A lot of guy's use a 5-10HP motor and an alternator for chargeing their track car's batter between runs. Fleet's use small diesel powered APU's that are like rotax diesel with a heavy duty alternator that has switable current and voltage for jump starting big rig's and heavy equipment.
Any battery/alternator ee gurus in the house
- Thread starter chefwong
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You showed me.
dont feel bad. he didnt take into account other electrical loads (lights etc) that consume amps the battery could use to charge. he also didnt consider parasitic loads on the battery from sitting overnight. the alternator must make up for these losses in addition to what was drained by actually starting the car.
A couple of side notes here, Many people don't know, (or don't understand), some of the oddities of lead acid batteries. I mentioned in another post that starting an engine and then immediately shutting it off, the voltage will drop some amount then after a short time will it will come back to nearly normal. If you run it down to the point that it wont crank, leave it set for an hour, a good battery will have recharged itself enough to get one more start out of it.
The other side of this is, a battery that is not at full charge, will resist accepting a charging current. It takes extra time and a higher voltage to get back to full charge and the closer it gets to full charge the longer it takes to get there. It's in the nature of the chemistry + the design. Clear as mud as right?
The other side of this is, a battery that is not at full charge, will resist accepting a charging current. It takes extra time and a higher voltage to get back to full charge and the closer it gets to full charge the longer it takes to get there. It's in the nature of the chemistry + the design. Clear as mud as right?
FWIW - my sister's Corolla's had issues with batteries for as long as she's owned it. Late last year, her battery died again and she went to Sears to have a DieHard Gold installed. I had her keep the old battery to see if it was really bad - so when she brought it over I plugged it into a quick charger. When disconnected after charging for about an hour it would show a good 12 or so volts, so we threw it on one of our cars and tried to crank it - and CLICK. Checked it again, bam, 10 volts. I discounted it as a dead cell and left the battery in the garage for about 8 months. Fast forward 8 months and I'm back in town. For the heck of it, I rig up an old cheesy car charger (the kind that plugged into the cigarette lighter to recharge the battery from there, it never worked really) and hook it up to that battery, and leave it hooked up for a few days. Then I put that battery in one of our cars, and bam! Works perfectly! That battery is being used today. Batteries are funny things, I figure that it was sulfited and needed the long slow recharge to convert the sulfites into active electrolyte. or whatever pseudo-scientific babble that they use to explain it.
Which are so large that the alternator only has 1/2 amp left to charge the battery so it takes a full hour to charge it back up after a startup?
I don't, for some reason, think so.
These are insignificant. 25mA over, say, 12 hours? 0.3 amp-hours. 25mA, by the way, is on the high side of what is typically considered acceptable parasitic load. Most cars are less.
That is correct, but those losses are very small indeed. If they aren't, the vehicle in question has a problem.
I've seen with my 130A alternator that it takes about 15 minutes at highway speeds for the battery to recover from starting. Most modern electronic controlled cars take 40-50 amps just to run.
A good test of the battery's health is the amount of current to keep the voltage in the float stage. Usually anything over 1/2 amp with a fully charged battery is not good. This is discounting any current needed to keep the car's electronics happy if still connected to the car.;
A good test of the battery's health is the amount of current to keep the voltage in the float stage. Usually anything over 1/2 amp with a fully charged battery is not good. This is discounting any current needed to keep the car's electronics happy if still connected to the car.;
my previous car, a protege, has an ampmetre installed on it. with the air and headlights on, that sucker would take 50 amps to run continous, and thats with a fully charged battery. granted it had a 70 amp alternator, but that only leaves 20 amps for charging. consider a car sitting overnight with the dome light on. wonder how long it would take for the alternator to fully charge that with youre running the air and headlights.
something else i thought of. this whole debate is a useless topic. no matter the outcome, it wont effect anyone so its nearly pointless to argue about trivial things. it doesnt really matter if you accounted for all the electrical loads or not. one way or another the battery will get charged, just a matter of time right?
i suggest we all get some fresh air and enjoy life and quit worrying about such silly topics.
im going for a sunday night drive.
i suggest we all get some fresh air and enjoy life and quit worrying about such silly topics.
im going for a sunday night drive.
Depends on how many amps the dome light takes and how many hours it was left on..it's a pretty simple problem to figure out once you know that.
Now, let me tell you about the time I couldn't start my 1988 Mustang GT because it had been sitting in my garage for a while, like a couple of months, without being driven. It simply wouldn't turn over. It wasn't that the battery was totally dead, it had just been sitting way too long without being driven.
I didn't have jumper cables long enough to reach and I didn't want to have to remove the battery from my other car to jump it.
I also didn't have a battery charger other than a 1.5amp maintainer.
So I tried connecting a 5-amp 13.8V power supply to the battery. I measured the current it was putting into the battery--it was about 3 amps.
Left it hooked up for about 15 minutes and tried starting the car. It fired right up.
It really didn't take much to get that battery to the point where it would start the car...3 amps over 15 minutes.
As for your other point, some cars do have barely-adequate alternators. The worst of them won't even charge the battery at idle with too many accessories turned on, because the idle output of the alternator is very low.
These are mainly older cars, like my 1988 Mustang GT, that do not have electric cooling fans. This came with a 75-amp 2G alternator. If I turned everything on at idle the voltage would drop as low as 13V. At 2000RPM it was the normal 13.8V.
Ford's replacement for the 2G alternator, the 3G, was designed for much improved output at idle. The 130-amp version puts out 80 amps at idle. (I've never found a specification for what the 75-amp 2G puts out at idle but I suspect it's around 20-30 amps) This sort of output at idle is important for cars with electric cooling fans, since those fans use quite a bit of power and are most likely to come on at idle.
I upgraded the Mustang GT with a 3G alternator when the 2G failed since it's an easy upgrade. Now I can turn everything on at idle and the voltage never dips below 13.6V.
Incidentally, I had a rewound 130-amp 2G alternator on that car for a while and the output at idle on that one was even worse than the 75-amp 2G I replaced it with. So the conclusion I came to is that an alternator needs to be specifically designed for high output at idle. The 3G is physically larger than 2G so it may be that the 2G simply isn't big enough to ever have good output at idle.
something i learned recently the hard way is there are many connectors to the battery and alt that can get corroded or dirty. i used 600 sandpaper and cleaned all the connectors, junctions, grounds, and pulled the hot wire off the alt and cleaned that too.
Volt meter now reads higher after startup and car feels like it's running better.
Volt meter now reads higher after startup and car feels like it's running better.
interesting. wnding alternators is something thats beyond me . i understand the theory, you can change the gauge of varnished wire to get more turns, or thicker gauge in the same area, but i dont think i could do that.
i stick to simpler things. my car on stock form puts out ab out 13.2v at idle. this is too low for me. my car has a simple 4 wire alternator. 1 power wire, 2 field control wires, and 1 voltage reference wire. i cut the voltage refeence wire and added 2 4 amp diodes in series with the wire. this dropped the voltage that the regulator sees by 1.2 volts. the regulator has to kick the voltage up by 1.2 to get back to what it percieved to be 13.2, which is now 14.4 (13.2 + 1.2= 14.4)
so a little trickery with 1 dollars wirth of radio shack parts has gotten me some prime looking voltage numbers. perhaps you might consider the same? that is, if its youre regulator thats the problem, and not the fact that youre alternator just blows.
It was just that the alternator blows, it wasn't a regulator problem. I had read somewhere that rewound alternators tend to have lower output at idle and this one sure confirmed it! That's why I replaced it with a 3G(along with the fact that the bearings on the rewound alternator went bad).
The 3G is the third alternator I've had in this car and it seems like it's going to be the last one.
So I have had:
OE 75amp 2G -- output sucks at idle
rewound 130amp 2G -- output really sucks at idle
OE 130amp 3G from a Taurus -- output at idle is great
I'd heard about adding diodes or a resistor to the voltage reference wire to get higher charging current, but the Ford voltage regulators seem to be set correctly, so I've had no need to do this. Plus they run the voltage reference wire all the way back to the battery which is where it's supposed to be connected--you want to sense the voltage at the battery, after any voltage drop in the wire between the alternator and the battery.
The 3G is the third alternator I've had in this car and it seems like it's going to be the last one.
So I have had:
OE 75amp 2G -- output sucks at idle
rewound 130amp 2G -- output really sucks at idle
OE 130amp 3G from a Taurus -- output at idle is great
I'd heard about adding diodes or a resistor to the voltage reference wire to get higher charging current, but the Ford voltage regulators seem to be set correctly, so I've had no need to do this. Plus they run the voltage reference wire all the way back to the battery which is where it's supposed to be connected--you want to sense the voltage at the battery, after any voltage drop in the wire between the alternator and the battery.
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