Is there such thing as too much Amps?

[SR77]

I am looking into buying a new alternator for my 96 5.0L Explorer and am interested in the 200amp one from mralternator so I don't have to worry about adding accessories down the road. My question is, my truck is still stock, so is the such thing as having to many amps for the alternator? Can the 200 amp alternator be installed on a stock explorer without any problems, like damage to the battery or blowing fuses or electrical fires etc...? Sorry if these question sound kind of dumb, but I am still learning about electrical/charging systems and i just don't want to do any damage?

Also, where can I find the specs on the alternatorrs like the 200 amp one and the stock one etc.. I hear people say that even though the 200 amp is better it has a worst idle output and that idle output should be no less then 55amps. Where can i find the specs on them so I can see their ratings? Thanks for all the help

 

[Billy177]

no you can't have too many amps the voltage regulator will only take what it needs. it will however not put out at idle as much as as the stocker i have found. you can also get a 130 amp from a limited that is a direct bolt on

 

[wilkin250r]

First, to add to my credibility, I am an Electrical Engineer. To fully explain, this is going to be a long post.

Electricity is like water in many respects. Imagine a water tank, and you pressurize the water tank to 150psi, but you haven't attached the hose. So, you have 150psi of water pressure just sitting there, waiting to be used.

Now, attach the hose, but only open the nozzle a little bit. Now you have a thin stream of water. It takes you 1 minute to fill a 1 gallon jug. If you increase the pressure in the tank, you get more water out.

How about if you keep the pressure the same, but open the valve more? You get more water out, right? The valve represents resistance.

Here is a fine point that applies to your particular situation. When you pressurize the water tank to 150psi, you don't automatically start flowing at 200 gallons per minute. The flow depends on the valve attached to the tank. If you only open the valve a little bit, you only get a little bit of water out.

What if you have a device that requires 150psi of water pressure? Well, you pressurize you tank to 150psi, and hook up your hose. The internal resistance of the device will limit the flow rate to whatever it needs, whether it is 2 gallons per minute or 100 gallons per minute.

So how does that apply to electricity? Voltage is pressure. The voltage is like the 150psi of pressure in the tank. If you don't connect the hose, it just sits there.

Amps are the flow rate. Just because your water tank CAN supply 100 gallons per minute, that doesn't mean it HAS TO all the time. If you flow too much, you can't keep your tank pressurized at 150psi, but if don't only flow 2 gallons per minute, you can still limit the pressure in your tank to 150psi.

The valve attached to the tank represents resistance. For a given pressure (150psi) by changing the resistance, you can flow more or less.

They are related by Ohms famous law of I=V/R where I is current. Current equals voltage divided by resistance.

So, you have a 200 amp alternator, which means your alternator is capable of supplying 200 amps without burning up, but that doesn't mean it ALWAYS has to supply 200 amps. It will be happy as a clam even if it neve went over 30 amps.

Your voltage is constant, between 12 and 14.4 volts, so that's an easy one.

The resistance is determined by your accessories. Your lights, your radio, electric fuel pump, power windows, ect.

So, in case you're falling asleep after reading this, the basic summary is: You're alternator produces a voltage, and the current that comes out is dependent on the resistance. As long as you don't connect so many devices that you exceed 200 amps coming from the alternator, you'll be fine.

 

[SR77]

thanks for the replys, especially wilkin250r for typing all of that. It definitly clears some things up. So I guess the voltage regulator regulates the volts output and the accessories or "loads" control the current output. Correct? The reason I am asked this and am thinking about a 200 amp alt. is because the one I have on there now will drop a good amount when at a stop with the heater, defroster and radio on. So I figured that i might as well add a more powerful alt. on now even though my truck is still stock for future accessories like a new stereo system.

My last question is, if my stock 130 alt. drops volts to where the truck almost stalls at idle with some accesories, will the 200 amp alt be even worst at a stop since i was told that it has a lower idle output? I am starting to think that a 200amp alt will not really solve my idle voltage problem.

 

[wilkin250r]

Absolutely. The 200 amp alternator won't solve your problems.

Here's the basics of how it works without too much detail.

When a wire is moved in a magnetic field, you get a VOLTAGE at the two ends of the wire. If you have mulitple wires, you can connect them together in a series to mulitply the voltage. Well, when you connect wires together in a series, you end up with a coil of wire with several loops. Let's simplify this, and pretend we have 12 loops, and each loop generates 1 volt each. Our total voltage is 12 volts. This is obviously an oversimplification, but I'll explain in more detail later on in this post.

Now if you connect some electrical device that has a resistance of 6 ohms to the two ends of your coil, you will get a current of 2 amps, based on Ohms law of I=V/R (current is equal to voltage divided by resistance) Now, this 2 amps needs to make a COMPLETE loop, so it goes through the electrical device AND the coil of wire. This is where your 200 amp rating comes in. Your alternator is built with wire big enough so that your alternator won't overheat up to 200 amps, that's all the rating means.

So how do they accomplish this? They use larger wire, less heat buildup. But there is only so much space in an alternator, so in order to get bigger wire, you need to decrease the number of loops in your coil to get everything to fit. That's where YOUR problem comes in.

Remember that oversimplification? The voltage depends on three main things. The strength of the magnetic field, the speed the coil is moving, and the number of loops in the coil. If you decrease the number of loops to fit bigger wire, you will decrease the voltage.

This isn't a problem at high RPMs, because the speed is so high that you are actually producing about 60 volts, but you have a voltage regulator to keep it at 14.4 volts. However, you can only regulate a voltage DOWN, you can regulate it up. If you're alternator is turning so slowly that it is only producing 11 volts, you can't regulate it UP to 14.4 volts. This is your problem at idle.

So, the 200 amp alternator will probably make your problem worse, because in order to increase the current rating, they had to decrease the number of loops in the coils, which means less voltage at idle.

 

[wilkin250r]

So I don't think the 200amp alternator will solve your problem. So how DO you solve your problem?

It sounds like your battery may be weak. Even if you turn your car off, so now your alternator is producing ZERO volts, your battery should be able to run all of your accessories for at least a half hour before dropping voltage, and then when your alternator voltage increases again, it will re-charge your battery.

So even if your alternator voltage drops, your battery should make up for it. It sounds like your battery isn't making up for it.

 

[wilkin250r]

Originally posted by SR77
thanks for the replys, especially wilkin250r for typing all of that. It definitly clears some things up. So I guess the voltage regulator regulates the volts output and the accessories or "loads" control the current output. Correct? The reason I am asked this and am thinking about a 200 amp alt. is because the one I have on there now will drop a good amount when at a stop with the heater, defroster and radio on. So I figured that i might as well add a more powerful alt. on now even though my truck is still stock for future accessories like a new stereo system.

By the way, this info is absolutely correct, the load controls the current.

Most loads are simple, and only have a simple fixed resistance associated, and are designed to operate at a given voltage. I'll use a light-bulb as an example, like the one found in your house. It operates at 120 volts, and a 60 watt light has a resistance of 240 ohms. Calculate the current with ohms law, I=V/R

I=120Volts/240ohms. I=0.5 amps

It's designed to operate with 0.5 amps going through it. If you have more than 0.5 amps, it will overheat. Since you can't change the resistance of the light bulb, the only way you can get more current is to connect it to a higher voltage.

So as long as the voltage is correct, everything is fine and happy. If you have a 12v motorcycle battery, you can jumpstart it with your car, because it's the same voltage. The car battery won't "overpower" the motorcycle battery. As long as the voltage is the same, everything is happy.

 

[Billy177]

it sounds as if your alternator is crapping out and that also killed your battery i would go with the 135amp and a yellow top optima for your setup

 

[SR77]

thank you wilkin250r, you have been a great deal of help and knowledge. One last thing if you don't mind. I am gonna go purchase a dig. voltmeter to play with and test, so can you tell me how i would go about testing my battery and alternator and what the readings should be with on both with the truck running and off. Thanks again for all you help and time.

Billy177, I might just replace the alt with a stock 130 amp, but why do you say the yellow top. The yellow top doesn't actually hold more amps or volts does it? I thought it just could deep cycle more often that a red top could without going bad. Plus the red top has more CCA.

 

[wilkin250r]

You don't want a deep-cycle battery, because you're not deep cycling.

Deep cycling is when you use the battery as a primary source of power for extended periods of time before recharging. Like the battery on your camper-trailer, or the battery for your trolling motor.

You are not deep cycling because you use your battery to start your engine, but as soon as it's runninga your battery begins re-charging.

You can do all tests across the terminals of the battery. Keep in mind, this is a general guideline, not absolute.

Before you start your car, measure across your battery. You should measure between 12.5 and 13 volts. Turn on your heater, radio, and headlights, (but without the engine running) and you should measure at least 12 volts. This will test your battery.

Turn the heater, headlights, and everything else off. Start the engine. Now you should measure about 14.4 volts across the battery terminals. Turn on the heater, radio, headlights again. You should measure at least 13.5 volts. If it is lower than 13volts, disconnect the battery while the engine is running. Check the voltage across the CABLES (not the battery) and see if it changes.

In case I forget to check the forum, email me at erikwilkin@hotmail.com if you get any funny readings, and we'll see if you need to replace your alternator or your battery.

 

[Billy177]

do not disconnect the battery with the engine running it will cause the alternator to go wide open and may burn out the diodes.

 

[wilkin250r]

Originally posted by Billy177
do not disconnect the battery with the engine running it will cause the alternator to go wide open and may burn out the diodes.

How so?

I'll admit, I'm not an expert automotive mechanic, but I know electricity, and I don't see how it can harm anything, and I've done it on many occasions myself. The only time you are going to burn anything is if you pull too many amps, or over-voltage. The voltage is regulated, so that leaves amps. If you disconnect the battery, you'll actually pull LESS amps, because you aren't charging the battery.

 

[BBQ_HotDogs]

This is good info here. Is this why the sterio shops sell us special deep cycle batteries when we are running allot of amps and acc's?

Question - I am having installed right now allot of sterio equipment to my explorer. A short breakdown would be a head unit, changer, 4 big amps, many speakers and subs, also to add DVD equipment after this install, only if I like it first. LOL. But how do I know if the deep cycle battery is enough? Do I need more batteries or larger ones? How do I know that the one red wire they run to the deep cycle battery is really charging it?

Thanks,
HotDogs

Originally posted by Billy177

do not disconnect the battery with the engine running it will cause the alternator to go wide open and may burn out the diodes.

I used this method all of my life, it was the way us old guys used to check to see if the alternator worked or not. Never heard this before.

 

[Billy177]

i would definatly get a deep cycle for your setup that big red wire is the wier for your amps probrally 0 gauge about the diamiter of a dime. that soes not charge your system, the wire from the alt charges the battery with that much your stock alt just wont cut it i forget the site but there is an alternator with high amps and real good idle output. i would also get at 2 capaciators so your lights don't dim when the subs hit and the angine stumble

 

[wilkin250r]

A deep cycle battery has it's benifits and its drawbacks.

If you and your friends are often gathered around, and you crank up your stereo without starting your car, then you really need a deep cycle battery.

However, if you never have your system on without your engine running, then there is no need for a deep cycle battery.

Now, it appears that the stock stator is 130 amps. If you have a huge system and you're pushing 2000 watts, at 12 amps that equates to 167 watts. Also, thats OUTPUT. If you account for about 85% efficiency across the amp, you're looking at nearly 200 watts just for you audio, not to mention you still need power for your headlights and such. You would need an aftermarket high-output stator.

So, unless you are running your system without your engine on, there is no need for you to fork out the money for a deep-cycle battery.

 

[wilkin250r]

I'll explain the capacitors.

Let's just pretend that you have a 1000Watt (peak power, not RMS) amp to your subwoofers. Your amplifier is designed so that it only pulls power when it needs it. So when there is no bass, your amp is sitting at low power draw, like 6 or 7 amp. Then suddenly the bass hits, and you amp changes from drawing 6 amps to suddenly drawing 80 amps.

Unfortunetely, for such a HUGE jump, your system can't react that fast. Yes, your system can supply the 80 amps, it just can't CHANGE as fast as you need it to, for reasons that would take at least 200 pages to explain (basically, the entire length of an Electronics 101 textbook) The problem isn't the amount of current, it's the CHANGE in current that is the problem. The result is, for that instant that you are trying to draw 80 amps, it will draw it from the ENTIRE electrical system, rather than just the alternator. This will momentarily drop the voltage everywhere. This is why your lights will dim when the bass hits.

The answer? A big capacitor. For reasons that are also lengthy to explain, a capacitor CAN react in the blink of an eye. As fast as you want it. A capacitor can go from 0 amps to 500 amps in the blink of an eye, as long as it doesn't have to sustain that 500 amps for an extended period of time. Luckily, it doesn't, because by the time your capacitor runs out of juice, the rest of your electrical system can catch up and supply the power you need, and re-charge the capacitor at the same time so the capacitor is ready for the next big bass hit.



We should change the title of this thread to "basic electronics"