These CS130D's have some features (some kind of chip on reg/rect) referred to as pulse width modulation (PWD) in the alt/gen world which I really don't fully understand...
Factory PWM? Or an aftermarket add-on? Would this be the mod you are referring to?:
http://www.perfectswitch.com/downloads/DELCOCS130D5020-B.pdf
PWM stands for Pulse Width Modulation. Basically, what it does, instead of just "turn it on and leave it on", it "turns it on and off very fast". That's the pulsing. Modulating the width of the pulse, means controlling how long it stays on, and how fast it switches on and off.
Typical automotive voltage regulators, will switch on the alternator when the voltage of the "12v bus" (the entire electrical system is the "bus") drops to around 13.5v. It will leave the alternator switched on, until the bus voltage gets to around 14.5v and then switch the alternator off. The loads will then start pulling down the bus voltage. When it gets to 13.5v, the regulator switches the alternator on again.
On and off, up and down - the end result is the bus voltage averages out more or less around 13.8v.
PWM doesn't do that. What it does is, as soon as it detects ANY drop in the bus voltage (anything sucking power out of the bus, will cause the voltage to drop), it gives the bus a quick shot of juice. A pulse.
If the bus voltage has dropped a lot, it will let the pulse last a little longer, or maybe start doing the pulses a lot faster - modulating the pulse width.
It will pulse as as long or as often as it needs to, to hold the bus at exactly the set voltage.
So a normal regulator is somewhat sloppy. It allows a lot - generally around a full volt - of variance, whereas a PWM regulator keeps the bus voltage within a very tight range.
Anyway, I plan to install yet another (3rd) AGM battery inside the passenger compartment its a big 100 lb unit w/120 ah rating. I was going to wire it with an 80 amp solenoid and fuse then wire it to an ignition on circuit to switch on for recharging it w/o need for stand alone charger. after reading this thread I suspect I need some good advice.
Are the CS130D's capable of this recharging of 3rd battery w/o over charging the other batteries, or do I need to wire in some solenoids to take the other batteries out of the mix unit 3rd battery is charged, or should I draw power to inverter through all the batteries to avoid charging issues and include some kind of voltage sensing alarm to warn against too much drain?
Overcharging won't be an issue. Even with a Mobi-Arc regulator with PWM, it's still just a
single-stage charger. I.e., it will hold the bus voltage at whatever it's set at - lemme just pull a number out of thin air...say 13.8v.
So, the voltage regulator will hold the bus at 13.8v, and all the batteries connected to the bus will absorb power at their own rate until they have all reached 13.8v and then everything just stays at 13.8v and that's that - no worries about overcharging anything.
So a solenoid isolator would work fine for that.
The worry about overcharging happens when you use a
multi-stage charger. Specifically a
3-stage charger.
With that sort of charger, the
absorb stage will hold a higher voltage until the amps flowing through it drops below a certain amount. Well, if one battery is already full, but another is still absorbing power, then the charger will continue holding the higher voltage, and the full battery will end up being held at that higher voltage for too long, and by the time the one battery finally gets full, the other battery ends up overcharged.
Not an issue with a 2-stage charger because a 2-stage charger omits the absorb stage.
Also not an issue with a single-stage charger such as an automotive voltage regulated alternator.
So, your main problem is not overcharging.
Your main problem, is that using a single-stage charging system to recharge a BigAss(TM) deep cycle battery, can take a VERY long time. If the voltage regulator just holds the bus at 13.8v, then it can take 8 or 16 (or more) hours for the big battery to finally absorb all it can.
Also, taking a big deep cycle only only up to 13.8v is only going to get it 90 or 95 percent full. It will never really reach "fully absorbed". That can measurably shorten it's life.
So, depending on how much you use that big battery, and how far you drain it when you use it, you'll probably get a lot longer life out of it if you use a multi-stage charger rather than just using a solenoid to tie it to the 12v bus.
(For that battery alone that is - the cranking batteries will be just fine being charged off the bus, and you don't want to use a charger with an absorb stage on multiple batteries anyway.)
I've got a 115ah deep cycle battery in my camper. I use a solenoid and let it charge off the vehicle bus while driving, and use a small generator and battery charger for charging it when I'm not driving (or I can use shore power).
If I had an expensive battery, then I'd probably invest in a DC-DC multi-stage charger. That's basically the same as a shore powered 3-stage charger, except it gets it's power from the vehicle's 12v bus.
That will take the 13.8v from the bus, kick it up to 14.4v and then do a proper multi-stage (with absorb) charge on the big battery.
Or, yes you could also power an inverter from the vehicle bus, and use the inverter to power a multi-stage charger. One advantage of that scheme, is that you can also use that same charger from shore power when you want.
EDIT: One big disadvantage, is that you better make damned sure it's turned off when the engine is off - or you'll suck down your cranking batteries.
