A SEEKER said:
About 2 to 3x what the original OEM/ Stock charging circuit could pass. Is this only because the cable is large enough to pass the higher current?
Yes, this is most of it, but fat cabling on the alternator circuit also allows the voltage regulator to 'see' the depleted house battery. Often people take the power for charging the house battery from the starter battery if they use a solenoid or some other automatic type combiner/isolator.
This has two issues.
1. The original alternator to starter battery cable is not very thick. it is as thin as the manufacturer thought they could get away with. It was designed to charge a starting battery which is 90%+ charged( and which will not ask for much current), and power the vehicles electronics/ engine management systems lights, ect.
When a deep cycle battery is tacked onto the end of this circuit, well a depleted deep cycle battery can ask for twice as much current as required by the stock electrical system. One can see how this this original cable is not adequate for passing all the current the extra battery can ask for when depleted.
My depleted 130 amp hour flooded battery can ask for 65 to 70 amps from the alternator.
My depleted 90 amp hour AGM just maxes out the alternator, 90 to 110 amps if there is enough rpm. Big banks of depleted healthy AGM batteries over fat wiring can easily burn out an alternator, and thinner wiring can be utilized to reduce the strain upon it. So busting out the 4/0 gauge wiring pretty much requires an alternator upgrade to one which can handle a higher duty cycle without overheating.
As the batteries charge up they ask for less, require less current to be held at any given voltage. Once the batteries are brought up to the vehicle's voltage regulator maximum allowed voltage, then the current tapers, as more voltage would be required to allow more current to flow and the current required to hold the battery at that voltage becomes less and less.
Number 2 issue, is the issue of the fully charged starting battery. If voltage regulator does not see the depleted house battery as a big load on the starter battery, and it will not if the cabling between starter battery and house battery is thin, then the voltage regulator will believe the starter battery is very close to full, and will drop the maximum voltage down to ~13.6. When this happens, the current flowing into the house battery falls into the low single digits. If it were allowed to be fed at 14.5 volts, much higher charging current would be required to get that battery upto 14.5v and hold it there, and the battery charges significantly faster.
With the blue seas manual switches I utilize, the alternator current first goes to the original battery (+) cable, then to the manual ignition switch, then to either or both batteries. I have added a parallel circuit, basically skipping all the original cabling. It goes right from alternator (+) stud to My manual ignition switch, through a 150 amp Circuit breaker. This makes for a much shorter and much fatter cable for less voltage drop, and allows the voltage regulator in my engine computer to see the depleted house battery, and allows the alternator to make all it can, limited only by available rpm, and what the battery itself can ask for. It also allows 14.9v to be held for longer, in my vehicle, but not long enough. If I remove the fully charged starting battery from the alternator circuit, then the 14.9 v is allowed for longer too. so there is some outwitting of the voltage regulator going on to get the most into the depleted battery.
These parallel circuits can be added to almost any method one uses to separate/ combine their batteries, and will greatly help to charge the depleted batteries much faster. These parallel circuits need to be fused.
The ground path needs to be beefed up too. If one uses the Chassis as a ground path for the house bank, then add another ground strap from chassis to alternator (-) too. Take extra care with chassis grounds. Make sure they are very shiny and clean very tight, and protected from corrosion with grease or liquid electrical tape, as they are prone to develop high resistance which can greatly reduce charging current, and cause other issues as well.
Fatter cabling in the alternator circuit will not have much of an effect with house batteries above 80% state of charge, as at this SOC, batteries cannot accept much current and the original wiring is adequate for this.
When deep cycle batteries are depleted, i want mine to charge up as fast as possible, and the alternator when wired with fat cables, can be very effective at bringing the batteries upto 80% state of charge. It can do in a half hour what might take a 200 watt solar system, in good sun, 5 or 6 hours.
When one can blast the thirsty batteries with some alternator amperage, and let the solar do the low and slow thing for a good 6 hours afterward, the batteries will come very close to that elusive 100% mark which is in fact very difficult to achieve, because it takes so much time.
Those with flooded batteries, need to get a hydrometer and see that when any charging source indicates the battery is fully charged, that the specific gravity of the battery will say otherwise.
Often automatic charging sources indicate a full charge, but are still charging at a fairly good rate. Mine will flash the green light, yet the battery willl still be taking 6 amps. If i did not have tools to count current, if i believed the green light, I'd be unplugging the charger extremely prematurely.
If you suspect your charger is a bald faced liar, load the battery until voltage drops below 12.8, and restart it. It will not restart if it sees battery voltages over 12.8v. I had to do this 10 times in a row on some one else's abused batteries to get the specific gravity approaching the point where it should be. They batteries had lost capacity, but the force starting the charger over and over again got them up to near their maximum capacity.
Really, with abused flooded batteries, one needs to be able to bring them up to 16 volts for a proper equalization charge, and very few chargers can do this.
So a solar controller that allows one to change the voltages can be a thing of beauty.
Last night, I noticed my battery was dropping a bit lower than i was used to seeing. The solar held it 14.9v for 2.5 hours in the early afternoon, then went to 15.3v, where I have set my float voltage. After an hour it was taking 1.6 amps to hold 15.3, and i busted out my hydrometer.
Full charge is 1.285, the 3 easy to check cells were at 1.255 .1260 and 1.270. i reprogrammed for 16 volts and 45 minutes later the lowest cell was 1.275, but then i lost the sun before reaching 1.285.
Right now it is reading 0.15 volts higher than this time last night, and the amp consumption is pretty much the same, but tomorrow I am going to get the SG upto 1.285 on all the cells
