Charging battery with alternator

[Soundguy]

Whenever I jump someone off, I always do that. I hookup my cables and let it run 10 minutes, then actually shut my truck off before they jump. don't want my alternator to see that .001 ohm load of that starter on their vehicle..


soundguy

 

[Keoke]

I looked this up. This link Alternator Output vs. Engine RPM
Shows that at 575 rpm engine speed the output of a 63 amp alternator is only 16 amps. Yes they are better than generators, but they do drop. At idle and a few loads on you may be discharging your battery.

Hi, an alternator is a three phase unit a dc generator is a single phase unit. So, one shaft turn on an alternator cuts thru three magnetic fields and can produce three times as much current as a single phase dc unit.
The reason 80/100 amp alternators are common today is beacuse we need a lot amps at idle so that we can run almost all electrical loads from the alt and not the battery when sitting at a light.
This trend started when we switched over to electric fans for cooling radiator and A/C became almost standard on most vehicles.
cheers,

 

[BobRip]

how many cars you got that idle at 575 rpm?

all my vehicles are around 800.

specs i see show up to 60% of rated amps at normal idle speeds.. least a 10/12SI gm does..

soundguy

Just tested my Tundra V8 idle using my OBDII COMPUTER. It was just below 700. Sorry to be so picky. My points are.

1. Alternators are pretty tough and they take care of themselves pretty well. I have had many go to over 150,000 miles and still counting.

2. Do not expect full current at normal idle.

3. It is a lot cheaper to charge a battery with a charger than a large gasoline engine. It saves wear and fuel cost. If you got a charger use if, if not use the alternator.

 

[Johnp33]

When you are boosting a low battery, I also leave it connected for a while before starting. I use my multimeter to check the voltage before I connect it. When you are boosting a vehicle, your boost battery supplies very little amperage, what it supplies is voltage.
If you have a very dead battery that is why it will not start, the cables can not get enough amperage threw the cables to get the voltage up to at least 9.6 volts while cranking to allow it to start.
I enjoyed the talk about GM. I have a Duramax and everything is always fully covered. Those new Fords with the 6.7's have a fuel filter that allows water threw it, it destroys the fuel system, it is only between $8,500 and $10,000 in parts. It is not covered by warranty period. Go on a ford enthusiast site and look it up.
And if you want a vehicle with a great place to access a battery, that would be a Chrysler Intrepid you have to remove the tire. and the alternator you have to lift the motor, some you need to remove the radiator. 2.5 hours if you have done it before, and 5 if you have not.

 

[EE_Bota]

Thanks, I was searching for a good link and saw that one you supplied. I am rather skeptical of what searches turn up, just wondering if anybody here on TBN had real life experiences with the situation. The part that most interests me about the issue is just how much charge a jump start puts back into a low battery.

I cant' tell you how much charge a jump start puts into a battery..but it can be right considerable. Many times I have seen that when the cables are first connected, the lights will dim in the donor car, but the receiving car won't start.
Within around 5 minutes, it will start.

Based on the spark I see when I connect, I am guessing around 65 amps. It could be higher, and I could be badly fooled. If we knew the resistance of all the components, we could calculate it.

I forget the numbers, but by the time a battery drops to (say) 12 volts, it is mostly discharged. That difference between 12 and 12.6 volts represents most of its charge.

I have never ruined an alternator charging a flat battery...because I make sure it has descent charge before the start.

Batteries left loaded to depletion are not bad batteries. They are depleted (and harmed some by that.) They will aggressively absorb charge.

But many flat batteries are bad batteries..if you hook them to a charger, you will see that they charge up much quicker than the lack of charge would have indicated was possible. Those batteries have lost their capacity and cannot hold much charge. Therefore, they may not represent much challenge to an alternator.

When I use jumper cables, I typically let the cars sit connected for around 5 minutes minimum before I attempt to start. This practice may have saved me some alternator problems. Frequently, I will let them stay connected for around 3 minutes so both systems can charge the weakened battery, and to make sure that the receiving car is warm enough not to risk stalling, forcing me to repeat the process.

 

[Johnp33]

My multimeter has a min - max function and will display the voltage the receiver battery goes to. The one I am interested in is the minimum. If while cranking you do not have 9.6 volts a lot of vehicles will not start. I always leave my vehicle running.
When I am boosting a vehicle, I normally leave the cables connected for about 5 minutes it allows the boosted vehicles battery to get the added charge from the donor vehicle. It also allows the boosted vehicles alternator to get threw the highest out-put cycle at a lower rate. They really do get hot.
I have very good cables, some day I will connect the clamp meter and see how much amperage goes threw the cables on a start.

 

[Keoke]

Whenever I jump someone off, I always do that. I hookup my cables and let it run 10 minutes, then actually shut my truck off before they jump. don't want my alternator to see that .001 ohm load of that starter on their vehicle..


soundguy

Hi, the amount of watts a starter draws depends on the size,comp.ratio and friction of the engine that needs turning over. Most fully charge batteries dip to 10.2 to 10.4 volts while cranking over. Battery cold cranking amp rating plays a big role here. What any starter needs is watts so the higher the static supply voltage while cranking the lower the amps will be. Amps generate heat and cause voltage drops so it's best to get the watts needed from voltage.
Soundguy's idea of turning off his vehicle when lending a boost is a smart one.
Voltage regulator from boost vehicle seeing a 10.2/10.4 voltage signal will go to full charge for as long as it sees it. This is not conducive to long electrical component life.
While it is true that the dead cars electrical system will suck up most of these boost amps it is still a good idea not to tempt fate.
cheers,

 

[JDgreen227]

I remember in the older days the advice for jump starting usually told us to turn off the radios and all electrical items in the car being boosted, the idea was that by not having lights, etc. on, the battery being boosted would have more current to send to the starter, and by having the radio off, it wouldn't be "damaged by a current surge"....:laughing:

Has anyone ever known about a radio that was left on and was damaged? I never heard of that happening.

 

[BobRip]

Just tested my Tundra V8 idle using my OBDII COMPUTER. It was just below 700. Sorry to be so picky. My points are.

1. Alternators are pretty tough and they take care of themselves pretty well. I have had many go to over 150,000 miles and still counting.

2. Do not expect full current at normal idle.

3. It is a lot cheaper to charge a battery with a charger than a large gasoline engine. It saves wear and fuel cost. If you got a charger use if, if not use the alternator.

I noticed that when I turn on the AC the engine rev go up about 100 RPM. So this would give more alternator output.

 

[Soundguy]

Just tested my Tundra V8 idle using my OBDII COMPUTER. It was just below 700. Sorry to be so picky. My points are.

1. Alternators are pretty tough and they take care of themselves pretty well. I have had many go to over 150,000 miles and still counting.

2. Do not expect full current at normal idle.

3. It is a lot cheaper to charge a battery with a charger than a large gasoline engine. It saves wear and fuel cost. If you got a charger use if, if not use the alternator.

agreed on all points.

oem alts seem to last the longest.. replacements and rebuilds from there seem to be a roll of the dice.

I don't expect max rated output at idle.. I expect enough output at idle that it will handle all of the vehicles rated functions without having a discharge situation at idle.. thus why you see a car with 90a or higher alternators.. that way they can idle and still put out 45+ or higher amps..

a bat charger is better if ya got it.

if stranded in a desolate area and you got a jump pack and it will get you going.. you do what ya gotta do..

soundguy