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How is "cold battery" sensed? I want the charge.

604 Views 21 Replies 6 Participants Last post by  Markgm
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
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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.
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.
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.
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.
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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.
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