Powermaster Alternator

Having a alternator that is a little too large the extra parasitic drag is negligible. A large alternator running at 50% will have the almost same horsepower requirement as a alternator half the size at full output. An alternator running at full output will have y shorter lifespan than a lager unit at 50% of full output.

Heres my best guess on your electrical system load:
Cooling fans 20-40 amps
Fuel injection 10amps
Headlights/running lights 15amps
heater 5amps
wipers 3-5amps
fog lights/misc. 10amps
Right there is an 85 amp draw, you may not be using everything at one time but you should have the ability to with out drawing down the battery.

Also some alternator don't reach full output until 5000 rpm (at alternator) and the output at idle is around half of full rated output. Some alternator manufacturers cheat and give you the outputs specs at room temperature which are a higher than what you will actually get with it at under hood temps.

heres an output curve for the 10si series:

the alternator rpm is around 3 times what the crankshaft rpm is due to the diffrence in the pulley size, so at idle its around 2000rpm

 

Here is a little deal about Horsepower and alternators...in case anyone wants to know. In my line of work I have done some "odd ball" testing to see what made and cost power (I have a dyno in my shop) anyway...One week was dedicated to alternators...What started this is that all my friend who drag race were removing their alt to gain more power at the track...And I was wondering just how much they were really saving.

We went through many styles and amp rating. Most were shocked to find out that you average run of the mill alternator only cost them about 1 to 1.5 hp when charging hard....Of course...a drag car really only needs enough to power a few switches, an electric pump or two and the ign system.
We on the other hand like higher output alts...for obvious reasons.
There is actually mathematical formula to figure out how much HP a certain amp alt is taking from you.
If memory serves me...it goes something like this.
Volts*Amps= Watts
Then you take those Watts and divide them by 745.7 (that would be one hp) That will equal X amount of HP. This is the amount of hp PRODUCED by the alternator...Now...we take that amount and we multiply it by 15%...15% is a rough (but close) estimate of lost efficiency of the alt while making that power.
Then we take what hp the alt put out and we add it to the number we just came to by multiplying 15% and this will get you VERY close to what kind of HP your Jeep's high output alternator is taking...
Here's an example of a 100 amp alt used in the formula above.

14.5 volts*100 amps = 1450 Watts
1450 Watts / 745.7 = 1.94 Horsepower
So the alt is making 1.94 HP...we have to figure out how much HP it is costing us for it to make that 1.94 hp...because there is no free lunch.
As I said before...there is about a 15% efficacy loss from the power it takes to make the alt have 1.94...So...
we take 1.94 and multiply it by 15% 1.94*15%= 0.291.
That 0.291 represents wasted HP.
So you take the wasted HP and add it to the hp made by the alt.
0.291+1.94=2.23.

So...a 100 amp alternator will cause a loss of 2.23 horsepower when it is running full tilt. Meaning...using all 100 amps and charging 14.5 volts.

 

But if we were talking about an F-head or L-head that 2.25hp is a fairly decent percentage of gross HP

 

Yeah, if you're only running 3 to start with...that would take some of the zip right out of it.

1.44% loss on an f head.

 

High5, going back to your original Q... I have a PowerMaster 1-wire that I got from Baxter Auto Partsfor $75 (sale price + exch.). It's a 80-100, but the tag on it stated its real rating was 85-120 (which verified the salesmans statement that the PowerMasters run higher than advertised rates). Hook up was simple, as 1-wires tend to be. The main issue that I had (YMMV) was my mounting bracket was too narrow by 3/4". Easy fix tho, I cut the bracket in the middle, and shaped and welded a 3/16"X3/4" strap in.
I have more than enough power for what I have for lights, driving lights, radio, etc. I will be comfortable adding that wench (oops, I mean WINCH) later.
Happy Buying ...

 

Interesting on that HP breakdown because I had been told many years ago that a 60 Amp Alt at full load output would suck up about 7 Hp. Thanks for the info.

 

That's funny...that is the exact number I have been told myself...and is the number that all my buddies had been told too (before the testing).
Wonder where that started at?

 

Not intending to steal this thread, but... I did a single wire conversion on my 74 years ago. I am not sure what I did wrong, but the alternator won't start charging until about 2k rpm. Then it charges fine unless the engine speed drops below about 500 rpm, like when I almost stall it starting out. Then it is off line until I reach about 2k rpm. The drag is that this is a ranch/hunting jeep and most the time is idled around well below 2k rpm. Ideas?

 

The single wire uses a different internal reg. to stop this.
A 2 wire has one wire called the exciter.
Which triggers the charge when volts are low.

If you do a search here you can find tons of info on it.

 

You know....I have a single wire alt myself...and mine does need a quick blip of the throttle to excite itself...but mine does not stop charging once it has been exited until I shut it off. Then again...I'm not sure how many times my engine gets under 500 rpm. Either way...it does not sound as if it's working up to snuff.

 

I wish I could remember where I purchased it. Seems that I paid big bucks for some fancy one that charges at low RPM to help keep up with my winch. I have been thinking that maybe if I change the pulley size on it, I can keep it charging at low RPM?

 

Last night I noticed when I had the lights on, heater on, Jeep on, and the fans kicked in the voltmeter would drop to 12.5. Is that too low???? Should I upgrade to a better alternator now???

High5

 

While 12.5 is not draining your battery...your alt is most likely working at 100%. So if you added just one more item...it would start to discharge the battery. I would say yes...you should get a little bigger alt.

 

It was at idle. I will try again with some throttle and see what happens.

Thanks

High5

 

I need some help understanding the amp meter vs volt meter thing...I'm not disagreeing with the "you need an amp meter" theory. I think I just don't quite grasp what is being said....Here is how I personally see it...tell me if it's wrong.
If a volt meter reads 14 to 14.5 volts....that means everything is charging correctly...a Volt meter is telling you the actual result of what the alt is doing. So...if an alt can only keep the battery at 12.5 volts with everything on...that means your alt does not have enough "juice" to make the battery stay at 14.5 volts.
An amp meter will tell you how many amps are being pulled from the alt. So what is it that the amps tell you that volts will not is my question.
If it won't keep the batt at 14 or close...then you know that your charging system is not quite enough to run all your stuff. If the charging system fails...then you will see it...the voltage will drop and continue to drop. If it is over charging...you will see the voltage rise to high.
An amp meter on the other hand...it measures flow from the alt only, when the battery is charged and there is no pull on it...the amp gauge goes back to zero...What is the belt was slipping or the alt went bad...it would measure zero wouldn't it? So really...you would think everything was just fine.

But forget all that...
What I would like to know is what amps tell you that volts won't. If his system drops to 12.5...then that is a large percent of amps being used...because the alt won't charge the 14 volts. How will knowing the exact amount of amps being pulled from an alt that won't charge 14 volts be useful in whether or not he should buy a larger alt?

 

Think of it like a garden hose. Volts is the pressure pushing the water through the hose. Amps is the water that is flowing to do whatever work needs doing. You have to have enough volts to push the amps. You have to have enough amps to actually do the work. You have to have both to have an operable charging system to keep up with demand. If the alternator can't produce enough volts, or pressure, the amps can't get to where they're going to do the work. If the alternator can't produce enough amps to do the work then you are not going to be able to do the work.
Disclaimer: this is a highly simplified explanation so please don't beat me up too much!R)
Nickmil

 

So let me ask you this...If you only have a volt gauge...and it reads below 12 volts with all of your stuff on...Do you need an amp gauge to tell you that you need a bigger alt?
If you're only charging..say...11 volts according to the volt meter.....would that tell you that there is something wrong with the charging system...like, not enough...or does your gauge only reading 11 volts not mean anything? Do you need an amp gauge to let you know that 11 volts is not okay?

 

http://www.madelectrical.com/index.shtml

Check out this web page for alternators and how to wire them correctly. Enough said, I think the good read here will explain what you need to do.

cw pup