I almost never turn my manual Blue Seas 6007 battery switch to OFF.
Doing so with the engine running is a big No NO, and doing so with the engine off resets the engine computer, and makes the engine run a bit crusty for the first few miles as it relearns the various sensors, so I try to avoid doing so.
My battery switches are in a lockable cabinet, so if i do turn it OFF, it would make it more difficult for some scumbag to attempt to steal my Van.
Sometimes when I am working on the van, something electrical, I will turn the switch to OFF as well, but removing the ground cables from both the batteries would be safer.
Basically I always start the engine on the fully charged engine battery. The engine always starts quickly and nearly instantly the battery voltage rises to 14.9v, the maximum my vehicle's voltage regulator allows. About 30 amps are required from the alternator to bring the voltage to 14.9v, and the amps required to hold 14.9v taper down to the single digits within 30 seconds.
At this point, If my house battery is depleted and I desire to quench it with some good old alternator amps, I will turn my Switch to BOTH, and instantly the engine note changes as the alternator went from providing about 10 to 15 amps total to about 70 amps, with over 60 of those going into the thirsty depleted battery. This is harder on the switch's contacts than it is the alternator.
Sometimes I turn the switch further to the other battery, basically removing the engine battery completely from the alternator circuit. There are some advantages to doing this I will not go into here as the biggest advantage might only be applicable to my 89 dodge van.
Each 25 amps the alternator makes require 1 engine HP so the alternator can present a significant load on the cold engine. If it is cold or wet outside I might wait a bit longer before bringing the depleted battery into the loop. Sometimes it makes the alternator belt squeal as it slips.
The 70 amp number is dependent on how depleted the house battery is. This 70 amp number will climb higher with more engine rpm if the battery is depleted enough. The battery will take everything the alternator can make when depleted. Once these high amperages get the house battery to 14.9v, the alternator amps required to hold 14.9v begins to taper. How quickly the amps tapers depends on how depleted the battery is. My AGM battery, although smaller, can suck more alternator amperage for longer periods before the voltage climbs to 14.9v, as it has much lower internal resistance. My system allows me to choose either battery for either house or engine duties, but in general I cycle the flooded and use the AGm for the engine, 13 days of every 14.
My alternator is rated at 130 amps, but this is basically rated in a lab when cold at very high rpm when there exists 130 amp + load and cabling capable of passing this much current.
70 amps will heat up the alternator quickly. It is a significant load on the alternator. When asked to do 70 amps for a long time, it will wear out the alternator faster. Higher rated alternators should, in theory, deal with the heat they can generate better than lower rated alternators.
When the alternator heats up, it is not able to make as much amperage as it could when cold. Often, my alternator, at hot idle speed, cannot keep up with the vehicles demands, such as the Hvac blower motor on high speed and the lights, and no charging occurs. The battery is actually providing about 10 amps at hot idle speed with blower motor on high and headlamps on. Battery voltage can drop and the headlights can dim, depending on how long I sit at the redlight, idling
All vehicles will vary in this regard, how much amperage they can make when hot at idle speeds. Mine does pretty poorly. Do not believe the ratings or claims of alternator manufacturers as to idle speed amperage, as they don't state the actual armature rpm or what temperature the alternator is, and the ratings are marketing, which is basically trickery to make it appear better than it is, as there is no truth in advertising, and almost pride in deceiving.
Some higher rated alternators can actually do worse at hot idle speeds than the lower rated alternator they replaced!!
Idling to recharge can be extremely ineffective. If you do not have the tools to measure how much the alternator makes at hot idle speeds, do not assume that idling your engine is doing anything significant to recharge the depleted engine battery. Stop by an Auto electricians and have them slap a clamp on DC Ammeter over one cable leading to your house battery. You might be very surprised and extremely disappointed to see low single digit numbers.
My solar controller's absorption voltage is set to 14.9v as well. My solar will contribute all it can until 14.9v is reached. Sometimes these two charging sources, the alternator and the solar charge controller confuse each other. There is no danger. Usually what happens is that the solar stops contributing.
But there are times when the Van's voltage regulator, located in my engine computer, decides 14.9v is too much and only allows 13.7 or 13.9v, and the solar still says 'I've got to reach 14.9v and hold it for 2.5 hours( where i have it set for). When this happens the solar is partially powering the vehicle electronics and the alternator might produce nothing. Usually this only occurs if the house battery is 90% or more charged.
Many variables with this whole scenario and nothing is set in stone. The solar can reduce the load on the alternator, and the longer the sun has been up to recharge the battery, then the less thirsty the battery is when the alternator is fired up to feed the depleted battery, reducing the strain on the alternator.
When I shut the engine down, I try to remember to turn my battery switch back to only the engine battery, as it does not need any solar current, I want all solar current to go to the depleted battery. If I am out running errands sometimes I don't bother bringing the house battery into the alternator loop. Sometimes I do and just allow the house battery to assist engine starting, but turn the fridge off. If there is good sun, and I know the solar can finish top charging the house battery I will not bother turning the switch at all after starting the engine.
I do not want my house battery assisting the engine battery during restarts as this might damage some delicate electronics hooked to the house battery, like my compressor fridge. During the daytime this is a bigger concern than worrying about starter battery depletion.
I rarely forget to turn my battery switch isolating engine and house batteries come sundown. If I do, usually it is very obvious when i look at my voltmeter, as I will expect to see 12.6v or so, and will see 12.9v instead, and then I know my AGM engine battery is still in parallel with the house flooded battery. I don't mind charging these batteries in parallel, but I do not want them in parallel when resting or when discharging. Once or twice here and there is not going to kill the AGM, but overtime it will degrade it as it has a higher resting voltage and will always be feeding the flooded battery.
If one is really concerned about alternator life, the best thing to do is make a Cold Air Intake, so that the alternator fan can pull in ambient air temperature instead of underhood temperatures. The cooler the alternator, the happier the alternator and the better it can do its job, and the longer it can do it for.
My alternator is located right next to my exhaust manifold, the rectifier about 2 inches away. I made a heat shield between the two, and my hot idle speed amps increased by ~5 amps.
My alternator pulls in air from the back and exhausts the air out the front near the belt, but not all alternators are the same in how they are designed to pull air through them, but all of them have forced air cooling, either with an internal or external fan. In general the ones with the fan right next to the pulley, suck in air from the back of the unit.
One day I plan on making a CAI for the alternator. This alternator is one I got from Kragen Autoparts in 2004 with a lifetime warranty. I replaced it 5 times between 2004 and 2007. Either the remanufacturer did a bad job, or my ignorance of battery loads killed them, or some combination of both.
I got solar in 2007. I have not replaced the alternator since.
Either I got a good remanufactured model, or my Solar has taken a serious load off the alternator since solar does not allow me to drain the battery so low so often,
or some combination of both.
People who rely solely on their alternator to recharge as much as possible in as short a time as possible and have thick cabling that can allow the alternator to feed the thirsty battery properly, will be replacing their alternator well before they would otherwise. Thinner cables reduce the effectiveness but increase alternator life, at the expense of battery life.
If one wants to take it another step further, one can get an external rectifier so that the alternator is not producing any significant heat within its case.
http://www.ebay.com/itm/Alternator-...al-Rectifier-Alternator-Upgrade-/161173273360
