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Alternator Charging
#1
The quick and dirty version.

How well an alternator can charge a battery, is dependent on the voltage the vehicle's voltage regulator seeks and several other factors which will not be a focus in this post.

Most vehicle voltage regulators are designed solely to recharge a slightly depleted engine battery, and prevent it from discharging with the maximum available stock DC loads on teh system.

They are NOT designed to quickly charge a battery tacked onto the starter battery through some sort of isolation device.

Ideally, for fast recharging of a well depleted  77f house battery, the voltage would be allowed to seek and hold ~14.7v until it is full.  This would likely max out the alternator for an unknown  period of time until the battery itself achieves 14.7v.  

A  relatively healthy group 31 marine battery depleted to 50% state of charge will accept about 40 amps for nearly a half hour before voltage rises to 14.7v and amps taper. it could likely accept 60 amps for 15 minutes before attaining 14.7 and amps begin to taper. With 100 amps it might instantly achieve 14.7v and amps instantly begin to taper.


The problem is, that most vehicles only allow mid 14 volts for a short period of time, and then they drop to a safe and slow 13.6 ish volts.

Do not think the voltage seen just after engine start up is the voltage always seen, as so many many many seem to do.

Do not assume that a 130 amp alternator, is going to feed a depleted battery any significant portion of that 130 amps.

The battery itself might only require 20 amps to be held at 14.7v, and it might only require 6 amps to be held at 13.6v.  The lower the electrical pressure, the less flow there is, The more resistance to flow, the less that will flow.


In general while a fast spinning cold alternator can be a very powerful charging source, it is simply not allowed to do so, and could only do so when spinning fast while still cool, when the voltage regulator is asking for high voltage, and there is a big DC load( which a depleted battery is) and thick enough cabling to safely pass than much amperage.

What any specific vehicle allows as to system voltage and how long it holds theat max voltage is hugely variable and has a HUGE effect on how well it charges your depleted  batteries.

Unfortunately most assume that when driving their house battery is being charged as fast as possible, and 99.9% of the time this is an extreme falsehood which will shorten the battery life can cause the owner to spend more money sooner than otherwise. 

More to come.
[-] The following 5 users say Thank You to sternwake for this post:
  • Cammalu (11-05-2017), AbuelaLoca (11-05-2017), Optimistic Paranoid (11-05-2017), heron (11-10-2017), TWIH (11-27-2017)
#2
So the main takeaway from the post above should be that the voltage sought by the system has a huge effect on how fast a depleted battery can be charged,.

Also the voltages allowed by any one specific vehicle can be extremely different than another vehicle.

There are ways to trick/ manipulate/bypass the vehicles voltage regulator, that will be the subject of another post, and is highly vehicle dependent.

The best thing one can do, when setting up an Aux battery, is to introduce as little voltage droppingf resistance as possible, within reason, so that voltage is NOT lost on the wiring and its connectors and isolation devices, between alternator and depleted battery, on both the (+) and the (-) ground path.

While one might not be able to influence the voltage regulator, they can present as little resistence as possible in the alternator to house/Aux battery circuit to allow maximum electrical pressure to reach the Aux battery.

In general 4awg is sufficient for upto 220Ah of depleted battery, but one can go bigger on the wire diameter for less resistance.

As important as wire gauge/thickness is the total circuit length.

While most Aux battery systems are set up to take power from engine battery for charging house battery, this is in effect tacking on a 'hopefully thick'thick circuit at the end of a minimally accepable thin stock alternator circuit system, which was never ever designed to also support the charging of a depleted house battery bank.

When taking power from starting battery from engine battery the stock wiring in effect becomes an electrical bottle neck, dropping voltage and perhaps also not allowing the vehicles voltage regulator to 'see'that there is in effect a need for higher voltage for longer.

Much much much more effective is to take power for Aux battery, from the alternator (+) output stud itself. This is not always so easy to accomplish, stacking another ring terminal onto this stud, but it is well worth it if alternator charging is important to the user.

Since the vehicle's stock alternator to engine battery circuit is already fused, there is no need to add another fuse when power is taken from Alternator (+) stud, but a fuse IS required if one is taking power from the engine battery. A fuse, and the ire terminations all introduce voltage dropping resistance.

What are we trying to avoid? Voltage dropping resistance which can greatly slow battery recharging.

Also Since most Aux batteries are not in the engine compartment, taking power from the Alternator (+) stud is also likely a shorter circuit path. Shorter circuit path = less resistance= less voltage drop = faster battery charging.

Shorter circuit path also mean less copper needed, Le$$ copper means less $$ spent, or perhaps spent, but on even thicker copper.

The Importance of proper ring terminal connections cannot be understated, not only from a resistance and long time low resistance durability, but safety as well. Some people do not add a fuse close to Aux battery and if a thick cable shorts out a battery can send out enough current to melt anything it touches and could go all Fukushima.

If one cannot make their own proper battery cable terminations, with a hydraulic crimper with the proper size dies, they should use an outfit like genuinedealz.com which will make top quality custom cables and which are likely cheaper than the auto parts store cables, and also much much much better quality components.

Autoparts store battery cables might be convenient, but most use stamped steel ring terminals. Steel is not a good conductor and will rust and corrode badly in the presence of moisture or battery charging cumes.

AVOID battery cables sold in auto parts stores. you will save no money and will introduce way more resistance into the system while killing reliability.

The (+) side of the circuit is only hald of the circuit path.

The ZGround path is just as important and should be just as thick.

While it is possible to use the vehiucle frame as the ground path, this strategy then requires that the vehicles original framwe to engine ground carry all the charging current for the house battery.

If using the frame as a ground path, one should then add another cable inbetween vehicle frame and the alternator's case, or one if its mounting bolt.

When using the frame as a ground path for Aux battery, these frame grounds become highly resistive all too soon. Every effort should be made to make the mating surfaces pristine, and flat, that the fastener cannot back out, adn then cover the whole connection with perhaps liquid electrical tape in may layers, or grease, or shoegoo.

I recommend not using frame grounds at all, and instead run another cable, black, next to the red one, and attach it to the alternator frame or one of its mounting bolts.

The red cable should be further protected from chafing via some split loom, and proteced from vibrating by adequate hardware so they cannot sag and vibrate in the first place.

This post does not touch on the many dozens of different solenoids, isolation methods and products out there. Some of those products can also act as DC to DC upconverters dealing with the vehicle voltage regulator's shortcomings, but those are the topic of a different post in this thread.

But many will choose a continuous Duty Solenoid for this task. These should be rated for at least 90 amps continuous, and one can find these for as little as 15$. But buyer BEWARE!

The cheaper ones have soft electrica contacts which are asked to pass the current, and can wear out quickly, introducing more resistance,m slowing charging, and when they fail, they usually fail with the circuit closed, meaning no battery isolation, and the starter battery is getting depleted with the house battery.

I recommend one pay more for quality solenoids rated for higher amps and which have heavier duty main contacts. This can easily save you your starter battery, thus paying for itself.

The Solenoid can be placed anywhere in the circuit from alternator to Aux/house battery. Most seem to think this must be placed on the firewall but it could be placed next to , but not above , the Aux battery itself.

Keep the Alternatort to house/Aux battery circuit short, keep it thick, use high quality cable terminations. Do NOT try to save money on these components, it will cost you more money, the only variable is the time it takes to cost you more money.

There needs to be a fuse close to the Aux battery in this circuit.
This fuse rating should be for the minimum wire sized used in the circuit. Going smaller on thre fuse rating than required is not going to be any safer, and will introduce .....more resistance.

Please beware of tutorials on some other forums, or on Youtube , regarding setting up Aux battery systems designed to charge from the alternator. There is some serious halfwittery in some of them which can be dangerous.
[-] The following 2 users say Thank You to sternwake for this post:
  • TWIH (11-27-2017), ukenukem (10-21-2019)
#3
I think the isolation products/methods one puts between the alternator and the fuse for the house battery should comprise its own thread.

Regarding how to manipulate the alternators voltage, Well I only know specifically how to do so on my Dodge Van.

The long story short is I added a 50 watt 10 OHM resistor on the original ring terminals which originally mounted on my 50/120 chrysler alternator. 50/120 means it should be able to produce 50 amps at adle and maxes out at 120. This appears very accurate but 50 amps will drop to high 30s when alternator is really hot and engine idling at 525 rpm..

This resistor tricks the engine computer into thinking its internal voltage regulator is still connected to the alternator. Without it, the check engine light would illuminate, the computer would not observe any signals from the coolant temp sensor or the 02 sensor or the map sensor to adjust fuel air mixture or spark timing. Engine smoothness power and MPG all suffer when the check engine light is triggered without this resistor tricking the computers voltage regulator. if I had to do it over I would use a 100 watt resistor instead of a 50. Sucker does get HOT.

I now control voltage with a a transpo 540HD voltage regulator, removed its icro adjustement potentiometer, soldered wires to the legs, mounted a 10 turn potentiometer to my dashboard next to my digital voltmeters and ammeter.

I added a heat sink and a fan to teh VR's belly. It is mounted behind my glove box. This modification required grounding one of the alternator field terminals.

I will due a more indepth how to regarding this modification ,in the sternwake files, but I can basically choose any dang Voltage I dang well please , as i drive, and it is freaking awesome to be able to do so, and recharge as fast as possible, although when hot at idle sometimes the super depleted battery can eat more than the alternator can deliver and voltage drops.

Other vehicles can likely be persuaded to allow for different voltages either by using a voltage dropping diode on the voltage sense circuit, or perhaps modifying the internally regulated alternator into an externally regulated one.

i have not done that, no experience and while aware of the possibilities am not going to pretend i could do it to your vehicle without some serious research and compensation.

The DC to DC conversion products, i also have no experience with, and will not comment on them. But they exist, and they do work to increase the rate at which the battery charges, and can do so automatically for those that freak out at the thought of having to twist a dial at a certain time.

Done.
[-] The following 4 users say Thank You to sternwake for this post:
  • Cammalu (11-06-2017), Matlock (11-06-2017), TWIH (11-27-2017), ukenukem (10-21-2019)


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