[Markgm]

Hello,
I am a new owner of a used 2000 Legacy wagon. I have very interesting living conditions. Living in the car, I use my laptop all day. Sometimes, it's a little cold outside, too. So I break the rules and idle my car from time to time. I have a power bank/inverter that I charge, and the laptop via inverter uses 15-20 watts. Well, this car doesn't give out extra current for much.

When I start the car cold, it gives battery charge current, and I really enjoy using that. It reminds me of the charging of the old days, when the battery was always being charged. Well, I think I want to do this here. I want to charge the battery all of the time. I will use it.

Does my car have a battery temperature sensor, or is it another temp-related sensor somewhere else, that gives me this high cold-start charge? Secondly, I am wondering if there is a way to trick it into always being "cold", so to speak, so that the higher voltage/charge would always be on?

Cheers, Mark

 

[SilverOnyx]

I'm wondering if your alternator simply provides less current and voltage when it gets hot, not that it's being commanded to lower output.

While it may not help, probably good to check and possibly improve all the grounds. Some people add a ground to the body of the alternator if there isn't one, since grounding through the bracket could degrade with aluminum oxidation etc.

 

[brucep]

Does my car have a battery temperature sensor, or is it another temp-related sensor somewhere else, that gives me this high cold-start charge?

Some cars have a temperature sensor underneath the battery (Chrysler products)... I am not sure that Subaru does.

I do know that some newer Subaru has a CURRENT sensor on the battery-negative terminal. The computer will boost alternator output based on electrical load.

Some common electrical loads which will increase alternator output:

• Starting engine.
  • Obviously, starting engine drains battery hence there is high electrical load for several minutes after starting.
  • Cold ambient temperatures demands more battery power hence increases this temporary alternator boost
• Headlights ON
• Blower on HIGH
• A/C ON
  • do not forget that turning on AC also turns on both radiator fans.
• Rear window defrost ON
• windshield defrost ON
  • remember that windshield defrost also turns ON A/C (ref. A/C above)

 

[bryancraftyhands]

I don't know of a battery temperature sensor either, unless someone installed one aftermarket. Otherwise, the car would probably pull the data from the intake air, and engine temperature sensors.
You might want to look into acquiring another battery or two suited for deep cycles such as found in marine, RV, & solar power systems. They can be wired to take a charge from the alternator, and can have a kill switch installed so that they don't drain the car's main battery.
A hack I don't see mentioned often is if you have a dc motor, that say, has a set of fan blades, it can be used as a power producing windmill.

 

[brucep]

I am a new owner of a used 2000 Legacy wagon.

I am wondering if there is a way to trick it into always being "cold", so to speak, so that the higher voltage/charge would always be on?

I am not sure if you found an answer in my last post.... I am trying again...

Your 2000- does NOT have the current-sensor on the battery-negative post. Hence, if you have the 2.5 engine, the alternator should NOT have any funky control from the computer.
In other words, You do not need to "trick it into always being cold".... the alternator should put out full current as-needed when the detected voltage drops below setpoint.

Dont forget, when you think it is being "cold"... it is really just the battery being recharged from cold-startup.
Your inverter should work just fine. If it is not, there is a different issue we can discuss.

 

[Markgm]

Some cars have a temperature sensor underneath the battery (Chrysler products)... I am not sure that Subaru does.

I do know that some newer Subaru has a CURRENT sensor on the battery-negative terminal. The computer will boost alternator output based on electrical load.

Some common electrical loads which will increase alternator output:

• • Cold ambient temperatures demands more battery power hence increases this temporary alternator boost

A general search for battery temperature sensor at O'Reilly. I haven't messed around with this before, but I have read about it. General to the industry, there is a known thing, which is to give more charge to the battery when it is cold, and not just when turning the starter, because batteries don't have as much voltage when they are colder.

I have a voltage gauge, and I watch it all the time. When I start my car cold, it goes over 14v for a little while, like 10 minutes. After that, I expect to see less - sometimes 13.2v. Sometimes, when I'm drawing more with my stuff, down to 12.6v or so. But a cold start gives me 10-15 minutes of higher voltage, more current.

Another approach to tricking out my charging system is to install a diode in the voltage sense line from the battery to the alternator. This would drop it by a half a volt, and trick the alternator to make more charge for the battery. It's just that I thought I might be able to fool the thing another way, if I could make it think it was still cold.

 

[brucep]

I have a voltage gauge, and I watch it all the time. When I start my car cold, it goes over 14v for a little while, like 10 minutes. After that, I expect to see less - sometimes 13.2v. Sometimes, when I'm drawing more with my stuff, down to 12.6v or so. But a cold start gives me 10-15 minutes of higher voltage, more current.

again... It sound to me as if you are mis-interperting the voltage readings you are seeing.

Risking repeating myself a third time:

1. Starting engine drains battery slightly
2. hence, for several minutes after starting, the alternator sees higher electrical load and responds accordingly.
   • This temporary voltage-increase has NOTHING to do with temperature-sensor. (on your 2000)
3. After battery-charge is replenished, the electrical-load goes down (and alternator output goes down)

You are correct that higher voltage can mean more current.... but this correlation is based on electrical loading, alternator RPM, voltage-regulator setpoint...etc

It is FARRRR more likely you are dealing with a combination of factors including poor grounds.

Using sensitive voltmeter to take VOLTAGE DROP measurements would be the approach I would begin with to isolate where the voltage is getting lost.

BOTTOM LINE ==> Do not assume that higher voltage always means more current. You have jumped to conclusions which have no basis in facts.

Infact, it is more likely that the lower voltage you are seeing (after few minutes) may represent HIGHER current which is pulling down the voltage. (if the regulator were not involved)

Before you move forward with adding diodes to 'trick' the regulator to produce more voltage (0.7V per diode BTW)... it would be better if you perform the VOLTAGE DROP measurements at appropriate nodes in the circuit.

 

[Markgm]

Bruce, I guess what you are saying is that you don't think I should be seeing the behavior that I do. I can say that I am limited in what power I draw, for charging my storage devices for example. When I am charging my power bank (inverter), it's PSU says 15V, 2A, so 30W is its draw, and it drops my voltage to power it. I think that is less than wiper motors would use, but I do not see built-in accessories causing a change in the voltage.

 

[bryancraftyhands]

Bruce, I guess what you are saying is that you don't think I should be seeing the behavior that I do. I can say that I am limited in what power I draw, for charging my storage devices for example. When I am charging my power bank (inverter), it's PSU says 15V, 2A, so 30W is its draw, and it drops my voltage to power it. I think that is less than wiper motors would use, but I do not see built-in accessories causing a change in the voltage.

Figure your alternator is designed to put out so many volts and watts, typically what the car may use, plus whatever a cigarette lighter may use. I think they are somewhere around 100 amp output. The alternator typically puts out a little more than enough charge to power the built in vehicle accessories. There is a voltage regulator keeping the voltage at 12VDC to those systems while letting anything in excess go to charging the battery. Typically an alternator puts out about 14V.
Extra accessories running off the vehicle's alternator would cause more draw. I'm guessing this inverter you speak of is tapped onto the battery. Inverters themselves use power to work, on top of whatever it is you are plugging into it. Perhaps you might want to look into a high output alternator. They put out around 200 amps.

 

[Radar]

A year 2000 car has a basic alternator without sensors or any external control. The alternator is going to charge the car battery as much or as little as the battery needs at that time. You can't influence that, but if you could, you'd probably damage the battery. The reason you see it charging at a higher voltage when it's cold is because the battery gets discharged more. A cold battery loses some output, and a cold engine takes more power from the starter motor to turn.

 

[bryancraftyhands]

Yes, once the battery is discharged, there is going to be a higher current draw going into it until it is charged, then it will drop to zero once it is charged. This will happen regardless of the temperatures. There will be more of a discharge to recharge when colder however.

 

[plain OM]

I have the impression that most, if not all, of the examples of low voltage/low current are based on the engine idling.

The alternator's ability to generate current is dependent on rpm, On a "cold start" the engine idling rpm is usually raised above normal until the engine warms. That, along with the colder alternator temperature (see paragraph below), helps maintain higher alternator output to replenish the battery charge that was lost to start the engine. Once the engine and alternator are warmed up, the idle speed is lower, leading to lower alternator output capacity as this table from the 2000 FSM indicates for the factory-original equipment (left column is MT, right is AT).

At idle, the alternator is not going to be able to sustain very much beyond the basic power train needs and perhaps some lighting or other accessory.

Also, the alternator's average output voltage is dependent on its temperature (which is a proxy for the temperature of the battery in the engine compartment). On a "cold start", the voltage will be higher; low to mid-14 v is normal. As the temperature of the alternator increases, the average regulated output voltage will decrease, but usually not lower than the upper 13 V range. The temperature control is built into the alternator's regulator itself, and does not use an external sensor.

 

[brucep]

Bruce, I guess what you are saying is that you don't think I should be seeing the behavior that I do.

Incorrect! I am not saying that at all.

I have tried to help you several times by explaining from various perspectives.

I truly hope you are not relying solely on the display of your fancy 'inverter' to troubleshoot the issue you are seeing. If so, that may explain the lower voltage readings. I hope it is obvious that the voltage drops when a load is applied... this is why a voltmeter DOES NOT draw any current (high impedance input)

Have you taken the VOLTAGE DROP measurements with voltmeter yet? Do not forget that there MUST be a load on the circuit to get valid readings.

Feel free to use [search] to review my other postings which detail VOLTAGE DROP measurements.

If you wish more help from me, PLEASE describe how your inverter is connected to the vehicle and detail the results of your VOLTAGE DROP measurements. I troubleshoot these kinds of things for breakfast and I am sure we can get you going if you participate.

 

[Markgm]

I have taken some measurements. Previously, I had mentioned voltages in a mix of whether I was running or charging something or not. GEAR: I have an inverter in my car wired to the battery. I have another inverter which I will call a power bank. I have a voltage gauge in parallel with the inverter when it is plugged in, and I have a multimeter for tests. [Edit-add: "plugged in" means the inverter is via the lighter socket; my max use would be 50-60W].

On a cold start, ground tests for voltage drop are under 0.1V, except for between the alternator RED and battery RED, which does hit 0.1V.. The system voltage I measure on a cold start is around 14.2V. I can turn on headlights, wipers, or blower on high, and the system compensates and keeps the voltage up. But under these circumstances, when I plug in my power bank to be charged, it will drop a full volt. If I then add the laptop, it will drop a bit more than that. When the car is warmed up, the system goes down to around 13.2V, but at that point, powering my two things will drop it below 12.6V, even down to around 12.2V. So, I guess the problem is that it can give more power to built-in things, but when I want the power, then it won't give it to me. Cheers.

 

[bryancraftyhands]

When the car is warmed up, the system goes down to around 13.2V, but at that point, powering my two things will drop it below 12.6V, even down to around 12.2V.

When the car is warmed up, the idle speed is down, the alternator is will put out what it does. There is a voltage regulator that will prevent it from putting out any more than a set voltage.
Running any electrical circuit will cause a voltage drop.
A house typically has a 120V, 100 amp service.
A car typically has a 12V, 100 amp service.
The current (amp service) is what you are lacking, and would need a higher output alternator if you are drawing too much power. You could add more batteries, but the cost and weight of them would be impractical.
Another option would be to find another power source. Perhaps a small collapsible solar panel, or windmill. Maybe a small generator with a sufficient power output. I have a 2200 watt dual fuel that weighs about 50 lbs, and makes about 53 db in noise with no load for example. Small enough to carry in the car, and set up in minutes outside when needed.

 

[Markgm]

When the car is warmed up, the idle speed is down, the alternator is will put out what it does. There is a voltage regulator that will prevent it from putting out any more than a set voltage. ... The current (amp service) is what you are lacking, and would need a higher output alternator if you are drawing too much power. ...

This is what I guess I have wanted to point out. It has more power if it needs it at warm idle, to run the blower to MAX. But, this power is not available without turning the blower to MAX (and that just goes to the blower). I think this may be because it is being fuel efficient, and won't induce drag on the motor if it doesn't see the need.

 

[bryancraftyhands]

Yes, there are circuits that when switched on, also boost the idle speed. They run through the ECM and or the VCM.
Again, the idle speed is brought up to increase the amount of current available from the alternator to meet the need. The voltage generated stays the same. The active circuit will cause a voltage drop, thus causing the appearance that there is more voltage being generated at other times.

 

[Markgm]

Yes, there are circuits that when switched on, also boost the idle speed. They run through the ECM and or the VCM.
Again, the idle speed is brought up to increase the amount of current available from the alternator to meet the need. ...

My engine idle speed is not going up when I turn on my blower to MAX, but the voltage stays where it is, and sometimes with a little boost.

 

[Markgm]

I have learned a lot. I will share a few links here to go with it. I came across a guy here who mod'd a gen5 charging system, by cutting the ECM line to the alternator: Alternator Mod for higher output . I then found a guy on youtube who did the same thing in I think a more elegant way, at the fusebox instead: 2015 wrx alternator charge fix .

My old gen2 doesn't have that smart-charge system. I have a voltage sense line from battery, via fuse box, to alternator. I have seen a guy add a diode to another kind of car to raise his alternator voltage successfully. So now it has occurred to me that "default alternator voltage" might be had if I just pull the fuse, and make it so the alternator cannot see battery voltage, and that appears to have worked. I'm holding at 14.2V at idle, when warm.

It would be more graceful to get the diode, I think, because just pulling the fuse leaves my battery light on when the car is running. Perhaps of note, MotorTrend has an article about achieving more power at lower rpm by using a 1/4" smaller pulley on the alternator, which will increase fan speed and cooling. High-Output Alternators Save the Day

The only thing I do not know at this point is how high the voltage goes on a cold start, but I think that is also alternator-controlled. I may come back to post that. Cheers.

[Edited: Had my laptop plugged in at the time... Holding at 14.2V, not 14.]

 

[plain OM]

The only thing I do not know at this point is how high the voltage goes on a cold start, but I think that is also alternator-controlled.

When the sense line is disconnected, the alternator is unregulated; there's no control. The output voltage might go well over 16 V (I've seen them higher than 20 V), which could cause premature failure of light bulbs and affect the electronic systems. Also, when the alternator voltage is being regulated, the average output voltage will normally remain fairly steady, but without regulation, it could change a lot with changing rpm or load.

These alternators are not designed to be used for extended periods without a functioning regulator. Continuous operation could lead to failure of the rotor brushes or the regulator circuitry that the rotor current passes through, and would mean loss of any output. That's why the Battery warning light is on when the sense fuse is removed.

Based on the FSM specs, at idle (~700 rpm), the alternator is designed to deliver at least 36 or 39 Amps (depending on transmission type). The alternator itself might not meet the original specs, perhaps due to age, or because it's an inferior replacement. Has it been tested for capacity at both low and high rpm and low and high loads to see if it meets the specs?

Similarly, if the battery is faulty, it could be loading the alternator excessively, leaving less spare alternator capacity to provide current for your added loads at idle. Has the battery been properly tested?