Easiest, simplest, cheapest power set up?

[TMG51]

I suppose one would notice the lights or fan going out and it would still take a willful response to make a load change and reconnect the battery (turning lights off and back on, maybe). Seems to me a less likely set of circumstances that this would happen accidentally, but I suppose it could happen, perhaps while plugging in more than one small electronic to charge during the daytime. Still seems like a good first line of defense when talking about a simple setup like this.

 

[Ticklebellly]

.... this van doubles as my work vehicle. ............... I was thinking one battery (which one?), and some sort of solar charger. ................ I guess I could put something on the roof. 

If the van is your work vehicle then it is likely you drive it every day.   An alternator charge to the largest vehicle battery you can fit would see the battery fully charged by the end of each day????   A modest drain over night is unlikely to result in a flat battery next morning.   Some have already said that low voltage protection is available so you don't get stuck.

Scope creep might get you wanting a bit more.   When does a fridge become a desirable upgrade?   An expandable setup, minimum, would be an AGM house battery, say 100AH.   A 100 watt solar panel would be insurance and do the charging bit when you don't start the vehicle that day.

I have a 92 AH AGM as a start battery.   110AH AGM as a house battery.   Have a 120 watt Solar Panel on the roof and that panel is set up to be portable.   Alternator and panel go to a CTEK D250S.   Output of the 250S charges the battery.   DIY installation was pretty simple and not real high tech because the most complicated bit was crimping proper size connectors on the wiring.  Solar panel is portable so I can park in the shade and position the panel in the sun.

Phone charger goes on the vehicle battery every night and LED lighting is also run from the vehicle battery.   TV, fridge, computer, and sometimes an inverter, come off the house battery.   My setup can handle 3 days of no sun and no alternator charge.

 

[RVTravel]

Rather than a cutoff device I would rather have a device that beeps at a certain voltage?

 

[skyl4rk]

A hundred bucks on Amazon.
https://www.amazon.com/gp/aw/d/B0030A10V0/

I wouldn't mind having one of these on my starter battery and my house batteries in my current van.

With regard to cheapest, simplest system:

Alternative 1, $200, Marine Battery replacement and LVD

$100 for the low voltage disconnect, and $100 for a deep discharge battery to replace the starter battery. No wiring to do other than installing the low voltage disconnect.  You can run led lights and charge usb devices without worrying.  You could charge a laptop and it might take all the power, but it will automatically shut off before it damages the starting battery. A fan could be used for a few hours.  It would probably not be a good idea to run a fridge.  You would have to drive daily or every other day for an hour or so to charge.  

Alternative 2, $230, Solenoid, Marine Battery Box

$100 for a solenoid installation and wire to a separate house battery.  $100 deep discharge battery. $30 for battery box, fusing and connecters.  Battery capacity is about the same as Alternative 1. You have no protection against inadvertently using all your power.  You would have to drive daily or every other day for an hour or so to charge.  You have to find room to securely mount the battery box.

Alternative 3, $150, Switch and Marine Battery Box

$100 for a deep discharge battery.  $50 for wire to battery, switch, battery box, fusing and connectors. As long as you remember to turn the switch on for charging and off for use, it will work the same as Alternative 2.

I think Alternative 1 makes the most sense.  I could reduce my power use to things that could be powered by Alternative 1 and still have good quality of life.  No battery in the van living area, no danger of shorts and fire due to mistakes in installation or moving stuff around and hitting electrical connecters.  

The down side is that you would have to drive every other day or so to keep the battery charged.  But solar, and additional battery capacity move the system out of the Easy, Simple and Cheap category.

 

[skyl4rk]

Alternative 4, $240, Marine Battery replacement, Solar Charge Controller with Low Voltage Disconnect

20A Solar charge controller with LVD: $100, Deep discharge battery replacing the starter battery: $100, Wire, fusing and connecters to connect charge controller to battery, and to a cigarette lighter outlet: $40.

This is a charge controller with LVD that I use and have had good experiences with, there may be other ones out there.

https://www.solar-electric.com/ss-20l.html

Connect battery + and - to the battery connectors on the charge controller with a 20A fuse near the battery on the + line.  Connect one or more cigarette lighter outlets to the Load connectors on the charge controller.  Or direct wire lighting, usb voltage regulators, etc to the Load connectors on the charge controller. 

You could then add a solar panel to reduce the need for driving to charge the vehicle (not included in price).

One should not rely on the Low Voltage Disconnects for protecting the battery in daily use.  The disconnect voltage is too low, it causes battery damage, so the user needs to monitor battery voltage or otherwise avoid excessively discharging the battery.

 

[skyl4rk]

Alternative 5, $180, Low Voltage Disconnect and Marine Battery Replacement

Low Voltage Disconnect: $40, Deep discharge battery replacement: $100, Wire, fusing and connectors to connect LVD to battery, and to a cigarette lighter outlet: $40
Similar installation to the solar charge controller above. This LVD can be set to disconnect at 12V, which is higher than the solar charge controller or the other option above. This would help prevent battery damage.

https://www.amazon.com/Voltage-Battery-Disconnect-Auto-Detect/dp/B0147DYUN8/ref=sr_1_3

 

[RVTravel]

nm

 

[highdesertranger]

just remember the battery should be returned to 100% everyday. charging a battery from an alternator takes a lot longer than a hour. if you were to take it to 50% it would take hours and hours to fully charge(about 8 hours). I am not saying don't hook up your battery the alternator, I am just saying it takes much longer then most people think to fully charge a depleted battery. highdesertranger

 

[SternWake]

just remember the battery should be returned to 100% everyday.  charging a battery from an alternator takes a lot longer than a hour.  if you were to take it to 50% it would take hours and hours to fully charge(about 8 hours).  I am not saying don't hook up your battery the alternator,  I am just saying it takes much longer then most people think to fully charge a depleted battery.  highdesertranger

Well, Ideally, the battery would be returned to 100% every day.

Not achieving that simply reduces its lifespan/longevity/performance.  How much reduction is directly related to how close to 100% it gets, how depleted it gets drawn how long it reamins less than fully charged, and how often, if ever, it does get to that ideal true 100% state of charge.

Far too many people believe the alternator is some magical near instant battery recharger.  While they can produce very high amperages when cool and spinning fast, over cables thick enough to pass high amps, and loads requiring it. They are limited by the vehicles voltage regulator, which are timid and will not hold high 14.x voltages for very long.

The batteries themselves when 80% charged or more are limiting factors.  80% to 100% on a healthy battery cannot be accomplished in less than 3.5 hours, at ideal charge voltages, and no vehicle( but mine ;> ) holds ideal charge voltages when driving. It does not matter whether a vehicle has a 130 amp alternator or 2 200amp alternators, If the battery can only accept 15 amps at 14.7v, the only way it could accept slightly more than 15 amps is at a higher voltage, and voltages over 15 should be avoided unless in cold weather.

The closer to 100% the battery is, the slower it recharges. Sucks but it is a simple fact without any regard for human emotion or desire, as facts oftentimes are.

If a 50% depleted but healthy battery is quickly brought to ( at high amps) and  held at 14.7v, it will take 6 to 8 hours to reach 100% true full charge, but 'could' be brought to 80% charged in one hour.

If a 50% depleted but healthy battery is only allowed to reach and achieve 13.6v, it will take about 96 hours for it to reach 100% full charge. if unhealthy, it will never reach 100% charged no matter how long 13.6v is applied.

Do not simply measure charging voltage after engine starting and think this is the voltage the vehicle's voltage regulator always allows.  most will allow 14+ volts for 15 minutes or so before reversion to 13.6 or so.

It is highly vehicle dependent how high and how long it holds 14+ volts.

i recommend users have a 3 wire voltmeter visible on the dashboard for house and engine battery.  the 3rd wire is a voltage sense wire.

the following link has 3 wire voltmeters which can be calibrated:
  https://www.amazon.com/dp/B00YALUXH0/ref=twister_B00YALUULY?_encoding=UTF8&psc=1

I have 2 of those and one of these on my dashboard:
https://www.amazon.com/bayite-Digit...UTF8&qid=1481335210&sr=8-6&keywords=voltmeter

My ammeter reads total alternator current, but I will eventually move the sensor to read only amps into or out of battery.

When a flooded battery accepts 1.5 to 2% of its 20Hr capacity at absorption voltage, one can then consider it very near truly 100% full charged, verify with hydrometer.

AGM battery, 0.5% of capacity at absorption voltage.

Do not assume that a solar controller dropping to float voltage means the battery is fully charged. This overwhelmingly false assumption is a battery killer that has Battery manufactuers( not their retailers) dance for joy.

Do not have battery manufacturers dance for joy.

 Check flooded batteries with a hydrometer.  With AGM batteries make sure that amps taper to 0.5% of capacity or less, at absorption voltage( 14.4 to 14.8v).

Batteries are just rented, however the length of that rental contract, and the Cycles achieved per $ spent, is nearly entirely upto the person who rented them, if they choose to be aware of the influencing variables.

What is acceptable to user A, or user B, is likely NOT acceptable to ME

One does not need to achieve Ideal, but one should know what ideal consists of, before saying this works just fine for me and will be just fine for you.

As far as the easiest, simplest, cheapest power set up for a user with light electrical loads.  My opinion is  to cycle current engine battery until it fails, then replace with the largest 12v marine battery which can be shoehorned into the original location.

Carry a Lead acid jumper pack for self jumping for when battery is overdepleted.  After a dozen jump starts or so it is likely engine start battery will fail completely and absolutely require replacement.

If a simple L/A jumper pack's price s still too high, the batteries within them are just a 12 or 18AH cheapo chinese AGM battery like these:

https://www.amazon.com/ExpertPower-...e=UTF8&qid=1481336334&sr=8-1&keywords=ub12180

CArry quality 8 awg or thicker gauge jumper cables and hook this fully charged 33$ 18AH AGM spill proof battery to depleted engine starting battery and self jumpstart.

Simplest easiest cheapest can be initially accomplished for 33$, if one already owns jumper cables. later on the new marine battery adds 100$ or more, but perhaps the owner decides to hit up a junkyard for a used battery.

Diesel engines  or big carb'd v8 engines in colder weather will of course require a bigger jumper battery.
Fuel injected engines start so quickly they do not really require a huge jumper battery in most instances, but much depends on the health and depletion level of the vehicles engine starting battery.

Recharging this jumper pack battery can be accomplished many different ways, but recharging it to full, so it is ready to go when needed, takes time.  they should be recharged to full every 30 days even if not used for jumpstarting

Many of these jumperpacks hit garage sale tables for very cheap, and replacing the batteries within, or harvesting the jumper cable clamps off of them, is very simple if one knows how to turn a screwdriver and has some DIY ability in them, as most van dwellers will.  Some jumper packs will require a long shanked torx bit though to reach the screw heads.
 
 In the early 2000's, I  drove across the country 3 times over 18 months with just a jumper pack, before wiring up a dedicated house battery, but my loads consisted of a stereo and Incandescent lights only.  That jumper pack was used to jump others more than myself.

 

[skyl4rk]

Alternative 6, $135, Low Voltage Disconnect and Marine Battery Replacement

Low Voltage Disconnect: $20, Deep discharge battery replacement: $100, Cigarette lighter plug and outlet: $10, Plastic box for LVD: $5.

https://www.amazon.com/dp/B018TK5WIM/

Connect a male cigarette lighter plug to the battery + and - connectors.  Connect a female cigarette lighter outlet to the load + and - connectors.

Plug LVD in to a fused cigarette lighter outlet that is always on, not just when the ignition is on.  

This price assumes that a fused, always on cigarette lighter outlet is available in the vehicle.

 

[wjffineww]

WOW a lot to chew on there. Thank you all for the responses. I think I want to keep the back separate from the front. If I get a separate battery for the back, and run all my power off that, is there a small portable solar charger I could get and hook up to the battery when needed?

 

[Optimistic Paranoid]

WOW a lot to chew on there. Thank you all for the responses. I think I want to keep the back separate from the front. If I get a separate battery for the back, and run all my power off that, is there a small portable solar charger I could get and hook up to the battery when needed?

Renogy is fairly well thought of here, several people have and recommend their products.  They have a complete kit that includes a portable panel.

https://www.renogy.com/renogy-100-watt-portable-rv-kit/

 

[TMG51]

Well, Ideally, the battery would be returned to 100% every day.

Not achieving that simply reduces its lifespan/longevity/performance.  How much reduction is directly related to how close to 100% it gets, how depleted it gets drawn how long it reamins less than fully charged, and how often, if ever, it does get to that ideal true 100% state of charge.

Far too many people believe the alternator is some magical near instant battery recharger.  While they can produce very high amperages when cool and spinning fast, over cables thick enough to pass high amps, and loads requiring it. They are limited by the vehicles voltage regulator, which are timid and will not hold high 14.x voltages for very long.

The batteries themselves when 80% charged or more are limiting factors.  80% to 100% on a healthy battery cannot be accomplished in less than 3.5 hours, at ideal charge voltages, and no vehicle( but mine ;> ) holds ideal charge voltages when driving. It does not matter whether a vehicle has a 130 amp alternator or 2 200amp alternators, If the battery can only accept 15 amps at 14.7v, the only way it could accept slightly more than 15 amps is at a higher voltage, and voltages over 15 should be avoided unless in cold weather.

The closer to 100% the battery is, the slower it recharges. Sucks but it is a simple fact without any regard for human emotion or desire, as facts oftentimes are.

If a 50% depleted but healthy battery is quickly brought to ( at high amps) and  held at 14.7v, it will take 6 to 8 hours to reach 100% true full charge, but 'could' be brought to 80% charged in one hour.

If a 50% depleted but healthy battery is only allowed to reach and achieve 13.6v, it will take about 96 hours for it to reach 100% full charge. if unhealthy, it will never reach 100% charged no matter how long 13.6v is applied.

Do not simply measure charging voltage after engine starting and think this is the voltage the vehicle's voltage regulator always allows.  most will allow 14+ volts for 15 minutes or so before reversion to 13.6 or so.

It is highly vehicle dependent how high and how long it holds 14+ volts.

i recommend users have a 3 wire voltmeter visible on the dashboard for house and engine battery.  the 3rd wire is a voltage sense wire.

the following link has 3 wire voltmeters which can be calibrated:
  https://www.amazon.com/dp/B00YALUXH0/ref=twister_B00YALUULY?_encoding=UTF8&psc=1

I have 2 of those and one of these on my dashboard:
https://www.amazon.com/bayite-Digit...UTF8&qid=1481335210&sr=8-6&keywords=voltmeter

My ammeter reads total alternator current, but I will eventually move the sensor to read only amps into or out of battery.

When a flooded battery accepts 1.5 to 2% of its 20Hr capacity at absorption voltage, one can then consider it very near truly 100% full charged, verify with hydrometer.

AGM battery, 0.5% of capacity at absorption voltage.

Do not assume that a solar controller dropping to float voltage means the battery is fully charged. This overwhelmingly false assumption is a battery killer that has Battery manufactuers( not their retailers) dance for joy.

Do not have battery manufacturers dance for joy.

 Check flooded batteries with a hydrometer.  With AGM batteries make sure that amps taper to 0.5% of capacity or less, at absorption voltage( 14.4 to 14.8v).

Batteries are just rented, however the length of that rental contract, and the Cycles achieved per $ spent, is nearly entirely upto the person who rented them, if they choose to be aware of the influencing variables.

What is acceptable to user A, or user B, is likely NOT acceptable to ME

One does not need to achieve Ideal, but one should know what ideal consists of, before saying this works just fine for me and will be just fine for you.

As far as the easiest, simplest, cheapest power set up for a user with light electrical loads.  My opinion is  to cycle current engine battery until it fails, then replace with the largest 12v marine battery which can be shoehorned into the original location.

Carry a Lead acid jumper pack for self jumping for when battery is overdepleted.  After a dozen jump starts or so it is likely engine start battery will fail completely and absolutely require replacement.

If a simple L/A jumper pack's price s still too high, the batteries within them are just a 12 or 18AH cheapo chinese AGM battery like these:

https://www.amazon.com/ExpertPower-...e=UTF8&qid=1481336334&sr=8-1&keywords=ub12180

CArry quality 8 awg or thicker gauge jumper cables and hook this fully charged 33$ 18AH AGM spill proof battery to depleted engine starting battery and self jumpstart.

Simplest easiest cheapest can be initially accomplished for 33$, if one already owns jumper cables. later on the new marine battery adds 100$ or more, but perhaps the owner decides to hit up a junkyard for a used battery.

Diesel engines  or big carb'd v8 engines in colder weather will of course require a bigger jumper battery.
Fuel injected engines start so quickly they do not really require a huge jumper battery in most instances, but much depends on the health and depletion level of the vehicles engine starting battery.

Recharging this jumper pack battery can be accomplished many different ways, but recharging it to full, so it is ready to go when needed, takes time.  they should be recharged to full every 30 days even if not used for jumpstarting

Many of these jumperpacks hit garage sale tables for very cheap, and replacing the batteries within, or harvesting the jumper cable clamps off of them, is very simple if one knows how to turn a screwdriver and has some DIY ability in them, as most van dwellers will.  Some jumper packs will require a long shanked torx bit though to reach the screw heads.
 
 In the early 2000's, I  drove across the country 3 times over 18 months with just a jumper pack, before wiring up a dedicated house battery, but my loads consisted of a stereo and Incandescent lights only.  That jumper pack was used to jump others more than myself.

As always, your electrical advise is second to none! However I would draw your attention to the second adjective of the thread title; simplest.

Have you considered writing a technical manual? It might be cathartic for you.

 

[SternWake]

Well, I did write this in amongst all that technobabble.

As far as the easiest, simplest, cheapest power set up for a user with light electrical loads. My opinion is to cycle current engine battery until it fails, then replace with the largest 12v marine battery which can be shoehorned into the original location.

Carry a Lead acid jumper pack for self jumping for when battery is overdepleted.

:0

 

[Larry48]

Well, I did write this in amongst all that technobabble.

:0

Assuming he started out with a fully charged 12 volt Marine battery , how much would his 
State of charge drop when he started the van?

Also , assumming he only powered light loads , 2 amps of L.e.d lights and charging his phone , could he get away with the Alternator being the only charging source?

 

[29chico]

Assuming he started out with a fully charged 12 volt Marine battery , how much would his 
State of charge drop when he started the van?

Also , assumming he only powered light loads , 2 amps of L.e.d lights and charging his phone , could he get away with the Alternator being the only charging source?

To know for sure you would have to know the average watts per day.  I suspect even a shallow regular discharge would need a couple hours a day of driving, not idling, to bring the battery back up to full charge.  So it is probably cheaper overall to simply plan on not getting over a year or so out of a battery and not stressing out when it no longer meets your needs.  Even a small amount of solar charging to bump up the ever so important absorption phase, when high current is not needed, would really extend the battery life. 

Having a cheap manual charger, that had 6-8 or more amps output and could exceed 15v by a bit, on hand for when shore power was available is another way of extending useful battery life.

 

[SternWake]

Actual starting the (presumably fuel injected) engine consumes Extremely little of the battery capacity.

If I did the video thing I could show just how soon it is replaced.

I have typed before that an AGM battery can be considered fully charged when it accepts 0.5amps or less, per 100Ah of capacity, when held at absorption voltage(14.4 to 14.8v).

My AGM battery will actually, given enough time at Absorption or Float voltage, taper to 0.0X ampsat 14.7v
(0.0X because my Ammeter does not register 100th of a volt, but it has to be at least 9 100ths but likely 5 100ths or less)

So My battery is fully charged, accepting 0.0X amps at 14.7v, Bursting full.

Start engine. My ammeter does not refresh at a super fast rate, but I have seen the starter motor consume as much as 160 amps cold and as little as a 60amps hot, and will regularly see 116 amps cold at 65F, when my engine catches and -116.x amps flips around and goes to 60+ amps if the battery is not full.

But when starting the engine with a fully charged battery, just after starting, my ammeter usually starts at 32 amps, voltage instantly climbs to 14.7v, and amps quickly taper. Once amps they taper to 0.0x Again at 14.7v, the battery can be considered fully charged again.

How long does this take?
Under 30 seconds.
State of charge, goes from 100% to 99.9x% or something inconsequential when it only cranks for a second before catching.

But my low compression V8 (Mopar 318)engine also catches very quickly, usually in under a second. A carb'd engine which needs to crank for longer would require more battery capacity, but not a huge amount. A diesel Engine would require much more as the compression is higher and there are the glow plugs and or grid heaters to deal with, and this is frequently why they come with two starting batteries.

If the battery were not fully charged, then the voltage would fall lower, and the amps the starter would pull, would be higher, and overall consume more capacity from the battery but not a huge % more.

Regarding question 2 about the light loads, say the 100Ah marine battery was depleted to 80%. It could not be recharged to 100% in less than 4 hours.

Stating batteries in most daily driver vehicles are never truly brought upto 100%, and most vehicle batteries last for several years. If not in a hot environment and the daily driver never depletes battery with engine off , never lets the vehicle sit undriven with parasitic loads and self discharge slowly depleting the battery, it can last 10 or more years bfore its capacity and cold cranking amps fall to the point where cold weather reveals that it is time to replace the battery.

The problem of much shortened battery life and performance come when the battery is always hovering below 80% charged. Below 80% and the plates grow sulfation, which reduced the surface area for the chemical reaction to take place, which reduces the battery capacity. the longer these sulfates remian, the harder they become, and the more difficult it will be to redissolve them into the electrolyte when charging voltages are applied high enough for long enough.

A person with only light loads can certainly get away with only the alternator. A person with heavy loads can get away with just the alternator. The variable is HOW LONG before battery capacity and it cold cranking amps, declines to the point where there is not enough buffer to consume the regular loads, and still reliably be able to start the engine when the weather gets cold.

So much is about getting the battery above 80%, and how close to 100% it gets plays a huge part in battery longevity Know that 80 to 100% charged, under ideal battery voltages, takes a minimum of 3.5 hours on a healthy battery, and considerably longer on a battery that is less than healthy.

One can perhaps cycle their battery from 50 to 80% for a 200 cycles before the capacity is so diminished that it no longer has the gusto to crank the engine. Perhaps more, or less. Impossible to really guess at wihtout knowinng the starter amperage, and original battery capacity and all the other influencing variables which contribute to capacity decline.

For example, I had a 6 year old wally world marine group 27 battery. I always kept it fully charged and its only duty from 24 months to 6 years, was to start my engine, which I have already stated requires very little of the battery capacity and is quickly returned after engine starting.
Now my dome lights are still tied to engine battery, and at the time they were not LED, and If I left door ajar for an hour, a ~1.1 amp load, consuming 1.1 amps from battery that when new, was 115 claimed AH capacity, this 1.1a load for an hour was enough of a load that the battery could not start my engine. Having a relatively healthy house bank all I had to do was turn a switch and was in no Danger of stranding myself. I did not want to buy just a starting battery. I wound up using that severely capacity compromised battery that would likely only produce 250CCa of the original 650, and never pass any load test, lasted for another year before my house bank also required replacing and I replaced all 3 batteries at once.
And it alone, could still start my engine when I bought all new batteries.

Granted it was not cranking the starter with anything that could be considered gusto, and could have shorted a cell anytime, and my ambient temperatures rarely drop below 50F, and I rarely left the dome lights on, and often would allow the solar to hold it in the 14.8 volt range every so often, topping it up, but this severely compromised battery was able to start the engine for far longer than I expected it to.

But at 6 years it could not charge my cell phone and then start my engine. But I did not replace it for another year.

Is this a praising of a wally world battery, No, not at all, It merely shows that a severely compromised low quality flooded marine battery, with a small fraction of its original capacity and CCA figure, was still able to start my engine as long as I never used it for house loads, no matter how minor, and kept it fully charged.

Many people with tiny house loads and horrendously poor recharging systems, like which happens when one uses a double male Ciggy plug to charge a secondary battery though 2 ciggy plug outlets and 16awg wire over a 35 foot circuit length, can last a long time powering light loads and never reaching full charge.

But plug in that new laptop to an inverter and pull 65 watts for an hour, and that inverter low voltage alarm will start screaming all too quickly, Driving to replace what the laptop used in one hour, will likely take several hours, and reaching a full charge, never gonna happen, not when driving.

Enter the fully charged jumper pack, and one can lightly use their engine battery for quite a while before its replacement becomes necessary and not risk a stranding.

But heavier loads, applied for longer, requires better charging sources over thicker wiring, applied for longer, and the full size secondary battery powering all loads, keeping the engine battery As fully charged as possible, will be much more reliable with much less stress to the driver, and likely be cheaper after that first warranty return of the murdered battery.

 

[Ticklebellly]

As always, your electrical advise is second to none! However I would draw your attention to the second adjective of the thread title; simplest.

Excellent listing of some of the complexities that can be had in deciding just what to do, eventually.   A very large crank battery, carefully managed, is probably the simplest.

I just found out about the complexity of how to charge a seriously discharged deep cycle battery in the shortest time possible.   Seems direct alternator charge initially can be used to push a large bulk charge current into the flat battery then a DC to DC charger can be used to keep a high charge current rate up until very close to full charge is achieved.

In a loose use of the technical terms, I use about 12 AH running stuff overnight and parked up.   In full sun, my solar panel delivers about 8 Amps to the DC to DC charger.   Engine running, the DC to DC charger delivers 20 Amps to the battery.   Ergo, I need full sun (Peak Sun Hours) on my panel for about 1 1/2 hours or just under an hour of Alternator to put back what I used over night.     Of course, day time draw is happening while the night time draw down is being replaced.

In deciding what is simplest, having knowledge of how to manage the system might have an effect on that decision.

 

[SternWake]

The Dc to DC charger on the alternator circuit is to defeat the vehicle's voltage regulator which likes to revert to 13.6ish volts, and which greatly slows battery charging and ensures it never gets close to full, even on a long drive. the dc to dc converter will take 13.6v and convert it to 14.xv for X amount of time, and generally try to apply a 3 stage charging profile to the battery.

However, I'd cringe at a 20 amp limit on a dc to dc converter when an high amperage alternator forced into seeking a higher voltage can deliver a hundred amps or more into a depleted battery.

I have bypassed my vehicles voltage regulator, tricked the ECM into believing I have not, and installed an adjustable voltage regulator. I wired the VR so that the adjustment dial is on my Dashboard, next to my voltmeter, and can choose any voltage from 12.8 to 15.3v.

But if I choose to dial a voltage over 14.7v the ECM eventually sees that it has been tricked and shows the check engine light, reverts to some open loop fuel air mixture and spark timing, ignoring the sensors, and MPG takes a Nose dive. Resetting the ECM by removing power to it is the cure, or simply not allow more than 14.7v for 30 seconds that it takes to trigger the code.

I've gotten 106 alternator amps into my battery, when it was new and depleted, but now at ~430 deep cycles and 3 years of Age, it only takes about 85 amps to bring it instantly to 14.7v.

 

[frater secessus]

Have you considered writing a technical manual? It might be cathartic for you.

It also might be a decent source of income.  I think there's an "Electrical Systems for Vandwellers" ebook in him, maybe a series. 

"Go SternWake, go SternWake, it's your birfday, it's your birfday"