steveh2112 said:
i found this interesting:
http://www.fridge-and-solar.net/dual_bat.htm
he's recommending to use a battery isolator (he also sells them).
from that article: "When you start your engine the Enerdrive VSR works by first letting your starter battery recover it’s charge from the alternator, it lets the cranking battery achieve 13.3 volts, at this point that battery now has about as much charge in it as it's going to get, now once the Enerdrive VSR sees this 13.3 volts it closes the contacts on the solenoid, this links both batteries together for charging purposes."
the interesting part is "now once the Enerdrive VSR sees this 13.3 volts it closes the contacts on the solenoid, this links both batteries together for charging purposes.". so this article is confirming what you said, link both batteries together for charging purposes. i guess the isolator is just there to make it a bit more automatic but for the $80 or so, i can hook up some jumper cables.
there is another isolator here
http://www.amazon.com/WirthCo-20092...8043789&sr=1-1-catcorr&keywords=Enerdrive+VSR
Never remove the battery cables from the battery while the engine is running. This can make the diodes in the alternator go poof. I know a lot of old timers use this trick to test to see if the alternator is working, and it was applicable when cars used generators and not alternators, but now it is a foolish method than can have disastrous results.
A simple voltmeter placed on the battery terminals can tell you if the charging system is working or not.
While the fully charged engine battery can indeed screw with the voltage regulator and cause it to drop voltage prematurely and thus charging amps into the house battery suffer, one should not remove the cables at the engine battery, ever, while the engine is running.
if one is worried about this, then wiring a solenoid to take power from the alternator (+) output instead of the engine battery (+) pretty much eliminates that issue. I recommend people do this anyway when the house battery is not located in the engine compartment. it yields a shorter circuit that is more effective for both being shorter and not allowing the engine starting battery dictate the voltage regulator behavior to the detriment of the house battery.
Many smart solenoids exist. Some work on a time delay, only paralleling the batteries after a certain amount of time, others do it when battery voltage reaches a certain number, like 13.3. Some even use both.
now my opinion, these are not worth their extra, as the benefits are little.
13.3 volts happens on My van instantly after engine starting. granted my engine starting battery is almost always fully charged so the very little alternator current is needed to get it past 13.3v.
So in my vehicle, the extra money spent on this "smart" solenoid would be a complete waste of money. Someone who does indeed cycle their engine starting battery could benefit too, especially if their charging circuit is thin. Even when my house battery is depleted 50%, when I allow it into the alternator charging circuit, amps jump upto the low 60 range, and voltage climbs over 13.3 in a second or two, so again, no benefit to getting this Smart solenoid whatsoever in most cases, and Never in my vehicle.
Some of these smart solenoids are dual sense, meaning they will combine the batteries when EITHER battery receives charging voltages. now if the engine battery is already fully charged, and one has solar, well the engine battery does not need any current going to that battery, and worse, it requires about 1 amp to hold such a solenoid closed, so 1 amp of solar energy which could be going into the depleted house battery is going into holding the solenoid closed, and the engine battery which likely does not need to be pushed upto 14.7 for 2 hours, is also requiring an amp or two to be brough upto that voltage. All that extra current would be much better off going into the depleted battery, not holding a solenoid closed, or bringintg a batery which does not need time at 14.7, to 14.7v.
Now there are latching solenoids which only require a momentary burst of 12 volts to parallel and unparallel batteries.
In My opinion the DUMB, continuous solenoid, triggered to activate only when the engine is running, is the simplest, cheapest , most effective manner of battery isolation which charges the house battery when the engine is running.
There are many ways to accomplish this goal. The simple dumb solenoid rated at at least 100 amps is easy to do and inexpensive.
http://www.amazon.com/s/ref=nb_sb_n...ducts&field-keywords=Continuous duty solenoid
If one has indeed deleted their engine battery, and wants to insure it gets all the alternator current, the solenoid can have a lighted manual switch installed on the trigger circuit, so the driver decides when to allow the batteries to parallel. If this circuit is only live with the engine running, then there is no danger if one forgets to flip the switch back to off.
Finding a circuit to trigger the dumb solenoid which is live only with the engine running is not hard either, though it might seem so when one has not done it before.
If one wants even more manual control, then a 1/2/both/off marine switch can be employed, but thee are dangers to forgetting, and dangers to the alternator if switched to OFF with the engine running.
I employ 3 manual switches, one for my Ignition/alternator circuit, one for all my house loads, and one for my Solar and other charging sources. So I can choose either of my two batteries to be the engine starting battery or house battery, and I regularly do swap their duties, or charge one independently while discharging the other, which comes in handy when my flooded battery needs a 16volt equalization cycle to restore maximum remaining capacity after 2 weeks of hard deep cycling. Voltages over 15 can be dangerous to some devices so it is noce not having to unhook battery cables to perform one, merely turn a switch.
