Lucky mike said:
first off get a battery isolator......
your alternator's charging circuit passes thru a regulator that when it see's a charge cycle is complete will stop the charging output....this is where the bucket is half full comes in....half charge in one battery .....half charge in the other = full bucket!....in other words your regulator only see's one battery volume/ charge
an isolators job is to charge the main battery first and then divert the full charge to the secondary bank(battery)... it also works as a switch so you dont draw off your primary (starting )battery
Please show me a picture of this magical regulator which alternator current passes through and protects the battery.
Now if you are talking about the voltage regulator, this device is outside the alternator charging circuit, but on some vehicles this device might be internal to the alternator, yet it is still not "in" the charging circuit. It is an external influencer.
Voltage is electrical pressure. The more pressure the more current can flow. If there is too much pressure then the battery voltage will climb too high.
So the voltage regulators job is to basically throttle the alternator output, to make sure it can both keep up with loads such as lights and blower motor and stereo and top off the starting battery, yet keep the battery from going above or below a certain threshold voltage.
Stock alternator charging circuit wiring is not designed to properly recharge another battery tacked onto the starting battery through the many various methods available to isolate the engine battery from Auxiliary(house) loads, yet allow alternator current to get to the extra battery.
An 'Isolator' in RV/ marine terms, generally refers to a Diode based device which acts like a one way valve. Alternator current can get through to charge the Aux/house battery, but loads placed on the Aux/house battery cannot pull any current from the starting battery.
These Diode isolators have an issue with voltage drop. The Diode drops voltage anywhere from 0.3 volts to 0.7 volts. Combine this voltage drop with thin wiring ( or even thick wiring) and the voltage drop is so significant there is very very little current that makes it to the house/Aux battery, because there is so little electrical pressure difference between the 2 batteries, or the Aux battery and the isolator.
No/limited/little recharging current = undercharged battery.
Undercharged battery= short lifespan battery.
Short lifespan battery = indignation by the ignorant undercharger, warranty service, and higher prices for us all.
Now the manufacturers of these Diode based alternators have gotten all sensitive about their bad press in this regard. Sure their product might keep the engine battery from getting depleted via house loads but if very little current makes it to the house battery from the alternator, it is chronically undercharged and dies a premature death. perhaps they think their job ends at keeping the engine battery from seeing house loads.
To counteract this, some of these diode based isolators complicate things by trying to trick the voltage regulator. When wired to do so successfully, the alternator is now told to produce 15.x volts so that 14.x volts makes it to the isolator and presumably to the house batteries and allows them to recharge at a higher rate at which they desire.
This complicates the wiring of such a system, and if done incorrectly might cause the engine battery and all stock vehicle electronics to see voltages in the mid 15 range, which might be dangerous for them, and 15.3 v on a starting battery will overcharge it, boiling off the electrolyte, causing positive plate erosion, Long story short, it might kill the engine battery, and its sole purpose is to protect this battery.
See an issue here?
Diode base isolators are encased in a large aluminum box covered with Finned heat sinks. That 0.3 to 0.7 volt drop causes a lot of heat. This is energy created by the burning of gasoline to spin the alternator to make enough current to recharge a battery, but a significant portion of this current is getting released to the atmosphere through the diode's heat sinks. This is current which could be going to recharging the batteries instead.
So a warning here, And the lone opinion in this particular post...... Diode based isolators are no good.
They can be made to work if properly to recharge batteries if they are designed, and wired, to trick the voltage regulator into allowing the alternator to overproduce, to counteract the voltage drop inherent in the design. If you get the correct model, and IF you wire it properly to trick your alternator, then only a percentage of that extra current will be dissipated by the heatsinks on this diode based isolator. Some vehicles ( Dodge's 1988+) have voltage regulation built into the engine computer. Successfully manipulating the Alternator field wires can be complex. I'd recommend NOT trying. Especially if you live in a state with Smog tests. Most manipulations of the VR on Dodges will illuminate the Check engine light. Cant pass a smog test with the check engine light illuminated.
Now the diode base isolator is but one method to allow engine recharging of an Auxiliary/additional/house battery.
Other methods are simple solenoids. Continuous duty solenoids. When this solenoid sees a 12v Switched source, an electromagnet is activated parallelling/ Combining the engine battery to the starting battery allowing the alternator to charge both.
This switched source can be a manual toggle switch, or something live when the key is turned to on, or even a circuit which is only live when the engine is actually running. I like the blower motor circuit for the latter option as on most vehicles the blower motor is not active during engine cranking.
There also exist "Smart" solenoids. These might activate after a period of time has passed. Or after a certain voltage threshold has passed. The time delay is to allow the starting battery to receive the bulk of the alternator output to replenish what was taken from the starter battery, before allowing the house/aux battery to feed on the current too.
The voltage sense Smart solenoid, instead of relying on a time delay, decides when it sees 13.x volts from the alternator, that starting battery can dang well share the current, and parallels the batteries When the charging source is removed, once the voltage falls below a certain threshhold, then the smart solenoid isolates the engine battery from the house battery.
Other options exist too that are somewhat outside the Smart or Dumb Solenoid. One is the Automatic charge relay like the:
http://www.bluesea.com/resources/1366/Automatic_Charging_Relay_[ACR]_Explained.
These are The simplest to install. A single sense relay senses charging voltages on the engine battery and parallels the house battery.
A dual sense relay senses charging voltages on Either battery and parallels/ combines the batteries. Single and dual sense solenoids exist too.
While a solenoid requires 0.5 to 1.5 amps to hold the magnet and the contacts together, the Blue seas ACR does not require this current, and this current can then be fed into the batteries instead, recharging them quicker.
There are also latching solenoids where a brief burst of 12 volts is required to close the contacts paralleling the batteries and another 12 volts burst required to separate the batteries. These latching solenoids do not actually consume current when latched or unlatched. Latching solenoids should not see a continuous 12v source to activate them. They will overheat, and are pretty much a manual device. A low draw very visible light should be wired and installed so that the user knows whether the solenoid is latched or not.
Another option is A manual Switch like this:
http://www.bluesea.com/products/6007/m-Series_Mini_Selector_Battery_Switch_-_Red
This one requires the user to remember to isolate the batteries. IE Not automatic, Not Foolproof. Also it requires that the user NOT turn the switch to OFF while the engine is running. Doing so can destroy the alternator and perhaps other electronics powered at the time the switch was turned to off. Some manual switched have an AFD, an alternator field disconnect. When the Field wires to the alternator( if an externally regulated alternator) are run through this switch, then turning this manual switch to off with the engine running will not destroy the alternator.
It is not certain that turning the switch to "OFF" while the engine is running will destroy the alternator. It is more likely to be destroyed the more current it was being asked to make at the time the switch was turned to OFF. This is a load dump situation. All that current it was making has nowhere to go when switched to OFF and voltages can spike Way too high possible destroying electronics and blowing the Rectifier in the alternator.
Now no doubt some have heard of a certain test to see if the charging system is still working properly. That is to remove the battery cable while the engine is running, and if the engine stalls,the alternator is bad, and if it keeps running everything is fine.
THIS IS NO LONGER a VALID test, except for perhaps on some vehicles pre 1980. This is Grandpa's Knowledge which should stay with grandpa's old cars, when cars had generators, not alternators. If you want to see if the charging syytem is working, Put a voltmeter on the battery terminals. Anything over 12.8v indicates charging but one hopes to see 13.6 or higher. Revving the engine should raise the voltage to these levels 13.6+, even if the battery is depleted. Generally if the alternator is not upto snuff the battery voltage will hold in the high 12's or it will be in the 11's and rebound a bit with the engine shut off.
Back to the methods of Aux battery Isolation.
Yet another option is a DC to DC Solid state device which will take whatever battery charging voltage it is fed, and step it up to the mid 14's so that the batteries can feed at the voltages they were designed to be properly recharged at. Sterling and a few other companies make these devices. I am not really up on all the manufacturers. Many of them are limited in current they can pass. They might be more effective in squeexing in the last 25% into the battery but a properly wired alternator to house battery circuit would most likely bring them to 75% much faster.
All These Non Diode options will work much better at recharging the House/Aux battery, as they will allow full voltage through the device itself. The wiring and the quality of the connections between alternator and house battery will be the limiting factors on how well the battery recharges. The battery itself will regulate how much it can take at the voltage allowed by the regulator through the cabling between the two.
There is NO device inline on the charging circuit intentionally limiting current.
Thin long wiring over multiple connections might be engineered into a system to prevent overcharging, but no one in their right mind living off an Auxiliary battery should intentionally limit what the battery should be allowed to have. The voltage regulator will keep it from overcharging. Small thin and too long of wiring only insures undercharging which is a death knell for deeply cycled batteries.
Having very fat cabling with minimal voltage drop through one of the latter isolating methods can indeed stress out the alternator when the house battery(s) is/are very depleted and can shorten its lifespan. But it will recharge the battery much much better, at least from the xx% to 80% State of charge stage.
Very few people will actually OVERwire their House battery, thus causing their alternator to be overworked. Most will not spend the $$ required for long lengths of 2 awg cable or thicker. Many will just say do as I do use 10 awg, because 10 AWG is rated at such and such a current and that is all I want be battery to feed upon.
A Distant depleted battery fed with 10awg wire is like a 5000 yard runner allowed to breathe only through a cocktail straw. Put a Diode base alternator in the middle of that cocktail straw and see how well that already oxygen deprived runner fairs.
One other option for recharging the house battery when the engine is running is to run an inverter hooked directly to the engine battery. From this inverter runs a regular household extension cord to a battery charger which is hooked to the house/ Auxiliary battery.
This is a good method for travel trailers or 5th wheels or any vehicle where the distance between alternator and house batteries is a great distance. It requires the inverter be switched off when the engine is switched off. Also the charger might be required to be turned on after it is given 120Vac from the inverter. Also if it is a high amp battery charger, the alternator might not feed the starting battery enough to keep it from discharging while it is charging the distant house batteries.
Idling to recharge is pretty ineffective on many vehicles but if using this inverter to battery charger method it could very well be a case of robbing Peter to pay Paul, and One should pretty much be keeping eter bathed in charging current, because Peter's job is to make sure that engine can always start.
