Adding a Second Battery

Kat - it sounds like you do not have a problem. You know which is your alternator output. Curiosity only - although you say the alternator's 3-phase output is "through a rectifier and regulator", I presume you mean it is rotor controlled regulation - or is it a stator system where the regulator is a heavy-duty dump or pass system? And some comments on 2.12's earlier references:

two12 wrote: Split Charge Diodes are dated and do not work properly! http://www.smartgauge.co.uk/diodes.html

The problem of not sensing the correct voltage is easily overcome except with D+ alternators (with charge light only connections). For 3-wire alternators, merely connect the Sense wire to the relevant battery's +12V. For 2-wire alternators, the ignition merely energises a relay that connects the relevant battery's +12V to the alternator's Ig (or S) terminal. And in both cases, hope sensed-battery's Split Charge diode doesn't go open circuit thereby cooking the other batteries!! Not that diodes are a good way to go anyhow - it might be simple, but it isn't clever for a several reasons - most of which have been covered. And with a charge light or similar controlled relay, there is negligible voltage drop; it present full voltage to all batteries; uses commonly available relays and is probably cheaper then high-power diodes.

two12 wrote: heres a couple of different types of systems: http://www.smartgauge.co.uk/smartbank.html http://www.powerstream.com/battery-isolator.htm Im still undecided as to whats the best way but my set up is a bit more complicated with more than two batteries and more than two charge sources.

The SmartBank seems nothing more than the two systems I've discussed. It does not do any current limiting, nor can it individually regulate its paralleled batteries.     The SmartBank has an optional flash (looking) voltmeter. I just mounted a $20 LCD voltmeter in my dash instead so I know if I'm over or undercharging, or my battery is dying. And I'm happy enough with the alternator's charge lamp control of the Aux battery relay. (I too will be connecting several batteries like that - each with its own relay from the alternator.)    For my battery loads like fridges etc, I'm happy enough with the trimpot setting of the K227 and its designed hysteresis and time delays. As to any delays before connecting auxiliary batteries, as I said, I cannot see the point. If I did, I'd probably add a timer, else maybe a manual override. I love the PowerStream's "state-of-the art microprocessor"! Is it digital? If so, I'd be very worried! If it's an analog computer - ie, op-amp, comparator, zenor diode etc, then ignore that uPC crap. It's not much different to the K227 kit, nor my "simple relay" (though mine stays on whilst the alternator signals that it is charging). The K227 doesn't have a manual connection for "jump starting" (maybe it can be modified?), and my relay system just needs a switch with some OR-ing diodes (that's the full-blown diagram.) Although in both cases, I'd probably use a separate relay rated for staring (which I have - old type solenoids with manual activation as backup!) Not that I mean to poo poo good products. But if they don't serve a reasonable purpose, why use them? (Bling & status exempted.) I've certainly seen many costly products that serve little purpose - in some cases they may impair functionality. With the above I see little more than a switch with potential for voltage averaging. There is no battery monitoring (meaning alarms or condition reports), no active equalisation, not even a separation of paralleled batteries (which I dislike unless adequately monitored). As to 2 charge sources, the simplest is isolation between the two, though all batteries & circuit can be commoned when charging off ONE system only.   (EG - a recent standard system with additional 250A alternator & 2 extra batteries - still just a normal relay etc.)

If it's a dump or pass, then you probably don't have the charge lamp option. Hence the "universal" voltage sensing circuit is required. But your "alternator" should still only have one output. If not, what is the other output for? (Where to? What power? Or is it the rotor field or battery "Sense" wire.) I would be inclined to use the original battery's +12V as the connection point since it solves any issues. IE - you have that battery's charging voltage to the second battery; whether the alternator puts out a much higher voltage is of no consequence. Else - what point am I missing? (Not the desired AGM charge characteristic?)

katman, do you actually ride the scooter with a huge boat battery attached to it? one of my old bikes has a 6volt system. Id like to learn how to have a dual battery set up on it with the secondary being 12volt. I wonder if thats possible without rewiring the stator? mabey with a step-up transformer? ahhh.. too many other projects at the moment. oldspark, thats some good info! thanks but ya kinda got too far out on the trailer wiring thread and I want to stay on topic there right now. (one step at a time) would your example for charging two batteries work for three or more batteries simoultaneously with a one wire altenator (GM)?

No, the battery is not that big.  Google Odyssey PC-680 for dimensions.  It takes up half the battery box which is a UM-1 size.  The battery fits numerous motorcycles including some BMW and Harley models."All paid jobs absorb and degrade the mind."

Aristotle

oh, I misunderstood this part:

katman wrote: I mounted the battery and charging system in a UM-1 size battery box commonly used in trolling motor applications for fishing boats.

katman wrote: I was thinking the difference between connecting to the 12V+ of the main battery would not take advantage of the Voltage Sencing Rely of the dual battery charging system instead of via the B+ of the charging system.

Nope. It is the battery voltage sensing which is the key - not the B+. As I indicated, they should be much the same. But if B+ is 20V whilst at the battery it is 13.8V-14.4V, then you want the battery voltage don't you? Remember that all vehicle charging systems are geared to suit the battery (voltages). (Excluding competitive vehicles & audio systems etc that may be geared for brightest lights or highest power etc.)

two12 wrote: ... a 6volt system .... a dual battery set up on it with the secondary being 12volt .... without rewiring the stator?

Can be done but "impractical" (two DC-DC converters etc.) Most 6V vehicles get rewired for 12V. Or converters for specifics like GPS, audio etc. "too far out on the trailer wiring thread"???   Do you mean I pointed out some functionality issues (with the alarms)? Tee-hee. Alas the importance of brainstorming, a bouncing-wall etc. The obvious is only obvious is retrospect. Trust me - I have been bounced a lot! (If only modern designs were!!) But as always - an idea, a proposal, SWOT, improvement, revisit the "aim" (not the solution!), research, review, design, rest, review, ask others (especially stoners), etc etc. Else there is the good old suck-it&see approach if you have the money and are prepared to risk future time wastage. BTW - nothing is impossible, it's just that some things are a bit trickier than others, or impracticable.

two12 wrote: would your example for charging two batteries work for three or more batteries simoultaneously with a one wire altenator (GM)?

Any aux-battery system can be extended to any number of batteries - whether on relay for parallel batteries (bad) or individual relay per battery or battery groups. The main difference is that - in particular for the charge-lamp system - the sensing circuit (alternator L or D+) only drive one relay; then that relay drives the others. (Hence f.ex using existing fuel-pump relays (for carby systems) to control the Aux battery relay. Keep in mind that the D+ system (1-wire charge-Lamp only) AFAIK senses its B+ output. Hence no risk of overcharging (except for alternator faults), but there is no compensation for voltage drops between B+ and the reference battery. (Unless the regulator can be tapped into - but that's what a 3-wire system is for, and a 2-wire system can be wired for (with a relay).) The beauty of whatever sensing system but with individual relays is that the batteries and their circuits are ONLY connected together whilst charging. (This can be applied to those other systems too.) At any other time they are totally independent so that a bad circuit will not effect the others - eg, a bad battery will not discharge and ruin other batteries - ie, the parallel-battery problem. A shortcoming is where a battery is so bad it drags the alternator down and even starts discharging other batteries. But that's where a voltmeter is best. And maybe temp sensors on each battery. Otherwise - especially if the battery is an AGM - it will finally melt, explode, flame and burn the installation down. FYI: On another forum, a "new yellow-top" dude thought he solved his under-charging problems with an alternator upgrade. (He "just didn't get it!"). Several weeks later, the undercharging reappeared. He picked the faulty yellow-top (a collapsed cell or 2) from its radiant heat! Hopefully he then understood why I kept asking for battery voltages and warned him about AGM thermal runaway. It was a nice boot-mounted hot-spot next to the fuel tank etc. Though luckily - as somebody else on that forum explained - the boots in those cars can NEVER burn or explode because its holes and gaps are TOO SMALL for oxygen to get through! Wow, learn something every day eh?

(Don't worry - some guys there were such dorks they preferred a boot fire to an engine-bay fire. It seems they did not know how to extinguish vehicle fires.)