school me on car alternators

[steveo3002]

if we said a car uses 10amps to run and you have 100 amp alternator

on a jump started car -how /what says how many amps recharge the battery , and how would you find out like where your home trickle charger might be 5/10 amp for example

would the same car with 200amp alternator charge twice as fast? or just more headroom for lights and gadgets

no particular reason to ask...just something i dont know the answer to

 

[the snooper]

The regulator sorts out what goes I to the battery and a higher out put charges faster and can power extra stuff such as spot lights without drain the battery aswell

 

[rtbcomp]

The battery and electrics take what they need, so if the demand is 20 amps and the alternator is 100 amps, the current draw will be 20 amps, the extra 80 would be headroom as you say.

On the other hand, if the demand is 120 amps, the extra 20 will be supplied by the battery until it becomes discharged to the point it can't provide sufficient current. The regulator will stop the alternator from being overloaded by reducing the output voltage, so lights will go dim and the electric things will gradually stop working.

The current draw is what the car needs to function plus any charging current the battery may need, so if you have trouble starting in winter and discharge the battery, and then run with all your lights on you may hear the fanbelt squeaking. This usually happens after a difficult start and the driver revs the engine.

Your home trickle charger should say on it what current it can supply, again this is the maximum, the state of the battery determines the actual current drawn.

 

[steveo3002]

yes so given my example of the car using 10amps to run and 100amp alternator , what goes to charge a flat battery ? 80 amps would surley blow it up ?

the regulator regulates volts doesnt it? what im getting at how can i find out how fast and what rate it charges a dead battery

 

[octo0072000]

varies due to state of battery will be different on every car high amps to start tailing off as battery gets charged

 

[the snooper]

yes so given my example of the car using 10amps to run and 100amp alternator , what goes to charge a flat battery ? 80 amps would surley blow it up ?

the regulator regulates volts doesnt it? what im getting at how can i find out how fast and what rate it charges a dead battery

Fit an amp meter, the load after starting is high this is why you often hear belt squeal when starting from cold, the reason is worn or badly adjusted belt but the extra load is shown through it

 

[rtbcomp]

yes so given my example of the car using 10amps to run and 100amp alternator , what goes to charge a flat battery ? 80 amps would surley blow it up ?

the regulator regulates volts doesnt it? what im getting at how can i find out how fast and what rate it charges a dead battery

No it wouldn't blow up, the battery takes what it needs, it's self regulating if you like.

The reg does regulate the voltage. As the load on the alternator increases its voltage tends to decrease, the regulator senses this and increases the field current to put the voltage back to where it should be. Vice-Versa if the load decreases.

If you want to measure the charging current install an ammeter.

 

[wookie]

yes so given my example of the car using 10amps to run and 100amp alternator , what goes to charge a flat battery ? 80 amps would surley blow it up ?

Ideally you shouldn't charge a small capacity battery at high amps, for example a 200Ah battery that is flat will be quite happy getting 100Amps shoved into it while a 50Ah battery will be less happy BUT because the the charge current reduces as the battery voltage rises then the smaller battery's voltage will quickly rise causing the charge current to fall.

You could fit a ammeter to measure the current if your really that interested but just be careful that the feed from the battery to the starter motor doesn't go through your ammeter because it probably will not like the current draw when starting.

You could fit the ammeter in a few different locations depending on what you want to measure, i.e. total output from alternator, whether the battery is charging or discharging etc etc

Also another headache to consider is unless your ammeter uses an separate shunt (to sense the current) then you will need to run thick cables to your ammeter unless you like having the ammeter fitted under the bonnet of your car by the battery

 

[steveo3002]

dont want to fit an ammeter just wanted a better unstanding what happens

 

[rtbcomp]

The current it takes will depend on the characteristics of the battery, and how fully it's charged.

You really need to get a graph of remaining battery capacity (ampere-hours) vs Charging current from the battery manufacturer. Such a graph would have several curves, one each for different charging voltages.

 

[Mee]

You also have to remember that a 100 A/H battery wont give 100 amps for 1 hour as it may give 100 amps but for only a couple of minutes as they are rated on the 20 hour rating, this means you divide the rating by 20, for a 100 amp battery it means you can get 5 amps out of it for 20 hours to get the full 100 amps out.

You also have to remember that a charging battery isn't consistent, the more charge a battery has in it, the higher charge rate it will accept; hence with a flat/low battery on a charger you will see it trickle charge for a period of time and the battery charge will rise.

 

[123hotchef]

that is why my fan belt is squeaking for 10-20 seconds in the morning

 

[DrDeAtH]

that is why my fan belt is squeaking for 10-20 seconds in the morning

Nope, your belt is worn and as such isn't tensioned correctly...
Re tension the belt if it looks ok, otherwise replace it. Flat batteries in winter aren't fun....

 

[123hotchef]

it has 2 belts on it only one slips cant tension it any tighter new belts have been in the garage for a year now!

 

[colnerov]

it has 2 belts on it only one slips cant tension it any tighter new belts have been in the garage for a year now!

Hi, That's probably due to manufacturing tolerances the two belts are not the same size, you need to investigate getting a matched pair. When I was at the bus company the Atlantean double deckers had three alternator belts and we used to get matched sets. Failing that you could see if your local motor factors would indulge you in finding two belts that were not too different, although unlikely.

Colin

 

[wookie]

Take both belts off and compare, one has probably stretched and is now slightly longer than the other, ideally you'll need to buy 2 brand new belts that are a matched pair.

Sometimes it's a combination of one set of pulleys slightly more worn than the other as well as one belt slightly stretched, in this scenario you can get an improvement by swopping the 2 belts over, been there, done that, got the T-shirt

 

[123hotchef]

Hi, That's probably due to manufacturing tolerances the two belts are not the same size, you need to investigate getting a matched pair. When I was at the bus company the Atlantean double deckers had three alternator belts and we used to get matched sets. Failing that you could see if your local motor factors would indulge you in finding two belts that were not too different, although unlikely.

Colin

Hi Colin, Funny It has only just started happening I have a pair of belts to go on when I can find the time to do it actually I have 4 belts as I have 2 L200s I also have a digital volt gauge and the V does drop when it slips but 10-20 seconds the slipping stops

 

[123hotchef]

Take both belts off and compare, one has probably stretched and is now slightly longer than the other, ideally you'll need to buy 2 brand new belts that are a matched pair.

Sometimes it's a combination of one set of pulleys slightly more worn than the other as well as one belt slightly stretched, in this scenario you can get an improvement by swopping the 2 belts over, been there, done that, got the T-shirt

I will replace them both silly not too

 

[Mee]

Hi Colin, Funny It has only just started happening I have a pair of belts to go on when I can find the time to do it actually I have 4 belts as I have 2 L200s I also have a digital volt gauge and the V does drop when it slips but 10-20 seconds the slipping stops

With Mitsubishi's you need to deglaze the pulleys before fitting new belts, the pulleys become so smooth they are like an ice rink, take some fine wet and dry and buff them in a circular motion to deglaze them as this allows them to bed in and get some bite.

 

[123hotchef]

With Mitsubishi's you need to deglaze the pulleys before fitting new belts, the pulleys become so smooth they are like an ice rink, take some fine wet and dry and buff them in a circular motion to deglaze them as this allows them to bed in and get some bite.

its going to be hard to get wet n dry in there to buff them up