Limits of the Stock Electrical system?

[chadsworth2]

Hello, Im new to this forum and the answere to this series of questions may already be out there. if so just link me to it!
So Ive recently purchased an older 87 ranger that was pretty rough.
Its come a long ways so far but now im getting into some modifications that are potentially putting a strain on the electrical system. ie... off-road lamps, winches, small amplifier for stereo, air compressor...
I want to make sure that im not taxing the system to much and potentially burning stuff up or constantly having a dead battery.
my questions are.

1> what are the stock specs of the electrical system. ie. how much availible wattage is left after the stock electical consuption from the radio, lights, blower motor and so on?

2> how does one go about testing for that availible power?

3> Ive read about adding a second battery and an isolator. does anyone have a wiring diagram of how to do that. do you thnk its necessary?

Thanks All!

 

[Aerkusa]

I imagine you probably don't have the OEM alternator on there anymore... what's the amperage of your Alt?

 

[Mazda]

From the "Tech Articles"

http://www.therangerstation.com/tech_library/DualBatteries.shtml

Also don't forget to relay/fuse everything that you hook up to the second battery. I used this.
http://www.amazon.com/Blue-Sea-Systems-Blade-Block/dp/B000THQ0CQ/?tag=959media-20

 

[RonD]

1987 to 1989 Rangers came with a 42amp to 80amp alternator, depends on engine size and options as to which you have.

The stock alternator will "generally" have 25% more amps than needed when engine is idling, common failure on all alternators is one of the three Fields going out, this cuts max. amps by 33%, but not Voltage.
Common sign if not enough amps is when head lights dim at idle, no that is NOT normal, lol, no car maker specs an alternator that can't provide enough amps at idle.
So this is a sign of a failed field, or too many electrical "add-ons".


General rule of thumb is that an alternator can only produce 50% of it's rated amps at idle(650rpm), it can't produce full amps until engine RPMs are 1,200 or above.
So if you have an 80amp alternator it can produce 40amps at idle.

For most of the time the engine is NOT at idle it is either off or above 1,200rpms so still has enough amps to maintain battery's charge and run all add-ons, even with a failed field.

Second battery is used for two reasons.
1. you want to run electrical devices without running the engine, i.e. camping, jobsite work.
Second battery gives piece of mind that primary battery will always have the ability to start the engine, some off-roaders have second battery just because two batterys are better than one when it's a long way to a "parts store", lol.

2. high amp draw is required for longer periods than say starting an engine, i.e. winch, snow plow, welder, ect...........
Second battery won't stress the alternator to provide that long term draw.

An Isolator allows power to flow from the alternator to the second battery, but not the other way around, so it is a one way street for power.
This allows alternator to recharge and maintain second battery when engine is running but prevents anything hooked to the second battery from drawing power from the Primary battery which is also hooked to the alternator.

If you want to test your system it is pretty easy with a volt meter hooked to the battery.
Key and engine off:
new battery will have 12.7volts
5 year old battery 12.3 or 12.4volts
when battery gets down to 12.2volts it is time to shop for battery sale , next cold morning you will get the "click, click, click" of a battery that doesn't have enough "juice" to get starter motor turning.

Engine started cold and idling, above 1,000rpms, all electrics off:
Battery voltage should be above 14.5volts, alternator is recharging battery's amps used up in starting the engine.
Voltage should slowly drop over next 5 minutes from engine idle going down and as battery gets recharged the voltage regulator reduces alternators output.
After initial recharge voltage regulator will set output at 1.1volt above "at rest" battery voltage, so if your battery tested as 12.5v(engine off) then you should see 13.6volts after 5 minutes of engine running.
This 1volt is a maintenance charge, battery won't drain and won't "cook"(overcharge and damage it's plates)

So with 13.6volts at battery start turning on electrics, head lights, blower(heater), radio, ect.......
Voltage at battery should drop when each thing is turned on and then come back up to 13.6volts, that the voltage regulator compensating for the extra power needed.
If voltage starts to drop and stay down then either alternator has a bad field or your add-ons have more amp draw than the rating for the alternator at idle.
Increase RPMs to 1,200 and watch if voltage can return to 13.6volts.

As far as the factory wiring goes you shouldn't add extra amps to it, the fuses and wire size are rated for the circuit.
When you add things like lights that you want to come on with the Main light switch you use a relay, and then another fuse for your add-ons.
If you upgrade the alternator for higher amps then you need to increase the size of the B+ wire on the back of the alternator, and usually its fuses.

 

[Aerkusa]

Well, that is extremely helpful. Tried to add reputation but I apparently already gave you some in a different thread so it won't let me.