I did NOT buy their mopar voltage regulator kit.  I bought a Ford voltage regulator, a Transpo540HD.  Inside of this VR, there is a little voltage adjustment potentiometer.
  It is a 2K ohm Bourns potentiometer:
http://www.bourns.com/docs/Product-Datasheets/3386.pdf?sfvrsn=3

There was a little plastic ring under this potentiometer and it was submerged in the potting.  I used a razor blade i bent with some heat, on some needle nose vice grips to cut the bond between ring and black potting and potentiometer.  Then I was able to bend the potentiometer upwards and with some magnification and a dremel with sharp bits, abraded the potting away from the 3 legs.  The two legs on the right are connected electrically,. no resistance between them, but there is resistance between them and the leg on the far left.  The shaft diameter on the dremel tools is 1/8" inch for a sense of scale.

I used some precision nippers and cut the potentiometer off at the legs,leaving me a few MM above the potting in which to attach wires.

After twisting  , sheathing and inserting the sheathing in a ferrite ring, I soldered the wires, and then used 'Amazing Goop' to hold wire sheathing tightly to VR.  I've read the POtentiometer leads are susceptible to RFI interference.  The ferrite ring and twisting the wires are an attempt to negate the RFI.

I messed up the location of the first hole, putting it on the top of the casing.  Out the side proved the better option.

The VR needs to be well grounded.  I crimped this 10awg into a standard ring terminal with yellow insulation removed with my HFT hydraulic crimper, and then soldered it to the body of the voltage regulator, having practiced this on my rebuilt alligator clamps. 

In the above photo one can see 4 letters on the black plastic, I  A  S  F

I......is for the idiot light, for now, I just covered this terminal with blue heatshrink.  I have a voltmeter facing the drivers seat. No light needed.
A..... is for the Always Hot. I ran this to the (+) stud on the alternator, but it would be better to have it go directly to battery(+) stud. Since I have thick cable between this stud and battery it is not as important

S is the switched hot. This is supposed to be live with the engine running. I found a unused and badly oxidized 12v terminal under my dashboard which accepted a quick connector.  When testing, I found this wire was not hot with ignition on, it was only hot with the engine actually running.  perfect for my intentions.

F.  This terminal goes to One of the two  Field connections on the externally regulated alternator.  The other field terminal must be grounded.

I ordered a new Bourns 2K ohm 10 turn potentiometer from Ebay fpr under 5$.  It took 9 weeks to arrive from China, kind of surprising as it is made in Mexico, and it came with a turns counter.  This will be mounted to my dashboard near my voltmeters.

This whole project is  about allowing me to choose any voltage I want when driving.

I tested it yesterday and danced a little jig, once I made sure no one was watching, then laughed like a maniac, then  proceeded to finalize the harness with proper terminations and much thicker wiring than required.  I retasked some quality 12awg which used to run from charge controller to battery.

Earless crimps are more desirable, but Oh well, the Hydraulic crimper dies are not perfectly sized for this 10-12 ring terminal.

I really like my 140 watt soldering gun.  i do this out of a sense of overkill/ anal retentiveness, and practice more than for better conductivity and or corrosion resistance.  As the crimp is solid, no solder can wick up the wire and possibly make it fragile.  Unneeded overkill.  Isn't that the name of a band?

I decided to locate the VR inside, behind my glove box.  Since it is well grounded directly to alternator, I do not even need to mount it to the firewall.  A bad ground on external voltage regulators is the cause of many charging system failures on pre 90's vehicles.

My new wiring harness also has a 6 foot long thermocouple which I have attached to the stator exterior with thermal epoxy.  Soon I will have some Data on how hot the alternator gets at and near maximum output, idling vs driving.

I mounted the 'trick the ECM' resistor on a much larger finned heatsink, and put it on the transmission fill tube nearby.  Not ideal but the other options were less desirable  That stainless wire can be snipped off and the resistor easily relocated.:

It  got really hot in my 5 minute long test, Which was dismaying as the battery was full at the time, the field current only 1.8 amps at 14.9v.  This resistor is simply to trick the ECM into not flashing the check engine light.  But I had started the engine without any voltage regulaltor attached, and the light did not come on.  My battery was able to maintain 12.8 volts, perhaps it would have come on if I had driven or after a period of time, or if voltage dropped lower, but perhaps it would not come on at all.

I did test the original ECM voltage regulator after my test of the transpo540hd VR and was not damaged by the test. It is still functional.  Very easy to return it to use if the Transpo VR fails.   

My vehicle uses 8.2 amps just to idle the engine without the alternator operational. Always wondered about that figure, never tested it before but did so when I was testing the 12v feed under the dash.

Anyways, If my insanity in regards to lead acid battery charging was not obvious to members here before, a potentiometer on my dashboard for controlling ideal voltages when I drive surely places me firmly in the looney bin.

The potentiometer installation on my gauge cowling is the last thing I 'need' to do to complete this project.

The ability to of this adjustable voltage regulator will open up the possibilities of charging Lifepo4  batteries in the future .  The 14.9v on LIfepo4 is way way too much.  It is too much for my AGM, but it handled it.

In my test I ranged the voltage from 13.1 to 14.9v, but did not push the dial past those extremes.  Could be a danger zone to electronics going much higher than 15 and perhaps dangerous to the VR if the battery voltage is higher than the intended output.  I know not.

I am not sure if another value resistor would keep the CEL off as well and get less hot.  I hate to think of the wasted power going to heating that 10 OHM resistor.  I also wonder if something in the ECM is getting that hot as well, that was not, before this modification. 

I'll have more pics when the Pot is mounted next to the 2 voltmeters on my dash.

I am not sure how this modification might be applicable to other makes and models, or if there is any interest in such a modification.

What should be neat is with the turns counter, i will know the value for say 13.1 volts, and on initial start up, instead of my ECM's VR seeking 14.9v right off the bat, and maxing out the alternator on a cold engine, the 13.1 volts will cause much less amps to have to flow, causing less stress on an engine whose cold oil is too thick to lubricate properly.  I've also had issues with a wet alternator belt screeching when the battery is depleted and asking for everything the alternator can make.  So this modification allows me to effectively limit alternator output, indirectly through voltage.

It is said each 25 amps the alternator has to produce eats up one engine HP, so when cold i could see this causing less start up wear, and give the deleted battery a little heads up before cramming 60+ amps down its throat at 14.5v

 

[WheelEstate USA]

Yup, past time for the looney bin

Seriously, way cool...quite the project. I'd be afraid to tinker with my charging system. Don't wanna charge house batts but with solar.

 

[SternWake]

 I'd be afraid to tinker with my charging system. Don't wanna charge house batts but with solar.

Baah, you just do not want to have to purchase all that thick copper needed to reach that battery some 16 feet( as a mosquito flies) distant from the alternator on your extra long extended van.

And you don't need to .

If my VR never allowed over 14.4v, I would have lived with its 13.7v proclivities, but 14.9v and 60+ amps repeatedly pushed  into a single depleted battery is abusive. 

Also, my Meanwell power supply charger has been fitted with a 10 turn potentiometer to change voltage.  I got addicted to manual voltage control, watching different amperages flow with different pressures on both sides, learning what a battery's acceptance limits are.

Now, to seek out the proper looney bin for this newly discovered mental health malady.  Perhaps Big Pharma already has a profitable pill lined up and can pester the whole  Nightly news watching populace with such a miracle drug, in between political commercials of course.

I can see the ad now.

"Tired of improper voltage being fed to your house batteries, Anxious, scared, have the shakes?  This is a verified serious medical condition known as voltagus incorrectus interruptus, and can be devastating to one's mental health, and possibly deterimental to the rented batteries.  You need this special pill, which makes everything fine, just fine.

It even comes with a blue tooth speaker which can automatically sense onset of symptoms and turn on and Whisper 'everything will be Fine, Juuuust fineeeee, in a soothing voice.  Over and over.  The blinking flashing and steady green lights are programmed to work in unison with the soothing voice, and of course the magic pill elixir, to get over this serious and debilitating disease called Voltages incorrectus interruptus."

Still discovering the scary possible side effects, we need guinea pigs willing to pay handsomely for that privilage.

 

[GotSmart]

I completely understood most of that, as well as the reasoning.   :s

I have a box filled with wires and parts.  Good thing it is snowing, or I would be outside taking things apart.   :huh:

Now I'm worried~~~ :-/

 

[highdesertranger]

very cool I like. do a follow up after awhile. highdesertranger

 

[SternWake]

Buttoned everything back up.


Another test revealed the Transpo VR was getting warm, so i thermal epoxied a finned aluminum heatsink to the surfaces opposite the heat producing transistors on the backside to help dissipate the heat and prolong the life of the components inside.

At hot idle, the voltage will sag from 14.4 to 14.1 but comes back with just 200 more engine rpm.  When voltage sags I can dial it up at idle.  When I dialed it way up, over 14.7v, the check engine light came on   set a code 46:

Alternator voltage too high.

When i lowered voltage back to 14.4v and restarted engine, the check engine light turned off and has remained off.

After running errands, with the alternator making about 28 to 38 amps total, including the 8.2 amps required to run the engine, My alternator was 119F about a minute after I put it in park

Continuing to idle at that ~28 amps total output level, but parked, alternator temperature rose to 140F and levelled off. 

I put clamp meter over field terminal wire.  At 14.4v and 28 amps total output, 2.63 amps were flowing through the field wire. Revving the engine lowered the field current by half or more.

Loading the alternator with 2 sets of halogen fog lights(30 amps), headlamps with high beams on (20 amps) and blower motor on high(18 amps), maxed it out at idle.  The battery still required 20+ amps t be held at 14.4v, but it was being discharged to make up for what the alternator could not produce at idle.  Voltage was sagging.

Field current went into the mid 8 amp range at idle with alternator at max output.  revving the engine to 2k rpm dropped field current to the low 4/ high 3 range range.

When I turned switch on clamp meter back to temperature it read 157F.  It rose 17 degrees in about 30 seconds of maximum output parked and Idling.  

The switched On 12v+ wire to the VR registers only 0.02 amps,  My 14 awg wire run here was several degrees of overkill.  if Only I though to test that wire on my original test.  Grrrrrrrr.

I consider the experiment a success.  Having a potentiometer on my dash controlling vehicle voltage, thius battery charging voltage,  is simply  awesome.

Will report back if problems arise. 
 Other threads with alternator temperature at different loads and comparison of moving vs idling parked,  are in the future.

Initially today when I first started the van I had voltage  set to to 13.2 volts and the battery, 33 AH from full, at 13.2 volts  wanted just 9 amps.

At 13.8v, it wanted 13.9 amps, at 14.7v it was accepting 32 amps.  So the extra 0.9 volts practically tripled the amps into the battery at cold idle, warming up.

So one can see why too low a voltage making it to the battery significantly reduces charging current.  Gotta love actual Data. 

When I lowered voltage to the 13,1 range, the solar was able to keep the battery at 13.1v and lowering the dial did not affect voltage anymore.  Basically the alternator was not having to make anything, and the engine note was super smooth an quiet.  Increasing voltage to 14.7v required 30+ amps and it was easy to hear the note of the engine change as the alternator exerted that load on the 5.2 liter v8 engine.

They say each 25 amps an alternator produces requires one engine HP once the losses re factored in.

Starting a cold engine with very little load on an alternator, could, should, in theory, reduce start up wear.

 

[SternWake]

Forgot to add the photos.


The red voltmeter behind 2 layers of window tint is a bit too dim for bright daylight but was necessary for the green ones. All my other dash lighting is red  too, so the green voltmeters days are limited.  Wish they sold 3 wire voltmeters with calibration adjustment AND resolution to 0.01 of a volt.

The potentiometer has a brake on it.  Herre is is set to 7.15 or so and this corresponds to 14.4v, once the engine starts 
Here the meter is set to degrees F, and the clamp is around the field wire.

Notice the black shallow finned heatsink on the VR's belly.
I have found a display which takes 4 of the K type thermocouple so I can have a more convenient display as well as more temperature options to collect temperature data on, Like the battery's rise in temp when it is drinking up 60+ amps, or if I have an underhood battery in the future, as currently that battery tray is empty.

Below is most of the wiring harness, minus the resistor, field to ground wire, and the Yellow wire to the mopar switched hot.

They sell  an HD model of this voltage regulator that claims it can handle 30 amps of field current.  My field current was in the 8 amp range at 50
It appears if one would have to drill out the rivets to access the internal potentiometer for voltage adjustment, unless of course 14.2v. always, is good enough for the user.

http://store.alternatorparts.com/pa...0316-ae4az-10316-bgr-540-agr-540-bgr-803.aspx


If this VR fails, I can return my ECM voltage regulator to service by removing field to ground wire and putting a jumper to the original field terminals, or just rebend them downwards to fit as originally designed.

Dead center in the photo below, barely visible in the flash glare is the thermocouple

One more data point, I have two parallel Alternator circuit paths to the battery.

The original Dodge 6awg that has a two connections as well asa 14 awg fusible link to the original battery clamp.  To this original (+)battery clamp,  I have 2awg going back under drivers seat , up through the floor to my electrical wall where it goes into a blue seas 300 amp 1/2/both/off switch.

The other Additional parallel  circuit path I added goes down the transmiision fill tube, around the engine under the floor and back up through the floor to a 140 amp circuit breaker.  I thought this wire was 4 awg jumper cables, both cables joined together in the same thick walled ring terminal, but closer inspection reveals it is more likely to be  doubled 6AWG.

Anyway, Clampmeter over both (+) circuit paths, registered 32 amps, about 8.2 of those running the engine, the rest basically going into the battery.

When i put the clampmeter over the doubled 6awg jumper cable it read 26.2 amps
When I put the Clampmeter over the 6 awg OEM charge circuit with 3 connectors in line as well as a short fusible link it read 3.8 amps.

A huge percentage of current was choosing the choosing the parallel circuit I added, compared to the OEM circuit whose circuit was actually shorter to the 8.2 amps of engine related  loads.

Then I tripped my 140 amp circuit breaker, and checked the amperage flowing through the OEM circuit.  it read 22 amps Total and voltage had dropped to 13.9 in a minute.  The fusible link got quite warm.

Reconnect clampmeter over both wires and then flip the 140 amp breaker back on,  and the engine note changed a little as now  38 quickly tapering to 32 amps brought the battery back upto 14.4v.


If the battery were more depleted these numbers would be even further apart, and shows how copper thickness significantly increases charge current at lower states of charge that the alternator can contribute.

Readers wanting more alternator contribution to their batteries when they are low, can add a parallel charge circuit to the original, and also by also adding another ground wire from battery(-) to alternator mounting bolt or (-) stud on alternator if one exists.

My data so far shows Idling  with a hot engine causes significant alternator heating on an alternator still well under half its maximum  rated output.

It appears i need to draw my battery down to 50% to properly test things.

I'm reading 34AH from full, 12.4v under a 3.9 amp load on a single 90AH northstar AGM battery that has not seen a full charge in 3 days.

 

[MikeRuth]

Good stuff! Thanks SW

Mike R\

 

[rvpopeye]

Stern

NICE!!
My old tron teacher would say "A+ now , what is it ????"
I LOVE building stuff like that !

BTW I think used to work for that band.

I can't count how many 140w Wellers I have burned up from constant use when doing a big project ( like completely re doing a stage snake) Yeah , I know OVERKILL!

Skuh kuh kuh kuh (popeye for bwaaa haaa haaaa)
(When I was a teen all my friends called me "the mad professor"
Now at 63 they just know to stay away!!!)

PS I does feel sooooo good when it works like you hoped it would...

 

[SternWake]

Still working properly, though there is some voltage sag when hot at idle speed that is less than Ideal. I got the check engine light to come on again when I cranked voltage upto 14.8v.

Apparently if the ECM's voltage regulator chooses 13.7v, but sees 14.8v via my Transpo Voltage regulator for 30 seconds, on comes the check engine light, but at 14.7v it will not.
The CEL goes out on the next restart as will stay out as long as I dont twist voltage upto 14.8v or higher. its illumination is of no importance, except if I ignore it thinking it is just the voltage regulator and something else fired the light.

I've not collected additional alternator temperature data yet. I have not yet had the battery super depleted where it can max out the alternator for a good while and really heat it up when driving, then parked.
Tonight's 14.8v choice which fired the CEL, was just so I could stuff in as much as I could on a 5 mile drive at dark as I plan on cycling deep tonight so I can collect some more alternator temperature data in the morning.

 

[SternWake]

Another 5 weeks passes and My VR modification is still working well. I really like insuring 14.4x+v is held as I drive to my spot after dark, and starting the cold engine with a target voltage of only 13.2v, to reduce load on the cold engine then cranking voltage upwards once it has warmed and I am driving.


Mainesail has a new write up on his site regarding Automotive alternators and voltage regulation which might help those interested to understand better the limitations of their vehicle's charging systems, which my VR modification has mostly let me bypass, for much better battery charging with the engine running.

http://www.pbase.com/mainecruising/automotive_alternators_vs_deep_cycle_batteries

 

[highdesertranger]

thanks for the follow up. highdesertranger

 

[rvpopeye]

Good to hear it's working as planned !

 

[SternWake]

An Update.

Still working well, but the voltage sag at idle is a little more pronounced than when newly installed. Perhaps there is some resistance developing on my connections or in alternator to battery cable. I do intend to upgrade this cable further at some point, but for now, Gefwif.

Also, If I do allow more than 14.79v and the CEL does come on, even if the CEL goes out next engine start after lowering voltage to less than 14.7, the code is stored and it appears the ECM goes into limp home mode where it does not use sensor inputs to adjust air fuel ratio and spark timing. As a result MPG and power and engine smoothness suffer.
Remedied by resetting ECM and not allowing more than 14.79v.

For a while it appeared I was only getting 7.5 to 8mpg around town, but after resetting ECM, clearing the code 41 or 2 or 43 whatever it was, CRS, I am back up to the normal 10mpg cruising up and down hills and sitting at traffic lights around town.

Still overall extremely pleased with this modification, and my Northstar AGM battery is performing very well being worked hard in both engine starting and house duties, but much of that longevity is my Meanwell power supply and 200 watts of solar seeking and holding the proper ABSorption Voltage each cycle, for the proper duration.

This VR mod simply allows my limited driving to be much more effective in later allowing the other two charging sources to hold ABSV for that proper duration.

Longer drives also indicate that engine heat really gets battery temperature much higher than expected, and a slightly lower absorption voltage is then my choice to help lessen battery temperature rise. really my modification is to prevent 14.9v on a hot fully charged battery, and prevent 13.7v limiting amp flow when the battery is still depleted.

The ECM's VR was NOT good at charging the battery properly, and I am glad it is now tricked and bypassed and i get the voltage control I desire, and a much happier battery and more capacity to use to my desire overnight.

 

[SternWake]

Since last update, all is well with Voltage regulator modification.

I added a Hall effect digital ammeter to my dashboard, above my two voltmeters. The sensor is located on the alternator to battery switch feed, next to my 120 amp circuit breaker which is in a cabinet behind driver's seat.  All I had to do was unbolt one ring terminal from alternator feed, slide the sensor over it, rehook cable to circuit breaker,  and run the sensor wires to the dashboard display.  I did add 5 feet of wire in the middle of the 3 wire ribbon cable. I hooked it to power from my voltmeter feeds which go to  glass fuse #5


Just took this photo.
Engine is not running, So 0.00 amps.  My Meanwell rsp-500-15 adjustable voltage power supply is holding my battery full. Should have cranked voltage to 14.7v for this photo.

The Voltage dial is just barely visible to the southwest of the Oil light.

The red voltmeter is my Northstar AGM battery located behind drivers seat below floor.  Dedicated (+) voltage sense line to battery(+) with fuse at battery.

The green voltmeter is usually the battery in my engine compartment.  However, There is no battery there at the moment. The green voltage sense line  now goes to original engine battery post clamp.  I have connected  11 feet of 2awg from this Original battery post clamp back to my 6007m battery Switch's common stud behind driver's seat. 

Really wishing the display was red instead of green.  There is one 8mm thick layer of smoked acrylic dimming the display.  It is kind of a hack job I need to refine a bit more .

My alternator (+) feed is a parallel circuit to the OEM/factory wiring, just shorter and fatter. For this sensor to read total alternator current correctly I had to disconnect the factory Alternator to engine battery cable, but Dodge made that easy with 2 different INline connectors on 6 gauge SAE cable, So I just disconnected one closest to alternator and protected it from shorting.

At some point I will move the sensor to read amps into or out of battery, instead of total alternator current. At that point I will reconnect the factory alternator circuit which has ~ 4 inches of 14 awg fusible link bottle neck inline on the 6 gauge cabling . 

 I hope to get fatter cabling for this direct alternator to battery switch feed. My existing feed is a pair of doubled 6 SAE gauge  jumper cables, equivalent of 3 gauge or so.   I want to use a 0 AWG or thicker cable.



Here is a pic of the low profile Heatsink and 60Mm fan I added to the underside of the Transpo540hd Voltage regulator.  It resides behind my glovebox. It only comes on when engine is running.  I have a thermocouple epoxied to the heatsink.  I was seeing temps as high as 129f before the fan, now rarely over 106f.  Overkill, but cool electronics are happy electronics.

 

[John61CT]

simply awesome

lots for a noob like me to learn parsing out the details , but I wouldn't want to risk damaging my new to me van, it's only 16 years old

but would love to try to get the same functionality, messing around with stuff mounted on a bench one day...

 

[SternWake]

Well, the only real issue is when the VR is inside the engine computer, and tricking the ECM with a resistor inline on the field wires is also pretty simple.

As long as i keep my vltage below 14.8v my computer is fine with it.



Some VRs are mounted inside the alternator, and can  be  modified external regulation.

If external regulation already exists, then upgrading to an adjustable VR is pretty simple.

http://www.pbase.com/mainecruising/automotive_alternators_vs_deep_cycle_batteries

 

[Mobilesport]

Loving it ,, could you make it to where it only engages when you shift into drive? 
I was thinking that you could get rid of the overheating issues that way during idling.
I actually  prefer the different  colored voltage amp meters instead of them all being the 
same color , like green for amps
                               Red for volts
If there all the same color I could  get confused. LOL
When you put the starting battery back under the hood will you need a
battery isolator solonoid?
Interesting project  to follow , my first thought was that this would be great for
people  that drive alot

 

[Mobilesport]

Oh yeah , that dash picture is super awesome

 

[SternWake]

1 could you make it to where it only engages when you shift into drive? 

When you put the starting battery back under the hood will you need a
battery isolator solonoid?


... this would be great for
people  that drive alot

The yellow wire in my photo goes back to a 12v live with engine running feed.  I could put a switch on here to control when the VR activates or not.  Very little current flows on this wire.. Mine is 14awg but could be 22.  The VR gets power from the A (always on) terminal.  Mine is hooked to my alternator (+) stud but it would be better if I ran it to battery(+) as it is also the voltage sense line, and voltage drop affects what the VR sees and then tries to modulate.  If/When I upgrade to 0 gauge cable, I might run a dedicated 12awg feed back to VR's 'A' terminal so there will be more precision, and less variability on voltage.

I can also just lower voltage to 12.8v and on a depleted battery very little amperage would flow.  I do this sometimes when engine is cold and belts wet and depleted battery could suck up 100 amps and make belt slip and squeal and glaze over.

I use a Blue seas 6007m 1/2/both/Off manual switch on my OEM circuit to switch it from house battery to engine battery.  Right now it is just turned to battery #2 which is the location for my under body battery tray which can house 2 group 27's, but now contains only one.  This switch has 3 large studs, One for battery one, one for battery two, and one common switch.

I have another 6007m switch that switches all house loads to either battery.
I have another 6007m switch that switches all external charging sources to either battery.( alternator not included)

To the  OEM's circuit  6007m  switch's common stud,  I have 2 AWG cable going back to the original engine battery post clamp underhood, and layered in electrical tape.  I also have my Alternator (+) direct feed connected to switch's common stud as well.  The switch then can be used to direct current to or from either battery or both.

I employ no Solenoids at this point, and never have. I started with a manual switch in 2002 and the human error factor has never left me stranded.

When I had 2 or more batteries I would turn switch to 'Both' after starting cold, and generally leave it in 'both' until sundown.   Depends on how low the battery was and how much sun there is and my mood, and the possible presence of Locusts.

But now with only the one battery I never really turn this switch at all. Most times  I do so now are when I allowed 14.8v for 30+ seconds and the check engine light came on initiating 'limp home' mode where MPG sucks and engine runs crustier.  other times are when i am working on the system, just turn switch to off and not have to worry about unhooking a battery cable, but this still leaves some room for error. Always safer to remove ground cables when working on systems.

I do not drive a lot, but when I do I want maximum alternator contribution, especially when moving 45mph or faster.  My Engine computer choosing 13.7v when battery was depleted was infuriating as only ~1/3 the amps flow at 13.7 compared to 14.7v.  Gimme 50+ amps, not 13 you SOB!!

On longer drives i would sometimes see the engine computer's  VR would again choose 14.9v randomly, when I knew the battery was already full, and hot, and this also seriously pissed me off.

So this is not just beneficial for longer drives, but it makes the most use of a very high amperage potential charging source, Which my single 90AH  AGM battery has no problems accepting, and in fact craves.

Alternator temperature is a concern, but my Data shows it only to be a concern if driving at low rpms under 25mph, or if idling with a huge load and hot engine.  Moving at 65Mph and my alternator casing even under max load has yet to stay over 129F,  and it can make nearly 100 amps at 2000 rpm.

With only my single AGM battery, there is little risk of me overheating the alternator, but a larger bank of depleted batteries would be more of a concern.  I can't stand Idling , especially to recharge.

My alternator is A lifetime warranty remanufactured alternator, not exactly the highest quality product.  Yet my previous one lasted 9 years despite being regularly maxed out, as I rarely Idled to recharge and overheated the thing.

but also, the premature initiation of 13.7v would also keep the alternator cooler.  Usually my ECM's VR would allow 14.9v for the first 10 minutes, so the alternator would be maxed out often initially, but when hot 13.7 was more regular.

I could certainly now overheat the alternator if I tried, but It would require me idling with all possible loads turned on with a depleted battery and y VR set to 14.7v or higher.  It will go as high as 15.3v, but this sets the Check engine light and initiates the limp home mode where MPG suffers and i need to reset ECM by turning switch to OFF, engine not running of course.

Never remove load completely from spinning alternator, Diodes can go Poof!

Older mechanics would recommend pulling a battery cable as a charging system check but this can destroy an alternator (and more) in a modern vehicle, But you will still see this 'test' recommended on online forums.

Disregard such recommendations