I just installed a new 1 wire alternator with one of those mini regulator on the back. I have underdrive pulleys. My guage is reading only 10 Volts. Can I get my alternator to excite before 2000 RPM?

 

Correct me if I'm wrong, but once you rev it up once, doesn't the alternator kick-in or does it only charge abobe X rpm?

 

I thought you just had to blip it over 2k and it would charge regularly

 

Sometimes underdriving will lower the alternator rpm's too much and it will not charge. Most of the modern one wire's have a tad smaller pulley compared to the ones of the day, so underdriving a one wire may prevent it from working at all (in the idle rpm range). There should be a test chart with the alternator that will show where it starts to work and where it maxes out. You can do the math and see what size pulley you need. Normally a 3 to 1 ratio (engine rpm 800 = alternator pulley rpm 2400) is about the normal, but keep in mind that some one wire's will not turn on untill they hit the 3000 rpm mark, this is only a few and normally most will start working at 2400 (that test chart is really handy). On the flip, the alt rpm needs to be kept under 18000 (race engines) and on these high winding engines you can over do it, and damage the alternator.

 

Why are you are running under drive pulleys? They are meant for cars with lots of pumps running off the crank. You only have a water pump and an alt so your net gains will be close to nothing but your giving your self all sorts of problems. Put a nice set of stock pulleys back on.

 

I have a 140 Amp PowerMaster one wire alternator on my car and yes you need to exceed 1200 RMP in order for it to kick on. You do not want to let your car sit idling for any long period of time. I don't think you have to worry about exceeding the 18000 RPM range. These are some facts off the PowerMaster web site:
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I noticed that my Powermaster one wire alternator has to be "revved up" to get the alternator to come on. Why?

A one wire alternator has a turn on point (sometimes called cut in, which is typically 1200 engine RPMs). This is the speed where the internal sense circuitry connects the battery to the voltage regulator, thereby turning the alternator on. Once the voltage regulator turns on, the alternator will remain on and charging until the engine comes to a complete stop. If the engine idle speed and pulley ratio combination do not allow the alternator to come up to this point during starting, the engine will have to be revved up to turn the one wire alternator on. The sense circuitry in the one-wire regulator can be bypassed to excite the alternator as soon as the ignition switch is turned on. This is called three-wire operation. This means the alternator will not be dependent on reaching a certain turn on RPM.


Will aftermarket underdrive pulleys (power pulleys) affect the output of the alternator?

YES, especially when using a one-wire alternator. Changing the pulley ratio of the alternator by slowing it down will generally keep the one wire regulator from cutting on. This may also produce a low voltage problem at engine idle speed, depending on the amount of reduction. Powermaster alternators are tested with a 3:1 pulley ratio in mind. This is the recommended street pulley ratio, and the ratio used in most OE applications.

 

"I don't think you have to worry about exceeding the 18000 RPM range"...........Hmmmmmm.......
I think you "DO" need to worry about this, and size the pulley system to keep the alternator working in the rpm band you plan to run. I often break 7200 RPM's in one of the cars, and if I done the math right, the alternator would be turning 21600 at a 3:1 ratio and "I" would worry about something flying apart. It sounds like for your purpose, LCC has given some good advice.

 

I think we need to qualify what type of car he has and how he plans on using it?
A friend of mine whose an electircal engineer for Ford was telling me that most alternators are good for 18000 RPM. Max ratio in a road car is 3-1 but for a race car reving past 7K 2.5-1 is a good guide for longevity of the brushes and bearings.

 

It is a street car. I had no problem with the charge until I switched to the 1 wire. I have run the pulley for 3 years with no problem. I upgade to a 100 amp from a 70 amp. I need to go thru and test the output. Has anybody ever done the bypass to have the alternator trip when the engine starts?

 

Post #7 "size the pulley system to keep the alternator working in the rpm band you plan to run", does'nt matter what type of car, the alternator needs to work within the limits of his engine RPM's, both high and low, and meet the demands placed on it by the electrical system (ie high wattage amps, halogen lamps, other goodies).

Post #4 "the alt rpm needs to be kept under 18000 (race engines) and on these high winding engines you can over do it, and damage the alternator". Kinda said that, as a personal rule, I like to keep them well under the 18k mark. Most often the alternator will supply all the amps you need at lower rpms (a good battery is a must though).

"Gunnerdog" I'm not sure I know what you mean by "trip" when the engine starts.
Do you have a copy of the test chart, it should have came with the alternator? How many wires come off the plug? One way that you may check is to use a volt meter and see when it starts to charge (engine rpms). There may be another problem.