Jeff Snyder
EF5
Also, remember that the "rating" on an alternator is for the maximum output, which occurs at higher RPMs. IF you're idling, you won't get anywhere near the "max" output from your alternator. Since chasing, while involving lots of driving, still deals with plenty of idle time or at least low-RPM (low-speed driving, cruising at 65 in top gear -- both which result in relatively low RPMs), I still think it'd be smart to spend the extra dinero for a more heavy-duty alternator.
Here is a little table* I found that seems to match what many manufacturers list/say:
RPM Cold/Hot Cold/Hot
2000 51/41 42/31
2500 78/63 73/58
3000 92/76 93/76
3500 102/85 107/87
4000 108/92 117/96
4500 114/96 123/102
5000 118/99 127/107
5500 121/102 131/110
6000 123/104 134/113
6500 124/106 136/116
As you can see, you don't get anywhere near the rated output amperage unless you're running high RPMs. Again, the higher the overall rater output, the higher the output at lower RPMs... Ever turn on AC on a hot day while parked somewhere? Notice how your car's voltage drops significantly? Mine drops usually from the running voltage of ~13.7v to ~12.5v if I'm running AC with max fans, denoting that I'm almost drawing straight from the battery, which is very bad news if you want your battery to last a long time...
Now, regarding loads... Yes, you have the standard, 'engine-on' load (Which I heard is more around 60amps for most vehicles), but all the add-ons can really "add on". Knowing that P = V * I ... Then I (in amps) = P / V ... At 55w each, assuming 14v running (most vehicles run between 13.5v and 14v when the engine is on), that's approx 4 amps per bulb. But wait, the 55w will be 55w "in" if the bulb were perfectly efficient, which isn't the case. Nonentheless, with five bulbs, that's about 20 amps. Now, say you're transmitting on a 50w ham radio, my manual for my rig tells me a max of 8.5amps. Car radio? Scanners? And don't even start with AC, which tends to put a rather signficant drag on everything... Yes, you may be "okay", but a stressed electrical system in your car is undesirable obviously, and tends to cut short battery life.
* - http://www.amplepower.com/products/alt/ which is similar to http://www.mechman.com/alt.htm and many others in terms of just showing the correlation between RPMs and alternator output.
Here is a little table* I found that seems to match what many manufacturers list/say:
RPM Cold/Hot Cold/Hot
2000 51/41 42/31
2500 78/63 73/58
3000 92/76 93/76
3500 102/85 107/87
4000 108/92 117/96
4500 114/96 123/102
5000 118/99 127/107
5500 121/102 131/110
6000 123/104 134/113
6500 124/106 136/116
As you can see, you don't get anywhere near the rated output amperage unless you're running high RPMs. Again, the higher the overall rater output, the higher the output at lower RPMs... Ever turn on AC on a hot day while parked somewhere? Notice how your car's voltage drops significantly? Mine drops usually from the running voltage of ~13.7v to ~12.5v if I'm running AC with max fans, denoting that I'm almost drawing straight from the battery, which is very bad news if you want your battery to last a long time...
Now, regarding loads... Yes, you have the standard, 'engine-on' load (Which I heard is more around 60amps for most vehicles), but all the add-ons can really "add on". Knowing that P = V * I ... Then I (in amps) = P / V ... At 55w each, assuming 14v running (most vehicles run between 13.5v and 14v when the engine is on), that's approx 4 amps per bulb. But wait, the 55w will be 55w "in" if the bulb were perfectly efficient, which isn't the case. Nonentheless, with five bulbs, that's about 20 amps. Now, say you're transmitting on a 50w ham radio, my manual for my rig tells me a max of 8.5amps. Car radio? Scanners? And don't even start with AC, which tends to put a rather signficant drag on everything... Yes, you may be "okay", but a stressed electrical system in your car is undesirable obviously, and tends to cut short battery life.
* - http://www.amplepower.com/products/alt/ which is similar to http://www.mechman.com/alt.htm and many others in terms of just showing the correlation between RPMs and alternator output.
