Frequently Asked Questions
about self-exciting alternators
>What is the rpm at which a normal alternator cuts in?
That depends on the alternator-typically in a multi-wire set-up they start
charging almost immediately. A normal alternator with nothing more than a
self-exciting regulator added can take as much as 7000 rpm of the rotor to
excite, which is much more than most governed speed engines (in tractors
etc.) can attain.
>Do self exciting alternators cut in all at once, or gradually?
They turn on when they reach sufficient rpm to do so (on the unit in
question it starts charging at 2000 rpm [or less] of the rotor-our 22amp model can excite as low as 900, but excites consistantly at 1200)-how much
they charge at that point is dependant on the battery's state of charge. In
an original equipment application of this style alternator it never saw a
rotor speed of less than 2160 rpm (Small block Chevy idling at 900 rpm with
a 6" crank pulley and a 2.5" alternator pulley) At 2000 rpm the SE unit of
mine charges @ 20 amps
>At what speed does a normal alternator become capable of providing a charge
to a battery?
They charge at idle speed too-full output capacity won't be reached until
4000-6000 rotor rpm, depending on the application
>At what rpm does your low speed cut-in model become capable
of providing charge to a battery?
Full output (37 amps) is available between 3500 and 4000 rpm
>Will a self exciting alternator bolt on in place of my generator?
No. At best-there will be minor modification to the existing bracket, at worst-a whole new bracket may have to be constructed, in between-you may have to purchase one of our bracket kits, they adapt your existing bracket to the alternator with no welding or fabrication required. You just choose the combination of brackets and spacers to get proper belt alignment and bolt it all together. The bracket kits come with a good set of illustrated instructions too.
>Do you have an alternator that excites at 500 rpm and is capable of producing 200 amps at 1500 rpm and will run all day at full output?
NO! That is beyond any reasonable expectation-everything that we have that are tested and proven are noted on our site-I am continually striving to achieve lower excitation speeds and lower rpm's for peak output, but if something that extreme isn't mentioned, you can pretty well bet that it isn't practical.
>Do you sell "self-excitors" seperately?
Generally not. There is more to a good performing self exciting alternator than just the regulator. We use selected and matched components to achieve the lower possible cut-in speed for a particular application-any other way is taking a shot in the dark. If you insist, we will sell just a regulator, but we do not guarantee that you'll be happy with the results!
>What voltage can I expect from your alternator?
That depends on the charge condition of the battery(ies) If the batteries aren't discharged much,you will have between 13.5 and 15 volts. If they are low enough to require a higher charge rate than the alternator is capable to produce, naturally, the voltage will be accordingly lower.
>Does the self-exciting field circuit take any current when
not charging?Is there any parasitic draw?
Not at all. It specifically relies on residual magnetism in the pole pieces to generate a minute current that gets things goin' (That residual magnetism can deteriorate after a long dormant period or a shocking blow)
>How much efficiency is lost due to the self-exciting?
Lost compared to what? and at what RPM?
Compared to the unaltered original type alternator that we modify running in it's intended RPM range? Total output is a lot less, but input requirements are less(but probably not enough to make the efficiency equal) so they are probably less efficient than a 63 "hard-wired" alternator-just one of the trade-offs necessary for one-wire low speed operation
Compared to the original operating at 1000RPM? The original hard-wired 63 amp would produce nothing at 1000 rpm compared to 3-5 amps from the SE unit so in that circimstance it is infinitely more efficient.
Efficiency loss compared to the same amperage unit without self-excitation-none.
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