Original Poster XJeff, your are forgetting to post a key portion of your alternator quote.
See below. All of these ratings are taken at 1800 alternator rpm and with the alternator HOT which for the calculation used is roughly 600 engine rpm. I see plenty of people at shows sitting at idle in the 12v range. Why is this? because they purchased a small case hairpin or other small case alternator (it may have been only fitment option) and they want 300+ amps. You cant cut the cake and pick the piece. You either get peak output, or you get good idle. To get a high peak output like everyone wants out of a small case hairpin you sacrifice idle. The ONLY way to make up for this is to spin the alt faster.
On a sedan such as your stratus it more than likely has a crank pulley around 6 inches. so to increase our pulley ratio we need to make a smaller alternator pulley. You can only go so small on the pulley. Lets say we can work a 1.75 inch pulley on there. If you have a 6 inch crank pulley and a 1.75 inch overdrive alternator pulley your pulley ratio is 3.42. Lets say worst case scenario your hot idle is 600. We do 600*3.42 to get alternator rpm at idle. Which is 2057 rotor (alternator rpm).
We look up at that DC Power chart posted above which is very accurate. Even at 2057 alternator rpm you are barely turning the alternator on. You will notice voltage fluctuation at idle with the 320. That is why I suggested going with the 240. You get a reliable idle as well as boosted peak output.
Please note that Below it states that more than likely your car will have better performance. These specs are worst case scenario and to emphesize to uneducated customers that Bigger more peak is not always better because you are sacrificing low end.
***All Alternator Idle ratings are measured at 1800 Alternator RPM. If your vehicle has a 3:1 pulley ratio (6" diameter crankshaft and 2" diameter pulley) this makes the engine rpm roughly 600. This idle rating covers 99% of vehicles made and more than likely, you will see higher ratings than we have posted.***
***All HOT ratings are measured at 6000 Alternator RPM. If your vehicle has a 3:1 pulley ratio, this makes the engine rpm roughly 2000. ***
***These ratings are much lower than our competitors who rate their alternators at an idle speed of 2500 Alternator RPM and a peak speed of 8000 Alternator RPM. These equal 833.33 idle engine rpm and 2666.67 engine rpm. ***
See below. All of these ratings are taken at 1800 alternator rpm and with the alternator HOT which for the calculation used is roughly 600 engine rpm. I see plenty of people at shows sitting at idle in the 12v range. Why is this? because they purchased a small case hairpin or other small case alternator (it may have been only fitment option) and they want 300+ amps. You cant cut the cake and pick the piece. You either get peak output, or you get good idle. To get a high peak output like everyone wants out of a small case hairpin you sacrifice idle. The ONLY way to make up for this is to spin the alt faster.
On a sedan such as your stratus it more than likely has a crank pulley around 6 inches. so to increase our pulley ratio we need to make a smaller alternator pulley. You can only go so small on the pulley. Lets say we can work a 1.75 inch pulley on there. If you have a 6 inch crank pulley and a 1.75 inch overdrive alternator pulley your pulley ratio is 3.42. Lets say worst case scenario your hot idle is 600. We do 600*3.42 to get alternator rpm at idle. Which is 2057 rotor (alternator rpm).
We look up at that DC Power chart posted above which is very accurate. Even at 2057 alternator rpm you are barely turning the alternator on. You will notice voltage fluctuation at idle with the 320. That is why I suggested going with the 240. You get a reliable idle as well as boosted peak output.
Please note that Below it states that more than likely your car will have better performance. These specs are worst case scenario and to emphesize to uneducated customers that Bigger more peak is not always better because you are sacrificing low end.
***All Alternator Idle ratings are measured at 1800 Alternator RPM. If your vehicle has a 3:1 pulley ratio (6" diameter crankshaft and 2" diameter pulley) this makes the engine rpm roughly 600. This idle rating covers 99% of vehicles made and more than likely, you will see higher ratings than we have posted.***
***All HOT ratings are measured at 6000 Alternator RPM. If your vehicle has a 3:1 pulley ratio, this makes the engine rpm roughly 2000. ***
***These ratings are much lower than our competitors who rate their alternators at an idle speed of 2500 Alternator RPM and a peak speed of 8000 Alternator RPM. These equal 833.33 idle engine rpm and 2666.67 engine rpm. ***
you cant compare large case alternators to small case alternators. THey just arent in the same league. The OP is talking about small case alternators. The large case hairpins such as the 370 elite is a great unit at idle and top end due to its larger stator size and larger winding size.
Please see this video to see difference between large case and small case stators.
Please see this video to see difference between large case and small case stators.
Excessive amperage only makes small case alts now. He makes 350a small case hairpins that do great at idel... Got one in the Hhr...
I have large case excessive alts and he said mine are the last large case he's going to build. This was like two months ago... Because his small case alts will do everything the large case alts will do.
Email from him
It's the large case design I was doing That I will not be making anymore. These are built using 2 different alternators and stator stack has to be cut down to fit in the front housing, rear housing has a mounting ear on it that has to be cut off and ground down, etc. Just a lot of time involved in making this style.
These take a while to build, whole different design and takes a lot of labor. That is why I started doing the small case to replace these. After these 2 I don't plan on doing any more of this style alternator.
So end of story is if you want a small case hair pin with ton of amperage at idel get excessive amperage.. The one is the Hhr is a beast!
I have large case excessive alts and he said mine are the last large case he's going to build. This was like two months ago... Because his small case alts will do everything the large case alts will do.
Email from him
It's the large case design I was doing That I will not be making anymore. These are built using 2 different alternators and stator stack has to be cut down to fit in the front housing, rear housing has a mounting ear on it that has to be cut off and ground down, etc. Just a lot of time involved in making this style.
These take a while to build, whole different design and takes a lot of labor. That is why I started doing the small case to replace these. After these 2 I don't plan on doing any more of this style alternator.
So end of story is if you want a small case hair pin with ton of amperage at idel get excessive amperage.. The one is the Hhr is a beast!
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What is the max speed an alt can spin?
If you were to put a different pulley on to get idle speed up around 4000 alt rpm, what is the max it can spin before destroying itself?
If you were to put a different pulley on to get idle speed up around 4000 alt rpm, what is the max it can spin before destroying itself?
You generally dont want to go above 15000 (15k) rpm continous on an alternator. at most for brief periods is 20k rpm maybe 25k rpm but that is really pushing it. I would never design something much over 20k.
the problem arises when you spin alt fast at idle, it spins too fast on top end.
the problem arises when you spin alt fast at idle, it spins too fast on top end.
Either depending on if yours is a computer related issue or if its just a different issue. Mike singer told me he can do a mod for that.
- Thread Starter
- #23
Wow thanks guys yeah I'll try going with the 240 looks like my best option. I really don't want to do much modding, I know h/a alt is a mod but besides that! I don't always cruise down the road bumping full blast, and I mean anything has to be better than my stock 80amp alt!
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